Liebsch, M., Traue, D., Barrabas, C., Spielmann, H., Uphill, P., Wilkins, S., McPherson, J., Wiemann, C., Kaufmann, T., Remmele, M., Holzhutter, H.G., Brantom, P., Aspin, P., and J.A. Southee. Prevalidation of the Epiderm^TM Skin Corrosivity Test. ATLA. 1999. 27: 350.

In 1996-1997, BASF, Huntingdon Life Sciences and ZEBET participated in ECVAM’s skin corrosivity validation study using the human skin model Skin^2TM. Since the production of Skin² was stopped by the end of 1996, the human epidermal EpiDerm^TM was chosen to undergo prevalidation according to ECVAM’s tiered prevalidation procedure. In phase I, ZEBET (laboratory 1) drafted a Standard Operating Procedure (SOP) and a project plan for the study. ZEBET's major task was a simplification of the time-course test protocol published by Perkins & Osborne in 1996. To evaluate the refined protocol and the prediction model, 50 chemicals were tested at ZEBET with 3-minute exposure. Statistical analysis revealed the predictive power was sufficient but the sensitivity as too low (71%), whereas specificity was very high (89%). In addition, ZEBET established acceptance criteria for negative and positive controls. ZEBET distributed a second draft of SOP, data recording software and documentation sheets, which allowed Good Laboratory Practice compliant quality assurance of each assay. Taking into account the enouraging results of phase I, it was decided to proceed to phase II. The main task in phase II was the production of sufficient data to assess reproducibility of the EpiDerm skin corrosivity test after transfer to laboratory 2 (Huntingdon Life Sciences). Four chemicals were used to establish the test at Huntingdon Life Sciences and six chemicals to assess reproducibility by testing each chemical at least four times, independently, in both laboratories. Statistical analysis revealed an excellent intralaboratory and interlaboratory reproducibility. In addition, ZEBET re-tested all chemicals of phase I classified non-corrosive (NC) after 3-minute exposure at extended exposure periods of 1 hour and 4 hours, revealing that test sensitivity could be increased by >10% if chemicals classified NC after 3 minutes of exposure were tested at 1 hour of exposure. Before phase III was started ZEBET drafted a refined final version of the SOP in which all chemicals had to be tested at 3-minute and 1-hour exposure. These two exposure times were included in the refined hierarchical prediction model. The refined method required new data recording software, which ZEBET developed and distributed with the final SOP. For the phase III blind trial, ECVAM selected 24 chemicals from the chemical set of the formal ECVAM Skin Corrosivity Validation Study. BIBRA International (UK) purchased, coded and distributed the chemicals to ZEBET, Huntingdon Life Sciences and BASF. Each chemical was tested twice independently and the data were submitted to Humboldt University (Berlin) for biometrical analysis, which revealed that the process of prevalidation had in fact improved the performance of the test. Without a negative effect on reproducibility, the refined method and PM resulted in a balanced mean prediction of 88% sensitivity and 86% specificity. In conclusion, the prevalidation exercise conducted with EpiDerm skin corrosivity test proved the applicability and usefulness of ECVAM's prevalidation scheme and revealed excellent predictivity of the EpiDerm skin corrosivity test for a wide spectrum of chemicals.