Increased susceptibility to mammary carcinogenesis and an opposite trend in endometrium in Trp53 heterozygous knockout female mice by backcrossing the BALB/c strain onto the background C3H strain.

Patients with dominantly inherited Li-Fraumeni syndrome have a loss-of-function mutation in TP53 and develop diverse mesenchymal and epithelial neoplasms at multiple sites. Trp53 +/- female mice with the BALB/c background provide unique characteristics for the study of breast cancer in Li-Fraumeni syndrome; however, we previously found that female C3H-Trp53+/ - mice did not spontaneously develop mammary tumors. Therefore, we obtained F1 and N2-N4 female mice by backcrossing the BALB/c strain and examined the incidence of mammary and other tumors in lifetime studies. Malignant lymphomas, osteosarcomas, and uterine adenocarcinomas spontaneously developed in approximately 20% or more of Trp53+/ - mice with the C3H background. In contrast, the incidence of uterine adenocarcinomas showed a tendency to decrease, while that of mammary adenocarcinomas gradually increased in mice with the BALB/c strain backcross. Wild-type BALB/c female mice are predisposed to a wide spectrum of neoplasms, including mammary tumors, partly due to genetic factors, whereas uterine tumors are uncommon not only in BALB/c mice but also C3H mice. Thus, genetic factors appear to contribute to a strain-specific predisposition to malignant neoplasms in Trp53+/- mice, and further studies are needed to clarify the detailed mechanisms.

Prostaglandin E receptor subtype EP(1) deficiency inhibits colon cancer development.

Prostaglandin E(2) exerts its biological activity through binding to its membrane receptors, E-prostanoid (EP) receptors. Our previous finding that lack of EP(1) receptor inhibits the early stages of colon carcinogenesis led us to investigate whether EP(1) receptor deficiency reduces colon cancer development induced by azoxymethane (AOM) using EP(1) receptor knockout mice. At 6 weeks of age 33 homozygous EP(1)-deficient (EP(1)(-/-)) mice and 28 wild-type (EP(1)(+/+)) mice were given i.p. AOM (10 mg/kg body wt) once a week for 6 weeks. At 56 weeks of age all animals were killed and intestinal tumors were examined. The results clearly indicated that lack of EP(1) receptor significantly reduced colon cancer incidence (27 versus 57%, P < 0.05) and multiplicity (0.30 versus 0.76, P < 0.05) as well as tumor volume (12.2 versus 75.6 mm(3), P < 0.05). In EP(1)(-/-) mice, silver stained nucleolar organization region protein count as cell proliferation marker was significantly reduced (1.35 versus 2.17, P < 0.001) and apoptosis was significantly increased (0.685 versus 0.077, P < 0.001) in colon tumors induced by AOM compared with those in EP(1)(+/+) mice. We confirmed that EP(1) receptor mRNA was overexpressed in colon cancers of EP(1)(+/+) mice using reverse transcription-polymerase chain reaction. These results provide strong evidence that the EP(1) receptor is of major importance for colon cancer development and it could be a new target for a mechanism-based chemoprevention strategy against colon cancer development.

Carcinogenicity of aminophenylnorharman, a possible novel endogenous mutagen, formed from norharman and aniline, in F344 rats.

A novel mutagenic compound, 9-(4'-aminophenyl)-9H- pyrido[3,4-b]indole (aminophenylnorharman, APNH), is shown to be formed by the in vitro enzymatic reaction of 9H-pyrido[3,4-b]indole (norharman) and aniline. APNH generates DNA adducts (dG-C8-APNH), and is potently genotoxic to bacteria and mammalian cells. APNH has also been demonstrated to be formed in vivo from norharman and aniline, and suggested to be a new type of endogenous mutagenic compound. To determine its carcinogenic activity, long-term administration of APNH was investigated in 93 male and 90 female F344 rats. Rats were fed diets containing 0, 20 or 40 p.p.m. from 7 weeks of age. All animals were killed after 85 weeks treatment and necropsy was performed. Hepatocellular carcinomas (HCCs) were induced at incidences of 10 and 79% in male rats fed 20 and 40 p.p.m. APNH, and 34% in female rats fed 40 p.p.m. of APNH, respectively. In addition, colon adenocarcinomas were found at incidences of 3 and 9% in male rats, and 4 and 13% in female rats fed 20 and 40 p.p.m. of APNH, respectively. Other tumors, including thyroid carcinomas and mononuclear cell leukemia, were also seen in rats fed APNH. Polymerase chain reaction-single strand conformation polymorphism analysis revealed beta-catenin gene mutations in 24% of HCCs and K-ras, beta-catenin and Apc gene mutations were found in 22, 44 and 33% of colon cancers induced by APNH, respectively. Most mutations occurred at G:C base pairs. beta-Catenin protein accumulations in the nucleus and cytoplasm were also revealed in both liver and colon tumors. Thus, APNH induced liver and colon cancers with K-ras, beta-catenin and Apc gene mutations in F344 rats.

