IE893866L - Peptide derivatives - Google Patents

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. [GB2225579A]

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 which are difficult to precisely localize by conventional diagnosis methods.

In vitro visualization of somatostatin receptors has been performed through autoradiography of tumoral tissues using radio-iodinated somatostatin or somatostatin analogues, e.g. [125I-Tyr11] somatostatin-14 (Taylor, J.E. et al., Life Science (1988) 43: 421), or [125I-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). 6 j 91 New somatostatin peptides useful in therapeutic and which can be labelled for iii vivo diagnostic and therapeutic applications have * now been found. m According to the invention, there is provided a somatostatin 5 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 10 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 15 with 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 straight-chain or cyclic polypeptide derived from that of the naturally occurring tetradecapeptide somatostatin wherein one or more amino acid units have been omitted and/or replaced by one or more other amino acid radical(s) and/or wherein 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 which 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 known 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 following somatostatin analogues: A. Analogues of formula I A' CH2-S-Yx Y2-S-CH2 \ i i •N-CH-CO-B-C-D-E-NH-CH-G A'' wherein A is Ci_i2alkyl, C7_i0phenylalkyl or a group of formula RCO-, whereby i) R is hydrogen, Ci_nalkyl, phenyl or C7.l0- phenylakyl, or ii) RCO- is a) an L- or D-phenylalanine residue optionally ring-substituted by F, Cl, Br, N02, NHj, OH, Ci.jalkyl and/or Ci.jalkoxy; b) the residue of a natural or synthetic a-amino acid other than defined! under a) above or of a corresponding D-aimino acid, or c) a dipeptide residue in which the individual amino acid residues are the same or different and are selected from those defined under a) and/or b) above, the a-amino group of amino acid residues a) and b) and the N-terminal amino group of dipeptide residues c) being optionally mono- or di-C1.12alkylated or substituted by Ci_ealkanoyl, A' is hydrogen, Cl_i2alkyl or Ci-iophenylalkyl, Yx and Y2 represent together a direct bond or each of Yi and Y2 is independently hydrogen or a radical of formulae (1) to (5) R.

I -CO-C-(CH2)a-H I Rb -CO-CH • CHj > I R«t -CO-(NH)p- f R«'l I c I I Rb'J -(CHj )t- ff Rs =7^9 (4) (5) vherein R* is methyl or ethyl Rb is hydrogen, methyl or ethyl m is a whole number from 1 to 4 n is a whole number from 1 to 5 Rc is (Ci_s)alkyl R 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 Cx_xx alkyl or C7-xo phenylalkyl, especially C7-10 phenylalkyl, more especially phenethyl, or RCO has the meanings a), b) or c). 2. When RCO has the meanings a), b) or c), the a-amino group o:t 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_9 alkylated, more especially -methylated. Most preferably the N-terminal is non-al-kylated. 1.3. When RCO has the meaning a) this is preferably a') an L-or D-phenylalanine or -tyrosine residue optionally mono-N-Ci_i2 alkylated. More preferably a') is an L- or D-phenylalanine residue. 1.4. When RCO has the meaning b) or c) the defined residue is preferably lipophilic. Preferred residues b) are thus b') a-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-naph-thyl)-alanine, pyridyl-methyl or tryptophane residue, said residues having the L- or D-configuration, and preferred residues c) are dipeptide residues in which 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 B', where B' is Phe or Tyr. 3. C is C', where C' is (D)Trp. 4. D is D', where D' is Lys or MeLys, especially Lys.

. E is E', where E' is Val or Thr, especially Thr.

