Metabolites identification of 17α-methyltestosterone mediated by Aspergillus niger RG13B1 and their cytotoxicity on cancer cells

17α-Methyltestosterone (MT) is a synthetic androgen combining both androgenic and estrogenic effects. In this study, the biotransformation of MT was performed using a cultivated human intestinal fungal strain (Aspergillus niger RG13B1) in vitro. Twelve metabolites, including three new metabolites (1−3) and nine known analogs (4−12), were obtained. Their structures were determined by extensive spectroscopic data, including 1D NMR, 2D NMR, and HRESIMS. Based on the structures of the MT metabolites, the main biotransformation reactions were revealed to be hydroxylation, oxidation, dehydrogenation, and reduction. In addition, the cytotoxic effects of MT and metabolites 1−12 were evaluated against human cancer cell lines, including glioblastoma cells U87 and LN229, cervical cells HeLa, colorectal cancer cells HCT-15, renal carcinoma cancer cells RCC-786-O, and breast cancer cells BT549. As a result, MT displayed cytotoxity against U87, LN229, and HeLa, among which a strongest inhibition rate of 82.4% against the HeLa cell line at 50 μM was observed, and metabolites 1−12 displayed no significant cytotoxicity at 50 μM. Therefore, MT could be metabolized by intestinal fungi and yield various metabolites displaying weak cytotoxicity.