Comparison of the standard and reduced pH Syrian hamster embryo (SHE) cell in vitro transformation assays in predicting the carcinogenic potential of chemicals

In Silico Approaches In Carcinogenicity Hazard Assessment: Current Status and Future Needs

Historically, identifying carcinogens has relied primarily on tumor studies in rodents, which require enormous resources in both money and time. In silico models have been developed for predicting rodent carcinogens but have not yet found general regulatory acceptance, in part due to the lack of a generally accepted protocol for performing such an assessment as well as limitations in predictive performance and scope. There remains a need for additional, improved in silico carcinogenicity models, especially ones that are more human-relevant, for use in research and regulatory decision-making. As part of an international effort to develop in silico toxicological protocols, a consortium of toxicologists, computational scientists, and regulatory scientists across several industries and governmental agencies evaluated the extent to which in silico models exist for each of the recently defined 10 key characteristics (KCs) of carcinogens. This position paper summarizes the current status of in silico tools for the assessment of each KC and identifies the data gaps that need to be addressed before a comprehensive in silico carcinogenicity protocol can be developed for regulatory use.

QSAR ligand dataset for modelling mutagenicity, genotoxicity, and rodent carcinogenicity

Five datasets were constructed from ligand and bioassay result data from the literature. These datasets include bioassay results from the Ames mutagenicity assay, Greenscreen GADD-45a-GFP assay, Syrian Hamster Embryo (SHE) assay, and 2 year rat carcinogenicity assay results. These datasets provide information about chemical mutagenicity, genotoxicity and carcinogenicity.

Combining machine learning models of in vitro and in vivo bioassays improves rat carcinogenicity prediction

In vitro genotoxicity bioassays are cost-efficient methods of assessing potential carcinogens. However, many genotoxicity bioassays are inappropriate for detecting chemicals eliciting non-genotoxic mechanisms, such as tumour promotion, this necessitates the use of in vivo rodent carcinogenicity (IVRC) assays. In silico IVRC modelling could potentially address the low throughput and high cost of this assay. We aimed to develop and combine computational QSAR models of novel bioassays for the prediction of IVRC results and compare with existing software. QSAR models were generated from existing Ames (n = 6512), Syrian Hamster Embryonic (SHE, n = 410), ISSCAN rodent carcinogenicity (ISC, n = 834) and GreenScreen GADD45a-GFP (n = 1415) chemical datasets. These models mapped the molecular descriptors of each compound to their respective assay result using machine learning algorithms (adaboost, k-Nearest Neighbours, C.45 Decision Tree, Multilayer Perceptron, Random Forest). The best performing models were combined with k-Nearest Neighbours to create a cascade model for IVRC prediction. High QSAR model performance was observed from ten time 10-fold cross-validation with above 80% accuracy and 0.85 AUC for each assay dataset. The cascade model predicted rat carcinogenicity with 69.3% accuracy and 0.700 AUC. This study demonstrates the novelty of a combined approach for IVRC prediction, with higher performance than existing software.

Use of Genotoxicity Data to Support Clinical Trials or Positive Genetox Findings on a Candidate Pharmaceutical or Impurity …. Now What?

Results from carcinogenicity studies are generally not available for drugs until the time of approval. Many people, including healthy volunteers are often exposed to pharmacologically active doses of the drug before carcinogenicity results are available. The Food and Drug Administration (FDA) Center for Drug Evaluation and Research uses results of genetic toxicology studies as a surrogate for carcinogenicity during the drug development phase (clinical trials). A number of issues are considered in deciding whether drugs that give positive results in genetic toxicology studies can be given to subjects in clinical trials. These relate to the drug indication, the target population, duration of treatment, and importance of the drug. In general, single-dose clinical studies are permitted regardless of the genetox results. In situations where a genetic toxicology assay showed a positive result, some review divisions have asked sponsors to perform a Syrian hamster embryo (SHE) cell transformation assay or a p53 carcinogenicity study prior to allowing repeat-dose clinical trials to proceed. This paper discusses alternatives to SHE cell and p53 assays when faced with a positive result in a genetic toxicology assay. In addition, this paper discusses factors to consider when setting limits for genotoxic impurities in drug substances and products.

Classification of agents using Syrian hamster embryo (SHE) cell transformation assay (CTA) with ATR-FTIR spectroscopy and multivariate analysis

The Syrian hamster embryo (SHE) cell transformation assay (pH 6.7) has a reported sensitivity of 87% and specificity of 83%, and an overall concordance of 85% with in vivo rodent bioassay data. To date, the SHE assay is the only in vitro assay that exhibits multistage carcinogenicity. The assay uses morphological transformation, the first stage towards neoplasm, as an endpoint to predict the carcinogenic potential of a test agent. However, scoring of morphologically transformed SHE cells is subjective. We treated SHE cells grown on low-E reflective slides with 2,6-diaminotoluene, N-nitroso-N-ethylnitroguanidine, N-nitroso-N-methylurea, N-nitroso-N-ethylurea, EDTA, dimethyl sulphoxide (DMSO; vehicle control), methyl methanesulfonate, benzo[e]pyrene, mitomycin C, ethyl methanesulfonate, ampicillin or five different concentrations of benzo[a]pyrene. Macroscopically visible SHE colonies were located on the slides and interrogated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy acquiring five spectra per colony. The acquired IR data were analysed using Fisher's linear discriminant analysis (LDA) followed by principal component analysis (PCA)-LDA cluster vectors to extract major and minor discriminating wavenumbers for each treatment class. Each test agent vs. DMSO and treatment-induced transformed cells vs. corresponding non-transformed were classified by a unique combination of major and minor discriminating wavenumbers. Alterations associated with Amide I, Amide II, lipids and nucleic acids appear to be important in segregation of classes. Our findings suggest that a biophysical approach of ATR-FTIR spectroscopy with multivariate analysis could facilitate a more objective interrogation of SHE cells towards scoring for transformation and ultimately employing the assay for risk assessment of test agents.