/Ri i 6. G is G', where G' is a group of formula -CO-N , XRl2 especially a group of formula -CO-N \h(Rx3)-XX (in which case Rn=H or CH3). In the latter case the moiety -CH(R13)-Xx preferably has the L-configuration. 6.1. Ru is preferably hydrogen. 6.2. As the substituent attached to the a-carbon atom of a natural amino acid (i.e. of formula H2N-CH(R13)-COOH), Ri3 is preferably -CH20H, -CH(CH3)-OH, isobutyl or butyl, or Ri3 is -(CH2)2-0H or -(CH2)3-0H. It is especially -CH20H or -CH(CH3)0H. 6.3. Xx is preferably a group of formula -CO-N or -CH2-ORxo» especially of formula -CH2-ORxo and R10 is preferably hydrogen or has the meaning given under 7 belov. Most preferably R10 is hydrogen.

The following individual compounds are illustrative of compounds of formula I: i 1 H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol also known as octreotide (D)Phe-Cys-Thr-(D)Trp-Lys-Val-Cys-ThrNH2 i 1 (D)Phe-Cys-Tyr-(D)Trp-Lys-Val-Cys-TrpNHj I I (D)Trp-Cys-Phe-(D)Trp-Lys-Thr-Cys-ThrNHj (D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-ThrNHj 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-0-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-0-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. iminodi-carboxylic 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',N'-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-isothiocyanato-benzyl-EDTA or -DTPA those derived from macrocyclic ligands, e.g. l,4,7,10-tetra-azacyclododecane-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-substi-tuted macrocyclic 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 0 0 0 It 11 tt R1_C-S-(CH2)n.-C-(TT)i-C- IV 0 0 tl ft R2-C-S-(CH2)a.-C-NH-CH2 0 Rj-C-S-(CH2)n.-C-NH V tt 0 0 12 wherein each of Rx, R2 and R3 independently is C1_6alkyl, C*_aaryl or C7_9arylalkyl, each optionally substituted by OH, Cx_4alkoxy, COOH or S03H, 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 wherein each of R20, R21, R22 and R2J independently is hydrogen or C1_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 X VI R /Sh ?Z N wherein X2 is as defined above, groups derived from propylene amine oxime derivatives, e.g. compounds of formula VIII wherein each of R24, Rjs, Rje, R27, R2s and R29 independently are hydrogen or C1.4alk.yl, and X2 and m' are as defined above, groups derived from diamide dimercaptides, e.g. compounds of formula IX OH OH HN NH q r Y S IX HgCgCO vherein Xj is a divalent radical optionally substituted and bearing a group capable of reacting vith the N-amino group of the peptide, e.g. Ci_4alkylene or phenylene bearing a group X2, and Ys is hydrogen or C02R30, vherein R30 is Ci_4alkyl, or groups derived from porphyrins, e.g. N-benzyl-5,10,15,20-tetrakis-(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 -(X4)b..-Xj vherein X4 is Ci_«alkylene; or Ct_«alkylene optionally attached to the carbon atom by an oxygen atom or -NH-, n" is 0 or 1 and X5 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]»>- 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 (al) Z—R3 5 —CO— ( ocj ) R35 is Cx-nalkylene, C2_nalkenylene 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-poly-carboxylic 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 poly-functional, 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 sul-phonic acid groups present in the chelating group, e.g. alkali metal salts such as sodium or potassium, or substituted or un-substituted 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 known methods.

The LIGANDS OF THE INVENTION may be produced for examplo as follows: a) removing at least one protecting group which is present in a somatostatin peptide bearing a chelating group, or b) linking together by an amide bond two 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 way 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 way 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 and recovering the LIGAND thus obtained in free form or in salt form.

The above reactions may be effected in analogy vith knovn methods, e.g. as described in the folloving examples, in particular processes a) and c). When 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.

When 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' 0 It 0 tl R!-C-S-(CH2)n.-C-(TT)i-C-X IV' 0 0 It It r2-C-S-(CH2)n.-C-NH-QH2 o n R3-C-S-(CH2)n--C-NH n n CH-C-X 0 0 vherein 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 (ai) 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 bridging-or 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 30 as ^ active ester. Examples of active ester groups or carboxy activating groups are e.g. 4-nitrophenyl, pentachlorophenyl, pentafluorophenyl, succinimidyl or 1-hydroxy-benzotriazolyl.

