Regulatory use of (Q)SARs in toxicological hazard assessment strategies

In 2001, the European Commission published a policy statement ("White Paper") on future chemicals regulation and risk reduction that proposed the use of non-animal test systems and tailor-made testing approaches, including (Q)SARs, to reduce financial costs and the number of test animals employed. The authors have compiled a database containing data submitted within the EU chemicals notification procedure. From these data, (Q)SARs for the prediction of local irritation/corrosion and/or sensitisation potential were developed and published. These (Q)SARs, together with an expert system supporting their use, will be submitted for official validation and application within regulatory hazard assessment strategies. The main features are: two sets of structural alerts for the prediction of skin sensitisation hazard classification as defined by the European risk phrase R43, comprising 15 rules for chemical substructures deemed to be sensitising by direct action with cells or proteins, and three rules for substructures acting indirectly, i.e., requiring biochemical transformation; a decision support system (DSS) for the prediction of skin and/or eye lesion potential built from information extracted from our database. This DSS combines SARs defining reactive chemical substructures relevant for local lesions to be classified, and QSARs for the prediction of the absence of such a potential. The role of the BfR database, and (Q)SARs derived from it, in the use of current and future (EU) testing strategies for irritation and sensitisation is discussed.

Animal testing and alternative approaches for the human health risk assessment under the proposed new European chemicals regulation

During the past 20 years the EU legislation for the notification of chemicals has focussed on new chemicals and at the same time failed to cover the evaluation of existing chemicals in Europe. Therefore, in a new EU chemicals policy (REACH, Registration, Evaluation and Authorization of Chemicals) the European Commission proposes to evaluate 30,000 chemicals within a period of 15 years. We are providing estimates of the testing requirements based on our personal experiences during the past 20 years. A realistic scenario based on an in-depth discussion of potential toxicological developments and an optimised "tailor-made" testing strategy shows that to meet the goals of the REACH policy, animal numbers may be significantly reduced below 10 million if industry would use in-house data from toxicity testing, which are confidential, if non-animal tests would be used, and if information from quantitative structure activity relationships (QSARs) would be applied in substance-tailored testing schemes. The procedures for evaluating the reproductive toxicity of chemicals have the strongest impact on the total number of animals bred for testing under REACH. We are assuming both an active collaboration with our colleagues in industry and substantial funding of the development and validation of advanced non-animal methods by the EU Commission, specifically in reproductive and developmental toxicity.

Optimisation of the EpiDerm test protocol for the upcoming ECVAM validation study on in vitro skin irritation tests

An ECVAM-funded prevalidation study (PV) was conducted during 1999 and 2000 to identify in vitro tests capable of reliably distinguishing between skin irritants (I) and non-irritants (NI) according to European Union risk phrases ("R38" or no classification). The tests evaluated were EpiDerm, EPISKIN, PREDISKIN, the non-perfused pig ear method, and the mouse skin integrity function test (SIFT). Whereas reproducibility of the two human skin model tests and SIFT was acceptable, none of the methods was deemed ready to enter a formal validation study due to their low predictivity. The ECVAM Skin Irritation Task Force therefore suggested improvements of protocols and prediction models for these tests. Furthermore, it was agreed that experience gained with the two human-skin models be shared, and a common protocol should be developed for EpiDerm and EPISKIN (Zuang et al., 2002). When we applied an improved EPISKIN protocol (Portes et al., 2002) to the EpiDerm model, an acceptable specificity (80%) was achieved, whereas the sensitivity (60%) was far too low. In 2003, the EPISKIN protocol was further refined by extension of the post-incubation period following chemical exposure. In the current study, we evaluated this EPISKIN refinement by applying it to EpiDerm. In addition, we developed technical improvements for the application of the test chemicals and rinsing procedure, which reduced the variability of results and increased the percentage of correct predictions. A set of twenty non-coded reference substances from the ECVAM prevalidation study phase III (Fentem et al., 2001) was tested with the final protocol in three independent runs. Both high sensitivity (80%) and high specificity (78%) were achieved, and the statistical probability of correct classifications was high, so that the test is now regarded ready for formal validation.

