Adjuvant tamoxifen in early breast cancer: occurrence of new primary cancers

The frequency of new primary cancers was studied in 1846 postmenopausal patients included in a randomised trial of tamoxifen as an adjunct to primary surgery for early breast cancer. The median follow-up was 4.5 years (range 0.5-10.5 years). The number of new cancers in the tamoxifen group (n = 57) did not differ significantly from that in the control group (n = 70). However, in tamoxifen patients second breast cancers occurred less often and endometrial cancer occurred more often than in the controls. The increase in endometrial cancers was probably related to the agonistic oestrogenic effects of tamoxifen and was most pronounced in those treated for over 2 years.

Association of exogenous estrogen and endometrial carcinoma

To determine the association between the incidence of endometrial cancer and the use of estrogen in menopausal and post-menopausal women, we retrospectively compared 317 patients with adenocarcinoma of the endometrium with an equal number of matched controls having other gynecologic neoplasms; 152 patients used estrogen, as compared to 54 of 317 controls. Thus, the risk of endometrial cancer was 4.5 times greater among women exposed to estrogen therapy. When estrogen use was adjusted for concomitant variables such as obesity, hypertension, diabetes, parity, referral pattern, age at diagnosis, year of diagnosis and other gynecologic neoplasms, the magnitude of the increased relative risk was associated with several of these variables, and was highest in patients without obesity and hypertension. Exogenous estrogen therapy is associated with an increased risk of endometrial carcinoma, but this increased relative risk is less apparent in patients with physiologic characteristics previously associated with an increased risk.

A novel inflammation-related mouse colon carcinogenesis model induced by azoxymethane and dextran sodium sulfate

To develop an efficient animal model for colitis-related carcinogenesis, male Crj: CD-1 (ICR) mice were given a single intraperitoneal administration (10 mg/kg body weight) of a genotoxic colonic carcinogen, azoxymethane (AOM), and a 1-week oral exposure (2% in drinking water) to a non-genotoxic carcinogen, dextran sodium sulfate (DSS), under various protocols. At week 20, colonic neoplasms (adenocarcinomas, 100% incidence with 5.60 +/- 2.42 multiplicity; and adenomas, 38% incidence with 0.20 +/- 0.40 multiplicity) with dysplastic lesions developed in mice treated with AOM followed by DSS. Protocols in which AOM was given during or after DSS administration induced a few tubular adenomas or no tumors in the colon. Immunohistochemical investigation of such dysplasias and neoplasms revealed that all lesions were positive for beta-catenin, cyclooxygenase-2 and inducible nitric oxide synthase, but did not show p53 immunoreactivity. The results indicate that 1-week administration of 2% DSS after initiation with a low dose of AOM exerts a powerful tumor-promoting activity in colon carcinogenesis in male ICR mice, and may provide a novel mouse model for investigating colitis-related colon carcinogenesis and for identifying xenobiotics with modifying effects.

Increased risk of endometrial carcinoma among users of conjugated estrogens

The possibility that the use of conjugated estrogens increases the risk of endometrial carcinoma was investigated in patients and a twofold age-matched control series from the same population. Conjugated estrogens (principally sodium estrone sulfate) use was recorded for 57 per cent of 94 patients with endometrial carcinoma, and for 15 per cent of controls. The corresponding point estimate of the (instantaneous) risk ratio was 7.6 with a one-sided 95 per cent lower confidence limit of 4.7. The risk-ratio estimate increased with duration of exposure: from 5.6 for 1 to 4.9 years exposure to 13.9 for seven or more years. The estimated proportion of cases related to conjugated estrogens, the etiologic fraction, was 50 per cent with a one-sided 95 per cent lower confidence limit of 41 per cent. These data suggest that conjugated estrogens have an etiologic role in endometrial carcinoma.

