Photoinactivation of cultured skin fibroblasts by sublethal doses of 8-methoxypsoralen and long wave ultraviolet light.

Cultured guinea pig skin fibroblasts were treated with 8-methoxypsoralen (8-MOP) and UVA light. Determination of 3H-TdR-uptake as well as counting of the number of adherent cells was carried out 24 hr later. Incubation of fibroblasts with varying concentrations of 8-MOP (10(-4) to 10 microgram/ml) or 1 to 5 J/cm2 UVA alone showed no effect. When 8-MOP-photosensitization was followed by UVA a dose response was observed. This ranged over 3 orders of magnitude of the concentration of 8-MOP. Changes in irradiation energy produced a higher inhibition of 3H-TdR incorporation as compared to changes in 8-MOP concentrations. Using the same energy of UVA changes in which 3H-TdR uptake was inhibited by 50% showed no loss of plating activity. A fraction of these cells underwent DNA synthesis and division after reseeding. The results indicate that under the dose regimens currently used for the treatment of various skin disorders a proportion of the cells may become sublethally photoinactivated to undergo division. When reseeded these cells still are able to perform cellular functions such as spreading and attachment.