Biomedical subjects

Hiroyuki Tsuda

Publications and source records attributed to Hiroyuki Tsuda.

At least 19 recordsLinked to original sources

PubMed2006

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.

Adenocarcinoma↗

PubMed2006

Establishment of an apoptosis-sensitive rat mammary carcinoma cell line with a mutation in the DNA-binding region of p53.

Seven mammary carcinoma cell lines were established from 7,12-dimethylbenz[a]anthracene-induced tumors developed in a human c-Ha-ras transgenic rat. Without apoptotic stimuli, a large amount of p53 protein was detected in the C11 cell line (C11), whereas all cell lines expressed variable levels of the assayed death receptor/ligand, bcl-2 family and p53 cascade-related genes. The p53 gene in C11 had a mutation at codon 246, in the DNA-binding region of p53. Transcriptional activity of the mutant protein appeared to be lower than that of the wild-type p53. Despite the presence of p53 mutation, C11 was more sensitive to apoptosis triggered by etoposide, paclitaxel and staurosporine than the cell lines expressing wild-type p53. These data suggest that the apoptosis induced by intracellular injury occurs via the transcriptionally impaired mutant p53 in C11.

Animals↗

PubMed2005

An animal model for the rapid induction of tongue neoplasms in human c-Ha-ras proto-oncogene transgenic rats by 4-nitroquinoline 1-oxide: its potential use for preclinical chemoprevention studies.

Oral squamous cell carcinoma is one of the most common human neoplasms, and prevention of this malignancy requires a better understanding of its carcinogenesis process. To this end, we tried to establish an animal model using the human c-Ha-ras proto-oncogene-carrying transgenic (Tg) rats and the carcinogen 4-nitroquinoline 1-oxide (4-NQO). 4-NQO (20 p.p.m.) was administered to Tg and non-Tg rats for 8 weeks in their drinking water, and then the occurrence of tongue carcinogenesis was compared during the experimental period of 22 weeks. In addition, we determined the DNA ploidy in tongue lesions and examined the immunohistochemical expression of five biomarkers such as cyclin D1, glutathione S-transferase placental form, cyclooxygenase (COX)-2, inducible nitric oxide synthase (iNOS) and beta-catenin. Next, the cancer chemopreventive effects of nimesulide, pioglitazone and a synthetic geranylated derivative, which have been reported to be inhibitors of tongue carcinogenesis, were examined in Tg rats treated with 4-NQO. Either during or after treatment with 4-NQO in the drinking water, tongue dysplasia and tumors were observed on the tongues of both Tg and non-Tg rats, with a greater incidence and multiplicity in Tg rats. Histopathologically, squamous cell dysplasia, papilloma and carcinoma with or without invasion were present in the tongue. Immunohistochemistry revealed that expression levels against five biomarkers increase with disease progression, and the changes correlated with those of the DNA ploidy pattern. Interestingly, a strong expression of COX-2, iNOS and beta-catenin was observed on the invasive front of squamous cell carcinomas. A subsequent chemoprevention study using Tg rats showed that the chemicals tested suppressed the occurrence of tongue carcinomas when they were administered after 4-NQO-exposure. These results may thus indicate that our 4-NQO-induced Tg rat tongue carcinogenesis model simulates many aspects of human oral carcinogenesis and it can be applied for an analysis of oral cancer development while also helping to identify potentially effective cancer chemopreventive agents against oral cancer.

4-Nitroquinoline-1-oxide↗

PubMed2005

Dietary supplementation with silymarin inhibits 3,2'-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in male F344 rats.

