IE62091B1

IE62091B1 - Detectable somatostatin derivatives containing a chelating group

Info

Publication number: IE62091B1
Application number: IE386689A
Authority: IE
Inventors: Rainer Albert; Eric P Krenning; Steven W J Lamberts; Janos Pless
Original assignee: Sandoz Ltd
Priority date: 1988-12-05
Filing date: 1989-12-04
Publication date: 1994-12-14
Also published as: NL8902981A; GB8927255D0; SE8904087D0; JP3686503B2; FR2639947B1; NL194828B; AU633859B2; MY106120A; PT92487B; DK612689A; AU4587189A; HU211468A9; CH678329A5; ATA901789A; AT403476B; JPH02184698A; DE3991505B4; GB2225579B; LU87633A1; HUT53375A

Abstract

Somatostatin peptides bearing at least one chelating group for a detectable element, said chelating group being linked to an amino group of said peptide, and said amino group having no significant binding affinity for somatostatin receptors, in free or salt form, are complexed with a detectable element and as such are useful as a pharmaceutical, e.g. a radiopharmaceutical for in vivo imaging of somatostatin receptor positive tumors or for therapy.

Description

DETECTABLE SOMATOSTATIN DERIVATIVES CONTAINING A CHELATING GROUP The.present invention relates to polypeptides, process for their production, pharmaceutical preparations containing them and their use as a pharmaceutical, e.g. for treatment of somatostatin receptor positive tumors or as in vivo diagnostic imaging agents.

In the last few years a high incidence of somatostatin receptors has been demonstrated in a variety of human tumors, e.g. pituitary tumors, central nervous system tumors, breast tumors, gastro-enteropancreatic tumors and their metastases. Some of them are small or slov-groving tumors vhich are difficult to precisely localize by conventional diagnosis methods.

In vitro visualization of somatostatin receptors has been performed through autoradiography of tumoral tissues using radioiodinated somatostatin or somatostatin analogues, e.g. [1251-Tyr11] somatostatin-14 (Taylor, J.E. et al., Life Science (1988) 43: 421), or [1J5I-Tyr3l SMS 201-995 also called [125I] 204-090 (Reubi, J.C. et al., Brain Res. (1987) 406: 891; Reubi, J.C. et al., J. Clin. Endocr. Metab. (1987) 65: 1127; Reubi, J.C. et al., Cancer Res. (1987) 47: 551; Reubi, J.C. et al., Cancer Res. (1987) 47: 5758).

New somatostatin peptides useful in therapeutic and vhich can be labelled for in vivo diagnostic and therapeutic applications have * nov been found.

According to the invention, there is provided a somatostatin peptide bearing at least one chelating group for a detectable element, this chelating group being linked to an amino group of said peptide, this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors, and the chelating group being other than a sugar residue.

These compounds are referred to thereafter as LIGANDS OF THE INVENTION. They possess one chelating group capable of reacting vith a detectable element, e.g. a radionuclide, a radioopaque element or a paramagnetic ion, to form a complex and further are capable of binding to somatostatin receptors, e.g. expressed or overexpressed by tumors or metastases.

The chelating group is linked by a covalent bond to the amino group of the peptide.

The chelating group is preferably attached to the terminal N-amino group of the somatostatin peptide.

According to the invention, the chelating group may be attached either directly or indirectly, e.g. by means of a spacer group, to the amino group of the somatostatin peptide.

One group of LIGANDS is that wherein the chelating group is attached directly to the amino group of the somatostatin peptide..

Another group of LIGANDS is that wherein the chelating group is attached indirectly by a bridging or a spacer group to the amino group of the somatostatin peptide.

Preferably the chelating group is attached by an amide bond to the peptide.

The term somatostatin peptides includes the naturally occurring somatostatin (tetradecapeptide) and its analogues or derivatives.

By derivatives or analogues as used herein is meant any straightchain or cyclic polypeptide derived from that of the naturally occurring tetradecapeptide somatostatin vherein one or more amino acid units have been omitted and/or replaced by one or more other amino acid radical(s) and/or vherein one or more functional groups have been replaced by one or more other functional groups and/or one or more groups have been replaced by one or several other isosteric groups. The term covers all modified derivatives of a biologically active peptide vhich exhibit a qualitatively similar effect to that of the unmodified somatostatin peptide, e.g. they bind to somatostatin receptors and decrease hormone secretion.

Cyclic, bridge cyclic and straight-chain somatostatin analogues are knovn compounds. Such compounds and their preparation are described e.g. in European Patent Specifications EP-A-1295; 29,579; 215,171; 203,031; 214,872; 298,732; 277,419 Preferred LIGANDS OF THE INVENTION are those derived from the folloving somatostatin analogues: A. Analogues of formula I A' CH2-S-Yx Y2-S-CH2 N-CH-CO-B-C-D-E-NH-CH-G I - 4 vherein A is Ci_i2alkyl, C7_i0phenylalkyl or a group of formula RCO-, vhereby i) R is hydrogen, Ci-nalkyl, phenyl or C7.i0phenylakyl, or ii) RCO- is a) an L- or D-phenylalanine residue optionally ring-substituted by F, Cl, Br, NO2, NH2, OH, Ci.jalkyl and/or Ci_jalkoxy; b) the residue of a natural or synthetic α-amino acid other than defined under a) above or of a corresponding D-amino acid, or c) a dipeptide residue in vhich the individual amino acid residues are the same or different and are selected from those defined under a) and/or b) above, the α-aaino group of amino acid residues a) and b) and the N-terminal amino group of dipeptide residues c) being optionally mono- or di-Ci.i2alkylated or substituted by Ci.aalkanoyl, A' is hydrogen, Ci_i2alkyl or C7_i0phenylalkyl, Yi and Y2 represent together a direct bond or each of Yi and Y2 is independently hydrogen or a radical of formulae (1) to (5) - 5 R.

I -CO-C-(CH,)„-3 I Rb -CO-CH CHj ‘(CH,), -CO-NHRc (1) (2) (3) -CO-NH-CH-COOR.

I Ra -CO-(NH)PR.') I C I Rb'J Re R, (4) (5) wherein Ra Rb n R« Ra R.

