application of the human dermal model skin(2) ZK 1350 to phototoxicity and skin corrosivity testing.

The human three-dimensional in vitro model Skin(2) ZK 1350(TM) [Advanced Tissue Sciences (ATS), La Jolla, USA] was tested for two in vitro toxicology applications, prediction of phototoxicity and classification of skin corrosivity. For phototoxicity testing chemicals were applied topically for 1 or 24 hr followed by 30 min of irradiation with a non-irritating dose of UVA. Phototoxicity was assessed 24 hr later by comparing cytotoxicity of UVA-exposed and non-exposed tissue in the MTT assay. In a European EC/COLIPA in vitro phototoxicity validation trial with 20 test chemicals (11 phototoxic and nine non-phototoxic), the best result was obtained with the Skin(2) ZK 1350 assay in the 24-hr exposure protocol where nine of the 11 phototoxins were classified correctly both at ATS and ZEBET. 6-Methylcoumarin could only be identified as a phototoxin when applied through the medium to the dermis side of the skin model for 24 hr. All of the nine non-phototoxic chemicals were identified correctly with either 1- or 24-hr preincubation. To classify chemicals as corrosive to the skin with an in vitro assay, ZEBET and two other laboratories tested 50 chemicals under blind conditions in the Skin(2) ZK 1350 model within a European ECVAM validation trial. The results obtained with the ZK 1350 assay showed a satisfactory classification of skin corrosive/non-corrosive chemicals and a sufficient prediction of the three UN Packing Groups for corrosive chemicals. Predictions obtained at ZEBET with the Skin(2) ZK 1350 model (sensitivity: 64%, specificity: 76%; positive and negative predictive values: 68%) compared with a sensitivity of 81% and a specificity of 77% as mean values for the three laboratories testing the model.