EP0647239A1 - Peptides de l'angiotensine iv, et recepteur - Google Patents

Peptides de l'angiotensine iv, et recepteur

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Publication number
EP0647239A1
EP0647239A1 EP93916733A EP93916733A EP0647239A1 EP 0647239 A1 EP0647239 A1 EP 0647239A1 EP 93916733 A EP93916733 A EP 93916733A EP 93916733 A EP93916733 A EP 93916733A EP 0647239 A1 EP0647239 A1 EP 0647239A1
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EP
European Patent Office
Prior art keywords
receptor
ain
binding
aiv
ligand
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
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EP93916733A
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German (de)
English (en)
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EP0647239A4 (fr
Inventor
Joseph W. Harding
John W. Wright
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University of Washington
Washington State University Research Foundation
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University of Washington
Washington State University Research Foundation
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Publication of EP0647239A1 publication Critical patent/EP0647239A1/fr
Publication of EP0647239A4 publication Critical patent/EP0647239A4/fr
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K5/00—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof
    • C07K5/04—Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing only normal peptide links
    • C07K5/10—Tetrapeptides
    • C07K5/1002—Tetrapeptides with the first amino acid being neutral
    • C07K5/1005—Tetrapeptides with the first amino acid being neutral and aliphatic
    • C07K5/101—Tetrapeptides with the first amino acid being neutral and aliphatic the side chain containing 2 to 4 carbon atoms, e.g. Val, Ile, Leu
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/705—Receptors; Cell surface antigens; Cell surface determinants
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K7/00—Peptides having 5 to 20 amino acids in a fully defined sequence; Derivatives thereof
    • C07K7/04—Linear peptides containing only normal peptide links
    • C07K7/14—Angiotensins: Related peptides
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K38/00—Medicinal preparations containing peptides

Definitions

  • This invention relates to the polypeptide ligand NYTHPF (angiotensin IN or AIN) and to related peptide ligands and polyaminoacid ligands that bind to, activate and/or antagonize a novel angiotensin AT4 receptor.
  • the ligands comprise at least three of the ⁇ -terminal amino acids of AIN, or AT4 receptor binding equivalents or analogs thereof. Engagement of the receptor by its ligand triggers acute physiological effects (e.g., vasodilation) and long-term effects in cells (e.g., hypertrophic growth).
  • the renin-angiotensin system has wide-ranging actions on numerous tissues in the body affecting blood pressure (pressor activity) and cardiovascular and electrolyte homeostasis. It is currently believed that angiotensins All and Affl are derived via enzymatic cleavage in the cascade depicted in Figure 1, steps 1, 2, and 3 (1). (Numbering herein of the amino acid residues in Al, All, AIII, and AIN is according to that appearing in Figure 1.) The renin-angiotensin cascade is thought to begin with the action of renin on angiotensinogen to release angiotensin I (Al), a biologically inactive decapeptide.
  • Angiotensin II (All), the bioactive octapeptide, is thought to be formed by the action of angiotensin converting enzyme (ACE) on circulating Al (2).
  • Des-AspAH Angiotensin III; Am
  • AHI in the adrenal gland (3) and brain (4). It has been reported that All and AUI are inactivated by enzymatic degradation through a series of smaller inactive fragments (5). Fragments smaller than AIII have been thought, for the most part, to be biologically inactive and of little physiological significance (6).
  • ATI ⁇ g ATI ⁇ g
  • AT2 receptors 9,10
  • An All receptor having components with molecular weights of 60-64kDa and 112-115kDa has reportedly been cloned from adrenal cortical cells as well as rat smooth muscle (11).
  • AII ⁇ -8 has been found to be much less active than All or AIII with regard to typical angiotensin-dependent pressor activity or stimulating water intake (9,10,12).
  • AII (3 . 8) while having little pressor activity or ability to stimulate aldosterone release, may under certain circumstances inhibit renin release from kidney (12,13).
  • Haberl et al. (14) reported a possible effect of AII ( 3_g ) on endothelium-dependent dilation in rabbit brain. Braszko et al.
  • the angiotensin field has often been fraught with complexity and conflicting information, particularly with regard to the levels of different All and AIII peptides required to elicit certain cellular responses, the concentrations predicted from receptor binding studies to be biologically active, and the levels of angiotensin peptides that may be measured in biological fluids. It has been reported that All and AIII are removed from, or destroyed in, circulation by enzymatic hydrolysis. Biological half- lives of the different metabolic fragments are reportedly quite short. Semple and co- workers (18) reportedly detected AHI, A ⁇ 3 .
  • AII ( 4_g ) in arterial and venous blood in man with half-lives for All, AIII, AII ( 3_g ) , and AII (4 .g ) of 4.4, 2.0, 1.9, and 2.4 minutes, respectively.
  • Blumberg et al. (19) reported that during transit through the kidney 72-76% of Al and All and 89% of A was metabolized.
  • Confusion has existed in the art as to how metabolic products of All and AIII can exhibit certain biological activities (e.g., inhibition of renin release and enhancement of cognitive function), while failing to bind to Al or All receptors.
  • Fragments of All smaller than A e.g., AII (3 .g ) and other smaller fragments, have not been reported to have specific saturable binding sites in tissues, and receptors for these fragments have not been identified previously.
  • the present invention provides partial explanation for certain previous confusing and contradictory findings, and provides novel AIN receptors (AT4), AIN ligands, peptides, analogs, agonists and antagonists that bind specifically to the AT4 receptor and not to Al (ATI) or All (AT2) receptors.
  • the AIV peptides and the AT4 receptor are labile and subject to proteolytic degradation.
  • the invention provides a specific angioteninase enzyme that converts All or AIII peptides to AIN peptides in a novel pathway. Summary of the Invention
  • AIN angiotensin AIN receptor
  • AT4 angiotensin AIN receptor
  • AIN ligand system for binding a small ⁇ -terminal hexapeptide fragment of Angiotensin II (referred to herein as AIN, with amino acid sequence Nal ⁇ -Tyr 2 -He 3 -His 4 -Pr ⁇ 5 -Phe 6 ) provides partial explanation for confusion in the prior art.
  • AIN binds saturably, reversibly, specifically, and with high affinity to membrane AT4 receptors in a variety of tissues and from many animal species.
  • the AT4 receptor is pharmacologically distinct from classic angiotensin receptors (ATI or AT2) in that the AT4 receptor displays no specificity for classic agonists (All and AIII) and antagonists (Sar ⁇ Ileg-AH).
  • ATI or AT2 classic angiotensin receptors
  • AT4 receptor displays no specificity for classic agonists (All and AIII) and antagonists (Sar ⁇ Ileg-AH).
  • the disclosure details the pharmacological and biochemical characterization of a newly discovered branch of the renin-angiotensin system that employs an AIN ligand as the signaling agent, and the AT4 plasma membrane receptor as the detection mechanism.
  • Angiotensin AIN appears to specifically mobilize calcium in vascular endothelial cells where AIN binding is evident. Binding to the endothelial AT4 receptor appears to trigger cellular proliferation. Binding of AIN to AT4 receptors in kidney and brain increases blood flow. In addition, binding of AIN to AT4 receptors in the brain facilitates learning and memory retention. AIN has also been shown to block the hypertrophic action of A on cardiocytes despite its inability to bind AT2 receptors. Since cardiocytes possess large numbers of AT4 receptors this action of AIN is most likely direct. Thus, in certain respects the action of AIN appears to neutralize, or act in apposition to the actions of All and AIII.
  • the invention provides an angiotensin AT4 receptor and receptor fragments (including the receptor binding site domain) that are capable of binding a VYIHPF angiotensin AIN ⁇ -terminal peptide, and related AIN ligands, but do not bind an angiotensin All or AIII ⁇ -terminal peptide, i.e., DRVYIHPF or RVYIHPF, respectively.
  • the AT4 receptor from adrenal cortical cells has a molecular size of about 140kD to about 150kD on SDS-PAGE following crosslinking, a K& of about 0.5nM for AIV peptides, and is widely expressed on the surface of adrenal cortical and medullary tissues in many mammalian species.
  • the receptor is expressed in all important organs and tissues including heart, lung, kidney, aorta, brain, liver, and uterus.
  • the invention further provides processes for identifying angiotensin AIV agonists and antagonists, and constructing diagnostic assays to specifically measure AIV and AT4 receptors.
  • FIGURE 1 is a schematic diagram depicting the amino acid sequence of angiotensinogen and its conversion by renin to Al, by angiotensin converting enzyme (ACE) to All, by angiopeptidase to AIII, and by a novel AIV angiotensinase, herein disclosed, to angiotensin AIV (AIV).
  • ACE angiotensin converting enzyme
  • AIV angiotensin AIV
  • FIGURE 2 A is a graphical representation of the results of equilibrium binding studies of 125 I-radiolabeled AIV to AT4 receptors isolated from bovine adrenal cortical membranes; as described in Example 1.
  • FIGURE 2B depicts graphically the structural requirements and specificity for binding of AIV ligand to the AT4 receptor from rabbit cardiac myocyte membranes; as described in Example 1.
  • FIGURE 3 compares AT2 and AT4 receptor localization in the Habenula region of the brain using receptor autoradiography with 125 I-Sar ⁇ ,Ileg-AII to localize AT2 receptors, and 125 I-ATV to localize AT4 receptors, as described in Example 2.
  • Panel A shows binding of 125 I-AIN to cells in the habenula, thalamus, cerebral cortex and hippocampus of guinea pig brain.
  • Panel B shows that the binding of 125 I-AIV is specifically competitively inhibited by lOOnM non-labeled AIV competitor.
  • Panel C shows that binding of 125 I-AIV is not competitively inhibited by lOOnM Sar ⁇ ,Ileg-AII.
  • Panel D shows a pattern of binding of 125 I-Sar ⁇ ,Ileg-AII to AT2 receptors that is different from the pattern observed with 125 I-AIV in Panel A.
  • Panel E shows that binding of 125 I-Sar ⁇ ,Ile 8 -AII is specifically inhibited by lOOnM of non-labeled All competitor.
  • Panel F shows that binding of 125 I-Sar ⁇ ,Ileg-AII is not inhibited by lOOnM non-labeled AIV competitor.
  • Panel G shows a "pseudo-color" photograph of 1 5 I-AIV binding.
  • Panel H shows a "pseudo-color photograph of 125 I-Sar ⁇ ,Ileg-AII binding.
  • Panel I shows a photomicrograph of a histology slide of a serial section of the same tissue as in Panels A-I.
  • FIGURES 5A and 5B are graphical representations of changes in blood flow that result from binding of agonist, Lys j AIN, to AT4 receptors in kidney, without changes in systemic blood pressure, as described in Example 4.
  • Figure 5A shows changes in arterial blood pressure following administration of Lys j AIV at 100pmole/25ml/min (open circles) or saline control (closed circles).
  • Figure 5B shows changes in renal blood flow following administration of Lysi AIN at 100pmole/25 ⁇ 1/min (open circles) or saline control (closed circles).
  • FIGURES 6A and 6B are graphical representations showing changes in blood flow that result from administering different doses of an agonist ⁇ orLeu j AIN (i.e., ⁇ orLeuYTHPF) that binds to AT4 receptors in kidney, without changes in systemic blood pressure, as described in Example 4.
  • ⁇ orLeuYTHPF an agonist ⁇ orLeu j AIN
  • FIGURES 6A and 6B are graphical representations showing changes in blood flow that result from administering different doses of an agonist ⁇ orLeu j AIN (i.e., ⁇ orLeuYTHPF) that binds to AT4 receptors in kidney, without changes in systemic blood pressure, as described in Example 4.
  • ⁇ orLeuYTHPF an agonist ⁇ orLeu j AIN
  • FIGURES 7A-7D, 8 and 9 are graphical representations of AIN binding, as described in Example 6.
  • Figure 7 A shows the results of kinetic analyses measuring binding of AIN to coronary venule endothelial cells (CVEC) showing maximal equilibrium binding in about 60 minutes with an apparent Ka of about 9.3 x 10 7 M- 1 .
  • Figure 7B shows the results of kinetic studies measuring the dissociation of AIV from CVEC endothelial cells with an apparent K- j of about 0.3nM.
  • Figure 7C shows the results of equilibrium binding of AIN to 2 separable types of AT4 receptor sites in coronary venule endothelial cells (CVEC).
  • Figure 7D shows the results of equilibrium binding of AIV to 2 separable types of AT4 receptor sites in aortic endothelial cells: one type of site with a K- j of about 4.4 +/- 0.8nM and a second type of site with a K- j of about 26.9 +/- 9pM.
  • Figure 8 shows competition of 125 I-AIV binding to coronary venule endothelial cells (CVEC) by non-radiolabeled AIV analogs.
  • Figure 9 shows association of AT2 receptors with G-protein in vascular smooth muscle cells (RVSMC), but non-association of AIV with G-proteins in endothelial cells (BAEC), as evidenced by the inhibility of GTP ⁇ S to inhibit AIV binding.
  • RVCSMC vascular smooth muscle cells
  • BAEC endothelial cells
  • FIGURES 10A and 10B show enhancement of cognitive function, i.e., learning, in AIV intracerebroventricularly (icv) injected animals but not in All-icv-injected animals. Testing of memory was conducted one day ( Figure 10 A), or one, two and three days ( Figure 10B), after the animals learned a passive avoidance response; as described in Example 7.
  • FIGURE 11 is a graphical representation of the comparative stability of
  • FIGURE 12 is a graphical representation of the effects of divalinal AIN (open squares), and divalinal AIV followed by LysiAIV (squares with dots), on blood pressure (Figure 12 A) and renal blood flow (Figure 12B), as compared to saline alone
  • Angiotensinogen is used herein to refer to a peptide having the sequence Asp 1 Arg2Val3Tyr4lle5His 6 Pro Phe His9Leu 10 Val 11 Ile 1 2His 1 3Ser 14 , abbreviated DRVYfflOPFHLVfflS (SEQ. ID. NO. 1)
  • Al and “angiotensin I” are terms used to refer to the decapeptide fragment of angiotensin having the N-terminal sequence
  • des-Asp Al “d-Asp Al” and “des-Asp angiotensin I” are terms used to refer to an angiotensin polypeptide having the N-terminal sequence
  • RVYIHPFHL (SEQ. ID. NO. 3).
  • angiotensin II is terms used to refer to an angiotensin, e.g., an octapeptide, having the N-terminal sequence Asp i Arg 2 Val3 Ty ⁇ IlesE ⁇ P ⁇ Pheg, abbreviated DRVYIHPF (SEQ. ID. NO. 4).
  • Am angiotensin m
  • Des-Asp AH Des-Asp AH
  • a ⁇ 2 . 8 are terms used to refer to the heptapeptide fragment of angiotensin having the N-terminal sequence abbreviated RVYIHPF (SEQ. ID. NO. 5).