R,' and Rb' Re and R9 is methyl or ethyl is hydrogen, methyl or ethyl is a whole number from 1 to 4 is a whole number from 1 to 5 is (Ci_6)alkyl represents the substituent attached to the α-carbon atom of a natural or synthetic a-amino acid (including hydrogen) is (Ci_s)alkyl are independently hydrogen, methyl or ethyl, are independently hydrogen, halogen, (Cj._3)alkyl or (Cx_j)alkoxy, is 0 or 1, is 0 or 1, and is 0, 1 or 2, B is -Phe- optionally ring-substituted by halogen, NO,, NH,, OH, C,_3alkyl and /or Ci_3alkoxy (including pentafluoroalanine), or β-naphthyl-Ala is (L)-Trp- or (D)-Trp- optionally a-N-raethylated and optionally benzene-ring-substituted by halogen, NO2, NH2, OH, Cx_3alkyl and/or Cx_3 alkoxy, is Lys, Lys in vhich the side chain contains 0 or S in ^-position, yF-Lys or 6F-Lys, optionally α-Ν-methylated, or a 4-arainocydohexylAla or 4-aminocyclohexylGly residue is Thr, Ser, Val, Phe, He or an aminoisobutyric or aminobutyric acid residue is a group of formula wherein R7 Rxo Rn Rn Rl3 wherein R7 Rio Rn Rn Rl3 is hydr~<*en or Cx_ j alkyl, is hyd~- en or the residue of a physiologically acceptable, physiologically hydrolysable ester, is hydrogen, Ct-3alkyl, phenyl or C7-ioPhenylalkyl, is hydrogen, Cx-jalkyl or a group of formula -CH(Rxj)-Xx, is CH2OH, -(CHj)j-OH, -(CH2)3-OH, or -CH(CHj)OH or represents the substituent attached to the α-carbon atom of a natural or synthetic a-amino acid (including hydrogen) and is a group of formula -COOR7, -CH2ORlo or /R14 -CO-N vherein R7 and Rio have the meanings given above, is hydrogen or Οχ_3alkyl and is hydrogen, Ci_jalkyl, phenyl or C7.10phenylalkyl, and is hydrogen or hydroxy, with the proviso that vhen Ri2 is -CH(Ru)-Xi then Ru is hydrogen or methyl, vherein the residues B, D and E have the L-configuration, and the residues in the 2-and 7-position and any residues Yi 4) and Y2 4) each independently have the (L)- or (D)- configuration.

The significances of A and A' in formula I are preferably selected so that the compound contains a terminal -NH- group capable of being linked to a chelating agent.

In the compounds of formula I, the folloving significances are preferred either individually or in any combination or sub-combination: 1. A is C7_io phenylalkyl, especially phenethyl, or a group of formula RCO. Preferably A is a group of formula RCO. 1.1. Preferably R is Ci.n alkyl or C7_i0 phenylalkyl, especially C7_io phenylalkyl, more especially phenethyl, or RCO has the meanings a), b) or c). 1.2. Vhen RCO has the meanings a), b) or c), the α-amino group of amino acid residues a) and b) and the N-terminal amino group of dipeptide residues c) is preferably non-alkylated or mono-Ci_i2 alkylated, especially -Ci_8 alkylated, more especially -methylated. Most preferably the N-terminal is non-alkylated. 1.3. Vhen RCO has the meaning a) this is preferably a') an Lor D-phenylalanine or -tyrosine residue optionally mono-NCi_i2 alkylated. More preferably a') is an L- or D-phenylalanine residue. 1.4. Vhen RCO has the meaning b) or c) the defined residue is preferably lipophilic. Preferred residues b) are thus b') α-amino acid residues having a hydrocarbon side chain, e.g. alkyl with 3, preferably 4, or more C atoms, e.g. up to 7 C-atoms, naphthyl-methyl or heteroaryl, e.g. 3-(2- or 1-naphthyl)-alanine, pyridyl-methyl or tryptophane residue, said residues having the L- or D-configuration, and preferred residues c) are dipeptide residues in vhich the individual amino acid residues are the same or different and are selected from those defined under a') and b') above. 1.5. Most preferably RCO has the meaning a) especially the meaning a')* 2. B is Β', where B' is Phe or Tyr. 3. C is C', where C' is (D)Trp. 4. D is D', vhere D' is Lys or MeLys, especially Lys.

. E is Ε', vhere E' is Val or Thr, especially Thr.

/Rn 6. G is G', vhere G' is a group of formula -CO-N , especially a group of formula -CO-N \h(Rx3)-Xx (in vhich case RXX=H or CH3). In the latter case the moiety -CH(Rx3)-Xx preferably has the L-configuration. 6.1. Rxx is preferably hydrogen. 6.2. As the substituent attached to the α-carbon atom of a natural amino acid (i.e. of formula H2N-CH(RX3)-COOH), RX3 is preferably -CH20H, -CH(CH3)-OH, isobutyl or butyl, or Rx3 is -(CH2)2-0H or -(CH2)3-0H. It is especially -CH20H or -CH(CH3)OH. 6.3. Xx is preferably a group of formula -CO-N Ri 4 Rl5 or -CH2-ORxo, especially of formula -CH2-ORX0 and Rxo is preferably hydrogen or has the meaning given under 7 belov. Most preferably Rxo is hydrogen.

The folloving individual compounds are illustrative of compounds of formula I: -ΙΟι-1 H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol also knovn as octreotide (D)Phe-Cys-Thr-(D)Trp-Lys-Val-Cys-ThrNH2 i-1 (D)Phe-Cys-Tyr-(D)Trp-Lys-Val-Cys-TrpNH2 I i (D)Trp-Cys-Phe-(D)Trp-Lys-Thr-Cys-ThrNH2 (D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-ThrNH2 i-1 3-(2-Naphthyl)-(D)Ala-Cys-Tyr-(D)Trp-Lys-Val-Cys-ThrNH2 3-(2-Naphthyl)-(D)Ala-Cys-Tyr-(D)Trp-Lys-Val-Cys-3-Nal-NH2 3-(2-Naphthyl)-(D)Ala-Cys-0-Nal-(D)Trp-Lys-Val-Cys-ThrNH2 I-1 (D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-B-Nal-NH2 B. Analogues of formula II I-1 H-Cys-Phe-Phe-(D)-Trp-Lys-Thr-Phe-Cys-ol II [see Vale et al., Metabolism, 27, Supp. 1, 139, (1978)] i-1 H-Cys-His-His-Phe-Phe-(D)Trp-Lys-Thr-Phe-Thr-Ser-Cys-OH III (see EP-A-200,188) The contents of all the above publications including the specific compounds are specifically incorportated herein by reference.

Particular preferred LIGANDS are those derived from H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol.

Suitable chelating groups are physiologically acceptable chelating groups capable of complexing a detectable element.

