the research leading to the invention has unexpectedly revealed an alternative route for effective in vivo targeting of somatostatin - positive tumors , namely the use of somatostatin receptor antagonists . most surprisingly and against their inability to internalize , such analogs have shown a much higher uptake and retention in animal xenografts and a very rapid washout from background tissues . a tentative explanation for the higher tumor uptake of somatostatin receptor antagonists is their ability to bind to a significantly higher number of the overall somatostatin receptor population available on the cell - membrane of cancer cells than their internalizing agonistic counterparts . according to the invention , grpr - antagonists are chemically modified to accommodate a diagnostic and / or therapeutic radionuclide that they stably bind . after administration in a human or an animal subject they serve as a molecular vehicle to transfer a radiodiagnostic signal and / or a radiotoxic load on the primary grpr + - tumor and its metastases . more specifically , it was found according to the invention that administration of certain novel grpr - antagonist - based radioligands unexpectedly resulted in an unprecedentedly high and specific uptake and a remarkably prolonged retention of human grpr + - xenografts in mice in contrast to [ 99m tc ] demobesin 1 . furthermore , these agents showed significantly higher metabolic stability after injection in mice , compared to [ 99m tc ] demobesin 1 . the grpr - antagonists of the invention have important structural differences in relation to the original [ 99m tc ] demobesin 1 motif . firstly , their labeling with a wide range of bi - and trivalent radiometals , but also with 99m tc and 186 / 188 re , is made possible by coupling of suitable bifunctional chelators at their n - terminus in addition to tetraamine - related frameworks . in this way , radiodiagnostic imaging is possible with spect and pet with gamma and positron - emitters while labeling with beta -, auger and alpha emitters is feasible as well , opening the opportunity for therapeutic applications . then , their metabolic stability and pharmacokinetic profile , especially in terms of tumor - retention has largely improved , as demonstrated by preclinical biodistribution results in female scid mice bearing human pc - 3 xenografts presented at length . a ) the chelator attached to the n - terminus — this can be either an acyclic or a cyclic tetraamine , hynic , n 3 s - chelators and derivatives thereof , linear or cyclic polyamines and polyaminopolycarboxylates like dtpa , edta , dota , nota , notaga , teta and their derivatives , a . o . in addition , a suitable group , such a prosthetic group or a tyr , for labeling with radiohalogens , can be introduced at this position ; b ) the radionuclide — this may be i ) a gamma emitter , such as 99m tc , 111 in , 67 ga , 131 i , 125 i , a . o ., suitable for imaging with a conventional gamma - camera , a spect or an hybrid spect / ct or spect / mri system ; ii ) a positron emitter , such as 68 ga , 66 ga , 64 cu , 86 y , 44 sc , 124 i , 18 f , a . o ., suitable for imaging with a pet or a hybrid pet / ct or pet / mri system , or iii ) a beta , auger or alpha emitter , such as 186 re , 188 re , 90 y , 177 lu , 111 in , 67 cu , 212 bi , 175 yb , 47 sc , 131 i , 125 i , etc ., suitable for radionuclide therapy ; c ) the spacer between the chelator and the peptide motif , which may vary in length , type and lipophilicity and may include pegx ( x = 0 - 20 ), natural and unnatural amino acids , sugars , alkylamino residues or combinations thereof ; d ) the peptide chain , with strategic amino acid replacements undertaken with d - amino acids , unnatural amino acids and other suitable residues . e ) the c - terminus , wherein the both leu 13 and met 14 - nh 2 in the native bbn sequence have been omitted . terminal his 12 is present as the amidated or ester form , whereby amides or esters may be represented by several mono - and di - alkylamides , aromatic amides or mixed alkyl - aryl amides , or alkyl and / or aryl esters . at least one ( radio ) metal ( m ) and a chelator ( c ) which stably binds m ; alternatively mc may represent a tyr - or