Validation of Alternative In Vitro Methods to Animal Testing: Concepts, Challenges, Processes and Tools

This chapter explores the concepts, processes, tools and challenges relating to the validation of alternative methods for toxicity and safety testing. In general terms, validation is the process of assessing the appropriateness and usefulness of a tool for its intended purpose. Validation is routinely used in various contexts in science, technology, the manufacturing and services sectors. It serves to assess the fitness-for-purpose of devices, systems, software up to entire methodologies. In the area of toxicity testing, validation plays an indispensable role: "alternative approaches" are increasingly replacing animal models as predictive tools and it needs to be demonstrated that these novel methods are fit for purpose. Alternative approaches include in vitro test methods, non-testing approaches such as predictive computer models up to entire testing and assessment strategies composed of method suites, data sources and decision-aiding tools. Data generated with alternative approaches are ultimately used for decision-making on public health and the protection of the environment. It is therefore essential that the underlying methods and methodologies are thoroughly characterised, assessed and transparently documented through validation studies involving impartial actors. Importantly, validation serves as a filter to ensure that only test methods able to produce data that help to address legislative requirements (e.g. EU's REACH legislation) are accepted as official testing tools and, owing to the globalisation of markets, recognised on international level (e.g. through inclusion in OECD test guidelines). Since validation creates a credible and transparent evidence base on test methods, it provides a quality stamp, supporting companies developing and marketing alternative methods and creating considerable business opportunities. Validation of alternative methods is conducted through scientific studies assessing two key hypotheses, reliability and relevance of the test method for a given purpose. Relevance encapsulates the scientific basis of the test method, its capacity to predict adverse effects in the "target system" (i.e. human health or the environment) as well as its applicability for the intended purpose. In this chapter we focus on the validation of non-animal in vitro alternative testing methods and review the concepts, challenges, processes and tools fundamental to the validation of in vitro methods intended for hazard testing of chemicals. We explore major challenges and peculiarities of validation in this area. Based on the notion that validation per se is a scientific endeavour that needs to adhere to key scientific principles, namely objectivity and appropriate choice of methodology, we examine basic aspects of study design and management, and provide illustrations of statistical approaches to describe predictive performance of validated test methods as well as their reliability.

Determination of skin irritation potential in the human 4-h patch test

Recently adopted legislation in Europe has increased the focus that must be placed on the development of in vitro alternatives to the traditional toxicology tests employed to identify the human health hazards associated with chemicals. Included in these is the rabbit skin-irritation test which is used to discriminate those substances which possess significant acute skin irritation potential from those which are of more limited irritation potential. So far, the considerable efforts to replace this assay with in vitro alternatives have not been successful, which may in part be due to the relatively poor quality of the existing in vivo dataset. To help address this problem, we have elected to present our complete database of information on the skin irritation potential of some 65 substances, all of which have been tested in a standard human 4-h patch test. These provide a high quality dataset, generated in man (the goal of toxicologists' health protection-related activities). The data are presented in the context of results with a concurrent positive skin irritation control to ensure that results from individual experiments can be correlated. Consequently, in vitro or in silico alternatives which can identify the significant acute human skin irritants in this group may well represent suitable alternatives to the rabbit.