PT - JOURNAL ARTICLE AU - Jie Chen AU - Xiao-Xia Yang AU - Min Huang AU - Ze-Ping Hu AU - Ming He AU - Wei Duan AU - Eli Chan AU - Fwu-Shan Sheu AU - Xiao Chen AU - Shu-Feng Zhou TI - Small Interfering RNA-Mediated Silencing of Cytochrome P450 3A4 Gene AID - 10.1124/dmd.106.009837 DP - 2006 Sep 01 TA - Drug Metabolism and Disposition PG - 1650--1657 VI - 34 IP - 9 4099 - http://dmd.aspetjournals.org/content/34/9/1650.short 4100 - http://dmd.aspetjournals.org/content/34/9/1650.full SO - Drug Metab Dispos2006 Sep 01; 34 AB - RNA interference (RNAi) is a specific and powerful tool used to manipulate gene expression and study gene function. The cytochrome P450 3A4 (CYP3A4) can metabolize more than 50% of drugs. In the present study, we investigated whether vector-expressed small interfering RNAs (siRNAs) altered the CYP3A4 expression and function using the Chinese hamster cell line (V79) overexpressing CYP3A4 (CHL-3A4). Three different siRNA oligonucleotides (3A4I, 3A4II, and 3A4III) were designed and tested for their ability to interfere with CYP3A4 gene expression. Our study demonstrated that transient transfection of CHL-3A4 cells with the 3A4III siRNAs, but not 3A4I and II, significantly reduced CYP3A4 mRNA levels by 65% and protein expression levels by 75%. All these siRNAs did not affect the expression of CYP3A5 at both mRNA and protein levels in V79 cells overexpressing CYP3A5. Transfection of CHL-3A4 cells with 3A4III siRNAs significantly diminished the cytotoxicity of two CYP3A4 substrate drugs, cyclophosphamide and ifosfamide, in CHL-3A4 cells, with the IC50 increased from 55 to 210 μM to >1000 μM. Nifedipine at 5.78, 14.44, and 28.88 μM was significantly (P < 0.01) depleted by approximately 100, 40, and 22%, respectively, in S9 fractions from CHL-3A4 cells compared with parental CHL-pIC19h cells. In addition, transfection of the CHL-3A4 cells with vectors expressing the 3A4III siRNAs almost completely inhibited CYP3A4-mediated nifedipine metabolism. This study demonstrated, for the first time, the specific suppression of CYP3A4 expression and function using vector-based RNAi technique. The use of RNAi is a promising tool for the study of cytochrome P450 family function. The American Society for Pharmacology and Experimental Therapeutics