Promotion of mouse two-stage skin carcinogenesis by diacylglycerol-rich edible oil.

Tumor promotion potential of diacylglycerol (DAG)-rich edible oil was examined using a two-stage mouse skin carcinogenesis model initiated with 7,12-dimethylbenz[a]anthracene (DMBA). Topical treatment with 75 mg DAG oil once a day for 5 days/week for 35 weeks caused papillomas in 4 of 23 (17%) DMBA-treated female ICR mice, while DMBA initiation alone and DAG treatment without DMBA initiation did not induce any skin tumors. Doubling the daily treatment (twice a day x 5 days/week) at doses of 75 and 30 mg caused both papillomas and squamous cell carcinomas after DMBA initiation, the incidences of tumors being 48% (12/25) and 44% (11/25), respectively, significantly higher than the 4% (1/23) in the DMBA+ 85 mg triacylglycerol group and 0% (0/24) in the DMBA+ vehicle-treated group. The results indicate that DAG-rich oil has promoting potential for skin carcinogenesis, and thus, further investigations of its tumor-promoting potential in other organs are warranted.

Periodic analysis of urethane-induced pulmonary tumors in living A/J mice by respiration-gated X-ray microcomputed tomography.

X-ray microcomputed tomography (micro-CT) with a respiratory gating system is a useful non-invasive approach to evaluate lung tumor development in living animal models. Here micro-CT was applied for the detection of lung lesions induced by a single intraperitoneal injection (250 mg/kg) of urethane in male A/J mice, at 2-week intervals from 10 to 30 weeks after carcinogen exposure. In micro-CT cross sections, lung tumor images were easily distinguished from surrounding non-tumorous tissues, the smallest detected tumor being approximately 0.5 mm in diameter. All of the urethane-treated mice (n = 15) developed lung tumors and the number of tumors developed in each mouse was 8.6 +/- 3.9. Six tumors, determined histopathologically to be adenocarcinomas, were detected, growing at different rates during the experimental period. The most aggressive carcinoma, increasing in diameter from 0.9 to 3.5 mm within 8 weeks, was a solid-type nodule with a clear tumor margin on the micro-CT imaging. Other tumors, histopathologically adenomas, grew slowly or moderately. The results provide evidence that micro-CT is a useful non-invasive imaging approach for evaluating the characteristics and growth of lung tumors in mice.

Occurrence of mutations in the epidermal growth factor receptor gene in X-ray-induced rat lung tumors.

Epidermal growth factor receptor (EGFR) gene alterations have been found in human lung cancers. However, there is no information on the factors inducing EGFR mutations. In rodents, K-ras mutations are frequently found in many lung carcinogenesis models, but hitherto, Egfr mutations have not been reported. Their presence was therefore investigated in representative lung carcinogenesis models with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosobis(2-hydroxypropyl)amine (BHP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and ethyl carbamate (urethane), as well as X-ray irradiation. With the chemical carcinogenesis models, no mutations were detected in Egfr, which is in clear contrast to the high rates observed in either codon 12 or 61 of K-ras (21/23 of the lung tumors induced with NNK, 4/5 with MeIQx, 1/4 with urethane and 7/18 with BHP). However, in the X-ray-induced lung tumors, Egfr mutations with amino acid substitution were observed in exons 18 and 21 (4/12, 33%), but no activating mutation of K-ras was detected. In addition, one and four silent mutations were identified in K-ras (exon 1) and Egfr (exons 18, 20 and 21), respectively. Most mutations in both Egfr and K-ras were G/C-->A/T transitions (7/8, 88% and 31/34, 91%, respectively). Although, the mutational patterns in equivalent human lesions were not completely coincident, this first report of Egfr mutations in an experimental lung tumor model suggests that X-rays or other factors producing oxygen radicals could cause EGFR mutations in some proportion of lung cancers in humans.

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.

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.

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.

