The inter-laboratory validation study of EpiSensA for predicting skin sensitization potential.

The Epidermal Sensitization Assay (EpiSensA) is a reconstructed human epidermis (RhE)-based gene expression assay for predicting the skin sensitization potential of chemicals. Since the RhE model is covered by a stratified stratum corneum, various kinds of test chemicals, including lipophilic ones and pre-/pro-haptens, can be tested with a route of exposure akin to an in vivo assay and human exposure. This article presents the results of a formally managed validation study of the EpiSensA that was carried out by three participating laboratories. The purpose of this validation study was to assess transferability of the EpiSensA to new laboratories along with its within- (WLR) and between-laboratory reproducibility (BLR). The validation study was organized into two independent stages. As demonstrated during the first stage, where three sensitizers and one non-sensitizer were correctly predicted by all participating laboratories, the EpiSensA was successfully transferred to all three participating laboratories. For Phase I of the second stage, each participating laboratory performed three experiments with an identical set of 15 coded test chemicals resulting in WLR of 93.3%, 93.3%, and 86.7%, respectively. Furthermore, when the results from the 15 test chemicals were combined with those of the additional 12 chemicals tested in Phase II of the second stage, the BLR for 27 test chemicals was 88.9%. Moreover, the predictive capacity among the three laboratories showed 92.6% sensitivity, 63.0% specificity, 82.7% accuracy, and 77.8% balanced accuracy based on murine local lymph node assay (LLNA) results. Overall, this validation study concluded that EpiSensA is easily transferable and sufficiently robust for assessing the skin sensitization potential of chemicals.

Inter-laboratory performance of ICE histopathology scoring to identify UN GHS Category 1 surfactants and non-extreme pH detergents.

The inter-laboratory performance of Isolated Chicken Eye (ICE) histopathology scoring was assessed for predicting EU CLP/UN GHS Cat. 1 surfactants. Furthermore, the predictive capacity of ICE histopathology was evaluated for the combined dataset of surfactants and existing data for non-extreme pH (2 < pH < 11.5) detergents. Use of ICE histopathology led to increased sensitivity compared to the ICE test method alone for surfactants. When combined with the existing dataset of detergents, use of histopathology in addition to the standard ICE test method decreased the false negative rates from 64% (14/22) to 27% (6/22); increased accuracy from 53% (16/30) to 77% (23/30); and led to acceptable level of false positives (from 0/8 to 1/8 (12.5%). Moreover, good reproducibility of ICE histopathology predictions conducted on the same slides was found between pathologists and peer-reviewers from three independent laboratories (10/12 or 83%) and over time. Use of ICE histopathology was therefore found suitable to predict EU CLP/UN GHS Cat. 1 surfactants and non-extreme pH detergents. In addition, appropriate reproducibility of ICE histopathology was found, provided that i) an internal peer-review system was in place; ii) original slides were assessed to enable evaluation of three dimensional effects; and iii) appropriate training and proficiency appraisal were conducted.

One science-driven approach for the regulatory implementation of alternative methods: A multi-sector perspective.

EU regulations call for the use of alternative methods to animal testing. During the last decade, an increasing number of alternative approaches have been formally adopted. In parallel, new 3Rs-relevant technologies and mechanistic approaches have increasingly contributed to hazard identification and risk assessment evolution. In this changing landscape, an EPAA meeting reviewed the challenges that different industry sectors face in the implementation of alternative methods following a science-driven approach. Although clear progress was acknowledged in animal testing reduction and refinement thanks to an integration of scientifically robust approaches, the following challenges were identified: i) further characterization of toxicity pathways; ii) development of assays covering current scientific gaps, iii) better characterization of links between in vitro readouts and outcome in the target species; iv) better definition of alternative method applicability domains, and v) appropriate implementation of the available approaches. For areas having regulatory adopted alternative methods (e.g., vaccine batch testing), harmonised acceptance across geographical regions was considered critical for broader application. Overall, the main constraints to the application of non-animal alternatives are the still existing gaps in scientific knowledge and technological limitations. The science-driven identification of most appropriate methods is key for furthering a multi-sectorial decrease in animal testing.

