FAILURE OF UVR DOSE RECIPROCITY FOR SKIN TUMORIGENESIS IN HAIRLESS MICE TREATED WITH 8-METHOXYPSORALEN

Abstract— 8-Methoxypsoralen (8-MOP) phototumorigenesis was studied in hairless albino mice irradiated with solar simulated radiation (SSR). Animals were exposed to three different daily doses of SSR after application of an oily vehicle with or without 8-MOP. Tumor production was dependent on daily SSR dose irrespective of topical treatment. The phototumorigenic potency of SSR was increased by the vehicle and to a much greater extent by inclusion of 8-MOP. Irrespective of topical treatment, a failure in dose reciprocity for tumorigenesis was demonstrated; in terms of cumulative SSR dose, the lower daily doses were more tumorigenic than the higher doses. This reciprocity failure in 8-MOP photosensitized mice is similar to that previously observed for UV-B phototumorigenesis. The relevance of these findings to therapeutic use of psoralens is discussed.