Celecoxib enhanced the sensitivity of cancer cells to anticancer drugs by inhibition of the expression of P-glycoprotein through a COX-2-independent manner.

The P-glycoprotein (p170, P-gp) encoded by human MDR1 gene functions as a pump to extrude anticancer drugs from cancer cells. Over-expression of p170 is closely related to primary and induced drug resistance phenotype of tumor cells. Recent studies have demonstrated that expression of cyclooxygenase-2 (COX-2) is positively correlated with the p170 level, suggesting a potential of COX-2 specific inhibitors in regulation of cytotoxicity of anticancer agents. Celecoxib is one of the specific inhibitors of COX-2 and has been widely used in clinic. However, its function in the response of cancer cells to anticancer drugs and the related mechanism are still waiting to be investigated. To explore the correlation of celecoxib and the p170-mediated drug resistance, the role of celecoxib in drug response of cancer cells was analyzed with flow cytometry, high performance liquid chromatography (HPLC), and colony formation experiments. Celecoxib (50 microM) was found to significantly enhance the sensitivity of MCF-7 and JAR/VP16 cells to tamoxifen and etoposide, respectively, by inhibition of p170 expression and increase in intracellular accumulation of the drugs. However, celecoxib did not affect pump function of p170. Enzyme activity and methylation analyses demonstrated that the inhibitory effect of celecoxib on p170 was independent on COX-2 but closely related to hypermethylation of MDR1 gene promoter. Our study suggested that celecoxib was a potential agent for enhancement of the sensitivity of cancer cells to anticancer drugs. It also provided a links between epigenetic change of MDR1 and drug response of cancer cells. (c) 2009 Wiley-Liss, Inc.