WO2002087631A1

WO2002087631A1 - Gastrin-receptor-avid peptide conjugates

Info

Publication number: WO2002087631A1
Application number: PCT/US2002/013840
Authority: WO
Inventors: Timothy J. Hoffman; Wynn A. Volkert; Gary Sieckman; Chrys-Ann Higginbotham; Ning Li; Hariprasad Gali; Charles J. Smith
Original assignee: University Of Missouri System
Priority date: 2001-05-02
Filing date: 2002-04-30
Publication date: 2002-11-07
Also published as: US7060247B2; CA2346154A1; US20020054855A1

Abstract

A compound for use as a therapeutic or diagnostic radiopharmaceutical includes a group capable of complexing a medically useful metal attached to a moiety which is capable of binding to a gastrin releasing peptide receptor. A method for treating a subject having a neoplastic disease includes administering to the subject an effective amount of a radiopharmaceutical having a metal chelated with a chelating group attached to a moiety capable of binding to a gastrin releasing peptide receptor expressed on tumor cells with subsequent internalization inside of the cell. A method of forming a therapeutic or diagnostic compound includes reacting a metal synthon with a chelating group covalently linked with a moiety capable of binding a gastrin releasing peptide receptor.

Description

GASTRIN-RECEPTOR-AVID PEPTIDE CONJUGATES

TECHNICAL FIELD

This invention relates to radionuclide-labeled compounds useful as radiopharmaceuticals. More particularly, the present invention relates to conjugates of bombesin (BBN) analogues and a metal complexing group which, when complexed to a radionuclide, are useful as therapeutic and imaging agents for cancer cells that express gastrin releasing peptide (GRP) receptors.

BACKGROUND OF THE INVENTION

Detection and treatment of cancers using radiopharmaceuticals that selectively target cancers in human patients have been employed for several decades. Unfortunately, only a limited number of site-directed radiopharmaceuticals that exhibit highly specific in vivo localization in or near cancer cells are currently in routine use as being approved by the United States Food and Drug Administration (FDA). There is a great deal of interest in developing new radioactive drugs due to the emergence of more sophisticated biomolecular carriers that have high affinity and high specificity for in vivo targeting of tumors. Several types of agents are being developed and have been investigated including monoclonal antibodies (MAbs), antibody fragments (FAB'S and (FAB)2'S), and receptor-avid peptides [Bushbaum, 1995; Fischman et al., 1993; Schubiger et al., 1996]. The potential utility of using radiolabeled receptor-avid peptides for producing radiopharmaceuticals is best exemplified by ¹¹¹ln-DTPA- conjugated octreotide (an FDA approved diagnostic imaging agent, Octreoscan®, marketed in the United States by Mallinckrodt Medical, Inc.) [Lowbertz et al. 1994]. This radiopharmaceutical is an ¹¹¹ln-DTPA conjugate of Octreotide, a small peptide analogue of the human hormone somatostatin. This drug specifically binds to somatostatin receptors that are over-expressed on neuroendocrine cancers (e.g., carcinoid Ca, neuroblastoma, etc.) as well as others [Krenning et al., 1994]. Since ^{1 i 1} indium (¹¹¹ln) is not the ideal radionuclide for scintigraphic imaging, other somatostatin analogues and other receptor-avid biomolecules that are labeled with ^99mTc (the optimal radionuclide for diagnostic imaging) are being studied and developed [Eckelman, 1995; Vallabhajosula et al., 1996]. Bombesin (BBN) is a 14 amino acid peptide that is an analogue of human gastrin releasing peptide (GRP) that binds to GRP receptors with high specificity and has an affinity similar to GRP [Davis et al., 1992]. GRP receptors have been shown to be over-expressed or uniquely expressed on several types of cancer cells. Binding of GRP receptor agonists (also autocrine factors) increases the rate of cell division of these cancer cells. For this reason, a great deal of work has been and is being pursued to develop BBN or GRP analogues that are antagonists [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Cai et al., 1994]. These antagonists are designed to competitively inhibit endogenous GRP binding to GRP receptors and reduce the rate of cancer cell proliferation [Hoffken, 1994]. Treatment of cancers using these antagonists with these non-radioactive peptides requires chronic injection regimens (e.g., daily, using large quantities of the drug).

In designing an effective receptor-avid radiopharmaceutical for use as a diagnostic or therapeutic agent for cancer, it is important that the drug have appropriate in vivo targeting and pharmacokinetic properties [Fritzberg et al., 1992; Eckelman et al., 1993]. For example, it is essential that the radiolabeled receptor-avid peptide have high specific uptake by the cancer cells (e.g., via GRP receptors). In addition, it is necessary that once the radionuclide localizes at a tumor site, it must remain there for an extended time to deliver a highly localized radiation dose to the tumor. In order to achieve sufficiently high specific uptake of radiolabeled BBN analogues in tumors, the binding affinity of promising derivatives must be high (i.e., K_d = 1-5 nmolar or less) with prolonged retention of radioactivity [Eckelman et al., 1995; Eckelman et al., 1993]. Work with ¹²⁵I-BBN derivatives has shown, however, that for cancer cells that bind the ¹²⁵I-BBN derivatives (whether they be agonists or antagonists), the radioactivity is either washed off or expelled from the cells (in vitro) at a rapid rate [Hoffman et al., 1997]. Thus, these types of derivatives have a low probability of remaining "trapped" at the tumor site (in vivo) sufficiently long enough to be effective therapeutic or diagnostic agents.

Developing radiolabeled peptides that are cleared efficiently from normal tissues is also an important and especially critical factor for therapeutic agents. When labeling biomolecules (e.g., MAb, FA_B'S or peptides) with metallic radionuclides (via a chelate conjugation), a large percentage of the metallic radionuclide (in some chemical form) usually becomes "trapped" in either the kidney or liver parenchyma (i.e., is not excreted into the urine or bile) [Duncan et al., 1997; Mattes, 1995]. For the smaller radiolabeled biomolecules (i.e., peptides or FA_B'S), the major route of clearance of activity is through the kidneys, which in turn retain high levels of the radioactive metal (i.e., normally > 10-15% of the injected dose) [Duncan et al., 1997]. This presents a major problem that must be overcome in the development of therapeutic agents that incorporate metallic radionuclides. Otherwise, the radiation dose to the kidneys would be excessive. For example, ¹¹¹ln-octreotide, the FDA approved diagnostic agent, exhibits high uptake and retention in kidneys of patients [Eckelman et al., 1995]. Even though the radiation dose to the kidneys is higher than desirable, it is tolerable in that it is a diagnostic radiopharmaceutical (it does not emit alpha- or beta- particles), and the renal dose does not produce observable radiation induced damage to the organ.

It has been found that conjugating non-metallated metal chelates to BBN derivatives can form GRP agonists that exhibit binding affinities to GRP receptors that are either similar to or approximately an order of magnitude lower than the parent BBN derivative. [Li et al., 1996a]. Recent results show that it is now possible to add radiometal chelates to BBN analogues to form conjugates which are agonists and retain GRP receptor binding affinities that are sufficiently high (i.e., approximately 1-5 nmolar K 's) for further development as potential radiopharmaceuticals. These agonist conjugates are transported intracellularly after binding to cell surface GRP receptors and are retained inside the cells for extended time periods. In addition, in vivo studies in normal mice have shown that retention of the radioactive metal in the kidneys was low (i.e., <5%), with the majority of the radioactivity excreted into the urine.

According to one aspect of the present invention, there is provided a BBN conjugate consisting of essentially a radio-metal chelate covalently appended to the receptor binding region of BBN [e.g., BBN(8-14) or BBN(7-14)] to form radiolabeled BBN analogues that have high specific binding affinities with GRP receptors. These analogues are retained for long periods of time inside GRP expressing cancer cells. Furthermore, their clearance from the bloodstream into the urine with minimal kidney retention is efficient. Preferably, the radiometals are selected from ^99mTc, ^186/188Re, ⁰⁵Rh, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y, ¹⁹⁹Au, ¹⁷⁷Lu, ¹⁴⁹Pr, or ¹¹¹ln, all of which hold the potential for diagnostic (i.e., ^99rπTc and ¹¹¹ln) or therapeutic (i.e., ^186/188Re, ¹⁰⁵Rh, ¹⁵³Sm,

166_Hθj 90_Yι 199_{AU (} 177_{LU j} 149p_{m j jn cancer}

patients [Schubiger et al, 1996; Eckelman, 1995; Troutner, 1978].

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a compound for use as a therapeutic or diagnostic radiopharmaceutical, which includes a group that is capable of complexing a metal attached to a moiety capable of binding to a gastrin releasing peptide receptor.

Additionally, in accordance with the present invention, a method for treating a subject having a neoplastic disease includes the step of administering to the subject an effective amount of a radiopharmaceutical having a metal chelated with a chelating group attached to a moiety capable of binding to a gastrin releasing peptide receptor on a cancer cell and being subsequently intracellularly transported and residualized inside the cell.

Additionally, in accordance with the present invention, a method of forming a therapeutic or diagnostic compound includes the step of reacting a metal synthon with a chelating group covalently linked with a moiety capable of binding a gastrin releasing peptide receptor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: FIGURE 1 illustrates a radiometal conjugate according to the present invention;

FIGURE 2 is an ORTEP drawing of the {Rh[16]aneS -olCI₂}⁺, illustrating the crystal structure a Rh macrocycle;

FIGURE 3 illustrates a coupling reaction wherein a spacer group is coupled to a bombesin agonist binding moiety;

FIGURE 4 illustrates a coupling reaction for coupling a metal chelate to a peptide;

FIGURE 5 illustrates several iodinated bombesin analogues including their ICso's; FIGURE 6 illustrates several tethered bombesin analogues;

FIGURE 7 illustrates several [16]aneS₄ bombesin analogues;

FIGURE 8 is a graph illustrating IC₅0 analysis wherein %-¹²⁵l-BBN total uptake versus molar concentration of displacing ligand is shown; FIGURE 9 illustrates several Rh-[16]aneS₄ bombesin analogues;

FIGURE 10 illustrates an HPLC chromatogram of Rh-BBN-37 wherein (A) illustrates ¹⁰⁵RhCI -BBN-37 and (B) illustrates RhCI₂-BBN-37; FIGURE 11 is a graph illustrating ¹²⁵l-Tyr⁴-bombesin intemalization efflux from Swiss 3T3 cells;

FIGURE 12 illustrates ¹²⁵l bombesin intemalization efflux in ¹²⁵l- free buffer wherein ¹²⁵l-Tyr⁴-BBN vs. ¹²⁵l-Lys³-BBN efflux from Swiss 3T3 cells is shown; FIGURE 13 is a graph illustrating the efflux of ¹⁰⁵Rh-BBN-37 from Swiss 3T3 cells;

FIGURE 14 illustrates several ¹⁰⁵Rh bombesin analogues including their IC₅o's;

FIGURE 15 is a graph illustrating ¹⁰⁵Rh-BBN-61 efflux from Swiss 3T3 cells;

FIGURE 16 is a graph illustrating the efflux of ¹⁰⁵Rh-BBN-22 vs. ¹⁰⁵Rh-BBN-37 from Swiss 3T3 cells;

FIGURE 17 is two graphs illustrating Pancreatic CA cell binding wherein (A) illustrates the efflux ¹²⁵l-Tyr⁴-BBN from CF PAC1 cells and (B) illustrates the efflux of ¹⁰⁵Rh-BBN-37 from CF PAC1 cells;

FIGURE 18 is two graphs illustrating Prostate CA cell binding wherein (A) illustrates the efflux of ¹²⁵l-Tyr⁴-BBN from PC-3 cells and (B) illustrates the efflux of ¹⁰⁵Rh-BBN-37 from PC-3 cells;

FIGURE 19 illustrates five [16]aneS₄ bombesin analogues which utilize amino acids as Linking Groups;

FIGURE 20 illustrates four Rh-[16]aneS₄ bombesin analogues and IC50 values obtained in 3 cell lines;

FIGURE 21 illustrates three different N₃S-BFCA conjugates of BBN(7-14); FIGURE 22 illustrates an HPLC chromatogram of ^99mTc-BBN- 122;

FIGURE 23 is a graph illustrating ^99mTc-BBN-122 intemalization into human prostate cancer cells (PC-3 cells); FIGURE 24 is a graph illustrating ^99mTc-BBN-122 intemalization into human pancreatic tumor cells (CFPAC-1 cells);

FIGURE 25 is a graph illustrating ^99mTc-RP-414-BBN-42 retention in PC-3 prostate cancer cells;

FIGURE 26 is a graph illustrating ^99mTc-42 retention in CFPAC-1 pancreatic cancer cells;

FIGURE 27 illustrates further radiometal conjugates according to the present invention;

FIGURE 28 is three HPLC chromatograms of (A) DOTA-BBN[7- 14-NH₂ (λ = 280 nm) (B) ln-DOTA-BBN[7-14]NH₂ (λ = 280 nm) and (C) ¹¹¹ln- DOTA-BBN[7-14]NH₂ (radiometric);

FIGURE 29 is a graph showing the competitive binding assay of ln-DOTA-8-Aoc-BBN[7-14]NH₂ v. ¹²⁵l-Tyr⁴-BBN in PC-3 ceils;

FIGURE 30 is a graph showing the intemalization of ¹¹¹ln- DOTA-8-Aoc-BBN[7-14]NH₂ in PC-3 cells; FIGURE 31 is a graph showing the efflux of ¹¹¹ln-DOTA-8-Aoc-

BBN[7-14]NH₂ in PC-3 cells; and

FIGURE 32 illustrates radiometal conjugate according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, compounds for use as diagnostic and/or therapeutic radiopharmaceuticals include a group capable of complexing a metal attached to a moiety capable of binding to a gastrin releasing peptide (GRP) receptor, as shown in Figure 1. These compounds can be prepared with either a diagnostic radiometal or a therapeutic radiometal, thus affording utilities as either a diagnostic agent to identify cancerous tissues within the body using scintigraphiG imaging techniques, or a therapeutic agent for the treatment and control of cancerous tissues. The moiety capable of specific binding to the GRP receptor is a GRP agonist. A GRP agonist activates or produces response by the GRP receptor upon interaction with the GRP receptor and is subsequently internalized inside of the cell by endocytosis. In contrast, a GRP antagonist counteracts the effect of an agonist and is not internalized inside of the cell. More specifically, the GRP agonist for the purpose of this invention is a compound such as selected amino acid sequences or peptidomimetics, which are internalized or residualized following binding with high affinity and selectivity to GRP receptors and can be covalently linked to the metal complexing group. Many examples of specific modifications of the BBN(7-14) or BBN(8-14) that can be made to produce sequences with high antagonistic and agonistic binding affinity for GRP repectors have been reported by numerous investigations [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Cai et al., 1994; Moody et al., 1995; Leban et al., 1994; Cai et al., 1992]. In a preferred embodiment of the present invention, the metal complexing group or moiety is a chelating agent or chelator which complexes to metals such as ^10δRh, ^186/188Re, ^99mTc, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y, ¹¹¹ln, ¹⁷⁷Lu, ¹⁴⁹Pm, ¹⁴⁹Sm or ¹⁹⁹Au. The chelating agent or chelator is attached or bound to the GRP agonist "binding region" through a spacer to produce a conjugate that retains its capability for high affinity and specific binding to GRP receptors.

