Genotoxic effects and DNA photoadducts induced in Chinese hamster V79 cells by 5-methoxypsoralen and 8-methoxypsoralen.

The induction of lethal effects and 6-thioguanine-resistant (6-TGr) mutants were studied in Chinese hamster V79 cells after treatment with the two bifunctional furocoumarins 5- and 8-methoxypsoralens (5-MOP, 8-MOP) in the presence of 365-nm radiation (UVA). The in vivo DNA-photobinding capacity of these two compounds was measured and in parallel the cross-linking capacities of 5-MOP and 8-MOP were determined using the alkaline elution technique. The results show that 5-MOP plus UVA was about 2.5 times more effective than 8-MOP plus UVA for inhibiting cell survival and for inducing the same frequency of 6-TGr mutants (10(-4]. The total number of photoinduced lesions by 5-MOP plus UVA was about 6 times higher than that induced by 8-MOP plus UVA. However, the cross-linking capacities of 5-MOP and 8-MOP were found to be within the same range at equal doses of UVA. At equal number of DNA photoadducts produced, the lesions induced by 5-MOP appeared to be less genetically active than those induced by 8-MOP. The apparently weaker genotoxicity of 5-MOP-induced lesions is likely to be due to the induction of a lower proportion of cross-links by 5-MOP at a given number of photoadducts.