Introduction.

Alternative approaches to animal testing are gaining momentum with an increasing number of test methods obtaining international acceptance, thanks in large part to the validation efforts conducted on these assays. The principles and process of validation were first established in the 1990s in Europe and USA, and further gained international recognition ensuring the broader acceptance of alternative test methods at a regulatory level. If these principles were successful in pioneering the regulatory acceptance of alternative methods for less complex endpoints, an evolution of concepts is needed to embrace emerging technologies and the increased complexity of endpoints. Innovative concepts and approaches of scientific validation can help to ensure the continued regulatory and international acceptance of novel alternative methods and technologies for toxicity testing such as human-based in vitro models derived from induced pluripotent stem cells and significant advances in bioengineering. This chapter provides a historical overview of the establishment and evolution of the principles of the scientific validation of alternative methods for toxicity testing as well as the challenges and opportunities for adapting those principles to keep pace with scientific progress whilst ensuring human safety and best serve the needs of society.

Evolving the Principles and Practice of Validation for New Alternative Approaches to Toxicity Testing.

Validation is essential for the translation of newly developed alternative approaches to animal testing into tools and solutions suitable for regulatory applications. Formal approaches to validation have emerged over the past 20 years or so and although they have helped greatly to progress the field, it is essential that the principles and practice underpinning validation continue to evolve to keep pace with scientific progress. The modular approach to validation should be exploited to encourage more innovation and flexibility in study design and to increase efficiency in filling data gaps. With the focus now on integrated approaches to testing and assessment that are based on toxicological knowledge captured as adverse outcome pathways, and which incorporate the latest in vitro and computational methods, validation needs to adapt to ensure it adds value rather than hinders progress. Validation needs to be pursued both at the method level, to characterise the performance of in vitro methods in relation their ability to detect any association of a chemical with a particular pathway or key toxicological event, and at the methodological level, to assess how integrated approaches can predict toxicological endpoints relevant for regulatory decision making. To facilitate this, more emphasis needs to be given to the development of performance standards that can be applied to classes of methods and integrated approaches that provide similar information. Moreover, the challenge of selecting the right reference chemicals to support validation needs to be addressed more systematically, consistently and in a manner that better reflects the state of the science. Above all however, validation requires true partnership between the development and user communities of alternative methods and the appropriate investment of resources.

International Harmonization and Cooperation in the Validation of Alternative Methods.

The development and validation of scientific alternatives to animal testing is important not only from an ethical perspective (implementation of 3Rs), but also to improve safety assessment decision making with the use of mechanistic information of higher relevance to humans. To be effective in these efforts, it is however imperative that validation centres, industry, regulatory bodies, academia and other interested parties ensure a strong international cooperation, cross-sector collaboration and intense communication in the design, execution, and peer review of validation studies. Such an approach is critical to achieve harmonized and more transparent approaches to method validation, peer-review and recommendation, which will ultimately expedite the international acceptance of valid alternative methods or strategies by regulatory authorities and their implementation and use by stakeholders. It also allows achieving greater efficiency and effectiveness by avoiding duplication of effort and leveraging limited resources. In view of achieving these goals, the International Cooperation on Alternative Test Methods (ICATM) was established in 2009 by validation centres from Europe, USA, Canada and Japan. ICATM was later joined by Korea in 2011 and currently also counts with Brazil and China as observers. This chapter describes the existing differences across world regions and major efforts carried out for achieving consistent international cooperation and harmonization in the validation and adoption of alternative approaches to animal testing.

Brazilian Center for the Validation of Alternative Methods (BraCVAM) and the process of validation in Brazil.