In a more preferred embodiment of the present invention, the GRP agonist is a bombesin (BBN) analogue and/or a derivative thereof. The BBN derivative or analog thereof preferably contains either the same primary structure of the BBN binding region [i.e., BBN(8-14) or BBN(7-14)] or similar primary structures, with specific amino acid substitutions, that will specifically bind to GRP receptors with better or similar binding affinities as BBN alone (i.e., Kd = 1-5 nmolar). Compounds containing this BBN binding region (or binding moiety), when covalently linked to other groups (e.g., a radiometal chelate), are also referred to as BBN conjugates. In general, the compounds of the present invention have a structure of the general formula:

X-Y-B wherein X is a group capable of complexing a metal such as a radiometal; Y is a covalent bond or a spacer group; and B is a bombesin agonist binding moiety.

The metal bound to the metal complexing group can be any suitable metal chosen for a specific therapeutic or diagnostic use including transition metals, lanthanides, auger electron emitting isotopes, α, β or γ emitting isotopes. Preferably, the metal is a radiometal such as ¹⁰⁵Rh, ^99mTc ^186/188Re, ¹⁵³Sm, ¹⁶⁶Ho, ¹¹¹ln, ⁹⁰Y, ¹⁷⁷Lu, ¹⁴⁹Pm, ¹⁵³Sm, and ⁹ Au whose chelates can be covalently linked (i.e., conjugated) to the specific BBN binding region via the N-terminal end of the primary binding sequence (e.g., BBN-8 or Trp⁸) as shown in Figure 1.

In a preferred embodiment, the radiometal complexes are positioned by being spaced apart from or remotely from the amino acid Trp⁸ by the spacer groups. The spacer groups can include a peptide (i.e., > 1 amino acid in length), a hydrocarbon spacer of C1-C₁0, or a combination thereof. Preferably, the hydrocarbon spacer is a C3-C9 group. The resulting radiolabeled BBN conjugates retain high binding affinity and specificity for GRP receptors and are subsequently internalized inside of the cell.

The BBN conjugates can further incorporate a spacer group or component to couple the binding moiety to the metal chelator (or metal binding backbone) while not adversely affecting either the targeting function of the BBN-binding moiety or the metal complexing function of the metal chelating agent. The term "spacer group" or "linker" refers to a chemical group that serves to couple the BBN binding moiety to the metal chelator while not adversely affecting either the targeting function of the BBN binding moiety or the metal complexing function of the metal chelator. Suitable spacer groups include peptides (i.e., amino acids linked together) alone, a non-peptide group (e.g., hydrocarbon chain), or a combination of an amino acid sequence and a non-peptide spacer. The types of spacer group used in most of the experimental studies described below in the Examples section were composed of a combination of L-glutamine and hydrocarbon spacers. A pure peptide spacer could consist of a series of amino acids (e.g., diglycine, triglycine, gly-gly-glu, gly-ser-gly, etc.), in which the total number of atoms between the N-terminal residue of the BBN binding moiety and the metal chelator in the polymeric chain is < 12 atoms.

The spacer can also include a hydrocarbon chain [i.e., Ri- (CH₂)_n-R₂] wherein n is 0-10, preferably n = 3 to 9, Ri is a group (e.g., H₂N-, HS-, -COOH) that can be used as a site for covalently linking the ligand backbone or the preformed metal chelator or metal complexing backbone; and R₂ is a group that is used for covalent coupling to the N-terminal NH₂- group of the BBN binding moiety (e.g., R₂ is an activated-COOH group). Several chemical methods for conjugating ligands (i.e., chelators) or preferred metal chelates to biomolecules have been well described in the literature [Wilbur, 1992; Parker, 1990; Hermanson, 1996; Frizberg et al., 1995]. One or more of these methods could be used to link either the uncomplexed ligand (chelator) or the radiometal chelate to the spacer group, or to link the spacer group to the BBN(8-14) derivatives. These methods include the formation of acid anhydrides, aldehydes, arylisothiocyanates, activated esters, or N- hydroxysuccinimides [Wilbur, 1992; Parker, 1990; Hermanson, 1996; Frizberg et al., 1995].

The term "metal complexing chelator" refers to a molecule that forms a complex with a metal atom that is stable under physiological conditions. That is, the metal will remain complexed to the chelator backbone in vivo. More particularly, a metal complexing chelator is a molecule that complexes to a radionuclide metal to form a metal complex that is stable under physiological conditions and which also has at least one reactive functional group for conjugation with the BBN agonist binding moiety. Metal complexing chelators can include monodentate and polydentate chelators [Parker, 1990; Frizberg et al., 1995; Lister-James et al., 1997; Li et al., 1996b; Albert et al., 1991; Pollak et al., 1996; de Jong et al., 1997; Smith et al., 1997] and include the DOTA chelators discussed in more detail below. Metal complexing chelators include tetradentate metal chelators which can be macrocyclic and have a combination of four nitrogen and/or sulfur metal- coordinating atoms [Parker et al., 1990; Li et al., 1996b] and are designated as N₄, S₄, N₃S, N₂S₂, NS₃, etc., as shown in Figure 2. A number of suitable multidentate chelators that have been used to conjugate proteins and receptor-avid molecules have been reported [Frizberg et al., 1995; Lister- James et al._f 1997; Li et al., 1996b; Albert et al., 1991; Pollak et al., 1996; de Jong et al., 1997] and include the DOTA chelators discussed in more detail below. These multidentate chelators can also incorporate other metal- coordinating atoms such as oxygen and phosphorous in various combinations. The metal binding complexing moiety can also include "3+1" chelators [Seifert et al., 1998].

For diagnostic purposes, metal complexing chelators preferably include chelator backbones for complexing the radionuclide metals ^99mTc and ¹¹¹ln. For therapeutic purposes, metal complexing chelators preferably include chelator backbones that complex the beta particle emitting radionuclide metals including ¹⁰⁵Rh, ^186/188Re, ¹⁵³Sm, ⁹⁰Y, ¹⁶⁶Ho, ¹⁹⁹Au, ¹⁷⁷Lu, ¹¹¹ln, ¹⁶⁶Dy, ¹⁷⁵Yb and ¹⁴⁹Pm [Schubiger et al., 1996; Hoffken, 1994].

As was briefly described above, the term "bombesin agonist" or "BBN agonist" refers to compounds that bind with high specificity and affinity to GRP receptors, and upon binding to the GRP receptor, are intracellularly internalized. Suitable compounds include peptides, peptidomimetics and analogues and derivatives thereof. In particular, previous work has demonstrated that the region on the BBN peptide structure required for binding to GRP receptors spans from residue 8 through 14 [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy, 1988; Cai et al., 1994]. The presence of methionine (Met) at position BBN-14 will generally confer agonistic properties while the absence of this residue at BBN-14 generally confers antagonistic properties [Hoffken, 1994].

It is well documented in the art that there are a few and selective number of specific amino acid substitutions in the BBN (8-14) binding region (e.g., D-Ala¹¹ for L-Gly¹¹ or D-Trp⁸ for L-Trp⁸), which can be made without decreasing binding affinity [Leban et al., 1994; Qin et al., 1994; Jensen et al., 1993]. In addition, attachment of some amino acid chains or other groups to the N-terminal amine group at position BBN-8 (i.e., the Trp⁸ residue) can dramatically decrease the binding affinity of BBN analogues to GRP receptors [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy, et al., 1988; Cai et al., 1994]. In a few cases, it is possible to append additional amino acids or chemical moieties without decreasing binding affinity. The effects of conjugating various side chains to BBN-8 on binding affinity, therefore, is not predicable.

The BBN conjugates of the present invention can be prepared by various methods depending upon the selected chelator. The peptide portion of the conjugate can be most conveniently prepared by techniques generally established and known in the art of peptide synthesis, such as the solid-phase peptide synthesis (SPPS) approach. Solid-phase peptide synthesis (SPPS) involves the stepwise addition of amino acid residues to a growing peptide chain that is linked to an insoluble support or matrix such as polystyrene. The C-terminal residue of the peptide is first anchored to a commercially available support with its amino group protected with an N- protecting agent such as a t-butyloxycarbonyl group (tBoc) or a fluorenylmethoxycarbonyl (fmoc) group. The amino protecting group is removed with suitable deprotecting agents such as TFA in the case of tBOC or piperidine for fmoc and the next amino acid residue (in N-protected form) is added with a coupling agent such as dicyclocarbodiimide (DCC). Upon formation of a peptide bond, the reagents are washed from the support. After addition of the final residue, the peptide is cleaved from the support with a suitable reagent such as trifluoroacetic acid (TFA) or hydrogen fluoride (HF).

The spacer groups and chelator components are then coupled to form a conjugate by reacting the free amino group of the Trp⁸ residue of the BBN binding moiety with an appropriate functional group of the chelator, metal chelator, or spacer group such as a carboxyl group or activated ester.

The BBN conjugate can also incorporate a metal complexing chelator backbone that is peptidic and compatible with solid-phase peptide synthesis. In this case, the chelator backbone can be added to the BBN binding moiety in the same manner as described above, or more conveniently, the metal complexing chelator backbone coupled to the BBN binding moiety can be synthesized in toto starting from the C-terminal residue of the peptide and ending with the N-terminal residue of the metal complexing chelator structure. The chelator backbones used in accordance with the present invention are commercially available or they can, be made by methods similar to those outlined in the literature [Frizberg et al., 1995; Lister-James et al., 1997; Li et al., 1996b; Albert et al., 1991 ; Pollak et al., 1996; de Jong et al., 1997; Smith et al., 1997; Seifert et al., 1998]. Attachment of the spacer groups to functionalizable atoms appended to the ligand backbone can be performed by standard methods known to those skilled in the art. For example, the HOBt/HBTU activated -COOH group on 5-aminovaleric acid (5- AVA) was reacted with the N-terminal amine on Gin⁷ to produce an amide linkage as shown in Figure 3. Similarly, the -COOH group attached to the characterized [16]aneS₄ ligand was conjugated to the amine group on the hydrocarbon spacer (shown below) by reaction of the HOBt/HBTU activated carboxyl group appended to the [16]aneS₄ macrocycle with the terminal amine group on 5-AVA to form BBN-37 as shown in Figure 4. Other standard conjugation reactors that produce covalent linkages with amine groups can also be used [Wilbur, 1992; Parker, 1990].

The chelating framework, conjugated via Trp⁸, that complexes the radiometals should form a 1 :1 chelator to metal ratio. Since ⁹⁹ Tc has a short half-life (6 hours) and is a diagnostic radionuclide, the method of forming the ^99mTc-BBN analogues should permit complexation (either directly or by transmetallation) of ^99mTc to the conjugated chelating framework in a one- step, high yield reaction (exemplified below in the Experimental Section).

In contrast, the longer half-lives of the therapeutic radionuclides (e.g., ¹⁰⁵Rh, ^186/188Re, ^1S3Sm, ¹⁶⁶Ho, ⁹⁰Y, ¹⁷⁷Lu, ^{1 9}Pm, ¹⁹⁹Au, ¹¹¹ln, ¹⁷⁷Lu) permit formation of the corresponding radiolabeled BBN analogues by either a one-step, high yield complexation step, or by performing a ⁰⁵Rh, ^{186 188}Re, ¹⁵³Sm, ¹⁶⁶Ho, ⁹⁰Y, ¹⁷⁷Lu, ¹¹¹ln or ¹⁴⁹Au chelate synthon followed by conjugation of the preformed complex to the N-terminal end of the BBN binding moiety. In all cases, the resulting specific activity of the final radiolabeled BBN derivative must be high (i.e., > 1Ci/μmole). Re- and Tc-coniugates

Re and Tc are both in row VI IB of the Periodic Table and they are chemical congeners. Thus, for the most part, the complexation chemistry of these two metals with ligand frameworks that exhibit high in vitro and in vivo stabilities are the same [Eckelman, 1995]. Many ^99mTc or ^{186 188}R_Θ complexes, which are employed to form stable radiometal complexes with peptides and proteins, chelate these metals in their +5 oxidation state [Lister- James et al., 1997]. This oxidation state makes it possible to selectively place ^99mTc- or ^{186 188}Re into ligand frameworks already conjugated to the biomolecule, constructed from a variety of ^99mTc(V) and/or ^{186 188}Re(V) weak chelates (e.g., ^99mTc- glucoheptonate, citrate, gluconate, etc.) [Eckelman, 1995; Lister-James et al., 1997; Pollak et al., 1996]. Tetradentate ligand frameworks have been shown to form well-defined, single chemical species in high specific activities when at least one thiol group or at least one hydroxymethylene phosphine group is present on the ligand backbone [Smith et al., 1997].

Ligands which form stable Tc(V) or Re(V) tetradentate complexes containing, but not limited to, amino N-atoms, amido-N-atoms, carboxy-O-atoms and thioether-S-atoms, are donor atoms that can also be present [Eckelman, 1995; Fritzberg et al., 1992; Parker, 1990; Frizberg et al., 1995; Pollak et al., 1996; Seifert et al., 1998]. Depending upon the mix of donor atoms (groups), the overall complex charge normally ranges from -1 to +1.

Incorporation of the metal within the conjugate can be achieved by various methods commonly known in the art of coordination chemistry. When the metal is ^99mtechnetium, the following general procedure can be used to form a technetium complex. A peptide-chelator conjugate solution is formed by initially dissolving the conjugate in water or in an aqueous alcohol such as ethanol. The solution is then degassed to remove oxygen. When an -SH group is present in the peptide, the thiol protecting group(s) are removed with a suitable reagent, for example with sodium hydroxide, and are then neutralized with an organic acid such as acetic acid (pH 6.0-6.5). In the labeling step, sodium pertechnetate obtained from a molybdenum generator is added to a solution of the conjugate with a sufficient amount of a reducing agent, such as stannous chloride, to reduce technetium, and is either allowed to stand at room temperature or is heated. The labeled conjugate can be separated from the contaminants ^99mTcO₄ ^" and colloidal ^99mTcO₂ chromatographically, for example with a C_.s Sep Pak cartridge [Millipore Corporation, Waters Chromatography Division, 34 Maple Street, Milford, Massachusetts 01757]. In an alternative method, the labeling can be accomplished by a transchelation reaction. The technetium source is a solution of technetium complexed with labile ligands facilitating ligand exchange with the selected chelator. Examples of suitable ligands for transchelation include tartrate, citrate, gluconate, and heptagluconate. It will be appreciated that the conjugate can be labeled using the techniques described above, or alternatively, the chelator itself may be labeled and subsequently coupled to the peptide to form the conjugate; a process referred to as the "prelabeled chelate" method. When labeled with diagnostically and/or therapeutically useful metals, peptide-chelator conjugates or pharmaceutically acceptable salts, esters, amides, and prodrugs of the present invention can be used to treat and/or detect cancers, including tumors, by procedures established in the art of radiodiagnostics and radiotherapeutics [Bushbaum, 1995; Fischman et al., 1993; Schubiger et al., 1996; Lowbertz et al., 1994; Krenning et al., 1994]. A conjugate labeled with a radionuclide metal, such as ^99mtechnetium, can be administered to a mammal, including human patients or subjects, by intravenous or intraperitoneal injection in a pharmaceutically acceptable carrier and/or solution such as salt solutions like isotonic saline. The amount of labeled conjugate appropriate for administration is dependent upon the distribution profile of the chosen conjugate in the sense that a rapidly cleared conjugate may be administered in higher doses than one that clears less rapidly. Unit doses acceptable for ^99mTc imaging radiopharmaceuticals are in the range of about 5-40 mCi for a 70kg individual. In vivo distribution and localization can be tracked by standard scintigraphic techniques at an appropriate time subsequent to administration; typically between 30 minutes and 180 minutes depending upon the rate of accumulation at the target site with respect to the rate of clearance at non-target tissue.

