The Cell Transformation Assay: A Historical Assessment of Current Knowledge of Applications in an Integrated Approach to Testing and Assessment for Non-Genotoxic Carcinogens

The history of the development of the cell transformation assays (CTAs) is described, providing an overview of in vitro cell transformation from its origin to the new transcriptomic-based CTAs. Application of this knowledge is utilized to address how the different types of CTAs, variously addressing initiation and promotion, can be included on a mechanistic basis within the integrated approach to testing and assessment (IATA) for non-genotoxic carcinogens. Building upon assay assessments targeting the key events in the IATA, we identify how the different CTA models can appropriately fit, following preceding steps in the IATA. The preceding steps are the prescreening transcriptomic approaches, and assessment within the earlier key events of inflammation, immune disruption, mitotic signaling and cell injury. The CTA models address the later key events of (sustained) proliferation and change in morphology leading to tumor formation. The complementary key biomarkers with respect to the precursor key events and respective CTAs are mapped, providing a structured mechanistic approach to represent the complexity of the (non-genotoxic) carcinogenesis process, and specifically their capacity to identify non-genotoxic carcinogenic chemicals in a human relevant IATA.

In Vitro Carcinogenicity Test of a Copper-Containing Intrauterine Device

The aim is to study the cellular carcinogenicity of a copper-containing intrauterine device (IUD). So we analyzed the chemical elements of copper-containing IUDs. After that, we used Bhas42 cells in initiation and promotion assays to evaluate the leaching solution that extracted from the copper-containing IUDs at serial dilutions. In the cell carcinogenic experiment, the number of cell foci with malignant transformation was calculated. Although we uncovered no significant differences between the leaching solution at different concentrations and the negative control in the initiation assay, the sample at four concentrations showed significant differences relative to the negative control in the promotion assay (chi-squared test, p < 0.01). Therefore, we preliminarily evaluated that copper-containing IUDs are nongenotoxic carcinogen. Impact statement For the first time, we executed two-stage transformation assays with Bhas42 cells to assess the potential carcinogenicity of a copper-containing intrauterine device (IUD). In this study, we demonstrated that the copper-containing IUD manifested nongenotoxic carcinogenicity, making this the first-ever published report regarding this type of IUD's nongenotoxic carcinogenicity and revealing that its use carries a cancer risk.

Stress-induced changes in CARF expression determine cell fate to death, survival, or malignant transformation

CARF (Collaborator of ARF) was discovered as an ARF-interacting protein that activated ARF-p53-p21WAF1 signaling involved in cellular response to a variety of stresses, including oxidative, genotoxic, oncogenic, or telomere deprotection stresses, leading to senescence, growth arrest, or apoptosis. Of note, whereas suppression of CARF was lethal, its enrichment was associated with increased proliferation and malignant transformation of cells. These reports have predicted that CARF could serve as a multi-stress marker with a predictive value for cell fates. Here, we recruited various in vitro stress models and examined their effect on CARF expression using human normal fibroblasts. We demonstrate that CARF levels in stress and post-stress conditions could predict the fate of cells towards either death or enhanced proliferation and malignant transformation. We provide extensive molecular evidence that (i) CARF expression changes in response to stress, (ii) it modulates cell death or survival signaling and determines the fate of cells, and (iii) it may serve as a predictive measure of cellular response to stress and an important marker for biosafety.

Recommended protocol for the BALB/c 3T3 cell transformation assay

The present protocol has been developed for the BALB/c 3T3 cell transformation assay (CTA), following the prevalidation study coordinated by the European Centre for the Validation of Alternative Methods (ECVAM) and reported in this issue (Tanaka et al. [16]). Based upon the experience gained from this effort and as suggested by the Validation Management Team (VMT), some acceptance and assessment criteria have been refined compared to those used during the prevalidation study. The present protocol thus describes cell culture maintenance, the dose-range finding (DRF) experiment and the transformation assay, including cytotoxicity and morphological transformation evaluation. Use of this protocol and of the associated photo catalogue included in this issue (Sasaki et al. [17]) is recommended for the future conduct of the BALB/c 3T3 CTA.

Prevalidation study of the BALB/c 3T3 cell transformation assay for assessment of carcinogenic potential of chemicals

The cell transformation assays (CTAs) have attracted attention within the field of alternative methods due to their potential to reduce the number of animal experiments in the field of carcinogenicity. The CTA using BALB/c 3T3 cells has proved to be able to respond to chemical carcinogens by inducing morphologically transformed foci. Although a considerable amount of data on the performance of the assay has been collected, a formal evaluation focusing particularly on reproducibility, and a standardised protocol were considered important. Therefore the European Centre for the Validation of Alternative Methods (ECVAM) decided to coordinate a prevalidation study of the BALB/c 3T3 CTA. Three different laboratories from Japan and Europe participated. In the study the following modules were assessed stepwise: test definition (Module 1) consisted of the standardisation of the protocol, the selection of the cell lineage, and the preparation of a photo catalogue on the transformed foci. The within-laboratory reproducibility (Module 2) and the transferability (Module 3) were assessed using non-coded and coded 3-methylcholanthrene. Then, five coded chemicals were tested for the assessment of between-laboratory reproducibility (Module 4). All three laboratories obtained positive results with benzo[a]pyrene, phenanthrene and o-toluidine HCl. 2-Acetylaminofluorene was positive in two laboratories and equivocal in one laboratory. Anthracene was negative in all three laboratories. The chemicals except phenanthrene, which is classified by IARC (http://monographs.iarc.fr) as group 3 "not classifiable as to its carcinogenicity to human", were correctly predicted as carcinogens. Further studies on phenanthrene will clarify this discrepancy. Thus, although only a few chemicals were tested, it can be seen that the predictive capacity of the BALB/c 3T3 CTA is satisfactory. On the basis of the outcome of this study, an improved protocol, incorporating some changes related to data interpretation, has been developed. It is recommended that this protocol be used in the future to provide more data that may confirm the robustness of this protocol and the performance of the assay itself. During the study it became clear that selecting the most appropriate concentrations for the transformation assay is crucial.

Role of oxidative stress in transformation induced by metal mixture

Metals are ubiquitous pollutants present as mixtures. In particular, mixture of arsenic-cadmium-lead is among the leading toxic agents detected in the environment. These metals have carcinogenic and cell-transforming potential. In this study, we used a two step cell transformation model, to determine the role of oxidative stress in transformation induced by a mixture of arsenic-cadmium-lead. Oxidative damage and antioxidant response were determined. Metal mixture treatment induces the increase of damage markers and the antioxidant response. Loss of cell viability and increased transforming potential were observed during the promotion phase. This finding correlated significantly with generation of reactive oxygen species. Cotreatment with N-acetyl-cysteine induces effect on the transforming capacity; while a diminution was found in initiation, in promotion phase a total block of the transforming capacity was observed. Our results suggest that oxidative stress generated by metal mixture plays an important role only in promotion phase promoting transforming capacity.