PURPOSE: Silymarin has been shown to be a potent anticarcinogenic agent. Here, we investigated the modifying effects of dietary feeding with a naturally occurring polyphenolic antioxidant flavonoid silymarin on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced prostatic carcinogenesis in male F344 rats. EXPERIMENTAL DESIGN: Male F344 rats were given s.c. injections of DMAB (25 mg/kg body weight) every other week for 20 weeks. They also received the experimental diet containing 100 or 500 ppm silymarin for 40 weeks, starting 1 week after the last dosing of DMAB. All of the rats were sacrificed 60 weeks after the start of the experiment. Histopathology and immunohistochemistry for proliferative cell nuclear antigen, cyclin D1, and apoptotic indices were done in the prostatic lesions, including invasive adenocarcinomas, intraepithelial neoplasms, and nonlesional glands. RESULTS: Dietary feeding with 500 ppm silymarin significantly inhibited the incidence of prostatic adenocarcinoma when compared with the DMAB-alone group (17.6% versus 50.0%, P < 0.05). The proliferative cell nuclear antigen- and cyclin D1-positive indices in adenocarcinomas, prostatic intraepithelial neoplasm, and nonlesional glands in rats treated with DMAB and silymarin were slightly lower than that of the DMAB-alone group. Also, dietary administration of silymarin increased apoptotic index in prostatic adenocarcinoma by measuring immunohistochemically positive nuclei for ssDNA. CONCLUSIONS: Our results indicate that silymarin exerts chemopreventive ability against chemically induced prostatic carcinogenesis through apoptosis induction and modification of cell proliferation.

Adenocarcinoma↗

PubMed2005

Lack of potential of low dose N-nitrosodimethylamine to induce preneoplastic lesions, glutathione S-transferase placental form-positive foci, in rat liver.

Induction of liver lesions in male F344 rats by the genotoxic and carcinogenic N-nitrosodimethylamine (NDMA) was studied at a wide range of dose levels, i.e. from 0.001 to 10 ppm, in drinking water for 16 weeks. Dose related and statistically significant increase of glutathione S-transferase placental form-positive foci, endpoint markers for hepatocarcinogenesis in rats, at 1 and 10 ppm dose groups was obtained, but no increment in foci could be detected with the lower doses (0.001, 0.01, and 0.1 ppm). This finding of a no-observed effect level supports our hypothesis that a threshold, at least in practical terms, exists in carcinogenesis proposed on the basis of extensive wide range dose-dependence studies of other genotoxic carcinogens.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

Full length and delta lactoferrin display differential cell localization dynamics, but do not act as tumor markers or significantly affect the expression of other genes.

Lactoferrin is a secreted protein related to transferrin. Lactoferrin indirectly protects host cells against foreign insults by killing bacteria, scavenging free iron, and binding to receptors required for viral invasion. However, lactoferrin is also proposed to act directly on cells as a transcription factor and tumor suppressor gene. In addition to full length lactoferrin, a truncated form, called delta lactoferrin, can also be produced by alternative splicing. We show here that transformed and nontransformed cells are equally able to express both full length and delta lactoferrin. Moreover, both forms of lactoferrin failed to substantially modulate the expression of other genes. Thus, lactoferrin does not seem to directly control gene expression or inhibit tumor cell growth.

Alternative Splicing↗

PubMed2004

Lactoferrin modifies apoptosis-related gene expression in the colon of the azoxymethane-treated rat.

Lactoferrin, an iron-binding glycoprotein, exhibits suppressive effects on development of azoxymethane (AOM)-induced tumors in the rat colon, but the mechanisms are largely unknown. In this study, we investigated the effect of lactoferrin on the gene expression of 10 apoptosis-related molecules in colon mucosa of AOM-treated rats during early and late stages of colon carcinogenesis by reverse transcription PCR. Here we document that a death-inducing receptor, Fas, and a pro-apoptotic Bcl-2 family member, Bid, are increased in the colon mucosa in proportion to decreases in AOM-induced aberrant crypt foci by lactoferrin. Similarly, increased expression of the pro-apoptotic Bcl-2 family member, Bax, was also observed in AOM-induced tumors in rats fed by lactoferrin. These results indicate that Fas and pro-apoptotic Bcl-2 members participate in the lactoferrin action and may contribute to suppressive effects on tumor development in the rat colon.

Administration, Oral↗

PubMed2004

Bovine lactoferrin inhibits tumor-induced angiogenesis.

