In vitro and in vivo evaluation of a 64Cu-labeled NOTA-Bn-SCN-Aoc-bombesin analogue in gastrin-releasing peptide receptor expressing prostate cancer

• Published in: Nuclear medicine and biology 2012-07, Vol.39 (5), p.609-616
• Main Authors: Craft, Jeffrey M., De Silva, Ravindra A., Lears, Kimberly A., Andrews, Rebecca, Liang, Kexian, Achilefu, Samuel, Rogers, Buck E.
• Format: Article
• Language: English
• Subjects: Animals; Binding, Competitive; Biological and medical sciences; Biological Transport; Bombesin; Bombesin - analogs & derivatives; Bombesin - metabolism; Bombesin - pharmacokinetics; Caprylates - chemistry; Cell Line, Tumor; Cell Transformation, Neoplastic; Copper Radioisotopes; Cu-64; Female; Gene Expression Regulation, Neoplastic; Gynecology. Andrology. Obstetrics; Heterocyclic Compounds - chemistry; Humans; Isothiocyanates - chemistry; Isotope Labeling; Male; Male genital diseases; Medical sciences; Mice; Multimodal Imaging; Nephrology. Urinary tract diseases; NOTA; Positron-Emission Tomography; Prostate cancer; Prostatic Neoplasms - diagnostic imaging; Prostatic Neoplasms - metabolism; Prostatic Neoplasms - pathology; Receptors, Bombesin - metabolism; Tomography, X-Ray Computed; Tumors; Tumors of the urinary system; Urinary tract. Prostate gland
• ISSN: 0969-8051; 1872-9614
• DOI: 10.1016/j.nucmedbio.2011.12.004

Bombesin (BN) is an amphibian peptide that binds to the gastrin-releasing peptide receptor (GRPR). It has been demonstrated that BN analogues can be radiolabeled for potential diagnosis and treatment of GRPR-expressing malignancies. Previous studies have conjugated various chelators to the eight C-terminal amino acids of BN [BN(7-14)] for radiolabeling with 64Cu. Recently, (1,4,7-triazacyclononane-1,4,7-triacetic acid) (NOTA) has been evaluated as the five-coordinate 64Cu complex, with results indicating GRPR-specific tumor uptake. This study aimed to conjugate S-2-(4-isothiocyanatobenzyl)-NOTA (p-SCN-Bn-NOTA) to BN(7-14) such that it could form a six-coordinate complex with 64Cu and to evaluate the resulting peptide. p-SCN-NOTA was conjugated to 8-aminooctanoic acid (Aoc)-BN(7-14) in solution to yield NOTA-Bn-SCN-Aoc-BN(7-14). The unlabeled peptide was evaluated in a cell binding assay using PC-3 prostate cancer cells and 125I-Tyr4-BN to determine the IC50 value. The peptide was radiolabeled with 64Cu and evaluated for internalization into PC-3 cells and for tumor uptake in mice bearing PC-3 xenografts using biodistribution and micro-positron emission tomography imaging studies. The binding assay demonstrated that NOTA-Bn-SCN-Aoc-BN(7-14) bound with high affinity to GRPR with an IC50 of 1.4 nM. The radiolabeled peptide demonstrated time-dependent internalization into PC-3 cells. In vivo, the peptide demonstrated tumor-specific uptake and imaging that were comparable to those of previously reported 64Cu-labeled BN analogues. These studies demonstrate that 64Cu-NOTA-Bn-SCN-Aoc-BN(7-14) binds to GRPR-expressing cells and that it can be used for imaging of GRPR-expressing prostate cancer.