@article {Mao919, author = {Xu Mao and Jian Wang and Qian Wang and Lan Yang and Yilin Li and Hao Lin and Ying Peng and Jiang Zheng}, title = {Nitidine Chloride{\textendash}Induced CYP1 Enzyme Inhibition and Alteration of Estradiol Metabolism}, volume = {47}, number = {8}, pages = {919--927}, year = {2019}, doi = {10.1124/dmd.119.086892}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The cytochrome P450 (P450) 1 family is an important phase I enzyme involved in carcinogen activation. Nitidine chloride (NC) is a pharmacologically active alkaloid with polyaromatic hydrocarbon found in the roots of Zanthoxylum nitidum (Roxb.) DC, a traditional medicinal herb widely used in China. We examined the inhibitory effects of NC on CYP1A1, 1B1, and 1A2. NC significantly inhibited CYP1A1- and 1B1-catalyzed ethoxyresorufin O-deethylation activity (IC50 = 0.28 {\textpm} 0.06 and 0.32 {\textpm} 0.02 μM, respectively) in a concentration-dependent manner, but only showed slight inhibition of CYP1A2 activity (IC50 \> 50 μM). Kinetic analysis revealed that NC competitively inhibited CYP1B1 with a Ki value of 0.47 {\textpm} 0.05 μM, whereas NC caused a mixed type of inhibition on CYP1A1 with Ki and KI values of 0.14 {\textpm} 0.04 and 0.19 {\textpm} 0.09 μM, respectively. The observed enzyme inhibition neither required NADPH nor revealed time dependency. Molecular docking manifested the generation of strong hydrogen-bonding interactions of Ser116 in CYP1A1 and Ser127 in CYP1B1 with methoxy moiety of NC. Additionally, NC-induced alteration of estradiol (E2) metabolism was also investigated in the present study. Hydroxyestradiols, including 2-hydroxyestradiol [(2-OHE2) nontoxic] and 4-hydroxyestradiol [(4-OHE2) genotoxic] generated in recombinant enzyme incubation systems and cultured MCF-7 cells were analyzed, and NC was found to preferentially inhibit the nontoxic 2-hydroxylation activity of E2 mediated by CYP1A1. In conclusion, NC was a mixed type inhibitor of CYP1A1 and a competitive inhibitor of CYP1B1. The remarkable inhibition on E2 2-hydroxylation might increase the risk of 4-OHE2{\textendash}induced genotoxicity.SIGNIFICANCE STATEMENT CYP1 enzymes catalyze oxidative metabolism of a variety of compounds and are known to play a crucial role in the development of cancer. CYP1A1 and CYP1A2 are responsible for hydroxylation of estradiol (E2) at the C-2 position, resulting in the formation of 2-OHE2, which is proposed to be a detoxification pathway. However, CYP1B1-mediated hydroxylation of E2 at the C-4 position has been suggested to be a tumor initiator. The present study found that nitidine chloride is a mixed type inhibitor of CYP1A1 and a competitive inhibitor of CYP1B1. NC preferentially inhibited the nontoxic E2 2-hydroxylation pathway mediated by CYP1A1, which might increase the risk of 4-OHE2{\textendash}induced genotoxicity and cause severe drug-drug interactions.}, issn = {0090-9556}, URL = {https://dmd.aspetjournals.org/content/47/8/919}, eprint = {https://dmd.aspetjournals.org/content/47/8/919.full.pdf}, journal = {Drug Metabolism and Disposition} }