The need for the creation of a Brazilian centre for the validation of alternative methods was recognised in 2008, and members of academia, industry and existing international validation centres immediately engaged with the idea. In 2012, co-operation between the Oswaldo Cruz Foundation (FIOCRUZ) and the Brazilian Health Surveillance Agency (ANVISA) instigated the establishment of the Brazilian Center for the Validation of Alternative Methods (BraCVAM), which was officially launched in 2013. The Brazilian validation process follows OECD Guidance Document No. 34, where BraCVAM functions as the focal point to identify and/or receive requests from parties interested in submitting tests for validation. BraCVAM then informs the Brazilian National Network on Alternative Methods (RENaMA) of promising assays, which helps with prioritisation and contributes to the validation studies of selected assays. A Validation Management Group supervises the validation study, and the results obtained are peer-reviewed by an ad hoc Scientific Review Committee, organised under the auspices of BraCVAM. Based on the peer-review outcome, BraCVAM will prepare recommendations on the validated test method, which will be sent to the National Council for the Control of Animal Experimentation (CONCEA). CONCEA is in charge of the regulatory adoption of all validated test methods in Brazil, following an open public consultation.

Retrospective analysis of the Draize test for serious eye damage/eye irritation: importance of understanding the in vivo endpoints under UN GHS/EU CLP for the development and evaluation of in vitro test methods.

For more than two decades, scientists have been trying to replace the regulatory in vivo Draize eye test by in vitro methods, but so far only partial replacement has been achieved. In order to better understand the reasons for this, historical in vivo rabbit data were analysed in detail and resampled with the purpose of (1) revealing which of the in vivo endpoints are most important in driving United Nations Globally Harmonized System/European Union Regulation on Classification, Labelling and Packaging (UN GHS/EU CLP) classification for serious eye damage/eye irritation and (2) evaluating the method's within-test variability for proposing acceptable and justifiable target values of sensitivity and specificity for alternative methods and their combinations in testing strategies. Among the Cat 1 chemicals evaluated, 36-65 % (depending on the database) were classified based only on persistence of effects, with the remaining being classified mostly based on severe corneal effects. Iritis was found to rarely drive the classification (<4 % of both Cat 1 and Cat 2 chemicals). The two most important endpoints driving Cat 2 classification are conjunctiva redness (75-81 %) and corneal opacity (54-75 %). The resampling analyses demonstrated an overall probability of at least 11 % that chemicals classified as Cat 1 by the Draize eye test could be equally identified as Cat 2 and of about 12 % for Cat 2 chemicals to be equally identified as No Cat. On the other hand, the over-classification error for No Cat and Cat 2 was negligible (<1 %), which strongly suggests a high over-predictive power of the Draize eye test. Moreover, our analyses of the classification drivers suggest a critical revision of the UN GHS/EU CLP decision criteria for the classification of chemicals based on Draize eye test data, in particular Cat 1 based only on persistence of conjunctiva effects or corneal opacity scores of 4. In order to successfully replace the regulatory in vivo Draize eye test, it will be important to recognise these uncertainties and to have in vitro tools to address the most important in vivo endpoints identified in this paper.

Risks for animal and human health related to the presence of polychlorinated naphthalenes (PCNs) in feed and food.

EFSA was asked for a scientific opinion on the risks for animal and human health related to the presence of polychlorinated naphthalenes (PCNs) in feed and food. The assessment focused on hexaCNs due to very limited data on other PCN congeners. For hexaCNs in feed, 217 analytical results were used to estimate dietary exposures for food-producing and non-food-producing animals; however, a risk characterisation could not be performed because none of the toxicological studies allowed identification of reference points. The oral repeated dose toxicity studies performed in rats with a hexaCN mixture containing all 10 hexaCNs indicated that the critical target was the haematological system. A BMDL20 of 0.05 mg/kg body weight (bw) per day was identified for a considerable decrease in the platelet count. For hexaCNs in food, 2317 analytical results were used to estimate dietary exposures across dietary surveys and age groups. The highest exposure ranged from 0.91 to 29.8 pg/kg bw per day in general population and from 220 to 559 pg/kg bw per day for breast-fed infants with the highest consumption of breast milk. Applying a margin of exposure (MOE) approach, the estimated MOEs for the high dietary exposures ranged from 1,700,000 to 55,000,000 for the general population and from 90,000 to 230,000 for breast-fed infants with the highest consumption of breast milk. These MOEs are far above the minimum MOE of 2000 that does not raise a health concern. Taking account of the uncertainties affecting the assessment, the Panel concluded with at least 99% certainty that dietary exposure to hexaCNs does not raise a health concern for any of the population groups considered. Due to major limitations in the available data, no assessment was possible for genotoxic effects or for health risks of PCNs other than hexaCNs.

