TY - JOUR T1 - Rolapitant is a reversible inhibitor of CYP2D6 JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.118.085928 SP - dmd.118.085928 AU - Sarah M. Glass AU - Sabrina M. Leddy AU - Michael C. Orwin AU - Garret P. Miller AU - Kyle A. Furge AU - Laura Lowe Furge Y1 - 2019/01/01 UR - http://dmd.aspetjournals.org/content/early/2019/04/05/dmd.118.085928.abstract N2 - Rolapitant (Varubi®) is a high affinity NK1 receptor antagonist that was approved in September 2015 as a treatment for nausea and vomiting caused by chemotherapy. In vivo rolapitant moderately inhibits CYP2D6 for at least seven days after one 180 mg dose. Due to the long inhibition time, we investigated rolapitant as a possible mechanism-based inactivator of CYP2D6. Rolapitant docked in the active site of CYP2D6 and displayed type I binding to CYP2D6 with Ks of 1.2 ± 0.4 µM. However, in NADPH-, time-, and concentration-dependent assays of CYP2D6 activity, no evidence for mechanism-based inactivation and no metabolites of rolapitant were observed. Stopped-flow binding studies yielded kon/koff (Kd) of 6.2 µM. The IC50 for rolapitant inhibition of CYP2D6 activity was 24 µM suggesting that inhibition is not due to tight-binding of rolapitant to CYP2D6. By Lineweaver-Burk analysis, rolapitant behaved as a mixed, reversible inhibitor. Ki values of 20 µM and 34 µM were determined by Dixon analysis, with bufuralol and dextromethorphan as reporter substrates, respectively, and drug-drug interaction modeling did not predict the reported in vivo inhibition. The interaction of rolapitant with CYP2D6 was also examined in 1 µsec molecular dynamics simulations. Rolapitant adopted multiple low energy binding conformations near the active site, but at distances not consistent with metabolism. Given these findings, we do not see evidence that rolapitant is a mechanism based inactivator. Moreover, the reversible inhibition of CYP2D6 by rolapitant may not fully account for the moderate inhibition described in vivo. ER -