MyD88-mediated signaling prevents development of adenocarcinomas of the colon: role of interleukin 18

Signaling through the adaptor protein myeloid differentiation factor 88 (MyD88) promotes carcinogenesis in several cancer models. In contrast, MyD88 signaling has a protective role in the development of azoxymethane (AOM)/dextran sodium sulfate (DSS) colitis-associated cancer (CAC). The inability of Myd88(-/-) mice to heal ulcers generated upon injury creates an altered inflammatory environment that induces early alterations in expression of genes encoding proinflammatory factors, as well as pathways regulating cell proliferation, apoptosis, and DNA repair, resulting in a dramatic increase in adenoma formation and progression to infiltrating adenocarcinomas with frequent clonal mutations in the beta-catenin gene. Others have reported that toll-like receptor (Tlr) 4-deficient mice have a similar susceptibility to colitis to Myd88-deficient mice but, unlike the latter, are resistant to CAC. We have observed that mice deficient for Tlr2 or Il1r do not show a differential susceptibility to colitis or CAC. However, upon AOM/DSS treatment Il18(-/-) and Il18r1(-/-) mice were more susceptible to colitis and polyp formation than wild-type mice, suggesting that the phenotype of Myd88(-/-) mice is, in part, a result of their inability to signal through the IL-18 receptor. This study revealed a previously unknown level of complexity surrounding MyD88 activities downstream of different receptors that impact tissue homeostasis and carcinogenesis.

Long-term neoplasia risk after azathioprine treatment in inflammatory bowel disease

The incidence of various cancers, especially non-Hodgkin lymphoma (NHL), is higher among patients who receive azathioprine for immunosuppression after organ transplants than in the general population. We have studied the risk of neoplasia after azathioprine in 755 patients treated for inflammatory bowel disease. The patients received 2 mg/kg daily for a median of 12.5 months (range 2 days to 15 years) between 1962 and 1991; median follow-up was 9 years (range 2 weeks to 29 years). Overall there was no significant excess of cancer: 31 azathioprine-treated patients developed cancer before age 85 compared with 24.3 expected from rates in the general population (observed/expected ratio 1.27, p = 0.186). There was a difference in the frequency of colorectal (13) and anal (2) carcinomas (expected 2.27; ratio 6.7, p = 0.00001); these tumours are recognised complications of chronic inflammatory bowel disease. There were 2 cases of invasive cervical cancer (expected 0.5), but no case of NHL. Among patients with extensive chronic ulcerative colitis there was no difference in cancer frequency between 86 who had received azathioprine and 180 matched patients who had never received it. Thus, azathioprine treatment does not substantially increase the risk of cancer in inflammatory bowel disease.

The Forkhead Box m1 transcription factor stimulates the proliferation of tumor cells during development of lung cancer

The proliferation-specific Forkhead Box m1 (Foxm1 or Foxm1b) transcription factor (previously called HFH-11B, Trident, Win, or MPP2) regulates expression of cell cycle genes essential for progression into DNA replication and mitosis. Expression of Foxm1 is found in a variety of distinct human cancers including hepatocellular carcinomas, intrahepatic cholangiocarcinomas, basal cell carcinomas, ductal breast carcinomas, and anaplastic astrocytomas and glioblastomas. In this study, we show that human Foxm1 protein is abundantly expressed in highly proliferative human non-small cell lung cancers (NSCLC) as well as in mouse lung tumors induced by urethane. To determine the role of Foxm1 during the development of mouse lung tumors, we used IFN-inducible Mx-Cre recombinase transgene to delete mouse Foxm1 fl/fl-targeted allele before inducing lung tumors with urethane. We show that Mx-Cre Foxm1-/- mice exhibit diminished proliferation of lung tumor cells causing a significant reduction in number and size of lung adenomas. Transient transfection experiments with A549 lung adenocarcinoma cells show that depletion of Foxm1 levels by short interfering RNA caused diminished DNA replication and mitosis and reduced anchorage-independent growth of cell colonies on soft agar. Foxm1-depleted A549 cells exhibit reduced expression of cell cycle-promoting cyclin A2 and cyclin B1 genes. These data show that Foxm1 stimulates the proliferation of tumor cells during progression of NSCLC.

Risk of endometrial cancer following estrogen replacement with and without progestins

BACKGROUND

Unopposed estrogen replacement therapy (i.e., estrogen without progestins) increases the risk of endometrial cancer. In this study, we examined the endometrial cancer risk associated with combined estrogen-progestin regimens currently in use, since the safety profiles of these regimens have not been clearly defined.

METHODS

We conducted a nationwide population-based, case-control study in Sweden of postmenopausal women aged 50-74 years. We collected information on use of hormone replacement from 709 case patients with incident endometrial cancer and from 3368 control subjects. We used unconditional logistic regression to calculate odds ratios (ORs) as estimates of relative risks. All individual comparisons were made with women who never used the respective hormone replacement regimens.

