Cellular resistance to mitomycin C is associated with overexpression of MDR-1 in a urothelial cancer cell line (MGH-U1)

Objective To compare multidrug resistance (MDR)-1 and MDR-3 gene expression in a new urothelial cancer cell line (MGHU-1, with resistance to mitomycin C) against controls and the established (epirubicin-resistant) MDR clone, and to correlate MDR with cytotoxicity data. Materials and methods Resistance to mitomycin C was induced by the long-ter m exposure of wild-type MGHU-1 cells to increasing concentrations (20-400 n mol/L) of mitomycin C. The cytotoxicity of mitomycin C or epirubicin was th en compared in MGHU-1, MGHU-MMC (mitomycin C-resistant) and MGHU-1R (establ ished MDR) cells, using the tetrazolium biomass assay. The expression of MD R-1 and -3 was investigated by the reverse transcriptase-polymerase chain r eaction, using cDNA-specific primers after titration, and compared with DNA and negative controls. Results MDR-1 and -3 were significantly and equally overexpressed in MGHU-1 R, and associated with a dramatic increase in the 50% inhibitory drug conce ntration (P < 0.001) for mitomycin C and epirubicin against controls. In MG HU-MMC, the overexpression of MDR-1 was three times greater than that of MD R-3. The cytotoxicity profile for both agents was very similar to that of M GHU-1R. Trace amounts of MDR-1, but not MDR-3, were identified in the MGHU- 1 wild-type. Conclusions Urothelial cancer cell resistance to mitomycin C is associated with cross-resistance to epirubicin and overexpression of MDR-1, suggesting that mitomycin C falls within the MDR category. Clinical application of th is methodology may allow patients to be identified who are unlikely to bene fit from intravesical chemotherapy.