Suppressing effects of 6-(2,5-dichlorophenyl)-2,4-diamino-1,3,5-triazine and related synthetic compounds on azoxymethane-induced aberrant crypt foci in rat colon

Colon cancer chemoprevention by a novel NO chimera that shows anti-inflammatory and antiproliferative activity in vitro and in vivo

Chemopreventive agents in colorectal cancer possess either antiproliferative or anti-inflammatory actions. Nonsteroidal anti-inflammatory drugs (NSAID) and cyclooxygenase-2 inhibitors have shown promise, but are compromised by side effects. Nitric oxide donor NSAIDs are organic nitrates conjugated via a labile linker to an NSAID, originally designed for use in pain relief, that have shown efficacy in colorectal cancer chemoprevention. The NO chimera, GT-094, is a novel nitrate containing an NSAID and disulfide pharmacophores, a lead compound for the design of agents specifically for colorectal cancer. GT-094 is the first nitrate reported to reduce aberrant crypt foci (by 45%) when administered after carcinogen in the standard azoxymethane rat model of colorectal cancer. Analysis of proximal and distal colon tissue from 8- and 28-week rat/azoxymethane studies showed that GT-094 treatment reduced colon crypt proliferation by 30% to 69%, reduced inducible NO synthase (iNOS) levels by 33% to 67%, reduced poly(ADP-ribose)polymerase-1 expression and cleavage 2- to 4-fold, and elevated levels of p27 in the distal colon 3-fold. Studies in cancer cell cultures recapitulated actions of GT-094: antiproliferative activity and transient G(2)-M phase cell cycle block were measured in Caco-2 cells; apoptotic activity was examined but not observed; anti-inflammatory activity was seen in the inhibition of up-regulation of iNOS and endogenous NO production in lipopolysaccharide (LPS)-induced RAW 264.7 cells. In summary, antiproliferative, anti-inflammatory, and cytoprotective activity observed in vivo and in vitro support GT-094 as a lead compound for the design of NO chimeras for colorectal cancer chemoprevention.

Aberrant crypt foci and beta-catenin accumulated crypts; significance and roles for colorectal carcinogenesis

Preneoplastic or precancerous lesions in the large bowel have been characterized in terms of morphology and histochemical phenotype. However, the detailed histogenesis and relation of particular lesions to malignancies has not yet to be unequivocally clarified. Aberrant crypt foci (ACF), identified in whole-mount preparations of colonic mucosa in rodents and also recognized in human colon, are now frequently used as effective surrogate biomarkers for experimentally detection of chemopreventive agents against colorectal cancers, but the preneoplastic or precancerous nature of ACF in rodents and humans still remains inconclusive. Relatively recently, early appearing beta-catenin accumulated crypts (BCAC) have been described in en face preparations of colonic mucosa in rodents which differ from ACF in many features. BCAC are suggested to be premalignant rather than preneoplastic. The pathological significance of both lesions, including their advantages and disadvantages as surrogate end points for large bowel neoplasms, and roles in colorectal carcinogenesis are discussed here.

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.

Induction of apoptosis in colonic epithelium treated with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and its modulation by a P4501A2 inducer, beta-naphthoflavone, in male F344 rats

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is one of the mutagenic heterocyclic amines derived from cooked meat. In long-term experiments using rodents, carcinogenicity of PhIP in colon, mammary gland and prostate has been demonstrated. In this study, an experiment was designed to determine the apoptosis-inducing capacity of PhIP in colonic epithelium, a target organ for PhIP carcinogenicity, and possible modulating effects of beta-naphthoflavone (beta-NF), a P4501A2 inducer, on the apoptosis in rats. Out of eight groups of male F344 rats, four were given beta-NF in diet (1000 ppm) for a week beginning at 5 weeks of age. Four groups were given PhIP (100 mg/kg body weight) by gavage at 6 weeks of age. Twenty-four hours after the dosing of PhIP, cell death with typical morphology of apoptosis was apparent in the colon and the apoptotic index was significantly greater (P < 0.01) than of the control rats without exposure to PhIP. Prior administration of beta-NF caused significant acceleration of the induction of apoptosis by PhIP. Since PhIP requires metabolic activation by P4501A2 to exert genotoxic activities, the modulating effect of beta-NF on the PhIP-induced apoptosis will be through a P4501A2-dependent mechanism. Such assay of apoptotic indices in the colon may be useful not only for the evaluation of genotoxicity and/or the initiating capability of chemical agents with potentials for colorectal cancer, but also for the analysis of modifying agents on the carcinogenesis in the large bowel.

Triazine derivatives inhibit rat hepatocarcinogenesis but do not enhance gap junctional intercellular communication

We report here novel candidate chemopreventive agents active against experimental hepatocarcinogenesis. The triazine derivatives 6-(2-chlorophenyl)-2,4-diamino-1,3,5-triazine (2CPDAT), 6-(3-chlorophenyl)-2,4-diamino-1,3,5-triazine (3CPDAT), 6-(4-chlorophenyl)-2,4-diamino-1,3,5-triazine (4CPDAT), 6-(4-pyridyl)-2,4-diamino-1,3,5-triazine (PyDAT), and 6-(pyridine N-oxid-4-yl)-2,4-diamino-1,3,5-triazine (PyNODAT), synthesized in our laboratory, in addition to 6-(2,5-dichloro-phenyl)-2,4-diamino-1,3,5-triazine (DCPDAT), or irsogladine, which is a widely used anti-ulcer drug, were investigated for potential chemopreventive effects in a rat liver medium-term bioassay system. A significant inhibitory influence on enzyme-altered liver foci was found for 2CPDAT, 3CPDAT, 4CPDAT, and PyNODAT, but not for DCPDAT or PyDAT. The involvement of gap junctional intercellular communication in the inhibition was studied, but no change in gap junctional intercellular communication capacity in rat liver cells in vitro or in gap junction protein (connexin 32) expression in rat liver in vivo was noted. These results indicate that, although these irsogladine analogues exert inhibitory effects on rat liver carcinogenesis, their action is independent of modification of gap junctional intercellular communication.