Stem cell-derived models to improve mechanistic understanding and prediction of human drug-induced liver injury.

Current preclinical drug testing does not predict some forms of adverse drug reactions in humans. Efforts at improving predictability of drug-induced tissue injury in humans include using stem cell technology to generate human cells for screening for adverse effects of drugs in humans. The advent of induced pluripotent stem cells means that it may ultimately be possible to develop personalized toxicology to determine interindividual susceptibility to adverse drug reactions. However, the complexity of idiosyncratic drug-induced liver injury means that no current single-cell model, whether of primary liver tissue origin, from liver cell lines, or derived from stem cells, adequately emulates what is believed to occur during human drug-induced liver injury. Nevertheless, a single-cell model of a human hepatocyte which emulates key features of a hepatocyte is likely to be valuable in assessing potential chemical risk; furthermore, understanding how to generate a relevant hepatocyte will also be critical to efforts to build complex multicellular models of the liver. Currently, hepatocyte-like cells differentiated from stem cells still fall short of recapitulating the full mature hepatocellular phenotype. Therefore, we convened a number of experts from the areas of preclinical and clinical hepatotoxicity and safety assessment, from industry, academia, and regulatory bodies, to specifically explore the application of stem cells in hepatotoxicity safety assessment and to make recommendations for the way forward. In this short review, we particularly discuss the importance of benchmarking stem cell-derived hepatocyte-like cells to their terminally differentiated human counterparts using defined phenotyping, to make sure the cells are relevant and comparable between labs, and outline why this process is essential before the cells are introduced into chemical safety assessment. (Hepatology 2017;65:710-721).

Finding synergies for 3Rs - Toxicokinetics and read-across: Report from an EPAA partners' Forum.

The European Partnership for Alternative Approaches to Animal Testing (EPAA) convened a Partners' Forum Toxicokinetics and Read-Across to provide an overview on research activities to develop in vitro toxicokinetics methods and physiologically-based kinetic (PBK) models and to find synergies to enhance use of toxicokinetic data to strengthen read-across. Currently, lacking toxicokinetic data often prevent the application of read-across. Preferably, toxicokinetic data should be generated using in vitro and in silico tools and anchored towards human relevance. In certain sectors, PBK modelling is being used for risk assessment, but less so in others. Specific activities were identified to facilitate the use of in vitro and in silico toxicokinetic data to support read-across: The collation of available tools indicating the parameters and applicability domains covered; endpoint-specific guidance on toxicokinetics parameters required for read-across; case studies exemplifying how toxicokinetic data help support read-across. Activities to enhance the scientific robustness of read-across include the further user-friendly combination of read-across tools and formal guidance by the authorities specifying the minimum information requirements to justify read-across for a given toxicity endpoint. The EPAA was invited to continue dissemination activities and to explore possibilities to collate a contemporaneous list of open toxicokinetics tools that assist risk assessment.

Skin sensitisation--moving forward with non-animal testing strategies for regulatory purposes in the EU.

In a previous EPAA-Cefic LRI workshop in 2011, issues surrounding the use and interpretation of results from the local lymph node assay were addressed. At the beginning of 2013 a second joint workshop focused greater attention on the opportunities to make use of non-animal test data, not least since a number of in vitro assays have progressed to an advanced position in terms of their formal validation. It is already recognised that information produced from non-animal assays can be used in regulatory decision-making, notably in terms of classifying a substance as a skin sensitiser. The evolution into a full replacement for hazard identification, where the decision is not to classify, requires the generation of confidence in the in vitro alternative, e.g. via formal validation, the existence of peer reviewed publications and the knowledge that the assay(s) are founded on key elements of the Adverse Outcome Pathway for skin sensitisation. It is foreseen that the validated in vitro assays and relevant QSAR models can be organised into formal testing strategies to be applied for regulatory purposes by the industry. To facilitate progress, the European Partnership for Alternative Approaches to animal testing (EPAA) provided the platform for cross-industry and regulatory dialogue, enabling an essential and open debate on the acceptability of an in vitro based integrated strategy. Based on these considerations, a follow up activity was agreed upon to explore an example of an Integrated Testing Strategy for skin sensitisation hazard identification purposes in the context of REACH submissions.

Optimised testing strategies for skin sensitization--the LLNA and beyond.

As toxicology in the 21st century progresses towards a future which aims at avoiding the use of in vivo testing, the endpoint of skin sensitisation can now be found in the front line. Accordingly, it was appropriate for several industry sectors to meet and review what has been learned from the currently most widely used in vivo method, the local lymph node assay (LLNA), and to consider the status of progress as we attempt to move beyond that test. No toxicology test is perfect, an experience brought into focus by issues of false positives and, to a lesser extent, false negatives in the LLNA. Use of weight of evidence arguments for classification and labelling, as well as for risk assessment was emphasised and it was also noted that a sufficient body of evidence now exists for conduct of methods other than the LLNA for carefully defined chemical classes. In terms of in vitro alternatives, progress towards methods which will deliver mainly hazard identification is being made, with some entering the final stages of validation, whereby (Q)SAR tools still need improvement to be used on a large scale in practise. As various other challenges also remain, e.g. testing lipophilic substances, as well as the development of non-animal methods which deliver reliable information on potency for risk assessment, these will remain a topic for continuing research and development.

The European Partnership for Alternative Approaches to Animal Testing (EPAA): promoting alternative methods in Europe and beyond.

Here in we introduce the European Partnership for Alternative Approaches to Animal Testing (EPAA) and its activities, which are focused on international cooperation toward alternative methods. The EPAA is one of the leading organizations in Europe for the promotion of alternative approaches to animal testing. Its innovative public-private partnership structure enables a consensus-driven dialogue across 7 industry sectors to facilitate interaction between regulators and regulated stakeholders. Through a brief description of EPAA's activities and organizational structure, we first articulate the value of this collaboration; we then focus on 2 key projects driven by EPAA. The first project aims to address research gaps on stem cells for safety testing, whereas the second project strives for an approach toward demonstration of consistency in vaccine batch release testing. We highlight the growing need for harmonization of international acceptance and implementation of alternative approaches and for increased international collaboration to foster progress on nonanimal alternatives.