ROS-triggered signaling pathways involved in the cytotoxicity and tumor promotion effects of pentachlorophenol and tetrachlorohydroquinone

Free radical-triggered tissue damage is believed to play an essential role in a variety of human diseases. Pentachlorophenol (PCP) is applied as a pesticide worldwide in both industries and homes. It is used extensively as a biocide and wood preservative. Tetrachlorohydroquinone (TCHQ) was proved as a major toxic metabolite of PCP, contributing the release of free radicals during PCP metabolism. PCP has been proposed as a tumor promoter; however, only limited knowledge is available regarding the mechanisms of tumor promotion induced by PCP and its metabolite, TCHQ. A growing amount of literature suggests that a link between reactive oxygen species (ROS) and tumor promotion could exist. Herein, we summarize the findings regarding the ROS-triggered signaling pathways involved in the cytotoxicity and tumor promotion effects of PCP and TCHQ. Some of the notable findings demonstrated that TCHQ can induce DNA lesions and glutathione depletion in mammalian cells; meanwhile, oxidative stress and apoptosis/necrosis can be found both in vivo and in vitro. Interestingly, PCP and TCHQ were proved as mild tumor promoters in two-stage tumorigenesis models, in which the possible mechanism could be through ROS generation and changed Bcl-2 gene expression. We also found significant effects of antioxidants in attenuating the oxidative stress, cyto- and genotoxicity, and apoptosis/necrosis induced by PCP and/or TCHQ. In addition, mitogen-activated protein kinase (MAPK) activation is involved in PCP/TCHQ-triggered cytotoxicity, as evidenced by the finding that higher doses of TCHQ could lead to necrosis of freshly isolated splenocytes through the production of a large amount of ROS and sustained ERK activation. These results could explain partly the underlying molecular mechanisms contributing to the tumorigenesis induced by PCP. However, the detailed mechanisms of free radicals in triggering PCP/TCHQ-mediated tumor promotion and toxicity are still not completely resolved and need to be investigated further.

Cytotoxicity and genotoxicity of panel of single- and multiwalled carbon nanotubes: in vitro effects on normal Syrian hamster embryo and immortalized v79 hamster lung cells

Carbon nanotubes (CNTs) belong to a specific class of nanomaterials with unique properties. Because of their anticipated use in a wide range of industrial applications, their toxicity is of increasing concern. In order to determine whether specific physicochemical characteristics of CNTs are responsible for their toxicological effects, we investigated the cytotoxic and genotoxic effects of eight CNTs representative of each of the commonly encountered classes: single- SW-, double- DW-, and multiwalled (MW) CNTs, purified and raw. In addition, because most previous studies of CNT toxicity were conducted on immortalized cell lines, we decided to compare results obtained from V79 cells, an established cell line, with results from SHE (Syrian hamster embryo) cells, an easy-to-handle normal cell model. After 24 hours of treatment, MWCNTs were generally found to be more cytotoxic than SW- or DWCNTs. MWCNTs also provoked more genotoxic effects. No correlation could be found between CNT genotoxicity and metal impurities, length, surface area, or induction of cellular oxidative stress, but genotoxicity was seen to increase with CNT width. The toxicity observed for some CNTs leads us to suggest that they might also act by interfering with the cell cycle, but no significant differences were observed between normal and immortalized cells.

Cell transformation assays: are we barking up the wrong tree?

There has been a current resurgence of interest in the use of cell transformation for predicting carcinogenicity, which is based mainly on rodent carcinogenicity data. In view of this renewed interest, this paper critically reviews the published literature concerning the ability of the available assays to detect IARC Group 1 agents (known human carcinogens) and Group 2A agents (probable human carcinogens). The predictivity of the available assays for human and rodent non-genotoxic carcinogens (NGCs), in comparison with standard and supplementary in vitro and in vivo genotoxicity tests, is also discussed. The principal finding is that a surprising number of human carcinogens have not been tested for cell transformation across the three main assays (SHE, Balb/c 3T3 and C3H10T1/2), confounding comparative assessment of these methods for detecting human carcinogens. This issue is not being addressed in the ongoing validation studies for the first two of these assays, despite the lack of any serious logistical issues associated with the use of most of these chemicals. In addition, there seem to be no plans for using exogenous bio-transformation systems for the metabolic activation of pro-carcinogens, as recommended in an ECVAM workshop held in 1999. To address these important issues, it is strongly recommended that consideration be given to the inclusion of more human carcinogens and an exogenous source of xenobiotic metabolism, such as an S9 fraction, in ongoing and future validation studies. While cell transformation systems detect a high level of NGCs, it is considered premature to rely only on this endpoint for screening for such chemicals, as recently suggested. This is particularly important, in view of the fact that there is still doubt as to the relevance of morphological transformation to tumorigenesis in vivo, and the wide diversity of potential mechanisms by which NGCs are known to act. Recent progress with regard to increasing the objectivity of scoring the transformed phenotype, and prospects for developing human cell-based transformation assays, are reviewed.

