Selection of drugs to test the specificity of the Tg.AC assay by screening for induction of the gadd153 promoter in vitro

Genotoxic evaluation of the insecticide endosulfan based on the induced GADD153-GFP reporter gene expression

Endosulfan is one of the few organochlorine insecticides still in use in China for protecting crops from a variety of insects. Endosulfan is toxic in fishes and rodents in the in vivo assays, but its genotoxicity in mammalian cells has not been well tested. In this work, a genotoxic testing system has been developed based on the induction of a HepG2/GADD153-GFP reporter gene expression in response to the DNA-damaging agents. Methyl methanesulfonate, a known carcinogenic and genotoxic agent, was used to test the effects of damage dose and post-treatment incubation time on GADD153-GFP expression. Subsequently, the system was applied to the genotoxicity evaluation of endosulfan. Endosulfan was able to cause the increase of GADD153-GFP expression at a sublethal dose (0.02-20 mg/L). In particular, it induced a maximum green fluorescent protein expression at the tested concentration of 0.2 mg/L, with 4.07-fold inflorescence relative to untreated cells. The results suggest that endosulfan has the potential genotoxicity for HepG2 cell line by inducing DNA damage. The study also confirms that the induced GADD153-GFP expression system is an appropriate and sensitive method for the assessment of genotoxicity from a broad range of pesticides with the DNA-damaging potential.

A stable and sensitive testing system for potential carcinogens based on DNA damage-induced gene expression in human HepG2 cell

In order to analyze potential carcinogenic and genotoxic responses caused by exposure to pollutants existing in environment, a screening method has been established in our laboratory that uses a stably transfected HepG2 cell lines containing gadd153 promoter regions which drive a luciferase reporter gene. Activation of the exogenous gadd153 promoter was quantified using the luciferase activity following drug exposure. Twenty four agents were used to evaluate this screening assay. We selected the agents, ranging from DNA alkylating agents, oxidative agent, radiation, DNA cross-linking agent, nongenotoxic carcinogens, precarcinogenic agents, which included cadmium chloride, chromium trichloride, mercuric chloride, lead nitrate, dichloro-diphenyl-trichloroethane, deltamethrin, biphenylamine, 2-aminofluorene, benzo[a]pyrene, 2,3,7,8,-tetracblorodibenzo-p-dioxin, diethyl-stilbestrol, carbon tetrachloride, mitomycin C, hydroxycamptothecin, UV, sodium fluoride, acrylamide, hydrogen peroxide. In addition, two complex genotoxic agents (water samples) existing in the environment were selected. The results showed that all 20 tested known carcinogenic and genotoxic agents were able to induce gadd153-Luc expression at a sublethal dose. In contrast, four tested non-carcinogens, included 4-acetylaminofluorene, pyrene, benzylpenicillin sodium and vitamin C, were unable to induce gadd153-Luc expression. In conclusion, this reporter system can facilitate in vitro screening for potential carcinogens. Therefore, the gadd153-Luc test system we have developed appears to be a useful and complementary system to existing genotoxic and mutagenic tests.

Mechanisms of enhancement of TRAIL tumoricidal activity against human cancer cells of different origin by dipyridamole

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has emerged as an attractive cytokine that selectively targets cancer cells, however its efficacy has been challenged by a number of resistance mechanisms. Therefore, the current study investigated the potential of dipyridamole to enhance TRAIL efficacy and the probable underlying mechanisms. Dipyridamole dramatically sensitized p53-mutant human cancer cell lines: SW480, MG63 and DU145, to the antitumor activity of TRAIL, as evidenced by enabling TRAIL to efficiently cleave initiator and executioner caspases. Although dipyridamole upregulated both DR4 and DR5 and increased their cell surface expression, RNA interference revealed a preferential dependence on DR5. Moreover, dipyridamole inhibited survivin expression and its important consequences were confirmed by small interfering RNA. Mechanistically, dipyridamole induced transcriptional shutdown of survivin expression accompanying G(1) arrest that was characterized by downregulation of D-type cyclins and cdk6. In addition, a transcriptional mechanism powered by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) induction was responsible for DR5 upregulation by dipyridamole. Importantly, dipyridamole-induced enhancement of TRAIL efficacy and alterations of protein expression were independent of either protein kinase A or protein kinase G. In conclusion, findings of the present study described novel mechanisms of dipyridamole action and highlighted its promising use as a potential enhancer of TRAIL efficacy.

The use of human cell line reporter gene-based assays in chemical toxicity testing

Genetically modified rodents allow greater sensitivity in monitoring DNA damage or gene expression than traditional rodent bioassays and have become increasingly used for toxicity testing, particularly with the greater availability of protein and DNA-based toxicity biomarkers. Here, the advantages and limitations of several in vitro reporter assays already used to study the mechanisms of toxicity are discussed in relation to the in vivo traditional and reporter-based bioassays for carcinogenicity, mutagenicity, endocrine changes and inflammation endpoints to examine the scope for refining and replacing transgenic in vivo models.

Animal carcinogenicity studies: 3. Alternatives to the bioassay

Conventional animal carcinogenicity tests take around three years to design, conduct and interpret. Consequently, only a tiny fraction of the thousands of industrial chemicals currently in use have been tested for carcinogenicity. Despite the costs of hundreds of millions of dollars and millions of skilled personnel hours, as well as millions of animal lives, several investigations have revealed that animal carcinogenicity data lack human specificity (i.e. the ability to identify human non-carcinogens), which severely limits the human predictivity of the bioassay. This is due to the scientific inadequacies of many carcinogenicity bioassays, and numerous serious biological obstacles, which render profoundly difficult any attempts to accurately extrapolate animal data in order to predict carcinogenic hazards to humans. Proposed modifications to the conventional bioassays have included the elimination of mice as a second species, and the use of genetically-altered or neonatal mice, decreased study durations, initiation-promotion models, the greater incorporation of toxicokinetic and toxicodynamic assessments, structure-activity relationship (computerised) systems, in vitro assays, cDNA microarrays for detecting changes in gene expression, limited human clinical trials, and epidemiological research. The potential advantages of non-animal assays when compared to bioassays include the superior human specificity of the results, substantially reduced time-frames, and greatly reduced demands on financial, personnel and animal resources. Inexplicably, however, the regulatory agencies have been frustratingly slow to adopt alternative protocols. In order to decrease the enormous cost of cancer to society, a substantial redirection of resources away from excessively slow and resource-intensive rodent bioassays, into the further development and implementation of non-animal assays, is both strongly justified and urgently required.