Metabolism of N,N,N-Triethylenethiophosphoramide by CYP2B1 and CYP2B6 Results in the Inactivation of Both Isoforms by Two Distinct Mechanisms

Abstract

The anticancer drug N,N,N-triethylenethiophosphoramide (tTEPA) inactivated CYP2B6 and CYP2B1 in the reconstituted system in a time-, concentration-, and NADPH-dependent manner indicative of mechanism-based inactivation. The KI value for the inactivation of CYP2B1 was 38 M, the kinact was 0.3 min1, and the t1/2 value was 2.5 min. Spectral carbon monoxide (CO) binding and high-performance liquid chroma-tography heme studies of the tTEPA-inactivated CYP2B1 sug-gest that the loss in the enzymatic activity was primarily due to the binding of a reactive tTEPA intermediate to the 2B1 apo-protein. Inactivation by tTEPA in the presence of 7-ethoxycou-marin, an alternate substrate, reduced the rate of inactivation of CYP2B1. Incubations with tTEPA and NADPH resulted in greater than 90 % loss in the 7-ethoxy-4-(trifluoromethyl)cou