Recent studies have demonstrated that bovine lactoferrin (bLF) suppresses tumor growth and metastasis in the mouse and rat and moreover may inhibit angiogenesis. To determine whether angiogenesis inhibition might contribute to antitumor activity, we examined the influence of bLF on tumor-induced angiogenesis and endothelial cell functions as well as angiogenesis-related cytokine production. Bovine LF exhibited dose-dependent inhibition of angiogenesis on 4-6-day-old chick embryo chorioallantoic membranes (CAMs) that lack a mature immune response. This inhibition was reversed when bLF was simultaneously treated with basic fibroblast growth factor (bFGF). It also inhibited in vitro formation of tube-like structures of mouse endothelial KOP2.16 cells. Moreover, it potently suppressed bFGF- or VEGF-induced proliferation of mouse endothelial KOP2.16 cells, but not of mouse fibroblast A31 cells and Lewis lung carcinoma (3LL) cells. In mice, both orally and intraperitoneally administered bLF significantly and dose-dependently suppressed 3LL cell-induced angiogenesis in a dorsal air sac assay. As orally administered bLF was reported to exhibit antitumor activity through production of interferon (IFN)-gamma and interleukin (IL)-18 in intestinal mucosa (Kuhara T et al., Nutr Cancer 2000;38:192-9), production of these cytokines in mouse serum and peritoneal macrophages by bLF was examined. IFN-gamma was not detected in serum by bLF administration. However, bLF markedly elevated IL-18 concentration in serum by oral administration, but not by intraperitoneal administration. It also induced IL-18 in peritoneal macrophages in vitro. These results suggest that bLF participates as a regulator of angiogenesis, possibly explained by blocking endothelial function and inducing IL-18 production. Antitumor activity of bLF may thus be partly mediated by angiogenesis inhibition.

Administration, Oral↗

PubMed2004

Lactoferrin enhances Fas expression and apoptosis in the colon mucosa of azoxymethane-treated rats.

Bovine lactoferrin, a multifunctional glycoprotein, has been shown to strongly inhibit development of azoxymethane (AOM)-induced rat colon tumors. Little, however, is known about the inhibitory mechanisms. We have demonstrated recently that lactoferrin enhances the expression of a member of the tumor necrosis factor receptor family, Fas, in the colon mucosa during both early and late stages of carcinogenesis. Thus, Fas could be involved in bovine lactoferrin-mediated inhibition of tumor development. To investigate this possibility, we studied the influence of bovine lactoferrin on Fas-mediated apoptosis with regard to expression of Fas, activation of caspase-8 and caspase-3, and DNA fragmentation in the colon mucosa of AOM-treated rats. Western blot analysis demonstrated a >2.5-fold increase in Fas protein expression, as well as elevation of the active forms of both caspase-8 and caspase-3. Immunohistochemical analysis revealed Fas-positive cells and apoptotic cells preferentially within the proximal colon region, clearly at the site of bovine lactoferrin-mediated tumor inhibition. These results suggest that apoptosis caused by elevated expression of Fas is involved in chemoprevention by lactoferrin of colon carcinogenesis.

Animals↗

PubMed2004

Normal cells control the growth of neighboring transformed cells independent of gap junctional communication and SRC activity.

The growth of many types of cancer cells can be controlled by surrounding normal cells. However, mechanisms underlying this phenomenon have not been defined. We used a layered culture system to investigate how nontransformed cells suppress the growth of neighboring transformed cells. Direct physical contact between transformed and nontransformed cells was required for growth suppression of transformed cells in this system; communication by diffusible factors was not sufficient. However, significant gap junctional communication was not required, indicating that other intercellular junctions mediated this growth regulatory response. We also report that the Src kinase activity in transformed cells was not directly inhibited by contact with nontransformed cells. Instead, nontransformed cells increased the expression of serum deprivation-response protein and the transcription factor four and a half LIM domain 1 in tumor cells. In addition, these results suggest mechanisms by which normal cells may block Wnt signaling, inhibit insulin-like growth factor activity, and promote host recognition of neighboring tumor cells.

Animals↗

PubMed2004

Orally administered bovine lactoferrin induces caspase-1 and interleukin-18 in the mouse intestinal mucosa: a possible explanation for inhibition of carcinogenesis and metastasis.