  • AIV angiotensin IV
  • Des-Arg Am are terms used to refer to the hexapeptide fragment of angiotensin having the N-terminal sequence Val 1 Tyr2lle 3 His4Pr ⁇ 5Phe 6 , abbreviated VYIHPF (SEQ. ID. NO. 6).
  • AIV refers to physiological angiotensin II ( 3_ ) fragments formed in a variety of animal species.
  • An "AIV peptide ligand” is a ligand capable of binding to an AT4 receptor. AIV is a representative example of an AIV peptide ligand, as are AIV analogs.
  • Des-x also abbreviated “d-x,” is used to refer to an amino acid sequence that lacks the amino acid residue "x". Des-Asp All is used to refer to an angiotensin II lacking the N-terminal Asparagine residue; d-Nal ⁇ AIV is used to refer to AIV lacking the valine residue (position 1) at the ⁇ -terminus of AIV. " ⁇ -terminal” and “ ⁇ -terminus” are used interchangeably to refer to the
  • the N-terminal amino acid is the amino acid located at the NH terminus of the peptide.
  • Protein and polypeptide are used interchangeably to refer to a serial array of amino acids peptide bonded one to another of at least three amino acids in length to preferably six amino acids in length, but also up to many hundreds of amino acids in length.
  • AIV Ligand refers to a compound that is capable of filling the three-dimensional space in a receptor binding site so that electrostatic repulsive forces are minimized, electrostatic attractive forces are maximized, and hydrophobic and hydrogen bonding forces are maximized.
  • Representative ligands include "AIV peptides” and "ATV analogs”.
  • Ligands bind to their specific receptor in a specific saturable manner, e.g., specificity may determined by the ability of an AIV ligand to bind to an AT4 receptor in a manner that is not competitively inhibited in the presence of an excess (e.g., 1000-fold molar excess) of a competitor peptide (e.g., Al or All).
  • ATV peptide is used interchangeably with "angiotensin IV peptide” to refer to an AIN ligand that is a peptide having, or corresponding to, at least three of the ⁇ -terminal ten amino acid residues (preferably three of the ⁇ -terminal eight amino acid residues, and most preferably three of the ⁇ -terminal six amino acid residues), comprising three amino acids selected from among N, Y, I, H, P, F, L, K, A, H, ⁇ Nal, ⁇ Leu, or Orn; preferably from among N, Y, I, P, K, ⁇ Nal or ⁇ Leu; and most preferably from among N, Y, K, ⁇ Nal, or ⁇ Leu.
  • AIN peptides have an amino acid sequence related to the AIN ⁇ -terminal sequence NYIHPFX, i.e., by conservative and nonconservative substitutions of amino acids, or by derivatization or covalent modification, (as described below), and wherein X is any non-interfering amino acid.
  • Representative AIN peptides are polypeptides from 3 amino acids in length to many tens of amino acids in length.
  • AIN peptides include peptides that are capable of antagonizing binding of "AIN” to its receptor, i.e., “antagonists” (as defined below), and other "AIN ligands” are capable of binding to the AT4 receptor and exerting effects similar to “AIN", i.e., "agonists” (as defined below).
  • AIV analog is intended to mean a chemical compound that mimics or improves on the electronic, steric, hydrophobic, and 3 -dimensional space-filling requirements of the constituent amino acid residues involved in binding of the AIV peptide to the AT4 receptor (e.g., a mimetic chemical AIV composition).
  • AIV analogues may be polypeptides, i.e., having amino acids bonded by peptidic linkages, or may be non-peptides, i.e., having amino acids not bonded by peptidic linkages.
  • Representative examples of AIV analogs include chemical mimetic compounds that are capable of antagonizing binding of AIV to its receptor, i.e., antagonists (as defined below), and other AIV ligands are capable of binding to the AT4 receptor and exerting effects similar to ATV, i.e., agonists (as defined below).
  • Agonist as used herein means an AIV peptide or AJN analog that is capable of spacially conforming to the molecular space filled by an AIN ligand and that is further capable of combining with AT4 receptors to initiate an action that is initiated by a physiological AIN molecule when it binds to its specific AT4 receptors on cells in vivo or in vitro. Representative examples of actions initiated by AIN are illustrated in the Examples. Agonists possess binding affinity for AT4 receptor(s) and intrinsic activity for inducing the activities that are induced following the binding of AIN to AT4 receptor.
  • agonists include NYEHPFX, ⁇ vaYIHPFX, and OrnYTHPFX, wherein "X" is used to designate one or more non-interfering amino acids.
  • processes for recognizing agonists are described in Example 4.
  • Antagonist as used herein means an agent that spacially conforms to the molecular space filled by an AIN ligand and that is further capable of combining with the subject AT4 receptor(s) to inhibit, neutralize, impede or reverse, at least in part, an action of physiological AIN when it binds to its specific AT4 receptors on cells.
  • antagonists include KYIHPFX, and ⁇ Leu THPFX, wherein "X" is used to designate one or more non-interfering amino acids. Representative examples of processes for recognizing antagonists are described in Example 4.
  • AH ligand refers to a peptide having the ⁇ -terminal amino acid sequence DRNYTHPFX and capable of binding to an ATI or AT2 All receptor, where X is any non-interfering amino acid.
  • ⁇ on-interfering amino acid as used herein means any amino acid that when introduced into the C-terminus of an AIN peptide ligand does not interfere with binding of the AIN peptide ligand to its specific AT4 receptor.
  • ATI and “ATI receptor” and are terms used interchangeably to refer to a receptor subtype capable of binding AH.
  • AT2 and AT2 receptor are terms used interchangeably to refer to a second receptor subtype capable of binding AIL
  • AT4 receptor is the term used to refer to a receptor capable of binding an
  • AIN ligand but not an Al, All, or AIII ligand.
  • AT4 receptor fragments is a term used herein to refer to portions of the AT4 receptor that are smaller in size than an AT4 receptor isolated from a natural source, e.g., tissues, biological fluids and the like, but remain capable of binding AIN. Fragments may be prepared from an AT4 receptor isolated from a tissue and then subjected to proteolytic degradation or treatment with a chemical such as cyanogen bromide. In the latter case the fragments of the receptor are conveniently purified before use, e.g., by reverse-phase HPLC or immune affinity chromatography.
  • fragments of the AT4 receptor may be prepared by expression of a portion of a nucleotide sequence of a genomic or cD ⁇ A clone capable of expressing the AT4 receptor, e.g., a portion of the AT4 nucleotide sequence in an expression plasmid or vector introduced into a cell, wherein the cell manufactures the AT4 receptor fragment and the fragment can be purified (as above).
  • fragments of the AT4 receptor that contain the AIN ligand binding domain of the receptor may be soluble in biological fluids and aqueous solutions and may bind AIN ligand with a greater or less K-j than AT4 receptor under these conditions.
  • the binding affinity, expressed as the K-j, of the AT4 receptor fragment for an AIN ligand is about 30nM to about 0.003nM, preferably about lnM to about O.OlnM, and most preferably the binding affinity is about 0.5nM to about O.OlnM.
  • activation of the AT4 receptor are used interchangeably to refer to conformational and/or structural or activity changes resident in an AT4 receptor following binding of an AIN ligand; e.g., conformational changes may be evident by changes in the near UN spectra of the receptor or changes in the circular dichroism (CD) spectra; structural changes may be evident as covalent modification of the receptor, e.g., by phosphorylation; and, activity changes may be evident as an increase in enzyme activity, e.g., an innate tyrosine kinase activity.
  • conformational changes may be evident by changes in the near UN spectra of the receptor or changes in the circular dichroism (CD) spectra
  • structural changes may be evident as covalent modification of the receptor, e.g., by phosphorylation
  • activity changes may be evident as an increase in enzyme activity, e.g., an innate tyrosine kinase activity.
  • a receptor that has interacted with an AIN ligand and has undergone the process of "triggering” is also referred to herein as a "triggered AT4 receptor.”
  • “Substantially purified” as used herein refers to a preparation that contains a peptide, ligand, or receptor that is enriched greater than about 10-fold from the natural source material, e.g., membrane preparations of a tissue, and that also contains less than 5% impurities detectable by one-dimensional SDS-PAGE.
  • the substantially purified AT4 receptor approaches homogeneity at purification levels greater than about lOOOx.
  • ATV angiotensinase refers to a dipeptidylpeptidase capable of catalyzing hydrolysis of an arginine-valine peptide bond in an angiotensin, e.g., Al, All, or AIII, without catalyzing hydrolysis of any of the other peptide bonds in the angiotensin.
  • Pressure activity is used to refer to blood pressure changes induced by an agent, e.g., AH.
  • angiotensin II angiotensin II
  • bovine adrenal cortex During attempts to purify the angiotensin II (AT2) receptor from bovine adrenal cortex, the curious observation was made that as purification proceeded the apparent specificity of the receptor changed. While isolated membranes bound stable All analogs better than Am, the solubilized receptor exhibited the opposite order of ligand specificity with AHI binding better than All. Following purification it became apparent that the receptor had all but lost its ability to bind All, and was slowly losing its ability to bind Am, despite taking steps to inhibit proteases.
  • AT2 angiotensin II
  • a reevaluation of binding in purified membrane preparations demonstrated the presence of two different and distinct receptors, one for All and a second for A ⁇ -g ) . Further, neither All nor AII (3 _g ) ligand effectively displaced the other. The results, thus, strongly suggested the presence of two distinct receptors, one for All and a second for AII (3 _ 8) .
  • All ⁇ . ) is referred to as AIN and the novel AII (3 _ ) receptor is referred to as the AT4 receptor.
  • the notion of two separate and distinct receptors was confirmed by solubilizing, isolating, and substantially purifying the AT4 receptor under conditions that did not solubilize the AT2 receptor.
  • angiotensin IN angiotensin All
  • AII 3 _g
  • angiotensin IN angiotensin IN
  • AIN angiotensin IN
  • the angiotensin AT4 receptor is characterized in the Examples, with respect to structural requirements for ligand binding, species and tissue distribution of the receptor, physiological role of the AIN ligand- AT4 receptor system, intracellular messenger signaling pathways activated by the receptor, conditions for isolation and purification, and molecular size of the receptor.
  • compositions which comprise substantially purified angiotensin AT4 receptor or fragments thereof, that are capable of binding an angiotensin AIN ligand but not an angiotensin Al or All ligand.
  • the AT4 receptor binds AIN ligands, and does not bind to a peptide having the All ⁇ -terminal sequence, i.e., DRNYIHPF.
  • AT4 receptors of the invention are specific for AIN and AIN ligands, and are more fully characterized by the following properties: a) AT4 receptor has a K ⁇ for AIV of about 30nM to about 0.003nM, preferably about 3nM to about O.OlnM, and most preferably about InM to about 0.1 nM (representative examples of binding properties of AT4 receptors are summarized in Table 1); b) AT4 receptor binds to AIV ligands in a saturable and reversible manner; c) the binding of an AIV ligand to the AT4 receptor is competitively inhibited less than about 1% to about 10% by an angiotensin All preparation (e.g., Sar ⁇ Ileg-AII) that contains less than 0.1% of an AIV ligand when the competition of AIV binding is measured in the presence of about a 1000-fold molar excess concentration of the competing ligand using the assay conditions described in Example 1.
  • an angiotensin All preparation
  • AT4 receptors having these properties may be isolated from bovine adrenal cortical membranes (e.g., described in Example 1). Isolated AT4 receptors from this source have the kinetic, equilibrium binding, and physical properties set forth below in Example 1.
  • the AT4 receptor of the invention has a molecular size of about 120kD to about 200kD on SDS-PAGE, preferably about 140kD to about 160kD, and most preferably about 140kD to about 150kD.
  • an AT4 receptor of the invention is present in membrane preparations of adrenal glands of most mammalian species (e.g., cow, pig, horse, dog, cat, rabbit, and guinea pig) and, as purified from bovine adrenal membranes, the AT4 receptor has an apparent molecular size of about 146kDa on SDS-PAGE. AT4 receptors are also expressed in guinea pig aorta, heart, kidney, liver, lung, vascular smooth muscle, pituitary, and uterus, as well as vascular endothelial cells and brain.
  • mammalian species e.g., cow, pig, horse, dog, cat, rabbit, and guinea pig
  • AT4 receptors has an apparent molecular size of about 146kDa on SDS-PAGE. AT4 receptors are also expressed in guinea pig aorta, heart, kidney, liver, lung, vascular smooth muscle, pituitary, and uterus, as well as vascular end
  • the invention further provides AT4 receptor ligands that specifically bind to, activate and/or antagonize the AT4 receptor.
  • the ATV ligands generally comprise at least 3 of the N-terminal amino acid residues of AIN, or analogues or AT4 receptor binding equivalents thereof.
  • the amino acid residues of the ligands may be bonded by peptidic linkages, or may be bonded by non-peptidic linkages.
  • the ligands generally have a K d for the AT4 receptor below about 3 x 10 _6 M.
  • the AIN ligands of the invention are based on the structure of AIN.
  • the AIN ligands may be obtained by constructing AIN analogs that have one amino acid substituted for by another of like properties, i.e., a neutral polar amino acid for another neutral polar (e.g., G, A, N, I, L, F, P, or M), a neutral nonpolar amino acid for another neutral nonpolar (e.g., S, T, Y, W, ⁇ , Q, C), an acidic amino acid for another acidic (e.g., D or E), or a basic for a another basic (e.g., K, R, or H).
  • a neutral polar amino acid for another neutral polar e.g., G, A, N, I, L, F, P, or M
  • a neutral nonpolar amino acid for another neutral nonpolar e.g., S, T, Y, W, ⁇ , Q, C
  • an acidic amino acid for another acidic e.
  • the AIN ligands may alternatively be obtained by constructing an AIN analog that is covalently modified, e.g., wherein an amino acid residue is substituted by amidation, adenylation, methylation, acylation, phosphorylation, uridylation, fatty-acylation, glycosylation, and the like to form a "substituted amino acid residue".
  • the AIN ligands of the invention may contain one or more stereoisomers of the constituent amino acids residues; i.e., may contain one or more substituted or unsubstituted amino acid residues in the D-configuration.
  • the invention provides angiotensin AIN ligands and ligand compositions that include AIN analogs, AIN peptide derivatives, and covalently modified AIN peptides, all of which are capable of binding to an angiotensin AT4 receptor.
  • AIN ligands of the invention are generally defined by the formula
  • Rj is a substituted or unsubstituted amino acid residue having a neutral or positively charged aliphatic side chain Z j , said amino acid being selected from among N, I, L, A, G, F, P, M, K, norvaline, norleucine, and ornithine;
  • R 2 is a substituted or unsubstituted neutral nonpolar amino acid selected from the group consisting of Y, W, ⁇ , Q, F, or C;
  • R 3 is a substituted or unsubstituted neutral polar amino acid selected from the group consisting of G, A, N, I, L, F, P, or M;
  • X is nothing, R 4 , R 4 -R 5 , or R 4 -R 5 -R 6 , wherein R 4 is a substituted or unsubstituted basic amino acid residue selected from the group consisting of K, R and H, R 5 is a substituted or unsubstituted neutral polar amino acid residue selected from the group consisting of G, A, N, I, L, F, P, and M, and Rg is a substituted or unsubstituted neutral polar amino acid residue selected from the group consisting of G, A, N, I, L, F, P, M, and polyamino acid residues containing one or amino acid residues which do not prevent binding of the AIN ligand with the AT4 receptor.