The compounds of the present invention can be administered to a patient alone or as part of a composition that contains other components such as excipients, diluents, radical scavengers, stabilizers, and carriers, all of which are well known in the art. The compounds can be administered to patients either intravenously or intraperitoneally.

There are numerous advantages associated with the present invention. The compounds made in accordance with the present invention form stable, well-defined ^99mTc or ^186/188R_Θ conjugate analogues of BBN agonists. Similar BBN agonist analogues can also be made by using appropriate chelator frameworks for the respective radiometals to form stable well-defined products labeled with ¹⁵³Sm, ⁹⁰Y, ¹⁶⁶Ho, ¹⁰⁵Rh, ¹⁹⁹Au, ¹⁴⁹Pm, ¹⁷⁷Lu or ¹¹¹ln. The radiolabeled BBN agonist conjugates selectively bind to neoplastic cells expressing GRP receptors, become internalized, and are retained in the tumor cells for extended time periods. Incorporating the spacer group between the metal chelator and the BBN agonist binding moiety maximizes the uptake and retention of the radioactive metal inside of the neoplasts or cancer cells. The radioactive material that does not reach (i.e., does not bind) the cancer cells is preferentially excreted efficiently into the urine with minimal radiometal retention in the kidneys. Radiotherapeutics

The diagnostic application of these compounds can be as a first- line diagnostic screen for the presence of neoplastic cell using scintigraphic imaging, as an agent for targeting neoplastic tissue using handheld radiation detection instrumentation in the field of radioimmuno guided surgery (RIGS), as a means to obtain dosimetry data prior to administration of the matched pair therapeutic compound, and as a means to assess GRP receptor population as a function of treatment over time.

The therapeutic application of these compounds can be defined either as an agent that will be used as a first-line therapy in the treatment of cancer, as combination therapy where these radiolabeled agents could be utilized in conjunction with adjuvant chemotherapy, and as the matched pair therapeutic agent. The matched pair concept refers to one compound which can serve as both a diagnostic and a therapeutic agent depending on the radiometal with the appropriate chelate selected, and can be understood in connection with the data set forth below.

Radioisotope therapy involves the administration of a radiolabeled compound in sufficient quantity to damage or destroy the targeted tissue. After administration of the compound (e.g., by intravenous or intraperitonal injection), the radiolabeled pharmaceutical localizes preferentially at the disease site (in this instance, tumor tissue that expresses the GRP-receptor). Once localized, the radiolabeled compound damages or destroys the diseased tissue with the energy that is released during the radioactive decay of the isotope that is administered.

The design of a successful radiotherapeutic involves several critical factors:

1. selection of an appropriate targeting group to deliver the radioactivity to the disease site;

2. selection of an appropriate radionuclide that releases sufficient energy to damage that the disease site, without substantially damaging adjacent normal tissues; and

3. selection of an appropriate combination of the targeting group and the radionuclide without adversely affecting the ability of this conjugate to localize at the disease site. For radiometals, this often involves a chelating group that coordinates tightly to the radionuclide, combined with a linker that couples said chelate to the targeting group, and that affects the overall biodistribution of the compound to maximize uptake in target tissues and minimizes uptake in normal, non-target organs.

The present invention provides radiotherapeutic agents that satisfy all three of the above criteria through proper selection of targeting group, radionuclide, metal chelate and linker. Radiotherapeutic agents optionally contain a chelated+3 metal ion from the class of elements known as the lanthanides (elements of atomic number 57-71) and their analogs (i.e., M³⁺ metals such as yttrium and indium). Typical radioactive metals in this class include the isotopes ⁹⁰Yttrium, ¹¹¹lndium, ¹⁴⁹Promethium, ^1δ3Samarium, ¹⁶⁶Dysprosium, ¹⁶⁶Holmium, ¹⁷⁵Ytterbium, and ¹⁷⁷Lu. All of these metals (and others in the lanthanide series) have very similar chemistries, in that they remain in the +3 oxidation state and prefer to chelate to ligands that bear hard (oxygen/nitrogen) donor atoms, as typified by derivatives of the well-known chelate DTPA (diethylenetriaminepentaacetic acid) and polyaza-polycarboxylate macrocycles such as DOTA (1 ,4,7,10-tetrazacyclododecane-N, N^N^N'"- tetraacetic acid) and its close analogs. The structures of these chelating ligands in their fully deprotonated form are shown below.

These chelating ligands encapsulate the radiometal by binding to it via multiple nitrogen and oxygen atoms, thus preventing the release of free (unbound) radiometal into the body. This is important as in vivo dissociation of +3 radiometals from their chelate can result in uptake of the radiometal in the liver, bone and spleen [Brechbiel MW, Gansow OA, "Backbone-substituted DTPA ligands for ⁹⁰Y radioimmunotherapy, Bioconj. Chem. 1991 ; 2: 187-194; Li, WP, Ma DS, Higginbotham C, Hoffman T, Ketring AR, Cutler CS, Jurisson, SS, "Development of an in vitro model for assessing the in vivo stability of lanthanide chelates," Nucl. Med. Biol. 2001 ; 28(2): 145- 154; Kasokat T, Urich K. Arzneim-Forsch, "Quantification of dechelation of gadopentetate dimeglumine in rats", 1992; 42(6): 869-76]. Unless one is specifically targeting these organs, such non-specific uptake is highly undesirable as it leads to non-specific irradiation of non-target tissues, which can lead to such problems as hematopoietic suppression due to irradiation of bone marrow.

For radiotherapy applications, forms of the DOTA chelate [Tweedle MF, Gaughan GT, Hagan JT, "1-Substituted-1 ,4,7- triscarboxymethyl-1,4,7,10-tetraazacyclododecane and analogs" US Patent 4,885,363, Dec. 5, 1989] are particularly preferred, as the DOTA chelate is expected to dechelate less in the body than DTPA or other linear chelates.

General methods for coupling DOTA-type macrocycles to targeting groups through a linker (e.g., by activation of one of the carboxylates of the DOTA to form an active ester, which is then reacted with an amino group on the linker to form a stable amide bond), are known to those skilled in the art. (See e.g., Tweedle et al., US Patent 4,885,363). Coupling can also be performed on DOTA-type macrocycles that are modified on the backbone of the polyaza ring. The selection of a proper nuclide for use in a particular radiotherapeutic application depends on many factors, including: a. Physical half-life - This should be long enough to allow synthesis and purification of the radiotherapeutic construct from radiometal and conjugate, and delivery of said construct to the site of injection without significant radioactive decay prior to injection. Preferably, the radionuclide should have a physical half-life between about 0.5 and 8 days. b. Energy of the emissions) from the radionuclide - Radionuclides that are particle emitters (such as alpha emitters, beta emitters and Auger electron emitters) are particularly useful as they emit highly energetic particles that deposit their energy over short distances, thereby producing highly localized damage. Beta emitting radionuclides are particularly preferred as the energy from beta particle emissions from these isotopes is deposited within 5 to about 150 cell diameters. Radiotherapeutic agents prepared from these nuclides are capable of killing diseased cells that are relatively close to their site of localization, but cannot travel long distances to damage adjacent normal tissue such as bone marrow. c. Specific activity (i.e. radioactivity per mass of the radionuclide) - Radionuclides that have high specific activity (e.g., generator produced ⁹⁰Y, ¹¹¹ln, ¹⁷⁷Lu) are particularly preferred. The specific activity of a radionuclide is determined by its method of production, the particular target that is used to produce it, and the properties of the isotope in question.

Many of the lanthanides and lanthanoids include radioisotopes that have nuclear properties that make them suitable for use as radiotherapeutic agents, as they emit beta particles. Some of these are listed in the table below.

Pm:promethium, Sm:samarium, Dy:dysprosium, Ho:holmium, Yb.ytterbium,

Lu:lutetium, Y:yttrium, ln:indium

Methods for the preparation of radiometals, such as beta- emitting lanthanide radioisotopes are known to those skilled in the art and have been described elsewhere [e.g., Cutler CS, Smith CJ, Ehrhardt GJ.; Tyler TT, Jurisson SS, Deutsch E., "Current and potential therapeutic uses of lanthanide radioisotopes." Cancer Biother. Radiopharm. 2000; 15(6): 531- 545]. Many of these isotopes can be produced in high yield for relatively low cost, and many (e.g., ⁹⁰Y, ¹⁴⁹Pm, ¹⁷⁷Lu) can be produced at close to carrier- free specific activities (i.e., the vast majority of atoms are radioactive). Since non-radioactive atoms can compete with their radioactive analogs for binding to receptors on the target tissue, the use of high specific activity radioisotope is important to allow delivery of as high a dose of radioactivity as possible to the target tissue.

Radiotherapeutic derivatives of the invention containing beta- emitting isotopes of rhenium (¹⁸⁶Re and ¹⁸⁸Re) are also particularly preferred.

Proper dose schedules for the radiotherapeutic compounds of the present invention are known to those skilled in the art. The compounds can be administered using many methods which include, but are not limited to, a single or multiple IV or IP injections, using a quantity of radioactivity that is sufficient to cause damage or ablation of the targeted GRP-R bearing tissue, but not so much that substantive damage is caused to non-target (normal) tissue. The quantity and dose required is different for different constructs, depending on the energy and half-life of the isotope used, the degree of uptake and clearance of the agent from the body, and the mass of the tumor. In general, doses can range from a single dose of about 30-50 mCi to a cumulative dose of up to about 3 Curies. The radiotherapeutic compositions of the invention can include physiologically acceptable buffers and can require radiation stabilizers to prevent radiolytic damage to the compound prior to injection. Radiation stabilizers are known to those skilled in the art and may include, for example, para-am inobenzoic acid, ascorbic acid, gentistic acid and the like.

The following examples are presented to illustrate specific embodiments and demonstrate the utility of the present invention.

Experimental Section EXAMPLE 1 : Synthesis and in vitro binding assessment of synthetic BBN analogues employing hydrocarbon chain spacers

A. Synthesis:

Many BBN analogues were synthesized by Solid Phase Peptide Synthesis (SPPS). Each peptide was prepared by SPPS using an Applied Biosystems Model 432A peptide synthesizer. After cleavage of each BBN analogue from the resin using Trifluoracetic acid (TFA), the peptides were purified by C18 reversed-phase HPLC using a Vydac HS54 column and CH₃CN/H₂0 containing 0.1 % TFA as the mobile phase. After collection of the fraction containing the desired BBN peptide (approximately 80-90% yield in most cases), the solvent was evaporated. The identity of each BBN peptide was confirmed by FAB-mass spectrometry, Department of Chemistry - Washington University, St. Louis, MO.

Various amino acid sequences (in some cases including different chemical moieties) were conjugated to the N-terminal end of the BBN binding region (i.e., to BBN-8 or Trp⁸). BBN analogue numbers 9, #15, #15i, 16, 16i and 18 were synthesized as examples of N-terminal modified peptides as shown in Figure 5.

Various tethered N-terminal (via Trp⁸) BBN analogues were also synthesized by SPPS as exemplified by BBN-40, BBN-41, BBN-42, BBN-43, BBN-44, BBN-45, and BBN-49 as shown in Figure 6. In these particular tethered peptides, a Glu residue was attached to Trp⁸ followed by attachment of fmoc protected terminal amine groups separated from a -COOH group by 3-, 4-, 5-, 6-, 8- and 11 -carbon chain (CH) spacers (Figure 6). These fmoc protected acids were added as the terminal step during the SPPS cycle. As described previously, each of the BBN analogues was purified by reversed- phase HPLC and characterized by high resolution mass spectroscopy. Peptide 49 employed only glutamine as the spacer group.

The [16]aneS₄ macrocyclic ligand was conjugated to selected tethered BBN analogues shown in Figure 6. The -OCH₂COOH group on the [16]aneS₄ macrocycle derivative was activated via HOBt/HBTU so that it efficiently formed an amide bond with the terminal NH₂ group on the spacer side arm (following deprotection). The corresponding [16]aneS₄ tethered BBN derivatives were produced and examples of four of these derivatives (i.e., BBN-22, -37, -46 and -47) are shown in Figure 7. As previously described, each [16]aneS BBN derivative was purified by reversed-phase HPLC and characterized by FAB mass spectroscopy. B. In Vitro Binding Affinities: The binding affinities of the synthetic BBN derivatives were assessed for GRP receptors on Swiss 3T3 cells and, in some cases, on a variety of human cancer cell lines that express GRP receptors. The IC50 value of each derivative was determined relative to (i.e., in competition with) ¹²⁵l-Tyr⁴-BBN (the Kd for ¹²⁵l-Tyr⁴-BBN for GRP receptors in Swiss 3T3 cells is reported to be 1.6+0.4 nM) [Zueht et al., 1991]. The cell binding assay methods used to measure the ICso's is standard and used techniques previously reported [Jensen et al., 1993; Cai et al., 1994; Cai et al., 1992]. The methods used for determining IC₅o's for all GRP receptor binding compounds on all cell lines were similar. The specific method used to measure ICso's on Swiss 3T3 cells is briefly described as follows: Swiss 3T3 mouse fibroblasts are grown to confluence in 48 well microtiter plates. An incubation media was prepared consisting of HEPES (11.916g/l), NaCl (7.598 g/l), KCI (0.574 g/l), MgCI₂ (1.106 g/l), EGTA (0.380 g/l), BSA (5.0 g/l), chymostatin (0.002 g/l), soybean trypsin inhibitor (0.200 g/l), and bacitracin (0.050 g/l). The growth media was removed, the cells were washed twice with incubation media, and incubation media was returned to the cells. ⁱ²⁵l-Tyr⁴-BBN (0.01 uCi) was added to each well in the presence of increasing concentrations of the appropriate competitive peptide. Typical concentrations of displacing peptide ranged from 10^'12 to 10^"5 moles of displacing ligand per well. The cells were incubated at 37°C for forty minutes in a 95%O₂/5%CO₂ humidified environment. At forty minutes post initiation of the incubation, the medium was discarded, and the cells were washed twice with cold incubation media. The cells were harvested from the wells following incubation in a trypsin/EDTA solution for five minutes at 37°C. Subsequently, the radioactivity, per well, was determined and the maximum percent total uptake of the radiolabeled peptide was determined and normalized to 100%. C. Results of Binding Affinity Measurements: The ICso values measured for the BBN derivatives synthesized in accordance with this invention showed that appending a peptide side chain and other moieties via the N-terminal BBN-8 residue (i.e., Trp⁸) produced widely varying IC₅o values. For example, see ICso values shown for BBN 11 , 15i, 16i, and 18 in Figures 5 and 8. The observations are consistent with previous reports showing highly variable ICso values when derivatizing BBN(8- 13) or BBN(8-14) with a predominantly short chain of amino acid residues [Hoffken, 1994]. In contrast, when a hydrocarbon spacer of 3- to 11 -carbons was appended between BBN(7-14) and the [16]aneS₄ macrocycle, the ICso's were found to be surprisingly relatively constant and in the 1-5 nM range. The following IC₅o values were obtained from the unmetallated compounds BBN- 22, -37, -46, and -47 (structures shown in Figure 7). COMPOUND JCgo D

BBN-22 3.01 + 0.21

BBN-37 1.79 + 0.09

BBN-46 2.34 + 0.53

BBN-47 4.19 ± 0.91

These data suggest that using relatively simple spacer groups to extend ligands some distance from the BBN binding region [e.g., BBN(8-14)] can produce derivatives that maintain binding affinities in the 1-5 nmolar range. P. Cell Binding Studies With Metal Complexes: The following ICso values were obtained for the metallated Rh complexes shown on Figure 9.