Validation successes: chemicals

The ECVAM validation concept, which was defined at two validation workshops held in Amden (Switzerland) in 1990 and 1994, and which takes into account the essential elements of prevalidation and biostatistically defined prediction models, has been officially accepted by European Union (EU) Member States and by the Federal regulatory agencies of the USA and the OECD. The ECVAM validation concept was introduced into the ongoing ECVAM/COLIPA validation study of in vitro phototoxicity tests, which ended successfully in 1998. The 3T3 neutral red uptake in vitro phototoxicity test was the first experimentally validated in vitro toxicity test recommended for regulatory purposes by the ECVAM Scientific Advisory Committee (ESAC). It was accepted by the EU into the legislation for chemicals in the year 2000. From 1996 to 1998, two in vitro skin corrosivity tests were successfully validated by ECVAM, and they were also officially accepted into the EU regulations for chemicals in the year 2000. Meanwhile, in 2002, the OECD Test Guidelines Programme is considering the worldwide acceptance of the validated in vitro phototoxicity and corrosivity tests. Finally, from 1997 to 2000, an ECVAM validation study on three in vitro embryotoxicity tests was successfully completed. Therefore, the three in vitro embryotoxicity tests, the whole embryo culture (WEC) test on rat embryos, the micromass (MM) test on limb bud cells of mouse embryos, and the embryonic stem cell test (EST) including a permanent embryonic mouse stem cell line, are considered for routine use in laboratories of the European pharmaceutical and chemicals industries.

Currently available in vitro methods used in the regulatory toxicology

About two decades ago in vitro mutagenicity tests were adopted as the first in vitro methods in regulatory toxicology. For reasons of animal welfare and better science, many validation studies of various in vitro methods were performed between 1985 and 1995 for their potential to replace the Draize eye irritation test. Albeit the fact that four in vitro methods (HET-CAM, BCOP, IRE, and ECE) have gained regulatory tolerance in Europe for the classification of severe eye irritants, the lessons learned mainly from these validation studies led to the definition of internationally harmonised OECD validation principles and acceptance criteria (Final Report of the OECD Workshop on Harmonization of Validation and Acceptance Criteria for Alternative Toxicological Tests Methods, 1996. OECD Publication Office, Paris, France). Application of these principles to prevalidation and validation studies, and additional special studies performed in Europe with the support of ECVAM, ended in the scientific validation of new in vitro methods for the prediction of skin corrosivity and phototoxicity. They were accepted for regulatory use in Europe and adopted on 8 June 2000 as test methods B. 40 and B. 41 of Annex V of Directive 67/548/EEC. In quite a different approach, European industry has submitted in-house validation data to support a Draft OECD Test Guideline for in vitro dermal absorption testing, which-after peer review and a long lasting international discussion-will now be adopted by the OECD. The increasing importance of regulatory measures derived from quantitative cytotoxicity tests, and some examples of regulatory accepted in vitro methods, where the specific purpose is restricted to a specific regulation (e.g. testing of medicinal products, or medical devices), are also addressed.

Follow-up to the ECVAM prevalidation study on in vitro tests for acute skin irritation. The European Centre for the Validation of Alternative Methods Skin Irritation Task Force report 2

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.

[Report on the ICCVAM workshop on in vitro methods for assessing acute systemic toxicity]

It was suggested in the ICCVAM workshop that the Register of Cytotoxicity (RC), using in vitro cytotoxicity data to predict the in vivo starting doses, should be implemented into acute toxicity testing as soon as possible. The validity of the in vitro cytotoxicity data to establish appropriate starting doses for acute toxicity testing will be assessed experimentally. Secondly, in order to replace the use of animals in acute lethality testing a formal validation will be conducted in which the ability to predict rodent LD50 values and toxicity classes from cytotoxicity data will be evaluated.

[Permanent embryonic mouse germ cell-lines, an in vitro alternative to in vivo germ cell mutagenicity tests]

Germ cell mutagenesis is required by the 7th amendment of the directive 67/548 EEC into the national regulations on existing chemicals. Officially accepted in vivo test systems for stage specific mutagenicity are the dominant lethal (DL) test and the specific locus test (SLT) in mice. An acceptable in vitro alternative designed to address germ cell mutagenesis and discriminate between male and female specific effects is not available at present. In order to offer a sensitive and predictive in vitro method to assess the genotoxic potential of chemical agents on male and female reproduction, we established primordial germ (PG) cell-derived permanent embryonic germ (EG) cell lines of the mouse (strain BALB/cJ). The differences in developmental sensitivity of the EG(3) cell line and differentiated fibroblast cells 3T3 were comparatively tested with cytotoxicity assay (MTT test ) and genotoxic studies (SCE-assay) under identical test conditions. The concentration-response curves reflected the female cell line EG(3) to be extremely sensitive concerning cytotoxic and genotoxic endpoints. Therefore this cell line was used to classify in vivo genotoxic and non-genotoxic test substances with different potential endpoints. Applying linear discriminant analysis three endpoints were identified for the correct classification (100%) of all test chemicals, namely the SCE(200) value (increase of 200% in the mean number of SCEs per metaphase spread) for EG(3) (3 hrs and 24 hrs assay) and the IC(5)0 value for EG(3) after 3 hrs of exposure to test chemicals.