  • the AIN ligands of the invention are generally amino acid chains that contain 3, 4, 5, or 6 amino acid residues corresponding to the ⁇ -terminal 3, 4, 5 or 6 amino acid residues of AIN (the polypeptide, VYIHPF), or may optionally extended at the C-terminal end with one or more amino acid residues that do not prevent binding, due to spatial, conformational, electrostatic or other considerations, to the AT4 receptor.
  • the amino acid residues may be linked in the amino acid chain by peptidic linkages to form peptides, or the ATV ligands of the invention may contain one or more non-peptidic linkages, such as methylene or C- ⁇ linkages, to enhance metabolic stability or other properties of the AIN ligands, as is hereinafter further described.
  • Representative AIN ligands of the invention include, but are not limited to C-terminal truncated forms of AIN, such as AIN ( i_5 ) , AIN ⁇ ) , and AIN ( i.
  • AIN such as D-H 4 AIN, D-P 5 AIN, and D-F 6 AIN
  • full or truncated forms of AIN with modified amino acid residues such as G4 AIN, G 5 AIN, G 6 AIN, ⁇ lei AIN, K AIN, F AIN, Ii AIN, P, AIN, ⁇ va 2 AIN, O ⁇ AIN, Y 6 AIN, I 6 AIN, ⁇ leYI, KYI, and ⁇ leYI, derivatives of AIN with one or more non-peptide linkages between amino acid residues, such as ⁇ le al 1 AIN (wherein the designation al 1 refers to a methylene -CH 2 - linkage between the amino acid residue in position 1 ( ⁇ le) and the amino acid residue in position 2 (Y)), ⁇ le al 1 Nal 3 AIN, Kal 1 Nal 3 AIN, Kal 1 AIN, Nal 1 AIN, Nal 3 AIN, and Nal 1 Nal 3 AIN, and Nal 1 Nal 3
  • the physical properties of the AT4 receptors that determine binding of the AIN ligands were mapped using synthetic peptides and analogs, as described below in detail in the examples.
  • the structure of the ⁇ -terminus of AIN is most important for high affinity binding of an AIN peptide to an AT4 receptor.
  • the AT4 receptor binding site is a coordinated multidomain binding site wherein binding in one subdomain may be excluded by high affinity binding at a second subdomain through an induced conformation change in the AT4 receptor binding site hydrophobic pocket subdomain. At least three binding site subdomains in the AT4 receptor were mapped using synthetic peptides and analogs.
  • the binding site is stereospecific at a first subdomain for L-Naline in ⁇ -terminal amino acid position 1 (Nalj) of AIV; at a second subdomain for L-Tyrosine in position 2 (Ty ⁇ ) of AIV; and at a third site for L-isoleucine (Ile3) in position 3 in AIV.
  • Valj in AIV may interact laterally with the walls of the groove of the receptor while T3T2 in AIV may interact with the receptor binding site through van der Waals forces and hydrogen bonding.
  • AIV peptides having a weak hydrophobic amino acid at the N-terminus with an aliphatic side chain bind to the AT4 receptor with a higher binding affinity than AIV (binding of KYIHPF is 50-fold higher than AIV, and NleYHPF has a Kj of about 10" 12 M).
  • N-terminal extension of AIV is incompatible with binding, as is deletion of the N-terminal valine (Val residue. Deletion of Val reduced binding affinities 1000-fold; substitution of Val i with Sar decreased binding affinity; addition of D-arginine to the N-terminal Val x reduced affinity for the receptor by 100-fold.
  • the receptor binding site domain of the AT4 receptor contains a hydrophobic pocket conforming closely to the space filled by norleucine (i.e., engaging the Valj residue of ATV) and in close apposition with a negatively charged residue (i.e., engaging the primary amine of the N-terminus of Val j ). Removal of the N-terminal amino group decreases by 1000-fold.
  • the C-terminus of the AIN peptide is relatively less important in the receptor binding and C-terminal extension of AIN ligands of the invention with "X" is allowed. However, removal of both the Pro 5 and Ph ⁇ 6 residues from AIN reduced binding affinity by about 21-fold to a Kj of 500nM.
  • the C-terminus of the AIN peptide may determine receptor subtype specificity of binding.
  • AT4 receptors isolated from bovine adrenal cortical membranes do not effectively bind AIN peptides synthesized with an ⁇ -terminal extension with Sar or GABA.
  • the illustrative AT4 receptors effectively bind peptides having the N-terminal L-Nal replaced with D-Nal or Sar.
  • removal of the N-terminal L-Val from AIN all but eliminates binding to the AT4 receptor.
  • AT4 receptors of the invention have a receptor binding site that is stereospecific for L-Naline.
  • D-NaliYTHPF has 1000-fold lower binding affinity for the AT4 receptor than L-Va ⁇ YIHPF.
  • the illustrative AT4 receptor isolated from bovine adrenal cortical membranes contains a binding site that prefers weak hydrophobic amino acids in the number 1 position (i.e., Ri) of the AIN ligand, i.e., increasing hydrophobicity by replacing Nal j with Phe (i.e., FiYTHPF) decreases binding affinity 4-fold, but replacement of Nalj with another weak hydrophobic amino acid (i.e., IiYTHPF) results in only a slight change (an increase) in binding affinity.
  • Ri number 1 position
  • Phe i.e., FiYTHPF
  • IiYTHPF another weak hydrophobic amino acid
  • ⁇ -terminal extension is incompatible with binding, deletion of the terminal valine residue eliminates binding (Kj >10" 6 ), substitution with Sar decreased binding affinity, substitution with He results in equivalent binding, substitution with Phe resulted in a 5-10-fold decrease in the affinity of binding, Pro-substituted AIN peptides bind with 100-fold lower affinity, Lys-substituted AIV peptides bind with 10-fold higher affinity, and AIV ligands having a norleucine in the number 1 position (also abbreviated herein Nle, NLe, NLeu, NLeu j , or Nlei) bound with 1000-fold higher affinity.
  • Nle norleucine
  • the interaction between the AT4 receptor binding site and AIV ligand may be dictated by requirements for an AIV ligand containing a flexible aliphatic carbon side chain, (i.e., as opposed to a relatively rigid aromatic ring), rather than by the degree of hydrophobicity of the side chain.
  • substitution of Val ⁇ with Aspi results in an analog with no binding affinity for the AT4 receptor (i.e., has a K d > lO ⁇ M).
  • the AT4 receptor binding sites of the invention may prefer a flexible aliphatic carbon side chain having 4 carbon atoms that lack a positively charged residue.
  • Heptanoylj AIV with a 5 carbon side chain has reduced affinity as compared to Nlej AIV.
  • Nlei YTHPF has higher binding affinity for an illustrative AT4 receptor than Lysi YTHPF, which was higher than NVal j YIHPF, which is in turn higher than OrniYIHPF.
  • the AIV peptide ligands of the invention having norleucine substituted for Nal j i.e., ⁇ le j YIHPFX
  • the AT4 receptor binding site interacts specifically with the ⁇ -terminal amino acid residue (i.e., Ri ), and the latter interaction is specific with respect to both absolute space occupancy volume (i.e., of the receptor binding site) and charge (i.e., of the AIN ligand).
  • methylation of isoleucine in Ilei of IiYTHPF reduces affinity of the illustrative receptor for the peptide by 67-fold; substitution of the Nalj primary amine ( ⁇ H 3 ) with a secondary amine (-NH-; in this case by substituting Proj for Nal j , to form PYIHPF) reduces the affinity of binding to the illustrative receptor by 8-fold; substitution of Nal ⁇ with benzoic acid or 6-amino-hexanoic acid gives peptides with a K j >lmM; and r replacing Nal j ⁇ GABA (gamma-amino butyric acid; to form GAB A- YTHPF) decreases binding affinity by 250-fold for the illustrative receptor.
  • substitution of the Nalj primary amine ( ⁇ H 3 ) with a secondary amine (-NH-; in this case by substituting Proj for Nal j , to form PYIHPF) reduces the affinity
  • the AT4 receptor binding sites of the invention also appear to be stereospecific for Tyr 2 (i.e., Y) in the R 2 position of the subject AIN peptide ligands.
  • Y i.e., Y
  • substitution of D-Tyr 2 or Ph ⁇ 2 (with a benzyl ring) for Tyr 2 (with a phenolic ring) results in analogs (i.e., N[D-Y 2 ]IHPF, or NF 2 LHPF, respectively) with very low affinity for the illustrative adrenal cortical receptor.
  • Phenolic side chains in the Tyr 2 residue may also interact with residues in the subject AT4 receptors through hydrophobic and/or hydrogen-bonding.
  • the AT4 receptor binding sites of the invention tolerate replacement of the V 1 -Y 2 peptide bond with a non-carbonyl bond that has a similar bond length, but is non-planar and has a non-rigid carbon-nitrogen bond.
  • the latter replacement bond may preferably be resistant to proteolytic hydrolysis thereby conferring additional stability on the AIV ligand and enhancing utility in therapeutic compositions for oral delivery.
  • replacement of the N 1 -Y 2 peptide bond with a methylene bond reduces receptor binding affinity by only 5-fold; and, replacement of both the N 1 -Y 2 and I 3 -H 4 peptide bonds with methylene bonds results in N-N,-CH 2 -NH-Y 2 N 3 -CH 2 -NH-H 4 P 5 F 6 -C (also referred to herein as Vali Val 3 AIN or divalinal AIN) that has an affinity equal to or better than NYTHPF.
  • the binding site of the AT4 receptors of the invention is a coordinated, multidomain binding site wherein binding in one subdomain of the binding site may be enhanced or inhibited by binding at a distant second subdomain.
  • substitution of He for Phe at the R position of NYTHPF 6 results in an analog (i.e., NYIHPI 6 ) that binds to AT4 receptor (i.e., through the Nj subdomain sites) with a higher affinity than the parent VYIHPF molecule.
  • substitution of Ile 6 for Ph ⁇ 6 in KYTHPF 6 results in an analog (i.e., KYIHPI 6 ) that binds to the receptor (i.e., through the Nj subdomain site) with a lower affinity than the parent KYIHPF 6 molecule.
  • the C-terminus of the subject AIN peptide ligands appears to be relatively less important in receptor binding.
  • deletion of the C-terminal Pheg from VYIHPF i.e., to form Ni Y 2 I 3 H 4 P 5
  • C-terminal extension with histidine does not alter binding (i.e., to form N1Y 2 I 3 H 4 P 5 F 6 H 7 ); and, addition of both bis and leu reduces affinity only 2-fold (i.e., Vi Y 2 I 3 H 4 P 5 F 6 H 7 L 8 ).
  • Truncation of the C-terminus, i.e., at the R 5 position decreases binding.
  • removal of Pr ⁇ 5 from VYTHP to give NYTH decreases binding 21 -fold, and gives an analog with a Kj>500nM.
  • the binding site domains of the subject AT4 receptor of the invention recognize the ⁇ -terminus of the subject AIN peptide ligands with a high degree of specificity and while the receptor interacts less closely with the C-terminus this region of the subject AIN ligand may determine receptor subtype specificity.
  • antagonists of AIN are provided that bind to the AT4 receptor.
  • Presently particularly preferred antagonists of the invention include the non-peptide divalinal AIN and the C-terminal substituted tripeptide ⁇ leYi amide, as described in Example 4, although other antagonists will be readily apparent from the data and disclosure set forth herein.
  • aspects of the invention include processes for identifying AIN peptide ligands, i.e., by structural examination of the receptor binding requirements of test preparations (e.g., with respect to both blocking and/or promoting binding of the alternative peptide) to AT4 receptors such as those in heat-treated purified membrane preparation that are free of peptidase activity and devoid of other angiotensin receptors, i.e., ATI or AT2 receptors.
  • AIN peptide binding activity can be tested, e.g., using the receptor binding assays described herein, and that analogs, AIN peptide derivatives, and covalently modified AIN peptide or non-peptide ligands may exhibit activity as antagonists, agonists, promoters, or enhancers of AIN binding to its AT4 receptor.
  • AIN peptides may be prepared with substitution of other L-amino acids having different steric, electronic, and hydrophobic character for the L-Nal in the natural AIN ligand.
  • the first or second messenger intracellular pathways triggered in cells by interaction of an AIN ligand with an AT4 receptor may be used to test a series of peptides, analogs, derivatives, or covalently modified AIN peptides for their ability to bind to the AT4 receptor and trigger the intracellular signal. For instance, activities such as tyrosine kinase, guanylate cyclase, Protein kinase C, Ca “1”” * " flux changes, phospholipase C (PLC) activity, or prostaglandin or endocrine or exocrine hormone release from cells, may be monitored to determine whether the peptide triggered the AT4 receptor, and the receptor then signaled an increased or decreased activity in the cell.
  • activities such as tyrosine kinase, guanylate cyclase, Protein kinase C, Ca “1”” * " flux changes, phospholipase C (PLC) activity, or prostaglandin or endocrine or
  • the AIN peptides, AIN analogs, agonists and antagonists, and derivatives and covalently modified forms of the AIN peptides of the invention are recognized by their ability to bind the AT4 receptor with an equilibrium dissociation constant (K-i) below 3 x lO ⁇ M, more preferably below 3 x 10" 8 M and most preferably below 3 x 10 _9 M, and to a low binding affinity for ATI and AT2 receptors with a K (j greater than 1 x lO ⁇ M.
  • K-i equilibrium dissociation constant
  • processes are provided for identifying and characterizing a physiological effect of an angiotensin AIN peptide by assaying the effect(s) of the peptide on a selected in vitro cellular process.
  • an angiotensin AIN peptide by assaying the effect(s) of the peptide on a selected in vitro cellular process.
  • it may be convenient to assay renal blood flow, or in vitro cellular processes of endothelial cells and/or vascular smooth muscle cells.
  • assays may examine the effects of an AIV peptide on growth of a cardiomyocytes in vitro.
  • the processes disclosed herein are also useful in identifying how the in vitro activities of physiological AIV may be blocked or promoted by AIV peptides, AIV analogs, or derivatives or covalently modified forms of AIN peptides, as well as AT4 receptor fragments and the like.
  • Representative examples of useful assays for identifying the subject AIN peptide ligands and AIN ligands are provided in the examples.
  • cellular processes is intended to mean biological activities that may be measured in vitro or in vivo by quantitative and/or qualitative assay.