COMPOUND ICfio (nM)

RhCI₂BBN-22 37.5 + 10.5

RhCI₂BBN -37 4.76 ± 0.79

RhCI₂BBN -46 3.38 ± 0.69

The results illustrated in Figure 9 show that when the RhCI₂-[16]aneS₄ complexes separated from Trp⁸ by only a glutamine (Glu⁷), the ICso of this conjugate (i.e., Rh-BBN-22) was 37.5 nM. However, when a five (5) carbon spacer or an eight (8) carbon spacer was present (i.e., Rh-BBN-37 and Rh- BBN-47), the IC₅o's remained below 5 nM. These data demonstrate that a straight chain spacer (along with Glu⁷) to move the +1 charged Rh-S₄-chelate away from the BBN binding region, will result in a metallated BBN analogue with sufficiently high binding affinities to GRP receptors for in vivo tumor targeting applications.

E. ¹⁰⁵Radiolabeled BBN Analogues:

The ¹⁰⁵Rh conjugates of BBN-22, BBN-37, BBN-46 and BBN-47 were synthesized using a ¹⁰⁵Rh-chloride reagent from the Missouri University

Research Reactor (MURR). This reagent was obtained as ¹⁰⁵Rh-chloride, a no-carrier-added (NCA) product, in 0.1-1.0M HCI. The pH of this reagent was adjusted to 4-5 using 0.1-1. OM NaOH dropwise and it was added to approximately 0.1 mg of the [16]aneS₄-conjugated BBN derivatives in 0.9% aqueous NaCl and 10% ethanol. After the sample was heated at 80°C for one hour, the ¹⁰⁵Rh-BBN analogues were purified using HPLC. In each case, an NCA or high specific activity product was obtained since the non-metallated S₄-BBN conjugates eluted at a retention time well after the ¹⁰⁵Rh-BBN conjugates eluted. For example, the retention time of ^1oεRh-BBN-37 was 7.1 minutes while BBN-37 eluted at 10.5 minutes from a C.s-reversed phase column eluted with CH₃CN/H₂O containing 0.1% TFA as shown in Figure 10A- B.

EXAMPLE 2: Retention of ¹⁰⁵Rh-BBN analogues in cancer cells

Once the radiometal has been specifically "delivered" to cancer cells (e.g., employing the BBN binding moiety that specifically targets GRP receptors on the cell surface), it is necessary that a large percentage of the "delivered" radioactive atoms remain associated with the cells for a period of time of hours or longer to make an effective radiopharmaceutical for effectively treating cancer. One way to achieve this association is to internalize the radiolabeled BBN conjugates within the cancer cell after binding to cell surface GRP receptors. In the past, all of the work with synthetic-BBN analogues for treatment of cancers focused on synthesizing and evaluating antagonists [Davis et al., 1992; Hoffken, 1994; Moody et al., 1996; Coy et al., 1988; Cai et al., 1994; Moody et al., 1995; Leban et al., 1994; Cai et al., 1992]. After evaluating synthetic BBN analogues that would be predicted to be either agonists or antagonists, applicants found that derivatives of BBN(8-14) (i.e., those with the methionine or amidated methionine at BBN-14) are rapidly internalized (i.e., in less than two minutes) after binding to the cell surface GRP receptors. Several radiolabeled BBN(8-14) analogues that were studied to determine their intemalization and intracellular trapping efficiencies were radioiodinated (i.e., ¹²⁵l) derivatives. The results of these studies demonstrated that despite rapid intemalization after ¹²⁵l-labeled BBN analogue binding to GRP receptors in Swiss 3T3 cells, the ¹²⁵l was rapidly expelled from the cells [Hoffman et al., 1997] as shown in Figure 11. Thus, these ²⁵I-BBN derivatives were not suitable for further development. In contrast, the ¹⁰⁵Rh-BBN(8-14) derivatives that bind to GRP receptors are not only rapidly internalized, but there is a large percentage of the ¹⁰⁵Rh activity that remains trapped within the cells for hours (and in some cell lines greater than 24 hours). This observation indicates that these radiometallated BBN derivatives have real utility as radiopharmaceuticals for in vivo targeting of neoplasms expressing GRP receptors.

Experiments designed to determine the fraction of a radiotracer internalized within cells were performed by adding excess ¹²⁵l- or ¹⁰⁵Rh-BBN derivatives to the cell incubation medium. After establishment of equilibrium after a forty-minute incubation, the media surrounding the cells was removed and the cells were washed with fresh media containing no radioactivity. After washing, the quantity of radioactivity associated with the cells was determined (i.e., total counts per minute (TCPM) of ¹²⁵l or ¹⁰⁵Rh associated with the cells). The cells were then incubated in a 0.2M acetic acid solution (pH 2.5) which caused the surface proteins (including GRP receptors) to denature and release all surface-bound radioactive materials. After removing this buffer and washing, the cells were counted again. The counts per minute (c.p.m.) associated with the cells at that point were only related to the ¹²⁵l or ¹⁰⁵Rh that remained trapped inside of the cells.

To determine intracellular retention, a similar method was employed. However, after washing the cells with fresh (non-radioactive) incubation media, the cells were incubated in the fresh media at different time periods after washing away all extracellular ¹²⁵l- or ¹⁰⁵Rh-BBN analogues. After each time period, the methods used to determine TOTAL c.p.m. and intracellular c.p.m. after washing with a 0.2M acetic acid solution at pH 2.5 were the same as described above, and the percent ¹²⁵l or ¹⁰⁵Rh remaining trapped inside of the cells was calculated. Figure 12 is a graph of results of efflux experiments using Swiss 3T3 cells with ¹²⁵l-Lys³-BBN. The results show that there is rapid efflux of the ¹²⁵l from inside of these cells with less than 50% retained at fifteen minutes and by sixty minutes, less than 20% remained as shown in Figure 12.

In contrast, studies with all of the ¹⁰⁵Rh-[16]aneS₄-BBN agonist derivatives that are internalized inside of the cells showed substantial intracellular retention of ¹⁰⁵Rh by the GRP receptor expressing cells. For example, results of studies using ¹⁰⁵Rh-BBN-37 (see Figure 9) in conjunction with Swiss 3T3 cells showed that approximately 50% of the ¹⁰⁵Rh activity remains associated with the cells at sixty minutes post-washing, and approximately 30% of ¹⁰⁵Rh remained inside of the cells after four hours as shown in Figure 13. Note that at least 5% of the ¹⁰⁵Rh is surface bound at greater than or equal to sixty minutes. The ¹⁰⁵Rh-BBN derivatives shown in Figure 9 all have an amidated methionine at position BBN-14 and are expected to be agonists [Jensen et al., 1993]. Therefore, they would be predicted to rapidly internalize after binding to GRP receptors on the cell surface [Reile et al., 1994; Bjisterbosch et al., 1995; Smythe et al., 1991], which was confirmed by Applicants' data. Referring to Figure 14, ¹⁰⁵Rh-BBN-61, a BBN analogue with no amino acid at position BBN-14 (i.e., a ¹⁰⁵Rh-BBN(8-13) derivative), was synthesized and studied. This BBN analogue has a high bonding affinity (i.e., ICso = 4.1 nM). This type of derivative is expected to be an antagonist, and as such, will not internalize [Jensen et al., 1993; Smythe et al., 1991]. Results of efflux studies with ¹⁰⁵Rh-BBN-61 using Swiss 3T3 cells showed that immediately following washing with fresh incubation buffer (i.e., t=0), essentially all of the ¹⁰⁵Rh associated with these cells is on the cell surface, as expected. Furthermore, after only one hour of incubation, less than 10% remained associated with these cells in any fashion (comparing the results with the antagonist (see Figure 15) to those of the agonist (see Figure 16)). These data indicate that ¹⁰⁵Rh-antagonists with structures similar to the ^10SRh- BBN agonists (i.e., those shown in Figure 9) are not good candidates for development of radiopharmaceuticals since they are neither trapped in nor on the GRP receptor expressing cells to nearly the same extent as the radiometallated BBN agonists.

EXAMPLE 3: Human Cancer Cell Line Studies

In vitro cell binding studies of ¹⁰⁵Rh-BBN-37 with two different human cancer cell lines that express GRP receptors (i.e., CF-PAC1 and PC-3 cell lines), which are tumor cells derived from patients with prostate CA and pancreatic CA, as shown in Figures 17A-B and 18A-B, respectively) were performed. Results of these studies demonstrated consistency with ¹⁰⁵Rh- BBN-37 binding and retention studies using Swiss 3T3 cells. Specifically, the binding affinity of Rh-BBN-37 was high (i.e., IC₅o = 7 nM) with both human cancer cell lines as shown in Table 1. In addition, in all cells, the majority of the ¹⁰⁵Rh-BBN-37 was internalized and perhaps a major unexpected result was that the retention of the ¹⁰⁵Rh-tracer inside of the cells was significantly better than retention in Swiss 3T3 cells as shown in Figures 17 and 18. For example, it is particularly remarkable that the percentage of ¹⁰⁵Rh-BBN-37 that remained associated with both the CFPAC-1 and PC-3 cell line was greater than 80% at two hours after removing the extracellular activity by washing with fresh incubation buffer (see Figures 17 and 18). EXAMPLE 4: In Vivo Studies

Biodistribution studies were performed by intravenous (I.V.) injection of either ¹⁰⁵Rh-BBN-22 or ¹⁰⁵Rh-BBN-37 into normal mice. In these studies, unanesthetized CF-1 mice (15-22g, body wt.) were injected I.V. via the tail vein with between one to five μCi (37-185 KBq) of the ¹⁰⁵Rh- labeled agent. Organs, body fluids and tissues were excised from animals sacrificed at 30, 60 and 120 minutes post-injection (PI). The tissues were weighed, washed in saline (when appropriate) and counted in a Nal well counter. These data were then used to determine the percent injected dose (% ID) in an organ or fluid and the %ID per gram. The whole blood volume of each animal was estimated to be 6.5 percent of the body weight. Results of these studies are summarized in Tables 2 and 3.

Results from these studies showed that both the ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 were cleared from the bloodstream, predominantly via the kidney into the urine. Specifically, 68.4 ± 6.6% and 62.3 ± 5.8% of the ID was found in urine at two hours Pi of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37, respectively (see Tables 2 and 3). An unexpected finding was that the % ID of ¹⁰⁵Rh that remained deposited in the kidneys of these animals was only 2.4 ± 0.6 % ID and 4.6 ± 1.3 % ID at two hours post injection of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 (see Tables 2 and 3). This is much less than would be expected from previously reported data where radiometallated peptides and small proteins have exhibited renal retention of the radiometal that is greater than 10% ID and usually much greater than 10% [Duncan et al., 1997]. The reason for reduced renal retention of ¹⁰⁵Rh-BBN analogues is not known, however, this result demonstrates a substantial improvement over existing radiometallated peptides.

Biodistribution studies also demonstrated another important in vivo property of these radiometallated BBN analogues. Both ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 are efficiently cleared from organs and tissues that do not express GRP receptors (or those that do not have their GRP receptors accessible to circulating blood). The biodistribution studies in mice demonstrated specific uptake of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 in the pancreas while other non-excretory organs or tissues (i.e., heart, brain, lung, muscle, spleen) exhibited little or no uptake or retention (Tables 2 and 3). Both ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 were removed from the bloodstream by both the liver and kidneys with a large fraction of the ¹⁰⁵Rh removed by these routes being excreted into the intestines and the bladder, respectively. It is important to note that the % ID/gm in the pancreas of ¹⁰⁵Rh-BBN-22 and ¹⁰⁵Rh-BBN-37 was 3.9 + 1.3 % and 9.9 + 5.4 %, respectively at two hours, Pi. Thus, the ratios of % ID/gm of ¹⁰⁵Rh-BBN-22 in the pancreas relative to muscle and blood were 16.2 and 7.6, respectively. The ratios of % ID/gm of ¹⁰⁵Rh-BBN-37 in the pancreas relative to muscle and blood were 25.4 and 29.1, respectively. These data demonstrated selective in vivo targeting of these radiometallated BBN analogues to cells expressing GRP receptors [Zhu et al., 1991; Qin et al., 1994] and efficient clearance from non-target tissues. If cancer cells that express GRP receptors are present in the body, these results indicate radiometallated BBN analogues will be able to target them with a selectivity similar to the pancreatic cells. A comparison of the pancreatic uptake and retention of ¹⁰⁵Rh-

BBN-22 with ¹⁰⁵Rh-BBN-37 demonstrated that ¹⁰⁵Rh-BBN-37 deposits in the pancreas with a two-fold better efficiency than ¹⁰⁵Rh-BBN-22 (i.e., 3.6 ± 1.2% ID and 2.3 ± 1.0 % ID) for ¹⁰⁵Rh-BBN-37 at one and two hours pi, respectively, versus 1.2 ± 0.5% ID and 1.0 ± 0.1% ID for ¹⁰⁵Rh-BBN-22 at one and two hours pi). This data is consistent with the greater than two-fold higher uptake and retention of ¹⁰⁵Rh-BBN- 37 found in the in vitro studies shown in Figure 16.