Lessons learned from validation of in vitro toxicity test: from failure to acceptance into regulatory practice

As no scientific approach or regulatory guidelines existed for the experimental validation of in vitro toxicity tests, in 1990 a US/European validation workshop agreed in Amden (Switzerland) on a simple definition of the validation process. Several international validation studies failed, although they were conducted according to these recommendations. Taking into account the lessons learned from this experience, a second validation workshop was held by ECVAM in Amden in 1994 to develop a more precisely defined validation concept. Prevalidation and the development of biostatistically defined prediction models were added as essential elements to the validation process. In 1995/1996 the ECVAM validation procedure was officially accepted by EU member countries and at the international level by the US regulatory agencies and the OECD. The improved validation concept was immediately introduced into ongoing validation studies. In 1996 the ECVAM/COLIPA validation study of the in vitro phototoxicity test, which was conducted according to the ECVAM/OECD validation concept, was finished successfully and in 1998 a supporting study on UV-filter chemicals was undertaken. In 1998 the 3T3 NRU PT in vitro phototoxicity test was the first experimentally validated in vitro toxicity test that was recommended for regulatory purposes by ESAC, the ECVAM Scientific Advisory Committee, and by the DG ENV of the EU Commission. Meanwhile, two in vitro skin corrosivity tests have successfully been validated by ECVAM. Finally, in June 2000 the three experimentally validated tests were accepted by EU member states for regulatory purposes as the first in vitro toxicity tests. In addition, ECVAM has funded a successful validation study of three in vitro embryotoxicity tests, which was conducted in 12 European laboratories and finished in July 2000. The three tests validated in this study were the whole embryo culture (WEC) test applied to rat embryos, the micromass (MM) test employing primary cultures of dissociated mouse limb bud cells and the mouse embryonic stem cell test (EST). Examples will be given of successful validation studies during the past decade with particular reference to in vitro toxicity tests that were evaluated for regulatory purposes either by the US validation centre ICCVAM or ECVAM in the fields of sensitisation, phototoxicity and embryotoxicity

Permanent embryonic germ cell lines of BALB/cJ mice--an in vitro alternative for in vivo germ cell mutagenicity tests

To offer a sensitive and predictive in vitro method to assess germ cell mutagenicity, we established primordial germ (PG) cell-derived permanent female and male embryonic germ (EG) cell lines of the mouse (strain BALB/cJ). The differences in developmental sensitivity of EG cells and differentiated fibroblast cells of the mouse cell line 3T3 to genotoxicants were tested comparatively under identical test conditions. Cytotoxicity assay was measured by the MTT test and genotoxic effects were determined by sister chromatid exchanges (SCE) rates induced by standard reference mutagens. Both methods are used to assign the chemicals to two classes of in vivo reproductive toxicity, non- and strongly genotoxic to germ cells. Applying linear discriminant analysis, a biostatistical prediction model (PM) was developed for the female cell line EG(3). This procedure identified a single variable, the Ig(SCE(200)EG(3)) as the statistically significant concentration related increase of 200% in the mean number of SCEs per metaphase spread after 3 h of exposure to be sufficient for separation into the classes: non- and strongly genotoxic to germ cells. Applying this PM to the training set of five genotoxic and three non-genotoxic test chemicals, 100% correct classifications were obtained.

