Background and Objectives: SM-1 is a new synthetic small molecule compound with antitumor activity. The metabolism of SM-1 is a key parameter that needs to be evaluated to provide further insight into drug safety and efficacy in the early phases of drug development.
Methods and Results: In this study, the biotransformation process of SM-1 including the metabolic pathways and major metabolites was investigated based on a liquid chromatography-mass spectrometry method. Upon incubation of SM-1 with human liver microsomes, five metabolites were identified, namely dihydrodiol formation (R1), hydroxylation (R2, R3 and R5), and debenzylation (R4) of SM-1, with R1 and R4 being the major metabolites. The enzyme kinetic parameters of SM-1 were determined by a liquid chromatography tandem mass spectrometry method. The enzyme kinetics of SM-1 obeyed the Michaelis-Menten equation. The Vmax, Km, and CLint of SM-1 in HLMs were 14.5 nmol/mg protein/h, 6.32 μM, and 2.29 mL/mg protein/h, respectively. The chemical inhibition studies showed that CYP450 isoenzymes were responsible for SM-1 metabolism in HLMs and CYP3A4 was the major CYP450 isoenzyme involved in the metabolism of SM-1; these findings were confirmed by using the human recombinant CYP3A4.
Conclusions: Through identification of the biotransformation pathways and enzyme kinetics of SM-1, the metabolic enzymes for SM-1 in HLMs are characterized.