Regulatory assessment of in vitro skin corrosion and irritation data within the European framework: Workshop recommendations.

Validated in vitro methods for skin corrosion and irritation were adopted by the OECD and by the European Union during the last decade. In the EU, Switzerland and countries adopting the EU legislation, these assays may allow the full replacement of animal testing for identifying and classifying compounds as skin corrosives, skin irritants, and non irritants. In order to develop harmonised recommendations on the use of in vitro data for regulatory assessment purposes within the European framework, a workshop was organized by the Swiss Federal Office of Public Health together with ECVAM and the BfR. It comprised stakeholders from various European countries involved in the process from in vitro testing to the regulatory assessment of in vitro data. Discussions addressed the following questions: (1) the information requirements considered useful for regulatory assessment; (2) the applicability of in vitro skin corrosion data to assign the corrosive subcategories as implemented by the EU Classification, Labelling and Packaging Regulation; (3) the applicability of testing strategies for determining skin corrosion and irritation hazards; and (4) the applicability of the adopted in vitro assays to test mixtures, preparations and dilutions. Overall, a number of agreements and recommendations were achieved in order to clarify and facilitate the assessment and use of in vitro data from regulatory accepted methods, and ultimately help regulators and scientists facing with the new in vitro approaches to evaluate skin irritation and corrosion hazards and risks without animal data.

ECVAM and new technologies for toxicity testing.

The development of alternative empirical (testing) and non-empirical (non-testing) methods to traditional toxicological tests for complex human health effects is a tremendous task. Toxicants may potentially interfere with a vast number of physiological mechanisms thereby causing disturbances on various levels of complexity of human physiology. Only a limited number of mechanisms relevant for toxicity ('pathways' of toxicity) have been identified with certainty so far and, presumably, many more mechanisms by which toxicants cause adverse effects remain to be identified. Recapitulating in empirical model systems (i.e., in vitro test systems) all those relevant physiological mechanisms prone to be disturbed by toxicants and relevant for causing the toxicity effect in question poses an enormous challenge. First, the mechanism(s) of action of toxicants in relation to the most relevant adverse effects of a specific human health endpoint need to be identified. Subsequently, these mechanisms need to be modeled in reductionist test systems that allow assessing whether an unknown substance may operate via a specific (array of) mechanism(s). Ideally, such test systems should be relevant for the species of interest, i.e., based on human cells or modeling mechanisms present in humans. Since much of our understanding about toxicity mechanisms is based on studies using animal model systems (i.e., experimental animals or animal-derived cells), designing test systems that model mechanisms relevant for the human situation may be limited by the lack of relevant information from basic research. New technologies from molecular biology and cell biology, as well as progress in tissue engineering, imaging techniques and automated testing platforms hold the promise to alleviate some of the traditional difficulties associated with improving toxicity testing for complex endpoints. Such new technologies are expected (1) to accelerate the identification of toxicity pathways with human relevance that need to be modeled in test methods for toxicity testing (2) to enable the reconstruction of reductionist test systems modeling at a reduced level of complexity the target system/organ of interest (e.g., through tissue engineering, use of human-derived cell lines and stem cells etc.), (3) to allow the measurement of specific mechanisms relevant for a given health endpoint in such test methods (e.g., through gene and protein expression, changes in metabolites, receptor activation, changes in neural activity etc.), (4) to allow to measure toxicity mechanisms at higher throughput rates through the use of automated testing. In this chapter, we discuss the potential impact of new technologies on the development, optimization and use of empirical testing methods, grouped according to important toxicological endpoints. We highlight, from an ECVAM perspective, the areas of topical toxicity, skin absorption, reproductive and developmental toxicity, carcinogenicity/genotoxicity, sensitization, hematopoeisis and toxicokinetics and discuss strategic developments including ECVAM's database service on alternative methods. Neither the areas of toxicity discussed nor the highlighted new technologies represent comprehensive listings which would be an impossible endeavor in the context of a book chapter. However, we feel that these areas are of utmost importance and we predict that new technologies are likely to contribute significantly to test development in these fields. We summarize which new technologies are expected to contribute to the development of new alternative testing methods over the next few years and point out current and planned ECVAM projects for each of these areas.