Preferably the chelating group has substantially a hydrophilic character. Examples of chelating groups include e.g. iminodicarboxylic groups, polyaminopolycarboxylic groups, e.g. those derived from non cyclic ligands e.g. ethylene diaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), ethylene glycol-0,0'-bis(2-aminoethyl)-N,N,N',Ν'-tetraacetic acid (EGTA), N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) and triethylenetetramine hexaacetic acid (TTHA), those derived from substituted EDTA or -DTPA, e.g. p-isothiocyanatobenzyl-EDTA or -DTPA those derived from macrocydic ligands, e.g. l,4,7,10-tetra-azacydododecane-N,N' ,N'' ,N' * '-tetraacetic acid (DOTA) and 1,4,8,11-tetraazacyclotetradecane-N,N',N ,N'-tetraacetic acid (TETA), those derived from N-substituted or C-substituted macrocydic amines including also cyclames, e.g. as disclosed in EP 304,780 Al and in VO 89/01476-A, groups of formula IV or V Ri-C-S-iCHjjn.-C-iTTji-CIV tf Rj-C-S-(CH2)a.-C-NH-CH2 0 CH-CR3-C-S-(CH2)n.-C-NH vherein each of Rx, R2 and R3 independently is C3_6alkyl, C^aryl or C7_9arylalkyl, each optionally substituted by OH, Cx_4alkoxy, COOH or SO3H, n' is 1 or 2, i is an integer from 2 to 6, and TT are independently a or 0 amino acids linked to each other by amide bonds, groups derived from bis-aminothiol derivatives, e.g. compounds of formula VI NH VI vherein each of R20, R22, R22 and R23 independently is hydrogen or Cx_4alkyl, X2 is a group capable of reacting vith the N-amino group of the peptide, and m' is 2 or 3, groups derived from dithiasemicarbazone derivatives, e.g. compounds of formula VII - 13 VII wherein X2 is as defined above, groups derived from propylene amine oxime derivatives, e.g. compounds of formula VIII wherein each of R24, Rjs, Rae, R2 7» Rj s and R29 independently are hydrogen or Ci_4alkyl, and X2 and m* are as defined above, groups derived from diamide dimercaptides, e.g. compounds of formula IX 0.

IX vherein X3 is a divalent radical optionally substituted and bearing a group capable of reacting vith the N-amino group of the peptide, e.g. Οχ.«alkylene or phenylene bearing a group X2, and Y5 is hydrogen or C02R30, vherein R30 is C2.«alkyl, or groups derived from porphyrins, e.g. N-benzyl-5,10,15,20tetrakis-(4-carboxyphenyl)porphine or TPP bearing a group X2 as defined above.

Aryl is preferably phenyl. Arylalkyl is preferably benzyl.

Examples of X2 include radicals of formula -(X«)n*''*X5 vherein X« is Cx-eslkylene; or Cx_«alkylene optionally attached to the carbon atom by an oxygen atom or -NH-, n'' is 0 or 1 and X9 is -NCS, a carboxy group or a functional derivative thereof, e.g. acid halide, anhydride or hydrazide. It is understood that X2 is attached to one of the carbon atom of -(CH2]a·- or -CH-CB· in replacement of an hydrogen atom.

The chelating group may be attached either directly or indirectly to the N-amino group of the somatostatin peptide. Vhen it is attached indirectly, it is preferably linked through a bridging or spacer group, for example a group of formula (ed) - 15 Z-R35-CO(«ι) R35 is Cx_ijalkylene, C2_u alkenylene or -CH(R')- wherein R' is the residue attached in a to a natural or synthetic a-amino acid, e.g. hydrogen, Ci_ualkyl, benzyl, optionally substituted benzyl, naphthyl-methyl, pyridyl-methyl, Z is a functional moiety capable of covalently reacting vith the chelating agent.

Z may be for example a group vhich can form an ether, ester or amide bonding vith the chelating group. Z is preferably amino.

The chelating groups, vhen comprising carboxy, -S03H and/or amino groups may exist in free form or in salt form.

Preferred chelating groups are those derived from polyamino-polycarboxylic groups, e.g. those derived from EDTA, DTPA, DOTA, TETA or substituted EDTA or DTPA. Chelating groups derived from DTPA are most preferred.

In the LIGANDS OF THE INVENTION the chelating group, vhen polyfunctional, may be linked either to a single somatostatin peptide molecule or to more than one somatostatin peptide molecules e.g. to tvo somatostatin peptide molecules.

The LIGANDS OF THE INVENTION may exist e.g. in free or salt form. Salts include acid addition salts vith e.g. organic acids, polymeric acids or inorganic acids, for example hydrochlorides and acetates, and salt forms obtainable vith the carboxylic or sulphonic acid groups present in the chelating group, e.g. alkali metal salts such as sodium or potassium, or substituted or unsubstituted ammonium salts.

The present invention also includes a process for the production of the LIGANDS OF THE INVENTION. They may be produced by analogy to knovn methods.

The LIGANDS OF THE INVENTION may be produced for example as follovs: a) removing at least one protecting group vhich is present in a somatostatin peptide bearing a chelating group, or b) linking together by an amide bond tvo peptide fragments each of them containing at least one amino acid or amino alcohol in protected or unprotected form and one of them containing the chelating group, vherein the amide bond is in such a vay that the desired amino acid sequence is obtained, and stage a) of the process is then optionally effected, or c) linking together a chelating agent and the desired somatostatin peptide in protected or unprotected form in such a vay that the chelating group is fixed on the desired N-amino group of the peptide, and stage a) is then optionally effected or, d) removing a functional group of an unprotected or a protected peptide bearing a chelating group or converting it into another functional group so that another unprotected or protected peptide bearing a chelating group is obtained and in the latter case stage a) of the process is effected, or e) oxidising a somatostatin peptide modified by a chelating group in vhich the mercapto groups of Cys radicals exist in free form so as to produce an analogue in vhich tvo Cys radicals are joined by an S-S-bridge - 17 and recovering the LIGAND thus obtained in free form or in salt form.

The above reactions may be effected in analogy vith known methods, e.g. as described in the folloving examples, in particular processes a) and c). Vhen the chelating group is attached by an amide bond, this may be carried out analogously to the methods used for amide formation. Where desired, in these reactions, . protecting groups vhich are suitable for use in peptides or for the desired chelating groups may be used for functional groups vhich do not participate in the reaction. The term protecting group may also include a polymer resin having functional groups.

Vhen it is desired to attach the chelating group to the terminal N-amino group of a peptide or peptide fragment used as starting material, and vhich comprises one or more side chain amino groups, these side chain amino groups are conveniently protected vith a protecting group , e.g. as used in peptide chemistry.

Vhen it is desired to attach the chelating group to a side chain amino group of a peptide or peptide fragment used as starting material, and the peptide comprises a free terminal N-amino group, the latter is preferably protected vith a protecting group.

The peptide fragment bearing the chelating group and used in stage b) may be prepared by reacting the peptide fragment comprising at least one amino acid or amino alcohol in protected or unprotected form vith the chelating agent. The reaction may be performed in analogy vith stage c).

The chelating groups of formula IV or V may be linked to a peptide by reacting a chelating agent of formula IV' or V' - 18 r^C-S-CCH, )η. -C-(TT)i-C-X IV' •I R3-C-S-(CH2)n.-C-NH R,-C-S-(CH2)η.-C-NH- CH-C-X V' wherein X is an activating group capable of forming an amide bond vith the N-amino group of the peptide. The reaction may be performed as disclosed in EP 247,866 Al.

