In Vivo Evaluation of a Bombesin Analogue Labeled with Ga-68 and Co-55/57

The purpose of this study was to apply an analogue of bombesin, NOTA-AMBA, labeled with Co-55 or Ga-68, for preclinical imaging of prostate cancer. The peptide NOTA-AMBA was labeled with Ga-68 or Co-55 by microwave irradiation. Biodistribution in xenograft mice (PC3) was performed at 1, 4, and 24 h (only cobalt at 24 h) using a fixed amount of peptide. Four weeks post-inoculation, xenograft mice were positron emission tomography/X-ray computed tomography scanned after tail vein injection of [Ga-68]NOTA-AMBA or [Co-55]NOTA-AMBA. Labeling with Ga-68 and Co-55/57 was achieved in yields greater than 90 %. A radiochemical purity (RCP) of 95 and 90 % were obtained for Ga-68 and Co-55, respectively. Both radiopeptides showed high uptake in the intestines, stomach, pancreas, and in the tumor ([Ga-68]NOTA-AMBA, 10.3 %ID/g at 1 h to 6.4 %ID/g at 4 h; [Co-57]NOTA-AMBA, 8.2 %ID/g at 1 h to 5.3%ID/g at 24 h). Normal tissue cleared over time improving tumor-to-background ratios. NOTA-AMBA was labeled in high yields and RCP with Ga-68 and Co-55/57. High tumor uptake in a subcutaneous mouse prostate cancer model was observed. At 24 h, [Co-55/57]NOTA-AMBA showed better tumor-to-organ ratios than [Ga-68]NOTA-AMBA at both 1 and 4 h post-injection. Hence, for imaging, [Co-55]NOTA-AMBA was found to be superior compared to [Ga-68]NOTA-AMBA.