Transformation of BALB/c-3T3 cells: I. Investigation of experimental parameters that influence detection of spontaneous transformation

An optimization protocol for Swiss 3T3 feeder cell growth-arrest by Mitomycin C dose-to-volume derivation strategy

Feeder cell functionality following growth-arrest with the cost-effective Mitomycin C vis-à-vis irradiation is controversial due to several methodological variables reported. Earlier, we demonstrated variability in growth arrested Swiss 3T3 feeder cell life-span following titration of feeder cell densities with Mitomycin C concentrations which led to the derivation of doses per cell. Alternatively, to counter the unexpected feeder regrowth at high exposure cell density, we proposed titration of a fixed density with arithmetically derived volumes of Mitomycin C solution that corresponded to permutations of specific concentrations and doses per cell. We now describe an experimental procedure of inducing differential feeder cell growth-arrest by titrating with such volumes and validating the best feeder batch through target cell growth assessment. A safe cell density of Swiss 3T3 tested for the exclusion of Mitomycin C resistant variants was titrated with a range of volumes of a Mitomycin C solution. The differentially growth-arrested feeder batches generated were tested for short-term and long-term viability and human epidermal keratinocyte growth supporting ability. The feeder cell extinction rate was directly proportional to the volume of Mitomycin C solution within a given concentration per se. The keratinocyte colony forming efficiency and the overall growth in mass cultures were maximal with a median extinction rate produced by an intermediate volume, while the faster and slower extinction rates by high and low volumes, respectively, were suboptimal. The described method could counter the inadequacies of growth-arrest with Mitomycin C.

Detection of cell carcinogenic transformation by a quadruplex DNA binding fluorescent probe

Cancer can be easily treated when found early. A probe capable of detecting cell transformation may increase the success rate of early diagnosis of cancer. In this report we have tested the ability of a fluorescent, quadruplex DNA binding probe, 3,6-bis(1-methyl-4- vinylpyridinium) carbazole diiodide (BMVC), to detect cell transformation in vitro. BMVC was applied to living cells in several different models of cell transformation, and the fluorescence signals of BMVC were measured. The degrees of cell transformation in these models were characterized by alterations in cellular morphological phenotype and subcellular organization. When BMVC probes were applied, the number of BMVC-positive cells increased in accordance with the degree of transformation. BMVC was capable of significantly detecting formation of foci, increased cellular motility, cell proliferation, cell apoptosis, anchorage-independent growth, and increased invasiveness of transformed cells. These results demonstrate the ability of BMVC probes to detect cell transformation and indicate that BMVC is of promise for use as a probe in early cancer detection.

An optimised data analysis for the Balb/c 3T3 cell transformation assay and its application to metal compounds

The Balb/c3T3 cell transformation assay (CTA) is an available in vitro system to detect the carcinogenic potential of chemicals. Currently, the European Centre for the Validation of Alternative Methods (ECVAM) is validating this test, assessing its reliability and relevance. Its endpoint is the formation of type III foci, which is, when using clone A31-1-1, a very rare event that usually does not occur at all for negative controls. The carcinogenic potential of a compound tested is assessed by comparing the number of foci in treated and untreated cells. The objective of the present work is to optimise the data analysis for this endpoint by applying the most commonly used approach by a t-test and the Fisher's exact test as an alternative approach. For this purpose selected metal compounds classified as carcinogenic (NaAsO2, CdCl2, cisPt), as suspected carcinogenic (C6H5)4AsCl, CH3HgCl), or as compounds without evidence of carcinogenic properties in humans ((NH4)2PtCl6, NaVO3) as well as a non-carcinogenic (AgNO3) were analysed. Our evaluation revealed that the t-test approach, which assumes normality of data, is not appropriate. The results demonstrated that the statistical analysis by Fisher's exact test, better reflecting the data properties, greatly facilitates the interpretation of Balb/c3T3 CTA data regarding carcinogenic potential.

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.

Application of in vitro cell transformation assays to predict the carcinogenic potential of chemicals

Genotoxicity test batteries have become a standard fool for identifying chemicals that may have potential carcinogenic risk to humans. It is now apparent, however, that the use of genotoxicity batteries for assessing carcinogenic potential has limitations including an overall low specificity and a limited ability to detect carcinogens acting via 'nongenotoxic' mechanisms. In vitro cell transformation models, because they measure a chemical's ability to induce preneoplastic or neoplastic endpoints regardless of mechanism, may fulfil the current need for an in vitro biologically relevant model with increased predictiveness for determining carcinogenic potential. This review will focus on data demonstrating the similarities of chemically induced cell transformation in vitro to carcinogenesis in vivo. Furthermore, a growing database demonstrating a high overall correlation between cell transformation results with those of the rodent bioassay will also be discussed. Finally, the inclusion of cell transformation approaches for assessing the carcinogenic potential of chemicals relative to currently used genotoxicity batteries will be presented.