Application of in vitro cell transformation assays in regulatory toxicology for pharmaceuticals, chemicals, food products and cosmetics

Two year rodent bioassays play a key role in the assessment of carcinogenic potential of chemicals to humans. The seventh amendment to the European Cosmetics Directive will ban in 2013 the marketing of cosmetic and personal care products that contain ingredients that have been tested in animal models. Thus 2-year rodent bioassays will not be available for cosmetics/personal care products. Furthermore, for large testing programs like REACH, in vivo carcinogenicity testing is impractical. Alternative ways to carcinogenicity assessment are urgently required. In terms of standardization and validation, the most advanced in vitro tests for carcinogenicity are the cell transformation assays (CTAs). Although CTAs do not mimic the whole carcinogenesis process in vivo, they represent a valuable support in identifying transforming potential of chemicals. CTAs have been shown to detect genotoxic as well as non-genotoxic carcinogens and are helpful in the determination of thresholds for genotoxic and non-genotoxic carcinogens. The extensive review on CTAs by the OECD (OECD (2007) Environmental Health and Safety Publications, Series on Testing and Assessment, No. 31) and the proven within- and between-laboratories reproducibility of the SHE CTAs justifies broader use of these methods to assess carcinogenic potential of chemicals.

Rodent cell transformation assays-a brief historical perspective

In vitro cell transformation is a process characterized by a series of progressive distinctive events that often emulate manifestations occurring in vivo and which are associated with neoplasia. Attendant cellular and sub-cellular alterations include, among others: cellular immortality, phenotypic changes, aneuploidy, genetic variability, cellular disarray, anchorage-independent growth, and tumorigenicity in vivo. Early chemically induced neoplastic transformation studies involved the use of normal diploid (Syrian) hamster embryo (SHE) cells and monitored the formation of morphologically altered colonies. Later investigations employed primarily two established mouse cell lines, i.e. the BALB/c 3T3 A31 cell line and the C3H 10T 1/2 cell line, and monitored the induction of morphologically aberrant foci. In either case, such transformed cellular clusters (colonies and foci) could induce tumors upon inoculation in vivo. Some subsequent noteworthy advancements using these systems included pH adjustments, metabolic supplementation, amplification of expression of formerly latent transformed foci, concurrent detection of mutagenesis and transformation, and use of a Bhas 42 cell line (v-Ha-ras transfected BALB/c 3T3 cells) to detect both tumor initiators and promoters. Over time, such transformation assay systems have been found useful in academic, industry and regulatory laboratories, generally for research purposes, but also occasionally as screening tools for potential chemical carcinogens. Nevertheless, to date, use of these assays for decision-making purposes in the regulatory arena remains elusive and will require comprehensive validation to gain universal acceptance.

ECVAM prevalidation study on in vitro cell transformation assays: general outline and conclusions of the study

The potential for a compound to induce carcinogenicity is a key consideration when ascertaining hazard and risk assessment of chemicals. Among the in vitro alternatives that have been developed for predicting carcinogenicity, in vitro cell transformation assays (CTAs) have been shown to involve a multistage process that closely models important stages of in vivo carcinogenesis and have the potential to detect both genotoxic and non-genotoxic carcinogens. These assays have been in use for decades and a substantial amount of data demonstrating their performance is available in the literature. However, for the standardised use of these assays for regulatory purposes, a formal evaluation of the assays, in particular focusing on development of standardised transferable protocols and further information on assay reproducibility, was considered important to serve as a basis for the drafting of generally accepted OECD test guidelines. To address this issue, a prevalidation study of the CTAs using the BALB/c 3T3 cell line, SHE cells at pH 6.7, and SHE cells at pH 7.0 was coordinated by the European Centre for the Validation of Alternative Methods (ECVAM) and focused on issues of standardisation of protocols, test method transferability and within- and between-laboratory reproducibility. The study resulted in the availability of standardised protocols that had undergone prevalidation [1,2]. The results of the ECVAM study demonstrated that for the BALB/c 3T3 method, some modifications to the protocol were needed to obtain reproducible results between laboratories, while the SHE pH 6.7 and the SHE pH 7.0 protocols are transferable between laboratories, and results are reproducible within- and between-laboratories. It is recommended that the BALB/c 3T3 and SHE protocols as instituted in this prevalidation study should be used in future applications of these respective transformation assays. To support their harmonised use and regulatory application, the development of an OECD test guideline for the SHE CTAs, based on the protocol published in this issue, is recommended. The development of an OECD test guideline for the BALB/c 3T3 CTA should likewise be further pursued upon the availability of additional supportive data and improvement of the statistical analysis.

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

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.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Evaluation of mutagenic effects of formocresol: detection of DNA-protein cross-links and micronucleus in mouse bone marrow

OBJECTIVE

The genotoxic potential of formocresol was assessed by comet assay on human peripheral blood lymphocytes and in vivo micronucleus in mice.

STUDY DESIGN

Peripheral blood lymphocytes, obtained from healthy donors, were exposed directly with different dilutions of formocresol for 45 minutes at 37 degrees C. To verify the possibility of formocresol to induce DNA-protein cross-links, treated lymphocytes were incubated with proteinase K. Micronucleus test was performed on male Swiss mice treated with several dilutions of formocresol by single intraperitoneal injection. After treatment, bone marrow was sampled 24 and 48 hours after formocresol administration.

RESULTS

Formocresol did not produce detectable DNA damage as evaluated by comet assay. However, after proteinase K exposure, a dose-dependent increase of DNA migration was observed. Formocresol induced a significant increase in micronucleus frequencies at the highest dilution only at 24 hours after administration.

