In Vitro To Estimate Diethylstilbestrol Cause DDI Possibilities

Objective:Aim to investigate the inhibitory effects of Diethylstilbestrol(DES) towards the five major cytochrome P450 (CYP) isoforms and evaluate its potential drug-drug interactions (DDI) due to inhibition of these CYP isoforms.Methods:Pooled human liver microsomes (HLMs) were used to incubate with different concentrations of DES (or positive inhibitors) and probe substrates for the five major cytochrome P450 (CYP)at 37oC. The formation of metabolites was detected by HPLC-UV and IC50 values were calculated according to the formation rates of metabolites at various concentrations of DES.Furthermore,using various concentrations of probe substrate (cover Km) and DES (cover IC50), the metabolic rates were determined. Lineweaver-Burk and Dixon plots were employed to evaluate the inhibitory type, and second plot of slopes from Lineweaver-Burk plot vs. DES concentrations was utilized to calculate the inhibition constants Ki. Single-point inactivation method was adapted to determine whether DES showed mechanism-based inhibition towards the five major cytochrome P450 (CYP). In vivo DDI magnitude was predicted using Ki and maximum plasma concentration of DES.Result: DES exhibited inhibitory effects on the activity of CYP3A4, CYP2C8, CYP2C9 and CYP 2E1, with IC50 values of 6μmol·L^-1,4.9μmol·L^-1, 3.6μmol·L^-1 and 30μmol·L^-1, respectively. CYP1A2, was not inhibited by Diethylstilbestrol.Both Lineweaver-Burk and Dixon plots demonstrated that inhibition of CYP3A4, CYP2C8,CYP2C9 and CYP 2E1by DES was best fit for competitive type, and Ki values were calculated to be 4.4μmol·L^-1 (CYP3A4),8.0μmol·L^-1 (CYP2C8)3.0μmol·L^-1 (CYP2C9)and 5.0μmol·L^-1(CYP2E1).DES showed no time-dependent inhibitory effects on CYP3A4, CYP2C8,CYP2C9 and CYP 2E1. Based on maximum plasma concentration of DES (Coax=18.7μmol·L^-1), the increase value in AUC was predicted to be 4.3(for CYP3A4) and 2.3(for CYP2C8),6.2 (for CYP2C9)and 3.7(for CYP2E1)。.Conclusions: DES showed strong inhibitory effects on CYP3A4, CYP2C8, CYP2C9 and CYP 2E1, which could induce significant drug-drug interaction even at clinical dose. Therefore, potential drug-drug interactions should be paid more attention when DES are is co-administrated with drugs mainly metabolized by CYP3A4, CYP2C8, CYP2C9 and CYP 2E1.