The chelating agent used in process step c) may be knovn or prepared in analogy vith knovn procedures. The compound used is such that it allows the introduction of the desired chelating group on the somatostatin peptide, e.g. a polyaminopolycarboxylic acid as disclosed, a salt or anhydride thereof.

In the above process, vhen in the amino-acids, peptide fragments or peptides used as starting materials, the chelating group is attached through a bridging or spacer group to the peptide, e.g. a radical of formula (αχ) as defined above, such amino-acids, peptide fragments or peptides may be prepared by reacting in conventional manner the corresponding amino-acids or peptides free of bridging or spacer group vith a corresponding bridgingor spacer-yielding compound, for example an acid or reactive acid derivative comprising the bridging or spacer group, e.g. an acid of formula Z-R35-COOH or a reactive acid derivative thereof such as an active ester. Examples of active ester groups or carboxy activating groups are e.g. 4-nitrophenyl, pentachlorophenyl, pentafluorophenyl, succinimidyl or 1-hydroxy-benzotriazolyl. - 19 Alternatively the chelating agent may first be reacted vith a bridging or spacer group-yielding compound, in order to bear the bridging or spacer group and then be reacted in conventional manner vith the peptide, peptide fragment or amino-acid.

The LIGANDS OF THE INVENTION may be purified in conventional manner, e.g. by chromatography. Preferably the LIGANDS OF THE INVENTION contain less than 5X by veight of peptides free of chelating groups.

The LIGANDS OF THE INVENTION in free form or in the form of pharmaceutically acceptable salts are valuable compounds.

According to a further embodiment, the LIGANDS OF THE INVENTION can be complexed vith a detectable element.

Accordingly, the present invention also provides the LIGANDS OF THE INVENTION as defined above vhich are complexed vith a detectable element (hereinafter referred to as CHELATES OF THE INVENTION), in free form or in salt form, their preparation and their use for in vivo diagnostic and therapeutic treatment.

By detectable element is meant any element, preferably a metal ion vhich exhibits a property detectable in therapeutic or in vivo diagnostic techniques, e.g. a metal ion vhich emits a detectable radiation or a metal ion vhich is capable of influencing NMR relaxation properties.

Suitable detectable metal ions include for example heavy elements or rare earth ions, e.g. as used in CAT scanning (Computer axial tomography), paramagnetic ions, e.g. Gd3*, Fe3*, Mn2* and Cr2*, fluorescent metal ions, e.g. Eu3*, and radionuclides, e.g. γ-emitting radionuclides, β-emitting radionuclides, a-emitting radionuclides, positron-emitting radionuclides e.g. e8Ga. - 20 Suitable γ-emitting radionuclides include those which are useful in diagnostic techniques. The γ-emitting radionuclides advantageously have a half-life of from 1 hour to 40 days, preferably from 5 hours to 4 days, more preferably from 12 hours ;o 3 days. Examples are radionuclides derived from Gallium, Indium, Technetium, Ytterbium, Rhenium and Thallium e.g. e7Ga, Χ111η, i,9aTc, 169Yb and 186Re. Preferably the γ-radionuclide is selected depending on the metabolism of the LIGAND OF THE INVENTION or somatostatin peptide used. More preferably the LIGAND OF THE INVENTION is chelated vith a γ-radionuclide having a longer half-life than the half-life of the somatostatin peptide on the tumor.

Further radionuclides suitable for use in imaging are positronemitting radionuclides, e.g. as mentioned above.

Suitable β-emitting radionuclides include those vhich are useful in therapeutic applications, for example 90Y, e7-Cu, 186Re, ieeRe, l«9Er, 121Sn, lJ7Te, l«3Pr, 19«Au, 109pd, 16 5^, 3JP> 142Pr. The β-radionuclide advantageously have a half-life of from 2.3 hrs to 14.3 d, preferably from 2.3 to 100 hrs. Preferably the β-emitting radionuclide is selected in order to have a longer half-life than the half-life of the somatostatin peptide on the tumor.

Suitable α-emitting radionuclides are those vhich are used in therapeutic treatments, e.g. 211At, 2l2Bi.

The CHELATES OF THE INVENTION may be prepared by reacting the LIGAND vith a corresponding detectable element yielding compound, e.g. a metal salt, preferably a water-soluble salt. The reaction may be carried out by analogy vith knovn methods, e.g. as disdo- 21 sed in Perrin, Organic Ligand, Chemical Data Series 22. NY Pergamon Press (1982); in Krejcarit and Tucker, Biophys. Biochem. Res. Com. 77: 581 (1977) and in Vagner and Welch, J. Nucl. Med. 20: 428 (1979).

Preferably the complexing of the LIGAND is effected at a pH at vhich the LIGAND OF THE INVENTION is physiologically stable.

Alternatively the detectable element may also be provided to the solution as a complex vith an Intermediate chelating agent, e.g. a chelating agent vhich forms a chelate complex that renders the element soluble at the physiological pH of the LIGAND but is less thermodynamically stable than the CHELATE. Example of such an intermediate chelating agent is 4,5-dihydroxy-l,3-benzene-disulfonic acid (Tiron). In such a process, the detectable element exchanges the ligand.

The CHELATES OF THE INVENTION may also be produced by linking together a chelating agent complexed vith the detectable element, and a somatostatin peptide in protected or unprotected form and if desired removing at least one protecting group vhich is present. The same reaction may be performed vith a chelating agent complexed vith a non detectable metal ion and then in the resulting complexed peptide the metal ion may be replaced by the desired detectable element.

The CHELATES OF THE INVENTION may also be produced by linking together a chelating agent complexed vith the detectable element, and a somatostatin peptide fragment comprising at least one amino acid in protected or unprotected form and then continuing the peptide synthesis step by step until the final peptide sequence is obtained and if desired removing at least one protecting group vhich is present. Instead of the detectable element the chelating agent may be complexed vith a non detectable metal and this metal - 22 may then be replaced by the detectable element in the resulting complexed somatostatin peptide.

Vhere the chelating group is attached through a bridging or spacer group to the somatostatin peptide, e.g. through a radical of formula (αχ) as defined above, either the somatostatin peptide or peptide fragment or the chelating agent may bear said bridging or spacer group.

The above mentioned reactions may be effected in analogy tc* known methods. Depending on the chelating group present, the labeling efficiency may approach 1OOX so that purification is not required. Radionuclides such as for example Technetium-99m may be used in oxidized form, e.g. Tc-99m pertechnetate, vhich may be complexed under reducing conditions.

The above mentioned reactions are conveniently effected under conditions avoiding trace metal contamination. Preferably distilled de-ionized vater, ultrapure reagents, chelation-grade radioactivity etc..are used to reduce the effects of trace metal.