[Prediction of human lethal concentrations by cytotoxicity data from 50 MEIC chemicals]

Procedures for predicting human toxicity on the basis of cytotoxicity data for different chemicals are of current interest. The study was designed to clarify the possibility of predicting human toxicity by using the cytotoxicity values IC(50x) of the 50 MEIC chemicals listed in the Registry of Cytotoxicity (RC). All calculations with the data of cytotoxicity and in vivo toxicity were carried out uniformly by using standardised methods with the aim of comparing the results in the literature with each other. The following results were achieved: Firstly, the IC(50x) values in the RC are suited better for predicting human toxicity than IC(50) values determined in cell culture experiments with one cell type and one cytotoxic endpoint. This result is correct for the values of linear regression parameters as well as for the values of the prediction error (PE) defined by Ponsoda et al. (1997). Secondly, by using the geometrical mean of four lethal concentrations (LCx) - calculated from the tabulated lethal concentration (LC), lethal plasma concentration (LPC), clinical lethal concentration (CLC) and forensic lethal concentration (FLC) - the parameters for predicting the human toxicity were slightly improved. Moreover, these comparative examinations demonstrate that in all cases the cytotoxicity data are suited better for predicting acute animal toxicity than for predicting acute human toxicity. The results confirm, once more, the reliability and general validity of RC cytotoxicity data for examinations of different problems in cytotoxicology.

[ERGATT/ECVAM Workshop on Acceptance of Validated Alternative Methods: Amden III]

Since validated in vitro toxicity tests have so far not been accepted by regulators the third international ERGATT/ECVAM validation workshop was held from January 26-30, 1998, in Amden/Switzerland. Scientific and political reasons for a delay of the acceptance of alternative methods were identified in the areas of phototoxicity, skin penetration and skin corrosivity and strategies to promote the acceptance were suggested. The OECD will harmonise the formal of criteria for the regulatory acceptance of new experimentally validated tests and of established tests from industry for which in-house and literature data exist. In vitro tests for phototoxicity and skin penetration will be accepted shortly by the OECD. For skin corrosivity two in vitro tests will be put forward to the OECD later this year. The Amden III workshop suggests that, the same acceptance criteria must be used for animal and in vitro tests. Finally, the OECD should remove tests that cause pain and distress to test animals from the official OECD list of official test guidelines if validated alternative methods exist. When obsolete animal tests are taken from the list of official OECD test guidelines, they will not any longer be accepted at the international level. Thus, the third Amden workshop has contributed new concepts for the regulatory acceptance of alternative toxicity tests which are supported by regulators in Europe, the USA and the OECD.

[Reduction of the numbers of animals used for the classification of the acute oral toxicity of chemicals by taking into account cytotoxicity data from the Registry of Cytotoxicity]

Using cytotoxicity data a new classification procedure is introduced which will allow to allocate chemicals to the four toxicity classes for acute oral toxicity according to EU regulation. Simultaneously, the new procedure allows to reduce animals in experiments for determination these four toxicity classes. The cytotoxicity data estimated from in vitro cultivated mammalian cell lines were taken from the "Registry of Cytotoxicity" (RC) in which the mean IC50 (IC50x) of 347 chemicals are stored as well as the acute oral toxicity data (LD50) for rats and mice taken from NIOSH registry. As we have been used to calculate a standard regression line for predicting the dosage range of acute oral toxicity in the two species. The maximum, mean and minimum dosages of oral toxicity were predicted from the RC data and furthermore, these dosages were the basis for allocating chemicals into the four classes of acute oral toxicity defined by the EU. The accuracy for predicting the toxicity classes of the 347 chemicals registered in the RC in comparison to the toxicity classes of the corresponding NIOSH LD50 values amounts 80 percent to 88 percent. We have developed a tier testing strategy for the classification of chemicals into EU toxicity classes which takes into account the cytotoxicity data as predicted mean LD50 in connection with the protocol steps described in Acute Toxic Class (ATC) method. Compared with the ATC method the new combined RC-ATC procedure will allow to reduce animal numbers for allocating chemicals to the EU toxicity classes by about 30 percent. We suggest to validate the RC-ATC procedure in order to achieve regulatory acceptance at the international level.