CONCLUSION

Formocresol induced DNA-protein cross-links and an increased frequency of micronucleus.

The challenge of testing chemicals for potential carcinogenicity using multiple short-term assays: An analysis of a proposed test battery for hair dyes

Recent reports of the association of hair dyes usage with increased bladder cancer risk in women with the slow NAT-2 acetylator phenotype have resulted both in attempts to identify the putative carcinogen as well as in devising batteries of tests that could be used to screen for such putative carcinogens in hair dye formulations, their intermediates and final products. Analytical studies have reported the presence of traces ( approximately 0.5 ppm) of the carcinogen 4-aminobiphenyl in some hair dye preparations. In parallel, SCCNFP (Scientific Committee on Cosmetic and Non-Food Products Intended for Consumers) has suggested the deployment of a battery of six in vitro assays followed by an in vivo assay. The practicality of deploying and interpreting such a battery is analyzed herein as it is expected to result in 64 and 128 possible test results and SCCNFP does not provide detailed guidance of how the test results are to be interpreted. In this study we have applied a previously described Bayesian approach which takes advantage of the known predictive performances of individual assays, to analyze the possible outcomes of the 6-7 test batteries. While the SCCNFP battery is clearly risk-averse, it is shown that performing all of the assays is not always necessary and moreover it does not necessarily improve predictive performance. Finally, based upon the reported mutagenicity of 4-aminobiphenyl, it is doubtful that this "impurity" would be detected by the test battery.

An analysis of genetic toxicity, reproductive and developmental toxicity, and carcinogenicity data: I. Identification of carcinogens using surrogate endpoints

A retrospective analysis of standard genetic toxicity (genetox) tests, reproductive and developmental toxicity (reprotox) studies, and rodent carcinogenicity bioassays (rcbioassay) was performed to identify the genetox and reprotox endpoints whose results best correlate with rcbioassay observations. A database of 7205 chemicals with genetox (n = 4961), reprotox (n = 2173), and rcbioassay (n = 1442) toxicity data was constructed; 1112 of the chemicals have both genetox and rcbioassay data and 721 chemicals have both reprotox and rcbioassay data. This study differed from previous studies by using conservative weight of evidence criteria to classify chemical carcinogens, data from 63 genetox and reprotox toxicological endpoints, and a new statistical parameter of correlation indicator (CI, the average of specificity and positive predictivity) to identify good surrogate endpoints for predicting carcinogenicity. Among 63 endpoints, results revealed that carcinogenicity was well correlated with certain tests for gene mutation (n = 8), in vivo clastogenicity (n = 2), unscheduled DNA synthesis assay (n = 1), and reprotox (n = 3). The current FDA regulatory battery of four genetox tests used to predict carcinogenicity includes two tests with good correlation (gene mutation in Salmonella and in vivo micronucleus) and two tests with poor correlation (mouse lymphoma gene mutation and in vitro chromosome aberrations) by our criteria.

Assessment of genotoxicity of 14 chemical agents used in dental practice: Ability to induce chromosome aberrations in Syrian hamster embryo cells

To assess the genotoxicity of 14 chemical agents used as locally applied agents in dental practice, the ability of these agents to elicit chromosome aberrations was examined using Syrian hamster embryo (SHE) cells. Chromosome aberrations in SHE cells were induced by treatment with three of eight chemical agents used as endodontic medicaments, i.e. ethylenediaminetetraacetic acid (EDTA), formocresol (a mixture of formalin and tricresol), and sodium arsenite. The other five chemical agents, i.e. chloramphenicol, p-chlorophenol, p-phenolsulfonic acid, sodium hypochlorite, and tetracycline hydrochloride exhibited a negative response for chromosome aberrations. Assessment of three dyes used for disclosing dental plaque showed chromosome aberrations induced by basic fuchsin but not by acid fuchsin and erythrosine B. Three local anesthetics, lidocaine hydrochloride, prilocaine hydrochloride, and procaine hydrochloride, were negative for chromosome aberrations. Among the ten chemical agents that exhibited a negative response in the assay, p-chlorophenol, sodium hypochlorite, and erythrosine B induced chromosome aberrations in SHE cells when treated in the presence of exogenous metabolic activation. The percentages of cells with polyploidy or endoreduplication were enhanced by formocresol, sodium arsenite, p-chlorophenol, p-phenolsulfonic acid, sodium hypochlorite, erythrosine B, prilocaine hydrochloride, and procaine hydrochloride in the absence or presence of exogenous metabolic activation. Our results indicate that the chemical agents that had a positive response in the present study are potentially genotoxic to mammalian cells.

Ability of fourteen chemical agents used in dental practice to induce chromosome aberrations in Syrian hamster embryo cells

To assess the genotoxicity of 14 chemical agents used in dental practice, the ability of these agents to induce chromosome aberrations was examined using Syrian hamster embryo (SHE) cells. Statistically significant increases in the frequencies of chromosome aberrations were induced in SHE cells treated with 7 of 10 chemical agents used as endodontic medicaments, that is, carbol camphor, m-cresol, eugenol, guaiacol, zinc oxide, hydrogen peroxide, and formaldehyde. The other 3 chemical agents, that is, thymol, glutaraldehyde, and iodoform, did not increase the levels of chromosome aberrations. Of the 4 chemical agents that are used as an antiseptic on the oral mucosa, chromosome aberrations were induced by iodine, but not by the other 3 antiseptics, benzalkonium chloride, benzethonium chloride, and chlorhexidine. Among the 6 chemical agents exhibiting a negative response in the assay, only thymol induced chromosome aberrations in the presence of exogenous metabolic activation. Our results indicate that chemical agents having a positive response in the present study are potentially genotoxic to mammalian cells and need to be studied further in detail.