Prevention of carcinogenesis and cancer metastasis by bovine lactoferrin.

Increasing attention is being paid to chemopreventive agents for individuals at high risk of cancer. We have concentrated on bovine lactoferrin (bLF), an 80 kDa iron-binding glycoprotein known to have anti-microbial and immunoprotective effects. Lactoferrin is particularly abundant in colostrum, and is also present in tears, saliva and seminal and uterine secretions. However, only little is known regarding its influence on carcinogenesis. We have shown preventive effects of bLF and its fragment peptide, lactoferricin (bLFcin), consisting of a 25 amino acid sequence without iron binding capacity, on chemically-induced colon carcinogenesis in the rat and transplanted carcinoma cell metastasis in the mouse. The mechanisms are wide-spectrum, including elevation of caspase-1 and IL-18 in the small intestine, enhancement of the cell killing activity of cytotoxic T and natural killer (NK) cells, and anti-inflammatory and anti-angiogenic effects. It also inhibits the induction of liver CYP1A2, a carcinogen activating enzyme, and induces apoptosis in the colon epithelium of carcinogen treated rats. Thus, bLF possesses multi-functional potential to suppress carcinogenesis and is a good candidate for practical application in humans.

Prostaglandin E receptor EP3 deficiency modifies tumor outcome in mouse two-stage skin carcinogenesis.

We have recently shown that the prostaglandin E(2) (PGE(2)) receptor EP(3) plays an important role in suppression of colon cancer cell proliferation and that its deficiency enhances late stage colon carcinogenesis. Here we examined the effects of EP(3)-deficiency on two-stage skin carcinogenesis. 7,12-Dimethylbenz[a]anthracene (50 microg/200 microl of acetone) was thus applied to the back skin of female EP(3)-knockout and wild-type mice at 8 weeks of age, followed by treatment with 12-O-tetradecanoylphorbol-13-acetate (5 microg/200 microl of acetone) twice a week for 25 weeks. First tumor appearance was observed in EP(3)-knockout mice at week 10, which was 3 weeks later than in EP(3) wild-type mice, and multiplicity observed at week 11 was significantly lower in the EP(3)-knockout case. However, histological examination showed that the tumor incidence and multiplicity at week 25 were not significantly changed in knockout mice and wild-type mice (incidence, 19/19 versus 23/24; multiplicity, 3.58 +/- 0.51 versus 3.17 +/- 0.63, respectively). Interestingly, there were no squamous cell carcinomas (SCCs) in the EP(3)-knockout mice, while SCCs were observed in 3 out of 24 wild-type mice. Furthermore, benign keratoacanthomas only developed in EP(3)-knockout mice (6/19 versus 0/24, P < 0.01). The results suggest that PGE(2) receptor EP(3) signaling might contribute to development of SCCs in the skin.

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.

Cancer prevention by natural compounds.

Increasing attention is being paid to the possibility of applying cancer chemopreventive agents for individuals at high risk of neoplastic development. For this purpose by natural compounds have practical advantages with regard to availability, suitability for oral application, regulatory approval and mechanisms of action. Candidate substances such as phytochemicals present in foods and their derivatives have been identified by a combination of epidemiological and experimental studies. Plant constituents include vitamin derivatives, phenolic and flavonoid agents, organic sulfur compounds, isothiocyanates, curcumins, fatty acids and d-limonene. Examples of compounds from animals are unsaturated fatty acids and lactoferrin. Recent studies have indicated that mechanisms underlying chemopreventive potential may be combinations of anti-oxidant, anti-inflammatory, immune-enhancing, and anti-hormone effects, with modification of drug-metabolizing enzymes, influence on the cell cycle and cell differentiation, induction of apoptosis and suppression of proliferation and angiogenesis playing roles in the initiation and secondary modification stages of neoplastic development. Accordingly, natural agents are advantageous for application to humans because of their combined mild mechanism. Here we review naturally occurring compounds useful for cancer chemprevention based on in vivo studies with reference to their structures, sources and mechanisms of action.