[First results of an EC/COLIPA validation project of in vitro phototoxicity testing methods]

In a joint project six laboratories from the European cosmetics industry (COLIPA) as well as from FRAME (England) and ZEBET (Germany) are validating in vitro methods to be incorporated into new international guidelines for photoirritancy testing. During the first stage of the study it was attempted to select the most promising in vitro photoirritancy tests for further validation. Twenty chemicals with known photoirritation properties (12 phototoxins (PT), 4 non-PTs and 4 UV absorbing non-PTs) were tested under identical UV exposure conditions (5 J/cm2, UV-A sun simulator) in a standardized cytotoxicty assay using 3T3 fibroblasts (endpoint): Neutral red uptake, NRU). The chemicals were also tested with in vitro phototoxicity assays established in industrial laboratories, e.g. the photohaemolyses (Pape et al, 1993), histine oxidation, candida albicans (Johnson et al, 1986), and, furthermore two commercial tests (SOLATEX PItrade mark and Skin2trade mark). Data from the 3T3 NRU photoirritancy test, the red blood cell photohaemolysis test and the Skin2trade mark assay showed a better overall correlation to human in vivo data than results from the other tests. These simple assays therefore, seem very promising for further validation under blind conditions. The protocols of the other tests have to be improved and standardized to permit better interlaboratory comparison.

[History of the LAL-test: validation and regulatory acceptance]

Bacterial endotoxins gram-negative bacteria are the most relevant substances inducing hyperthermia in humans (pyrogens). Since endotoxins may contaminate pharmaceutical preparations during production process, purity is assured by monitoring the increase in body temperature of rabbits exposed to such preparations. This bioassay can be replaced by the LAL-test in which the clotting reaction of blood cells of the horseshoe crab limulus polyphemus is measured after contact with bacterial endotoxins. Although this reaction is significantly more sensitive to endotoxins than hyperthermia in rabbits, the LAL-test had to undergo 25-30 years of validation to achieve regulatory acceptance. Although endotoxin induced blood clotting in Limulus is quite similar to the same reaction in humans, acceptance of the assay as an alternative to testing in rabbits was delayed, since chemicals present in pharmaceutical preparations may interfere with the LAL clotting reaction. In addition, fever can be induced also by substances other than endotoxins. Therefore it has to be proven for each new preparation that the LAL-test can replace the rabbit pyrogen test in a case by case validation according to guidelines, as e.g. the German guideline, which was released in 1993. During the past decade some laboratories of the pharmaceutical industry in Germany were able to replace 95% of the rabbit pyrogen tests by the LAL-test without increasing the risk for humans.

[Development of a new in vitro test for dermal phototoxicity using a model of reconstituted human epidermis]

Results are reported using the human epidermis model (EpiDermtrade mark) in a test protocol that was adopted from the method developed by ZEBET for phototoxicity testing with the model Skin2. In the new phototoxicity test the cytotoxicity of test materials applied topically to EpiDermtrade mark is determined at five concentrations in the absence and presence of a non-cytotoxic dose of UVA and visible light (sun simulation). Cytotoxicity is determined one day after irradiation in the MTT assay. Experiments performed to optimise test conditions are presented. Using appropriate phototoxic and non-phototoxic test chemicals our results demonstrate that a reconstructed human epidermal model, e.g. EpiDermtrade mark, can be used in phototoxicity testing in the same way as a full skin model.

Application of the Three Rs Principle in the Compilation of “Technical Guidance Document in Support of Directive 98/8/EC Concerning the Placing of Biocidal Products on the Market, Part I, Guidance on Data Requirements for Active Substances and Biocidal Products”

In fulfilment of the aims of the European Union Biocidal Directive ( Directive 98/8/EC), Technical Guidance Documents are currently being compiled. Part I of these Technical Guidance Documents covers data requirements for active substances and biocidal products. The Three Rs principle has been applied in certain parts of the toxicity and ecotoxicity testing scheme for pesticides, such as testing for acute oral toxicity, skin and eye irritation, skin sensitisation, and dermal absorption. Further recommendations on how to proceed with regard to the continuing replacement, reduction and refinement of animal experiments in this field of regulatory testing are included for consideration. In this context, besides stressing the necessity to validate and accept further alternatives, emphasis is placed on providing the possibility of waiving unnecessary tests and on the continuous evaluation of whether certain tests are needed at all.

Eye Irritation Testing: The Way Forward. The Report and Recommendations of ECVAM Workshop 34

This is the report of the thirty-fourth of a series of workshops organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods which are of importance to the biosciences and which reduce, refine or replace the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures which would enable it to become well-informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organisation of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (1). The workshop on Eye Irritation Testing: The Way Forward was held in Egham, UK, on 15-17 June 1998, under the chairmanship of Michael Balls (ECVAM, Italy). The workshop had two aims, the first of which was to review some of the previous multi-laboratory validation studies on alternatives to the Draize eye test and assess why many promising alternative methods were not successful in these studies. The second aim was to discuss strategies for making progress toward the short-term reduction, refinement, and eventual replacement, of the Draize test, including: a new approach to the validation of in vitro tests for eye irritancy, based on the use of reference standards, which promises to overcome some of the problems encountered in previous studies; the use of stepwise testing strategies which reduce and refine the use of animals in eye irritation testing; the use of multivariate and other statistical techniques for the further analysis of data generated in previous validation studies; and a programme of research aimed at understanding the underlying mechanisms of eye irritation.

