New aspects of photogenotoxicity testing: Prevalidation of the photo-micronucieus test and the photo-comet assay
In the course of a collaborative study previously developed standard protocols for the Photo-micronucleustest and the Photo-Comet assay were evaluated at seven participating laboratories. Thirteen coded test chemicals were selected for the study based on their ability to absorb UV light. On the basis of published data eight were classified as photo-genotoxic (8-methoxypsoralen, chlorpromazine, lomefloxacin, ciprofloxacin, methylene blue, proflavine, dacarbazine, doxycycline) and five as non-photogenotoxic (three phototoxic: promazine, ketoprofen, acridine; two non-phototoxic: octylmethoxycinnamat, titanium dioxide) prior to the start of the study. Each compound was tested in two independent runs in both assays by 3-5 different laboratories using V79 cells.Good results were obtained for both test systems with respect to reproducibility within and between laboratories. Sensitivity in detecting photo-genotoxic properties of the test compound was high in the Photo-micronucleustest (98%) and somewhat lower in the Photo-Comet assay (76%). When assessing specificity both models seem to reach low levels at first sight since three phototoxic compounds classified as non-photo-genotoxic according to literature data showed predominantly positive findings. However, when looking into more detail it can be assumed that not in every case the available published data were adequate for a pre-study classification.In summary collected data suggest that the protocol used for the Photo-Comet assay and the Photo-micronucleustest were robust leading to reproducible data. Therefore, the ring trial described above can be considered as a reliable pre-validation study. Based on this experience validation of the test systems for the prediction of photo-genotoxicity and potential photo-carcinogenicity could be performed in the next step using the rules published by ECVAM (Hartung et al., 2004).
Brendler-Schwaab, S. / Kasper, P. / Aeby, P. / et al: New aspects of photogenotoxicity testing: Prevalidation of the photo-micronucieus test and the photo-comet assay. 2006.
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