title: Development of a radioimmunoassay for a pseudononapeptide bombesin/GRP antagonist with antitumor activity.
abstract: Bombesin-like and GRP-like peptides may act as autocrine growth factors in the proliferation of some cancers. A pseudononapeptide bombesin antagonist, [D-Tpi6,Leu13 psi(CH2NH)-Leu14]bombesin(6-14), and related analogs synthesized in our laboratory significantly inhibit tumor growth in various cancer models. A radio-immunoassay (RIA), suitable for determination of RC-3095 and its congeners in unextracted serum, was developed in order to facilitate further experimental and clinical evaluation of this bombesin/GRP receptor antagonist for the treatment of various tumors. Antibodies were generated against RC-3095 and Des-Tpi1-RC-3095, conjugated to bovine serum albumin with glutaraldehyde. Antiserum JH-631b was selected for further experiments based on the antibody characterization. At an antiserum dilution of 1:189,000, this antibody bound approximately 50% of 7 fmol of added radiolabeled Tyr1-RC-3095. The antibody crossreacted with C-terminal fragments of RC-3095. Fragments without the C-terminus and naturally existing peptides of the bombesin family or structurally unrelated peptides did not cross-react. The minimum detectable dose of RC-3095 was 0.4 pg/tube. Intra- and interassay coefficients of variation ranged from 3.2 to 4.4% and from 5.6 to 12.8%, respectively. The RIA is suitable for direct determination of RC-3095 in serum. The RIA should be of value for monitoring levels of this analog in serum during long-term therapy.
authors.affiliation: Endocrine, Polypeptide and Cancer Institute, Veterans Affairs Medical Center, New Orleans, Louisiana, USA.
authors.forename: K
authors.initials: K
authors.lastname: Groot
authors.forename: J E
authors.initials: JE
authors.lastname: Horvàth
authors.forename: R Z
authors.initials: RZ
authors.lastname: Cai
authors.forename: A V
authors.initials: AV
authors.lastname: Schally
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000032:analysis* / Q000493:pharmacokinetics / Q000494:pharmacology; D001839:Bombesin / Q000031:analogs & derivatives* / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000493:pharmacokinetics / Q000494:pharmacology; D019886:Gastrin-Releasing Peptide; D008297:Male; D009842:Oligopeptides / Q000032:analysis* / Q000494:pharmacology; D010446:Peptide Fragments / Q000032:analysis* / Q000493:pharmacokinetics / Q000494:pharmacology; D010455:Peptides / Q000037:antagonists & inhibitors*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D000970:Antineoplastic Agents; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; C071363:bombesin (6-14), Tpi(6)-Leu(13)-psi(CH2NH)-Leu(14)-; D019886:Gastrin-Releasing Peptide; D001839:Bombesin