a prosthetic group carrying a ( radio ) halogen . s is an optional spacer covalently linked between the n - terminal of p and c and may be selected to provide a means for ( radio ) halogenation ; p is a grp receptor peptide antagonist of the general formula : xaa 1 is not present or is selected from the group consisting of amino acid residues asn , thr , phe , 3 -( 2 - thienyl ) alanine ( thi ), 4 - chlorophenylalanine ( cpa ), α - naphthylalanine ( α - nal ), β - naphthylalanine ( β - nal ), 1 , 2 , 3 , 4 - tetrahydronorharman - 3 - carboxylic acid ( tpi ), tyr , 3 - iodo - tyrosine ( o - i - tyr ), trp , pentafluorophenylalanine ( 5 - f - phe ) ( all as l - or d - isomers ); z is selected from — nhoh , — nhnh 2 , — nh - alkyl , — n ( alkyl ) 2r or — o - alkyl wherein x is nh ( amide ) or o ( ester ) and r1 and r2 are the same or different and selected from a proton , a ( substituted ) alkyl , a ( substituted ) alkyl ether , an aryl , an aryl ether or an alkyl -, halogen , hydroxyl or hydroxyalkyl substituted aromatic group . z is preferably selected from one of the following formulae , wherein x is nh or o : in the grpr - antagonists of the invention p is preferably selected from the group consisting of : dtyr - gln - trp - ala - val - gly - his - co — nh — ch [ ch 2 — ch ( ch 3 ) 2 ] 2 ( seq id no : 4 ). the radionuclide , a metal m or a halogen , is suitable for diagnostic or therapeutic use , in particular for imaging or radionuclide therapy and preferably selected from the group consisting of 111 in , 33m in , 99m tc , 94m tc , 67 ga , 66 ga , 68 ga , 52 fe , 69 er , 72 as , 97 ru , 203 pb , 62 cu , 64 cu , 67 cu , 186 re , 188 re , 86 y , 90 y , 51 cr , 52m mn , 157 gd , 177 lu , 161 tb , 169 yb , 175 yb , 105 rh , 166 dy , 166 ho , 153 sm , 149 pm , 151 pm , 172 tm , 121 sn , 177m sn , 213 bi , 142 pr , 143 pr , 198 au , 199 au , 123 i , 124 i , 125 i , 18 f a . o . the metal chelator c is preferably a metal chelator for di - and trivalent metals , and is in particular a dtpa -, nota -, dota -, or teta - based chelator or a mono - or bifunctional derivative thereof . preferably , the metal chelator c is selected from the group consisting of : when the metal chelator c is a metal chelator for technetium or rhenium , it is preferably selected from acyclic tetraamine -, cyclam -, pnao -, or tetradentate chelators containing p 2 s 2 -, n 2 s 2 - and n 3 s - donor atom sets and mono - and bifunctional derivatives thereof , or hynic / co - ligand - based chelators , or bi - and tridentate chelators forming organometallic complexes via the tricarbonyl technology . the spacer s is linked between p and c by covalent bonds and may be selected to provide a means for using a radiohalogen , such as ( radio ) iodination . the spacer is preferably selected from the group consisting of : wherein paba is p - aminobenzoic acid , pabza is p - aminobenzylamine , pda is phenylenediamine and pambza is p -( aminomethyl ) benzylamine ; b ) dicarboxylic acids , ω - aminocarboxylic acids , α , ω - diaminocarboxylic acids or diamines of the formulae : c ) peg spacers of various chain lengths , in particular peg spacers selected from the formulae : d ) α - and β - amino acids , single or in homologous chains of various chain lengths or heterologous chains of various chain lengths , in particular : grpr - antagonists of the invention are preferably selected from the group consisting of compounds of the formulae : it is understood that specific chemical structures disclosed herein are illustrative examples of various embodiments of the invention and that grpr - antagonists of the general formula : mc - s — p are not limited to the structures of examples provided . the invention further relates to a therapeutic composition , comprising a grpr - antagonist as claimed and a therapeutically acceptable excipient . the invention also relates to the grpr - antagonists as claimed for use as a medicament . the medicament is preferably a diagnostic or therapeutic agent for diagnosing or treating primary and / or metastatic grpr + cancers , such as prostate cancer , breast cancer , small cell lung cancer , colon carcinoma , gastrointestinal stromal tumors , gastrinoma , renal cell carcinomas , gastroenteropancreatic