EXAMPLE 5: Synthesis and in vitro binding measurement of synthetic BBN conjugate analogues employing amino acid chain spacers

A. Synthesis:

Five BBN analogues were synthesized by SPPS in which between 2 to 6 amino acid spacer groups were inserted to separate a S₄- macrocyclic chelator from the N-terminal Trp⁸ on BBN(8-14) (Figure 19). Each peptide was prepared by SPPS using an Applied Biosystems Model 432A peptide synthesizer. After cleavage of each BBN analogue from the resin using Trifluoracetic acid (TFA), the peptides were purified by C₁₈ reversed-phase HPLC using a Vydac HS54 column and CH₃CN/H₂0 containing 0.1% TFA as the mobile phase. After collection of the fraction containing the desired BBN peptide, the solvent was evaporated. The identity of each BBN peptide was confirmed by FAB-mass spectrometry (Department of Chemistry - Washington University, St. Louis, MO).

Various amino acid sequences (in some cases containing different R-group moieties) were conjugated to the N-terminal end of the BBN binding region (i.e., to BBN-8 or Trp⁸). BBN analogue numbers 96, 97, 98, 99 and 101 were synthesized as examples of N-terminal modified peptides in which the [16]aneS₄ macrocycle BFCA was separated from Trp⁸ on BBN(8- 14) by various amino acid sequences as shown in Figure 19.

The [16]aneS₄ macrocyclic ligand was conjugated to selected tethered BBN analogues. The -OCH₂COOH group on the [16]aneS₄ macrocycle derivative was activated via HOBt/HBTU so that it efficiently formed an amide bond with the terminal NH₂ group on the spacer side arm (following deprotection). The corresponding [16]aneS₄ tethered BBN derivatives were produced and examples of five of these derivatives (i.e., BBN-96, 97, 98, 99 and 101) are shown in Figure 19. As previously described, each [16]aneS₄ BBN derivative was purified by reversed-phase HPLC and characterized by FAB mass spectroscopy. B. In Vitro Binding Affinities: The binding affinities of the synthetic BBN derivatives were assessed for GRP receptors on Swiss 3T3 cells, PC-3 cells and CF PAC-1 cells. The ICso's of each derivative were determined relative to (i.e., in competition with) ¹²⁵l-Tyr⁴-BBN. The cell binding assay method used to measure the ICso's is standard and was used by techniques previously reported [Jensen et al., 1993; Cai et al., 1992; Cai et al., 1994]. The methods used for determining ICso's with all BBN analogue binding to GRP receptors present on all three cell lines were similar. The specific method used to measure ICso's on Swiss 3T3 cells is briefly described as follows.

Swiss 3T3 mouse fibroblasts are grown to confluence in 48 well microliter plates. An incubation media was prepared consisting of HEPES (11.916g/l), NaCl (7.598 g/l), KCI (0.574 g/l), MgCI₂(1.106 g/l), EGTA (0.380 g/l), BSA (5.0 g/l), chymostatin (0.002 g/1), soybean trypsin inhibitor (0.200 g/1), and bacitracin (0.050 g/1). The growth media was removed, the cells were washed twice with incubation media, and incubation media was returned to the cells. ¹²⁵l-Tyr⁴-BBN (0.01 μCi) was added to each well in the presence of increasing concentrations of the appropriate competitive peptide. Typical concentrations of displacing peptide ranged from 10^"12 to 10^"5 moles of displacing ligand per well. The cells were incubated at 37°C for forty minutes in a 95% O₂/5% CO₂ humidified environment. At forty minutes post initiation of the incubation, the medium was discarded, and the cells were washed twice with cold incubation media. The cells were harvested from the wells following incubation in a trypsin/EDTA solution for five minutes at 37°C. Subsequently, the radioactivity, per well, was determined and the maximum percent total uptake of the radiolabeled peptide was determined and normalized to 100%. A similar procedure was used in performing cell binding assays with both the PC-3 and CF_a-PAC-1 human cancer cell lines. C. Results of Binding Affinity Measurements: The ICso values measured for the BBN derivatives synthesized in accordance with this invention showed that appending a chelator via amino acid chain spacer groups via the N-terminal BBN-8 residue (i.e., Trp⁸) produced a variation of IC50 values. For example, see IC50 values shown for BBN 96, 97, 98 and 101 in Figure 19. The observations are consistent with previous reports showing variable IC₅₀ values when derivatizing BBN(8-13) with a predominantly short chain of amino acid residues [Hoffken, 1994]. When the amino acid spacer groups used in BBN-98, 99 and 101 were appended between BBN(7-14) and the [16]aneS₄ macrocyle, the ICso's were found to be surprisingly constant and in the 1-6 nM range for all three cell lines (i.e., see IC₅0 values shown in Figure 19). These data suggest that using relatively simple spacer groups composed entirely of selected amino acid sequences to extend ligands some distance from the BBN region [e.g., BBN(8-14)] can produce derivatives that maintain binding affinities in the 1-6 nmolar range.

D. Cell Binding Studies with Rh-BBN-Coniuoates:

Results illustrated in Figure 20 show that when the corresponding RhCI [16]aneS₄ complex was separated from Trp⁸ on BBN(8-

14) by the four different amino acid spacer groups (see Figure 20), the IC₅₀'s of all four analogues (i.e., BBN-97, -98, -99, -101) were between 0.73 and

5.29 nmolar with GRP receptors on the PC-3 and CF PAC-1 cell lines. The

ICso's for these same Rh-BBN conjugates were somewhat higher with the Swiss 3T3 cell line (Figure 20). These data demonstrate that amino acid chain with spacer groups used to move the +1 charged Rh-S₄ chelate away from the BBN binding region will result in a metallated BBN analogue with sufficiently high binding affinities to GRP receptors for in vivo tumor targeting applications. EXAMPLE 6: Synthesis and in vitro binding assessment of a ^99mTc-labeled synthetic BBN analogue

A. Synthesis:

Several tetradentate chelating frameworks have been used to form stable ^99mTc or ¹⁸⁸Re labeled peptide and protein conjugates [Eckelman,

1995; Li et al., 1996b; Parker, 1990; Lister-James et al., 1997]. Many of these ligand systems contain at least one thiol (-SH) donor group to maximize rates of formation and stability (both in vitro and in vivo) of the resultant Tc(V) or

Re(V) complexes [Parker, 1990; Eckelman, 1995]. Results from a recent report indicates that the bifunctional chelating agent (BFCA) dimethylglycyl-L- seryl-L-cyteinyl-glycinamide) (N₃S-BFCA) is capable of forming a well-defined complex with ReO⁺³ and TcO⁺³ [Wong et al., 1997]. Since this ligand framework can be synthesized by SPPS techniques, this N₃S-BFCA was selected for use in forming ^99mTc-BBN-analogue conjugates. Three different NsS-BFCA conjugates of BBN(7-14) were synthesized (BBN-120, -121 and - 122) as shown in Figure 21 by SPPS. BBN-120, BBN-121 and BBN-122 represent a series of analogues where the N₃S-BFCA is separated from the BBN(7-14) sequence by 3, 5, and 8 carbon spacer groups (Figure 21). Each peptide was synthesized and purified using the SPPS and chromatographic procedures outlined in Example 1. The thiol group on cysteine was protected using the ACM group, which is not cleaved during cleavage of these BBN- conjugates from the resin using TFA. The identities of BBN-120, -121 and - 122 were confirmed by FAB mass spectrometry. Synthesis and purification of the N₃S-BFCA could also be readily accomplished using SPPS methods, followed by HPLC purification (see Example 1). The ACM group was used to protect the thiol group on cysteine during synthesis and cleavage from the resin.

B. In Vitro Binding Affinities:

Synthesis of ^99mTc-BBN-122 (Figure 22) was achieved by two methods [i.e., (1 ) by transchelation of ^99mTcO⁺³ from ^99mTc-gluconate; or (2) by formation of the "preformed" ^99mTc-BFCA complex followed by -COOH activation with tetrafluorophenyl and subsequent reaction with the C₅-carbon spacer group appended to BBN(7-14)]. In both cases, the ^99mTc-labeled peptide formed is shown in Figure 22. The structure of this Tc-BBN-122 conjugate was determined by using non-radioactive Re (the chemical congener of Tc). In these studies, the "preformed" ReO⁺³ complex with the N₃S-BFCA was prepared by reduction of ReO₄; with SnCI₂ in the presence of excess N3S-BFCA dissolved in sodium phosphate buffered water at pH 6-6.5 by a method previously published [Wong et al., 1997]. After purification of the ReO-N₃S-BFCA complex, the structure of this chelate was shown (by massspectropy) to be identical to that previously reported [Wong et al., 1997].

The ReO-N₃-S-BFCA complex was converted to the activated trifluorophenyl (TFP) ester by adding 10 mg of the complex to 6 mg (dry) EDC and the 50 μl of TFP. After the solution was vortexed for one minute, CH₃CN was added until disappearance of cloudiness. The solution was incubated for one hour at room temperature and purified by reversed-phase HPLC. To prepare the ReO-N₃S-BFCA complex BBN-122 conjugate (Figure 22), one μl microliter of the HPLC fraction containing the ReO-N₃S-BFCA complex was added to a solution containing one mg of the Ca-tethered BBN(7-14) peptide in 0.2 N NaHCO₃ at pH 9.0. After incubation of this solution for one hour at room temperature, the sample was analyzed and purified by reversed-phase HPLC. The yield of Re-BBN-122 was approximately 30-35%.

The method for preparation of the corresponding ^99mTc-BBN-122 conjugate, using the "preformed" ^99mTcO-N3S-BFCA complex, was the same as described above with the "preformed" ReO-N₃S-BFCA complex. In this case, ^99mTcθ₄, from a ⁹⁹Mo/" Tc generator was reduced with an aqueous saturated stannous tartrate solution in the presence of excess N₃S-BFCA. The yields of the ^99mTc-BBN-122 product using this "preformed" method were approximately 30-40%. Reversed-phase HPLC analysis of the ^99mTc-BBN- 122, using the same gradient elution program¹ as used for analysis of the Re- BBN-122 conjugate, showed that both the ^99mTc-BBN-122 and ¹⁸⁸Re-BBN-122 had the same retention time (i.e., 14.2-14.4 minutes) (See Figure 22). This provides strong evidence that the structures of both the ^99mTc-BBN-122 and Re-BBN-122 are identical. The binding affinities of BBN-122 and Re-BBN-122 were assessed for GRP receptors on Swiss 3T3 cells, PC-3 cells and CFPAC-1 cells that express GRP receptors. The ICso-s of each derivative were determined relative to (i.e., in competition with) ¹²⁵l-Tyr⁴-BBN (the Kd for ¹²⁵l- Tyr⁴-BBN for GRP receptors in Swiss 3T3 cells is reported to be 1.6±0.4nM) [Zhu et al., 1991]. The cell binding assay methods used to measure the ICso's

¹ Gradient elution program used in these studies was as follows.

Flow 1.5 ml/minute

Solvent A = HO with 0.1% TFA ^'

Solvent B = CHCN with 0.1 % TFA

Time (minutes. %A/%B

0 95/5

25 30/70 are standard and were used according to techniques previously reported

[Leban et al., 1994; Cai et al., 1994; Cai et al., 1992]. The methods used for determining ICso's with all GRP receptor binding of GRP receptors on all cell lines were similar and have been described previously for the other BBN- analogues and Rh-BBN analogues described in this document.

C. Results of Binding Affinity Measurements:

The ICso values measured for BBN-122 and Re-BBN-122 synthesized in accordance with this invention showed that appending an 8- carbon hydrocarbon chain spacer linked to the N₃S1-BFCA and the corresponding Re complex (i.e., Trp⁸) produced BBN conjugates with IC₅₀ values in a 1-5 nmolar range (See Table A). When ^99rτTc-BBN-122 was incubated with these same cells, it was shown that greater than or equal nmolar concentrations of BBN displaced this ^99mTc conjugate by more than 90%. This result demonstrates that ^99mTc-BBN-122 has high and specific binding affinity for GRP receptors. These data suggest that using relatively simple spacer groups to extend the N3S ligand framework and the corresponding Tc-or Re-N₃Sι, complexes some distance from the BBN binding region can produce derivatives that maintain binding affinities in the 1- 5 nmolar range. TABLE A.

Summary of IC50 values for GRP receptor binding for the non- metallated BBN-122 conjugate or the Re-BBN-122 conjugate in two cell lines (PC-3 and CF-PAC-1 cell lines that express GRP receptors). The IC50 values were measured using cell binding assays relative to ¹²⁵l-Tyr⁴-BBN.

35 95/5

EXAMPLE 7: Retention of ^99mTc-BBN-122 in Human Cancer Cells PC-3 and CF-PAC-1 cells) Once the radiometal has been specifically "delivered" to cancer cells (e.g., employing the BBN binding moiety that specifically targets GRP receptors on the cell surface), it is necessary that a large percentage of the "delivered" radioactive atoms remains associated with the cells for a period time of hours or longer to make an effective radiopharmaceutical for effectively treating cancer. One way to achieve this association is to internalize the radiolabeled BBN conjugates within the cancer cell after binding to cell surface GRP receptors.

Experiments designed to determine the fraction ^99rnTc-BBN-122 internalized within cells were performed by the same method previously described for ¹⁰⁵Rh-BBN-37. Briefly, excess ^99mTc-BBN-122 was added to PC-3 or CFPAC-1 cell incubation media and allowed to establish equilibrium after a 40 minute incubation. The media surrounding the cells was removed and the cells were washed with fresh media containing no radioactivity. After washing, the quantity of radioactivity associated with the cells was determined (i.e., total counts per minute ^99mTc associated with cells). The PC-3 and CFPAC-1 cells were then incubated in a 0.2M acetic acid solution (pH2.5), which caused the surface proteins (including GRP receptors) to denature and release all surface-bound radioactive materials. After removing this buffer and washing, the cells were counted again. The counts per minute (c.p.m.) associated with the cells at that point were only related to the ⁹⁹ Tc that remained trapped inside of the PC-3 or CFPAC-1 cells.

To determine intracellular retention of ^99mTc activity, a similar method was employed. However, after washing the cells with fresh (non- radioactive) incubation media, the cells were incubated in the fresh media at different time periods after washing away all extracellular ^99mTc-BBN-122. After each time interval, the methods used to determine total c.p.m. and intracellular c.p.m. by washing with a 0.2M acetic acid solution at pH 2.5. Studies with the ^99mTc-BBN-122 agonist show that the agonist is internalized inside of the PC-3 and CFPAC-1 cells (Figures 23-26), and that substantial intracellular retention of ^99mTc by the GRP receptor expressing cells occurs. For example, results of studies using ^99mTc-BBN-122 in conjunction with PC-3 cells showed a high rate of intemalization (Figure 23), and that approximately 75% of the ^99mTc activity remains associated with the cells at 90 minutes post-washing (Figure 25). Almost all of this ^99mTc cell- associated activity is inside of the PC-3 cells. Similar results were also found with the CFPAC-1 cells where there is also a high rate of ^99mTc-BBN-122 intemalization (Figure 24) and relatively slow efflux of ^99mTc from the cells (i.e., 50-60% retention at 120 minutes post-washing) (Figure 26).