Enhancement of colon carcinogenesis by prostaglandin E2 administration.

Although an accumulating body of evidence indicates that levels of prostaglandin E(2) (PGE(2)) in human and rodent colon cancers are higher than those in surrounding normal tissues, the precise contribution of PGE(2) to the process of colon cancer development has still been unclear. Therefore, we designed a study using a well-established azoxymethane (AOM)-induced colon carcinogenesis in male F344 rat model to investigate whether administration of exogenous PGE(2) has a real impact on colon carcinogenesis. Intraperitoneal PGE(2) injections (7.7 micro g) once a week for 25 weeks significantly increased the AOM-induced colon tumor incidence (percent rats with tumors, 92 versus 53%, P < 0.05), especially adenocarcinomas (92 versus 47%, P < 0.05), and multiplicity (number of tumors per rat, 2.8 versus 1.0, P < 0.05). PGE(2) treatment significantly increased 5-bromo-2'-deoxyuridine (BrdUrd) labeling index (11.8 versus 9.7%, P < 0.05) and reduced apoptotic index (0.34 versus 0.53%, P < 0.05) in colon cancers induced by AOM. PGE(2) exhibits its physiological functions through binding to E-prostanoid (EP) membrane receptors EP(1-4). All four types of EP receptors were detected in AOM-induced colon cancers using reverse transcription-polymerase chain reaction (RT-PCR). Our results provide evidence that PGE(2) enhances colon carcinogenesis through induction of cell proliferation and reduction of apoptosis.

Preventive effects of Cladosiphon fucoidan against Helicobacter pylori infection in Mongolian gerbils.

BACKGROUND: Recently, the acquisition by Helicobacter pylori of resistance to antibiotics has become a serious problem. Therefore, nonantibiotic substances are required to diminish H. pylori-induced gastric lesions. In the present study, the effects of Cladosiphon fucoidan were examined in terms of H. pylori attachment to porcine gastric mucin in vitro and Helicobacter pylori-induced gastritis in vivo. METHODS: The inhibitory effect of Cladosiphon fucoidan and other polysaccharides on H. pylori attachment to porcine gastric mucin was assayed in vitro with mucin-coated microtiter plates. The effect of Cladosiphon fucoidan on H. pylori-induced gastritis was examined in vivo using Mongolian gerbils. H. pylori-inoculated gerbils were given fucoidan in drinking water. Six weeks after H. pylori-inoculation, gerbils were sacrificed for macroscopic and microscopic examination of gastric lesions and counting of viable H. pylori in the gastric mucosa. RESULTS: Cladosiphon fucoidan inhibited the H. pylori attachment to porcine gastric mucin at pH 2.0 and 4.0. Two other sulfated polysaccharides, Fucus fucoidan and dextran sulfate sodium, also inhibited the attachment but only at pH 2.0. Inhibitory effects of these three sulfated polysaccharides were not observed at pH 7.2 and nonsulfated polysaccharides, such as mannan and dextran, exerted no influence at any pH. In the in vivo experiment, the H. pylori-induced gastritis and the prevalence of H. pylori infected animals were markedly reduced by fucoidan in a dose-dependent manner, at doses of 0.05 and 0.5% in the drinking water. CONCLUSION: Cladosiphon fucoidan may deserve particular attention as a safe agent that can prevent H. pylori infection and reduce the risk of associated gastric cancer.

Inhibitory effects of mofezolac, a cyclooxygenase-1 selective inhibitor, on intestinal carcinogenesis.

Cyclooxygenase (COX)-2, one enzyme isoform responsible for producing prostanoids from arachidonic acid, contributes to colon carcinogenesis. Recently, genetic disruption of COX-1, the other isoform, was shown to decrease the number of intestinal polyps and prostaglandin E(2) levels in intestinal mucosa, like the case with COX-2 gene disruption, in Min mice. We therefore investigated whether a COX-1 selective inhibitor, mofezolac, suppresses intestinal carcinogenesis in rodents. F344 male rats, receiving azoxymethane (AOM, 15 mg/kg body wt) s.c. injections at 5 and 6 weeks of age, were fed a diet containing 600 or 1200 p.p.m. mofezolac for 4 weeks. The number of aberrant crypt foci (ACFs) per rat and the bromodeoxyuridine labeling index of the crypt epithelium were dose-dependently decreased by administration of mofezolac, the value for the former at 1200 p.p.m. being 60% of control value. When Apc gene knockout mice (APC1309 mice) were given 600 or 1200 p.p.m. mofezolac in their diet for 8 weeks, the numbers of intestinal polyps were also dose-dependently decreased, with reduction to 59% of that in the control diet group at the higher dose. Nimesulide, a COX-2 selective inhibitor used as positive control, showed similar suppressive effects on the development of ACFs in AOM-treated rats and polyps in Apc gene knockout mice. The data indicate that both COX-1 and COX-2 can contribute to intestinal tumorigenesis.