  • cell growth or metabolism may be measured (e.g., radiolabeled amino acid synthesis into protein, glycolytic activity, oncogene expression, and the like); or, proliferation (e.g., 3 H-thymidine synthesis into D ⁇ A); or, marker expression (e.g., mR ⁇ A by Northern, protein by Western blot, antigen by immunoassay, in vitro selectable drug-resistance marker by cell survival in toxic drug, and the like); or, electrical activity (e.g., in neural cells).
  • compositions and methods for promoting or inhibiting cellular activity of neural cells e.g., neural motor, cognitive or analgesic activity of neural cells in the brain.
  • the effect of the AIN compounds on motor activity may be observed by examining alterations in activity as measured with open-field techniques.
  • the cognitive activity may be observed by passive avoidance testing, Morris swimming maze performance, and various operant tasks.
  • To assay the effects of an AIN composition on a cellular process it may be useful, for example, to measure cellular processes before and after addition of AIN peptides to make comparative observations in parallel cell cultures. In this manner antagonists, agonists, inhibitors, promoters, enhancers, and the like may be identified and characterized with respect to their physiological effects in vitro and possible effects in vivo.
  • the route of delivery of the AIN ligands, AT4 receptor, AT4 receptor fragments, and AIV monoclonal antibodies of the invention is determined by the disease and site where treatment is required.
  • the compounds or compositions of the invention may be applied topically, or by intravenous, intraperitoneal, intramuscular, subcutaneous, intranasal and intradermal injection, as well as by intrabronchial instillation (e.g., with a nebulizer), transdermal delivery (e.g., with a lipid-soluble carrier and skin patch), gastrointestinal delivery (e.g., with a capsule or tablet), intracerebroventricularly (icv) into brain, or intraspinally into cerebrospinal fluid (CSF).
  • the preferred therapeutic compositions will vary with the clinical indication.
  • AIV ligand per unit dose depends, among other things, on the particular ligand employed, on the body weight and the chosen inoculation regimen.
  • a unit dose of ligand refers to the weight of ligand without the weight of carrier, when a carrier is used.
  • An effective treatment will be achieved in the microenvironment of the cells at a tissue site as the concentration of AIV ligand approaches a concentration of 10" 5 M to 10 _11 M.
  • the most preferred method to achieve the therapeutic concentration is to gradually escalate the dosage and monitor both the biological effects and the concentration in the biological fluids (e.g., through the use of a diagnostic immunoassay, or radioisotopic or chemical label).
  • the initial dose, for such an escalating dosage regimen of therapy will depend upon the route of administration. For intravenous administration, for an agent with an approximate molecular weight of 10,000 daltons, an initial dosage of approximately 70mg/kg body weight is administered and the dosage is escalated at 10-fold increases in concentration for each interval of the escalating dosage regimen. Therapeutic efficacy in this example is achieved at 0.7-70mg/kg body weight of the theoretical 10,000 dalton peptide.
  • the compounds may be administered alone or in combination with pharmaceutically acceptable carriers, in either single or multiple doses.
  • suitable pharmaceutical carriers include inert solid diluents or fillers, sterile aqueous solutions, and various nontoxic organic solvents.
  • the pharmaceutical compositions formed by combining the ATV ligands or receptor fragments with the pharmaceutically acceptable carrier are then readily administered in a variety of dosage forms such as tablets, lozenges, syrups, injectable solutions, and the like.
  • These pharmaceutical carriers can, if desired, contain additional ingredients such as flavorings, binders, excipients, sweetening or flavoring agents, colored matter or dyes, emulsifying or suspending agents, and/or.
  • solutions of the AIN ligand or receptor fragment in sesame or peanut oil or in aqueous propylene glycol may be employed.
  • the present invention further provides processes for isolating inhibitors of an AT4 receptor- AIN ligand interaction by: a) selecting a cell type that expresses the AT4 receptor; b) adding an AIN ligand to a control culture of said cells; c) adding the AIN ligand and a putative inhibitor to a second test culture of the cells; and d) measuring the level of binding of the AIN peptide to the cells in said second test and control cultures. In the case that an inhibitor is present in the preparation, the level of binding in the test culture is lower than that in the control culture. (An example of such a process is provided in Example 1).
  • this process may be used to identify an inhibitor of an AT4 receptor- AIN ligand interaction in chromatographic fractions and the like during solubilization, isolation, and purification of said inhibitors, and that the subject inhibitors may act as agonists or antagonists of the action of AIN induced when AIN binds to its specific AT4 receptor.
  • the invention provides an AIN angiontensinase enzyme capable of hydrolyzing a peptide bond between an arginine and a valine residue in an angiotensin polypeptide, e.g., a polypeptide with a DR ⁇ VYIHPF ⁇ -terminal sequence, wherein " ⁇ " indicates the proteolytic cleavage site that gives rise to an AIV peptide, i.e., with an ⁇ -terminal sequence related (as described above) to the amino acid sequence VYTHPF.
  • Isolation and substantial purification of AIV angiotensinase may be conveniently accomplished, for example, by preparing an affinity resin having a non-cleavable or slowly-cleavable AIN ligand covalently bound to the resin, e.g., chemically modified derivatives of a peptide in an amino acid sequence selected from among DRNYIHPF, DRVYIHP, DRVYIH, DRVYI, DRNY, DRN, RNY, or ⁇ RNYIHPF, ⁇ RNYIHP, ⁇ RVYIH, ⁇ RVYI, ⁇ RVY, ⁇ RV.
  • an affinity resin having a non-cleavable or slowly-cleavable AIN ligand covalently bound to the resin, e.g., chemically modified derivatives of a peptide in an amino acid sequence selected from among DRNYIHPF, DRVYIHP, DRVYIH, DRVYI, DRNY
  • the peptide useful in this assay is selected based on its ability to bind the AIV angiotensinase and to be resistant to cleavage by the enzyme.
  • a test preparation of a cellular or tissue extract (or a biological fluid sample) is next chromatographed through the affinity resin; the bound polypeptide(s) is eluted, e.g., at low pH and high salt (e.g., pH2-3, and 2-3M ⁇ aCl, and the like), or the bound polypeptide is eluted by adding an excess of AIN ligand.
  • the presence of the AIN angiotensinase in the eluate can be determined by assaying for the ability of the column eluate to catalyze hydrolysis of an Arginine-Naline peptide bond in an angiotensin peptide (e.g., AIII), and subsequently confirming that the sequence of the product of the reaction has a Valine residue at ⁇ -terminal amino acid and an AIV peptide sequence.
  • the novel AIV ligand-AT4 receptor system of the invention is useful in a complementary or antagonistic role to All in mediating long-term effects of angiotensins, and in modulating the effects of Al, All, or AIII on cells.
  • AIV is derived from All (or AIII) directly (e.g., through the action of a specific AIV angiotensinase, and other peptidases); 2) AIN is very labile and will accumulate at physiologically significant concentrations only when high levels of All are present at the target site; 3) the AT4 receptor is specific for AIN ligand (with accompanying low affinity for the parent peptide, AIII). Under certain conditions, AIN begins to accumulate at angiotensin target tissues as the All levels rise. When ATV concentrations rise to near 0.5nM (i.e., the K-i of the receptor) auxiliary processes which modify the acute action of All will be engaged.
  • 0.5nM i.e., the K-i of the receptor
  • an intracellular signaling system different from that employed by AIL
  • the activation of such an intracellular system may potentiate or antagonize the target cell's short-term response to AIL
  • One physiological function of the AT4 receptor-ligand system may be to impart a longer- term response to high-level or chronic angiotensin stimulation in a tissue.
  • AIV angiotensinase
  • bovine adrenal tissues have shown that the AT4 receptor is specific, with almost no affinity for AIL
  • AIV is metabolized/hydrolyzed in bovine adrenal homogenates at 200 times the rate of All and 4 times the rate of AHI.
  • AIV may be derived directly from All by action of a dipeptidylaminopeptidase, termed herein AIV angiotensinase.
  • AIV angiotensinase The location of AT4 receptor sites in groups of cells in tissues allows a skilled artesian to predict likely functions for the AT4 receptor in different tissues.
  • All and/or Am
  • AT4 receptor-ligand interaction many activities previously attributed to the action of All (and/or Am) may be triggered or regulated instead by the AT4 receptor-ligand interaction.
  • ATV ligand acts as a negative-feedback agent thus enabling tighter control on the aldosterone release process.
  • the ATV ligand- receptor system may also be associated with a previously inexplicable up-regulation of the angiotensin receptor seen following chronic All exposure of cells in vitro.
  • Still other functions attributed to All that may be mediated instead by the AIN ligand- receptor system include altering the release of catecholamines from adrenal medullary cells or regulating adrenal blood flow.
  • the AIN ligand-receptor system modulates (i.e., increases or decreases) either the acute and/or the long-term synthesis and release of chromaffin catecholamines, e.g., by acting to stimulate intracellular expression of tyrosine hydroxylase (the rate limiting enzyme in the synthetic pathway).
  • AT4 receptor-ligand system may have a role as a mediator of long-term angiotensin effects on endothelial cells (e.g., cell growth; Example 5).
  • AIV ligand-receptor interactions also appear to activate processes in endothelial cells that are complementary or antagonistic to those activated by AIL
  • some of the ATV ligands that are embodiments of the invention are useful for increasing blood flow (e.g., renal blood flow as demonstrated in the examples).
  • Example 2 for physiological functions of AIV peptide ligands and AT4 receptors in controlling renal blood flow, for the cellular biology of AIV ligand-AT4 receptor interactions (e.g., second messenger pathways, G-proteins, phosphorylation, intracellular Ca* "1" , phosphoinositide turnover, and guanylate cyclase activity), for vascular effects on venular and aortic endothelial cells and vascular smooth muscle cells and G-protein linkage of certain ATN-receptors, for endocrine effects on adrenocortical cell catacholamine release for effects on cardiac myocytes (i.e., cardiocytes), and for characterization of brain AT4 receptors (e.g., in hippocampal cells and in cerebellum, hippocampus, piriform cortex, Par 1/2, Fr 1/2, caudate putamen, HDB, thalamus, and inferior coUuculus), as well as, neurological effects of intracerebroventricular injection of
  • AIN is active in endothelial cells in enhancing cellular proliferation (as evidenced by thymidine incorporation) and stimulating production of endothelial cell relaxing factor (EDRF).
  • EDRF endothelial cell relaxing factor
  • results set forth in the Examples further identify a role for the AIN ligand- AT4 receptor interactions in triggering normal and/or hyperplastic growth of endothelial cells in sites of tumors or traumatic or wound injury, and angiogenesis, and a therapeutic use for AIN analogs, agonists, antagonists, and derivatives and covalently modified AIN peptide ligands that are capable of inhibiting vascular smooth muscle cell growth in such hyperplastic states while at the same time promoting endothelial cell growth.
  • the agonist compositions are also useful for encouraging endothelial cell growth, e.g., in wound sites; antagonists for discouraging vascularization in tumor sites.
  • the AT4 receptor-ligand system may play a role in triggering vasodilation through a selective effect on subpopulations of endothelial cells that exist in particular vascular beds (e.g., in the heart, lung, liver, kidney, brain and the like).
  • endothelial cells that exist in particular vascular beds (e.g., in the heart, lung, liver, kidney, brain and the like).
  • vascular beds e.g., in the heart, lung, liver, kidney, brain and the like.
  • AIN ligand-receptor system mediates actions of angiotensin that fall within the bounds of cardiovascular regulation and body water homeostasis.
  • AIN analogs, ATV agonists and antagonists, and derivatives and covalently modified AIN peptide ligands include promoting renal blood flow (e.g., in chronic kidney diseases) or, alternatively, inhibiting renal blood flow (i.e., using inhibitors and antagonists of AIN), e.g., in conditions of hyperacute renal dysfunction and water loss, or during renal surgical procedures.
  • cardiac myocytes also termed herein “cardiocytes”
  • cardiac myocytes also termed herein “cardiocytes”
  • ACE angiotensin converting enzyme
  • AIN antagonizes the hypertrophic action of AIL
  • the control of cardiocyte growth may be regulated endogenously by a balance between the activating action of ALT and the inhibiting action of AIN.
  • AIN and AIN agonists will be effective in blocking the development of, and reversing the effects of, left ventricular hypertrophy in patients.
  • ACE inhibitor is due not to their inhibition of AH synthesis but to their ability to enhance the synthesis of AIN ligands such as results from the shunting of precursors from the All synthetic pathway into the AIN pathway.
  • beneficial effect of ACE inhibitors in treating cardiac hypertrophy may be due to ACE inhibitor enhancement of the formation of AIN.
  • AIN operate by separate receptors employing different intracellular signaling systems. It has been reported that ACE inhibitors may have a beneficial effect in reducing cardiac hypertrophy through effects at the level of All or AIII. Considering the results disclosed herein it is most likely that the long-term effects previously attributed to decreased ATI may in fact be mediated by the interaction of increased levels of endogenous AIN ligands with the AT4 receptor. Further, it is most likely that the antagonists and agonists of AIN ligands, disclosed herein, will provide improved pharmaceutical compositions for treating cardiac hypertrophy attributable to the renin-angiotensin system, e.g. ventricular hypertrophy. The inventors believe that the interaction between AIN and the AT4 receptor may trigger the receptor and inhibit growth in cardiomyocytes.
  • angiotensin In adrenal cells angiotensin All's role in the regulation of aldosterone release from the adrenal cortex is reportedly well established (27). As shown herein, certain activities (such as adrenocortical cell growth), previously attributed to ATT or ATI, are actually activated following AIN ligand binding to the AT4 receptor. All (and AIII) reportedly stimulates aldosterone release from adrenal glomerulosa cells.
  • the disclosure, herein, of high levels of AT4 receptors in adrenal cortical cells suggests a possible role of AIN ligand (i.e., rather than All or AIII) in triggering AT4 receptors on adrenal cells to inhibit All-mediated aldosterone release.
  • AT4 receptors may be to up-regulate the threshold level of All ligand required to trigger a cellular response by regulating the levels of cellular ATI and/or AT2 receptors and/or to regulate adrenal blood flow.
  • AT4 receptors are found at even higher levels in the adrenal medullary cells where All has previously been reported by others to potentiate catecholamine release.
  • AIN ligand may modulate release of catecholamines (i.e., increase or decrease the release) acutely (or possibly even long-term, e.g., by triggering the AT4 receptor and thereby stimulating increased or decreased expression of tyrosine hydroxylase, the rate- limiting enzyme in catecholamine synthesis.
  • AIN may act to inhibit growth of the cells thus opposing the action of AH.
  • Agonists of AIN binding to the AT4 receptor will be effective inhibitors of vascular smooth muscle growth and will be therapeutically useful in reducing neointimal growth which often occurs following angioplasty.