Possible enhancing effects of atrazine and nonylphenol on 7,12-dimethylbenz[a]anthracene-induced mammary tumor development in human c-Ha-ras proto-oncogene transgenic rats.

Our transgenic (Tg) strain carrying copies of the human c-Ha-ras proto-oncogene is highly susceptible to 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis, possibly due to activation of the transgene, and can be used in medium-term bioassay models to test for modifying effects of estrogenic environmental compounds on tumor development. The present study was conducted to assess the influence of dietary feeding of the endocrine disruptors atrazine and nonylphenol on DMBA-induced carcinogenesis in c-Ha-ras Tg rats. Animals of both sexes were given a single oral dose of DMBA (25 mg/kg body weight) at 50 days of age and thereafter received soybean-free diet containing 5, 50 or 500 ppm atrazine, or 10, 25, 100 or 250 ppm nonylphenol. In female Tg rats, atrazine at a dose of 5 ppm increased the incidences of mammary adenomas and adenocarcinomas (P < 0.01 and P < 0.05), while 50 ppm increased the adenocarcinoma incidence (P < 0.05). In males, skin tumor development, in contrast, was significantly decreased at the highest dose. Nonylphenol at 10 ppm increased adenocarcinoma and total mammary tumor multiplicity in female Tg rats (P < 0.05), but there was no dose dependence, a significant quadratic dose-response trend rather being observed (P < 0.05). In vitro, atrazine did not cause proliferation of MCF-7 cells at any of a range of doses tested. These results suggest that endocrine disruptors may enhance mammary carcinogenesis, but only in a certain limited dose range under the present experimental conditions. The doses applied, moreover, were all extremely high compared to the possible environmental human exposure levels.

Isoliquiritigenin, a flavonoid from licorice, reduces prostaglandin E2 and nitric oxide, causes apoptosis, and suppresses aberrant crypt foci development.

Isoliquiritigenin (ILTG), a flavonoid group compound, exists in some foodstuffs and herbal medicines such as licorice (Glycyrrhiza uralensis Fisher). Previously, we showed that ILTG can suppress azoxymethane (AOM)-induced colon carcinogenesis in ddY mice. In the present report, we present evidence that ILTG markedly decreases both prostaglandin E2 (PGE2) and nitric oxide (NO) production in RAW264.7 mouse macrophage cells. The decrease of PGE2 was dependent on cyclooxygenase-2 (COX-2) expression and the decrease of NO appeared due to a decrease in inducible nitric oxide synthase (iNOS) protein expression. In mouse and human colon carcinoma cells, ILTG treatment suppressed cell growth and caused apoptosis. Furthermore, in vivo administration of ILTG inhibited the induction of preneoplastic aberrant crypt foci (ACF) in the male F344 rat colon. Our results suggest that ILTG is a promising chemopreventive agent against colon carcinogenesis.

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.

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.

Lack of initiation activity in rat liver of low doses of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline.

It has been generally accepted that genotoxic carcinogens have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged for cancer risk assessment in humans. Here we examined low dose carcinogenicity of a food-derived, genotoxic hepatocarcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), using an in vivo medium-term bioassay to detect initiating activity for rat hepatocarcinogenesis. With MeIQx initiation at various doses followed by administration of phenobarbital, a well known hepatopromoter, no induction of glutathione S-transferase placental form-positive foci, assessed as preneoplastic lesions, was noted at doses of 0.001-1 ppm. The results imply a no-observed effect level for hepatocarcinogenicity with this genotoxic agent.

Inhibitory effects of 17beta-estradiol and 4-n-octylphenol on 7,12-dimethylbenz[a]anthracene-induced mammary tumor development in human c-Ha-ras proto-oncogene transgenic rats.

