A TIERED STRATEGY FOR IN VITRO PHOTOTOXICITY TESTING.

Of the materials used to demonstrate the value of the 3-D Skin Assay (in supporting and interpreting 3T3 NRU PT results), all of those predicted phototoxic in the 3T3 NRU PT were confirmed phototoxic in the 3-D Skin Assay, with the exception of one (material coded 10). This material was clearly defined as phototoxic to 3T3 cells at concentrations above 1000 g/ml. At this concentration level (and above), the rate of false positive results in this assay is increased. All materials predicted non-phototoxic in the 3T3 NRU PT were confirmed non-phototoxic in the 3-D Skin Assay. Of those materials that did not give a clear phototoxic/non-phototoxic result in the 3T3 NRU PT, two (Mercaptobenzoxazole and the material coded 04) resulted in a non-phototoxic result in the 3-D Skin Assay and one (material coded 11) was confirmed phototoxic in the 3-D Skin Assay. Of the 23 materials assessed using the tiered testing strategy, the 3-D Skin Assay gave the same prediction of phototoxic potential for 19 materials as in the 3T3 NRU PT (i.e. 83% accuracy). Of those three chemicals which gave an uncertain or borderline* phototoxic result in the 3T3 NRU PT, two classified as non-phototoxic in the 3-D Skin Assay. These materials are unlikely, therefore, to be human phototoxins because human skin models are more sensitive than human skin in vivo. The other chemical which gave an uncertain/borderline* phototoxic result in the 3T3 NRU PT was confirmed phototoxic in the 3-D Skin Assay. In conclusion, used as part of a tiered testing strategy for predicting phototoxic potential, the 3-D Human Reconstituted Skin Model assay is beneficial in many ways: A better mimic of the in vivo situation than the 3T3 NRU PT, and can allow potency comparisons with benchmark materials. Ingredients and formulations can be tested (solubility is not a limiting factor). It can confirm a positive/negative/borderline result from the 3T3 NRU PT, therefore assisting the interpretation of initial results. * A borderline result is defined as a PIF falling between 2 and 5. The Draft OECD Guideline states that a PIF >2 and

3-D Phototoxicity test, 3-D Reconstituted Human Skin Model Assay (3-D Skin Assay), 3T3 NRU PT, 8-methosypsoralen, Absorbance , Acridine, free base, Anthracene, Bergamot oil FCF-free, Chlorpromazine HCI, Coenzyme Q10, EpiDerm, Gamma oryzanol, MTT, MTT ET-50 tissue viability assay, MTT assay, Mercaptobenzoxazole, Musk ambrette, Non phototoxic, OECD, Octyl methoxcyinnamate, Photo irritation factor , Phototoxic , Phototoxic potential, Phototoxicity, Phototoxicity testing, Phototoxins, Rose bengal, Spectrophotometrically, Tiered testing

8-methosypsoraien, Acridine, free base, Anthracene, Bergamot oil FCF-free, Chlorpromazine HCI, Coenzyme Q10, Ferulic acid, Gamma Oryzanol, Mercaptobenzoxazole, Musk ambrette, Octylmethoxcyinnamate, Rose bengal, UVA/B