RESULTS

Treatment with estrogens alone was associated with a marked duration- and dose-dependent increase in the relative risk of endometrial cancer. Five or more years of treatment had an OR of 6.2 for estradiol (95% confidence interval [CI] = 3.1-12.6) and of 6.6 for conjugated estrogens (95% CI = 3.6-12.0). Following combined estrogen-progestin use, the association was considerably weaker than that for estrogen alone; the OR was 1.6 (95% CI = 1.1-2.4) after 5 or more years of use. This increase in risk was confined to women with cyclic use of progestins, i.e., fewer than 16 days per cycle (most commonly 10 days per cycle [OR = 2.9; 95% CI = 1.8-4.6 for 5 or more years of use]), whereas continuous progestin use along with estrogens was associated with a reduced risk (OR = 0.2; 95% CI = 0.1-0.8 for 5 or more years of use).

CONCLUSION

The risk of developing endometrial cancer is increased after long-term use of estrogens without progestins and with cyclically added progestins. Continuously added progestins may be needed to minimize the endometrial cancer risk associated with estrogen replacement therapy.

Increased susceptibility of Nrf2 knockout mice to colitis-associated colorectal cancer

The nuclear factor-erythroid 2-related factor 2 (Nrf2) plays a critical role in protecting various tissues against inflammation, which is a potential risk factor for colorectal and other cancers. Our previously published mouse model work showed that Nrf2 helps protect against dextran sulfate sodium (DSS)-induced colitis/inflammation, and others have shown that Nrf2 helps protect against inflammation-associated colorectal carcinogenesis (aberrant crypt foci). The present study extended these important earlier findings by exploring the role of Nrf2 in colitis-associated colorectal cancer in a mouse model involving azoxymethane/DSS-induced colorectal carcinogenesis in Nrf2 knockout mice. Azoxymethane/DSS-treated Nrf2 knockout mice had increased incidence, multiplicity, and size of all colorectal tumors, including adenomas, versus treated wild-type (WT) mice, and the proportion of tumors that were adenocarcinoma was much higher in knockout (80%) versus WT (29%) mice. Compared with WT mice, knockout mice also had increased markers of inflammation in tumor tissue (cyclooxygenase-2 and 5-lipoxygenase expressions and prostaglandin E(2) and leukotriene B(4) levels) and in inflamed colonic mucosa (nitrotyrosine expression), supporting the association of knockout mouse tumor formation with inflammation. The phase II detoxifying/antioxidant enzymes NAD(P)H-quinone reductase 1 and UDP-glucurosyltransferase 1A1 were elevated in the normal mucosa of WT, but not Nrf 2 knockout, mice treated with azoxymethane/DSS. Our findings show that Nrf2 plays a critical role in protecting against inflammation-associated colorectal cancer.

Mechanisms of extrahepatic tumor induction by peroxisome proliferators in male CD rats

