Sugiyama, M., Itagaki, H., Katsumura, Y., and S. Kato. Validation of the Neutral Red Uptake Phototoxicity Method Using Three Cell Lines. ATLA. 1999. 27: 355.

Many in vitro methods for predicting phototoxicity have been reported. The EU/COLIPA project on in vitro phototoxicity testing validated several of them. Based on the results of this validation study, the OECD draft guideline recommends the 3T3 mouse fibroblast neutral red uptake phototoxicity (3T3 NRU PT) test as a promising alternative. In this paper, we report the use of normal human epidermal keratinocytes and normal human skin fibroblasts for in vitro phototoxicity testing, using essentially the same protocol described in the OECD guideline, to compare the results with those using Balb/c 3T3 fibroblasts. Twenty-three chemicals (of which 9 were phototoxic and 14 were non-phototoxic in vivo in guinea-pigs) were tested and the phototoxic potential of test chemicals was assessed by determining the photoirritation factor (PIF) using a cut-off value of 5. For 17 chemicals (74%), results were reproduced in all three cell lines. The sensitivity, specificity, positive predicting value and negative predicting value for the assay in the three cell lines were 67-78%, 57-86%, 54-67% and 5-80%, respectively. The correlation between the in vitro and the in vivo studies were relatively high in all of the cell lines, but false negative results were observed for the same two or three chemicals. These results suggest that there is not much difference as far as safety assessment is concerned when the 3T3 NRU PT test employed with the three cell lines reported here.