Gastrin-releasing peptide receptor-based targeting using bombesin analogues is superior to metabolism-based targeting using choline for in vivo imaging of human prostate cancer xenografts

Purpose Prostate cancer (PC) is a major health problem. Overexpression of the gastrin-releasing peptide receptor (GRPR) in PC, but not in the hyperplastic prostate, provides a promising target for staging and monitoring of PC. Based on the assumption that cancer cells have increased metabolic activity, metabolism-based tracers are also being used for PC imaging. We compared GRPR-based targeting using the 68 Ga-labelled bombesin analogue AMBA with metabolism-based targeting using 18 F-methylcholine ( 18 F-FCH) in nude mice bearing human prostate VCaP xenografts. Methods PET and biodistribution studies were performed with both 68 Ga-AMBA and 18 F-FCH in all VCaP tumour-bearing mice, with PC-3 tumour-bearing mice as reference. Scanning started immediately after injection. Dynamic PET scans were reconstructed and analysed quantitatively. Biodistribution of tracers and tissue uptake was expressed as percent of injected dose per gram tissue (%ID/g). Results All tumours were clearly visualized using 68 Ga-AMBA. 18 F-FCH showed significantly less contrast due to poor tumour-to-background ratios. Quantitative PET analyses showed fast tumour uptake and high retention for both tracers. VCaP tumour uptake values determined from PET at steady-state were 6.7 ± 1.4%ID/g (20–30 min after injection, N = 8) for 68 Ga-AMBA and 1.6 ± 0.5%ID/g (10–20 min after injection, N = 8) for 18 F-FCH, which were significantly different ( p