Rapid induction of skin and mammary tumors in human c-Ha-ras proto-oncogene transgenic rats by treatment with 7,12-dimethylbenz[a]anthracene followed by 12-O-tetradecanoylphorbol 13-acetate

Possible Application of Human c-Ha-ras Proto-Oncogene Transgenic Rats in a Medium-Term Bioassay Model for Carcinogens

With the aim of developing a medium-term assay for screening of environmental carcinogens, we exposed mammary carcinogen sensitive human c-Ha-ras proto-oncogene transgenic (Hras128) rats to various carcinogens, including compounds that do not normally induce mammary tumors. Seven-week-old Hras128 rats and wild-type littermates received administrations of 3-methylcholanthrene (3-MC), benzo[a]pyrene (B[a]P), anthracene, pyrene, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), dimethylarsinic acid (DMA), diethylnitrosamine (DEN) or azoxymethane (AOM) and were sacrificed at week 12 (females) (at week 10 for the 3-MC group) or week 20 (males). Female Hras128 rats receiving NNK, DEN, or DMA showed a significant increase in mammary tumor incidence and/or multiplicity compared to the respective values with olive oil or deionized distilled water (DDW) vehicles. In male Hras128 rats, a significant increase in mammary tumors was also observed in groups administered 3-MC, B[a]P, anthracene, IQ, and NNK. Mutations of transgenes were observed in codons 12 and/or 61 in the induced tumors by PCR-RFLP except in the DEN group in female and in the MeIQx group in male Hras128 rats. Thus various carcinogens, not necessarily limited to those normally targeting the breast, were found to induce mammary carcinomas in Hras128 rats, especially in females, pointing to potential use for medium-term screening.

Purple corn color suppresses Ras protein level and inhibits 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis in the rat

Anthocyanins belong to the class of phenolic compounds collectively named flavonoids. Many anthocyanins are reported to have inhibitory effects on carcinogenesis. Purple corn color (PCC), an anthocyanin containing extract of purple corn seeds, is used as a food colorant. The major anthocyanin in PCC is cyanidin 3-O-beta-D-glucoside (C3-G). The present study was conducted to assess the influence of dietary PCC on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in rats. PCC significantly inhibited DMBA-induced mammary carcinogenesis in human c-Ha-ras proto-oncogene transgenic (Hras128) rats and in their non-transgenic counterparts. PCC and C3-G also inhibited cell viability and induced apoptosis in mammary tumor cells derived from Hras128 rat mammary carcinomas. At the molecular level, PCC and C3-G treatment resulted in a preferential activation of caspase-3 and reduction of Ras protein levels in tumor cells. It is proposed that C3-G could act as a chemopreventive and possibly chemotherapeutic agent for cancers with mutations in ras. Secondly, the in vitro-in vivo system used in this study can be utilized for screening for cancer preventive compounds that act via Ras down-regulation.

Possible enhancing activity of diacylglycerol on 4-nitroquinoline 1-oxide induced carcinogenesis of the tongue in human c-Ha-ras proto-oncogene transgenic rats

1,2-diacylglycerol (1,2-DAG) is involved in cell proliferation as an activator of protein kinase C (PKC) and has been shown to stimulate growth of cancer cells, raising the possibility of a role in tumor promotion. Ingested DAG oil, containing 70% 1,3-DAG and 30% 1,2-DAG, is digested and considered to be safe as edible oil. However, DAG may directly contact with oral cavity mucosa in undigested form. The present study was conducted to examine the effects of DAG oil on carcinogenesis in c-Ha-ras proto-oncogene transgenic (Tg) rats administered 4-nitroquinoline 1-oxide (4NQO, 10 ppm) in their drinking water for 10 weeks for initiation of mainly upper digestive organs. DAG oil added in basal diet at 5.5%, 2.75%, 1.38% and 0% with total fat made up to 5.5% with triacylglycerol (TAG) was administered during the initiation and post-initiation period. The study was terminated at week 12 (Tg females) and 20 (Tg males, wild females and males). The fatty acid composition of DAG oil was similar to TAG (linoleic acid 46.6% and oleic acid 38.9%). In Tg male rats, DAG oil administration was associated with significant increase (P<0.05) in the incidence of squamous cell carcinomas (SCC) of the tongue (5.5% DAG, 43.8%; 2.75% DAG, 20%; 1.38% DAG, 14.3%; 0%, 12.3%) with the Cochran-Armitage trend test and also number of tumors in coefficients for linear contrast trend tests. Tongue SCC induction of wild males and all females was not significant. The present results suggest that DAG oil may have enhancing and/or promotion potential for tongue carcinogenesis in male Tg featuring elevated ras expression.

Rapid induction of skin tumors in human but not mouse c-Ha-ras proto-oncogene transgenic mice by chemical carcinogenesis

The rasH2 transgenic mice carry human c-Ha-ras proto-oncogene, and are highly susceptible to chemical carcinogenesis. Previous studies showed that the mutation of c-Ha-ras induced by DMBA in the tumors of rasH2 were detected only in transgenes. To examine if the difference between the codons of the c-Ha-ras gene in human and mouse contributed to the tissue-specific sensitivity to DMBA, we generated a line of transgenic mice, mras, carrying mouse c-Ha-ras genome with its own promoter. Western blot analysis showed that the protein expression of H-RAS in the skin was increased in both rasH2 and mras compared with wild-type. Chemical skin carcinogenesis was induced by DMBA and TPA. In rasH2 mice, the latency of tumor formation was shorter than wild-type littermates. Both the number and the volume of skin tumors were increased in rasH2 than those of wild-type. However, in mras mice, enhancement of tumor formation was not observed as compared with wild-type. The mean number of tumors and the latency of tumor development was almost the same between mras and wild-type littermates. Mutational analysis showed only A to T transversion in human c-Ha-ras transgenes at codon 61 but not in murine endogenous c-Ha-ras gene in the tumors of rasH2. In the tumors of wild-type littermates and mras, A to T transversion in murine c-Ha-ras at codon 61 were detected. These results indicate that the differences in the codon of the c-Ha-ras gene between mouse and human might contribute to the tissue-specific sensitivity of DMBA.

