Inhibitory effect of flavonoids from Scutellariae Radix on human cytochrome P450 1A / 中国中药杂志

This study investigated the inhibitory effect of eight natural flavonoids in Chinese herb Scutellariae Radix on huamn cytochrome P450 1 A(CYP1 A), a key cancer chemo-preventive target. In this study, phenacetin was used as a probe substrate for CYP1 A, while human liver microsomes and recombinant human CYP1 A enzymes were used as enzyme sources. Liquid chromatography-tandem mass spectrometry was used to monitor the formation rates of acetaminophen, the O-deethylated metabolite of phenacetin. The dose-dependent inhibition curves were depicted based on the changes of the formation rates of acetaminophen, while the IC_(50) were determined. Inhibition kinetic analyses and docking simulations were used to investigate the inhibition modes and mechanism of wogonin(the most potent CYP1 A inhibitor in this herb), while the inhibition constants(K_i) of wogonin against both CYP1 A1 and CYP1 A2 were determined. Among all tested flavonoids, wogonin, 7-methoxyflavanone and oroxylin A displayed a strong inhibitory effect on CYP1 A(IC_(50)100 μmol·L~(-1)). Further investigations demonstrated that wogonin had a weak inhibitory effect on other human CYP enzymes, suggesting that it could be used as a lead compound for the development of specific inhibitors of CYP1 A. Furthermore, the inhibition kinetic analyses clearly demonstrated that wogonin could strongly inhibit phenacetin O-deethylation in both CYP1 A1 and CYP1 A2 in a competitive manner, with K_i values at 0.118 and 0.262 μmol·L~(-1), respectively. Molecular docking demonstrated that wogonin could strongly interact with CYP1 A1 and CYP1 A2 via hydrophobic and π-π interactions, as well as Ser120 and Ser116 in CYP1 A1 via hydrogen-bonding. In conclusion, this study found that some flavonoids in Scutellariae Radix displayed a strong inhibitory effect on CYP1 A, while wogonin is the most potent CYP1 A inhibitor with a relatively high selectivity towards CYP1 A over other human CYPs.

Inhibition of regorafenib against UDP-glucuronosyltransferases / 药学学报

This study was designed to investigate the inhibitory effects of regorafenib (REG) on the catalytic activities of 12 kinds of human UGT isoforms and human liver microsomes (HLM) in vitro. The broader potential of REG to perpetrate drug-drug interactions (DDI) arising from UGT enzyme inhibition is predicted by in vitro-vivo extrapolation (IV-IVE). Fifty mixed HLM and 12 kinds of recombinant UGTs were utilized as enzyme sources to evaluation the inhibitory effects of REG against UGTs. 4-Methylumbelliferone (4-MU) as a nonselective substrate of UGTs except for UGT1A4, N-(3-carboxypropyl)-4-hydroxy-1,8-napht-halimide (NCHN) and N-butyl-4-(4-hydroxyphenyl)-1,8-naphthalimide (NPHN) as the specific fluorescent substrate of UGT1A1, and trifluoperazine (TFP) as the specific substrate of UGT1A4. The half maximal inhibitory concentration (IC50) was calculated via the nonlinear regression analysis using Graphpad Prism 6.0, the inhibition kinetic types were selected and evaluated based on the intersection location of Lineweaver-Burk plot and Dixon plot, and Ki values were determined by the second plot of slopes. The potential DDI risk based on UGT1A1 inhibition was also evaluated through the in vitro parameters. The results demonstrated that REG displayed strong inhibitory effects against UGT1A1, 1A7, 1A9, and 2B7. The IC50 values were from 0.15 to 6.6 μmol·L-1 and Ki values from 0.027 to 14 μmol·L-1. The REG exerted competitive inhibition against UGT1A1-mediated 4-MU-O-glucuronidation and UGT1A1-mediated NPHN-O-glucuronidation, while the inhibition of NCHN-4-O-glucuronide by REG was suited to noncompetitive inhibition in both HLM and recombinant UGT1A1. Likewise, REG exhibited a mixed efficacy in inhibition of UGT1A7-, UGT1A9-, and UGT2B7-catalyzed 4-MU-O-glucuronidation. The AUC ratio of UGT1A1 specific substrates NPHN and NCHN can be increased by 101% to 302% and 13% to 109%, respectively. These results suggest that much caution should be exercised when REG is co-administered with UGT1A1 substrates.