Synthesis of bombesin analogues for radiolabeling with rhenium‐188

• Published in: Cancer Vol. 80; no. S12; pp. 2354 - 2359
• Main Authors: Safavy, Ahmad, Khazaeli, M. B., Qin, Haoyu, Buchsbaum, Donald J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York John Wiley & Sons, Inc 15-12-1997; Wiley-Liss
• Subjects: 3T3 Cells; Animals; Biological and medical sciences; Bombesin - analogs & derivatives; bombesin analogues; cancer imaging; cancer therapy; Contrast media. Radiopharmaceuticals; Humans; Isotope Labeling; Male; Medical sciences; Mice; Neoplasms - radiotherapy; Pharmacology. Drug treatments; Receptors, Bombesin - antagonists & inhibitors; Rhenium - therapeutic use; rhenium‐labeling; trisuccin
• ISSN: 0008-543X; 1097-0142
• DOI: 10.1002/(SICI)1097-0142(19971215)80:12+<2354::AID-CNCR4>3.0.CO;2-B

BACKGROUND
Gastrin‐releasing peptide receptors (GRPR) are overexpressed in small cell lung carcinoma and some other human cancers. Small molecule peptides with antagonistic activities toward these receptors are potential radiotherapeutic agents.
METHODS
A 7‐amino acid analogue of bombesin (BBN) was synthesized through solid‐phase techniques. The peptide was conjugated to trisuccin prior to cleavage from the resin. The conjugate was hydrogenated to remove the hydroxamate‐protecting benzyl groups followed by purification through reversed‐phase high performance liquid chromatography (RP‐HPLC). Rhenium‐188 (188Re)‐labeling of the trisuccin‐peptide conjugate was performed by a SnCl2‐reduced radioisotope and the labeled product was purified by RP‐HPLC. The labeled conjugate was incubated with BNR‐11 (3T3 mouse fibroblast cells stably transfected with murine GRPR) and PC‐3 human prostate carcinoma GRPR positive cells. The nonradioactive peptide analogue was used as a competitive inhibitor and 125I‐[Tyr4]‐BBN was used as a positive control.
RESULTS
Solid‐phase and solution phase synthesis afforded the conjugates of the hydroxamate ligand trisuccin with the 7‐amino acid BBN analogue. The molecules differed by either a direct attachment of the trisuccin to the peptide (TrisBBN) or connection through a 6‐carbon linker (TrisC6BBN). The overall yield for each synthesis was approximately 20%. Both conjugates showed the correct molecular weights on mass spectroscopy. Radiolabeling of the conjugates with 188Re were performed in ≥ 90% yield. Cell‐binding assays performed with BNR‐11 (TrisBBN and TrisC6BBN) and PC‐3 (TrisBBN) cell lines resulted in positive binding.
CONCLUSIONS
The synthesis and radiolabeling of Tris‐BBN conjugates with 188Re were shown to be feasible. The yields of chemical syntheses and radiolabeling and positive binding of the radiolabeled conjugates to GRPR‐ positive tumor cells reveal promise in the use of these molecules for cancer imaging and therapy. More work is needed and is in progress to optimize the cell‐binding properties. Cancer 1997; 80:2354‐9. © 1997 American Cancer Society.
Conjugates of the trihydroxamate chelating agent trisuccin with an analogue of the neuropeptide bombesin were synthesized by solid phase methods and labeled with rhenium‐188. Cell binding assays with BNR‐11 and PC‐3 cell lines showed positive binding.