This study describes characteristics of a mitomycin C (MMC)-resistant human bladder cancer cell line, )82/MMC-2, which was established by repeated in vitro exposures of a 6-fold MMC-resistant variant (J82lMMC) to 18 nM MMC. A 9.6-fold higher concentration of MMC was required to kill 50% of the )82/MMC-2 sub-line compared with parental cells ()82/WT). NADPH cytochrome P450 reductase and DT-diaphorase activities were significantly lower in J82/MMC-2 cells compared with J82/WT, suggesting that reduced sensitivity of )82/MMC-2 cells to MMC resulted from impaired drug activation. Consistent with this hypothesis, the formation of MMC-alkylating metabolites was significantly lower in )82/MMC-2 cells compared with J82iWT. Furthermore, DT-diaphorase activity in J82/MMC-2 cells was significantly lower compared with the 6-fold MMCresistant variant. Glutathione (GSH) levels were comparable in all 3 cell lines. Although GSH transferase (GST) activity was significantly higher in the )82/MMC-2 cells compared with )82/WT, this enzyme activity did not differ between 6-and 9.6-fold MMC-resistant variants. Whereas DNA polymerase Q mRNA expression was comparable in these cell lines, levels of DNA ligase I mRNA were slightly lower in both MMC-resistant variants relative to )82/WT. However, the DNA polymerase p mRNA level was markedly higher in the J82/MMC-2 cell line compared with either )82/WT or )82/MMC. Thus, emergence of a higher level of resistance to MMC in J82/MMC-2 cells compared with J82/MMC may be attributed to (i) impaired drug activation through further reduction in DT-diaphorase activity and (ii) enhanced DNA repair through over-expression of DNA polymerase p.o 1996 Wiley-Liss, Inc.Mitomycin C (MMC), a bioreductive alkylating agent, has demonstrated activity against various malignancies, including bladder cancer (Crooke and Bradner, 1976). However, the clinical usefulness of MMC may be limited at least in part due to drug resistance (Moertel et al., 1968; Wilson et al., 1987). Several different mechanisms have been proposed to account for tumor cell resistance to MMC, including impaired drug activation due to down-regulation of an MMC bioactivation enzyme(s) (Hoban et al., 1990; Pan et al., 1992;Xu et al., 1994a), reduced drug accumulation (Dorr et al., 1987;Shibata et al., 1995), decreased MMC-induced oxygen radical formation (Dusre et al., 1990), enhanced glutathione (GSH)/GSH transferase (GST)-mediated drug inactivation Singh et al., 1992; Xu et al., 19946) and increased DNA repair (Dulhanty et al., 1989).We previously reported characterization of a human bladder cancer cell line (J82/MMC) exhibiting about 6.0-fold more resistance to MMC compared with parental cells ( Xu et al., 1994a). The J82iMMC sub-line was established by repeated continuous exposures of J82/WT cells to increasing concentrations of MMC (9-18 nM) over a period of about 10 months. Previous studies from our laboratory have suggested that cellular resistance to MMC in the J82/MMC cell line may be manifested by multiple mechanisms, including impaired...
This study was undertaken to elucidate the mechanism(s) of cross-resistance to cisplatin (CDDP) in a mitomycin C (MMC)-resistant human bladder cancer cell line, J82/MMC. The J82/MMC cell line displayed 2- to 3-fold cross-resistance to CDDP and carboplatin when compared to the parental J82/WT cells. Drug uptake studies revealed that cross-resistance to CDDP in the J82/MMC cell line was independent of reduced platinum accumulation. The J82/MMC cell line exhibited approximately a 1.5-fold resistance to cadmium chloride, an indicator for increased metallothionein (MT) content, when compared to the J82/WT cells. Northern blot analysis showed a 2.7-fold higher level of MT-IIA mRNA in the J82/MMC cell line compared with J82/WT. We have reported previously that, whereas glutathione (GSH) level is comparable in these cells, GSH transferase (GST) activity is significantly higher in the J82/MMC cell line compared with J82/WT. Results of the present study showed that the elevated GST activity in the J82/MMC cell line was due to an over-expression of pi-type GST protein. Although buthionine-S,R-sulfoximine (BSO)-induced GSH depletion significantly enhanced CDDP cytotoxicity in both cell lines, the magnitude of potentiation was markedly higher in J82/MMC cells (about 2.1-fold) relative to J82/WT (about 1.6-fold). Our results suggest that cross-resistance to CDDP in the J82/MMC cell line may be due to alterations in cellular thiols.
This study was undertaken to elucidate the mechanism(s) of potentiation of cisplatin (CDDP) cytotoxicity by interferon alpha-2a (IFN alpha-2a) in human squamous carcinoma cell lines SCC-25 and SCC-4. IFN alpha-2a treatment significantly increased the cytotoxicity of CDDP in both cell lines in a dose-dependent manner. In SCC-25 cells, the cytotoxicity of CDDP was increased by about 2- and 4-fold, respectively, by treating the cells with 400 and 800 IU/ml IFN alpha-2a. Sensitivity of SCC-4 cells to CDDP was increased by about 3- and 7-fold, respectively, by 400 and 800 IU/ml IFN alpha-2a treatment. Drug uptake experiments revealed approximately 1.4- to 5-fold higher platinum accumulation in IFN alpha-2a-treated cells as compared to respective controls. Cellular levels of glutathione (GSH) and GSH transferase, which have been suggested to be important determinants of tumor cell sensitivity to CDDP, were not altered by IFN alpha-2a treatment in either of the cell lines. Northern blot analysis showed a moderate increase (about 30-40%) in the level of MT-IIA mRNA by IFN alpha-2a treatment in these cells. Our results suggest that IFN alpha-2a-mediated sensitization of SCC-25 and SCC-4 cell lines to CDDP in vitro may be due to an increase in intracellular platinum accumulation.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.