The CHELATES OF THE INVENTION may exist e.g. in free or salt form. Salts include acid addition salts vith e.g. organic acids, polymeric acids or inorganic acids,-for example hydrochlorides and acetates, and salt forms obtainable vith the carboxylic acid groups present in the molecule vhich do not participate to the chelate formation, e.g. alkali metal salts such as sodium or potassium, or substituted or unsubstituted ammonium salts.

The CHELATES OF THE INVENTION and their pharmaceutical acceptable salts exhibit pharmaceutical activity and are therefore useful either as an imaging agent, e.g. visualisation of somatostatin receptor positive tumors and metastases vhen complexed vith a paramagnetic, a γ-emitting metal ion or a positron-emitting - 23 radionuclide, or as a radiopharmaceutical for the treatment in vivo of somatostatin receptor positive tumors and metastases vhen complexed vith a a- or β-radionuclide, as indicated by standard tests.

In particular, the CHELATES OF THE INVENTION possess affinity for somatostatin receptors expressed or overexpressed by tumors and metastases, as indicated in standard in vitro binding assays.

A somatostatin receptor positive tumor originating from the human gastro intestinal tract is removed from a patient and immediately put on ice and vithin a maximal delay of 30 min frozen at - 80 0 C. For further autoradiography this frozen material is cut on a cryostat (Leitz 1720) in 10 ym sections, mounted on precleaned microscope slides and stored at - 20 0 C for at least 3 days to improve adhesion of the tissue to the slide. The sections are preincubated in Tris-HCl buffer (50 mM, pH 7.4), containing CaCl2 (2mH) and KCl (5mM), for 10 min at ambient temperature and then vashed tvice for 2 min in the same buffer vithout additional salts added. The sections are then incubated vith a CHELATE OF THE INVENTION for 2 hours at ambient temperature in Tris-HCl buffer (170 mM, pH 7.4), containing bovine serum albumin (10 g/1), bacitracin (40 mg/1) and MgCl2 (5 mM) to inhibit endogenous proteases. Non-specific binding is determined by adding the corresponding non-labelled, non-modified somatostatin peptide at a concentration of 1 yM. Incubated sections are vashed tvice for 5 min in cold incubation buffer containing 0.25 g/1 BSA. After a brief dip in distilled vater to remove excess salts, the sections are dried quickly and apposed to [3H]LKB films. After a time exposure of about 1 veek in X-ray cassettes, it is observed that the CHELATES OF THE INVENTION, e.g. a radionuclide CHELATE, give very good results in labeling the tumoral tissue vithout labeling the surrounding healthy tissue vhen added at a concentration of about 10-10 to 10 3 M. - 24 The affinity of the CHELATES OF THE INVENTION for somatostatin receptors can also be shown by in vivo testing.

Rats bearing transplantable exocrine pancreatic somatostatin receptor positive tumors are treated with an intravenous injection of a CHELATE OF THE INVENTION. Injection site is the penis vein. Immediately after administration, the animals are positioned on the collimator of a gamma-camera and the distribution of radioactivity is monitored at various time intervals.

Biodistribution of radioactivity may also be determined through serial sacrifice of a number of such treated rats and determination of the organ radioactivity.

After administration of a CHELATE OF THE INVENTION, e.g. a radionuclide CHELATE, for example a γ-emitting CHELATE, at a dosage of from 1 to 5 ug/kg of LIGAND labeled vith 0.1 to 2 mCi radionuclide the tumor site becomes detectable together vith the orgeins vhere excretion essentially takes place.

CHELATES OF THE INVENTION for use in in vivo detection are the CHELATES vhich are complexed vith a γ-emitting radionuclide, a positron-emitting radionuclide or a paramagnetic metal ion, e.g. as indicated above.

The CHELATES OF THE INVENTION for use as an imaging agent in method (1) may be administered parenterally, preferably intravenously, e.g. in the form of injectable solutions or suspensions, preferably in a single injection. The appropriate dosage vill of course vary depending upon, for example, the LIGAND and the type of detectable element used, e.g. the radionuclide. A suitable dose to be injected is in the range to enable imsiging by photoscanning procedures knovn in the art. Vhen a radiolabeled CHELATE OF THE INVENTION is used, it may advantageously be - 25 administered in a dose having a radioactivity of from 0.1 to 50 mCi, preferably 0.1 to 30 mCi, more preferably 0.1 to 20 mCi. An indicated dosage range may be of from 1 to 200 ug LIGAND labeled vith 0.1 to 50 mCi, preferably 0.1 to 30 mCi, e.g. 3 to 15 mCi, γ-emitting radionuclide, depending on the γ-emitting radionuclide used. For example vith In, it is preferred to use a radioactivity in the lover range, vhereas vith Tc, it is preferred to use a radioactivity in the upper range.

The enrichment in the tumorigenic sites vith the CHELATES may be folloved by the corresponding imaging techniques, e.g. using nuclear medicine imaging instrumentation, for example a scanner, γ-camera , rotating γ-camera, each preferably computer assisted; PET-scanner (Positron emission tomography); MRI equipment or CAT IK scanning equipment.

The CHELATES OF THE INVENTION, e.g. a major part of the γ-emitting CHELATES is substantially excreted through the kidneys and does not significantly accumulate in the liver.

CHELATES OF THE INVENTION for use in in vivo treatment are the CHELATES complexed vith a a- or β-radionuclide as defined above.

Dosages employed in practising the therapeutic method of the present invention vill of course vary depending e.g. on the particular condition to be treated, for exemple the volume of the tumor, the particular CHELATE employed, for exemple the half-life of the CHELATE in the tumor, and the therapy desired. In general, the dose is calculated on the basis of radioactivity distribution to each organ and on observed target uptake. For example the CHELATE may be administered at a daily dosage range having a radioactivity of from 0.1 to 3mCi/kg body veight, e.g. 1 to 3 mCi, preferably 1 to 1.5 mCi/kg body veight. An indicated daily dosage range is of from 1 to 200 ug LIGAND labeled vith 0.1 to - 26 3 mCi/kg body veight, e.g. 0.1 to 1.5 mCi/kg body veight a- or β-emitting radionuclide, conveniently administered in divided doses up to 4 times a day.

The a- or β-emitting CHELATES OF THE INVENTION may be adminis tered by any conventional route, in particular parenterally., e.g. in the form of injectable solutions or suspensions. They may also be administered advantageously by infusion, e.g. an infusion of 30 to 60 min. Depending on the site of the tumor, they may be administered as close as possible to the tumor site, e.g. by means of a catheter. The mode of administration selected may depend on the dissociation rate of the CHELATE used and the excretion rate.

The CHELATES OF THE INVENTION may be administered in free form or in pharmaceutically acceptable form. Such salts may be prepared in conventional manner and exhibit the same order of activity as the free compounds.