neuroendocrine tumors , oesophageal squamous cell tumors , neuroblastomas , head and neck squamous cell carcinomas , to name some of the few , as well as in vasculature of ovarian , endometrial and pancreatic tumors . the invention will be further illustrated in the examples that follows and which are not intended to limit the invention in any way . compounds of the invention were made and tested as described below . the following disclosed embodiments are merely representative of the invention which may be embodied in various forms . thus , specific structural , functional , and procedural details disclosed in the following examples are not to be interpreted as limiting . indium ( in - 111 ) chloride in 50 mm hcl was purchased from mallinckrodt medical b . v ., petten , the netherlands , at an activity concentration of 10 - 20 mci / ml . in general , dota - peptide conjugates of the present invention were radiolabeled with indium - 111 at specific activities of 0 . 1 - 0 . 2 mci in - 111 / nmol dota - peptide conjugate . briefly , 3 - 15 nmol of dota - peptide conjugate dissolved in water was mixed with 2 . 5 - 12 . 5 μl of 1 . 0 m ph 4 . 6 sodium acetate buffer , 1 - 5 μl of 0 . 1 m sodium ascorbate in water and 30 - 150 μl of 111 incl 3 ( 0 . 3 - 3 . 0 mci ). the radiolabeling reaction mixture was incubated in a boiling water bath for 20 to 30 min . for quality control a 2 μl aliquot of the radiolabeling solution was quenched with 28 μl of an acetate buffered solution of na 2 - edta ( 5 mm , ph 4 . 6 ). after a successful radiolabeling ( more than 95 % peptide - bound radioactivity ) na 2 - edta ( 0 . 1 m , ph 4 . 6 ) was added to the radiolabeling solution to a final concentration of 1 mm . gallium ( ga - 67 ) chloride was obtained either in dilute hcl at an activity concentration of 498 - 743 mci / ml from nordion , wesbrook mall , vancouver , canada or at an activity concentration of 80 mci / ml from mallinckrodt medical b . v ., petten , the netherlands . in general , dota - peptide conjugates of the present invention were radiolabeled with gallium - 67 at specific activities of 0 . 1 - 0 . 2 mci ga - 67 / nmol dota - peptide conjugate . briefly , 3 - 15 nmol of dota - peptide conjugate dissolved in water was mixed with 50 - 125 μl of 1 . 0 m ph 4 . 0 sodium acetate buffer and 5 - 15 μl of 67 gacl 3 ( 0 . 5 - 3 . 0 mci . the radiolabeling reaction mixture was incubated in a boiling water bath for 30 min . for hplc quality control a 2 μl aliquot of the radiolabeling solution was quenched with 28 μl of an acetate buffered solution of na 2 - edta ( 5 mm , ph 4 . 0 ). after a successful labeling ( more than 95 % peptide - bound radioactivity ) na 2 - edta ( 0 . 1 m , ph 4 . 0 ) was added to the radiolabeling solution to a final concentration of 1 mm . lutetium ( lu - 177 ) chloride in 50 mm hcl was purchased from idb radiopharmacy , the netherlands , at an activity concentration of 100 mci / ml . in general , dota - peptide conjugates of the present invention were radiolabeled with lutetium - 177 to a specific activity of up to 0 . 5 mci lu - 177 / nmol dota - peptide conjugate . briefly , 3 - 15 nmol of dota - peptide conjugate dissolved in water was mixed with 4 - 16 μl of 1 . 0 m ph 4 . 6 sodium acetate buffer and 15 - 75 μl of 67 gacl 3 ( 1 . 5 - 7 . 5 mci ). radiolysis was minimized by the addition of 5 μl of gentisic acid ( 80 mm ) dissolved in 0 . 2 m sodium ascorbate . the reaction mixture was incubated in a boiling water bath for 30 min . for hplc quality control a 2 μl aliquot of the radiolabeling solution was quenched with 28 μl of an acetate buffered solution of na 2 - edta ( 5 mm , ph 4 . 6 ). after a successful radiolabeling ( more than 95 % peptide - bound radioactivity ) na 2 - edta ( 0 . 1 m , ph 4 . 6 ) was added to the radiolabeling solution to a final concentration of 1 mm . tetraamine - coupled peptides were dissolved in 50 mm acetic acid / etoh 8 / 2 v / v to a final 1 mm peptide concentration . each bulk solution was distributed in 50 μl aliquots in eppendorf tubes and stored at − 20 ° c . labeling was conducted in an eppendorf vial , wherein the following solutions were consecutively added : i ) 0 . 5 m phosphate buffer ph 11 . 5 ( 50 μl ), ii ) 0 . 