Ability of 13 chemical agents used in dental practice to induce sister-chromatid exchanges in Syrian hamster embryo cells

To evaluate the genotoxic potential of 13 chemical agents used in dental practice, the abilities of these agents to induce sister-chromatid exchanges (SCEs) were examined using Syrian hamster embryo (SHE) cells. Statistically significant increases in the frequencies of SCEs were observed in SHE cells treated with all seven of the chemical agents used as endodontic medicaments: p-chlorophenol, m-cresol, formaldehyde, guaiacol, hydrogen peroxide, p-phenolsulfonic acid, and sodium hypochlorite (P < 0.01; Student t test). Assessment of two chemical agents that are applied to the oral mucosa as antiseptics showed that SCEs were induced by iodine (P < 0.01), but not by chlorhexidine. Of three chemical agents that are used as dyes for disclosing dental plaque, erythrosine B had no effect on SCE induction, while acid fuchsin and basic fuchsin increased the SCE frequencies in SHE cells (P < 0.01). Glutaraldehyde, which is used as a disinfectant for dental instruments and impressions, also induced SCEs (P < 0.01). Because SCE assays are used as a sensitive indicator for evaluating genetic toxicity of chemicals, the chemical agents that had a positive response in the present study are potentially genotoxic to mammalian cells.

Application of a two-stage Syrian hamster embryo cell transformation assay to cigarette smoke particulate matter

The induction of transformation in Syrian hamster embryo (SHE) cells is a multifactorial process, in comparison to endpoints induced in in vitro genotoxicity assays such as Ames, mouse lymphoma and cytogenetics [Y. Berwald, L. Sachs, In vitro cell transformation with chemical carcinogens, Nature (London) 200 (1963) 1182-1184]. Furthermore, a number of non-genotoxic carcinogens and promoters such as clofibrate and diethylhexylphthalate, have been positively identified in this assay, while giving false negative results in traditional genotoxicity assays [H. Yamasaki, J. Ashby, M. Bignami, W. Jongen, K. Linnainmaa, R.F. Newbold, G. Nguyen-Ba, S. Parodi, E. Rivedal, D. Schiffmann, J.W.I.M. Simons, P. Vasseur, Nongenotoxic carcinogens: development of detection methods based on mechanisms: a European project, Mutat. Res. 353 (1996) 47-63]. A high concordance between results obtained in this assay when compared with rodent carcinogenesis bioassays has also been noted [R.J. Isfort, G.A. Kerckaert, R.A. LeBoeuf, Comparison of the standard and reduced pH Syrian hamster embryo (SHE) in vitro cell transformation assays to predict the carcinogenic potential of chemicals, Mutat. Res. 356 (1996) 11-63]. Carcinogenesis is known to be a multistage process, with agents potentially acting at each stage. Specifically, mouse skin painting experiments established that tumour induction could be mechanistically divided into two distinct phases, termed initiation and promotion. Initiation, is defined as the stage at which a normal cell is converted to a latent tumour cell, followed by promotion where the latent tumour cell progresses to a tumour [W.F. Friedwald, P. Rous, The initiating and promoting elements in tumour production: analysis of the effects of tar, benzpyrene and methylcholanthrene on rabbit skin, J. Exp. Med. 80 (1944) 101-125]. A protocol for the pH 6.7 SHE transformation assay has been developed which allows separation of cell transformation process into two phases, potentially analogous to initiation and promotion in vivo. This allows chemicals found to be positive in the traditional SHE cell transformation assay to be further classified as initiators or promoters. Following validation with known initiators, benzo(a)pyrene and N-methyl-N'-nitro-N-nitrosoguanidine and promoters, 12-O-tetradecanoyl-phorbol-13-acetate and phenobarbitone, the two-stage model was applied to cigarette smoke particulates which was found to act both at the initiation and promotion stage of cell transformation.

Enhancement of the morphological transformation of Syrian hamster embryo (SHE) cells by reducing incubation time of the target cells

Syrian hamster embryo (SHE) cell transformation has been used for many years to study chemical carcinogenesis in vitro. It has been shown that this assay is probably the most predictive short-term test system for identifying rodent carcinogens. Although most of the operational difficulties encountered in the early stage of application of this assay have been overcome by culturing the SHE cells under slightly acidic conditions (pH 6.7), a relatively low level of induction of morphological transformation (MT) by known carcinogens still occurs for many cell isolates. In order to improve the response of this assay system to known carcinogens, the effect of incubation time of target SHE cells on the frequency of morphological transformation induced by benzo(a)pyrene (BaP) was investigated. It was shown that the morphological transformation frequency induced by BaP increased significantly (1.4-2.5-fold) when the incubation time of target cells was reduced from the usual 24h to less than 6h prior to seeding onto feeder layers. This improvement in sensitivity was consistent for different cell isolates. In addition, the enhanced response appeared to be a property of carcinogens because treatment with two non-carcinogens, l-ascorbic acid and 4-nitro-o-phenylenediamine, did not induce significant increases in the transformation frequency under the shortened incubation period for target cells. These results suggest that the response of the SHE cell transformation assay may be improved by optimizing the incubation time of the target SHE cells. In addition, the results of the present study provide further evidence to support the idea that morphological transformation of SHE cells results from a block of cellular differentiation of stem or stem-like cells.