A Study on UV Filter Chemicals from Annex VII of European Union Directive 76/768/EEC, in the In Vitro 3T3 NRU Phototoxicity Test

In 1996, the Scientific Committee on Cosmetology of DGXXIV of the European Commission asked the European Centre for the Validation of Alternative Methods to test eight UV filter chemicals from the 1995 edition of Annex VII of Directive 76/768/EEC in a blind trial in the in vitro 3T3 cell neutral red uptake phototoxicity (3T3 NRU PT) test, which had been scientifically validated between 1992 and 1996. Since all the UV filter chemicals on the positive list of EU Directive 76/768/EEC have been shown not to be phototoxic in vivo in humans under use conditions, only negative effects would be expected in the 3T3 NRU PT test. To balance the number of positive and negative chemicals, ten phototoxic and ten non-phototoxic chemicals were tested under blind conditions in four laboratories. Moreover, to assess the optimum concentration range for testing, information was provided on appropriate solvents and on the solubility of the coded chemicals. In this study, the phototoxic potential of test chemicals was evaluated in a prediction model in which either the Photoirritation Factor (PIF) or the Mean Photo Effect (MPE) were determined. The results obtained with both PIF and MPE were highly reproducible in the four laboratories, and the correlation between in vitro and in vivo data was almost perfect. All the phototoxic test chemicals provided a positive result at concentrations of 1μ/ml, while nine of the ten non-phototoxic chemicals gave clear negative results, even at the highest test concentrations. One of the UV filter chemicals gave positive results in three of the four laboratories only at concentrations greater than 100μ/ml; the other laboratory correctly identified all 20 of the test chemicals. An analysis of the impact that exposure concentrations had on the performance of the test revealed that the optimum concentration range in the 3T3 NRU PT test for determining the phototoxic potential of chemicals is between 0.1μg/ml and 10μg/ml, and that false positive results can be obtained at concentrations greater than 100μg/ml. Therefore, the positive results obtained with some of the UV filter chemicals only at concentrations greater than 100μg/ml do not indicate a phototoxic potential in vivo. When this information was taken into account during calculation of the overall predictivity of the 3T3 NRU PT test in the present study, an almost perfect correlation of in vitro versus in vivo results was obtained (between 95% and 100%), when either PIF or MPE were used to predict the phototoxic potential. The management team and participants therefore conclude that the 3T3 NRU PT test is a valid test for correctly assessing the phototoxic potential of UV filter chemicals, if the defined concentration limits are taken into account.

IRAG working group 2. CAM-based assays. Interagency Regulatory Alternatives Group

CAM-based assays, in which test material is applied to the chorion allantoic membrane (CAM) of embryonated chicken eggs, were assessed as alternatives to the Draize eye irritation test. Two general types of CAM-based assays are currently in use, the HET-CAM test and the CAMVA assay. Evaluations were made of five data sets produced with three different modifications of the HET-CAM test and two data sets obtained with the same CAMVA protocol. Data sets consisted of 9-133 test chemicals, usually from the sponsor's product line, and also from a validation trial. Each data set and assay protocol were analysed for quality of data, purpose and proposed use of the assay, range of responses covered, range of test materials amenable, current use in safety and risk assessment both in-house and for regulatory purposes. Since the MMAS Draize score was not available for all in vivo data sets, the sigma MMMIS, which correlates well with the MMAS, was used instead. In vitro/in vivo correlations calculated with Pearson's linear coefficient ranged from r = 0.6 to r = 0.9 for six of seven data sets. Corneal opacity and inflammation of the iris showed the best correlation to in vitro data. Prediction rates were significantly improved when partial linear regression was used, and the predictivity of three different HET-CAM protocols was almost the same. HET-CAM assays showed the best prediction with surfactants and surfactant-based formulations, whereas the CAMVA assay provided the best performance with alcohols.