1 m sodium citrate ( 5 μl , iii ) [ 99m tc ] natco 4 generator eluate ( 415 ml , 10 - 20 mci ), iv ) peptide conjugate stock solution ( 15 μl , 15 nmol ) and v ) freshly made sncl 2 solution in etoh ( 30 μg , 15 μl ). after reaction for 30 min at ambient temperature , the ph was brought to ˜ 7 by adding 1 m hcl ( 10 μl ). hplc analyses were conducted on a waters chromatograph ( waters , vienna , austria ) efficient with a 600 solvent delivery system ; the chromatograph was coupled to twin detection instrumentation , comprising a photodiode array uv detector ( either waters model 996 or model 2998 ) and a gabi gamma detector from raytest ( rsm analytische instrumente gmbh , germany ). data processing and chromatography were controlled via the millennium or empower 2 software ( waters , usa ). a xbridge shield rp18 column ( 5 μm , 4 . 6 × 150 mm , waters , ireland ) coupled to the respective 2 - cm guard column was eluted at 1 ml / min flow rate with a linear gradient system starting from 10 % b and advancing to 70 % b within 60 min , with solvent a = 0 . 1 % aqueous trifluoroacetic acid and solvent b = acetonitrile . a bolus containing the radioligand in normal saline ( 100 - 150 μl , ≈ 3 nmol , 200 - 500 μci ) was injected in the tail vein of swiss albino mice . animals were kept for 5 min in a cage with access to water and were then euthanized promptly by cardiac puncture while under a mild ether anesthesia . blood ( 500 - 900 μl ) was collected from the heart with a syringe and transferred in a pre - chilled eppendorf tube on ice . blood was centrifuged to remove blood cells ( 10 min , 2000 g / 4 ° c .). the plasma was collected , mixed with acetonitrile ( mecn ) in a 1 / 1 v / v ratio and centrifuged again ( 10 min , 15000 g / 4 ° c .). supernatants were concentrated to a small volume ( gentle n 2 - flux at 40 ° c . ), diluted with saline (≈ 400 μl ) and filtered through a millex gv filter ( 0 . 22 μm ). aliquots of plasma samples ( prepared as described above ) were loaded on a symmetry shield rpm column which was eluted at a flow rate of 1 . 0 ml / min with the following gradient : 100 % a to 90 % a in 10 min and from 90 % a to 60 % for the next 60 min ( a = 0 . 1 % aqueous tfa ( v / v ) and b = mecn ). elution of radiocomponents was monitored by a gamma detector . for 99m tc - radiopeptides , itlc - sg analysis was performed in parallel using acetone as the eluent to detect traces of tco 4 − release ( tco 4 − rf = 1 . 0 ). a ≈ 150 μl bolus containing a suspension of 1 . 5 × 10 7 freshly harvested human pc - 3 cells in normal saline was subcutaneously injected in the flanks of female scid mice . the animals were kept under aseptic conditions and 2 - 3 weeks later developed well - palpable tumors at the inoculation site ( 80 - 150 mg ). on the day of the experiment , the selected radiopeptide was injected in the tail vein of tumor - bearing mice as a 100 μl bolus ( 1 - 2 μci , 10 pmol total peptide ; in saline / etoh 9 / 1 v / v ). animals were sacrificed in groups of four under a mild ether anesthesia by cardiac puncture at predetermined time points pi ( postinjection ). additional sets of three to four animals were co - injected with excess [ tyr 4 ] bbn (≈ 40 nmol ) along with test radiopeptide and were sacrificed at 4 h pi ( blocked animals ). samples of blood and tissues of interest were immediately collected , weighed and measured for radioactivity in a γ - counter . stomach and intestines were not emptied of their contents , but measured as collected . biodistribution data were calculated as percent injected dose per gram tissue (% id / g ) using the microsoft excel program with the aid of suitable standards of the injected dose . the results of the various illustrative tests are described herebelow by referring to the corresponding figure . specific structural , functional , and procedural details disclosed in the following results are not to be interpreted as limiting . fig1 a : biodistribution of [ 111 in ] neobomb - 1 ( 111 in - dota -( p - aminobenzylamine - diglycolic acid )-[ d - phe 6 , his - nhch [( ch 2 ch ( ch 3 ) 2 ] 2 12 , des - leu 13 , des - met 14 ] bbn ( 6 - 14 )) in female scid mice bearing pc - 3 tumors ( hgrpr + ) at 4 h and 24 h pi . bars represent average uptake as % injected dose per gram (% id / g ) of at least 4 animals with standard deviation ; an additional group of animals received excess [ tyr 4 ] bbn ( 100 μg ) for in vivo receptor blockade at 4 h pi . bl = blood , li = liver , he = heart , ki = kidneys , st = stomach , in = intestines , sp = spleen , mu = muscle , lu = lungs , pa = pancreas , fe = femur and tu = pc - 3 tumor . high uptake and retention is observed in the experimental tumor with 28 . 