Radiochemical investigations of (99m)Tc-N(3)S-X-BBN[7-14]NH(2): an in vitro/in vivo structure-activity relationship study where X = 0-, 3-, 5-, 8-, and 11-carbon tethering moieties.
Bombesin (BBN), a 14 amino acid peptide, is an analogue of human gastrin releasing peptide (GRP) that binds to GRP receptors (GRPr) with high affinity and specificity. The GRPr is overexpressed on a variety of human cancer cells, including prostate, breast, lung, and pancreatic cancers. The specific aim of this study was to develop (99m)Tc-radiolabeled BBN analogues that maintain high specificity for the GRPr in vivo. A preselected synthetic sequence via solid-phase peptide synthesis (SPPS) was designed to produce N(3)S-BBN (N(3)S = dimethylglycyl-l-seryl-l-cysteinylglycinamide) conjugates with the following general structure: DMG-S-C-G-X-Q-W-A-V-G-H-L-M-(NH(2)), where the spacer group, X = 0 (no spacer), omega-NH(2)(CH(2))(2)COOH, omega-NH(2)(CH(2))(4)COOH, omega-NH(2)(CH(2))(7)COOH, or omega-NH(2)-(CH(2))(10)COOH. The new BBN constructs were purified by reversed phase-HPLC (RP-HPLC). Electrospray mass spectrometry (ES-MS) was used to characterize the nonmetalated BBN conjugates. Re(V)-BBN conjugates were prepared by the reaction of Re(V)gluconate with N(3)S-X-BBN[7-14]NH(2) (X = 0 carbons, beta-Ala (beta-alanine), 5-Ava (5-aminovaleric acid), 8-Aoc (8-aminooctanoic acid), and 11-Aun (11-aminoundecanoic acid)) with gentle heating. Re-N(3)S-5-Ava-BBN[7-14]NH(2) was also prepared by the reaction of [Re(V)dimethylglycyl-l-seryl-l-cysteinylglycinamide] with 5-Ava-BBN[7-14]NH(2). ES-MS was used to determine the molecular constitution of the new Re(V) conjugates. The (99m)Tc conjugates were prepared at the tracer level by each the prelabeling, post-conjugation and pre-conjugation, postlabeling approaches from the reaction of Na[(99m)TcO(4)] with excess SnCl(2), sodium gluconate, and corresponding ligand. The (99m)Tc and Re(V) conjugates behaved similarly under identical RP-HPLC conditions. In vitro and in vivo models demonstrated biological integrity of the new conjugates.
Smith
C Jeffrey
CJ
Research Services, Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri 65201, USA.
Gali
Hariprasad
H
Sieckman
Gary L
GL
Higginbotham
Chris
C
Volkert
Wynn A
WA
Hoffman
Timothy J
TJ
D000595:Amino Acid Sequence; D000818:Animals; D001839:Bombesin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D003432:Cross-Linking Reagents; D006801:Humans; D007267:Injections; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism; D015609:Organotechnetium Compounds / Q000138:chemical synthesis* / Q000378:metabolism / Q000493:pharmacokinetics; D010446:Peptide Fragments / Q000138:chemical synthesis* / Q000378:metabolism / Q000493:pharmacokinetics; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000378:metabolism / Q000493:pharmacokinetics; D018004:Receptors, Bombesin / Q000378:metabolism; D013329:Structure-Activity Relationship; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
C475565:(99m)Tc-N(3)S-X-BBN(7-14)NH(2); D003432:Cross-Linking Reagents; D009363:Neoplasm Proteins; D015609:Organotechnetium Compounds; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; D001839:Bombesin