Cell-Transforming Activity of Fourteen Chemical Agents Used in Dental Practice in Syrian Hamster Embryo Cells

Fourteen chemical agents used in dental practice were assessed for their cell-transforming activity using the Syrian hamster embryo (SHE) cell transformation assay system. The cell-transforming activity was quantitatively assessed by the frequency of morphological transformation (MT) in SHE cells induced by these agents. MT was induced by m-cresol, guaiacol, formaldehyde, sodium hypochlorite, hydrogen peroxide, sodium arsenite, acid fuchsin, and basic fuchsin, but not by p-chlorophenol, p-phenolsulfonic acid, glutaraldehyde, and erythrosine B. Iodine and chlorhexidine exhibited positive and pseudopositive responses, respectively. The chemical agents exhibiting a negative or pseudopositive response neither induced nor enhanced MT even in the presence of exogenous metabolic activation.

Surface reactivity, cytotoxicity, and transforming potency of iron-covered compared to untreated refractory ceramic fibers

Untreated and iron-coated refractory ceramic fibers (RCFs) 1, 3, and 4 were examined for their potential to generate free radicals and to catalyze hydrogen peroxide decomposition in cell-free assays and were compared for cytotoxic and transforming potencies in Syrian hamster embryo (SHE) cell system. Coating with a high quantity of iron increased the capability of RCFs to generate hydroxyl radicals and to catalyze the decomposition of hydrogen peroxide. In the SHE cells, the untreated RCFs had varying ability to induce inhibition of cell proliferation, cytotoxicity (as measured by the colony-forming efficiency, CE) and morphological transformation, in a concentration-dependent manner. According to cytotoxic and transforming potencies, they ranged as follows: RCF3 > RCF1 > RCF4. The lethal concentration 50 (LC50; decrease of CE to 50% of controls after 7 d of treatment) expressed per number of RCF3 and RCF1/cm(2) of culture dish was 2.5 x 10(4) and 3.7 x 10(4), respectively, whereas RCF4 was not cytotoxic up to the highest concentration tested (23.7 x 10(4) fibers/cm(2)). At LC50, RCF3 was 1.4-fold more transforming than RCF1, and the weakest, RCF4, induced less than 1% transformation. Iron coating of RCF1 and RCF3 markedly attenuated their cytostatic, cytotoxic, and transforming potencies without a linear concentration-transformation relationship. In contrast, iron coating of RCF4 affected slightly its low transforming potency, although the growth inhibitory effect was reduced. The observed decrease rather than increase in the cytotoxic and transforming potencies of the active samples RCF1 and RCF3 by their coating with large amounts of ferric iron suggests that it is not the quantity or any form of iron on the surface of fibers but the iron, even in trace, in a particular redox and coordinate state that might play a role in the fiber's surface reactivity with regard to the biological material. Surface chemical functions involved in the interaction with the cell could be inactivated by the deposition of a high quantity of Fe(III) on the surface of fibers. Physicochemical studies correlated to biological effects is an approach for understanding the properties of solids related to a given biological response and for elucidating the cellular and molecular mechanisms.

Background and framework for ILSI's collaborative evaluation program on alternative models for carcinogenicity assessment. International Life Sciences Institute

The willingness of the agencies involved in the regulation of pharmaceuticals to accept data from newly proposed models for carcinogenicity testing (eg, transgenic animals, neonatal rodent models, initiation-promotion models) has stimulated international interest in gaining experience and a greater understanding of the strengths and limitations of the specific models. Over a 4-year period, the International Life Sciences Institute (ILSI) Health and Environmental Science Institute (HESI) has coordinated a large-scale collaborative research program to help to better characterize the responsiveness of several models proposed for use in carcinogenicity assessment. The overall objective of this partnership among industry, government, and academic scientists was to evaluate the ability of these new models to provide useful information for human cancer risk assessment. This research program reflected a commitment of nearly US$35 million by over 50 industrial, govemment, and academic laboratories from the United States, Europe, and Japan. Evaluation of the models required the development of standardized protocols to allow reproducibility and comparability of data obtained across multiple laboratories. Test compounds were selected on the basis of mechanistically meaningful carcinogenic activity or noncarcinogenicity in the rodent bioassay as well as humans. Criteria were established for dose selection, pathology review, quality control, and for evaluation of study outcome. The database from these studies represents an important contribution to the future application of new models for human cancer risk assessment. Beyond the data, the collaborative process by which the models were evaluated may also represent a prototype for assessing new methods in the future.

The syrian hamster embryo (SHE) cell transformation assay: review of the methods and results

The Syrian hamster embryo (SHE) cell-transformation assay represents a short-term in vitro assay capable of predicting rodent carcinogenicity of chemicals with a high degree of concordance (LeBoeuf et al [1996]. Mutat Res 356: 85-127). The SHE assay models the earliest identifiable stage in carcinogenicity, morphological cell transformation. In contrast to other short-term in vitro assays, both genotoxic and epigenetic carcinogens are detected. The SHE assay, originally developed by Berwald and Sachs (J Natl Cancer Inst 35: 641-661) and modified as described by LeBoeuf and Kerckaert (Carcinogenesis 7: 1431-1440), was included in the International Life Sciences Institute, Health and Environmental Sciences Institute (ILSI/HESI). Alternative Carcinogenicity Testing (ACT) collaboration to provide additional information on the use of short-term in vitro tests in predicting carcinogenic potential. A total of 19 ILSI compounds have been tested in the SHE assay: 15 were tested for this project, whereas clofibrate, methapyrilene, reserpine, and Di(2-ethylhexyl)phalate (DEHP) were tested previously. Of the 3 noncarcinogenic compounds tested, 2 were negative in the SHE assay, whereas ampicillin was tested positive. The remaining 16 compounds tested were either known rodent carcinogens and/or human carcinogens. From this group, 15 tested positive in the SHE assay whereas phenacetin, a genotoxic carcinogen, was tested negative. Therefore, overall concordance between the SHE assay and rodent bioassay was 89% (17/19), whereas concordance with known or predicted human carcinogens was 37% (7/19). Based on these data, it is concluded that the SHE cell-transformation assay has utility for predicting the results of the rodent carcinogenesis bioassay but lacks the selectivity to distinguish between rodent and human carcinogens.