Application of evidence-based methods to construct mechanism-driven chemical assessment frameworks.

The workshop titled "Application of evidence-based methods to construct mechanism-driven chemical assessment frameworks" was co-organized by the Evidence-based Toxicology Collaboration and the European Food Safety Authority (EFSA) and hosted by EFSA at its headquarters in Parma, Italy on October 2 and 3, 2019. The goal was to explore integration of systematic review with mechanistic evidence evaluation. Participants were invited to work on concrete products to advance the exploration of how evidence-based approaches can support the development and application of adverse outcome pathways (AOP) in chemical risk assessment. The workshop discussions were centered around three related themes: 1) assessing certainty in AOPs, 2) literature-based AOP development, and 3) integrating certainty in AOPs and non-animal evidence into decision frameworks. Several challenges, mostly related to methodology, were identified and largely determined the workshop recommendations. The workshop recommendations included the comparison and potential alignment of processes used to develop AOP and systematic review methodology, including the translation of vocabulary of evidence-based methods to AOP and vice versa, the development and improvement of evidence mapping and text mining methods and tools, as well as a call for a fundamental change in chemical risk and uncertainty assessment methodology if to be conducted based on AOPs and new approach methodologies (NAM). The usefulness of evidence-based approaches for mechanism-based chemical risk assessments was stressed, particularly the potential contribution of the rigor and transparency inherent to such approaches in building stakeholders' trust for implementation of NAM evidence and AOPs into chemical risk assessment.

The usefulness of integrated strategy approaches in replacing animal experimentation.

It is currently well accepted that in general, more than one method is necessary to allow the full replacement of an animal experimentation. These so called partial replacement methods can be used within integrated strategy approaches that combine different methods and information sources. A number of integrated strategy approaches were implemented within recent years in different areas of safety and regulatory toxicology. Moreover, latest advances in biomedical research and bioengineering provide a major opportunity to make use of in vitro human-based and/or three-dimensional complex models that can contribute to achieve more physiologically-relevant models. Examples herein describe currently existing integrated strategy frameworks aiming at full or partial replacement purposes and/or at gaining mechanistic insights. Furthermore, a general concept is provided on how 3R methods might be integrated in a strategy approach in order to ensure that animal experimentation is conducted only as a last resort.

Value and limitation of in vitro bioassays to support the application of the threshold of toxicological concern to prioritise unidentified chemicals in food contact materials.

Some of the chemicals in materials used for packaging food may leak into the food, resulting in human exposure. These include so-called Non-intentionally Added Substances (NIAS), many of them being unidentified and toxicologically uncharacterized. This raises the question of how to address their safety. An approach consisting of identification and toxicologically testing all of them appears neither feasible nor necessary. Instead, it has been proposed to use the threshold of toxicological concern (TTC) Cramer class III to prioritise unknown NIAS on which further safety investigations should focus. Use of the Cramer class III TTC for this purpose would be appropriate if amongst others sufficient evidence were available that the unknown chemicals were not acetylcholinesterase inhibitors or direct DNA-reactive mutagens. While knowledge of the material and analytical chemistry may efficiently address the first concern, the second could not be addressed in this way. An alternative would be use of a bioassay capable of detecting DNA-reactive mutagens at very low levels. No fully satisfactory bioassay was identified. The Ames test appeared the most suitable since it specifically detects DNA-reactive mutagens and the limit of biological detection of highly potent genotoxic carcinogens is low. It is proposed that for a specific migrate, the evidence for absence of mutagenicity based on the Ames test, together with analytical chemistry and information on packaging manufacture could allow application of the Cramer class III TTC to prioritise unknown NIAS. Recommendations, as well as research proposals, have been developed on sample preparation and bioassay improvement with the ultimate aim of improving limits of biological detection of mutagens. Although research is still necessary, the proposed approach should bring significant benefits over the current practices used for safety evaluation of food contact materials.

