An animal model for screening topical and systemic drugs for potential use in the treatment of psoriasis.

A new hairless mouse model using ultraviolet light to stimulate increased epidermal cell turnover and hyperplasia and thus simulate psoriasis has been designed so that drugs may be tested both topically and systemically for possible therapeutic value in this disease. Two methods of determining drug antimitotic activity have been used, the mitotic index and the extraction of epidermal DNA and the determination of the radioactivity of the sample. Results show that 2% 5-fluorouracil in propylene glycol and 2% nitrogen mustard in water topically and cyclophosphamide systemically, which are drugs known to be effective in psoriasis, significantly reduce the mitotic index. DNA synthesis is similarly decreased by the latter two drugs. The effect of the topical agents is shown to be local and not systemic. Cyclophosphamide, which is ineffective topically in psoriasis, is ineffective in the model.