Pharmacogenetic CYP2B6 variants affect steroid hormone metabolism in human breast cancer cells

CYP2B6 is a key enzyme involved in the metabolism of steroid hormones such as testosterone and estradiol. Common genetic CYP2B6 variants (*4, *5, *6, *9) are associated with reduced enzymatic activity and have been linked to increased breast cancer risk and poor prognosis. However, the impact of these genetic variants on testosterone and estradiol metabolism in humans is not understood. Therefore, this study aimed to investigate how these pharmacogenetic CYP2B6 variants affect metabolism of these steroid hormones in a human breast cancer model and how this may contribute to altered steroid hormone profiles in breast cancer.

T47D breast cancer cells were engineered to stably overexpress CYP2B6 wild type and the variants *4, *5, *6 and *9 using a retroviral pMOWS vector system. The metabolites 16α-/16β-hydroxytestosterone and 2-/4-hydroxyestradiol were analysed using HPLC-MS/MS after incubation of testosterone or estradiol with CYP2B6 and CYP1B1 supersomes and the modified T47D cells. Conversion of testosterone metabolites to oestrogens by aromatase was also tested.

CYP2B6 supersomes predominantly formed 16β-hydroxytestosterone and 2-hydroxyestradiol, while CYP1B1 predominantly produced 16α-hydroxytestosterone and 4-hydroxyestradiol. CYP2B6*6 overexpression in T47D increased 16α-hydroxytestosterone formation, while *4 and 9 showed decreased metabolism compared to wild type. CYP2B6*5 produced reduced 16β-hydroxytestosterone levels. Aromatase converts 16α-metabolite to estriol and 16β-hydroxytestosterone to 16-epiestriol.

This study demonstrates that common CYP2B6 variants alter testosterone metabolism in a human breast cancer model, potentially disrupting steroid hormone balance and contributing to a tumour-promoting environment. These findings highlight the potential relevance of pharmacogenetic profiling in breast cancer risk assessment.