Metabolite analysis of [11C]Ro15-4513 in mice, rats, monkeys and humans

We performed in vitro and in vivo assays of the metabolism of [(11)C]Ro15-4513 over time in the plasma of mice, rats, monkeys and humans, using a radio-HPLC equipped with a sensitive positron detector, in order to compare the metabolic rates of the radiopharmaceutical agent among the different animal species and to establish a highly sensitive analytical method for the radiotracer agent. We also examined the metabolism of [(11)C]Ro15-4513 in the brain tissue of mice and rats. The analytical method used in this study permitted detection of even extremely low levels of radioactivity (approximately 5,000 dpm). In vitro experiments revealed that [(11)C]Ro15-4513 in the blood was metabolized to hydrolysate [(11)C]A. The species were classified in descending order of the metabolic rate of the radiotracer in vitro as follows; mice, rats, and monkeys/humans. In the in vitro experiment, the percentage of the unchanged drug in the plasma at 60 minutes postdose was 9% in mice, 70% in rats, 97% in monkeys, and 98% in humans. In vivo metabolite analysis in the blood showed the presence of two radioactive metabolites, consisting of one hydrolysate [(11)C]A and another unidentified substance. The species were classified in descending order of the metabolic rate of the radiotracer in vivo as follows; mice, rats/humans, and monkeys. The percentage of the unchanged drug in the plasma was 6% in mice, 21% in rats, 26% in humans, and 40% in monkeys. Furthermore, the in vitro and in vivo experiments conducted to analyze the metabolism of [(11)C]Ro15-4513 in the brain tissue of mice and rats revealed that the radiotracer was metabolized to some extent in the brain tissue of these animals. In the in vivo experiment, the percentage of the unchanged drug at 60 min postdose was 86% in the brain tissue of mice and 88% in the brain tissue of rats, while in the in vitro experiment, the corresponding percentage was 93% in mice, and 91% in rats.