title: Evaluation of radiolabelled bombesin analogues for receptor-targeted scintigraphy and radiotherapy.
abstract: The 14-aminoacid peptide bombesin (BN) has a high affinity for the gastrin-releasing peptide receptor which is expressed by a variety of tumours. Thus, radiometal-labelled DTPA-BN derivatives are potentially useful radioligands for receptor-targeted scintigraphy and radiotherapy of BN receptor-expressing tumours. A number of such DTPA-BN analogues, [DTPA-D-Tyr6]BN(6-13)NHEt (Et=ethyl), [DTPA-Tyr5,D-Phe6]BN(5-13)NHEt, [DTPA-D-Phe6,Leu13psiPhe14]BN(6-14), [DTPA-Tyr5,D-Phe6,Leu13psiPhe14]BN(5-14), [DTPA-Pro1,Tyr4]BN and [DTPA-Pro1,Tyr4,Nle14]BN, were synthesized and studied for their binding characteristics to the BN receptor on 7315b rat pituitary tumour cell membranes in competition with [125I-Tyr4]BN. The effects of the BN analogues were determined on basal and BN-stimulated prolactin secretion by 7315b cells to distinguish between their agonistic and antagonistic characteristics. Internalization of selected (111)In-labelled BN analogues was studied using the BN receptor-positive 7315b pituitary tumour and the CA20948 and AR42J exocrine pancreas tumour cell lines. The tissue distribution of these (111)In-labelled BN analogues was investigated in 7315b tumour-bearing rats. Two DTPA-conjugated analogues, the antagonist [DTPA-Tyr5,D-Phe6]BN(5-13)NHEt and the agonist [DTPA-Pro1,Tyr4]BN showed the highest affinity for the BN receptor on 7315b cell membranes. Despite similar affinity for the BN receptor, the (111)In-labelled agonist, but not the antagonist, was internalized by the BN receptor-positive tumour cells. Consonant with this observation, the agonist [(111)In-DTPA-Pro1,Tyr4]BN showed much higher specific uptake in BN receptor-positive tissues and tumour than the antagonist [(111)In-DTPA-Tyr5,D-Phe6]BN(5-13)NHEt, with concordant target to background ratios. We conclude that [(111)In-DTPA-Pro1,Tyr4]BN has promising characteristics for applications in nuclear medicine.
authors.affiliation: Department of Nuclear Medicine, University Hospital Dijkzigt, Rotterdam, The Netherlands. breeman@nuge.azr.nl
authors.forename: W A
authors.initials: WA
authors.lastname: Breeman
authors.forename: L J
authors.initials: LJ
authors.lastname: Hofland
authors.forename: M
authors.initials: M
authors.lastname: de Jong
authors.forename: B F
authors.initials: BF
authors.lastname: Bernard
authors.forename: A
authors.initials: A
authors.lastname: Srinivasan
authors.forename: D J
authors.initials: DJ
authors.lastname: Kwekkeboom
authors.forename: T J
authors.initials: TJ
authors.lastname: Visser
authors.forename: E P
authors.initials: EP
authors.lastname: Krenning
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D005260:Female; D007205:Indium Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use; D004369:Pentetic Acid; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D011388:Prolactin / Q000032:analysis; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000493:pharmacokinetics; D051381:Rats; D011915:Rats, Inbred BUF; D018004:Receptors, Bombesin / Q000032:analysis* / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; D004369:Pentetic Acid; D011388:Prolactin; D001839:Bombesin