6 ± 6 . 0 % id / g at 4 h and 25 . 9 ± 6 . 6 % id / g at 24 h . a high percentage of this uptake could be significantly reduced by co - injection of excess of a native bombesin analog . fig1 b : radiochromatogram of ex - vivo mouse blood 5 min after injection of [ 111 in ] neobomb - 1 . the percentage of parent peptide remaining intact is & gt ; 91 %. fig1 c : biodistribution of [ 177 lu ] neobomb - 1 ( 177 lu - dota -( p - aminobenzylamine - diglycolic acid )-[ d - phe 6 , his - nhch [( ch 2 ch ( ch 3 ) 2 ] 2 12 , des - leu 13 , des - met 14 ] bbn ( 6 - 14 )) in female scid mice bearing pc - 3 tumors ( hgrpr + ) at 4 , 24 and 72 h pi . bars represent average uptake as % injected dose per gram (% id / g ) of at least 4 animals with standard deviation ; an additional group of animals received excess [ tyr 4 ] bbn ( 100 μg ) for in vivo receptor blockade at 4 h pi . bl = blood , li = liver , he = heart , ki = kidneys , st = stomach , in = intestines , sp = spleen , mu = muscle , lu = lungs , pa = pancreas , fe = femur and tu = pc - 3 tumor . pancreatic uptake declines more rapidly with time than tumor uptake resulting in increasingly higher tumor - to - pancreas ratios , especially at 72 h pi . fig1 d : radiochromatogram of ex - vivo mouse blood 5 min after injection of [ 177 lu ] neobomb - 1 , shows that & gt ; 92 % parent peptide remains intact . fig1 e : biodistribution of [ 67 ga ] neobomb - 1 ( 67 ga - dota -( p - aminobenzylamine - diglycolic acid )-[ d - phe 6 , his - nhch [( ch 2 ch ( ch 3 ) 2 ] 2 12 , des - leu 13 , des - met 14 ] bbn ( 6 - 14 )) in female scid mice bearing pc - 3 tumors ( hgrpr + ) at 1 h and 4 h pi . bars represent average uptake as % injected dose per gram (% id / g ) of at least 4 animals with standard deviation ; an additional group of animals received excess [ tyr 4 ] bbn ( 100 μg ) for in vivo receptor blockade at 4 h pi . bl = blood , li = liver , he = heart , ki = kidneys , st = stomach , in = intestines , sp = spleen , mu = muscle , lu = lungs , pa = pancreas , fe = femur and tu = pc - 3 tumor . high tumor values (& gt ; 30 % id / g ) are achieved by the radiotracer at 1 and 4 h pi . fig1 f : radiochromatogram of ex - vivo mouse blood 5 min after injection of [ 67 ga ] neobomb - 1 , shows that & gt ; 97 % parent peptide remains intact . fig2 a : biodistribution of [ 99m tc ] neobomb - 2 ( 99m tc - n 4 -( p - aminobenzylamine - diglycolic acid )-[ d - phe 6 , his - nhch [( ch 2 — ch ( ch 3 ) 2 ] 2 12 , des - leu 13 , des - met 14 ] bbn ( 6 - 14 )) in female scid mice bearing pc - 3 tumors ( hgrpr + ) at 1 h , 4 h and 24 h pi . bars represent average uptake as % injected dose per gram (% id / g ) of at least 4 animals with standard deviation ; an additional group of animals received excess [ tyr 4 ] bbn ( 100 μg ) for in vivo receptor blockade at 4 h pi . bl = blood , li = liver , he = heart , ki = kidneys , st = stomach , in = intestines , sp = spleen , mu = muscle , lu = lungs , pa = pancreas and tu = pc - 3 tumor . high tumor values (˜ 30 % id / g ) are achieved by the radiotracer at 1 and 4 h pi , which remain exceptionally high (& gt ; 25 % id / g ) at 24 h pi . fig2 b : radiochromatogram of ex - vivo mouse blood 5 min after injection of [ 99m tc ] neobomb - 2 shows that & gt ; 88 % parent peptide remains intact .
the present invention relates to probes for use in the detection , imaging , diagnosis , targeting , treatment , etc . of cancers expressing the gastrin releasing peptide receptor . for example , such probes may be molecules conjugated to detectable labels which are preferably moieties suitable for detection by gamma imaging and spect or by positron emission tomography or magnetic resonance imaging or fluorescence spectroscopy or optical imaging methods .