Experiments were conducted to determine whether the natural estrogen and an environmental compound with estrogenic action, 4-n-octylphenol (4nOP), could modify tumor development in human c-Ha-ras proto-oncogene transgenic (Tg) rats which are highly susceptible to mammary and skin carcinogens. Female and male Tg and non-transgenic (non-Tg) rats were given a single oral dose of 7,12-dimethylbenz[a]anthracene (DMBA) (25 mg/kg body weight) at 50 days of age and thereafter subcutaneously implanted with cholesterol pellets containing 0.01, 0.1 or 1.0 mg beta-estradiol 3-benzoate (E2) per rat or received diets containing 1000 or 100 p.p.m. 4nOP for 12 weeks in females or for 20 weeks in males. E2 reduced the mammary tumor incidence and multiplicity in a dose dependent manner, especially in female Tg rats. In contrast, E2 increased mammary tumor incidence and multiplicity at the lowest dose (0.01 mg), however it reduced skin tumor induction in male Tg rats. 4nOP at a dose of 100 p.p.m. decreased mammary tumor multiplicity in female Tg rats (P < 0.001). No effects were observed in males. In separate in vitro studies, E2 at low doses (10(-11)-10(-8) M) enhanced the growth of both MCF-7 and T47D cells and this was similarly the case for 4nOP at high doses (10(-7)-10(-5) M) in T47D cells. The finding that E2 and 4nOP at high doses caused reduction in mammary tumor development in female Tg and possibly non-Tg rats, may indicate that excess estrogen can exert a paradoxical inhibitory influence. E2 also appears to have bipotential effects in males, promoting mammary, but inhibiting skin carcinogenesis. These contrasting observations may be caused by differences in background physiological estrogen levels. In addition, the results suggest that Tg rats can be used in medium-term bioassay models to test for the modifying effects of estrogenic environmental compounds on mammary tumor development.

Studies on cancer chemoprevention by traditional folk medicines XXIV. Inhibitory effect of a coumarin derivative, 7-isopentenyloxycoumarin, against tumor-promotion.

7-Isopentenyloxycoumarin (1) was isolated from Heracleum lanatum MICHX. (Umbelliferae). Compound 1 inhibited phospholipid metabolism and Epstein-Barr virus activation caused by a potent tumor promoter. In an in vivo experiment, topical application of 1 suppressed skin-tumor-formation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in 7,12-dimethylbenz[a]anthracene (DMBA) initiated mice. And it also suppressed ornithine decarboxylase activity stimulated by TPA on mouse skin. These results indicated that 7-isopentenyloxycoumarin is one of the effective compounds from natural resources for treating skin tumor formation.

Promotion of Liver Lesion Development in the Syrian Hamster by Dietary Fat Following Multi-organ Initiation is Inhibited by DHEA-S Administration.

The influence of dietary supplementation with dehydroepiandrosterone-sulphate (DHEA-S) at 0.6% was investigated in male Syrian golden hamsters initiated by treatments with azoxymethane(AOM), and dihydroxy-di-n-propyl nitrosamine (DHPN), timed after transfer from a choline-deficient to a normal diet. These carcinogens respectively target the colon, and the respiratory tract, the liver and pancreas. A total of 75 animals were divided into 6 groups, 1-3 (20 animals each) receiving the initiation protocol of during the first 8 weeks, and 4-6 (5 animals each) given the vehicles alone. The hamsters in groups 2,3 and 5,6 then received a high fat diet (20% corn oil) while DHEA-S was given in addition for 20 weeks to groups 3 and 6. Groups 1 and 4 served as controls on the basal diet. Assessment of development of preneoplastic and neoplastic lesions, after sacrifice at week 28, revealed increase in hepatocellular liver nodules and the index of BrdU incorporation in the hepatocellular cells of the liver in the initiated animals given the high fat diet. This was significantly reduced by the DHEA-S supplementation. Non-significant tendencies for high fat enhancement and hormone protection were also observed for lung and colon tumors.