Use of a cell transformation assay with established cell lines, and a metabolic cooperation assay with V79 cells for the detection of tumour promoters: a review

Extensive studies on the safety evaluation of chemicals have indicated that a considerable number of non-genotoxic chemicals are carcinogenic. Tumour promoters are likely to be among these non-genotoxic carcinogens, and their detection is considered to be an important approach to the prevention of cancer. In this review, the results are summarised for in vitro transformation assays involving established cell lines, and for an assay for inhibition of gap junctional intercellular communication for the detection of tumour promoters, which involves V79 cells. Although the number of chemicals examined is still too small to permit a full evaluation of the correlation between in vitro cell transformation and in vivo carcinogenicity, it is clear that the sensitivity of the focus formation assay is very high. In the case of the metabolic cooperation assay, the sensitivity appears to be rather poor, but the assay can be considered to be useful because of its simple procedure and its considerable database. These in vitro assays for tumour promoters are recommended as useful tools for the detection of non-genotoxic carcinogens.

Morphological transformation of C3H/M2 mouse fibroblasts by, and genotoxicity of, extracts of human milk

Breast cancer may be initiated by environmental/dietary agents and human milk may act as an ex vivo indicator of in vivo exposure of mammary epithelial cells to genotoxins. Extracts of human milk from UK-resident women (n=7) were tested for their abilities to morphologically transform C3H/M2 mouse fibroblasts. Genotoxicities were assessed in the Salmonella typhimurium reverse-mutation assay in the presence of S9 using strains TA1538 and YG1019, and in metabolically-competent human MCL-5 cells with the micronucleus and with the alkaline single cell gel electrophoresis (comet) assays. Two of the seven extracts were inactive in the transformation assay both in the presence or absence of S9, two appeared to be equally transforming either in the presence or absence of S9, and two other extracts induced increased transformation frequencies in the presence of S9. A seventh extract, tested only in the absence of S9, was inactive. Extracts were either active or inactive in at least three of the four tests applied. Four extracts were active or inactive in all four tests. The results suggest that human milk could be used as a resource for investigations of the as-yet-unidentified transforming agents previously detected in mammary lipid.

Mechanisms of cell transformation in the Syrian hamster embryo (SHE) cell transformation system

The Syrian hamster embryo (SHE) cell transformation system has been used for investigational studies of basic mechanisms of neoplastic transformation, as well as determining the carcinogenic potential of chemical, physical, and biological agents. Many of these investigations utilize an intermediate step in the SHE cell neoplastic transformation process, known as morphological transformation, as an indicator that the cells have acquired an increased potential to progress to malignancy. While the nature of the morphologically transformed phenotype is not completely understood, it is believed to result from a block in the cellular differentiation of stem cells present within the SHE cell population. In terms of determination of the transforming potential of biological/chemical/physical agents, more than 500 agents have been tested in the SHE cell transformation assay with an 80-90% correlation between MT and carcinogenic potential. As such, the SHE cell transformation assay has utility as a test to provide short-term information on the carcinogenic potential of chemicals. One class of agents of current interest with regard to SHE cell transformation assay utilization consists of growth and differentiation factors (GDFs). Analysis of the SHE cell transformation potential of the GDFs, epidermal growth factor (EGF), fibroblast growth factor 4 (FGF-4), platelet-derived growth factor AA (PDGF AA), PDGF AB, PDGF BB, and the antimitogenic GDF, transforming growth factor beta one (TGF-beta1), was performed. All GDFs, with the exception of TGF-beta1, induced SHE cell transformation. However, an interesting difference between the GDFs was observed--PDGF A/B and PDGF B/B, but not PDGF A/A, EGF, or FGF-4, induced transformation after both a transient 1-day exposure and a continuous 7-day exposure, while continuous 7-day exposure was required for transformation by PDGF A/A, EGF, and FGF-4. Interestingly, both transient 1-day and continuous 7-day TGF-beta1 exposure resulted in suppression of transformation induced by a variety of transforming agents including growth factors, Ames assay-positive carcinogens, Ames assay-negative carcinogens, and spontaneous transformation. Interestingly TGF-beta1 was not able to suppress transformation by the tumor promoter, TPA. Together, these data demonstrate the utility of the Syrian hamster embryo cell transformation system for analyzing the transforming potential of GDFs and for characterizing differences in transforming mechanisms between different GDFs.