We have previously demonstrated that oral administration of bovine lactoferrin (bLF) markedly inhibits lung metastatic colony formation, and that this inhibition was possibly due to the activation of T and NK cells. Furthermore, we found that interleukin-18 (IL-18) is induced in epithelial cells of the small intestine by bLF. The present study was undertaken to confirm cytokine production in response to bLF and to assess the underlying mechanisms. Markedly elevated IL-18 levels were found in the small intestine 1-3 h after a single administration of bLF, its pepsin hydrolysate (bLFH), or bTF. Importantly, while IL-18 was significantly increased after a regimen of seven daily administrations of bLF or bLFH, administration of bTF over the course of seven days had little or no effect. In addition to IL-18, a significant increase in caspase-1 activity and interferon-gamma (IFN-gamma) was found in the small intestine after administration of bLF. Similarly, in peritoneal macrophages, bLF markedly enhanced caspase-1 activity and IL-18 levels. Finally, a caspase-1 inhibitor significantly decreased bLF mediated induction of IL-18 in vitro. (bTF had no effect on either caspase-1 or IFN-gamma or on IL-18 in vitro.) These results demonstrate the possibility that elevation of caspase-1 activity by bLF and its hydrolysate may be important for production of mature IL-18 in vivo, and thus in potentiating the killing activity of T and NK cells against tumor cells.

Administration, Oral↗

PubMed2004

Terminal endbuds and acini as the respective major targets for chemical and sporadic carcinogenesis in the mammary glands of human c-Ha-ras protooncogene transgenic rats.

A rat strain carrying the human c-Ha-ras protooncogene, established by our laboratory, is highly susceptible to mammary chemical carcinogens. The transgenic rats exhibit increased number of terminal endbuds (TEBs) at the tips of developing ducts in the mammary gland compared to non-transgenic littermates. Confocal microscopy revealed the level of active mitogen-activated protein kinase to be elevated in these TEBs, and a close correlation between their numbers and tumorigenic response initiated by 7,12-dimethylbenz[a]anthracene was confirmed. Single injections of N-methyl-N-nitrosourea into the transgenic rats caused mutations in codon 12 of human c-Ha-ras transgene in TEBs before tumor development, supporting the conclusion that these structures are the major targets of chemical carcinogens. In contrast, with spontaneous development of lesions, alveolar hyperplasia with elevated expression levels of rat and human c-Ha-ras protooncogenes is the first morphological alteration which becomes apparent. Some but not all hyperplastic alveolar nodules were found to harbor mutations in the transgene. The results indicate that elevated expression of c-Ha-ras protooncogene is sufficient in itself to cause a highly proliferative phenotype of mammary alveoli. Our data suggest that TEBs and acini are the major targets for chemical and sporadic carcinogenesis, respectively, in the mammary glands of human c-Ha-ras protooncogene transgenic rats.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2004

Inhibition of breast cancer regrowth and pulmonary metastasis in nude mice by anti-gastric ulcer agent, irsogladine.

Irsogladine is a commonly used anti-gastric ulcer agent in Japan, and recent in vivo studies have shown it to have anti-angiogenic properties. The exact role of irsogladine as an inhibitor of angiogenesis remains uncertain. In this study, we show that irsogladine inhibited breast cancer regrowth and pulmonary metastasis but had no anti-angiogenic function against HUVEC cells. Irsogladine failed to inhibit proliferation, tubular formation, and the uPA/MMP-1 mRNA expression of HUVEC cells. We also examined the effect of irsogladine in an orthotopic transplant model of human breast cancer metastasis in athymic mice. Human MDA-MB-435 cells were injected into the mammary fat pads. After 9 weeks, the tumors were resected under general anesthesia. Irsogladine or vehicle was given p.o. daily thereafter. Daily administration of irsogladine at 120 mg/kg per day over a 5-week period had no effect on the body weight of the mice. Tumor regrowth, average volume of pulmonary metastases, and the number of metastases were inhibited by 40, 48 and 64%, respectively. These results suggest that irsogladine may be useful in the breast cancer adjuvant setting.

Animals↗

PubMed2004

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.

