Biodistribution and pharmacokinetics of the 19F-labeled radiosensitizer 3-aminobenzamide: assessment by 19F MR imaging

3-Aminobenzamide (3-ABA) is a potent radiosensitizer that inhibits the repair of DNA strand breaks. The aim of this study was to monitor the biodistribution and pharmacokinetics of a fluorinated 3-ABA derivative in tumor-bearing rats by magnetic resonance imaging (MRI). To this end, 3-ABA was labeled with fluorine-19 by trifluoroethylation [3-amino-N-2,2,2-trifluoroethylbenzamide (3-ABA-TFE)], which only slightly increased the cytotoxicity of the compound as demonstrated by colony-forming assays. After intraperitoneal injection of 400 mg/kg BW 3-ABA-TFE to nine Copenhagen rats with Dunning prostate adenocarcinoma, 19F MR images were acquired at a whole-body MR system with a spatial sampling of 10×10×15 mm3. While 3-ABA-TFE was observed in all major organs and the muscular system, only a small and heterogeneous signal could be detected in the adenocarcinoma. Serial MR measurements yielded maximum tissue signals about 2 days after 3-ABA-TFE administration. At this time point, the mean muscle-to-liver and tumor-to-liver signal ratio was 0.31±0.07 and 0.11±0.04, respectively. Application of the 19F MRI strategy makes it possible to measure the biodistribution and pharmacokinetics of 3-ABA-TFE in individual animals in a longitudinal manner. The results obtained for the prostate adenocarcinoma indicate that delivery of 3-ABA-TFE to solid tumors may be seriously hampered by tumor-specific factors and that the intratumoral uptake of the substance may be lower than in normal tissues. Therefore, the development of effective carrier systems is mandatory to improve tumor-selective delivery.