Regulatory Perspective on in Vitro Assays as Predictors of Phototoxicity and Photo Co-Carcinogenicity:

Drugs from a variety of chemical classes used for a wide range of therapeutic indications can be photosensitizers in humans. Several drugs are phototoxic in animal models as well; there are no nonclinical data for many. In vitro tests have been developed as predictors of phototoxicity and although they have been used as screens, none have replaced the in vivo tests done in rodents (usually mice or guinea pigs) since these have been good predictors of clinical phototoxicity. Some phototoxic drug classes are co-carcinogens with ultraviolet radiation (UVA and/or UVB) in hairless mice, specifically psoralens, retinoids, and fluo-roquinolones. Treatment with 8-methoxypsoralen and ultraviolet A radiation for psoriasis is also carcinogenic in humans. It has been suggested that in vitro photogenotoxicity assays using microorganisms or mammalian cells may be predictive of photo co-carcinogenicity. Some attractions of these in vitro assays, compared to the hairless mouse photo co-carcinogenicity assay, are their ge...