Characterization of the metabolites of H3B-6545 in vitro and in vivo by using ultra-high performance liquid chromatography combined with electrospray ionization linear ion trap-orbitrap tandem mass spectrometry

H3B-6545 is a selective ERα covalent antagonist, which has been demonstrated to be effective in anti-tumor. To fully understand its mechanism of action, it is necessary to investigate the in vitro and in vivo metabolic profiles. For in vitro metabolism, H3B-6545 (50 μM) was incubated with the hepatocytes of rat and human for 2 h. For in vivo metabolism H3B-6545 was orally administered to rats at a single dose of 10 mg/kg, and plasma, urine and fecal samples were then collected. All samples were analyzed by using ultra-high performance liquid chromatography combined with linear ion trap-orbitrap tandem mass spectrometry (UHPLC-LTQ-Orbitrap-MS) operated in positive ion mode. The structures of the metabolites were elucidated by comparing their MS and MS² spectra with those of parent drug. A total of 11 metabolites, including a GSH adduct, were detected and structurally identified. M2, M7 and M8 were further unambiguously identified by using reference standards. Among these metabolites, M1, M5, M7 and M10 were newly found and reported for the first time. The metabolic pathways of H3B-6545 included deamination (M8 and M9), dealkylation (M2, M3 and M10), N-hydroxylation (M6), hydroxylation (M1 and M4), formation of amide derivatives (M5 and M7) and GSH conjugation (G1).