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.


METHODS
Resistance to mitomycin C was induced by the long-term exposure of wild-type MGHU-1 cells to increasing concentrations (20-400 nmol/L) of mitomycin C. The cytotoxicity of mitomycin C or epirubicin was then compared in MGHU-1, MGHU-MMC (mitomycin C-resistant) and MGHU-1R (established MDR) cells, using the tetrazolium biomass assay. The expression of MDR-1 and -3 was investigated by the reverse transcriptase-polymerase chain reaction, 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-1R, and associated with a dramatic increase in the 50% inhibitory drug concentration (P < 0.001) for mitomycin C and epirubicin against controls. In MGHU-MMC, the overexpression of MDR-1 was three times greater than that of MDR-3. The cytotoxicity profile for both agents was very similar to that of MGHU-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 this methodology may allow patients to be identified who are unlikely to benefit from intravesical chemotherapy.
Hayes
M C
MC
Department of Urology, Southampton General Hospital, Southampton, UK.
Birch
B R
BR
Cooper
A J
AJ
Primrose
J N
JN
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000903:Antibiotics, Antineoplastic / Q000627:therapeutic use*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D016685:Mitomycin / Q000627:therapeutic use*; D014407:Tumor Cells, Cultured; D014571:Urologic Neoplasms / Q000188:drug therapy*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D016685:Mitomycin