SENSITIVITY TO CISPLATIN AND PLATINUM-CONTAINING COMPOUNDS OF SCHIZOSACCHAROMYCES-POMBE RAD MUTANTS

The role of genes that affect response to radiation in determining sen sitivity to platinum-containing compounds was studied using a panel of 23 strains of the yeast Schizosaccharomyces pombe. The radiation-hype rsensitive mutants all had the same genetic background and most of the m contained mutations that disabled either cell cycle checkpoints or D NA repair. The tested platinum compounds included cisplatin and two co mplexes containing diaminocyclohexane (oxaliplatin and tetraplatin), t wo ammine/cyclohexylamine complexes with different orientation of the leaving groups (JM216 and JM335) and a multinuclear platinum complex ( BBR 3464). The cytotoxic effect of the selected platinum complexes was evaluated by using a microtiter growth inhibition assay with a 48 hr exposure to drug. The mutants fell into three groups with respect to s ensitivity to cisplatin: four mutants (rad2, -7, -11, -15) exhibited m inimal change in sensitivity; fifteen mutants (rad4-6, -8-10, -12-14, -16-17, -19-21, and -22) were 5.1-21.7-fold hypersensitive; only rad1 and -3 mutants, defective in checkpoints, and rad18, defective in repa ir, displayed a marked hypersensitivity. None of the mutants demonstra ted appreciable change in sensitivity to JM216 presumably as a consequ ence of a lack of resistance of the wild-type strain, whereas a modera te increase in sensitivity to JM335 was observed for most of the mutan ts, and hypersensitivity to BBR3464 was observed only in rad1 and -3. No relevant changes in sensitivity to tetraplatin were observed. Most of the mutants, with the exception of rad2, -7, and -15, were hypersen sitive to oxaliplatin. These findings demonstrate that specific mutati ons have disparate effects on the profile of sensitivity to different members of the same class of cytotoxic agents, which provides genetic evidence that different mechanisms are involved in differential cytoto xicity induced by Pt compounds. The results also demonstrate the utili ty of such a panel of mutants, constructed on the same genetic backgro und, for detecting specific cellular response; presumably, this reflec ts the recognition or processing of specific DNA adducts. In conclusio n, because the rad1 and rad3 gene products are determinants of cellula r response to a large number of platinum-containing compounds, the pre sent results support a critical role of genes involved in cell cycle c ontrol in cellular sensitivity to these agents.