The ^99mTc-BBN-122 peptide conjugate shown in Figure 22 has an amidated methionine at position BBN-14 and is expected to be an agonist [Jensen et al., 1993]. Therefore, it would be predicted to rapidly internalize after binding to GRP receptors on the cell surface [Bjisterbosch et al., 1995; Smythe et al., 1991], which is confirmed by Applicants' data in Figures 23-26. EXAMPLE 8: In Vivo Studies.

Biodistribution studies were performed by intravenous (IN.) injection of ^99mTc-BBΝ-122 into normal mice. In these studies, unanesthetized CF-1 mice (15-22g, body weight) were injected IN. via the tail vein with between one to five μCi (37-185 KBq) of ⁹⁹ Tc-BBΝ-122. Organs, body fluids and tissues were excised from animals sacrificed at 0.5, 1 , 4 and 24 hours post-injection (pi). The tissues were weighed, washed in saline (when appropriate), and counted in a Nal well counter. These data were then used to determine the percent injected dose (% ID) in an organ or fluid and the % ID per gram. The whole blood volume of each animal was estimated to be 6.5 percent of the body weight. Results of these studies are summarized in Tables B and C.

Results from these studies showed that ⁹⁹ Tc-BBN-122 is cleared from the bloodstream predominantly via the hepatobiliary pathway, showing about 35% of the ^99mTc-activity cleared via the kidney into the urine. Specifically, 33.79±1.76% of the ID was found in urine at one hour post injection (Table B). The retention of ^99mTc activity in the kidneys and liver is very low (Table B). This is much less than would be expected from previously reported data where radiometallated peptides and small proteins have exhibited renal retention of the radiometal that is great than 10% ID and usually much greater 10% [Duncan et al., 1997]. The reason for reduced renal retention of ^99mTc-BBN-122 is not known; however, this result demonstrates a substantial improvement over existing radiometallated peptides. Biodistribution studies also demonstrated another important in vivo property of ⁹⁹ Tc-BBN-122 in that it is efficiently cleared from organs and tissues that do not express GRP-receptors (or those that do not have their GRP-receptors accessible to circulating blood). The biodistribution studies in mice demonstrated specific uptake of ^99mTc-BBN-122 in the pancreas while other non-excretory organs or tissues (i.e., heart, brain, lung, muscle, spleen) exhibited little or no uptake or retention. ^99mTc-BBN-122 is removed from the bloodstream by both the liver and kidneys with a large fraction of the ^99mTc removed by these routes being excreted into the intestines and the bladder, respectively. It is important to note that the percent ID/gm in the pancreas of ^99mTc-BBN-122 is 12.63%/gm at 1 hour and drops to only 5.05% at the four hours post injection (Table C). Thus, the ratios of % ID/gm of ^99mTc-BBN-122 in the pancreas relative to muscle and blood were 92.2 and 14.78 at four hours post injection, respectively. These data demonstrated selective in vivo targeting of this ^99mTc-labeled BBN analogue to cells expressing GRP receptors [Zhu et al., 1991 ; Qin et al., 1994] and efficient clearance from non- target tissues. If cancer cells that express GRP receptors are present in the body, these results indicate ^99mTc-BBN analogues will be able to target them with a selectivity similar to the pancreatic cells. EXAMPLE 9: Materials and Methods For Examples 9 and 10 The following abbreviations are used in the examples and derived from the following amino acids: Ava = 5-amino valeric acid Aoc = 8-amino octanoic acid Aun = 11 -amino undecanoic acid Reagents and Apparatus: All chemicals were obtained from either Aldrich Chemicals (St. Louis, MO) or Fisher Scientific (Pittsburgh, PA). All chemicals and solvents used in these studies were reagent grade and used without further purification. The resin and fmoc-protected amino acids were purchased from Calbiochem-Novabiochem Corp (San Diego, CA) and the other peptide reagents from Applied Biosystems, Inc. (Foster City, CA). The DOTA-tris(t-butyl ester) was purchased from Macrocyclics (Dallas, TX) and the fmoc-protected w-amino alkyl carboxylic acids from Advanced ChemTech (Louisville, KY). ¹²⁵1-Tyr⁴-Bombesin (¹²⁵l-Tyr⁴-BBN) was obtained from NEN Life Sciences Products, Inc (Boston, MA). ¹¹¹lnCl3 was obtained from Mallinckrodt Medical, Inc. (St. Louis, MO) as a 0.05N HCI solution. ⁹⁰Y was obtained from Perkin-Elmer (Biclerica, MA) as an HCI solution. Electrospray mass spectral analyses were performed by Synpep Corporation and T47D (Dublin, CA). Human prostate cancer PC-3 cells and MDA-MB-231 breast cancer cells were obtained from American Tissue Culture Collection (ATCC) and maintained and grown in the University of Missouri Cell and Immunology Core facilities. CF-1 mice were purchased from Charles River Laboratories (Wilmington, MA) and maintained in an in-house animal facility.

Solid Phase Peptide Synthesis (SPPS): Peptide synthesis was carried out on a Perkin Elmer - Applied Biosystems Model 432 automated peptide synthesizer employing traditional fmoc chemistry with HBTU activation of carboxyl groups on the reactant with the N-terminal amino group on the growing peptide anchored via the C-terminus to the resin. Rink Amide MBHA resin (25 μmol), fmoc-protected amino acids with appropriate side- chain protections (7 μmol), fmoc-protected amino alkyl carboxylic acids (75 μmol), and DOTA-tris(t-butyl ester) (75 gmol) were used for the synthesis. The final products were cleaved by a standard procedure using a cocktail containing thioanisol, water, ethanedithiol and trifluoroacetic acid in a ratio of 2:1:1 :36 and precipitated into methyl-t-butyl ether. Typical yields of the crude peptides were 80-85%. Crude peptides were purified by HPLC and the solvents were removed on a SpeedVac concentrator. The purified peptides were characterized by electrospray mass spectrometry. The mass spectral analysis results are shown in Table 4.

High performance liquid chromatography (HPLC): High performance liquid chromatography (HPLC) analyses for DOTA conjugates were performed on a Waters 600E system equipped with Varian 2550 variable absorption detector, Packard Radiometic 1 ⁵°TR flow scintillation analyzer, sodium iodide crystal radiometric detector, Eppendorf TC-50 column temperature controller, and Hewlett Packard HP3395 integrators. A Phenomenex Jupiter C.s (5μm, 300 A0, 4.6 X 250 mm) column was used with a flow rate of 1.5 ml/minute. HPLC solvents consisted of H20 containing 0.1% trifluoroacetic acid (Solvent A) and acetonitrile containing 0.1% trifluoroacetic acid (Solvent B). HPLC gradient conditions for 0 spacer to 8- carbon spacer analogs begin with a solvent composition of 80% A and 20% B, followed by a linear gradient to 70%A:30% B over thirty minutes. HPLC gradient conditions for the 11 -carbon spacer analysis are solvent composition of 75% A and 25% B, followed by a linear gradient to 50% A:50% B over thirty minutes.

Indium metallation: A solution of the unmetallated DOTA-BBN conjugates as shown in Table 4 (5.0 mg) in 0.2M tetramethylammonium acetate (0.5 ml) was added to indium trichloride (lnCI₃) (10.0 mg). The pH of the reaction mixture was adjusted to 5.5 (Scheme 1). The reaction mixture was incubated for one hour at 80°C. The resultant In-DOTA-BBN conjugate (Scheme 1) was purified by reversed-phase HPLC and analyzed by electrospray mass spectrometry. The mass spectral analysis results are shown in Table 4. The pure product was obtained as a white powder with a typical yield of 50-60%.

¹¹¹ Indium/ ⁹⁰Yttrium labeling: An aliquot of ¹¹lnCI₃ (1.0 mCi, 50 μl) was added to a solution of the unmetallated DOTA-BBN (100 μg) conjugates shown in Table 4 in 0.2M tetramethyiammonium acetate (500 μl). The pH of the reaction mixture was adjusted to 5.6. The reaction mixture was incubated for one hour at 80°C. An aliquot of 0.002M EDTA (50 μl) was added to the reaction mixture to complex the unreacted ¹¹¹ln⁺³. The resultant ^In- DOTA-BBN conjugate was obtained as a single product and purified by reversed-phase HPLC. The purified ¹¹¹ln-DOTA-BBN conjugate was then concentrated by passing through a 3M Empore C.s HD high performance extraction disk (7mm/3ml) cartridge and eluting with 33% ethanol in 0.1 M NaH₂PO₄ buffer (400 μl). The concentrated fraction was then diluted with 0.1M NaH₂PO buffer (2.3 ml, pH-7) to make the final concentration of ethanol in the solution <5%. The ⁹⁰Y DOTA-BBN complex was similarly prepared.

In Vitro Cell Binding Studies: The ICso of the various In- DOTA-BBN conjugates was determined by a competitive displacement cell binding assay using ¹²⁵l-Tyr⁴-BBN. Briefly, 3 X 104 cells suspended in RPMI medium 1640 at pH-7.4 containing 4.8 mg/ml HEPES, 0.1 μg/ml Bacitracin and 2 mg/ml BSA, were incubated at 37°C and a 5% CO₂ atmosphere for 40 minutes in the presence of 20,000 cpm ²⁵l-Tyr⁴-BBN and increasing concentration of the In-DOTA-BBN conjugates. After the incubation, the reaction medium was aspirated and cells were washed four times with media. The radioactivity bound to the cells was counted in a Packard Riastar gamma counting system. The percent ¹²⁵l-Tyr⁴-BBN bound to cells was plotted versus increasing concentrations of In-DOTA-BBN conjugates to determine the respective ICso values. Intemalization and efflux studies: In vitro studies to determine the degree of intemalization of the ¹¹¹ln-DOTA-8-Aoc-BBN[7-14]NH₂ conjugate were carried out by a method similar to that described by Rogers, et al. These studies were performed by incubating 3 X 104 cells suspended in RPMI medium 1640 at pH-7.4 containing 4.8 mg/ml HEPES, 0.1 μg/ml Bacitracin and 2 mg/ml BSA, at 37°C and a 5% CO₂ atmosphere for 40 minutes in the presence of 20,000 cpm ¹¹¹ln-DOTA-8-Aoc-BBN[7-14]NH₂ conjugate. After the incubation, the reaction medium was aspirated and cells were washed with media. The percent of cell-associated activity as a function of time (in the incubating medium at 37°C) was determined. The percentage radioactivity trapped in the cells was determined after removing activity bound to the surface of the cells by washing with a pH-2.5 (0.2M acetic acid and 0.5M NaCl) buffer one, two, three and four hours afterwards.

In vivo pharmacokinetic studies in CF-1 mice: The biodistribution and uptake of ¹¹¹ln-DOTA-BBN conjugates in CF-1 mice was studied. The mice (average weight, 25 g) were injected with aliquots (50-100 μl) of the labeled peptide solution (55-75 kBq) in each animal via the tail vein. Tissues and organs were excised from the animals sacrificed at one hour post- injection. The activity counted in a Nal counter and the percent injected dose per organ and the percent injected dose per gram were calculated. The percent injected dose (% ID) in the blood was estimated assuming a blood volume equal to 6.5% of the total body weight. Receptor blocking studies were also carried out where excess (100 μg) BBN was administered to animals along with the ¹¹¹ln-DOTA-8-Aoc-BBN[7-14]NH₂. In vivo pharmacokinetic studies in human tumor hearing SCID mice: The biodistribution studies of the ¹¹¹ln and ⁹⁰Y conjugates were determined in SCID mice bearing human tumor xenografts of either PC-3 (human androgen independent prostate cancer cell origin), or MDA-MB-231 (human breast cancer cell origin) cell lines. The xenograft models were produced by bilateral flank inoculation of 5 X 106 cells (PC-3 or MDA-MB-231 cells) per site. Four to six weeks post inoculation, palpable tumors were observed. At this point, the mice were injected with 4μCi of the complex in 100/μL of isotonic saline via the tail vein. The mice were euthanized and tissues and organs were excised from the animals at selected times post- injection (p.L), including 15 minutes, 30 minutes, 1 hour, 4 hours, 24 hours, 48 hours, and 72 hours p.i. Subsequently, the tissues and organs were weighed and counted in a Nal well counter, and the percent injected dose (%ID) and %ID/g of each organ or tissue calculated. The %ID in whole blood was estimated assuming a whole-blood volume of 6.5% total body weight. In vivo ore-clinical evaluation of single dose radiotherapy in human tumor bearing SCID mice: Pre-clinical therapeutic evaluation of the ⁹⁰Y-DOTA-8-Aoc-BBN[7-14]NH₂ conjugate was performed in SCID mice bearing PC-3 human androgen independent prostate cancer cell human tumor xenografts. The xenograft model was produced by bilateral flank inoculation of 5 X 106 PC-3 cells per site. Twenty-one days post inoculation, when palpable tumors appeared, single dose administration of ⁹⁰Y-DOTA-8- Aoc-BBN[7-14]NH₂ was initiated. Baseline weights, hematology profiles, and tumor measurements were obtained immediately prior to therapy administration. Four groups of animals were utilized: a saline placebo, a 5 mCi/kg single dose, a 10 mCi/kg single dose, and a 20 mCi/kg single dose. Tumor measurements and weights were obtained twice weekly throughout the 14 weeks post injection. Discussion

A series of BBN-agonists containing the DOTA chelation system separated by spacers have been synthesized and characterized [Figures 27 and 28; Tables 4 and 20].

The in vitro binding affinity of the Indium-BBN analogs was measured in two cell lines: the human prostate cancer cell line, PC-3; and the human breast cancer cell line, T47D. Of the compounds tested, optimum binding of the ln-DOTA-8-Aoc-BBN[7-14]NH₂ analog was demonstrated in both cell lines examined [Figure 29 and Table 5].

The ln-DOTA-8-Aoc-BBN[7-14]NH₂ analog underwent rapid receptor mediated endocytosis using an in vitro PC-3 cell assay system. Once internalized within PC-3 cells, the ln-DOTA-8-Aoc-BBN[7-14]NH₂ analog remained retained within the cells for a prolonged time period [Figures 30 and

31].

In vivo analysis of the DOTA-BBN analogs in CF1 mice demonstrates that ¹¹¹ln-DOTA-5-Ava-BBN[7-14]NH₂, ¹¹¹ln-DOTA-8-Aoc- BBN[7-14]NH₂, ¹¹¹ln-DOTA-11-Aun-BBN[7-14]NH₂ all target GRP receptor expression in vivo based on high uptake and accumulation of these compounds in the normal pancreas. Increasing hydrocarbon spacer length linking the DOTA metal chelation moiety to the GRP receptor binding moiety (BBN[7-14]NH₂), results in compounds with increased hydrophobicity, which subsequently shifts the clearance of these agents, from the renal system (hydrophilic agents) to the hepatobiliary system (hydrophobic agents). [Tables 6 and 7].

