1β-Hydroxydeoxycholic Acid as an Endogenous Biomarker in Human Plasma for Assessment of CYP3A Clinical Drug-Drug Interaction Potential.

4 β -Hydroxycholesterol (4 β -HC) in plasma has been used as a biomarker to assess CYP3A drug-drug interaction (DDI) potential during drug development. However, due to the long half-life and narrow dynamic range of 4 β -HC, its use has been limited to the identification of CYP3A inducers, but not CYP3A inhibitors. The formation of 1 β -hydroxydeoxycholic acid (1 β -OH DCA) from deoxycholic acid (DCA) is mediated by CYP3A, thus 1 β -OH DCA can potentially serve as an alternative to 4 β -HC for assessment of CYP3A DDI potential. To study this feasibility, we developed a sensitive liquid chromatography-tandem mass spectrometry method for the simultaneous quantitation of 1 β -OH DCA and its glycine and taurine conjugates in human plasma with the lower limit of quantitation of 50 pg/ml, which enabled the quantitation of basal levels and further reduction. The method was applied to a DDI study to assess how 1 β -OH DCA and its glycine and taurine conjugates would respond to CYP3A induction or inhibition. Rifampin induction resulted in an increase of 1 β -OH DCA and its conjugates in plasma, with 6.8-, 7.8-, 8.3-, and 10.3-fold increases of area under the curve from the time of dosing to the last measurable concentration (AUC LST ), area under the curve from the time of dosing to 24 hours (AUC 24h ), C max , and mean concentrations for total 1 β -OH DCA (total of all three forms), respectively. Importantly, inhibition with itraconazole resulted in notable reduction of these biomarkers, with 84%, 85%, 82%, and 81% reductions of AUC LST , AUC 24h , C max , and mean concentrations for total 1 β -OH DCA, respectively. These preliminary data demonstrate for the first time that total 1 β -OH DCA in plasma has the potential to serve as a biomarker for CYP3A DDI assessment in early clinical development and may provide key advantages over 4 β -HC. SIGNIFICANCE STATEMENT: The authors have reported the use of total 1 β -hydroxydeoxycholic acid (1 β -OH DCA) (sum of 1 β -OH DCA and its glycine and taurine conjugates) plasma exposure as a biomarker for CYP3A activity. Itraconazole inhibition led to an 81%-85% decrease of total 1 β -OH DCA plasma exposures, whereas rifampin induction led to a 6.8- to 10.3-fold increase of total 1 β -OH DCA plasma exposures. Using 1 β -OH DCA exposures in plasma also provides the benefit of allowing pharmacokinetic and biomarker assessment using the same matrix.