  • AIN ligands and the AT4 receptors may function as growth factors of the tyrosine kinase class indicates that certain inhibitors of tyrosine kinase growth factors may also serve as inhibitors of certain angiotensin AIN ligand-receptor system- mediated cellular hypertrophic processes (e.g., ventricular hypertrophy), and that nucleotide probes constructed for complementarity to portions of R ⁇ A encoding the AIN ligand and receptor sequence may be useful in identifying other members of the AIN family of growth factors.
  • the invention also provides diagnostic applications for the AIN peptide ligands and antibodies.
  • the role of the AT4 receptor-ligand system in cardiovascular regulation suggests a possible value to diagnostic tests for monitoring the levels of AIN ligand and AT4 receptor in biological fluids and tissues (i.e., rather than All or AIII).
  • Individuals with high renin-sodium profiles are reportedly at five times greater risk of myocardial infarction than individuals with low renin-sodium profiles despite adequate control of systemic blood pressure (28).
  • the AIN peptides, ligands, receptor fragments, and the like disclosed herein are useful in diagnostic assays, e.g., immunoassays, for the detection of the presence or amounts of AIN ligands or receptors in tissues, cells, and biological fluids of patients.
  • diagnostic assays e.g., immunoassays
  • the AIN peptides, ligands, analogs, derivatives, or covalently modified AIN peptides of the invention may be formulated in buffers with stabilizers, e.g., for use as positive or negative controls in diagnostic assay, or in reagent test kits for receptor- binding assays.
  • the AIN ligands of the invention may be readily employed using conventional techniques to produce polyclonal or monoclonal AIN ligand specific antibodies, and that the isolation and purification of the AT4 receptor provides materials useful for preparation of polypeptide fragments (e.g., using C ⁇ Br and proteolytic enzymes) that can be subjected to automated amino acid sequencing.
  • the amino acid sequence of the AT4 receptor provides the sequence data necessary for construction of conserved and degenerate nucleotide probes for cD ⁇ A or genomic molecular cloning of nucleic acids expressing the AT4 receptor, mutant AT4 receptor, or fragments of the AT4 receptor.
  • a convenient method for molecular cloning of the receptor is provided in Example 7. EXAMPLE 1
  • Table 3 The results of the equilibrium binding studies with membrane-bound AT4 receptor are summarized in Table 3.
  • 125 I-angiotensin IN binding to receptors in P2 membrane preparations from rabbit heart Comparisons were made of the binding of both AIN and of ATI, i.e., to the classical ATI receptor sites defined by binding of 125 I-Sar 1 ,Ile -AII. Binding studies were carried out in a buffer (below) containing an extensive cocktail of inhibitors that was designed to minimize metabolism of both the receptor and the test ligand, i.e., the buffer contained 5mM EDTA, 0.2% BSA, lO ⁇ M Bestatin, 50 ⁇ M Plummer's inhibitor, and lOO ⁇ M PMSF.
  • the buffer contained 5mM EDTA, 0.2% BSA, lO ⁇ M Bestatin, 50 ⁇ M Plummer's inhibitor, and lOO ⁇ M PMSF.
  • Angiotensin peptides (i.e., Al, All, AHI, or AIN) were stable in this buffer for 4 h at 37°C with less than 10% hydrolysis measured by reverse phase HPLC.
  • the studies were conducted as described in the Materials and Methods, below.
  • the association rate constant (k j ) for 125 I-AIN was determined to be 3.05 x 10 8 M _1 min -1 and the dissociation rate constant (k. ⁇ ) was 0.028 +/ 0.017 min" 1
  • the overall dissociation constant (K d ) measured under equilibrium binding conditions was determined to be 9.15 x 10 _11 M.
  • the results in Table 7, also include a summary of studies designed to analyze the structural features of the N-terminus of an AIN ligand that are required for binding to an AT4 receptor.
  • the results of these structural studies are also presented in Figure 2B.
  • the results show that modification of the ⁇ -terminal valine residue (i.e., by ⁇ -terminal shortening of AIN to AII (4 _ 8) ), or extending the ⁇ -terminus with a hydrophobic residue such as Sar or GABA, or changing the stereoisomer of the L-Nal to D-Nal, all drastically decrease binding of an AIN ligand to the AT4 receptor (Table 7).
  • the AT4 receptor also failed to bind DuP 743 (DuP, Figure 2B) or CGP 42112A (CGP, Figure 2B) and thus did not exhibit the pharmacological properties of a classic ATI binding site (26). As shown in Figure 2B, the ability of the various compounds to inhibit AIV binding to the solubilized AT4 receptor was tested.
  • DAAI1 desAsp angiotensin I (i.e., identical at the ⁇ -terminus to AIII; see open squares with a dot, Figure 2B); AIN, angiotensin IN (closed diamonds, Figure 2B); AH (open squares, Figure 2B); SIAII (All lacking the He residue at position 5, Figure 1; open diamonds, Figure 2B); DuP (Dup 743, an AH analog; open squares, Figure 2B); CGP (CGP 42112A, another All analog; closed triangles, Figure 2B); and, AIII (open triangles, Figure 2B.
  • ⁇ -terminal neutral polar amino acid e.g., valine
  • ⁇ -terminal extension is incompatible with binding
  • deletion of the terminal valine residue eliminates binding (K j >10" 6 )
  • substitution with Sar decreases binding affinity
  • substitution with Phe results in a 5- 10-fold decrease in the affinity of binding
  • Pro- substituted AIN peptides bind with 100-fold lower affinity, but substitution with He results in equivalent binding
  • Lys substitution results in 10-fold higher binding affinity of the KYIHPF AIN ligand (data not shown).
  • the D-substitution and glycine-substitution data confirms that positions 1-3 of the AIV molecule are critical for determining binding affinity to the receptor. Positions 4-6 are less critical. In fact removal of C-terminal groups appears to enhance binding affinity perhaps by reducing steric constraints. Ligands containing C-N nonpeptide bonds can be produced that possess high affinity. In general, highest affinity is obtainable by dual modifications at bonds between amino acids 1-2 and 3-4. Val(l)Val(3) AIV appears totally resistant to enzymatic degradation upon exposure to rat kidney homogenates. As further shown in Table 7, tripeptides containing straight chain aliphatic amino acids in position 1 exhibit high affinity.
  • Example 1 Materials and Methods: Peptide Synthesis The angiotensin analogs employed in this study were synthesized by the standard Merrifield method utilizing t-Boc protected amino acids and chloromethylated resins on a Vega 250 coupler automated synthesizer. Following synthesis, the crude peptides were purified by preparative reverse-phase HPLC using a 1 h gradient for elution at 9ml min. Initial conditions were 90% H 2 O, 10% acetonitrile, and 0.1% TFA and the final conditions at the top of the gradient were 65% H 2 O, 35% acetonitrile and 1% TFA. Purified peptides were amino acid analyzed to determine both peptide and total purity. Typically the peptides produced were greater than 99% pure and contain 20-25% acetate. Tissue Preparation: bovine adrenal cortical tissues
  • Adrenal cortex was removed from bovine adrenals obtained from a local slaughterhouse. The minced cortex was then homogenized in a Polytron as a 40:1 suspension in assay buffer at 10 sec/ml. The homogenate was then centrifuged at 500g for 10 min. to remove whole cells and nuclei. After a rehomogenization and recentrifugation the combined supernatants were spun at 40,000 x g for 20 min. The pellet was rehomogenized and respun at 40,000 rpm for 30 min. This final pellet was resuspended in assay buffer and layered on a discontinuous sucrose gradient (0.8M/1.2M). After a 100,000 x g spin for 90 min. the purified membranes were located at the density interface and were removed.
  • sucrose containing membrane suspension was diluted 1 :10 in assay buffer and spun a last time at 40,000 x g for 30 min.
  • the pellet was resuspended in assay buffer at a concentration of lOmg protein/ml and heat treated at 60°C for 30 min. in the presence of 20mM MgC ⁇ .
  • Binding studies bovine adrenal cortical membranes
  • Solubilization and characterization of the receptor from bovine adrenal membranes was accomplished by homogenizing the membranes (above) in hypertonic buffer followed by fractionation of the membranes by sucrose density gradient centrifugation.
  • the membrane preparation was then heat treated at 60°C in the presence of MgC-2 (to inactivate ATI receptors). The heat treatment also reduced endogenous peptidase activity in the preparations by 90-95%.
  • the AT4 receptor in the preparations was then solubilized using 1% zwitterionic detergent 3-[(3-cholamidopropyl) dimethyl ammonio]-l-propanesulfonic acid (CHAPS).
  • Binding studies rabbit heart P2 membranes from rabbit heart were prepared by homogenization and differential centrifugation at 4°C.
  • Binding was carried out in the presence of 5mM (EDTA), 0.2% heat-treated bovine serum albumin (HTBSA), lO ⁇ M Bestatin, 50 ⁇ M Plummer's inhibitor, lOO ⁇ M phenylmethylsulfonylfluoride (PMSF), and 50mM Tris, pH7.4, at 22°C. Binding was initiated by the addition of lOOmg protein and appropriate amounts of labeled ligand. (For kinetic binding studies the samples were incubated for 10, 20, 30, 40, 50, 60, 90, 120, 150, 180, and 220 minutes at 37°C.
  • Dissociation (i.e., of ligand from receptors) experiments were conducted by adding lmM unlabeled AIV ligand competitor to the assay at 120 minutes after initiating binding (at 37°C) with 0.5nM 125 I-AIV.
  • N.Det. not detectable, i.e., less than 1.8 finol mg protein.
  • Bacitracin is a polypeptide antibiotic with the sequence ICLEIKOIFHDD (i.e., O is ornithine), and it is often included in angiotensin binding assays to inhibit the action of nonspecific proteases (i.e., as an alternative substrate for the proteases).
  • bacitracin interference is of potential significance for at least two reasons: 1) previous investigators who have included bacitracin in their assay buffers may have inhibited AIV ligand binding to the AT4 receptor; and, 2) inhibition of AIN binding by this polypeptide (notably at a very high molar concentration) may provide an indication of amino acid sequences that may contribute to electrostatic interactions in the AT4 receptor binding site (e.g., R 1 IR 2 HR 2 , where R j is an amino acid with an aromatic side chain such as OH, SH, or ⁇ H, and R 2 is a polar amino acid).
  • R 1 IR 2 HR 2 where R j is an amino acid with an aromatic side chain such as OH, SH, or ⁇ H, and R 2 is a polar amino acid
  • Receptor autoradiography is a useful extension of radioligand binding studies since it provides detailed anatomical information about the location of receptors in tissues and groups of cells in tissues, and thus it facilitates understanding the function of the AIN ligands and AT4 receptors in those sites.
  • Autoradiographic analyses of serial sections of guinea pig brain (20mM thickness) were performed. The autoradiographs showed a pattern of distribution for AH receptors and AT4 receptors in the Habenula (Figure 3), Hippocampus (data not shown) Cerebellum (data not shown), Prefrontal Cortex (data not shown), and Thalamus (data not shown).
  • the receptor distribution in the tissue was determined by binding of 1 5 I-Sar ⁇ ,Ile -AII, or 125 I-AIN, respectively. Specificity of ligand binding in these autoradiographic studies was demonstrated by competing the binding of the specific ligand (i.e., All or AIN) with unlabeled lOOnM Sarj-Heg-AII, or lOOnM AIN, respectively.
  • the data demonstrate that while specific All and AT4 receptors are located at similar sites in the Habenula, Hippocampus, and Cerebellum of guinea pig brain, the two receptors are distinct with regard to exact groups of cells that express the two different receptors.
  • the findings of AT4 receptors in the Hippocampus suggest that the AIN ligand-receptor interactions in the Hippocampus may mediate unique angiotensin-dependent functions including memory enhancement.
  • the AIN ligand-receptor system may provide a link between the Hippocampus and memory.
  • the mutually exclusive cellular distribution of AIN and All receptors is demonstrated in the autoradiograph shown in Figure 3.
  • Panel A reveals intense 125 I-AIN binding in the habenula
  • Panel D indicates that 125 I-Sar ⁇ ,Ile 8 -AII binding is localized primarily to fiber tracts including the visual tegmental relay zone and the medial lemniscus.
  • Example 7 Quantitative aspects of binding in brain is presented in Example 7, and other tissues data is presented in Example 1, above.
  • the results show that all important cardiovascular tissues in guinea pigs contain the AT4 receptor. This result is not surprising in light of the observation (above) that vascular endothelial cells contain high concentrations of receptors, but this is not responsible for tissue binding of AIN ligand because every vascularized tissue will possess AT4 receptors, i.e., skin and skeletal muscle has low levels of receptor.
  • tissue sections were incubated in the radioligand in the presence and absence of lOOnM unlabeled ATI or AIN peptide. After appropriate washing, autoradiograms were prepared by apposing the slide-mounted tissue sections to X-ray film (Hyperfilm, Amersham) for an appropriate exposure time. The amount of radioligand binding in a tissue was quantified using densitometric techniques and 125 I standards (Microscales, Amersham, Arlington Hts, IL).
  • EXAMPLE 3 Receptor Isolation. Purification, and Properties and Production of Monoclonal Antibodies Receptor Isolation and Purification:
  • the AT4 receptor was solubilized in high yield from purified bovine adrenal membranes using the zwitterionic detergent CHAPS (1%) at 4°C over 4 h under conditions where peptidase activity and differential solubilization of the AT4 receptor (but not the ATI receptors) is permitted (see also Example 4, Materials and Methods, below).
  • membranes from a variety of different tissues and cells were incubated for 4 h in Hepes buffer (20mM, pH7.4) containing 1% CHAPS and a cocktail of protease inhibitors and alternative protease substrates, i.e., lO ⁇ M bestatin; 50 ⁇ M Plummers' inhibitor; 0.2% BSA (bovine serum albumin); and lOO ⁇ M PMSF (phenylmethylsulfonyl fluoride).
  • a most useful component of any AH receptor purification scheme was including a step wherein the solubilized membrane proteins were subjected to a heat treatment at 60°C, e.g., for 20 minutes and in the presence of 20mM Mg "1" *. This step was useful in destroying any residual All receptor leaving the AT4 receptor intact.
  • the AT4 receptor was stable to chromatofocusing and SDS-PAGE, allowing isoelectric focusing, or one- or two-dimensional PAGE or SDS-PAGE to be used for purification. Due to the slow-off rate of 125 I-AIN binding, the receptor was radiolabeled with 125 I-AIN ligand to allow ease of identification during purification. As an additional aid to purification, the receptor was successfully cross-linked to a 125 I-radiolabeled AIN analog ligand having a C-terminal extension, i.e., from residue 8, with lysine residues (i.e., 125 I-Lysu-AIN).
  • the Lys n -AIN analog binds to the AT4 receptor with a K, j that is similar to AIN ligand.
  • BS3 Bis (sulfosuccinimidly) suberimidate
  • the 125 I-Lys ⁇ j-AIN analog of AIV was bound to the AT4 receptor and then cross-linked to the AT4 receptor through the e-amino group of Lys.
