Adrenocortical carcinoma (ACC) is a rare disease with an extremely poor prognosis. Mitotane alone or in combination with other cytotoxic drugs is a common therapeutic option for ACC. In addition to its adrenolytic function, mitotane has been known for decades to increase the metabolic clearance of glucocorticoids. It was recently shown that the tyrosine kinase inhibitor sunitinib is also rapidly metabolized in patients treated with mitotane, indicating that mitotane engages in clinically relevant drug interactions. Although the precise mechanism of these interactions is not well understood, cytochrome P450 mono-oxygenase 3A4 (CYP3A4) is a key enzyme to inactivate both glucocorticoids and sunitinib. The nuclear receptor steroid and xenobiotic receptor (SXR (NR1I2)) is one of the key transcriptional regulators ofCYP3A4gene expression in the liver and intestine. A variety of xenobiotics bind to SXR and stimulate transcription of xenobiotic-response elements (XREs) located in theCYP3A4gene promoter. In this study, we evaluated the effects of mitotane on SXR-mediated transcriptionin vitroby luciferase reporter analysis, SXR–steroid receptor coactivator 1 (SRC1) interactions, quantitative real-time PCR analysis ofCYP3A4expression, SXR knockdown, and CYP3A4 enzyme activity assays using human hepatocyte-derived cells. We found that mitotane activated SXR-mediated transcription of the XREs. Mitotane recruited SRC1 to the ligand-binding domain of SXR. Mitotane increasedCYP3A4mRNA levels, which was attenuated by SXR knockdown. Finally, we showed that mitotane increased CYP3A4 enzyme activity. We conclude that mitotane can induceCYP3A4gene expression and suggest that mitotane is used cautiously due to its drug–drug interactions.
Steroid and Xenobiotic Receptor Signalling in Apoptosis and Autophagy of the Nervous System