Photoactivated 8-methoxypsoralen (8-MOP) has been proven to be clinically effective for a number of denmatobogical conditions including lichen planus, mycosis fungoides, and psoniasis. 8-MOP forms two types of covalent photoproducts with DNA, monoadducts, and bifunctional adducts which cross link the two DNA strands. Angelicin is a congener of 8-MOP which forms only monoadducts. We have used the combined density and isotopic labeling technique to study repair replication in cultured human fibro blasts treated with either of these compounds and exposed to near-ultraviolet bight.In human dipboid fibroblasts (Wb-38), the time course of repair replication for both compounds is similar. Drug concentration and ultraviolet dose responses are also similar for 8-MOP and angelicin. No repair replication was stimulated by either compound in xenodemmapigmentosum cells from Complementation Group A (XP12BE). These results suggest that repair replication in response to 8-MOP is primarily a response to monoadducts and that the enzymatic pathway for this repair synthesis shares at least one step with the pathway for repair of pynimidine dimens. Cross-link persistence in treated cells was assayed by use of the single-strand-specifi
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