Transformation of BALB/c-3T3 cells: IV. Rank-ordered potency of 24 chemical responses detected in a sensitive new assay procedure

This report introduces an improved method of detecting chemical-induced morphological transformation of A-31-1-13 BALB/c-3T3 cells. The new procedure uses an increased target cell population to assess chemical-induced damage by increasing the initial seeding density and by delaying the initiation time of chemical treatment. Furthermore, a newly developed co-culture clonal survival assay was used to select chemical doses for the transformation assay. This assay measured the relative cloning efficiency (RCE) of chemical treatments in high-density cell cultures. In addition, transformation assay sensitivity was enhanced through the use of improved methods to solubilize many chemicals. From a group of 24 chemicals tested in at least two trials, clear evidence of chemical-induced transformation was detected for 12 chemicals (aphidicolin, barium chloride-2H2O, 5-bromo-2'-deoxyuridine, C.I. direct blue 15, trans-cinnamaldehyde, cytosine arabinoside, diphenylnitrosamine, manganese sulfate-H2O, 2-mercaptobenzimidazole, mezerein, riddelliine, and 2,6-xylidine); 2 chemicals had equivocal activity [C.I. direct blue 218 and mono(2-ethylhexyl)phthalate], 9 chemicals were inactive [carisoprodol, chloramphenicol sodium succinate, 4-chloro-2-nitroaniline, C.I. acid red 114, isobutyraldehyde, mono(2-ethylhexyl)adipate, sodium fluoride, and 12-O-tetradecanoylphorbol-13-acetate), and 1 chemical had an indeterminate response (2,6-dinitrotoluene). All positive responses were detected in the absence of an exogenous activation system and exhibited significant activity at two or more consecutive doses. This report also presents a mathematical method that uses t-statistics for rank-ordering the potency of chemical-induced transformation responses. This model detects sensitivity differences in experiments used to evaluate chemical-induced transformation. Furthermore, it provides a method to estimate a chemical's transformation response in terms of the historical behavior of the assay, as well as its future activity. The most active of the 24 chemicals was mezerein, and the least active chemical was diphenylnitrosamine.

Transformation of BALB/c-3T3 cells: II. Investigation of experimental parameters that influence detection of benzo[a]pyrene-induced transformation

Benzo[a]pyrene (BaP) induced significant morphological transformation of clone A31-1-13 BALB/c-3T3 cells without exogenous activation. Therefore, BaP was selected as a model to determine the internal consistency of detection of chemical-induced transformation. BaP induced a continuum of type I-III foci of different sizes, and the ratio of type I-III to type III foci/vessel was usually about 2-fold. The major finding was that BaP induced highly significant transformation responses, and the magnitude of these responses were inversely correlated with the cytotoxicity of the treatment doses. Thus, the induction of BaP-induced transformation behaved as though it was caused by a mutational event. Variability among responses were shown to depend on the serum lot and the cryopreserved ampule of cells. In addition, experiments with low spontaneous transformation responses had an impaired ability to detect BaP; however, experiments with high or normal spontaneous responses had a normal ability to detect BaP. Because the expression of BaP-induced transformation depended on both the cytotoxicity of the treatment and the cumulative number of mitoses, the frequency of BaP-induced transformation should be reported as the number of foci/vessel, but not expressed as the number of foci/viable cell surviving the chemical treatment. These conclusions are important because the same 110 experiments described in this report were also used to evaluate the transformation responses of many different carcinogenic and noncarcinogenic chemicals. These data are being reported separately.

Transformation of BALB/c-3T3 cells: V. Transformation responses of 168 chemicals compared with mutagenicity in Salmonella and carcinogenicity in rodent bioassays

This report describes the activities of 168 chemicals tested in a standard transformation assay using A-31-1-13 BALB/c-3T3 cells. The data set includes 84 carcinogens, 77 noncarcinogens, and 7 research chemicals. Carcinogens included 49 mutagens and 35 nonmutagens; noncarcinogens included 24 mutagens and 53 nonmutagens. The transformation assay did not use an exogenous activation system, thus, all chemical responses depended on the inherent target cell metabolic capacity where metabolic activation was required. The upper dose limit was 100 milli-osmolar because the assay could not discriminate active and inactive chemicals tested above this concentration. Certain physicochemical properties resulted in technical problems that affected chemical biological activity. For example, chemicals that reacted with plastic were usually nonmutagenic carcinogens. Similarly, chemicals that were insoluble in medium, or bound metals, were usually nonmutagenic and nontransforming. Multifactorial data analyses revealed that the transformation assay discriminated between nonmutagenic carcinogens and noncarcinogens; it detected 64% of the carcinogens and only 26% of the noncarcinogens. In contrast, the transformation assay detected most mutagenic chemicals, including 94% of the mutagenic carcinogens and 70% of the mutagenic noncarcinogens. Thus, transformation or Salmonella typuimurium mutagenicity assays could not discriminate mutagenic carcinogens from mutagenic noncarcinogens. Data analyses also revealed that mutagenic chemicals were more cytotoxic than nonmutagenic chemicals; 88% of the mutagens had an LD50 < 5 mM, whereas half of the nonmutagens had an LD50 > 5 mM. Binary data analyses of the same data set revealed that the transformation assay and rodent bioassay had a concordance of 71%, a sensitivity for carcinogens of 80.0%, and a specificity for detecting noncarcinogens of 60%. In contrast, Salmonella mutagenicity assays and rodent bioassays had a concordance of 63%, a sensitivity of 58%, and a specificity of 69%. The transformation assay complemented the Salmonella mutagenesis assay in the identification of nonmutagenic carcinogens; thus, the two assays had a combined 83% sensitivity for all carcinogens and a 75% specificity for nonmutagenic noncarcinogens.