Specific in vivo GRP receptor binding was demonstrated by performing competitive blocking assays in CF1 normal mice, where greater than 98% of the normal receptor mediated uptake of ¹¹¹ln-DOTA-8-Aoc-

BBN[7-14]NH in normal pancreatic tissue was blocked by co-administration of an excess of bombesin [Tables 8 and 9].

Prolonged PC-3 human prostate tumor uptake was demonstrated for ¹¹¹ln-DOTA-8-Aoc-BBN[7-14]NH₂ and ⁹⁰Y -DOTA-8-Aoc- BBN[7-14]NH₂ using a xenograft mouse model [Tables 10-13].

Prolonged MDA-MB-23 1 human breast tumor uptake was demonstrated for ¹¹¹ln-DOTA-8-Aoc-BBN[7-14]NH₂ using a xenograft mouse model. [Table 14]. These in vivo pharmacokinetic studies in CF1 mice have demonstrated that the radiometallated bombesin analogues (¹¹¹ln and ⁹⁰Y) clear from the blood pool into the renal-urinary excretion pathway. Competitive Binding Assay Results The ¹¹¹ln and ⁹⁰Y complexes of one lead candidate, DOTA-8-

Aoc-BBN[7-14]NH₂, have been synthesized and evaluated in w^'fro and in vivo. In vitro competitive binding assays, employing PC-3 human prostate tumor cells, demonstrated an average ICso value of 1.69 nM for the ln-DOTA-8-Aoc- BBN[7-14]NH₂ complex. In Vivo Pharmacokinetic Results in PC-3 Tumor Bearing Mice

In vivo pharmacokinetic studies of ¹¹¹ln-DOTA-8-Aoc-BBN[7- 14]NH₂ in PC-3 prostate tumor bearing mice conducted at 1, 4, 24, 48, and 72 hours p.i. revealed efficient clearance from the blood pool (0.92 ± 0.58 % ID, 1 hour p.i.) with excretion through the renal and hepatobiliary pathways (87% ID and 8.5% ID, at 24 hours p.i., respectively). Similar pharmacokinetic properties were observed with ⁹⁰Y-DOTA-8-Aoc-BBN[7-14]NH₂. Tumor targeting of PC-3 xenografted SCID mice resulted in tumor uptake and retention values of 3.63 ± 1.11%ID/g, 1.78 ± 1.09%ID/g, and 1.56 ±^" 0.45%ID/g obtained at 1,4, and 24 hours p.i. respectively, for the ¹¹¹ln-DOTA- 8-Aoc-BBN-[7-14]NH₂ complex. ⁹⁰Y-DOTA-8-Aoc-BBN[7-14]NH₂ exhibited nearly identical PC-3 tumor uptake and retention values of 2.95 ± 0.99%ID/g, 1.98 ± 0.66%ID/g, and 1.08 ± 0.37%ID/g at 1, 4, and 24 hours p.i., respectively. Initial therapeutic assessment of the ⁹⁰Y complex in PC-3 xenografted mice demonstrated that radiation doses of up to 20mCi/kg were well tolerated with overall survival exhibiting a dose dependent response.

These pre-clinical observations show that peptide conjugates of this type exhibit properties suitable as clinical therapeutic/diagnostic pharmaceuticals.

EXAMPLE 10: Binding of DOTA-BBN Conjugates in Human Breast Cancer Cell Lines: Expression of Gastrin Releasing Peptide receptors (GRP-Rs) in a variety of cancers including breast, prostate, small cell lung, and pancreatic is well known. Recently, the first positive clinical images of GRP-R expression in human metastatic breast cancer patients were obtained [C. Van de Wiele et al., Eur. J. Nucl. Med. (2000) 27:1694-1699] with the compound, ^99mTc-N₃S-5-Ava-BBN(7-14)NH₂, initially developed in our laboratory. The continued efforts in the development of GRP targeted radiopharmaceuticals have led to the synthesis of a series of DOTA incorporated peptides for the complexation of ^In ^Y.

Methods: Six synthetic peptides were constructed in an X-Y-Z fashion where X = the DOTA chelation system, Y = the linking arm, and Z = the BBN(7-14)NH₂ sequence. The six peptides differed in the selection of linking arms, comprising either amino acid tethers: -G-G-G-, -G-S-G- or S-G- S-, or alkyl carbon chain tethers; 5-Ava, 8-Aoc, or 11-Aun. The In complexes of all peptides were prepared, purified by RPHPLC, and characterized by ES- MS as described in Example 9.

Results: Pharmacokinetic studies conducted in CF1 mice revealed that ¹¹¹ln-DOTA-8-Aoc-BBN(7-14)NH₂ exhibited optimum clearance kinetics while maintaining selective and high in vivo GRP receptor targeting. ¹¹¹ln-DOTA-8-Aoc-BBN(7-14)NH₂ exhibited an IC₆₀ value of 1.23 ±0.25nM for the GRP receptor expressed by the T47D human breast cancer cell line. Pharmacokinetic studies of ¹¹¹ln-DOTA-8-Aoc-BBN(7-14)NH₂ conducted in MDA-MB-231 human breast cancer cell line xenografted SCID mice demonstrated specific tumor targeting with 0.83 ± 0.23% ID/g obtained at one hour post injection. Residualization of the radiolabel within the tumor was observed with 46% and 28% of the initial uptake retained at 4, and 24 hours, respectively.

Conclusion: These results show that GRP-R specific radiopharmaceuticals incorporating the DOTA chelation system are beneficial for the development of diagnostic/therapeutic matched pair agents to target breast cancer.

EXAMPLE 11 : Lutetium DOTA-BBN Compounds

A conjugate, ⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂, was routinely prepared in high yield (>95%) by addition of ¹⁷⁷LuCl3 to an aqueous solution (Ammonium Acetate) of DOTA-8-Aoc-BBN[7-14]NH (3.4x10-8 mols) [pH = 5.5, Temp. = 800C, RT = 1 hour]. RCP determination demonstrated the stability of the conjugate over a wide range of pH values over a time course of 24 hours. The HPLC chromatogram of ¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂ showed a retention time of 19.0 minutes. Under identical chromatographic conditions, DOTA-8-Aoc-BBN[7-14]NH₂ has a retention time of 20.5 minutes, allowing for peak purification of the radiolabeled conjugate. Collection of and counting of the ¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂ eluant peak in a Nal well counter further demonstrated the stability of the new complex, as >95% of the activity loaded onto the column was recovered as a singular species.

The biodistribution studies of ¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂ were determined in tumor bearing (PC-3) SCID mice (TABLE 19). This ¹⁷⁷Lu- conjugate cleared efficiently from the bloodstream within one hour post- injection. For example, 0.62 ± 0.44%ID remained in whole blood at one hour p.i. The majority of the activity was excreted via the renal-urinary excretion pathway (i.e., 67.41 ±2.45% at one hour p.i. and 85.9 ± 1.4% at 24 hour p.i.), with the remainder of the radioactivity being excreted through the hepatobiliary pathway. Receptor-mediated, tumor targeting of the PC-3 xenografted SCID mice resulted in tumor uptake and retention values of 4.22 ± 1.09%ID/g, 3.03 ± 0.91%ID/g, and 1.54 ± 1.14%ID/g at 1, 4, and 24 hours, respectively.

EXPERIMENTAL: To 50μg (3.4x10-8 mols) of DOTA-8-Aoc- BBN[7-14]NH₂ in 50μL of 0.2M Ammonium Acetate was added 150μL of 0.4M Ammonium Acetate. To this solution was added 50μL of ¹⁷⁷LuCI₃ (2mCi in 0.05N HCI, Missouri University Research Reactor). The solution was allowed to incubate at 800C for one hour, after which 50μg of 0.002M EDTA was added in order to scavenge uncomplexed Lutetium. Quality control of the final product was determined by reversed-phase HPLC. Peak purification of the labeled species was performed by collecting the sample from the HPLC eluant, into a solution of 1mg/mL bovine serum albumin/0.1M Na₂HPO₄. All further analyses were carried out using the HPLC-purified products.

HPLC analysis of each of the new compounds was performed using an analytical C_.s reversed phase column (Phenomenex, 250x4.6mm, 5μm). The mobile phase consisted of a linear gradient system, with solvent A corresponding to 100% water with 0.1% trifluoroacetic acid, and solvent B corresponding to 100% acetonitrile with 0.1% trifluoroacetic acid. The mobile phase started with solvent compositions of 80%A:20%B. At time = 30 minutes, the solvent compositions were 70%A:30%B. Solvent compositions of the mobile phase remained as such (70%A:30%B) for a period of two minutes before being changed to 100%B. At time = 34 minutes, the solvent composition was again changed to 80%A:20%B for column re-equilibration. The flow rate of the mobile phase was 1.5ml_/minute. The chart speed of the integrator was 0.5cm/minute. The results of these analyses are shown in Table 20.

In vivo analysis of the DOTA-BBN analogs in CF1 mice demonstrates that ¹⁴⁹Pm-DOTA-5-Ava-BBN[7-14]NH₂ and ¹⁴⁹Pm-DOTA-8- Aoc-BBN[7-14]NH₂ target GRP receptor expression in vivo based on high uptake and accumulation of these compounds in the normal pancreas, which contain high levels of the GRP receptor [Tables 15 and 16].

In vivo analysis of the DOTA-BBN analogs in CF1 mice demonstrates that ¹⁷⁷Lu-DOTA-5-Ava-BBN[7- 1 4]NH₂, ¹⁷⁷Lu-DOTA-8-Aoc- BBN[7-14]NH₂, and ¹⁷⁷Lu -DOTA-11-Aun-BBN[7-14]NH₂ all target GRP receptor expression in vivo based on high uptake and accumulation of these compounds in the normal pancreas [Tables 17 and 18] The biodistribution studies of ¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂ were determined in SCID mice bearing human prostate cancer, PC-3 tumors. The mice were injected with 4μCi of the complex in 100μL of isotonic saline via the tail vein. The mice were euthanized by cervical dislocation. Tissues and organs were excised from the animals following at 1 hour, 4 hours, and 24 hours post-injection (p.i.). Subsequently, the tissues and organs were weighed and counted in a Nal well counter and the percent injected dose (%ID) and %ID/g of each organ or tissue calculated. The %ID in whole blood was estimated assuming a whole-blood volume of 6.5% the total body weight.

Prolonged PC-3 human prostate tumor uptake was demonstrated for ¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14] using a xenograft mouse model of human prostate cancer [Tables 19 and 20].

CONCLUSION: This pre-clinical evaluation of ¹⁷⁷Lu-DOTA-8-

Aoc-BBN[7-14]NH₂ and ¹⁴⁹Pm-DOTA-8-Aoc-BBN[7-14]NH₂ suggests the potential for peptide conjugates of this type to be used as site-directed, therapeutic radiopharmaceuticals.

Table B. Biodistribution of ⁹⁹ Tc-BBN-122 in normal CF-1 mice at 0.5, 1 , 4 and 24 hours post-IV injection. Results expressed as % ID/organ

Each value in the table represents the mean and SD from 5 animals in each group

At 4 and 24 hours, feces containing ^99mTc had been excreted from each animal and the % ID in the urine was estimated to be approximately 60% of the ID.

All other organs excised (incl. Brain, heart, lung and spleen) shown < 0.10% at t > 1 hr. d. % ID in the blood estimated assuming the whole blood volume is 6:5% of the body weight. Table C. Biodistribution of ^99mTc-BBN-122 in normal CF-1 mice at 0.5, 1 , 4 and 24 hours post IN. injection. Results expressed as % ID/gm.

a. Each value in the table represents the mean and SD from 5 animals in each group. b. % ID in the blood estimated assuming the whole blood volume is 6:5% of the body weight.

Table D Biodistribution of ^WmTc-BBN-122 in PC-3 tumor bearing SCID^' mice at 1 , a _anci 24 hr post-I.V. injection. Results expressed as % ID/organ. -

a. Each value in the table represents the mean and SD from 5 animals in each group. b. At 4 and 24 hr, fecεs containing ^{9 m}Tc had been excreted from each animal and the, % ID in the urine was estimated to be approximately 60% of the ID. c All other organs excised (incl. brain, heart, lung and spleen) showed < 0.10% at t >

1 hr. d. % ID in the blood estimated assuming the whole blood volume is 6:5% of the body weight. able E. Biodistribution of ^" c-BBN- in PC-3 tumor bearing SCID mice at 1 , 4 and

24 hr post-LV. injection. Results expressed as % ID/Gm.

a. • Each value in the table represents the mean and SD from 5 animals in each group. b. % ID in the blood estimated assuming the whole blood volume is 6:5 % of 'the body weight.

The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Throughout this application, various publications are referenced by citation and number. Full citations for the publication are listed below. The disclosure of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.

Tabic

iπdlng Affnity of R! BBN»37 i ftece. Expressed bo Mec m.

Complex 10S 105

R ~Pβpt_iάa22 R ~Pept_ide_22 10S

Kh-^'Peptide22 30 min 1 r 2 hr n«9 n_^9 Organ (%Dc.se)

Brain 0.08 0,04 0.06 0.02 0.01 x 0.09

Blood 4.48 l.ae 0.99 1.24 0.38 0.24

Heart 0.13 0.08 0.04 0.03 0.03 0.04

Lung 0.25 0.20 0.15 O.Oή 0.09 0.03-

Liver 7.i»7 8.51 8.57 2.85 2.33 2.04

Spl&en 0.07 0.09 ' 0.05 ≥ 0_s 0.03 .0.08 0.01

Stomach 1.11 0.59 0.30 m φ 0.76 0.21 0.16 li

Large Intestine O.73 ^{• '}3.21 6.91

I 0.16 3.38 3.79 .Small Intestine 6.29 6.98 3. a 1.87 1.87 1.76

Kidneys 4:25 3.25 2.44 1.33 0.60 0.64

Bladder 44.66 62.88 68.41 7.29. 3.84 6.63

Muβcle 0.06 0.03 0.01

±- 0.03 0.03 0.01

Pancreaa

Carcass 32.5*0 12.62 6.37 6.61 4.77 1.17

^•

(%Dose)

_*- cn f^» H

m -

« m

Table 4

ES-MS and HPLC data of DOTA-BBN[7-14]NH₂ and In-DOTA- BBN[7-14]NH₂ analogues.

Table 5

IC₅₀ (nM) values (n = 3 or 4 separate experiments performed in duplicate) of In-DOTA-

BBN[7-14]NH₂ analogues v rss.. ¹¹²²⁵⁵II--TTyyrr --BBBBNN iinn hhuummaann pprreostate PC-3 cells and human breast carcinoma T47D cells.

Table S

^{n ι}In-DOTA-SPACER-BBN[7-14]NH₂ biodistribution (Avg %_CD/gm. n = 5) in CFl normal mice after 1 hour post-injection.

Table 7

^{l l l}In-DOTA-SPACER-BBN[7-14jNH₂ biodistribution (Avg %ID, n = 5) in CFl normal mice after 1 hour post-injection.