Wyeth-14,643 (WY) and ammonium perfluorooctanoate (C8) belong to a diverse class of compounds which have been shown to produce hepatic peroxisome proliferation in rodents. From previous work, WY, but not C8, has been shown to produce hepatocellular carcinoma in rats, while C8 has been shown to produce Leydig cell adenomas. In addition, based on a review of bioassay data a relationship appears to exist between peroxisome-proliferating compounds and Leydig cell adenoma and pancreatic acinar cell hyperplasia/adenocarcinoma formation. To further investigate the relationship between peroxisome-proliferating compounds and hepatic, Leydig cell, and pancreatic acinar cell tumorigenesis, a 2-year feeding study in male CD rats was initiated to test the hypothesis that peroxisome proliferating compounds induce a tumor triad (liver, Leydig cell, pancreatic acinar cell), and to examine the potential mechanism for the Leydig cell tumors. The study was conducted using 50 ppm WY and 300 ppm C8. The concentration of WY in the diet was decreased to 25 ppm on test day 301 due to increased mortality. In addition to the ad libitum control, a second control was pair-fed to the C8 group. Interim sacrifices were performed at 1- or 3-month intervals. Peroxisome proliferation measured by beta-oxidation activity and cell proliferation were measured in the liver and testis at all time points and in the pancreas beginning at the 9-month time point (cell proliferation only). Serum hormone concentrations (estradiol, testosterone, LH, FSH, and prolactin) were also measured at each time point. Increased relative liver weights and hepatic beta-oxidation activity were observed in both the WY- and C8-treated rats at all time points. In contrast, hepatic cell proliferation was significantly increased only in the WY-treated group. Neither WY nor C8 significantly altered the rate of Leydig cell beta-oxidation or Leydig cell proliferation when compared to the control groups. Moreover, the basal rate of beta-oxidation in Leydig cells was approximately 20 times less than the rate of hepatic beta-oxidation. There were no biologically meaningful differences in serum testosterone, FSH, prolactin, or LH concentrations in the WY- and C8-treated rats when compared to their respective controls. There were, however, significant increases in serum estradiol concentrations in the WY- and C8-treated rats at 1, 3, 6, 9, 15, 18, and 21 months. At 12 months, only the C8-treated rats had elevated serum estradiol concentrations when compared to the pair-fed control. Histopathological evaluation revealed compound-related increases in liver, Leydig cell, and pancreatic acinar cell tumors in both WY- and C8-treated rats. The data support the hypothesis that the peroxisome-proliferating compounds induce the previously described tumor triad. In addition, both C8 and WY produced a sustained increase in serum estradiol concentrations that correlated with the potency of the 2 compounds to induce Leydig cell tumors (i.e., WY caused a more consistent sustained increase in serum estradiol throughout the entire study, and more specifically at the end of the study, than did C8). This study suggests that estradiol may play a role in enhancement of Leydig cell tumors in the rat, and that peroxisome proliferators may induce tumors via a non-LH type mechanism.

Inhibitory effect of aspirin on azoxymethane-induced colon carcinogenesis in F344 rats

Epidemiologic studies suggest that sustained use of aspirin may reduce the risk of development of and mortality due to colon cancer. Previous preclinical studies have shown that several non-steroidal anti-inflammatory drugs act as potential chemopreventive agents in experimentally induced colon cancer models. The present study was designed to investigate the chemopreventive effect of 40 and 80% maximum tolerated dose (MTD) levels of aspirin administered in the diet on azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. The MTD of aspirin as determined in male F344 rats was 500 p.p.m. Beginning at 5 weeks of age, all animals were randomly divided into various experimental groups (48 rats/group) and fed one of the semipurified diets containing 0, 200 p.p.m. (40% MTD), or 400 ppm (80% MTD) of aspirin. Two weeks later, all animals (36 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM at a dose level of 15 mg/kg body wt, once weekly for 2 weeks. All animals were continued on their respective dietary regimen for additional 52 weeks and necropsied. Histopathologic evaluation of colon tumors was performed by routine procedures. Basal levels and ex vivo production of colonic mucosal and tumor prostaglandin E2 (PGE2) were measured in all groups. The results indicate that daily oral administration of 200 and 400 p.p.m. aspirin significantly inhibited the incidence (% animals with tumors) and multiplicity (tumors/animal) of invasive adenocarcinomas of the colon as well as the size of adenocarcinomas. Colonic mucosal and tumor PGE2 levels (basal and ex vivo production) were significantly reduced in animals administered 200 and 400 p.p.m. aspirin. The results of this study support the epidemiologic evidence that ingestion of aspirin inhibits colon carcinogenesis. Although the precise mechanisms of aspirin-induced colon tumor inhibition remain to be determined, it is likely that the effect may be mediated through the modulation of prostaglandin synthesis.

Effects of long-term estrogen replacement therapy. I. Metabolic effects

Two groups of hypoestrogenic women are analyzed by retrospective comparisons. Patients were observed by a single group of physicians for at least five years; 301 patients were treated with replacement estrogen and 309 patients were untreated. Incidence figures for various metabolic diseases present at entry and both during and after estrogen therapy were compared by the usual statistical analysis and by statistical adjustments for certain group differences (Mantel-Haenszel statistic). The long-term administration of estrogen to these relatively young women with hypoestrogenism was associated with significantly lower rates of development of cardiovascular disease, hypertension, osteoporosis, and fractures. Detrimental effects were a higher rate of abnormal uterine bleeding and an increase in the likelihood of developing adenocarcinoma of the endometrium. Effects of estrogen preparation, dosage, method of therapy, duration of therapy, and the addition of synthetic progestins are presented.

