Survival and mutagenic responses of mitomycin C-sensitive mouse lymphoma cell mutants to other DNA cross-linking agents.

Mitomycin C-sensitive mutants MCN 151 (complementation group I) and MCE 50 (complementation group II) derived from mouse lymphoma L5178Y cells were found to be also highly sensitive to the lethal effects of other DNA cross-linking agents, such as photoaddition of 8-methoxypsoralen (8-MOP) and cis-diamminedichloroplatinum II (cis-DDP). They were less sensitive to the monofunctional derivative 3-carbethoxypsoralen (3-CPs) and to trans-DDP to trans-DDP than their bifunctional counterparts. Incorporation levels of labeled 8-MOP or 3-CPs in wild-type cells and 2 mutants were almost the same, indicating that the sensitivity is not caused by differential incorporation of the agents. The rates of photoinduced mutations to 6-thioguanine resistance in the mutants, per unit dose of 8-MOP, were about 4 times higher for MCN 151 and 3 times higher for MCE 50 than that in L5178Y cells. However, the rates of induced mutations per viable cells in the mutants were nearly equal to those in wild-type cells. Cross-link repair was compared between mutants and wild-type cells by using the alkaline sucrose-gradient sedimentation technique. The results show that normal cells and both mutants are able to incise the cross-linked DNA, which is the first step of cross-link repair.