Table 8

n i 'I₇n-DOTA-BBN[7-14]NH₂ analogues biodistribution (Avg % ID/gm, n = 5) in CFl normal mice after 1 hour post-injection.

Table 9

111 In-DOTA-BBN[7- 14]NK₂ analogues biodistribution (Avg %_D, n = 5) in CFl normal mice after 1 hour post-injection.

111 In-DOTA-8-Aoc-BBN[7-14]NH_ biodistribution (Avg %ED/gm, n = 5) in PC-3 tumor bearing niice.

s _τ¹

Table 12

⁹⁰Y-DOTA-8-Aoc-BBN[7-14]NH_ biodistπbution (Avg %ID/gm) in PC-3 tumor bearing mice.

Table 13

90 Y-DOTA-8-Aoc-BEN[7-l4]NH₂ biodistribucion (Avg %ID) in PC-3 tumor bearing mice.

Table 14

Table 15

⁹Pm-DOTA-SPACER-BBN[7-14]NH₂ biodistribution (Avg ID/gm, n = 5) in CFl normal mice after 1 hour post-injection.

. Table 16

149 Pm-DOTA-SPACER-BBN[7-l4]iN^"H₂ biodistribution (Avg % D, n = 5) in CFl normal mice after 1. hour post-injection.

Table 17

177- u-DOTA-SPACER-BBI [7-14]NH₂ biodistribution (Avg %ID/gm. n = 5) in CFl normal mice after 1 hour post-injection.

Table 18

¹⁷⁷Lu-DOTA-SPACER-BBN[7-14]NH₂ biodistribution (Avg __D, n = 5) in CFl normal mice after 1 hour post-injection.

Table 19

'Lu-DOTA-8-Aoc-BBN[7-14]NH₂ biodistribution (Avg %JD/g__i, π = 5) in PC-3 tumor bearing

TABLE 20.

¹⁷⁷Lu-DOTA-8-Aoc-BBN[7-14]NH₂ biodistribution (Avg %ID, n = 5) in PC-3 tumor bearing mice.

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Hoffman, T.J., Li, N., Volkert, W.A., Sieckman, G., Higginbotham, C.A., and Ochrymowycz, L.A., "Synthesis and Characterization of Rh-105 Labeled Bombesin Analogues: Enhancement of GRP Receptor Binding Affinity Utilizing Aliphatic Carbon Chain Linkers", 12th International Symposium on Radiopharmaceutical Chemistry, June, 1997.

Hoffman, T.J., Li, N., Higginbotham, C.A., Sieckman, G., Volkert, W.A., "Specific Uptake and Retention of Rh-105 Labeled Bombesin Analogues in GRP-Receptor Expressing Cells", European Society of Nuclear Medicine, August, 1997; Eur. J. Nucl. Med., 24(8), 901 , 1997.

Hoffman, T.J., Li, N., Sieckman, G.L., Higginbotham, C. Ochrymowycz, L.A., Volkert, W.A. "Rh-105 Bombesin Analogs: Selective In Vivo Targeting of Prostate Cancer with a Therapeutic Radionuclide", 45th Annual Meeting - Society of Nuclear Medicine, June 1998; J.Nucl. Med., 39(5), 222P, 1998.

Hoffman, T.J., Quinn, T.P., and Volkert, W.A., "Radiometallated Receptor- Avid Peptide Conjugates for Specific In Vivo Targeting of Cancer", Nuc. Med.& Biol. (Accepted), 2001.

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Hoffman, T.J., Smith, C.J., Gali, H., Owen, N.K., Sieckman, and Volkert, W.A., "In Vitro and In Vivo Evaluation of ^In/^Y Radiolabeled Peptides for Specific Targeting of Tumors Expressing Gastrin Releasing Peptide (GRP) Receptors", 92nd Annual Meeting of the American Association for Cancer Research, New Orleans, LA. Proceedings of the American Association for Cancer Research, Vol. 42, 773, #4148, March 2001.

Hoffman, T.J., Smith, C.J., Gali, H., Owen, N.K., Sieckman, Hayes, D.L., and Volkert, W.A., "Development of a Diagnostic Radiopharmaceutical for Visualization of Primary and Metastatic Breast Cancer", 48th Annual Meeting- Society of Nuclear Medicine, Toronto, Ontario, Canada, June 2001. (Accepted)

Hoffman, T.J., Smith, C.J., Gali, H., Owen, N.K., Sieckman, Hayes, D.L., Foster, B., and Volkert, W.A., "^In Y Radiolabeled Peptides for Targeting Prostate Cancer; A Matched Pair Gastrin Releasing Peptide (GRP) Receptor Localizing Radiopharmaceutical", 48th Annual Meeting-Society of Nuclear Medicine, Toronto, Ontario, Canada, June 2001. (Accepted) Hoffman, T.J., Smith, C.J., Sieckman, G.L, Owen, N.K., and Volkert, W.A., "Design, Synthesis, and Biological Evaluation of Novel Gastrin Releasing Peptide Receptor Targeting Radiopharmaceuticals" American Chemical Society Annual Meeting, August 2000, Washington, D.C. Hoffman, T.J., Smith, C.J., Simpson, S.D., Sieckman, G.L, Higginbotham, C, Jimenez, H., Eshima, D., Thornback, J.R., and Volkert, W.A. "Targeting Gastrin Releasing Peptide Receptor (GRP-R) Expression in Prostate and Pancreatic Cancer Using Radiolabeled GRP Agonist Peptide Vectors", American Association for Cancer Research Annual Meeting, San Francisco, CA, Proceedings of the American Association for Cancer Research, Vol. 41 , 529, #3374, April, 2000.

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Claims

CLAIMSWhat is claimed is:

1. A compound comprising a metal complexed with a chelating group attached to a gastrin releasing peptide (GRP) receptor agonist which includes a bombesin agonist binding moiety.

2. The compound according to claim 1 , wherein said compound has a structure of the formula X-Y-B wherein X is a metal chelating group, Y is a spacer group or covalent bond and B is a gastrin releasing peptide receptor agonist which includes a bombesin agonist binding moiety.

3. The compound of claim 2 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof.

4. The compound of claim 2 wherein X is selected from the group consisting of DOTA, DTPA, S , N₃S, N2S2, NS3 and derivatives thereof.

5. The compound of claim 4 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7- 14) and BBN(8-14).

6. The compound of claim 4 wherein X is DOTA or a derivative thereof.

7. The compound of claim 6 wherein Y is selected is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7-14) and BBN(8-14).

8. The compound of claim 7 wherein Y is a combination of L-glutamine and a hydrocarbon chain.

9. The compound of claim 8 wherein Y is a combination of L-glutamine and a C1 to C10 hydrocarbon chain.

10. The compound of claim 9 wherein Y is selected from the group consisting of glycine, β-alanine, gamma-aminobutanoic acid, 5- aminovaleric acid (5-Ava), 6-aminohexanoic acid, 7-aminoheptanoic acid, 8- aminooctanoic acid (8-Aoc), 9-aminononanoic acid, 10-aminodecanoic acid and 11-aminoundecanoic acid (11-Aun).

11. The compound of claim 4 wherein X is N₃S or a derivative thereof.

12. The compound of claim 11 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7- 14) and BBN(8-14).

13. The compound of claim 12 wherein Y is gly-ser-gly.

14. A complex comprising a metal and a compound having a structure of the formula X-Y-B wherein X is a metal chelating group, Y is a spacer group or covalent bond and B is a gastrin releasing peptide receptor agonist which includes a bombesin agonist binding moiety.

15. The complex of claim 14 wherein the metal is selected from the group consisting of transition metals, lanthanides, auger-electron emitting isotopes, and α-, β- or γ-emitting isotopes.

16. The complex of claim 14 wherein the metal is selected from the group consisting of: 105Rh-, ^99mTc-, ^186/188Re-, ¹⁵³Sm-, ¹⁶⁶Ho-, ¹¹¹ln-, ⁹⁰Y-, ¹⁷⁷Lu-, ¹⁴⁹Pm-, ¹⁶⁶Dy-, ¹⁷⁵Yb-, ¹⁹⁹Au- and ¹¹⁷mSn-.

17. The complex of claim 16 wherein X is selected from the group consisting of DOTA, DTPA, S₄, N₃S, N2S2, NS3 and derivatives thereof.

18. The complex of claim 17 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN (7- 14) and BBN(8-14).

19. The complex of claim 16 wherein X is DOTA or a derivative thereof.

20. The complex of claim 19 wherein Y is selected is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7-14) and BBN(8-14).

21. The complex of claim 20 wherein Y is a combination of L- glutamine and a hydrocarbon chain.

22. The complex of claim 21 wherein Y is a combination of L- glutamine and a C1 to C10 hydrocarbon chain.

23. The complex of claim 22 wherein Y is selected from the group consisting of glycine, β-alanine, gamma-aminobutanoic acid, 5- aminovaleric acid (5-Ava), 6-aminohexanoic acid, 7-aminoheptanoic acid, 8- aminooctanoic acid (8-Aoc), 9-aminononanoic acid, 10-aminodecanoic acid and 11 -aminoundecanoic acid (11 -Aun).

24. The complex of claim 23 wherein Y is 8-aminooctanoic acid.

25. The complex of claim 23 consisting of ⁹⁰Y-DOTA-8-Aoc- BBN(7-14)NH₂.

26. The complex of claim 23 consisting of ¹¹¹ln-DOTA-8-Aoc-

BBN(7-14) NH₂.

27. The complex of claim 23 consisting of ¹⁷⁷Lu-DOTA-8-Aoc- BBN(7-14) NH₂.

28. The complex of claim 23 consisting of ¹⁴⁹Pm-DOTA-8- Aoc-BBN(7-14) NH₂.

29. The complex of claim 23 consisting of ⁹⁰Y-DOTA-5-Ava- BBN(7-14)NH₂.

30. The complex of claim 23 consisting of ¹¹¹ln-DOTA-5-Ava- BBN(7-14) NH₂.

31. The complex of claim 23 consisting of ¹⁷⁷Lu-DOTA-5-Ava- BBN(7-14) NH₂.

32. The complex of claim 23 consisting of ¹⁴⁹Pm-DOTA-5- Ava-BBN(7-14) NH₂.

33. The complex of claim 16 wherein X is N₃S or a derivative thereof.

34. The complex of claim 33 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7- 14) and BBN (8-14).

35. The complex of claim 34 wherein Y is gly-ser-gly.

36. The complex of claim 34 consisting of ^99mTc-N₃S-gly-ser- gly-BBN(7-14)NH₂.

37. A method of treating a patient using radioisotope therapy by administering an effective amount of a pharmaceutical comprising a metal complex with a chelating group with a gastrin releasing peptide receptor agonist which includes a bombesin agonist moiety.

38. The method according to claim 37, wherein said method includes administering an effective amount of a complex comprising a metal and a compound having a structure of the formula X-Y-B wherein X is a metal chelating group, Y is a spacer group or covalent bond and B is a gastrin releasing peptide receptor agonist which includes a bombesin agonist binding moiety.

39. - The method of claim 38 wherein the metal is selected from the group consisting of transition metals, lanthanides, auger-electron emitting isotopes, and α-, β- or γ-emitting isotopes.

40. The method of claim 38 wherein the metal is selected from the group consisting of: ¹⁰⁵Rh-, ^99mTc-, ^186/188Re-, ¹⁵³Sm-, ¹⁶⁶Ho-, ¹¹¹ln-, ⁹⁰Y-, ¹⁷⁷Lu-, ¹⁴⁹Pm-, ¹⁶⁶Dy-, ¹⁷⁵Yb-, ¹⁹⁹Au- and ¹¹⁷mSn-.

41. The method of claim 40 wherein X is selected from the group consisting of DOTA, DTPA, S₄, N₃S, N2S2, NS3 and derivatives thereof.

42. The method of claim 41 wherein X is DOTA or a derivative thereof.

43. The method of claim 42 wherein Y is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7- 14) and BBN(8-14).

44. The method of claim 43 wherein Y is a combination of L- glutamine and a hydrocarbon chain.

45. The method of claim 44 wherein Y is selected from the group consisting of glycine, β-alanine, gamma-aminobutanoic acid, 5- aminovaleric acid (5-Ava), 6-aminohexanoic acid, 7-aminoheptanoic acid, 8- aminooctanoic acid (8-Aoc), 9-aminononanoic acid, 10-aminodecanoic acid and 11-aminoundecanoic acid (11-Aun).

46. v A method of imaging a patient by administering to a subject a diagnostically effective amount of a compound as set forth in claim 1.

47. The method of claim 46, wherein said method includes administering an effective amount of a complex comprising a metal and a compound having a structure of the formula X-Y-B wherein X is a metal chelating group, Y is a spacer group or covalent bond and B is a gastrin releasing peptide receptor agonist which includes a bombesin agonist binding moiety.

48. The method of claim 47 wherein the metal is selected from the group consisting of transition metals, lanthanides, auger-electron emitting isotopes, and α-, β- or γ-emitting isotopes.

49. The method of claim 48 wherein X is selected from the group consisting of DOTA, DTPA, S₄, N₃S, N2S2, NS3 and derivatives thereof.

50. The method of claim 49 wherein X is N₃S or a derivative thereof.

51. The method of claim 50 wherein Y is selected is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof and B is selected from the group consisting of BBN(7-14) and BBN(8-14).

52. The method of claim 51 wherein Y is gly-ser-gly.

53. A method of forming a therapeutic or diagnostic compound comprising the step of reacting a metal complexed with a chelating group with a gastrin releasing peptide receptor agonist which includes a bombesin agonist moiety.

54. The method of claim 53, wherein said method includes reacting a metal with a compound having a structure of the formula X-Y-B wherein X is a metal chelating group, Y is a spacer group or covalent bond and B is a gastrin releasing peptide receptor agonist which includes a bombesin agonist binding moiety.

55. The method of claim 54 wherein the metal is selected from the group consisting of transition metals, lanthanides, auger-electron emitting isotopes, and o , β- or γ-emitting isotopes.

56. The method of claim 54 wherein the metal is selected from the group consisting of: ^99mTc- and ^186/188Re-.

57. The method of claim 56 wherein Y is selected is selected from the group consisting of at least one amino acid residue, a hydrocarbon chain and a combination thereof.

58. The method of claim 57 wherein X is selected from the group consisting of DOTA, DTPA, S₄, N₃S, N2S2, NS3 and derivatives thereof.

59. The method of claim 58 wherein B is selected from the group consisting of BBN(7-14) and BBN(8-14).

60. The method of claim 59 wherein X is DOTA or a derivative thereof and Y is selected from the group consisting of glycine, β- alanine, gamma-aminobutanoic acid, 5-aminovaleric acid (5-Ava), 6- aminohexanoic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid (8-Aoc), 9- aminononanoic acid, 10-aminodecanoic acid and 11-aminoundecanoic acid (11-Aun).

61. The method of claim 59 wherein X is N₃S or a derivative thereof and Y is gly-ser-gly.