The isolation and genetic analysis of V79-derived etoposide sensitive Chinese hamster cell mutants: two new complementation groups of etoposide sensitive mutants

Abstract

Using a replica plating microwell method, three Chinese hamster V79-derived cell lines, designated ETO1, ETO2 and ETO3, which exhibit hypersensitivity to the non-intercalating topoisomerase II inhibitor etoposide have been isolated. Mutant lines ETO2 and ETO3 are cross-sensitive to the topoisomerase II inhibitors adriamycin and streptonigrin; however, neither mutant is sensitive to the topoisomerase I inhibitor camptothecin, the bifunctional alkylating agent mitomycin C, nor hydrogen peroxide. In contrast, ETO1 is cross-sensitive to camptothecin but displays only slight sensitivity to adriamycin, streptonigrin and hydrogen peroxide, and is not sensitive to mitomycin C. It has been established through extensive cell fusion studies that all three mutants are genetically distinct, and that ETO2 and ETO3 genetically complement all other known etoposide-sensitive Chinese hamster cell mutants (i.e., irs1, XR-1, xrs1, V3, BLM2, ADR1, ADR3, ADR4 and ADR5) thus defining two new complementation groups of etoposide sensitive mutants. Interestingly, the hybrids created by the fusion irs2TOR (thioguanine and ouabain resistant)×ETO1 and the reciprocal cross ETO1TOR×irs2 both exhibited a response to camptothecin intermediate with respect to V79 and ETO1. It has been hypothesised that this partial complementation may be the result of intragenic complementation and that both ETO1 and irs2 result from mutations in the gene XRCC8. This study indicates that cellular responses to topoisomerase II inhibitors are complex and hypersensitivity may result from mutations in many different genes.