Cell transformation assays for prediction of carcinogenic potential: state of the science and future research needs

Abstract

Cell transformation assays (CTAs) have long been proposed as in vitro methods for the identification of potential chemical carcinogens. Despite showing good correlation with rodent bioassay data, concerns over the subjective nature of using morphological criteria for identifying transformed cells and a lack of understanding of the mechanistic basis of the assays has limited their acceptance for regulatory purposes. However, recent drivers to find alternative carcinogenicity assessment methodologies, such as the Seventh Amendment to the EU Cosmetics Directive, have fuelled renewed interest in CTAs. Research is currently ongoing to improve the objectivity of the assays, reveal the underlying molecular changes leading to transformation and explore the use of novel cell types. The UK NC3Rs held an international workshop in November 2010 to review 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.

International regulatory needs for development ofan IATA for non-genotoxic carcinogenic chemical substances

“…Thus, in combination with toxicogenomics profiling highlighting the CTA mechanisms, the assay could in the future be considered a Level 3 assay, as the change in cytoskeleton may be used as a hallmark of the cancer microenvironment. This would be in keeping with the OECD recommendation (OECD, 2015a) that "When SHE CTA results are used as part of a testing strategy (not as results from a stand-alone assay) and/or in a weight of evidence approach, they may contribute to the assessment of carcinogenic potential of test chemicals (Creton et al, 2012). "…”

Analysis on the Performance of the Balb/c 3T3 Two-stage Assay in a Miniature Culture Area and in a Perfusion Culture Model

“…Such assays are time consuming and expensive, usually taking up to three years and involving the use of 600-800 animals per chemical and the histo-pathological examination of more than 40 tissues [4,5]. In vitro transformation assays are faster, more cost efficient and display a multistep process that closely models the multistage process of carcinogenesis [1,8].…”

“…In vitro cell transformation assays (CTAs) for the screening of chemical carcinogenic potential are becoming increasingly relevant as they aim to reduce or substitute rodent life-time bioassays that have been shown to be costly, time-consuming and, furthermore, true predictivity of animal carcinogenicity data to humans has been questioned [1][2][3][4][5][6][7].…”

Reassessing the two-year rodent carcinogenicity bioassay: A review of the applicability to human risk and current perspectives

“…Originally considered as most promising, clonogenic and tissue-based assays included technical difficulties associated with maintenance of tumor cell lines and aggregation (Hoffman, 1991;Weisenthal and Lippman, 1985).The use of traditional cell transformation assays and the observation of changes in cells in vitro according to phenotypic markers in common with tumor cells are inconsistent (Berwald and Sachs, 1965). Newer methods, so-called ''onomics'' assays, have sought markers for underlying molecular changes as precursors of biochemical pathway alterations, but these tests remain in their infancy and even multiple markers may not be comprehensive of the many mechanisms of cancer (Creton et al, 2012;Benigni et al, 2010a;Benigni and Bossa, 2011a, b;Poth et al, 2007;Steele et al, 1996). On the basis of aggressive tumor cells sharing the same characteristics as embryonic cells, studies with human stem cells have focused on convergence of embryonic and tumorigenic signaling pathways as therapeutic targets (Hendrix et al, 2007).…”