Quantitative analysis of multidrug-resistance mdr1 gene expression in head and neck cancer by real-time RT-PCR

Progression of head and neck cancer is always associated with changes of gene expression profile. In this study, we characterized the expression of multidrug-resistance mdr1 gene, which may play a role in tumorigenesis and multidrug resistance in head and neck cancer. A TaqMan one-step RT-PCR with a linear range for quantification across at least a 5 log scale of concentration of mdr1 mRNA was designed to determine the level of mdr1 expression in 50 pairs of normal vs. malignant head and neck tissues. Both the absolute level of mdr1 mRNA in tumor (T) and the relative mdr1 expression between tumor and its normal counterpart (T/N) were measured and their associations with several clinical variables were analyzed. Among the clinical variables analyzed, only the clinical stage of tumor was found to be associated with mdr1 expression. The distribution of clinical stages differed significantly (P<0.01) among the 27 specimens that had a T/N>1, with 59.3%, 22.2%, 14.8% and 3.7% in stage IV, III, II, and I, respectively. In addition, 76% of stage IV and 75% of stage III tumors had a T/N>1 compared to 25% of stage II and 20% of stage 1 tumors (P=0.004). Multivariate logistic regression analysis also indicated a significant difference of mdr1 expression between the early (I and II) and advanced (III and IV) stages tumors. The adjusted odds ratios (95% confidence intervals) were 1.477 (1.084-2.012) and 1.001 (1.000-1.002) for T/N (P<0.05) and T (P<0.05) treated as continuous variables, and 15.521 (3.414-70.550) and 5.074 (1.154-22.311) for T/N (P<0.001) and T (P<0.05) treated as binary variables, respectively. Taken together, the data presented here indicated that real-time RT-PCR provides a quantitative way to monitor mdr1 gene expression. The differential expression of mdr1 between early and advanced stages of head and neck cancer may shed light on the process of tumorigenicity and offer clues to the planning of new treatments.