CHARACTERIZATION OF A HUMAN BLADDER-CANCER CELL-LINE SELECTED FOR RESISTANCE TO MITOMYCIN-C

This study describes characteristics of a human bladder cancer cell li ne J82/MMC that is 6-fold more resistant to mitomycin C (MMC) than the parental cells. The J82/MMC subline was isolated by repeated continuo us exposures of the J82/WT cells to increasing concentrations of MMC. The J82/MMC cell line showed (1) collateral sensitivity to taxol, 5-FU and topoisomerase II inhibitors; and (2) cross-resistance to cisplati n, melphalan and MMC analogues BMY 25282 and BMY 25067. Levels of two key MMC activation enzymes, NADPH cytochrome P450 reductase and DT-dia phorase, were significantly lower in J82/MMC cells compared with J82/W T, suggesting that lower sensitivity of J82/MMC cells to MMC may resul t from deficient drug activation. Further support is indicated by: 1) reduction in the differential in toxicity between the 2 cell lines by BMY 25282; and 2) a higher effect of DT-diaphorase inhibitor dicumarol on the wild-type cells compared with J82/MMC. Although glutathione (G SH) levels did not differ in these cells, a small but significant incr ease in GSH transferase (GST) activity was noticed in J82/MMC cells. G ST inhibitor ethacrynic acid significantly enhanced MMC cytotoxicity i n the J82/MMC cell line. A small but significant increase in the level of anti-oxidative enzyme catalase, but not GSH peroxidase, was also o bserved in J82/MMC cell line compared with J82/WT. Thus, the possibili ty that relativity lower sensitivity of J82/MMC cells to MMC may resul t from reduced oxygen radical generation cannot be ruled out. MMC-indu cted DNA interstrand cross-linking was markedly lower in the J82/MMC c ell line compared with J82/WT. Our results suggest that the MMC resist ance in the J82/MMC cell line may be multifactorial. (C) 1994 Wiley-Li ss, Inc.