(18)F-AmBF3-MJ9: a novel radiofluorinated bombesin derivative for prostate cancer imaging.

A novel radiofluorinated derivative of bombesin, (18)F-AmBF3-MJ9, was synthesized and evaluated for its potential to image prostate cancer by targeting the gastrin releasing peptide receptor (GRPR). AmBF3-MJ9 was prepared from an ammoniomethyl-trifluoroborate (AmBF3) conjugated alkyne 2 and azidoacetyl-MJ9 via a copper-catalyzed click reaction, and had good binding affinity for GRPR (Ki=0.5±0.1nM). The (18)F-labeling was performed via a facile one-step (18)F-(19)F isotope exchange reaction, and (18)F-AmBF3-MJ9 was obtained in 23±5% (n=3) radiochemical yield in 25min with >99% radiochemical purity and 100±32GBq/μmol specific activity. (18)F-AmBF3-MJ9 was stable in mouse plasma, and was partially (22-30%) internalized after binding to GRPR. Positron emission tomography (PET) imaging and biodistribution studies in mice showed fast renal excretion and good uptake of (18)F-AmBF3-MJ9 by GRPR-expressing pancreas and PC-3 prostate cancer xenografts. Tumor uptake was 1.37±0.25%ID/g at 1h, and 2.20±0.13%ID/g at 2h post-injection (p.i.) with low background uptake and excellent tumor visualization (tumor-to-muscle ratios of 75.4±5.5). These data suggest that (18)F-AmBF3-MJ9 is a promising PET tracer for imaging GRPR-expressing prostate cancers.