Development of an in vitro test system with human skin cells for evaluation of phototoxicity

Photosensitizing compounds may cause severe skin reactions after appropriate light exposure. On the cellular level this cutaneous in vivo response can be demonstrated by an in vitro model system with adequate target cells of human skin. Normal keratinocytes and fibroblasts were used to establish a predictive assay for phototoxic compounds. To develop a sensitive, specific and easy-to-handle screening system we determined different viability and proliferation parameters, like neutral red (NR) uptake, MTT-reduction, kenacid blue (KB) test, [(3)H]thymidine incorporation and a fluorometric assay in response to UVA light after treatment with different classes of compounds. These experiments resulted in the selection of a final test pattern, which we used to screen 26 substances of different phototoxic potential in vivo. We found a qualitative correlation between the phototoxic response in vitro and phototoxicity reported in different test systems in vivo.