An animal model for screening drugs for antipsoriatic properties using hydroxyapatite to isolate DNA rapidly from the epidermis.

A new, rapid, simple and accurate procedure for extracting DNA from the epidermis is described involving hydroxyapatite. This compound has an unique property of high affinity for double stranded native DNA, but none for RNA and protein. The technique has been applied to a hairless mouse model for screening systemic and topical agents for cell inhibitory properties in proliferating epidermis for potential use in the therapy of psoriasis. Mitotic counts, autoradiography and a standard chloroform procedure for isolating DNA have confirmed the results obtained using hydroxyapatite column chromatography. In addition, compounds which are known to be effective in psoriasis, have been found to be effective in the system suggesting that it should be a good predictive screen for new therapies. Of several compounds screened for topical activity, cycloheximide has been found to be very effective in the system and preliminary clinical studies confirm its efficacy in psoriasis.