Analysis of MDR1 expression in normal and malignant endometrium by reverse transcription-polymerase chain reaction and immunohistochemistry

The purpose of this study was to quantitate the expression of human MDR1 mRNA levels in normal endometrium and in endometrial carcinoma and to determine the association of MDR1 levels with prognostic indicators. Endometrial samples from 43 postmenopausal patients with endometrial carcinoma and 38 patients (controls) with benign disease undergoing hysterectomy were snap-frozen. MDR1 levels were determined by quantitative reverse transcription-PCR (RT-PCR) and compared to sensitive and resistant cell lines. Immunohistochemistry was done with MM4.17, an anti-MDR1 antibody, on paraffin sections, and the results were compared to those obtained from RT-PCR. Data was analyzed using the Kruskal-Wallis and Bonferroni tests, setting the P value at 0.05. In both postmenopausal endometrial tissue and tumors, MDR1 expression was localized to the epithelial cell layer. Comparison of immunohistochemistry and RT-PCR results demonstrated a correlation of 80%. In control patients, MDR1 expression was significantly higher in postmenopausal endometrium (n = 15) than in the proliferative premenopausal endometrium (n = 15; P = 0.0024). MDR1 expression in all tumors was lower than that measured in the postmenopausal controls. Between each tumor group, there was no significant difference in the MDR1 levels observed. MDR1 expression was significantly lower in patients with high nuclear grade (n = 18) tumors when compared to patients with low nuclear grade (n = 14; P = 0.04) tumors. Comparison of MDR1 levels with multiple prognostic indicators for endometrial cancer was only significant for nuclear grade. The data indicate that MDR1 expression is not a major component of the drug resistance observed in primary endometrial tumors.