Microbial Biotransformation of the Sesquiterpene Carotol: Generation of Hydroxylated Metabolites with Potential Cytotoxic and Target-Specific Binding Activities

Carotol, the major sesquiterpene alcohol in carrot essential oil, possesses notable cytotoxic activity against various cancer cell lines, yet its metabolic fate remains poorly understood. This study explored microbial biotransformation as a tool for generating novel carotol derivatives with potential pharmacological value. Seventeen microbial strains were screened, with Absidia coerulea ATCC 6647 identified as the most effective biocatalyst. Preparative-scale fermentation with this strain afforded three new metabolites, CM1, CM2, and CM3, in yields of 30%, 9.96%, and 3.28%, respectively, which were structurally characterized by 1D and 2D NMR, HRMS, and single-crystal X-ray diffraction. These were identified as 9α-hydroxydaucol (CM1), 9α,13-dihydroxydaucol (CM2), and a diol derivative of daucol (CM3). Cytotoxicity evaluation against human carcinoma cell lines (HepG-2, HCT-116, MCF-7, A-549) and normal lung fibroblasts (MRC-5) revealed that carotol exhibited notable activity with IC50 values of 25.68 and 28.65 µM against HCT-116 and A-549 cell lines, respectively. Among the metabolites, CM2 showed selective cytotoxicity with IC50 values of 180.64 (HCT-116) and 138.21 µM (A-549), indicating that microbial transformation modulates the cytotoxic profile of carotol and yields metabolites with distinct bioactivity patterns. Molecular docking studies further revealed that carotol and CM2 demonstrated higher binding affinities and more stable interactions with human NADPH oxidase, suggesting that inhibition of this enzyme may underlie their cytotoxic effects. This work provides the first detailed microbial biotransformation pathway of carotol, highlighting A. coerulea as a promising source of new hydroxylated metabolites. The results underscore the potential of carotol derivatives in anticancer drug development and warrant further pharmacokinetic studies.