The CHELATES OF THE INVENIION for use in in vivo imaging or therapy may preferably be prepared shortly before the administration to a subject, i.e. the radiolabeling vith the desired detectable metal ion, particularly the desired α-, β- or γ-radionuclide, may be performed shortly before ihe administration.

The CHELATES OF THE INVENTION may be suitable for imaging or treating tumors such as pituitary, gastroenteropancreatic, central nervous system, breast, prostatic, ovarian or colonic tumors, small cell lung cancer, paragangliomas, neuroblastomas, pheochromocytomas, medullary thyroid carcinomas, myelomas, etc. and metastases thereof. - 27 According to a further embodiment of the invention, the γ-emitting CHELATES OF THE INVENTION may also be used as imaging agent for the evaluation of the kidney function.

Groups of five mice are used. Each mouse is injected intravenously through a tail vein vith 0.1 ml containing 1 mCi of a CHELATE OF THE INVENTION. The mice are then placed in metabolic cages for the collection of excreted urine. At 10 or 120 min. post-injection, the urethras are ligated and the mice anesthetized vith chloroform. Imaging of the uropoietic system is carried out using the usual imaging technique. In this test, the γ-emitting CHELATES OF THE INVENTION improves imaging of renal excretion vhen administered at a dosage of from 0.1 to 30 mCi. - 28 According to a further aspect of the invention, there is provided : i. a pharmaceutical composition comprising a LIGAND OF THE INVENTION in free or in pharmaceutically acceptable salt form, together vith one or more pharmaceutically acceptable carriers or diluents therefor; ii. a pharmaceutical composition comprising a CHELATE according to the invention in free or in pharmaceutically acceptable salt form, together vith one or more pharmaceutically acceptable carriers or diluents therefor.

Such compositions may be manufactured in conventional manner.

A composition according to the invention may also be presented in separate package vith instructions for mixing the LIGAND 5/ith the metal ion and for the administration of the resulting CHELATE. It may also be presented in tvin-pack form, that is, as a single package containing separate unit dosages of the LIGAND and the detectable metal ion vith instructions for mixing them and for administration of the CHELATE. A diluent or carrier may be present in the unit dosage forms.

In the folloving examples, all temperatures are in 0 C and [a]20o values uncorrected. The folloving abbreviations are employed: Boc tert.-butoxycarbonyl TFA trifluoroacetic acid DTPA diethylenetriamine-pentaacetic acid - 29 i-1 EXAMPLE 1: DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol 1.1 g of DPhe-Cys-Phe-DTrp-Lys(e-Boc)-Thr-Cys-Thr-ol in free base (1 mM), are dissolved in 5 1 of dioxan/H20 1/1 (v/v) and reacted vith 5 g NaHC03. The 520 mg of DTPA dianhydride is slovly added vith stirring. The reaction mixture is stirred for a further 30 min and dry-frozen. The residue is dissolved in 250 ml vater and the pH is adjusted to pH 2.5 vith concentrated HCl. The precipitated product is filtered out, vashed and dried over phosphorus pentoxide. After chromatography on a silica-gel column, the folloving products are isolated: 230 mg of DTPA-DPhe| I Cys-Phe-DTrp-Lys(e-Boc)-Thr-Cys-Thr-ol and 500 mg of the | I corresponding dimer DTPA-(DPhe-Cys-Phe-DTrp-Lys(s-Boc)-Thr-CysThr-ol)2. i3 ml of TFA are mixed vith 200 mg of DTPA-DPhe-Cys-Phe-DTrp-1 Lys(s-Boc)-Thr-Cys-Thr-ol. After 5 min at room temperature, the mixture is precipitated vith diisopropylether, filtered out and dried. The residue is desalted over Duolite and lyophilised to yield 150 mg of the title compound: [a)20 » - 26,6 · (c - 1 95 X AcOH).· D The starting material may be produced as follows: a) H-DPhe-Cys-Phe-DTrp-Lys(Boc)-Thr-Cys-Thr-ol 2.25 g of di-tert.butyl-pyrocarbonate, dissolved in 30 ml of DMF, are slovly added in drops at room temperature to a I I solution of 10 g of H-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-olacetate in 100 ml of DMF. After tvo hours at room tempe- 30 rature, the solvent is drawn off under vacuum, and 200 ml of diisopropylether are added to the residue. The deposit vhich is being formed is filtered off, vashed vith diisopropylether and dried. The crude product is purified by chromatography over silica gel (eluant: CH2Cl2/MeOH 9/1) and is then isolated as a vhite amorphous povder. [a]20 = 29.8 e (c - 1.28 in DMF). o I-1 EXAMPLE 2: DTPA-(DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol)^ The fraction containing the intermediate product DTPA-DPheI I Cys-Phe-DTrp-Lys(s-Boc)-Thr-Cys-Thr-ol)j as obtained in example 1 is treated as described above for the corresponding monomeric form, the Boc protecting groups being removed to yield the title compound: [a]20 = - 24,5 0 (c = 0,55 95 X AcOH). o Γ-1 EXAMPLE 3: H^N-(CH^)s-CO-DFhe-Cys-Fhe-DTrp-Lys-Thr-Cys-Thr-ol - ι I a. 0.56 g of H-DPhe-Cys-Phe-DTrp-Lys(BOC)-Thr-Cys-Thr-ol, 0.5 mmole of Fmoc-e-aminocaproic acid and 115 mg of hydroxybenzotriazole are dissolved in 10 ml of DMF and cooled to -30° C. To this solution is added a solution of 115 mg of dicyclohexylcarbodiimide in 5 ml of DMF (cooled to -10° C).

After a reaction time of 24 hours, during vhich the mixture varms to the room temperature, the resulting dicyclohexylurea is filtered off and the filtrate is diluted vith vater to ten times its volume. The precipitated reaction product is filtered off, vashed and dried over phosphorus pentoxide. The crude product is used vithout further purification for the - 31 next step. b. Fmoc-cleavage 0.5 g of crude product from coupling reaction (a) are treated for 10 minutes at room temperature vith 5 ml of DMF/piperidine 4/1 v/v (clear solution) and subsequently mixed vith 100 ml of diisopropylether. The reaction product vhich is thus precipitated is filtered off, vashed and dried. This crude product is used vithout further purification in the next step. c. BOC cleavage 300 mg of crude product obtained in (l.b) are treated for 5 minutes at room temperature vith 5 ml of 100 X TFA (completely dissolved) and subsequently mixed vith 50 ml of diisopropylether. After addition of 2 ml of HCI/diethylether, the resulting deposit is filtered off, vashed and dried in a high vacuum.

The end product is purified by chromatography on silica gel (CHCl3/MeOH/H2O/AcOH 7/3/0.5/0.5), vith subsequent de-salting over Duolite (gradient: H20/AcOH 95/5)---H20/dioxane/Ac0H 45/50/5).

The title compound is obtained as an acetate (vhite lyophilisate).