We have established a transgenic rat line carrying 3 copies of the human c-Ha-ras proto-oncogene with its own promoter region (Jcl/SD-TgN(HrasGen)128Ncc) (Hras128 rat), expression being detectable in almost all organs. We have already demonstrated that the rat is highly sensitive to mammary, esophagus and bladder carcinogenesis. In the present study, male and female transgenic and wild-type littermates were topically treated with 2.5 mg of 7,12-dimethylbenz[a]anthracene (DMBA) dissolved in 1.0 ml of acetone on the back skin at 50 days after birth. Starting 1 week thereafter, they were again topically treated with 100 nmol of 12-O-tetradecanoylphorbol 13-acetate (TPA) dissolved in 0.5 ml of acetone 3 times weekly for the following 31 weeks. In males treated with DMBA and/or TPA, skin tumors, including both squamous cell papillomas (SCP) and carcinomas (SCC), were preferentially induced at the DMBA-TPA painting sites: DMBA-TPA, 15/15 (100%); DMBA, 6/8 (75%); TPA, 1/6 (16.7%). They were also, unexpectedly, induced on remote scrotal skin: DMBA-TPA, 13/15 (86.7%); DMBA, 5/8 (62.5%); TPA, 0/6 (0%). Lesions were thus more frequent in the DMBA-TPA group than with DMBA or TPA alone. In females, adenomas and adenocarcinomas of the mammary glands were preferentially induced: DMBA-TPA, 12/14 (85.7%); DMBA, 6/8 (75%); TPA, 3/6 (50%), with only a few small skin papillomas at painting sites. Incidences and numbers of the mammary and skin tumors were much greater in Hras128 rats than in their wild-type counterparts. PCR-RFLP analysis of the transgene indicated that the percentage of the cell populations harboring a mutation in codons 12 and/or 61 ranged from 2% to 60% in individual tumors; skin tumors showed more mutations in codon 61 in the DMBA-treated groups. In contrast, no mutations were detected in the endogenous rat c-Ha-ras gene. These results indicate that the Hras128 rat is highly susceptible to DMBA-TPA skin and mammary carcinogenesis, thus providing a unique painting model for skin as well as mammary gland carcinogenesis, that would be suitable for investigating the role of transgene mutations.

Animals↗

PubMed2004

Lack of modifying effects of 4-ter t-octylphenol and benzyl butyl phthalate on 3,2-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in rats.

The modifying effects of dietary feeding of two estrogenic compounds, 4-tert-octylphenol (tOP) and benzyl butyl phthalate (BBP), on 3,2-dimethyl-4-aminobiphenol (DMAB)-induced prostatic carcinogenesis were investigated in male F344 rats. We also assessed the effects of the test compounds on the proliferating cell nuclear antigen (PCNA) index in induced neoplasms, prostatic intra-epithelial neoplasm (PIN), and non-lesional glands in the prostate. To induce prostatic neoplasms, rats were given subcutaneous injections of DMAB (25 mg/kg body weight) every other week, 10 times in total. They also received the experimental diet containing 10 or 100 ppm tOP and BBP for 40 weeks, starting 1 week after the last dosing of DMAB. DMAB exposure produced prostatic adenocarcinoma with an incidence of 41.2% at the end of the study (week 60). Dietary administration of tOP and BBP did not affect the incidence of prostatic adenocarcinoma: 43.8% in the DMAB --> 10 ppm tOP group; 25.0% in the DMAB --> 100 ppm tOP group; 43.8% in the DMAB --> 10 ppm BBP group; and 43.8% in the DMAB --> 100 ppm BBP group. The PCNA indices in adenocarcinomas, PIN, and non-lesional glands in rats treated with DMAB and tOP or BBP were slightly lower than that of the DMAB alone group, but the differences were not statistically significant. These results might suggest that dietary feeding of the estrogenic compounds tOP and BBP did not modulate DMAB-induced prostatic carcinogenesis in rats.

Adenocarcinoma↗

PubMed2004

Preferential mammary carcinogenic effects of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human c-Ha-ras proto-oncogene transgenic rats.

In order to clarify the susceptibility of the Hras128 rat harboring copies of the human c-Ha-ras proto-oncogene to 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), Hras128 rats were intragastically treated with 100 mg/kg PhIP 8 times (females) or 80 mg/kg PhIP 10 times (males) over a 9-week period, then sacrificed at weeks 12 and 30. Multiple mammary tumors of adenocarcinoma type were induced in all females, while 83% of treated males developed adenocarcinomas, sarcomas and transitional carcinosarcomas, as evidenced by casein and vimentin immunoreactivity. All tumors examined had mutations in the c-Ha-ras transgene, while the endogenous rat c-Ha-ras gene was intact. Our results indicate that 1) Hras128 rats of both sexes are preferentially susceptible to mammary carcinogenesis with PhIP; 2) activation of the transgene, but not the endogenous c-Ha-ras gene, may be important in this regard; 3) the variety of tumor types evident in male rats indicates that immature mammary gland cells of the terminal end buds may be a target of PhIP; 4) although the transgene is expressed in all organs, susceptibility to PhIP is limited to mammary glands.

Animals↗