Effect of pretreatment with N-methyl-N-nitrosourea or streptozotocin on the cytotoxicity and the induction of sister chromatid exchanges in human and rodent brain tumor cells treated with chloroethylnitrosourea
Tokuda, K.
Hokkaido Journal of Medical Science 67(4): 462-474
1992
ISSN/ISBN: 0367-6102 PMID: 1427592 Document Number: 398233
Effects of pretreatment with N-methyl-N-nitrosourea (MNU) or streptozotocin (STZ) on cytotoxicity and induction of sister chromatid exchanges (SCE) in human and rodent brain tumor cells treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) or 1-(2-chloroethyl)-1-nitrosourea (CNU) were investigated. 9L-2 and SF-188 cells were more resistant to the cytotoxic effects of chloroethylnitrosourea than 9L and SF-126 cells. SF-295 cells were more resistant to the cytotoxic effects than SF-126, but more sensitive than SF-188 cells. Pretreatment of 9L-2 cells with MNU or STZ resulted in a dose-dependent increase in cytotoxicity and SCE induction by BCNU. Treatment with 1mM MNU or 1.5mM STZ completely reversed the cellular resistance of 9L-2 cells to BCNU but did not potentiate either cytotoxicity or SCE induction in 9L cells. Pretreatment of SF-188 and SF-295 cells with MNU or STZ resulted in a dose-dependent increase in cytotoxicity and SCE induction by CNU. Treatment with 500 microM MNU or 1.5mM STZ for SF-188 cells, and with 250 microM MNU or 1.5mM STZ for SF-295 cells completely reversed the cellular resistance to CNU. These results are consistent with the hypothesis that pretreatment with MNU or STZ inhibits O6-alkylguanine-DNA-alkyltransferase (O6-AT) and inhibition of the enzyme allows the formation of DNA interstrand cross-links resulting in increase in cytotoxicity and induction of SCE in resistant cells treated with chloroethylnitrosourea. In this regard, O6-AT plays an important role in determining the cytotoxicity and induction of SCE by chloroethylnitrosourea in both rodent and human brain tumor cells.