THE INTERNATIONAL EU COLIPA IN-VITRO PHOTOTOXICITY VALIDATION-STUDY -RESULTS OF PHASE-II (BLIND TRIAL) - PART 1 - THE 3T3 NRU PHOTOTOXICITY TEST/

To date, no standardized international guideline for the testing of ch emicals for phototoxic potential has been accepted for regulatory purp oses. In 1991, the European Commission (EC), represented initially by the Directorate General XI and later by ECVAM (The European Centre for the Validation of Alternative Methods) and COLIPA (the European Cosme tic, Toiletry and Perfumery Association), agreed to establish a joint EU/COLIPA programme on the development and validation of ill vitro pho totoxicity tests. The first phase (phase I, 1992-93) was designed as a prevalidation study, to identify in vitro test procedures and test pr otocols for a formal validation trial under blind conditions. In the s econd phase (phase II, 1994-95), the formal validation study, the most promising in vitro phototoxicity tests were validated with 30 careful ly selected test chemicals in 11 laboratories in a blind trial. The 3T 3 mouse fibroblast neutral red uptake phototoxicity test (3T3 NRU PT) was performed as a core test in nine laboratories, since it provided t he best results in phase I of the study. The purpose of phase II was t o confirm the reliability and relevance of the ii? vitro\ tests for pr edicting phototoxic effects and for identifying phototoxic chemicals. In phase II the phototoxic potential of test chemicals in the 3T3 NRU PT test was either assessed by determining the phototoxicity factor (P IF) by using a cut-off value of 5 as in phase I of the study, or by de termining the mean photo effect (MPE) by using a cut-off value of 0.1, as recently proposed by Holzhutter (1997). Results obtained with both approaches in the 3T3 NRU PT test in phase II were reproducible in th e nine laboratories, and the correlation between in vitro and in vivo data was very high. Therefore, ECVAM and COLIPA conclude from this for mal validation trial under blind conditions that the 3T3 NRU PT test i s a scientifically validated in vitro test which is ready to be consid ered for regulatory purposes for assessing the phototoxic potential of chemicals. A draft OECD Guideline for ''In Vitro Phototoxicity Testin g'', incorporating the standard protocol of the 3T3 NRU PT test, will be submitted to the OECD test guidelines programme in due course. (C) 1998 Elsevier Science Ltd. All rights reserved.