Report of the Validation and Technology Transfer Committee of the Johns Hopkins Center for Alternatives to Animal Testing. Framework for validation and implementation of in vitro toxicity tests

Progress toward the Validation of Alternative Tests

ECVAM's role in the practical validation of replacement alternative methods for use in regulatory testing is reviewed, including an outline of the criteria which have been used in determining ECVAM's priorities. Some of the difficulties which have arisen in validation studies are discussed, and solutions to these are proposed, with particular emphasis on ensuring that methods are sufficiently well-developed to enter the validation process, and on the ECVAM prevalidation scheme for encouraging protocol optimisation and the prior assessment of interlaboratory transferability. Comments are made on problems encountered in selecting test materials backed by adequate in vivo data and in undertaking appropriate in vivo/in vitro comparisons.

Mechanisms in tumor promotion: guidance for risk assessment and cancer chemoprevention

In mouse skin, tumor development promoted by 'non-genotoxic' carcinogens is closely related to the wound response. In both cases endogenous factors such as cytokines and eicosanoids released primarily from 'activated keratinocytes' play a key role as mediators of inflammation and cellular hyperproliferation. The liberation of interleukin-1 alpha and arachidonic acid from human keratinocytes has been used as an in vitro parameter of irritancy. The results (from experiments with 15 different chemicals) being validated at present in a clinical study indicate a quantitative relationship between irritancy in vivo and mediator release in vitro. In the course of experimental skin carcinogenesis an overproduction of eicosanoids due to a constitutive overexpression of the corresponding enzymes (i.e. PGH synthase-II and 8- and 12-lipoxygenase) is observed. Enzyme inhibitors, for instance nonsteroidal antiinflammatory drugs (NSAIDs), exert a strong tumoristatic effect. Thus, the approach of multistage skin carcinogenesis provides a suitable animal model for a mechanistic evaluation and further improvement of chemopreventive measures such as the inhibition of colorectal tumor development in humans by NSAIDs ('aspirin effect').

Scientific Validation: A Crucial and Unavoidable Prerequisite to the Acceptability of New Tests and Testing Strategies

— The use of in vitro techniques in fundamental pharmacotoxicological research is widespread, but relatively little progress has been made in applying the knowledge and experience gained to regulatory toxicity testing. This is largely because specific tests of various kinds are required by national and international laws and regulations, before chemicals and products of many types can be manufactured, transported or marketed. These requirements have led to the publication of standardised test guidelines by various regulatory authorities. Although there is an increasing willingness to accept, in principle, the incorporation of non-animal tests and testing strategies into regulatory practice, their relevance and reliability must first be established in recognised validation studies, the outcomes of which must be assessed by independent groups of experts. The formal validation of alternative methods is not progressing satisfactorily. The reasons for this are discussed and some suggestions for improvements are made.