  • Purification of the AT4 receptor may also be achieved, for example, by ion exchange, lectin chromatography, hydrophobic chromatography with conventional techniques, HPLC, or FPLC.
  • Identification of the family to which a receptor belongs commonly permits predictions to be made about possible improvements in purification, useful methods for stabilizing the receptor during purification, cellular sources and assays useful for molecular cloning of the receptor, and identification of novel physiological roles for a receptor.
  • neurotransmitters and hormones are known to interact with four types of plasma membrane receptors: 1) multisubunit receptors that regulate an intrinsic ion channel; 2) G-protein linked receptors that, via the G-protein, can activate membrane channels and enzymes; 3) guanylate cyclase receptors that possess intrinsic guanylate cyclase activity in a single membrane spanning polypeptide chain; and, 4) protein tyrosine kinase receptors that have intrinsic tyrosine kinase activity capable of phosphorylating multiple protein substrates.
  • the AH receptor may be a member of the G-protein-linked family of cellular receptors.
  • the majority of known peptide receptors belonging to this family are characterized by seven membrane-spanning alpha-helical regions and when stimulated are capable of activating membrane-bound enzymes like adenylate cyclase, phosphodiesterase, and phospholipase C. (30). Additionally, membrane channel or ion transporter properties can be indirectly modified by the intervening G-protein (31).
  • many strategies have been devised to test a particular receptor's linkage with a G-protein, three strategies seem to predominate.
  • these include the following approaches: 1) GTP and its analogs are known to alter the binding affinity of agonists to their receptors. Therefore, the ability of GTP or analogs to change agonist-binding affinity is diagnostic of a G-protein-linked receptor. In the presence of GTP, dissociation of the G-protein subunits from the receptor results in a lowered affinity for agonists. This was examined (see Example 5) by the direct assessment of GTP (of GTP ⁇ S) effects on agonist binding via changes in dissociation rates or total binding over a range of GTP concentrations, or indirectly by monitoring shifts in IC50 values for agonists during competition for antagonist binding.
  • G-protein linkage Another indication of G-protein linkage is the ability of agonists to stimulate the intrinsic GTPase activity of the alpha subunit of G-proteins. This GTPase activity is triggered following receptor occupation and subsequent dissociation of alpha and beta-gamma subunits. 3) A final approach is to determine whether an agonist can facilitate nucleotide cycling. A crucial step in G-protein signal transduction is the agonist-stimulated dissociation of GDP from the alpha-subunit and its replacement with GTP. Changes in cycling are often assessed by comparing the binding of radiolabeled irreversibly bound GTP analogs before and after agonist stimulation.
  • AT4 receptor may be G-protein linked in certain cells (see Example 5) the AT4 receptor does not belong to the classical family of G-protein-linked receptors for at least three reasons: namely, 1.) Solubilization and stability characteristics of the All receptor (i.e., binding 125 I-Sar 1 ,He 8. AII) and the AT4 receptors (i.e., binding 125 I-AIN) are significantly different which is consistent with: a) large structural differences between the two receptors, and, b) differences in the structural basis of receptor integration into membranes. Thus, it is reasonable to assume that if the ATI/ ATI receptor is a member of the G-protein linked family of receptors, then the AT4 receptor probably is not.
  • BS3 cross-linked bovine adrenal AT4 receptor These molecular sizes are significantly different from the molecular weights of 55KDa to 65KDa that are commonly associated with members of the G-protein-linked family of receptors.
  • the AIN site is not a classical G-protein-linked receptor, then to what family of receptors does it belong?
  • Evidence in recent years indicates the presence of peptide receptors with intrinsic guanylate cyclase activity.
  • These receptors best exemplified by the mammalian A ⁇ P receptor, consist of a single polypeptide chain with one membrane-spanning region that possesses guanylate cyclase activity that resides near the intracellular C-terminus (32). Since only two such mammalian receptors have been identified (to date), the A ⁇ P and rat intestinal enterotoxin receptor, it is difficult to speculate on the probability that the AT4 receptor is a member of such a family of receptors. Nevertheless, the similarity in the molecular weights and in ion requirements of the ANP and AT4 receptors necessitates the consideration that the AT4 receptor may be a member of such a family.
  • the final receptor family to which the AT4 receptor may belong is the tyrosine-kinase growth factor family of receptors. These receptors are characterized by a protein kinase activity which preferentially phosphorylates tyrosine residues. Among the substrates of phosphorylation are the receptor itself and phospholipase C, which when phosphorylated initiates the inositol phosphate cascade (33).
  • the tissue response to prototypical peptides which act as tyrosine kinase receptors includes long- term alterations that invariably involve changes in the transcription rate of selective mRNAs.
  • tyrosine kinase receptors often "cross talk" with other cellular receptor types (34) in response to physiological and chemical stimuli. This type of role is precisely the function envisaged for the ATV ligand-receptor system.
  • a comparison of the solubilization, physical properties, and functional activities of the AT4 receptor with the cellular biology of members of the tyrosine kinase family of growth factor receptors suggests a closer relationship of the AT4 receptor to this family of receptors than to the guanylate cyclase family of receptors.
  • both the AT4 receptor and the FGF receptor have related biochemical characteristics, e.g., the FGF receptor has a molecular weight of about 140-150kDa (35), is relatively heat stable (i.e., at 56°C), and has divalent ion requirements (28).
  • AT4 receptors appear to have growth factor activity on at least endothelial cells and myocytes. (In the latter case, the tissue distribution and the activities of AT4 receptors are also consistent with a role for AT4 receptors in growth regulation. For instance, as disclosed above, high concentration of AT4 receptors is present in cardiovascular tissues where angiotensins are reported to enhance tissue growth.)
  • the molecular weight of the AT4 receptor is in the range of members of the tyrosine kinase families of receptors.
  • the AT4 receptor like members of both the tyrosine kinase families of receptors, is characterized by divalent cation binding sites (i.e., Mg "1""1" ).
  • the AT4 receptor like members of the tyrosine kinase and guanylate cyclase families of receptors, is characterized by relatively high heat stability (i.e., 60°C/20minutes).
  • the epidermal growth factor receptor (EGF) is heat stable at 50°C for 30 min., and has specific binding sites for Mn "1"1” and Mg "1-1” [28]).
  • the AT4 receptor appears to be a member of the tyrosine kinase family of receptors, and not the G-protein-linked family of receptors.
  • Experimental approaches to validate this vision are presented below, the experiments examine the ability of AIN ligand to stimulate phosphorylation of tyrosine residues in membrane proteins.
  • Cross-linking 125 I-AIN to the AT4 receptor can be accomplished with Bis (sulfosuccinimidyl) suberimidate (BS3) as discussed above.
  • the cross-linked receptor (approx. mw of 146,000) can then be electroeluted from PAGE gel slices in a substantially pure form for use as an electrophoretic standard.
  • For cross-linking one milligram of total solubilized membrane protein containing AT4 receptor was incubated with 30 x 10-6cpm of 125 I-AIN in 50mM Tris, pH7.4 and 150mM ⁇ aCl containing a cocktail of protease/peptidase inhibitors for 2 hr at 37°C (final volume 0.5ml).
  • Monoclonal antibodies are useful for purification of receptor, and for identifying the receptor (and fragments thereof) in tissues, cells, and biological fluids.
  • Purified or semi-purified AT4 receptor (preferably nondenatured) can be used as an in vivo or in vitro immunogen.
  • Those skilled artisans will recognize a variety of options available to them for evoking monoclonal and polyclonal antibodies, e.g., see Harlow, E. and D. Lane, Eds. "Antibodies: A Laboratory Manual” Cold Spring Harbor Laboratory, 1988).
  • antigen can be incubated in picogram quantities with murine, rat, or human lymphocytes.
  • Production of antibodies can be screened by testing for the ability of 125 I-AIV-prelabeled receptor to bind to antibodies adsorbed on a polystyrene plastic surface, e.g., in 96 well plates; or, alternatively, by testing the ability of the antibody to inhibit binding of a purified labeled receptor to AIN ligand adsorbed to a solid phase. In either case, antibody producing cells are identified, cultured, and cloned. The monoclonal antibody product of the cloned cell lines can bind the AT4 receptor in ligand-binding and non- binding domains of the AT4 receptor.
  • ⁇ on-binding domains can include structural regions of the molecule as well as enzyme active sites, phosphorylation sites, glycosylation sites, and the like.
  • the presence of antibodies specific for the ligand- binding domain can be assessed directly via the ability of the mono to competitively inhibit in binding assays.
  • antibodies are useful for receptor purification and immunohistochemical studies designed to elucidate the cellular location of receptors and also in structure/activity studies designed to map functional domains in the receptor.
  • AIN Receptor Antagonists and Agonists To test the ability of synthesized AIN ligands to competitively inhibit for 125 I-AIN ligand binding to the AT4 receptor, displacement curves were constructed using heat-treated (60°C for 20 min. in 20mM MgCl 2 ) purified bovine adrenal cortical membranes using Methods described in Example 1, above. Effects of AIN analogues on renal blood flow were determined as described in Example 6. The design of AIN analogs followed a question based approach. The unifying question: What are the essential ligand domains for receptor binding and activation? Individual chemical modifications were made to ask specific questions about spacial orientation of molecular surfaces, charge, hydrophobicity and occupancy of space (volume occupied at a specific location).
  • Agonist versus antagonist activity was assessed using a laser doppler to monitor renal cortical blood flow following infusion of a test analog into the renal artery (see Example 6). Maximal response was compared to the response (increased in flow) to AIN. (Note that under these conditions All produces a decrease in blood flow in this assay.) Interprestation of physiologic and binding data was based on the precept of a lock and key model of receptor binding and that dynamic change of the receptor upon interaction of the ligand was required for activation (full agonist activity; with second messenger activation).
  • Ligands with the highest affinity, when modeled in an energy minimized conformation offer a visual representation of the receptor binding site field surface (i.e., hydrophobic charge interactions) and charge locations in the "pre-binding state” and "non-activated state” (i.e., just as a clay imprint on a well fitting key represents the interaction surface of the lock).
  • Specific ligand domains induce changes in the receptor upon binding that produce cellular responses.
  • Ligands that fit the "pre-binding" receptor with high affinity may not activate the receptor, i.e., they may act as antagonists, while structures that induce changes in the conformation of the receptor may be compatible with, and part of, the changes that produce high affinity binding, i.e., they may act as agonists.
  • Fragments containing less than positions #1 through #4 have K i *s>500nM.
  • Figure 5 A shows no significant changes in arterial blood pressure following adminstration of KYTHPF at 100pmole/25ml min (open circles) or saline control (closed circles).
  • Figure 5B shows changes in renal blood flow following adminstration of KYIHPF at 100pmole/25ml min (open circles) or saline control (closed circles), with the increased blood flow being equal to 38% of the maximum attainable with a strong vasodilatory agent (i.e., bradykinin, as described above).
  • a strong vasodilatory agent i.e., bradykinin, as described above.
  • the receptor contains a binding site sub-domain that closely interacts with the primary amine function in the Ri residue with respect to absolute space occupancy (volume) and probably a electrostatic charge, i.e., the receptor non-planar ⁇ H3-binding component of the Ri -binding sub-domain (the same non-planar sub-domain component described in response to Question #1 above), most likely is a negatively charged residue that resides adjacent to the l°-amine when the R j group is engaging the receptor sub-domain.
  • Nle-substituted AIV had a 4-fold greater affinity for the AT4 receptor than Orn-substituted AIV.
  • Nle-substituted ATV had a remarkable binding affinity 60-fold higher than Lys-substituted AIV: i.e., NlejYIHPF had a K j of ⁇ 1 x 10" 12 M, a virtually irreversible binding ligand and indicative of partial-agonist activity.
  • NlejYIHPF had a K j of ⁇ 1 x 10" 12 M, a virtually irreversible binding ligand and indicative of partial-agonist activity.
  • Figure 6A shows changes in arterial blood pressure following adminstration of NorLeu YTHPF at 100pmole/25ml/min (open circles), 50pmole/25ml min (open squares) or saline control (closed squares).
  • Figure 6B shows changes in renal blood flow following adminstration of NorLeu YTHPF at 100pmole/25ml min (open circles), 50pmole/25ml/min (open squares) or saline control (closed squares).
  • the infusion of 0.05pmole NorLeui THPF had no effect on mean arterial pressure (Figure 6A) but increased renal blood flow in a dose-dependent manner: a maximum of 19% increase in renal blood flow was observed with infusions of 0.05pmole (Figure 6B); 19% also at O.l pmole (Figure 6B); 21% at lOpmole ( Figure 6B); and, lOOpmole NorLeui YTHPF increased renal blood flow by 30% ( Figure 6B).
  • Infusion of 0.15M NaCl in control animals were without any significant effect.
  • R-group protection was: Tosyl for His and 2,6-dichlorobenzyl for Tyr. Synthesis occurred on a t-Boc-Phe substituted resin (0.76mmol gram of 1% cross- linked divinyl benzene resin from Peninsula).
  • methylene chloride wash 1X1 min; 45% w/v trifluoroacetic acid and 0.08% indole in methylene chloride deprotection: 1X3 min and 1X30 min; methylene chloride wash: 5X1 min; isopropanol wash: 3X1 min; methylene chloride wash: 3X1 min; 10% v/v triethylamine in methylene chloride neutralization: 1X1 min and 1X5 min; methylene chloride wash: 2X1 min; isopropanol wash: 2X1 min; methylene chloride wash: 2X1 min; isopropanol wash: 2X1 min; methylene chloride wash: 3X1 min; amino acid coupling with a 2.5 or 5-fold excess of amino acid and EDC in methylene chloride: reaction times of 1.5 to 3.5 hours; methylene chloride wash: 3X1 min; isopropanol wash: 3X1 min; methylene chloride wash: 3X1 min; amino
  • Nalinal ( ⁇ -t-Boc-L valine aldehyde from Peninsula) was linked to the free amino-terminal of the growing peptide by formation of a Schiffs base intermediate with subsequent bond reduction.
  • the above protocol was utilized with the following alterations: prior to coupling, the resin was washed with dimethyl formamide 3X1 min; a 5-fold excess of valinal was added in 1% acetic acid/dimethyl formamide; a 10-fold mole ratio excess of sodium cynoborohydride (Sigma) was dissolved in 3 ml 1% acetic acid dimethyl formamide and added in equal aliquots at 0,3,5,10,15,20,25,30,40 and 50 min with concurrent nitrogen purge; the coupling was allowed to continue for 70 additional min; the resin was washed with dimethyl formamide 3X1 min. Linkage was assessed with the Kaiser test and revealed a slightly reddish color of the beads when greater than 94%.
  • the finished N-terminal deprotected resin-linked peptide was cleaved from the resin and side chain deprotected with anhydrous HF containing 10% anisole at 0°C for 40 min.
  • the HF and anisole were removed under vacuum and the peptide washed with anhydrous ether.
  • the peptide was extracted with 20% glacial acetic acid and lyophilized.