Ductal origin of pancreatic adenocarcinomas induced by conditional activation of a human Ha-ras oncogene in rat pancreas

Pancreatic ductal adenocarcinoma is one of the most debilitating malignancies in humans. Currently, radiation and chemotherapy are ineffective, with median survival times after treatment of <12 months. Animal models that reflect the human condition and can be used to explore screening and therapeutic approaches are clearly desirable. One feature of human pancreatic adenocarcinoma is an exceedingly high frequency of K-ras mutation. The present study was conducted to determine if targeted activation of a human oncogenic-ras transgene in rat pancreas would induce carcinomas correspondent to human pancreatic ductal adenocarcinomas. We established transgenic (Hras250) rats in which expression of a human Ha-rasG12V oncogene is regulated by the Cre/lox system. Targeted pancreatic activation of the transgene was accomplished by injection of Cre-carrying adenovirus into the pancreatic ducts and acini through the common bile duct. Adenoviral infection of injected animals was exclusive to the pancreas; infected cells could be identified in duct, intercalated duct, centroacinar and, less frequently, acinar cells, but not in endocrine islet cells. Four weeks after injection, proliferative lesions in the duct epithelium, intercalated ducts and centroacinar cells, but not acinar cells, were widespread. Tumorigenesis in other tissues was not observed. Most lesions, including atypical duct proliferative lesions, PanIN-like lesions and carcinomas, were positive for cytokeratins 19 and 7, cyclooxygenase 2 and MMP-7 but negative for amylase and chymotrypsin. Many adenocarcinoma lesions were positive for EGF and EGFR. Duct epithelial and atypical duct proliferative lesions and carcinoma lesions were all positive for transduced Ha-rasG12V oncogene expression. The cytogenesis of pancreatic ductal type carcinoma was depicted. This model exhibits important similarities to the human disease and promises to advance our understanding of the behavior of pancreas adenocarcinomas and expedite screening and therapy.

Rapid induction of malignant tumor in Sprague–Dawley rats by injection of RK3E-ras cells

Several tumor animal models have been provided as a tool for developing cancer therapy. Here, we developed rapid, easy-to use, and cost-effective new rat animal model for invasion and metastasis of cancer using genetically k-ras-induced rat kidney cells (RK3E-ras). We observed tumor as early as 3 days after injection of RK3E-ras cells in subcutaneous of Sprague-Dawley rats. Tumor size and volume were increased exponentially for 2 weeks. The tail vein injected rats obtained the lethal infiltration in the lung within 2 weeks. This tumor animal model has great potential for studying cancer processes and short-term screening of variable cancer therapy strategy.

Lack of urinary bladder carcinogenicity of sodium L-ascorbate in human c-Ha-ras proto-oncogene transgenic rats

Sodium L-ascorbate (Na-AsA) is widely known to be a tumor promoter of rat bladder carcinogenesis but tests negative in standard 2-year bioassays. In the present study, bladder-cancer-susceptible transgenic rats designated Hras128 were used to further examine the tumorigenicity of Na-AsA. A total of 40 7-week-old male transgenic (Tg) and 42 littermate nontransgenic (Non-tg) rats were divided into 4 groups and given powdered MF diet with or without 5% Na-AsA for 57 weeks. Tg rats showed significantly short survival compared with Non-tg, independent of Na-AsA treatment. Tg rats treated with Na-AsA showed a slightly higher incidence of carcinoma (29.6%) as compared to those without Na-AsA treatment (15.4%), but this was without statistical significance. Moreover, the total bladder tumor incidences, including papillomas, did not differ statistically (with Na-AsA, 37.0%; without Na-AsA, 30.8%). No bladder tumor was detected in Non-tg rats. Various kinds of other lesions in various organs were noted in Tg rats treated with or without Na-AsA treatment, but no intergroup differences were evident. In conclusion, Na-AsA did not show tumorigenicity in highly bladder-cancer-susceptible transgenic Hras128 rats. These results suggest that Na-AsA is a pure promoter but not a complete carcinogen in rats.

High susceptibility of human c-Ha-ras proto-oncogene transgenic rats to carcinogenesis: A cancer-prone animal model

Transgenic animals carrying human c-Ha-ras proto-oncogene, v-Ha-ras transgenic mice, pim-1 transgenic mice and several knockout mice deficient of tumor suppressor genes, such as p53, have been shown to exhibit increased carcinogen susceptibility. As a result, studies into practical application and medium-term screening of environmental carcinogens are under way. Given the advantages of rat models characterized by larger organ size, abundant information regarding preneoplasias and virus-free constitution, we have concentrated on the generation of transgenic rats bearing copies of the human c-Ha-ras proto-oncogene and shown the Hras128 strain to be extremely sensitive to the induction of mammary carcinomas, and to a lesser extent, lesions in the urinary bladder, esophagus and skin. In most, if not all, the mammary cancers mutations of the transgene but not the endogenous H-ras gene are present, appearing to occur early in the process of tumorigenesis, which involves proliferation of cells in TEB and intraductal hyperplasia before carcinomas arise. Preliminary findings suggest that this is independent of endogenous ovarian hormones, although inhibited by soy isoflavones and promoted by atrazine and nonylphenols. Although further studies of the mechanisms are clearly necessary, the model appears to have great potential for screening purposes, not only for modifiers active in the breast, but also other organs where tumors characterized by ras gene mutations develop.