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 5% by veight of peptides free of chelating groups.

The LIGANDS OF THE INVENTION in free form or in the form of pharmaceutical^ 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. y-emitting radionuclides, 3-emitting radionuclides, a-emitting radionuclides, positron-emitting radionuclides e.g. 68Ga.

Suitable y-emitting radionuclides include those vhich are useful in diagnostic techniques. The y-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 10 3 days. Examples are radionuclides derived from Gallium, Indium, Technetium, Ytterbium, Rhenium and Thallium e.g. S7Ga, llxIn, <)9aTc, 169Yb and 186Re. Preferably the y-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 y-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 positron-emitting radionuclides, e.g. as mentioned above.

Suitable 0-emitting radionuclides include those vhich are useful in therapeutic applications, for example 90Y, <7-Cu, 18*Re, iasRe, i«»Er, l21Sn, 127Te, 143Pr, l98Au, 109Pd, ls5Dy, 32P, i4 2pr. The ^-radionuclide advantageously have a half-life of from 2.3 hrs to 14.3 d, preferably from 2.3 to 100 hrs. Preferably the Remitting radionuclide is selected in order to have a longer half-life than the half-life of the somatostatin peptide on the tumor.

Suitable a-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 vater-soluble salt. The reaction may be carried out by analogy vith knovn methods, e.g. as disclo sed in Perrin, Organic Ligand, Chemical Data Series 22. NY Perga-mon Press (1982); in Krejcarit and Tucker, Biophys. Biochem. Res. Com. 77: 581 (1977) and in Wagner and Welch, J. Nucl. Med. 20: 428 (1979).

Preferably the complexing of the LIGAND is effected at a pH at vhich the LIGAND OF TBE 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-di-sulfonic 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 may then be replaced by the detectable element in the resulting complexed somatostatin peptide.

Vhere the chelating group is attached through a bridging or 5 spacer group to the somatostatin peptide, e.g. through a radical of formula (ai) 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 to knovn methods. Depending on the chelating group present, the labeling efficiency may approach 1002 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 com-15 plexed 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 20 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 25 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 y-emitting metal ion or a positron-emitting radionuclide, or as a radiopharmaceutical for the treatment in vivo of somatostatin receptor positive tumors and metastases vhen complexed vith a a- or ^-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 pm sections, mounted on pre-15 cleaned 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 (2mM) and KC1 (5mM), for 10 min at ambient temperature and then vashed tvice for 2 min in the same buffer 20 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 determi-25 ned by adding the corresponding non-labelled, non-modified soma tostatin peptide at a concentration of 1 pM. 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 [3HJ-2q LKB films. After a time exposure of about 1 veek in X-ray casset tes, 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 shovn by in vivo testing.

Rats bearing transplantable exocrine pancreatic somatostatin receptor positive tumors are treated with an intravenous infection 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 r-emitting CHELATE, at a dosage of from 1 to 5 yg/kg of LIGAND labeled vith 0.1 to 2 mCi radionuclide the tumor site becomes detectable together vith the orgsins vhere excretion essentially takes place.

CHELATES OF THE INVENTION for use in in vivo detection are the CHELATES vhich are complexed vith a r-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 imaging by photoscanning procedures knovn in the art. Vhen a radiolabeled CHELATE OF THE INVENTION is used, it may advantageously be 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 yg LIGAND labeled with 0.1 to 50 mCi, preferably 0.1 to 30 mCi, e.g. 3 to 15 mCi, y-emitting radionuclide, depending on the y-emitting radionuclide used. For example with In, it is preferred to use a radioactivity in the lower range, whereas with Tc, it is preferred to use a radioactivity in the upper range.

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

The CHELATES OF THE INVENTION, e.g. a major part of the y-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 with a a- or 3-radionuclide as defined above.