  • the crude peptide was then purified by preparative reversed phase HPLC in two steps, the first an isocratic method using acetonitrile:triethylamine-phosphate, pH3 followed by a second gradient method using acetonitrile:water (0.1% TFA).
  • the purified product was analyzed by analytical reversed phase HPLC (acetonitrile:triethylamine-phosphate, pH3) gradient method (12-18% over 60 min at 2ml/min).
  • the metabolish of 125 I-ATV and 125 I-Dival AIV by rat kidney membranes was determined as follows: Rat membranes (25 ⁇ g protein) were incubated with .6nM 125 I-peptide at room temperature in a buffer containing Tris, 50mM, pH7.4; ⁇ aCl, 150mM; BSA, 0.1%; EDTA. 5mM; bestatin, 20 ⁇ M; and Plummer's inhibitor, 50 ⁇ M. Metabolism was stopped by the addition of acetonitrile (final concentration 50%), and the samples were analyzed by reverse phase (C 18 ) HPLC. As can be seen in Figure 11, ATN is rapidly degraded while Dival AIN remains 100% intact after 4 hr of incubation.
  • AT4 receptor binding site domain binds analogues in which the peptide bond has been replaced with a non-carbonyl (non- peptidase sensitive) bond that has a similar bond length, and that is non-planar and has a non-rigid carbon-nitrogen bond.
  • ⁇ on-peptide bonds offer pharmacological advantages for a therapeutic composition, i.e., prolonged half-life.
  • the model capable of explaining this behavior has the following component parts: a) The receptor binding site sub-domain interactions with the side groups (i.e., of Ri) determines receptor activation; b) The interaction at the R j -sub-domain binding site involves a hydrophobic pocket; c) The space in the latter hydrophobic pocket conforms very closely with the 4 carbon side chain of norleucine; d) Nlej (i.e., in NleiYTHPF) interacts with the hydrophobic pocket without changing the conformation of the pocket; e) Vali (i.e., in VYIHPF) must occupy an "expanded" hydrophobic pocket, i.e., where the receptor hydrophobic pocket is displaced laterally to accomodate the branched carbon side chain in these residues.
  • Lys ⁇ i.e., in KYIHPF
  • Lys ⁇ must similarly occupy an "expanded" hydrophobic pocket because of the charge repulsion from the hydrophobic "walls" of the pocket; and, f)
  • the process of "expanding" the hydrophobic pocket constitutes a molecular trigger for the process transitioning the receptor from the "pre-binding state" to the "binding state".
  • Nle 1 -ATV (1 . 5) i.e., NleYIHP
  • Nle r AIN i.e., ⁇ leYIH
  • ⁇ le ⁇ -ATV i_3
  • NleYI may be useful for testing space-filling modifications that can be made to alter binding in the receptor binding site sub-domains. It is considered highly likely that independent modifications that can be made to alter the binding of the latter small Nlei peptides into the AT4 receptor binding site sub-domains will be paralleled when the modification are incorporated into larger AIV ligands.
  • Nal ⁇ lle 6 -AIN had a higher binding affinity for the AT4 receptor than AIN (i.e., VYfflPI >VYHTPF); and Lys 1 Ile 6 -AIV had a lower affinity than Lys r AIV (i.e., KYIHPI ⁇ KYIHPF).
  • the AT4 receptor binding site is a multi-domain binding site with interactions such that binding in one sub-domain (e.g., within the hydrophobic pocket of the Ri sub-domain) can be excluded by high affinity binding at a distant sub-domain site (e.g., within the subdomain with specificity for the C-terminal Ile6 or Pr ⁇ 5 residues; i.e., at the R ⁇ subdomain binding site in the receptor).
  • the induced-fit model supplied above in response to Question #8 is compatible with the observed exclusionary binding properties: i.e., binding of R hydrophobic pocket that constitutes the Ri -binding subdomain requires flexibility of expansion in the pocket, and binding of Rg in the R sub-domain binding site confers a rigidity to the receptor that inhibits flexibility in the R j -binding subdomain.
  • Binding was carried out as described in Example 1, above, in siliconized glass culture tubes containing 0.2nM 125 I-AIV, 25 ⁇ g of membrane protein, and the desired analogue over a concentration range of 10" 12 to lO ⁇ M using half-log dilutions. All binding incubations were carried out in duplicate at 37°C for 2 h in a buffer containing: 50mM Tris, 150mM NaCl, 5mM EDTA, lO ⁇ M bestatin, 50 ⁇ M Plummer's Reagent, lOO ⁇ M PMSF and 2% BSA (Assay buffer) in a total volume of 0.25ml.
  • AIN analogues that are peptides were synthesized by the standard Merrifield method utilizing t-Boc protected amino acids and chloromethylated resins on a Nega 250 coupler automated synthesizer (as described in Example 1, above). Following synthesis, the crude peptides were purified by preparative reverse-phase HPLC. The amino acid composition of the purified peptides was determined with respect to both composition and total purity. Typically the peptides used in these studies were greater than 99% pure and contained about 20-25% acetate. EXAMPLE 5
  • endothelial cells such as bovine coronary venular endothelial cells
  • endothelial cells such as bovine coronary venular endothelial cells
  • angiotensins were reported to be capable of stimulating angiogenesis (22).
  • studies in the inventors' laboratory over the past ten years have failed no less than six times to demonstrate detectable levels of
  • the competitive binding affinities of analogues to the receptor showed affinites that (in decreasing order) were ATV >AII (3 _ 7) >AHI >AII >Sar ⁇ Ile 8 -AII, or AII (4 _ 8) »DUP 753, or CGP42112A.
  • the AT4 receptor in endothelial cells may not be G-protein linked because the non-hydrolyzable GTP analog GTP ⁇ S had no effect on 1 5 I-AIN binding to receptors in BAEC cells.
  • association rat constant (1 ⁇ ) 0.084 +/- 0.013.
  • RVSMC rat vascular smooth muscle cells
  • BAEC bovine aortic endothelial cells
  • This study is the first to describe a novel angiotensin binding site in vascular endothelium that exhibits high affinity and specificity for the hexapeptide AIV fragment of angiotensin AIL
  • the AT4 receptor is distinct from the ATI or AT2 receptors in vascular tissue. Analysis of the binding characteristics indiactes that the AT4 receptor binds AIV in a saturable and reversible manner, and that 125 I-AIV reaches equilibrium in binding to the AT4 receptor in membrane preparations in approximately 60 min. at 37°C. Binding of AIN to its receptor remains stable for at least 4 h ( Figure 7 A) with less than 10% degradation of the ligand under these binding conditions.
  • the first component is a high affinity component that exhibits K d 's of 14 and 27pM with B max 'S of 6 and lOfmol/mg protein for receptors in CVEC and BAEC membrane preparations, respectively.
  • the second binding component is a lower affinity component with K ⁇ s of 1.4 and 4.4nM (i.e., in CVEC and BAEC, respectively).
  • the second component displays a high concentration of Ugand binding commensurate with large numbers of such receptor sites in the membrane preparations: i.e., these sites bind 594 and 434fmol/mg protein in CVEC and BAEC membrane preparations, respectively.
  • the overall binding affinity (i.e., K d , single or composite site fit produced by LIGAND) was calculated to be 0.7nM for CVEC and l.OnM for BAEC. These results are in good agreement with the K d calculated from the results of kinetic binding studies (0.3nM).
  • AIV bound to these AT4 receptors in vascular tissues is presented in Figure 8 and Table 11, above.
  • This profile reveals a strict structural requirement for the N-terminus of the AIV ligand, i.e., removal of the N-terminus (Vali) of the ATV ligand results in a 200-fold decrease in affinity of the AIN ligand for the AT4 receptor in vascular tissues (i.e., an increase in the Kj).
  • ⁇ -terminal extension i.e., beyond Nali, is detrimental to the binding of AIN ligands to the vascular AT4 receptor as indicated by the inability of All and Sarj -es-AII to competitively inhibit binding of AIN to the AT4 receptor, (i.e., note the 200-fold increase in Kj seen with All and Sar ⁇ fleg-AH, when compared with AIN in Table 11).
  • the apparent affinity of AIII for the vascular AT4 receptor i.e., 20-fold higher Kj than AIN, Table 11
  • 125 I-AHI binding to bovine adrenal AT4 receptors was directly proportional to the amount of Am hydrolyzed to AIN.
  • the vascular AT4 receptor appears to exhibit less specificity for the C-terminus than exhibited for the ⁇ -terminus: i.e., the AIN ( i_ 7) fragment (with the C-terminal Phe 8 deleted still bound with reasonable affinity to the receptor (i.e., only a 7-fold increase in Kj over AIN).
  • the vascular AT4 receptors do not apparently bind either DUP 753 or CGP 42112A (i.e., Kj >10" 4 ), but ATI or AT2 receptors are well-known to do so (Timmermans, P. et al. ⁇ PS 12:55-62, 1991; Whitebread, S. et al. Biochem. Biophys. Res. Comm. 163:284-291, 1989). (This property of failure to bind either DUP 753 or CGP 42112A distinguishes AT4 receptors of the invention from ATI and AT2 receptors.)
  • Binding of 125 I-AIN to vasular endothelial AT4 receptors was not sensitive to inhibition by guanine nucleotides.
  • binding of All to ATI and AT2 receptors in membrane preparations of rat vascular smooth muscle cells was sensitive to inhibition by guanine nucleotides in a dose-dependent manner, i.e., the affinity of the ATI receptor for AH was shifted to a lower value when the receptor was uncoupled from G-proteins by the presence of the GTP analogue GTP ⁇ S ( Figure 9).
  • This shift in binding affinity in response to gunaine nucleotides is a characteristic of the high affinity form of the ATI receptor (Glossmann, H. et al. J.
  • AIV ATV-like fragments of All may have unique biological attributes.
  • AIN-like fragments of AH In cultured chick myocytes, AIN-like fragments of AH have been reported to antagonize the effects of All-induced increases in cytosolic free calcium, protein synthesis, and hypertrophic cell growth while being unable to competitively inhibit for 125 I-AII binding (Baker, K.M. et al. Am. J. Physiol. 259:H610-H618, 1990).
  • Topical application of both All and AIN-like fragments of ATI have been reported to mediate endothelium-dependent vasodilation in rabbit brain arterioles.
  • the following protocols are useful for: 1) confirming the vasodilating potential of an AIN ligand, demonstrating that ligand action is dependent on an AT4 receptor, and showing that the action is independent of Al or All receptors; 2) establishing that any observed vasodilation is endothelium dependent; 3) determining whether the mechanism of vasodilation involves prostaglandins, EDRF, or other factors like EDHF as second messengers; and 4) determining the functionality of the many AIN analogues (i.e., such as those synthesized in Example 4) as either AIN ligands or as agonists, antagonists, inhibitors, or promoters of the AIN ligand-receptor interaction.
  • AIN analogues i.e., such as those synthesized in Example 4
  • AIN and ATI ligands and various analogues (Example 4) in the presence or absence of angiotensin inhibitors (e.g., Sar ls Ile 8 -AII, DUP 753, and CGP42112A) were screened for the vasodilating activity using rabbit aorta and inferior vena cava rings or spiral strips suspended in 20ml organ baths containing Krebs solution at 37°C and continuously gassed with 5% CO 2 in oxygen. After a 1 h equilibration period, cumulative dose-response curves were constructed for the analogues over a concentration range of 10" 10 M to 10" 5 M.
  • angiotensin inhibitors e.g., Sar ls Ile 8 -AII, DUP 753, and CGP42112A
  • AIN ligand on endothelial cells was examined by measuring growth of bovine endothelial cells.
  • Cells were grown at 37°C in 35mm culture plates CO 2 /air under 5% CO 2 /95% air in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 5 ⁇ g/ml insulin and 10% (v/v) newborn bovine serum ( ⁇ BBS).
  • DMEM Dulbecco's Modified Eagle's Medium
  • ⁇ BBS newborn bovine serum
  • the test medium was supplemented with 3 H-thymidine and either All ligand (50nM) or AIN ligand (50nM) or lOng/ml acidic or basic FGF (as a positive control). Negative controls were also included using ethidium bromide (lmM).
  • the cells were harvested at various times, and cellular lysates were prepared for scintillation counting by lysing and washing the cells on glass fiber filters.
  • VYIHPF VYIHPF
  • AII (3 _ 7) VYHTP
  • AII (4 . 8) YIHPF
  • All reagents and other peptides were obtained from Sigma Chemical Co., with the exception of: Plummer's inihibitor (Calbiochem); bestatin (Peninsula Biochem); DUP 753 was a gift from Dr. Ron Smith of Dupont Merck and CGP 42112A was a gift from Dr. Marc de Gasparo of Ciba- Geigy. Angiotensin fragments numbering was based on the sequence of All ( Figure 1).
  • Bovine coronary venular endothelial cells were isolated by a bead- perfusion technique and characterized as described previously (Schelling, M.E. et al. Am. T. Physiol. 254:H1211-H1217, 1988).
  • Bovine aortic endothelial cells were a gift from Dr. Stephen Schwartz (University of Washington).
  • Cells were grown to confluence in 100mm culture dishes. Dishes were washed once in Ca ++ /Mg ++ -free PBS, pH7.4 at 37°C follwed by the addition of 2ml of cold isotonic assay buffer (150mM NaCl, 50mM Tris, ImM PMSF, lO ⁇ M bestatin, 50 ⁇ M Plummer's inhibitor, pH7.4 at 4°C). Cells were then removed from the plates with a rubber policeman and homogenized in 5ml assay buffer for approximately 10 sec (Polytron, Brinkman Inst. Co.).
  • AIV AIV Iodination of AIV AIV (and other peptides) were iodinated using an immobilized lactoperoxidase-glucose oxidase system (Enzymobeads, Biorad Laboratories) to a specific activity of 2176Ci mmole.
  • 125 I-AIV was separated from unlabeled peptide by HPLC (Beckman) using a reverse phase C ⁇ 8 column (5mm x 250mm; Adsorbosphere, Alltech, Associates). Receptor binding assays
  • the apparent pseudo-first order association rate constant k ⁇ was deterimined by the non-linear curve fitting program LIGAND.
  • the apparent dissociation rate constant, k.j was determined by LIGAND.
  • Bovine aortic endothelial cells were grown at 37°C in 35mm culture plates under 5% CO 2 in air in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 5 ⁇ g/ml insulin and 10% (v/v) newborn bovine serum (NBBS). The medium was aspirated 10-12 hours after seeding and replaced with serum-free medium. The medium was again aspirated 10-12 hours later and replaced with either test or control medium. Control medium was DMEM with 5g/ml insulin and 2%, 5%, or 10% (v/v) NBBS as indicated. The test medium was supplemented with either All or AIN ligand ⁇ the antagonist Sar ⁇ ,He 8 -AH at various concentrations. The medium was changed every 48 h (i.e., with supportive DMEM medium for the remainder of the experiment).
