Minor role of pregnane-x-receptor for acquired multidrug resistance in head and neck squamous cell carcinoma in vitro

Abstract

Purpose: Acquired multidrug resistance (MDR) has been linked to overexpression of drug-metabolising and transporting proteins mediated by pregnane-x-receptor (PXR). The aim of this work was to establish the relevance of PXR for MDR in head and neck squamous cell carcinoma (HNSCC). Methods: Using eight HNSCC cell lines, we determined the efficacy of paclitaxel, cisplatin and 5-fluorouracil (5-FU) via proliferation assays and determined the expression and activity of PXR through quantitative real-time polymerase chain reaction, western blotting and luciferase-based reporter gene assay. PXR knockdown approaches using shRNA-encoding vectors were applied to estimate the role of PXR for native MDR. Results: Drug resistance ranged between 5.2 and 620 nM for paclitaxel, varied between 4.5 and 58 μM for cisplatin, and varied between 1.1 and 5,467 μM for 5-FU. Lack of PXR mRNA expression was mostly accompanied by the absence of mRNA expression of cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp, ABCB1) expression. Neither mRNA nor protein expression of PXR correlated with drug resistance. However, PXR activity tended to correlate with IC50 values of paclitaxel (p = 0.08). Knockdown of PXR in one of the cell lines had a slight but not significant impact on paclitaxel efficacy compared to scrambled sequence control. Surprisingly, only in two cell lines, PXR activity was increased by the well-known inductor rifampicin. Conclusion: This study suggests a malfunctioning of PXR and thus a minor relevance for iatrogenic chemotherapy resistance in HNSCC.