Alternatives to Carbon Dioxide-Taking Responsibility for Humanely Ending the Life of Animals.

Carbon dioxide (CO2) is commonly used to kill rodents. However, a large body of research has now established that CO2 is aversive to them. A multidisciplinary symposium organized by the Swiss Federal Food Safety and Veterinary Office discussed the drawbacks and alternatives to CO2 in euthanasia protocols for laboratory animals. Dialogue was facilitated by brainstorming sessions in small groups and a "World Café". A conclusion from this process was that alternatives to CO2 were urgently required, including a program of research and extension to meet the needs for humane killing of these animals. The next step will involve gathering a group of international experts to formulate, draft, and publish a research strategy on alternatives to CO2.

The HaCaT/THP-1 Cocultured Activation Test (COCAT) for skin sensitization: a study of intra-lab reproducibility and predictivity.

The Cocultured Activation Test (COCAT) consists of cocultured HaCaT (human keratinocyte cell line) and THP-1 cells (surrogate of antigen presenting cells). Individually, these cell lines are used to address key event 2 and 3 of the skin sensitization Adverse Outcome Pathway (AOP). Their exposure in coculture was found to have the potential to increase their response to sensitizing chemicals, enable the detection of pro-haptens and support the identification of skin sensitization potency. The present study was undertaken to assess the predictive capacity of COCAT to both skin sensitization hazard and potency and to assess the intra-laboratory reproducibility of COCAT based on the blind testing of chemicals. Results showed a reproducibility between runs of 80 % for 15 coded chemicals. 100 % sensitivity (9/9), 75 % specificity (3/4) and 92.3 % accuracy (12/13) was found for skin sensitization hazard prediction, while the tests of two chemicals were inconclusive. Including additional chemicals tested during the optimization phase in addition to the blind tested chemicals, the skin sensitization UN GHS sub-categories were correctly predicted for 85.7 % (12/14) Sub-category 1A chemicals, 83.3 % (10/12) Sub-category 1B chemicals and 92.3 % (12/13) 'No Category' chemicals, resulting in an overall accuracy of 87.4 % (34/39). The present study shows the COCAT to be a promising method for the identification of skin sensitization hazard and potency sub-categorization according to the UN GHS classification.

A novel in vitro metabolomics approach for neurotoxicity testing, proof of principle for methyl mercury chloride and caffeine.

There is a need for more efficient methods giving insight into the complex mechanisms of neurotoxicity. Testing strategies including in vitro methods have been proposed to comply with this requirement. With the present study we aimed to develop a novel in vitro approach which mimics in vivo complexity, detects neurotoxicity comprehensively, and provides mechanistic insight. For this purpose we combined rat primary re-aggregating brain cell cultures with a mass spectrometry (MS)-based metabolomics approach. For the proof of principle we treated developing re-aggregating brain cell cultures for 48 h with the neurotoxicant methyl mercury chloride (0.1-100 microM) and the brain stimulant caffeine (1-100 microM) and acquired cellular metabolic profiles. To detect toxicant-induced metabolic alterations the profiles were analysed using commercial software which revealed patterns in the multi-parametric dataset by principal component analyses (PCA), and recognised the most significantly altered metabolites. PCA revealed concentration-dependent cluster formations for methyl mercury chloride (0.1-1 microM), and treatment-dependent cluster formations for caffeine (1-100 microM) at sub-cytotoxic concentrations. Four relevant metabolites responsible for the concentration-dependent alterations following methyl mercury chloride treatment could be identified using MS-MS fragmentation analysis. These were gamma-aminobutyric acid, choline, glutamine, creatine and spermine. Their respective mass ion intensities demonstrated metabolic alterations in line with the literature and suggest that the metabolites could be biomarkers for mechanisms of neurotoxicity or neuroprotection. In addition, we evaluated whether the approach could identify neurotoxic potential by testing eight compounds which have target organ toxicity in the liver, kidney or brain at sub-cytotoxic concentrations. PCA revealed cluster formations largely dependent on target organ toxicity indicating possible potential for the development of a neurotoxicity prediction model. With such results it could be useful to perform a validation study to determine the reliability, relevance and applicability of this approach to neurotoxicity screening. Thus, for the first time we show the benefits and utility of in vitro metabolomics to comprehensively detect neurotoxicity and to discover new biomarkers.