Genistein chemoprevention: timing and mechanisms of action in murine mammary and prostate

We investigated the potential of genistein, the primary isoflavone of soy, to protect against breast and prostate cancers in animal models. For mammary cancer studies, Sprague-Dawley rats were fed AIN-76A diet plus minus 250 mg genistein/kg diet. Dimethylbenz[a]anthracene was administered by gavage at d 50 postpartum to induce mammary tumors. Mammary cancer chemoprevention was demonstrated after prepubertal and combined prepubertal and adult genistein treatments but not after prenatal- or adult-only treatments, demonstrating that the timing of exposure to genistein is important for mammary cancer chemoprevention. The cellular mechanism of action was found to be mammary gland and cell differentiation, as shown by whole-mount analysis and beta-casein expression. An imprinting effect was shown for epidermal growth factor receptor expression in mammary terminal end buds. For prostate cancer studies, we used two models. The first was a chemically (N-methylnitrosourea) induced prostate cancer rat model. Genistein in the diet inhibited the development of invasive adenocarcinomas in a dose-dependent manner. The second model was a transgenic mouse model that resulted in spontaneously developing adenocarcinoma tumor of the prostate. Genistein in the diet reduced the incidence of poorly differentiated prostatic adenocarcinomas in a dose-dependent manner and down-regulated androgen receptor, estrogen receptor-alpha, progesterone receptor, epidermal growth factor receptor, insulin-like growth factor-I, and extracellular signal-regulated kinase-1 but not estrogen receptor-beta and transforming growth factor-alpha mRNA expressions. We conclude that dietary genistein protects against mammary and prostate cancers by regulating specific sex steroid receptors and growth factor signaling pathways.

Diallyl sulfide, a flavor component of garlic (Allium sativum), inhibits dimethylhydrazine-induced colon cancer

Diallyl sulfide, a thioether found naturally in garlic, when given by gavage to C57BL/6J mice inhibited by 74% the incidence and reduced the frequency of colorectal adenocarcinoma induced by 20 weekly injections of 1,2-dimethylhydrazine. This result was predicted from a short-term assay measuring defects in nuclear morphology in mouse colon epithelial cells. This chemical is representative of a class of naturally occurring sulfur compounds with profound pharmacologic activity, one aspect of which may be cancer prevention.

High-grade endometrial carcinoma in tamoxifen-treated breast cancer patients

PURPOSE

Several reports have associated tamoxifen administration with endometrial carcinoma. A retrospective study of the histologic features of uterine cancer in patients with a history of breast carcinoma was undertaken to determine the effect of treatment with tamoxifen.

MATERIALS AND METHODS

A computer search of the Yale-New Haven Hospital Tumor Registry from 1980 to 1990 identified 53 patients with a history of breast carcinoma who subsequently developed a malignant tumor of the uterine corpus.

RESULTS

Fifteen patients received tamoxifen for breast carcinoma and 38 did not. The mean ages of the two groups were not significantly different. The mean interval between detection of breast and endometrial cancers was 5 years in the tamoxifen group and 12 years in the nontreated group (P = .0023). Sixty-seven percent of patients in the tamoxifen group had poorly differentiated endometrioid carcinomas (including adenosquamous carcinoma) or carcinomas associated with poor outcome (eg, uterine papillary serous carcinoma, clear-cell carcinoma, or mixed müllerian tumor), as compared with 24% in the nontreated group (P = .03). Patients in the tamoxifen group were much more likely to die of endometrial cancer (33.3% v 2.6% of the nontreated group, P = .005).

CONCLUSION

From this retrospective study, it appears that women receiving tamoxifen as treatment for breast cancer who subsequently develop uterine cancer are at risk for high-grade endometrial cancers that have a poor prognosis. These findings also indicate that tamoxifen-associated uterine cancers may have a different basis from those associated with steroidal estrogen treatment.

