EFFECT OF D,L-BUTHIONINE-S,R-SULFOXIMINE ON CYTO-TOXICITY AND DNA CROSS-LINKING INDUCED BY BIFUNCTIONAL DNA-REACTIVE CYTOSTATIC DRUGS IN HUMAN-MELANOMA CELLS

  • 1 January 1988
    • journal article
    • research article
    • Vol. 48  (1) , 19-26
Abstract
The effects of D,L-buthionine-S,R-sulfoximine (BSO) on cytotoxicity and DNA cross-linking induced by bifunctional DNA-reactive cytostatic agents in a human melanoma cell line (RPMI 8322) were investigated. RPMI 8322 cells were exposed to 0.01 mM BSO for 24 h, which resulted in a decrease in cellular glutathione to 14% without any reduction of cell proliferation of plating efficiency. BSO pretreatment significantly enhanced cytotoxicity of melphalan with a dose modification factor (DMF) of 3.4 and nitrogen mustard (HN2) (DMF 3.3). The increased cytotoxicity was paralleled by similar increases in DNA cross-linking (melphalan: DMF 2.2, HN2: DNF 2.5). A small but significant potentialation by BSO of cis-diamminedichloroplatinum(II) toxicity was seen (DMF 1.5), with a corresponding minor but significant increase in DNA cross-linking (DMF 1.1). Similarly, the potential of bischloroethylnitrosurea toxicity was small but significant (DMF 1.1), with no significant increase in DNA cross-linking (DMF 1.0). No effect of BSO pretreatment on the rate of removal of HN2-induced DNA cross-links was observed. Thus, the observed sensitization of RPMI 8322 cells to melphalan, HN2, cis-diamminedichloroplatinum (II), and bischloroethylnitrosourea was correlated to similar changes in drug-induced DNA cross-linking. Despite the increased cytotoxicity and DNA cross-linking BSO did not significantly increase the intracellular concentration of intact melphalan. These findings support the hypothesis that the potentiation of the cytotoxicity of bifunctional alkylating agents by BSO is due to an increased DNA cross-linking caused by a reduced intracelluar conjugation of drug with glutathione, which results in an increased binding of drug to DNA targets.