[«I20 -- 32 0 (c - 0.5 95 X AcOH).

D The resulting compound may be used for reaction vith DTPA in accordance vith the procedure of Examples 1 and 2.

EXAMPLE 4: By folloving the procedure disclosed in Examples 1 and 3, the folloving LIGAND can be prepared: - 32 ι ι DTPA-HAla-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol. [a]20 = - 14,8 0 (c = 0.5 95 X AcOH).

D ,-, EXAMPLE 5: Ulin labeled DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-CysThr-ol I-1 mg DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol is dissolved in 5 ml 0.01M acetic acid. The resulting solution is passed through a 0.22u Mille/S-GV filter (Registered Trade Mark) and dispensed in 0.1 ml portions and stored at -20°C. lllInCl3 (Amersham, mCi/100 ul) is prediluted in an equal volume of 0.5M sodium acetate and labeling is carried out by mixing the ligand vith the InCl3 solution and gentle homogenisation at room temperature.

HEPES buffer, pH 7.4, is then added to make a solution 10~6 M.

EXAMPLE 6: —Y labeled DTPA-DPhe-Cys-Phe-PTrp-Lys-Thr-CysThr-ol 90Y is obtained from a * 90Sr-90Y radionuclide generator. The construction of the generator, its elution and the conversion of the [90Y]EDTA to the acetate complex are performed in accordance vith the method disclosed by M.Chinol and D.J. Hnatovich in J. Mud. Med. 28, 1465-1470 (1987). 1 mg of DTPA-DPhe-Cys-Phe-DTrp-LysThr-Cys-Thr-ol dissolved in 5ml 0.01M acetic acid is alloved to vara to room temperature and 1.0 mCi of 90Y in 50 ul sterile 0.5M acetate is added. The mixture is then left undisturbed for 30 min to 1 hr to maximize chelation.

One group of somatostatin peptides of the invention are e.g. somatostatin analogues, vhich contain at least on one of the amino acid units a chelating group vhich is attached to said amino group by an amide bond, the chelating group being other than a sugar residue, in free form or in salt form.

One group of CHELATES OF THE INVENTION are the somatostatin peptides just mentioned above complexed vith a detectable element, e.g. a metal ion, in free form or in salt form.

Claims

1. A somatostatin peptide bearing at least one chelating group capable of complexing an element detectable by therapeutic or in vivo diagnostic techniques, the chelating group being covalently linked to an amino group of said peptide, this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors, and the chelating group being other than a sugar residue, in free form or in salt form.

2. A somatostatin peptide bearing at least one chelating group complexed vith an element detectable by therapeutic or in vivo diagnostic techniques, the chelating group being covalently linked to an amino group of said peptide and this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors, in free form or in salt form.

3. A somatostatin peptide according to claim 1 or 2, vherein the chelating group is attached to the terminal amino group of the somatostatin peptide.

4. A somatostatin peptide according to any one of the preceding claims, vherein the chelating group is attached directly or indirectly to the amino group of said peptide.

5. A somatostatin peptide according to any one of the preceding claims, vherein the chelating group is attached by an amide bond to said peptide. - 35

6. A somatostatin peptide according to any one of the preceding claims, vherein the chelating group is selected from the group consisting of iminodicarboxylic groups, polyaminopolycarboxylic groups, groups derived from macrocyclic amines, groups of formula IV or V 0 0 0 ·· n if R 1 _C-S-(CH 2 ) n .-C-(TT) i -C- IV r 2 -C-S-(CHj) n .-C-NH-CHj 0 11 CH-Cr 3 -C-S-(CH 2 ) n .-C-NH' n ti vherein each of R x , R 2 and R 3 independently is Ci_ 6 alkyl, C 6 _ 8 aryl or C

7.$arylalkyl, each optionally substituted by OH, Ci_ 4 alkoxy, COOH or S0 3 H, n' is 1 or 2, i is an integer from 2 to 6, and TT are independently a or 0 amino acids linked to each other by amide bonds, groups derived from bis-aminothiol derivatives, from dithiasemi carbazone derivatives, from propylene amine oxime derivatives, from diamide dimercaptides or from porphyrins, in free form or in salt form. - 36 7. A somatostatin peptide according to claim 6, vherein the chelating group is derived from a compound of formula VI VI vherein each of R 20 , R 21 , R 22 and R 23 independently is hydrogen or C 2 _ 4 alkyl, X 2 is a group capable of reacting vith the N-amino group of the peptide, and m' is 2 or 3, from a compound of formula VII HS NH VII vherein X 2 is as defined above, from a compound of formula VIII NH OH OH VIII - 37 10 wherein each of R 24 , R 2 s> R26» ^27» R28 and R 29 independently are hydrogen or C x _ 4 alkyl, and X 2 and m' are as defined above, or from a compound of formula IX IX wherein X 3 is a divalent radical optionally substituted and bearing a group capable of reacting vith the N-amino group of the peptide, and Y 5 is H or CO 2 R 3o wherein R 30 is C 3 _ 4 alkyl.

8. A somatostatin peptide according to claim 6, vherein the chelating group is derived from ethylene diaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), ethylene glycol-0,0'-bis(2-aminoethyl)-N,N,N',Ν'-tetraacetic acid (EGTA), N,N'-bis(hydroxybenzyl)ethylenediamine-N,N'diacetic acid (HBED), triethylenetetramine hexaacetic acid (TTHA), substituted EDTA or -DTPA 1,4,7,10-tetra-azacyclododecane-Ν,Ν',N'' ,N'''-tetraacetic acid (DOTA) and 1,4,8,11-tetraazacyclotetradecane-N,Ν',N'' ,N' -tetraacetic acid (ΤΕΤΑ),ίη free form or in salt form. - 38

9. A somatostatin peptide according to claim 8, vherein the chelating group is derived from diethylene triamine pentaacetic acid (DTPA), in free form or in salt form.