A feasibility study developing an integrated testing strategy assessing skin irritation potential of chemicals.

The regulatory assessment of chemical safety is still driven by hazard testing in animals. The Registration, Evaluation, Authorisation and restriction of Chemicals (REACH) legislation and new technologies require a shift in the way in which safety assessments are conducted. Integrated testing strategies (ITSs) help in providing such a framework. Many of the ITS building blocks are already in use, but the concepts for their integration and application in a regulatory setting have yet to be fully implemented. This paper describes a feasibility study investigating how a combination of in silico, in vitro, and in vivo information could be applied in the assessment of skin irritation hazard. Therefore, a database of 100 existing and new chemicals was compiled. A number of strategies, both animal-free and inclusive of animal data were constructed and subsequently evaluated considering predictive capacities, severity of misclassifications and testing costs. Comparison of constructed ITS based on these assessment parameters identified best performing strategies for chemical classification. However, defining the in vivo test as the reference test limited the evaluation of the ITS inclusive of animal data. This study demonstrated that ITS can be constructed, evaluated and compared in a systematic fashion. To promote ITS, further guidance on construction and multi-parameter evaluation need to be developed.

Advanced Good Cell Culture Practice for human primary, stem cell-derived and organoid models as well as microphysiological systems.

A major reason for the current reproducibility crisis in the life sciences is the poor implementation of quality control measures and reporting standards. Improvement is needed, especially regarding increasingly complex in vitro methods. Good Cell Culture Practice (GCCP) was an effort from 1996 to 2005 to develop such minimum quality standards also applicable in academia. This paper summarizes recent key developments in in vitro cell culture and addresses the issues resulting for GCCP, e.g. the development of induced pluripotent stem cells (iPSCs) and gene-edited cells. It further deals with human stem-cell-derived models and bioengineering of organo-typic cell cultures, including organoids, organ-on-chip and human-on-chip approaches. Commercial vendors and cell banks have made human primary cells more widely available over the last decade, increasing their use, but also requiring specific guidance as to GCCP. The characterization of cell culture systems including high-content imaging and high-throughput measurement technologies increasingly combined with more complex cell and tissue cultures represent a further challenge for GCCP. The increasing use of gene editing techniques to generate and modify in vitro culture models also requires discussion of its impact on GCCP. International (often varying) legislations and market forces originating from the commercialization of cell and tissue products and technologies are further impacting on the need for the use of GCCP. This report summarizes the recommendations of the second of two workshops, held in Germany in December 2015, aiming map the challenge and organize the process or developing a revised GCCP 2.0.

The usefulness of toxicogenomics for predicting acute skin irritation on in vitro reconstructed human epidermis.

In vitro models aiming at replacing the traditional animal test for determining the skin irritation potential of a test substance have been developed, evaluated in prevalidation studies and recently validated by the European Center for the Validation of Alternative Methods (ECVAM). To investigate the usefulness of toxicogenomic technologies to identify novel mechanistic endpoints for skin irritation responses, the present work challenged the human reconstituted epidermis model validated by ECVAM with four irritant chemicals and four non-classified chemicals tested at subcytotoxic concentrations. Using a specifically designed low-density DNA array, about 50 genes out of 240 were found to be significantly and differentially expressed between tissues exposed to irritant and non-irritant chemicals for at least one test chemical when compared to the seven others. These genes are involved in cell signalling, stress response, cell cycle, protein metabolism and cell structure. Among them, 16 are expressed in the same way whatever the irritant compound applied. The differential gene expressions might represent new or additional endpoints useful for the mechanistic understanding and perhaps also the hazard assessment of the skin irritation potential of chemicals and products.