prevalidation

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The ECVAM Prevalidation Study on the Use of EpiDerm for Skin Corrosivity Testing

Manfred Liebsch, Dieter Traue, Christa Barrabas, Horst Spielmann, Patricia Uphill, Susan Wilkins, Janet P. McPherson, Christiane Wiemann, Tanja Kaufmann, Martina Remmele and Hermann-Georg Holzhütter

In 1996 and 1997, ECVAM supported a formal validation study on in vitro methods for predicting skin corrosivity. Two of the in vitro tests included in the study employed human skin models, the Skin2 ZK1350 and EPISKIN models. In the ECVAM validation study, BASF, Huntingdon Life Sciences (HLS) and ZEBET tested the Skin2 human skin model, production of which ceased in October 1996, while the validation study was still in progress. Since both of the skin models had shown basic usefulness for corrosivity testing and, in particular, the EPISKIN corrosivity test had proved to be a scientifically valid test, the three laboratories decided to conduct a study to determine whether another commercially available human skin model, EpiDerm, could also be successfully used to predict skin corrosivity. The study was performed according to the ECVAM prevalidation scheme, to allow for refinement of the test protocol and the prediction model, as well as for independent assessment of the performance of the refined methodology in a final blind trial in the three laboratories. In phase I of the study, ZEBET (Laboratory 1) drafted a Standard Operating Procedure (SOP), including a prediction model (PM1), and the project plan for the study. It was a major task to simplify an existing EpiDerm test protocol, which used the time-course of cytotoxicity as its endpoint. To evaluate the predictivity of the simplified method, which used only a 3-minute exposure to test chemicals, 50 chemicals representing a wide spectrum of chemical entities were tested, revealing that the test sensitivity was too low (65%), whereas the specificity was very high (88%). In addition, acceptance criteria for the negative and positive controls were established. Before proceeding to the next phase of the study, ZEBET distributed a refined SOP, data-recording software and documentation sheets, which allowed Good Laboratory Practice (GLP)-compliant quality assurance for each assay. The main goal of phase II was to produce sufficient data to assess the reproducibility of the EpiDerm skin corrosivity test after transfer to Laboratory 2 (HLS). Repeated testing of several chemicals in both laboratories revealed excellent intralaboratory and interlaboratory reproducibility. In addition, chemicals classified as "non-corrosive" (NC) with a 3-minute exposure in phase I, were re-tested by ZEBET with extended exposure periods of 1 hour and 4 hours. The test sensitivity could be significantly increased, if chemicals classified NC with a 3- minute exposure were tested with a 1-hour exposure. Before proceeding to the final blind trial, a refined SOP was drafted, according to which all chemicals had to be tested with exposure times of 3 minutes and 1 hour, and data for these two exposure times were used in the refined hierarchical prediction model, PM2. In phase III, the blind trial, BASF (Laboratory 3) joined the study. ECVAM selected 24 chemicals from the test chemical set used in the ECVAM skin corrosivity validation study, and BIBRA International (UK) purchased, coded and distributed the chemicals. Each chemical was tested twice, independently, according to the principles of GLP, and coded data were submitted to the Humboldt University (Berlin, Germany) for biostatistical analysis. The analysis revealed that the final test protocol and the refined prediction model (PM2) provided a highly balanced prediction of 88% sensitivity and 86% specificity, which is regarded as the best predictivity an in vitro skin corrosivity test can be expected to achieve. In conclusion, the EpiDerm skin corrosivity test gives an excellent prediction for a wide spectrum of chemicals, and could be used within the context of the new Annex V (EU Dangerous Substances Directive) test method (human skin model assay) for skin corrosion. The results obtained were reproducible, both within and between laboratories, and showed that EpiDerm could be used for testing a wide range of chemicals (both liquids and solids), including organic acids and bases, neutral organics, inorganic acids and bases, electrophiles and phenols. The concordances between the skin corrosivity classifications derived from the in vitro data were very good, and the test was able to distinguish between corrosive and non-corrosive chemicals for all of the chemical types studied
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The Importance of the Prediction Model in the Validation of Alternative Tests