10. A somatostatin peptide according to any one of the preceding claims, vherein the somatostatin peptide is derived from a compound of formula I \/: CH 2 -S-Y X Y 2 -S-CH 2 I I N-CH-CO-B-C-D-E-NH-CH-G I vherein A is C x _ x2 alkyl, C 7 _ x0 phenylalkyl or a group of formula RCO-, vhereby i) R is hydrogen, Οχ.χχalkyl, phenyl or C 7 . X0 phenylakyl, or ii) RCO- is a) an L- or D-phenylalanine residue optionally ring-substituted by F, Cl, Br, N0 2 , NH 2 , OH, C x _ 3 alkyl and/or C x _ 3 alkojqr; b) the residue of a natural α-amino acid other than defined under a) above, naphthyl-methyl or pyridyl-methyl or a residue of a corresponding D-amino acid, or - 39 c) a dipeptide residue in vhich the individual amino acid residues are the same or different and are selected from those defined under a) and/or b) above, the α-amino group of amino acid residues a) and b) and the N-terminal amino group of dipeptide residues c) being optionally mono- or di-Ci_ 12 alkylated or substituted by Ci_ a alkanoyl, A' is hydrogen, Ci_i 2 alkyl or C7_i 0 phenylalkyl, Yi and Y 2 represent together a direct bond or each of Y x and Y 2 is independently hydrogen or a radical of formulae (1) to (5) R. -CO-C-(CH 2 )„-H R b (CH 2 ) n -CO-NHR c (1) (2) (3) -CO-NH-CH-COOR. -CO-(NH) P Rd R.'' I c I R b 'J -(CH 2 ) r -< Re Rs (4) (5) vherein R. Rb m n is methyl or ethyl is hydrogen, methyl or ethyl is a vhole number from-1 to 4 is a vhole number from 1 to 5 - 40 R c Ra R. R a ' and R b ' R 8 and R 9 P q r is (C 1 _ 6 )ai. 1 represents ’be substituent attached to the α-carbon atom of a natural α-amino acid (including hydrogen) is (Ci-s)alkyl are independently hydrogen, methyl or ethyl, are independently hydrogen, halogen, (Cx_ 3 )alkyl or (C 2 _ 3 )alkoxy, is 0 or 1, is 0 or 1, and is 0, 1 or 2, B is optionally by halogen, N0 2 , NH 2 , OH, Ci_ 3 alkyl and/or Ci_ 3 alkoxy ring-substituted Phe (including pentafluorophenylalanine), or fJ-naphthyl-Ala C is (L)-Trp- or (D)-Trp- optionally a-N-methylated and optionally benzene-ring-substituted by halogen, N0 2 , NH 2 , OH, C 2 . 3 alkyl and/or Ci_ 3 alkoxy, D is Lys, /.,ys in vhich the side chain contains 0 or S in β-position, yF-Lys or SF-Lys, optionally α-Ν-methylated, or a 4-aminocyclohexylAla or 4-aminocyclohexylGly residue E is Thr, Ser, Val, Phe, lie or an aminoisobutyric or aminobutyric acid residue is a group of formula —COOR7, —CH 2 ORio, wherein R7 is hydrogen or Ci_ 3 alkyl, Rio is hydrogen or the residue of a physiologically acceptable, physiologically hydrolysable ester, Rn is hydrogen, Ci_ 3 alkyl, phenyl or ¢7-1 0 phenylalkyl, Ri2 is hydrogen, Ci_ 3 alkyl or a group of formula -CH(Ri 3 )-Xi, Ri 3 is CHjOH, -(CH 2 ) 2 -OH, -(CH 2 ) 3 -OH, or -CH(CH 3 )OH or represents the substituent attached to the α-carbon atom of a natural α-amino acid (including hydrogen), butyl or naphthyl-methyl, and Xi is a group of formula -COOR7, -CO-N —CH 2 ORio or l 15 wherein R 7 and Ri 0 Ri 4 Ris Rl 6 have the meanings given above, is hydrogen or C x _ 3 alkyl and is hydrogen, Ci_ 3 alkyl, phenyl or C 7 _iophenylalkyl, and is hydrogen or hydroxy, with the proviso that when Ri 2 is -CH(Ri 3 )-Xi then Rn is hydrogen or methyl, - 42 wherein the residues B, D and E have the L-configuration, and the residues in the 2-and 7-position and any residues Yj 4) and Y 2 4) each independently have the (L)- or (D)- configuration in free form or in salt form.

11. A somatostatin peptide according to claim 10, wherein in formula I A is RCO and A' is hydrogen.

12. A somatostatin peptide according to claim 10 or 11, wherein in formula I G is -CO-NH-CH(Rj3)-Xj wherein R 13 is -CH 2 OH, -CH(CH 3 )-0H, -(CH 2 ) 2 -0H, -(CH 2 ) 3 -0H, isobutyl or butyl, and X x is -CO-NRuRjs or -CH 2 ORjo wherein Rj 0 , 8» and Rj 5 are as defined in claim 10.

13. A somatostatin peptide according to any one of the preceding claims, wherein the somatostatin peptide is derived from ι ι H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol also knovn as octreotide.

14. A somatostatin peptide according to any one of claims 1 to 13, wherein the chelating group is attached to said peptide through a spacer group of formula Z—R 3 5 —CO— ( Rj5 is C x _ijalkylene, C 2 _jjalkenylene or -CH(R')- wherein R' is the residue attached in a to a natural ct-amino acid, and - 43 Z is a functional moiety capable of covalently reacting with the chelating agent.

15. A somatostatin peptide bearing a chelating group, which is DTPA-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol in free form or in salt form, the chelating group DTPA being covalently linked to the terminal amino group of said peptide, this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors.

16. A somatostatin peptide according to any one of claims 2 to 14, vherein the detectable element is a γ-emitting radionuclide.

17. A somatostatin peptide according to claim 16, vherein the detectable element is lll In or “Tc.

18. A somatostatin peptide bearing a chelating group in complexed form, vhich is I-1 X11 ln labelled DTPA-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol, in free form or in pharmaceutically acceptable salt form, the chelating group DTPA being covalently linked to the terminal amino group of said peptide and this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors. - 44

19. A somatostatin peptide according to any one of claims 2 to 14, vherein the detectable element is an a- or β-emitting radionuclide.

20. A somatostatin peptide according to claim 19, vherein the detectable element is 90 Y.

21. A somatostatin peptide bearing a chelating group, vhich is 90 Y labelled DTPA-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol, in free form or in pharmaceutically acceptable salt form, the chelating group DTPA being covalently linked to the terminal amino group of said peptide and this amino group having no significant binding affinity for somatostatin receptors, the thus modified somatostatin peptide having binding affinity for somatostatin receptors.

22. A somatostatin peptide according to any one of claims 2 to 14 and 16 to 21, in free form or in pharmaceutically acceptable salt form for use as a pharmaceutical.

23. A somatostatin peptide according to any one of claims 16 to 18, in free form or in pharmaceutically acceptable salt form for use as an imaging agent of somatostatin receptor positive tumors or metastases.

24. A somatostatin peptide according to any one of claims 19 to 21, in free form or in pharmaceutically acceptable salt form for use in radiotherapy of somatostatin receptor positive tumors or metastases.

25. A somatostatin peptide as claimed in claim 1, substantially as hereinbefore described with reference to the Examples. - 45

26. A somatostatin peptide, as claimed in claim 2, substantially as hereinbefore described with reference to the Examples.

27. A somatostatin peptide, as claimed in claim 15, substantially as hereinbefore described with reference to the Examples.

28. A somatostatin peptide, as claimed in claim 18, substantially as hereinbefore described with reference to the Examples.

29. A somatostatin peptide, as claimed in claim 21, substantially as hereinbefore described with reference to the Examples.