In vitro prediction of carcinogenicity using a bovine papillomavirus DNA--carrying C3H/10T 1/2 cell line (T1). II: Results from the testing of 100 chemicals

A new in vitro test for identifying carcinogens is evaluated against a testing database of 100 chemicals including the following groups: steroids, antineoplastics, PCBs, dioxins, alkyl halides, aromatic amines, nitrogen heterocycles, polyaromatic hydrocarbons, mustards, and benzodioxoles. The assay uses focus formation in a stable, BPV-1-DNA-carrying C3H/10T 1/2 mouse embryo fibroblast cell line (T1), which does not require transfection, infection with virus, or isolation of primary cells from animals. For this group of chemicals, the T1 assay correctly predicted the rodent carcinogenicity or noncarcinogenicity of 77% of the chemicals for which carcinogenicity is reported. Based on published data the bacterial mutagenicity assay would have correctly predicted carcinogenicity or noncarcinogenicity of 53% of the chemicals. The Syrian hamster embryo test would have correctly predicted carcinogenicity or noncarcinogenicity of 61% of the chemicals. We also demonstrate dose--response relationships for two of the chemicals. We report the responses of T1 cells to the group of chemicals used in the International Life Sciences Institute's program for screening of alternative methods of predicting carcinogenicity.

A refined protocol for conducting the low pH 6.7 Syrian hamster embryo (SHE) cell transformation assay

The Syrian hamster embryo (SHE) cell transformation assay evaluates the potential of chemicals to induce morphological transformation in karyotypically normal primary cells. Induction of transformation has been shown to correlate well with the carcinogenicity of many compounds in the rodent bioassay. Historically the assay has not received wide-spread use due to technical difficulty. An improved protocol for a low pH 6.7 assay was developed by LeBoeuf et al. [R.A. LeBoeuf, G.A. Kerckaert, M.J. Aardema, D.P. Gibson, R. Brauninger, R.J. Isfort, Mutat. Res., 356 (1996) 85-127], that greatly reduced many of the technical difficulties associated with the SHE assay. The purpose of this paper is to describe the most current execution of the pH 6.70 protocol including protocol refinements made since the publication of a comprehensive protocol for this assay in Kerckaert et al. [G.A. Kerckaert, R.J. Isfort, G.J. Carr, M.J. Aardema, Mutat. Res., 356 (1996) 65-84].

Morphological transformation and effect on gap junction intercellular communication in Syrian hamster embryo cells as screening tests for carcinogens devoid of mutagenic activity

A large fraction of chemicals observed to cause cancer in experimental animals is devoid of mutagenic activity. It is therefore of importance to develop methods that can be used to detect and study environmental carcinogenic agents that do not interact directly with DNA. Previous studies have indicated that induction of in vitro cell transformation and inhibition of gap junction intercellular communication are endpoints that could be useful for the detection of non-genotoxic carcinogens. In the present work, 13 compounds [chlordane, Arochlor 1260, di(2-ethylhexyl)phthalate, 1,1,1-trichloro-2, 2-bis(4-chlorophenyl)ethane, limonene, sodium fluoride, ethionine, o-anisidine, benzoyl peroxide, o-vanadate, phenobarbital, 12-O-tetradecanoylphorbol 13-acetate and clofibrate] have been tested for their ability to induce morphological transformation and affect intercellular communication in Syrian hamster embryo cells. The substances were selected on the basis of being proven or suspected non-genotoxic carcinogens, and thus difficult to detect in short-term tests. The data show that nine of the 13 compounds induced morphological transformation, and seven of the 13 inhibited intercellular communication in hamster embryo cells. Taken together, 12 of the 13 substances either induced transformation or caused inhibition of communication. The data suggest that the combined use of morphological transformation and gap junction intercellular communication in Syrian hamster embryo cells may be beneficial when screening for non-genotoxic carcinogens.

Induction of micronuclei in Syrian hamster embryo cells: comparison to results in the SHE cell transformation assay for National Toxicology Program test chemicals

Sixteen chemicals currently being tested in National Toxicology Program (NTP) carcinogenicity studies were evaluated in the Syrian hamster embryo (SHE) cell in vitro micronucleus assay. Results from these studies were compared to the results from the SHE cell transformation assay for the same chemicals The overall concordance between induction of micronuclei and transformation of SHE cells was 56%, which is far lower that the 93% concordance between these two tests reported previously by Fritzenschaf et al. (1993; Mutation Res. 319, 47-53). The difference between our results appears to be due to differences in the types of chemicals in the two studies. Overall, there is good agreement between the SHE cell micronucleus and transformation assays for mutagenic chemicals, but, as our study highlights, the SHE cell transformation assay has the added utility of detecting nonmutagenic carcinogens. The utility of a multi-endpoint assessment in SHE cells for carcinogen screening is discussed.

Aneuploidy and consistent structural chromosome changes associated with transformation of Syrian hamster embryo cells

To gain a better understanding of the role of specific numerical and structural chromosome changes in the multistage process of transformation of Syrian hamster embryo (SHE) cells, we analyzed seven benzo(a)pyrene (BP)-induced immortal SHE cell lines, and one spontaneously immortalized cell line. In addition, we analyzed chromosome changes in early passage tumor-derived cell lines induced by injection of four immortalized cell lines into neonate hamsters. Of particular interest was the observation of a deletion in the short arm of chromosome 2 in four of the seven BP-immortalized cell lines. Other types of alterations in chromosome 2 were observed in two other cell lines. Loss of one copy of chromosome 16 was also observed in more than 90 to 100% of the cells in three of seven BP-immortalized cell lines. In contrast, the only chromosome alteration seen in the spontaneously immortalized cell line was a deletion in the short arm of chromosome 20. Genetic instability, as indicated by increased numerical or structural chromosome changes, was observed in all tumor-derived cell lines compared to the immortal cell line from which they originated. These results, along with previous reports in the literature, suggest that alterations in specific chromosomes, like chromosome 2, may be involved in transformation of SHE cells.