Pregnane X receptors regulate CYP2C8 and P-glycoprotein to impact on the resistance of NSCLC cells to Taxol

Cytochrome P450 2C8 (CYP2C8) is one of the enzymes that primarily participate in producing metabolisms of medications and P-glycoprotein (P-gp) has been regarded as one of the important molecules in chemotherapeutically induced multidrug resistance (MDR). In addition, the pregnane X receptor (PXR) is involved in regulating both CYP2C8 and P-gp. We aim to research the effect of PXR on Taxol-resistant non-small-cell lung cancer (NSCLC cells) via regulating CYP2C8 and P-gp. NSCLC cells were treated with SR12813, LY335979, or PXR siRNA. Cell counting kit (CCK-8) assay was used to detect cell vitality. Colony formation assay was used to observe cell proliferation. Western blotting, real-time polymerase chain reaction (RT-PCR), and immunofluorescence staining were conducted to analyze the expressions of PXR, CYP2C8, and P-gp. Taxol and its metabolic products were detected by high-performance liquid chromatography (HPLC). The expression of PXR in A549 cell line was higher than that in other cell lines. The accumulation of PXR was observed in the nucleus after cells were treated with SR12813. Besides, SR12813 induced higher expressions of CYP2C8 and P-gp proteins. We also discovered that pretreatment with SR12813 reversed the inhibition of cell viability and proliferation after the Taxol treatment in comparison to the SR12813 untreated group. Furthermore, the hydroxylation products of Taxol analyzed by HPLC were increased in comparison to the SR12813 untreated group, indicating that high expressions of CYP2C8 and P-gp enhanced the resistance of A549 cells to Taxol. For cells treated with PXR siRNA, cell viability, cell proliferation, and Taxol metabolites were significantly reduced after the Taxol treatment in comparison to the siRNA-negative group. The cell viability, cell proliferation, and Taxol metabolites were regulated by the expressions of PXR, P-gp, and CYP2C8. That is, PXR expression has an important effect on the resistance of NSCLC cells to Taxol via upregulating P-gp and CYP2C8.