Mammary tumor suppression by transforming growth factor beta 1 transgene expression

In cell culture, type alpha transforming growth factor (TGF-alpha) stimulates epithelial cell growth, whereas TGF-beta 1 overrides this stimulatory effect and is growth inhibitory. Transgenic mice that overexpress TGF-alpha under control of the mouse mammary tumor virus (MMTV) promoter/enhancer exhibit mammary ductal hyperplasia and stochastic development of mammary carcinomas, a process that can be accelerated by administration of the chemical carcinogen 7,12-dimethylbenz[a]anthracene. MMTV-TGF-beta 1 transgenic mice display mammary ductal hypoplasia and do not develop mammary tumors. We report that in crossbreeding experiments involving the production of mice carrying both the MMTV-TGF-beta 1 and MMTV-TGF-alpha transgenes, there is marked suppression of mammary tumor formation and that MMTV-TGF-beta 1 transgenic mice are resistant to 7,12-dimethylbenz[a]anthracene-induced mammary tumor formation. These data demonstrate that overexpression of TGF-beta 1 in vivo can markedly suppress mammary tumor development.

Prepubertal genistein exposure suppresses mammary cancer and enhances gland differentiation in rats

Genistein, a component of soy, was administered to prepubertal female Sprague-Dawley CD rats and investigated for chemoprevention against mammary cancer. Genistein, at 500 microgram/g body wt or an equivalent volume of the vehicle, dimethylsulfoxide (DMSO), was injected (s.c.) on days 16, 18 and 20 post-partum. At day 50 post-partum all animals were exposed to 80 microgram dimethylbenz[a]anthracene (DMBA) per g body wt. Animals treated prepubertally with genistein as compared to DMSO had reduced incidence and significantly fewer adenocarcinomas per animal. Mammary whole mount analysis showed that prepubertal genistein treatment resulted in mammary glands of 50-day-old rats developing fewer terminal end buds and more lobules II. Cell proliferation studies with bromodeoxyuridine (BrdU) showed that terminal end buds from mammary glands of 50-day-old females treated prepubertally with genistein had significantly fewer cells in S-phase of the cell cycle. Serum genistein concentrations in 21- and 50-day-old females following prepubertal genistein treatment were 4.2 +/- 0.6 micromol and 102 +/- 30 nM, respectively. Animals treated prepubertally with genistein as compared to vehicle spent more time in the estrus phase of the estrus cycle, although all animals did cycle. In 50-day-old females, circulating estradiol-17 beta and progesterone concentrations were not significantly altered by the prepubertal genistein treatment. Oocyte/follicle counts and numbers of atretic follicles and corpora lutea were not significantly different between the genistein- and vehicle-treated animals. We conclude that genistein treatment during the prepubertal period can suppress the development of chemically-induced mammary cancer without significant toxicity to the endocrine/reproductive system.

Long-term adverse effects of neonatal exposure to bisphenol A on the murine female reproductive tract

The developing fetus is uniquely sensitive to perturbation by chemicals with hormone-like activity. The adverse effects of prenatal diethylstilbestrol (DES) exposure are a classic example. Since concern has been mounting regarding the human health and environmental effects of bisphenol A (BPA), a high-production-volume chemical with estrogenic activity used in the synthesis of plastics, we investigated its long-term effects in an experimental animal model that was previously shown useful in studying the adverse effects of developmental exposure to DES. Outbred female CD-1 mice were treated on days 1-5 with subcutaneous injections of BPA (10, 100 or 1000 microg/kg/day) dissolved in corn oil or corn oil alone (Control). At 18 months, ovaries and reproductive tract tissues were examined. There was a statistically significant increase in cystic ovaries and cystic endometrial hyperplasia (CEH) in the BPA-100 group as compared to Controls. Progressive proliferative lesion (PPL) of the oviduct and cystic mesonephric (Wolffian) duct remnants were also seen in all of the BPA groups. More severe pathologies of the uterus following neonatal BPA treatment included adenomyosis, leiomyomas, atypical hyperplasia, and stromal polyps. These data suggest that BPA causes long-term adverse effects if exposure occurs during critical periods of differentiation.

