In Vitro and In Vivo Primary Metabolic Characterization of F18, a Novel Histone Deacetylase-6 (HDAC6) Inhibitor, Using UHPLC–QqQ–MS/MS and Q-TOF–MS Methods

F18, N -hydroxy-4-(2-methoxy-5-(methyl (2-methylquinazolin-4-yl) amino) phenoxy) butanamide, is a novel selective HDAC6 inhibitor with good antitumor activity. In the early drug development, drug-metabolism studies are a crucial and indispensable part. In this study, we proposed to evaluate the in vitro primary metabolism of F18 in phase Ι in liver microsomes from human, rat, dog, monkey and mouse and investigate the metabolite profile both in vitro and in vivo using LC–MS/MS methods. F18 showed high metabolic stability in human, rat, dog, monkey and mouse liver microsomes over 120 min, with t 1/2 >8 h in human, rat, and dog, and t 1/2 <3.5 h in monkey, with almost no clearance in mouse. Human cytochrome P450 (P450) phenotyping showed that F18 was predominantly metabolized by CYP2C9, CYP2E1, CYP2D6 and CYP3A4. The investigation of the effect of F18 on CYP enzymes in HLM demonstrated that this compound did not significantly inhibit CYP 1A2 (IC 50 >100 μM), was a moderate inhibitor of CYP3A4 (IC 50 = 1.63 μM) and had negligible effects on CYP3A1/2 activity in rats. The results will be valuable in understanding drug–drug interactions (DDI) when F18 is co-administered with other drugs. The metabolites of F18 were investigated in rat plasma, urine, feces and different liver microsomes in NADPH samples, yielding at least 11 metabolites in these biological samples. The prominent metabolic pathways were de-methylation, de-amination, de-oxidation and O -glucuronidation. In summary, this work provides the first clues regarding F18 metabolism, providing important information for comprehensive understanding of F18 metabolites.