Dosages employed in practising the therapeutic method of the present invention will 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 weight, e.g. 1 to 3 mCi, preferably 1 to 1.5 mCi/kg body weight. An indicated daily dosage range is of from 1 to 200 yg LIGAND labeled vith 0.1 to 3 mCi/kg body weight, e.g. 0.1 to 1.5 mCi/kg body weight a- or g-emitting radionuclide, conveniently administered in divided doses up to A times a day.

The a- or 3-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 pharmaceutical^ 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 INVENTION 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 a-, 3- or y-ra-dionuclide, may be performed shortly before the 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.

According to a further embodiment of the invention, the y-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 with 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 with chloroform. Imaging of the uropoietic system is carried out using the usual imaging technique. In this test, the y-emitting CHELATES OF THE INVENTION improves imaging of renal excretion when administered at a dosage of from 0.1 to 30 mCi.

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 pharmaceutical^ acceptable salt form, together vith one or more pharmaceutical^ acceptable carriers or diluents therefor; ii. a pharmaceutical composition comprising a CHELATE according to the invention in free or in pharmaceutical^ acceptable salt form, together vith one or more pharmaceutical^' 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 vith 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]20- D values uncorrected. The folloving abbreviations are employed: Boc tert.-butoxycarbonyl TFA trifluoroacetic acid DTPA diethylenetriamine-pentaacetic acid I 1 EXAMPLE 1; DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol l i 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 NaEC03. 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 vate'r 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 i Cys-Phe-DTrp-Lys(e-Boc)-Thr-Cys-Thr-ol and 500 mg of the I I corresponding dimer DTPA-(DPhe-Cys-Phe-DTrp-Lys(e-Boc)-Thr-Cys- Thr-ol)2. i 3 ml of TFA are mixed vith 200 mg of DTPA-DPhe-Cys-Phe-DTrp- 1 Lys(e-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 0 (c - 1 95 X AcOH). d The starting material may be produced as follovs: i j 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-ol-acetate in 100 ml of DMF. After tvo hours at room tempe rature, the solvent is drawn off under vacuum, and 200 ml of diisopropylether are added to the residue. The deposit which is being formed is filtered off, washed with diisopropylether and dried. The crude product is purified by chromatography over silica gel (eluant: CH2Cl2/Me0H 9/1) and is then isolated as a white amorphous powder. [a]20 . 29.8 0 (c - 1.28 in DMF).

D I 1 EXAMPLE 2: DTPA-(DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol The fraction containing the intermediate product DTPA-DPhe- i i Cys-Phe-DTrp-Lys(e-Boc)-Thr-Cys-Thr-ol)2 as obtained in example 1 is treated as described above for the corresponding monom«ric form, the Boc protecting groups being removed to yield the title compound: [a]20 = - 24,5 0 (c - 0,55 95 X AcOH). o r 1 EXAMPLE 3: N-(CH2)5-CO-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol I 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 hydroxy-benzotriazole 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 which the mixture warms 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 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/piperi-dine 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/Me0H/H20/Ac0H 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 lyophili-sate). [a]20 - - 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: i i DTPA-3Ala-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol. [a]20 = - 14,8 0 (c = 0.5 95 X AcOH). d , , EXAMPLE 5; lllln labeled DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol m 1 1 1U 1 mg DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol is dissolved in ml 0.01M acetic acid. The resulting solution is passed through a 0.22u Mille^®-GV filter (Registered Trade Mark) and dispensed in 0.1 ml portions and stored at -20°C. lllInCl3 (Amersham, 1 mCi/100 yl) is prediluted in an equal volume of 0.5M sodium 15 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: 1S.Y labeled DTPA-DPhe-Cys-Phe-DTrp-Lys-Thr-Cys-Thr-ol 90Y is obtained from a 90Sr-90Y radionuclide generator. The cons- truction 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. Hud.

Med. 28, 1465-1470 (1987). 1 mg of DTPA-DPhe-Cys-Phe-DTrp-Lys- Thr-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, which contain at least on one of the amino acid units a chelating group which 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 with a detectable element, e.g. a metal ion, in free form or in salt form.