  • DMEM Dulbecco's Modified Eagle's Medium
  • NBBS newborn bovine serum
  • cells can be harvested on various days during the culture period by washing the plates with calcium free medium (CMF) two times for 5 min. followed by incubation in 0.1% trypsin in CMF for 5 min. The cells can then be washed free from the plate and aspirated by Pasteur pipet into 15ml centrifuge tubes containing 3 ml DMEM with 20% (v/v) ⁇ BBS. The plates can be washed with an additional 1ml DMEM 20% ⁇ BBS which was transferred to the appropriate centrifuge tube and spun at 300 x g for 10 min. Excess medium was aspirated and the pellet resuspended in a final volume of 1ml of the control medium. Aliquots can then be counted using a hemocytometer and cell number expressed as cells/plate.
  • CMF calcium free medium
  • thymidine incorporation was measured.
  • D ⁇ A synthesis [methyl- 3 H]thymidine (60Ci/mmol, lOmCi per plate) was added to cultures 12 h after addition of the All or AIN. Twelve h later, medium was removed and 1ml of a 1% aqueous solution of Triton X-100 was added. The cells were incubated with this solution for 5 min. and the entire contents of the plate transferred to 10ml of absolute ethanol. This material was then filtered under vacuum through 2.4cm glass fiber filters (GF/A, Whatman), and the filters were washed twice with 10ml of absolute ethanol and assayed for radioactivity by scintillation counting.
  • GF/A 2.4cm glass fiber filters
  • EXAMPLE 6 Physiological Function of Angiotensin IN Receptor and Ligand Angiotensins Al, AH, and Am are reported to have a wide variety of effects on target issues, some of which are acute while others appear more long-term. All reportedly has a cellular effect of increasing c-fos levels in cultured vascular smooth muscle cells (17), and c-fos is reported to be one common pathway for triggering cell growth. Considering the widespread distribution of AT4 receptors in many organs and tissues (EXAMPLES 1 and 2, above), it is Ukely that AIN has multiple functions, including long-term effects on cells by triggering increased expression of c-fos, i.e., activities previously mistakenly attributed to All and AHI.
  • AIN ligand-receptor system may play in three organs enriched in AT4 receptors: blood vessels, kidney, and adrenal glands. (Other organs such as brain or heart which also possess high levels of specifically localized AT4 receptors can be studied in a similar manner.) Renal Blood Flow: The AIN Receptor and All Receptor Have Physiologically Distinct and Opposing Activities:
  • AIN ligand in the regulation of renal blood flow.
  • the rationale for initially choosing to examine the kidney was at least two-fold.
  • the AT4 receptor is found in high concentrations in kidney and endothelial cells (Example 1 and 2, above).
  • Second, vascular endothelial cells are reported to regulate vascular tone and to play a role in the control of renal blood flow.
  • Superficial blood flow in the rat kidney was assessed using laser doppler methods in anesthetized rats following direct infusion of a test substance into the renal artery.
  • the infusion of experimental compounds and saline had no effect on systemic arterial blood pressure (see results in Example 4).
  • AIV ligand-receptor effects on renal functions was provided by analyzing distribution of radio-labeled insulin and p-aminohippicuric acid; in combination with measurements of urine flow, urine osmolality, urine ⁇ a + and K + , and hematocrit.
  • the effects of AIV ligand, All, and other AIV analogues were determined, i.e., a) on renal blood flow, b) glomerular filtration rate, c) osmolal clearance, d) filtration fraction, and e) tubular function.
  • Dose-response curves for AIV ligand and AH ligand were constructed in the presence and absence of the AH antagonist Sar ⁇ Iles-AII.
  • AIV analogues with special in vitro properties were tested in a similar manner (above) to determine their effects on renal function. Studies were carried out as acute preparations in anesthetized rabbits and using jugular and urethral catheters.
  • AIV Ugand is produced locally in neural tissues, i.e., by synthesis of Al and conversion to ATV.
  • ATV ligand is produced locally from precursors synthesized in the tissue.
  • circulating ATV precursors e.g., AT, All or AHI
  • the first or second scenario is an operative mechanism in a particular tissue can be determined by introducing radiolabeled precursors (i.e., 125 I-AI) into the bodily fluid bathing the tissue (e.g., plasma or CNS fluid), and by then collecting samples of the fluid at different times and assaying by reverse-phase HPLC to determine if the AIV precursor has been converted to ATV ligand in the fluid. If it has been converted, the second scenario is operative; if it has not been converted a second series of experiments is conducted. In the second series of experiments biosynthesis of ATV precursors is evaluated (i.e., with radiolabeled amino acids) and conversion of the precursor into AIV ligand is examined in pulse-chase type experiments. If biosynthetically radiolabeled AIN precursor chases into AIN ligand, then the first scenario is operative in the tissue. Changes in the AIN-Ligand-Receptor System in Response to Neurological Effects:
  • AT4 receptors in brain A representative experimental protocols for showing changes in the AIN- ligand-receptor system in response to neurological and physiological effects is described in the Materials and Methods, below.
  • AT4 receptors in brain A representative experimental protocols for showing changes in the AIN- ligand-receptor system in response to neurological and physiological effects is described in the Materials and Methods, below.
  • AT4 receptors in brain A representative experimental protocols for showing changes in the AIN- ligand-receptor system in response to neurological and physiological effects is described in the Materials and Methods, below. AT4 receptors in brain:
  • Hippocampal AT4 receptors identified in tissues by receptor autoradiography in Example 2, above, were evaluated further by isolating hippocampal membranes (i.e., including hypothalamus, thalamus, septum, anteroventral third ventricular area, HSTA, above) and then solubilizing the receptor. (A similar approach may be employed with AT4 receptors in other tissues.) The results presented below show that the guinea pig hippocampal AT4 receptor binds AIN ligand with a high affinity (K d 1.29 ⁇ 0.18nM, mean ⁇ SD, Hill Coeff.
  • Memory Retrieval The effects of AIN ligand on learning and memory were tested in rats by measuring the passive avoidance response, i.e., the mean latency period (time in seconds) for which the animal avoided a dark compartment. Training was conditioned to avoid the dark compartment by administering a 0.25mA foot shock over a period of 2 seconds with the door to a lighted compartment closed. On day 2 retrieval of the cognitive memory was tested 5 minutes after intracerebroventribular (icv) injection of AH or AIN.
  • icv intracerebroventribular
  • the tissue was homogenized in 40 volumes of hypotonic buffer containing 50mM Tris, pH7.4 and 5mM EDTA, and spun at lOOOg for 10 min. The supernatant was removed and recentrifuged at 40,000g for 30 min. The pellet was rehomogenized in hypotonic buffer and recentrifuged. The 40,000g pellet was homogenized in isotonic buffer (50mM Tris, pH7.4, 5mM EDTA, 150mM ⁇ aCl, 20mM bestatin, 50mM Plummer's inhibitor, lOOmM PMSF, and 0.1% heat treated BSA) and recentrifuged a final time at 40,000 x g.
  • hypotonic buffer containing 50mM Tris, pH7.4 and 5mM EDTA, and spun at lOOOg for 10 min. The supernatant was removed and recentrifuged at 40,000g for 30 min. The pellet was rehomogenized in hypotonic buffer and recentr
  • the pellet was resuspended at a concentration of 2.5mg protein/ml as determined by the Lowry protein assay.
  • Binding assays which totaled 250ml, contained 10ml 125 I-AIN ligand (sp. act-2176 Ci mmol), 10ml tissue homogenate, 10ml unlabeled peptide (if employed), and the remainder isotonic buffer. Incubations were carried out for 2 h at 37°C. Preliminary experiments demonstrated that incubation for 1 h at 37°C was necessary for equilibrium to be reached and that binding was stable for at least 4 h. At that time less than 10% of the 125 I-AIN was shown to be by HPLC analysis.
  • tissue sections mounted on slides. Slices were initially preincubated in isotonic buffer for 30 min at room temperature, then incubated in labeled ligand (O. ⁇ nM) for 2 h, rinsed, dried, and exposed to X-ray film as previously described.
  • labeled ligand O. ⁇ nM
  • AIII to AIV may result from the action of nonspecific proteases but these enzymes may also cleave all angiotensins at sites other than the All R 2 -N 3 . and are not termed herein AIV angiotensinase.). In either case, cleavage of the AH Arg 2 -Val 3 peptide bond in Al, AH, or AIII generates AIV.
  • AIN angiotensinase enzyme i.e., that cleaves Al, All, and AHI in an efficient manner to permit regulatable formation of AIN.
  • the AIN angiotensinase enzyme may be identified, isolated, and purified using the experimental approaches described below, in the Materials and Methods, in combination with the assays described in the Examples above (see Example 1). Data presented herein indicate that AH and Am are exceUent and specific inhibitors of 125 I-AIN formation from 125 I-AI. Materials and Methods: Experiment #1. Formation of AIN Ligand From AIN Precursors in Circulation.
  • 125 I-labeled angiotensins (10 7 dpm) - Al, All, or AHI, and tetradecapeptide can be injected into the carotid artery of a guinea pig and blood samples (50 ⁇ l) can be collected at 30-sec or 1-min. intervals from a second cannula in the femoral artery into lOO ⁇ l of 20% TCA for 10 min. Samples may be analyzed by reverse-phase HPLC utilizing methods that have been reported previously (47). The data are analyzed to determine the rate of formation of AIN Ugand from potential AIN precursors. Experiment #2: Formation of AIN from Precursors via Action of Adrenal Enzymes.
  • Guinea pig adrenals were excised and homogenized in a Krebs-Ringer buffer containing the full complement of ions (as above in Example 1). After a low speed spin at 500g for 10 min. to remove whole cells and nuclei, the supernatant is centrifuged at 40,000g for 30 min. The supernatant is recentrifuged at 100,000g for 90 min. yielding both a soluble (100,000g supernatant) and a microsomal (100,000g pellet) fraction. The 40,000 x g pellet is rehomogenized and fractionated on a discontinuous sucrose fractionated gradient (0.4M-1.2M sucrose, in 0.2M steps).
  • the membranes at the 0.8M to l.M and IM to 1.2M interfaces can be collected and combined, resuspended in a 10X excess of Krebs buffer. The membranes were then centrifuged at 40,000 x g for 30 min. After a final resuspension in Krebs buffer and centrifugation at 40,000 x g for 30 min., the final plasma membrane fraction is ready for the assay. Soluble, membrane, and microsomal fractions may be incubated at various protein concentrations and times at 37°C with 10 6 cpm of 125 I-AI, AH, AIII, and tetradecapeptide.
  • guinea pig adrenal tissue (as expected) possesses an AIN angiotensinase
  • the specificity of the enzyme(s), its activity on various substrates, and metal ion requirements can be established by incubating preparations of the isolated enzyme with angiotensins (e.g., in the presence of inhibitors of nonspecific proteases), and followed by examination of the hydrolytic products on reverse-phase HPLC.
  • the sequence of the hydrolytic products may be determined by automated amino acid sequencing. Incubation conditions with varying concentrations of the angiotensin substrate were used to develop data for double reciprocal plots thus allowing the affinity of enzyme(s) for the different angiotensins to be determined.
  • Pandiella A., Bequinot, L., Nincentini, L.M., and Meldotesi, I, TIPS 10,

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Abstract

L'invention concerne un nouveau système unique de récepteurs de l'angiotensine AT4 et de ligand AIV pour la liaison d'un petit fragment exapeptide à terminaison N de l'angiotensine II (appelé AIV, avec la séquence d'acides aminés Val1-Tyr2-Ile3-His4-Pro5-Phe6). Le ligand HIV se fixe de manière saturée, réversible, spécifique et avec grande affinité sur la membrane des récepteurs AT4 d'une variété de tissus, y compris ceux du c÷ur, des poumons, des reins, de l'aorte, du cerveau, du foie et de l'utérus de nombreuses espèces animales. Le récepteur AT4 est pharmacologiquement distinct des récepteurs d'angiotensine classique (AT1 ou AT2). Le système utilise des peptides AIV ou des peptides semblables à AIV à terminaison C tronqués ou étendus (p. ex. VYIHPFX) en tant qu'agent indicateur, et le récepteur de la membrane plasmique AT4 en tant que mécanisme de détection. Le récepteur AT4 de l'angiotensine et les fragments récepteurs (y compris le domaine du site de liaison du récepteur) sont capables d'une fixation d'un peptide à terminaison N de l'angiotensine AIV VYIHPF mais non d'un peptide à terminaison N de l'angiotensine AII ou AIII, à savoir DRVYIHPF ou RVYIHPF, respectivement. L'invention concerne également des procédés d'isolement du récepteur AT4 et de l'angiotensinase AIV, d'identification d'agonistes et d'antagonistes de l'angiotensine AIV, et de constructions de dosage diagnostiques afin de mesurer de manière spécifique l'angiotensinase spécifique à AI et à AIV dans des fluides biologiques.
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US6592877B1 (en) 1995-09-01 2003-07-15 Corixa Corporation Compounds and methods for immunotherapy and diagnosis of tuberculosis
AU6861796A (en) * 1995-10-30 1997-05-22 Brigham And Women's Hospital Angiotensin iv and analogs as regulators of fibrinolysis
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DE19825494A1 (de) * 1998-06-08 1999-12-09 Hoechst Marion Roussel De Gmbh Neuer Angiotensin Rezeptor, Herstellung und Verwendung desselben
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US20020049162A1 (en) * 2000-01-27 2002-04-25 Rodgers Kathleen E. Methods for inhibiting smooth muscle cell proliferation
EP1420800B1 (fr) 2001-08-02 2011-09-28 Howard Florey Institute Of Experimental Physiology And Medicine Modulation de l'activite du recepteur (at 4) d'aminopeptidase (irap)/d'angiotensine iv regulee par l'insuline
EP2043675A2 (fr) 2006-07-07 2009-04-08 Washington State University Research Foundation Régulation du récepteur c-met par des ligands du récepteur de l'angiotensine iv (at4)
US8236761B2 (en) 2006-07-07 2012-08-07 Washington State University Research Foundation C-Met receptor regulation by angiotensin IV (AT4) receptor ligands
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A. J. PHYSIOL., vol. 257, no. 6/2, 1989, pages R1551-R1557, XP000613920 WRIGHT, J.W.ET AL.: "Structure-function analyses of brain angiotensin control and pressor action in rats" *
J. PHARMACOL. EXP. THER., vol. 266, no. 2, 1993, pages 1036-42, XP000613867 HANESWORTH J.M. ET AL.: "Elucidation of a Specific Binding Site for Angiotensin II(3-8), Angiotensin IV, in Mammalian Heart Membranes" *
PEPTIDES, vol. 14, 1993, pages 949-954, XP000613877 SARDINIA M.F. ET AL.: "AT4 Receptor Binding Characteristics: D-Amino Acid- and Glycine-Substituted Peptides" *
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