P-glycoprotein activity in renal clear cell carcinoma

Background: The mechanism by which renal cancer patients show poor response to chemotherapy has not been well understood. The aim of this study was to evaluate the functional activity of P-glycoprotein (P-gp) in renal clear cell carcinoma (RCCC) and its possible role in chemotherapy resistance. Methods: We studied 11 patients who underwent radical nephrectomy due to RCCC; from each patient we obtained a sample from the cancer tissue, and another from normal renal tissue. These biopsies were mechanically disaggregated to allow individual cells analysis. Cells were incubated with daunorubicin (a fluorescent drug extruded by P-gp) at 37°C and 4°C for 30 min. P-gp activity was analyzed using flow cytometry. Results were expressed as the percentage of cells with P-gp activity (i.e., low fluorescence). Results: The analysis of renal cells showed that there was no significant difference in size between normal and cancer cells; however there were clusters of cells with different granularities. We divided the cells according to their granularity. The proportion of cells capable of extruding daunorubicin was significantly higher on tumor cells than in normal renal cells independently of the cell granularity. Our results are congruent with those obtained when mRNA or immunohistochemical test were used. This is the first report quantifying the P-gp activity from fresh samples obtained from kidney cancer in humans. Conclusions: Percentage of cells extruding daunorubicin in RCCC is elevated, indicating that P-gp activity may contribute to multidrug resistance in RCCC.