Species differences in FMO and CYP enzymes metabolism of TG100435

TG100435, a novel multi-targeted src+ kinase inhibitor, is an orally active anti-cancer agent. The current in vitro studies evaluated the N-oxidation of TG100435 following co-incubation with human, rat dog, and mouse liver microsomes. The result suggested that TG100435-N-oxide (TG100855) production represented 10% – 40% of TG100435 total metabolism. Interestingly, during the incubation, TG100855 was converted back to TG100435 by CYP enzymes. Subsequent metabolic studies to evaluate TG100855 conversion were designed where TG100435 or TG100855 was co-incubated with the liver microsomes in the presence or the absence of 1-aminobenzotriazole (non-specific CYP inhibitor) or methimazole (specific Flavin-containing monooxygenases (FMO) inhibitor) under a variety of incubation conditions. The results showed that N-oxidation of TG100435 was due to FMO while the conversion of TG100855 back to TG100435 was due to CYP450. The formation of TG100855 from TG100435 was markedly inhibited following microsomal heat treatment or methimazole co-incubation (88% and 95%, respectively). Dog liver microsomes showed 8, 15, or 60 fold higher TG100855 formation than rat, mouse or human liver microsomes, respectively. In summary, TG100435 and TG100855 are metabolically inter-converted and the N-oxidation reaction was induced by FMO while the conversion of TG100855 back to TG100435 was due to CYP enzymes.