INTERACTION OF 8-METHOXYPSORALEN AND NEAR-UV LIGHT CAUSES MUTATION AND CYTOTOXICITY IN MAMMALIAN CELLS

Abstract The interaction of near-UV light and a photosensitizer, 8-methoxypsoralen (8-MOP), was studied in the Chinese hamster ovary cell/hypoxanthine-guanine phosphoribosyl transferase system; cell survival (cloning efficiency) and mutation induction (resistance to 6-thioguanine) were quantified. Exposure of cells to either 8-MOP up to 20 μg/m l (93 μ M ) or near–UV light up to 40000 J/m² had no effect on either survival or mutation frequency. Preincubation of cells with 8–MOP from 5 to 120 min prior to irradiation with various fluences did not affect cell survival or mutation frequency. Survival decreased and mutation frequency increased linearly when either the 8-MOP concentration or fluence was increased while the other factor was held as a constant. Mutation frequency appears to show reciprocity relative to the product of 8-MOP concentration times fluence of near–UV light (μg/m l )·(J/m²)] throughout a range apparently limited by high cell lethality. The observed pooled data on mutation, f (x), as a function of (μg/m l )·(J/m²), x , fit a linear dose–response line, f (x) = (34.2 + 0.05 x ) × 10^-6. Cell survival, however, does not appear to exhibit such reciprocity.