Andrew P. Worth and Michael Balls

An overview is presented of the validation process adopted by the European Centre for the Validation of Alternative Methods, with particular emphasis on the central role of the prediction model (PM). The development of an adequate PM is considered to be just as important as the development of an adequate test system, since the validity of an alternative test can only be established when both components (the test system and the PM) have successfully undergone validation. It is argued, however, that alternative tests and their associated PMs do not necessarily need to undergo validation at the same time, and that retrospective validation may be appropriate when a test system is found to be reliable, but the case for its relevance remains to be demonstrated. For an alternative test to be considered "scientifically valid", it is necessary for three conditions to be fulfilled, referred to here as the criteria for scientific relevance, predictive relevance, and reliability. A minimal set of criteria for the acceptance of any PM is defined, but it should be noted that required levels of predictive ability need to be established on a case-by-case basis, taking into account the inherent variability of the alternative and in vivo test data. Finally, in view of the growing shift in emphasis from the use of standalone alternative tests to alternative testing strategies, the importance of making the PM an integral part of the testing strategy is discussed.
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ECVAM’s Contributions to the Implementation of the Three Rs in the Production and Quality Control of Biologicals

Marlies Halder, Coenraad Hendriksen, Klaus Cussler and Michael Balls

A summary is presented of the activities initiated, and the progress achieved, between April 1993 and December 2001 in implementing the Three Rs in one of the main priority areas of the European Centre for the Validation of Alternative Methods (ECVAM) - the production and quality control of biologicals. These have included organising eight key workshops, and financial contributions to, and sponsorship of, relevant international workshops, symposia and conferences. Noteworthy activities include financial support and/or participation in a number of prevalidation and validation studies. These involved alternative methods for the batch potency testing of: human tetanus vaccines; human and veterinary tetanus antisera and immunoglobulin; rabies vaccines; Leptospira hardjo vaccines; Clostridium perfringens vaccines; and erysipelas vaccines. They also involved a cell culture test for specific toxicity testing of diphtheria toxoid vaccines. In addition, ECVAM funded a study on the use of humane endpoints for vaccine quality control tests involving severe suffering, such as the potency testing of erysipelas, rabies and pertussis vaccines. ECVAM has also contributed financially to the compilation of manuals and expert reports, and to training in test methods. Following the report of an ECVAM Task Force, ECVAM financially supported the prevalidation of some in vitro methods for the potency testing of a recombinant hormone. A proposal is presented for promotion of regulatory acceptance, and suggestions are made for possible future activities.
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Follow-up to the ECVAM Prevalidation Study on In Vitro Tests for Acute Skin Irritation

Valérie Zuang, Michael Balls, Philip A. Botham, Alain Coquette, Emanuela Corsini, Rodger D. Curren, Graham R. Elliott, Julia H. Fentem, Jon R. Heylings, Manfred Liebsch, Jesús Medina, Roland Roguet, Johannes J.M. van de Sandt, Christianne Wiemann and Andrew P. Worth1

The European Centre for the Validation of Alternative Methods (ECVAM) Skin Irritation Task Force was established in 1996, to review the status of the development and validation of alternative tests for skin irritation and corrosion, and to identify appropriate non-animal tests for predicting human skin irritation that were sufficiently well-developed to be prevalidated and validated by ECVAM. The EpiDerm™ method, based on a reconstituted human skin model, was proposed as being sufficiently well advanced to enter a prevalidation (PV) study. Based on a review of test protocols, prediction models (PMs), and data submitted by test developers on ten specified chemicals, with 20% sodium lauryl sulphate as a reference standard, the task force recommended the inclusion of four other tests: EPISKIN™ and PREDISKIN™, based on reconstituted human epidermis or on human skin; the non-perfused pig-ear test, based on pig skin; and
the skin integrity function test (SIFT), with ex vivo mouse skin. The prevalidation study on these methods was funded by ECVAM, and took place during 1999-2000. The outcome of the PV study was that none of the methods was ready to enter a formal validation study, and that the protocols and PMs of the methods had to be improved in order to increase their predictive abilities. Improved protocols and PMs for the EpiDerm and EPISKIN methods, the pig ear test, and the SIFT were presented at an extended Task Force meeting held in May 2001. It was agreed that, in the short term, the performance of the revised and harmonised EpiDerm and EPISKIN methods, as well as the modified SIFT, should be evaluated in a further study with a new set of 20 test chemicals. In addition, it was decided that the SIFT and the pig-ear test would be compared to see if common endpoints (transepidermal water loss, methyl green-pyronine stain) could be identified.
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Evaluation and Prevalidation of an Immunotoxicity Test Based on Human Whole-blood Cytokine Release

