Safety and therapeutic effectiveness of selected psoralens in psoriasis

This review summarizes the most important facts regarding the clinical effectiveness of oral photochemotherapy for psoriasis with UV radiation at 320-400 nm (UVA) and selected furocoumarins. The most widely used compound is 8-methoxypsoralen (8-MOP); its effectiveness has been documented by many clinical trials. Oral 5-methoxypsoralen (5-MOP) has been evaluated as an alternative drug because it is less erythemogenic and thus reduces the danger of accidental over-exposure. It has been as effective as 8-MOP in clearing psoriasis, but the UVA doses required were considerably higher. Although oral 4,5',8-trimethylpsoralen does not clear psoriasis satisfactorily, excellent treatment results have been recorded when it was applied topically. The 3 drugs produce bifunctional adducts with DNA (cross-links), which may be of particular importance for mutagenesis and tumor formation. In an attempt to reduce possible oncogenic hazards, investigators are currently testing non-crosslinking furocoumarins for their therapeutic effectiveness. At present, these compounds are available for topical use only. 3-Carbethoxypsoralen has been reported to produce excellent treatment results by others but was ineffective in our clinical trials. Similarly disappointing was the application of 4,5'-dimethylangelicin and 5-methylangelicin. Although monofunctional compounds also inhibit cell proliferation in vitro, it appears that cross-linking is a prerequisite for the therapeutic success in psoriasis. The actual important of cross-links, however, remains to be clarified.(ABSTRACT TRUNCATED AT 250 WORDS)