Claims (29)

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, wherein the chelating group is selected from the group consisting of iminodicarboxylic groups, polyaminopoly-carboxylic groups, groups derived from macrocyclic amines, groups of formula IV or V R1_C-S-(CH2)n.-C-(TT)i-C- IV R2_C-S-(CH2)„.-C-NH-CH2 0 II CH-C- R3-C-S-(CH2)n.-C-NH' n tt vherein each of Rx, R2 and R3 independently is Ci._6alkyl, C6_8aryl or C7_9arylalkyl, each optionally substituted by OH, Ci_4alkoxy, COOH or S03H, 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 dithia-semicarbazone 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, wherein the chelating group is derived from a compound of formula VI each of R20» ^2i» R22 and R23 independently is hydrogen or Cj.^alkyl, X2 is a group capable of reacting with the N-amino group of the peptide, and m' is 2 or 3, from a compound of formula VII X VI wherein VII wherein X2 is as defined above, from a compound of formula VIII VIII OH OH - 37 - vherein each of R24, R2s> r2 6> r2 7> R28 and R29 independently are hydrogen or Ci_4alkyl, and X2 and m' are as defined above, or from a compound of formula IX 10 HN NH Y/ 3 H5C6C0 coc-h- 0 3 IX 15 vherein X3 is a divalent radical optionally substituted and bearing a group capable of reacting vith the N-amino group of the peptide, and 20 y5 is H or CO2R30 vherein R30 is Cx_4alkyl.

8. A somatostatin peptide according to claim 6, vherein the chelating group is derived from ethylene diaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), 25 ethylene glycol-0,0'-bis(2-aminoethyl)-N,N,N',N'-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-azacyclodo-decane-N,N' ,N" ,N' "-tetraacetic acid (DOTA) and 30 1,4,8,ll-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid (TETA),in free form or in salt form. - 38 -

