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

Abstract

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/m 2 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/m 2 )] 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/m 2 ), 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.