1β-Hydroxydeoxycholic Acid as an Endogenous Biomarker in Human Plasma for Assessment of DDI with moderate CYP3A inhibitor

1β-Hydroxydeoxycholic acid (1β-OH DCA) in plasma has been shown to be a promising biomarker to assess drug-drug interaction (DDI) with a strong CYP3A inducer or a strong CYP3A inhibitor. The changes in total 1β-OH DCA (sum of 1β-OH DCA, 1β-OH glycine deoxycholic acid, and 1β-OH taurine deoxycholic acid equivalents) were more significant than those observed from 4β-hydroxycholesterol, which has been limited to the identification of CYP3A inducers, not CYP3A inhibitors. The significant reduction in total 1β-OH DCA in response to strong CYP3A inhibitors led us to further explore its utility as a biomarker for DDI with moderate CYP3A inhibitors. Building from the previously reported biomarker method, we further improved the quantified assay by introducing the stable labeled 1β-OH DCA internal standard, optimizing the extraction and chromatographic conditions for better sample cleanup and separation of these biomarkers from other endogenous components in human plasma. Inhibition with a moderate CYP3A inhibitor fluconazole resulted in notable changes in these biomarkers, with 39%, 39%, and 18% reductions in total 1β-OH DCA Cmax, area under the curve (AUC; 0-24 hours after administration of fedratinib), and AUC (0-216 hours after administration of fedratinib), respectively, compared with those without fluconazole. The geometric mean ratio of total 1β-OH DCA AUC (0-24 hours after administration of fedratinib) and Cmax showed good correlations with the geometric mean ratio of fedratinib (CYP3A4 substrate) exposures with and without fluconazole administration. To our knowledge, these preliminary data demonstrate for the first time that total 1β-OH DCA in plasma has the potential to serve as a biomarker covering a wide range of CYP3A activity, complementing current DDI assessment strategies, including DDI prediction with a moderate CYP3A inhibitor. SIGNIFICANCE STATEMENT: This study reported the use of total 1β-hydroxydeoxycholic acid (1β-OH DCA) (sum of 1β-OH DCA and its glycine and taurine conjugate equivalents) plasma concentration as a biomarker to predict drug-drug interaction with a moderate CYP3A inhibitor. Fluconazole inhibition led to a 40% decrease in total 1β-OH DCA plasma exposures; using total 1β-OH DCA exposures in plasma may allow the prediction of both moderate and strong CYP3A inhibition that has not been achieved by any other biomarkers, including 4β-hydroxycholesterol.