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

10. A somatostatin peptide according to any one of the preceding claims, wherein the somatostatin peptide is derived from a compound of formula I 25 A' ■ CHj-S-Yx Y2-S-CH2 10 \ i i .N-CH-CO-B-C-D-E-NH-CH-G k wherein A is Ci_i2alkyl, CT-xoplienylalkyl or a group of 15 formula RC0-, whereby i) R is hydrogen, Ci_nalkyl, phenyl or C7.10. phenylakyl, or 20 ii) RCO- is 30 a) an L- or D-phenylalanine residue optionally ring-substituted by F, CI, Br, N02, NH2, OH, Ci_3alkyl and/or Ci_3alkoxy; b) the residue of a natural a-amino acid other than defined under a) above, naphthyl-methyl or pyridyl-methyl or a residue of a corresponding D-amino acid, or 35 10 15 - 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 a-amino group of amino acid residues a) and b) and the N-terminal aunino group o£ dipeptide residues c) being optionally mono- or di-Ci-x2alkylated or substituted by Ci_ a alkanoyl, A' is hydrogen, Cx.i^alkyl or C7_i0phenylalkyl, Yj. and Y2 represent together a direct bond or each of Yx and Y2 is independently hydrogen or a radical of formulae (1) to (5) R. I -CO-C-(CH2)„-B -CO-CH -CO-NHRc Rb 20 (1) (2) (3) 25 -CO-NH-CH-COOR. I Rd -C0-(NH)p- f R."1 I c I Rb'J -(CH2)r-< Rs R9 30 (4) vherein R. Rb m n (5) is methyl or ethyl is hydrogen, methyl or ethyl is a whole number from-1 to 4 is a vhole number from 1 to 5 35 - 40 - Rc is (C]._6 )ai~. I Rd represents vhe substituent attached to the a-carbon atom of a natural a-amino acid (including hydrogen) R. is (C1_5)alkyl Ra' and Rb' are independently hydrogen, methyl or ethyl, R8 and R9 are independently hydrogen, halogen, (Ci_3)alkyl or (Ci_3)alkoxy, p is 0 or 1, q is 0 or 1, and r is 0, 1 or 2, B is optionally by halogen, N02, NH2, OH, Ci_3alkyl and/or Ci_3alkoxy ring-substituted Phe (including pentafluorophenylalanine), or {J-naphthyl-Ala C is (L)-Trp- or (D)-Trp- optionally a-N-methyl- ated and optionally benzene-ring-substituted by halogen, N02, NH2, OH, Ci-3alkyl and/or Ci_3 alkoxy, D is Lys, ,.ys in vhich the side chain contains 0 or S in 3-position, rF-Lys or 5F-Lys, optionally a-N-methylated, or a 4-aminocyclohexylAla or 4-aminocyclohexylGly residue is Thr, Ser, Val, Phe, lie or an aminoisobutyric or aminobutyric acid residue 30 35 - 41 - is a group of formula 30 V1 6 /Ri i -C00R7, -CH2ORio, -CON or -CO-N 5 XRl2 wherein R7 is hydrogen or C1_3alkyl, I Rio is hydrogen or the residue of a physiologically 10 acceptable, physiologically hydrolysable ester, Rn is hydrogen, Ci_3alkyl, phenyl or C7_i0phenyl alkyl, R12 is hydrogen, Ci_3alkyl or a group of formula -CH(R13)-Xlf 15 R13 is CH20H, -(CH2)2-OH, -(CH2)3-0H, or -CH(CH3)0H or represents the substituent attached to the a-carbon atom of a natural a-amino acid (including hydrogen), butyl or naphthyl-methyl, and 20 xi is a group of formula -COOR7, -CH2ORi0 or -CO-N' wherein 25 R7 and Rio have the meanings given above, R14 is hydrogen or C!_3alkyl and Ris is hydrogen, Ci_3alkyl, phenyl or C7_i0phenyl- alkyl, and Ri6 is hydrogen or hydroxy, with the proviso that when R12 is -CH(R13)-Xx then Ru is hydrogen or methyl, 35 - 42 - wherein the residues B, D and E have the L-configuration, and the residues in the 2-and 7-position and any residues Yx 4) and Y2 4) each independently have the (L)- or (D)- configuration 5 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. 10

12. A somatostatin peptide according to claim 10 or 11, wherein in formula I G is -CO-NH-CH(Rx3)-Xi wherein R13 is -CHjOH, -CH(CH3)-0H, -(CH2)2-0H, -(CH2>3-0H, 15 isobutyl or butyl, and Xx is -CO-NR14R15 or -CH2ORio wherein Rio> R14 and Rxs are as defined in claim 10.

13. A somatostatin peptide according to any one of the preceding 20 claims, wherein the somatostatin peptide is derived from 25 1 1 H-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol also known 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 ax 30 Z-R35-CO- (ax) wherein R35 is Cx_xialkylene, C2-xxalkenylene or -CH(R')- wherein R' is the residue attached in a to a natural a-amino acid, and 35 - 43 - 10 15 20 25 30 Z is a functional moiety capable of covalently reacting with the chelating agent.

15. A somatostatin peptide bearing a chelating group, which is l~ 1 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, wherein the detectable element is a y-emitting radionuclide.

17. A somatostatin peptide according to claim 16, wherein the detectable element is lllIn or "BTc.

18. A somatostatin peptide bearing a chelating group in complexed form, which is I 1 X11ln labelled DTPA-(D)Phe-Cys-Phe-(D)Trp-Lys-Thr-Cys-Thr-ol, in free form or in pharmaceutical^ 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. 35 - 44 -

19. A somatostatin peptide according to any one of claims 2 to 14, wherein the detectable element is an a- or 3-emitting radionuclide.

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

21. A somatostatin peptide bearing a chelating group, which i» 90Y 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 t:o 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 5 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. 10

29. A somatostatin peptide, as claimed in claim 21, substantially as hereinbefore described with reference to the Examples. TOMKINS & CO. 15 20 25 30 35