A number of additional areas for further work were suggested at the workshop, including evaluation of a wider set of chemicals with a range of known modes/mechanisms of action to better define which mechanisms the assays are sensitive to, and genomic analysis following treatment with known non-carcinogens and genotoxic and non-genotoxic carcinogens to gain an insight on mechanisms and markers of transformation. the current state of the art in this field and provide directions for future research. This paper outlines the key points highlighted at this meeting. Introduction Assessment of the potential for a compound to induce carcinogenicity is a key consideration in the safety evaluation of chemicals, agrochemicals, consumer products and pharmaceuticals. The standard approach to carcinogenicity testing in some of these industries is to conduct 2-year bioassays in rats and mice. These assays use large numbers of animals and are time consuming and expensive: testing in both species can involve 600C800 animals per chemical, involves the histopathological examination of more than 40 tissues and costs 1 million (1). Cancer bioassays are therefore of limited practicality for use in large-scale chemical testing programmes such as the EU regulation REACH (Registration, Evaluation, Authorisation and restriction of Chemicals) (2), while the Seventh Amendment to the EU cosmetics directive will ban the bioassay for cosmetic ingredients from 2013 (3). For all these reasons, there is a need for alternative methods for carcinogenicity testing Finafloxacin hydrochloride that are faster, more cost efficient and have reduced reliance on animals. assays for detecting potential genotoxicity and/or mutagenicity are available and accepted as part of regulatory test strategies, but they have a significant irrelevant positive rate (4,5) and follow-up animal testing is used in order to confirm whether such effects occur genotoxicity Finafloxacin hydrochloride result. Several cell transformation assays (CTAs) have been developed as quicker and more cost effective alternative methods for detection of carcinogenic potential. These assays measure induction of phenotypic alterations characteristic of tumourigenic cells, and cells transformed have been shown to induce tumours when injected into immunosuppressed experimental animals (6,7). CTAs mimic some key stages of multistep carcinogenesis and have been shown to have a good concordance with rodent bioassay results, detecting both genotoxic and non-genotoxic carcinogens (8). CTAs are currently used by the chemical, agrochemical, cosmetic and pharmaceutical industries and academia for screening purposes and to investigate basic mechanisms of carcinogenicity, but they are not widely accepted for regulatory purposes due to a number of reservations. Historically, three main concerns have been raised: reproducibility of results between laboratories, the subjective nature of using morphological characteristics for assessing transformation and a lack of understanding of the molecular mechanisms underlying transformation. Interest in CTAs has fluctuated over the years but the recent drivers for developing faster nonanimal methods for assessing carcinogenicity has led to a resurgence. The performance of the various methods has recently been reviewed (1,8), and several lines of new research seeking to Rabbit Polyclonal to CROT improve the objectivity of the assays, explore the use of novel cell types and reveal the underlying mechanistic changes are ongoing. In view of these recent developments, the UK NC3Rs held an international workshop, sponsored by the UK Environmental Mutagen Society (UKEMS), to review the state of the science of CTAs and inform the direction of future research in this area. This paper sets out and expands upon the key themes that were discussed at the meeting. Background: established CTAs Malignant transformation of Syrian hamster embryo (SHE) cells by chemical carcinogens was first reported in the 1960s (6,7,9), and efforts have been ongoing since this time to develop assays for detection of carcinogenic potential and assess mechanistic events associated with neoplasia. It has been reported that at least four stages seem to be involved in cell transformation (8,10). The stages are (i) a block in cellular differentiation (detected as morphological transformation Finafloxacin hydrochloride in the SHE assay); (ii) acquisition of immortality expressed by unlimited lifespan and aneuploid karyotype and genetic instability; (iii) acquisition of tumourigenicity associated with foci formation and anchorage-independent growth obtained in the BALB/c 3T3, C3H10T1/2 and Bhas 42 assay systems and (iv) full malignancy when cells are injected in a suitable host animal. The Syrian hamster dermal (SHD) mass culture system was used to demonstrate that induction of cellular immortality is an early gatekeeper Finafloxacin hydrochloride event essential for transformation by powerful chemical carcinogens (11) and also by active oncogenes (12). Furthermore, using the cloned human oncogene and are expected to support the development of OECD test guidelines for the SHE assays. Validation studies have also recently been conducted for the Bhas 42 assay using both the initiation and the promotion protocols; three inter-laboratory studies (one Japanese and two international studies) coordinated by the Japanese New Energy and Industrial Technology Development Organisation (NEDO) and the Japanese Centre for Validation.