CHARACTERIZATION OF A HUMAN BLADDER-CANCER CELL-LINE SELECTED FOR RESISTANCE TO BMY-25067, A NOVEL ANALOG OF MITOMYCIN-C

This study describes characteristics of a human bladder cancer cell li ne, SCaBER/R, selected for resistance to a mitomycin C (MMC) analogue BMY 25067. The SCaBER/R cell line was isolated by repeated 24 h exposu res of the parental cells to 0.09 mu M BMY 25067 (IC90, 24 h drug expo sure) over a period of about 180 days. Approximately 2.2-foid higher c oncentration of BMY 25067 was required to kill 50% of the SCaBER/R cel l line compared with parental cells (P < 0.001). The IC20 and IC90 val ues for BMY 25067 were also significantly higher in the SCaBER/R cell line than in SCaBER. Unlike most MMC resistant cell lines, the SCaBER/ R cell line displayed a marked cross-resistance to 1,3-bis(2-chloroeth yl)-1-nitrosourea (BCNU) and lacked cross-resistance to cisplatin, dox orubicin or VP-16. The SCaBER/R cell line also displayed a marked cros s-resistance to the parent drug (MMC) and BMY 25282, another analogue of MMC. NADPH cytochrome P450 reductase activity, an enzyme implicated in bio-reductive activation of MMC, did not differ significantly in t hese cells. DT-diaphorase activity, another MMC activation enzyme, was significantly lower in the SCaBER/R cell line when compared to the SC aBER cells. These results suggest that relatively lower sensitivity of SCaBER/R cell line to MMC and BMY 25067 may result from impaired drug activation. Cellular levels of glutathione (GSH) and GSH-transferase (GST), which have been suggested to affect the cytotoxicity of MMC, we re comparable in SCaBER and SCaBER/R cell lines. BMY 25067 induced DNA interstrand cross-links (DNA-ISC) could not be detected in either of the cell lines even at drug concentrations which produced a significan t cell kill, These findings suggest that (a) cellular resistance to BM Y 25067 in the SCaBER/R cell line may be due to impaired drug activati on, and (b) the nature of the cytotoxic lesions produced by BMY 25067 may be different from that of MMC.