Ingrid Langezaal, Sebastian Hoffmann, Thomas Hartung, & Sandra Coecke

Immunotoxicology is a relatively new field in toxicology, and is one of emerging importance, because immunotoxicity appears to contribute to the development of cancer, autoimmune disorders, allergies and other diseases. At present, there is a lack of human cell-based immunotoxicity assays for predicting the toxicity of xenobiotics toward the immune system in a simple, fast, economical and reliable way. Existing immunotoxicity tests are mainly performed in animals, although species differences favour humanbased testing. Whole-blood cytokine release models have attracted increasing interest, and are broadly used for pharmacological in vitro and ex vivo studies, as well as for pyrogenicity testing. We have adapted those methods for immunotoxicity testing, to permit the potency testing of immunostimulants and immunosuppressants. Following stimulation with a lipopolysaccharide or staphylococcal enterotoxin B, monocytes and lymphocytes release interleukin-1β and interleukin-4, respectively. Thirty-one pharmaceutical compounds, with known effects on the immune system, were used to optimise and standardise the method, by analysing their effects on cytokine release. The in vitro results were expressed as IC50 values for immunosuppression, and SC4 (fourfold increase) values for immunostimulation, and compared with therapeutic serum concentrations of the compounds in patients, and in vivo LD50 values from animal studies. The in vitro results correlated well with the in vivo data, so the test appears to reflect immunomodulation. Results were reproducible (CV = 20 ± 5%), and the method could be transferred to another laboratory (r2 = 0.99). We therefore propose this method for further validation and for use in immunotoxicity testing strategies.
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Comparison and Validation of Novel Pyrogen Tests Based on the Human Fever Reaction

Thomas Hartung and Members of the Human(e) Pyrogen Test Study Group

The Limulus amoebocyte lysate (LAL) test has replaced about 80% of the use of the rabbit pyrogen test. Ideally, human-based in vitro tests are needed, to replace the remaining use of the rabbit test and the use of the LAL test. The progress of an EU-funded project is described, in which a number of in vitro tests based on the human fever reaction are passing through a prevalidation study on the way to evaluation in a formal validation study.
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ECVAM’s Activities in Validating Alternative Tests for Skin Corrosion and Irritation

Julia H. Fentem and Philip A. Botham

ECVAM has funded and managed validation studies on in vitro tests for skin corrosion, resulting in the validities of four in vitro tests being endorsed by the ECVAM Scientific Advisory Committee: the rat skin transcutaneous electrical resistance (TER) assay, two tests based on the use of commercial reconstituted human skin equivalents, EPISKIN™ and EpiDerm™, and another commerciallyproduced test, CORROSITEX®. In the European Union (EU), a new test method on skin corrosion (B.40), incorporating the rat skin TER and human skin model assays, was included in Annex V of Directive 67/548/EEC in mid-2000, thereby making the use of in vitro alternatives for skin corrosion testing of chemicals mandatory in the EU. At the recommendation of its Skin Irritation Task Force, ECVAM has funded prevalidation studies on five in vitro tests for acute skin irritation: EpiDerm, EPISKIN, PREDISKIN™, the pig-ear test, and the mouse-skin integrity function test (SIFT). However, none of the tests met the criteria (set by the Management Team for the studies) for inclusion in a large-scale formal validation study. Thus, to date, there are no validated in vitro tests for predicting the dermal irritancy of chemicals. Following further work on the EPISKIN, EpiDerm and SIFT test protocols and/or prediction models after the completion of the prevalidation studies, it appears that the modified tests could meet the performance criteria defined for progression to a validation study. This will now be assessed independently by the ECVAM Skin Irritation Task Force, with the objective of taking a decision before the end of 2002 on whether to conduct a formal validation study.
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ECVAM’s Activities on Biologicals

Marlies Halder, Michael Balls, Coenraad Hendriksen, and Klaus Cussler

This paper summarises key activities initiated and the progress achieved between April 1993 and June 2002 in implementing the Three Rs in one of ECVAM's priority areas - the production and quality control of biologicals. These have included: organising nine key workshops; financially supporting and/or participating in a number of prevalidation and/or validation studies; financial contributions and sponsorship to relevant international workshops, symposia and conferences; and financial support for the compilation of manuals and expert reports, and training in test methods. The paper complements the papers of Hendriksen et al. and Cussler et al. included in these proceedings.
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ECVAM’s Collaboration with Academia

Richard Clothier

The encouragement of ECVAM's connections with academia through direct collaboration and co-sponsored studentships has resulted in the successful achievement of higher degree qualifications for the young participants, and the development and promotion of alternative methods. So far, 26 students have been registered for higher degrees, 13 of which have been awarded so far, and 16 university departments in nine European countries have been directly involved. When other collaborations are included, the number of ECVAM's interactions with academic institutions rises to 33 departments in eleven countries, including the USA. In addition, through contracts awarded to academic institutions and other forms of collaboration, the prevalidation and validation of alternative methods have been progressed.
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