The nuclear eicosanoid receptor, PPARgamma, is aberrantly expressed in colonic cancers

Continuous use of nonsteroidal anti-inflammatory drugs (NSAIDs) lowers the relative risk of colorectal cancer in humans and decreases tumor yield in rodents treated with carcinogens. One well documented target for NSAIDs is prostaglandin endoperoxide synthase (cyclooxygenase) and two isoforms of this enzyme have been identified, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). COX enzymes produce eicosanoid products, some of which have recently been shown to activate transcription mediated by the nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARgamma), whose expression is largely restricted to adipose tissue. The present study was undertaken to determine if PPARgamma was expressed in colonic tumors. PPARgamma messenger RNA (mRNA) and protein levels were assayed in colonic tumors and normal adjacent mucosa, as well as in a variety of human colon cancer cell lines. There was a marked increase in PPARgamma RNA levels in four out of four of the colonic tumors compared to paired normal mucosa, where little expression of PPARgamma was detected. Western blotting analysis showed that PPARgamma protein was expressed in four out of five colonic tumor samples. PPARgamma was also expressed in a subset of polyps, and in certain human colon cancer cell lines as well. Additionally, we were able to demonstrate that an eicosanoid, 15 deoxy-delta12,14 PGJ2, transactivated transcription of a PPRE-driven promoter in CaCo-2 cells. Thus, we have shown that PPARgamma gene and protein expression is elevated in rodent colon tumors, in selected human colon cancer cell lines and that the PPARgamma receptor is functional in CaCo-2 cells. Since PPARgamma is a ligand-modulated transcription factor, it may provide a novel target for chemopreventive strategies for colorectal cancer.

Antitumorigenic activity of the prebiotic inulin enriched with oligofructose in combination with the probiotics Lactobacillus rhamnosus and Bifidobacterium lactis on azoxymethane-induced colon carcinogenesis in rats

Prebiotics such as fructans, and probiotics such as Lactobacilli or Bifidobacteria, or a combination of prebiotics and probiotics (synbiotics) are thought to be protective against colon cancer. Therefore, we studied whether the prebiotic inulin enriched with oligofructose (Raftilose-Synergy1, briefly, Synergy1, 10% of the diet), probiotics [Bifidobacterium lactis (Bb12) and Lactobacillus rhamnosus (LGG), each at 5x10(8) c.f.u./g diet] or synbiotics (a combination of the two) protect rats against azoxymethane (AOM)-induced colon cancer. Male F344 rats were divided into: Controls; PRE, which were fed a diet containing Synergy1; PRO, fed a diet containing LGG and Bb12; PREPRO, fed a diet containing Synergy1, LGG and BB12. Ten days after beginning the diets, rats were treated with AOM (15 mg/kg s.c. two times); dietary treatments were continued for the entire experiment. Thirty-one weeks after AOM, rats treated with Synergy1 (PRE and PREPRO groups) had a significantly lower (P < 0.001) number of tumours (adenomas and cancers) than rats without Synergy1 (colorectal tumours/rat were 1.9 +/- 1.7, 1.1 +/- 1.1, 2.2 +/- 1.4 and 0.9 +/- 1.2 in Controls, PRE, PRO and PREPRO groups, respectively, means +/- SD). A slight, not significant effect of probiotics in reducing malignant tumours was also observed (P = 0.079). Caecal short-chain fatty acids (SCFA) were higher (P < 0.001) in the groups treated with Synergy1. Apoptosis was increased in the normal mucosa of the PRO group, while no variation was observed in the tumours. Colonic proliferation was lower in the PRE group as compared with Controls. Glutathione S-transferase placental enzyme pi type expression, and to a lesser extent, inducible NO synthase were depressed in the tumours from rats in the PRE and PREPRO groups. Cycloxygenase-2 expression was increased in the tumours of control rats but not in those from PRE, PRO or PREPRO rats. In conclusion, prebiotic administration in the diet decreases AOM-induced carcinogenesis in rats.

A pharmacogenetic study to investigate the role of dietary carcinogens in the etiology of colorectal cancer

Susceptibility to colorectal cancer, one of the most common forms of cancer in the Western world, has been associated with several environmental and dietary risk factors. Dietary exposure to food derived heterocyclic amine carcinogens and polycyclic aromatic hydrocarbons have been proposed as specific risk factors. Many polymorphic Phase I and Phase II drug metabolizing enzymes are responsible for the metabolism and disposition of these compounds and it is therefore possible that inheritance of specific allelic variants of these enzymes may influence colorectal cancer susceptibility. In a multicenter case-control study, 490 colorectal cancer patients and 593 controls (433 matched case-control pairs) were genotyped for common polymorphisms in the cytochrome P450 (CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2C9, CYP2C19 and CYP2D6), glutathione S-transferase (GSTM1, GSTP1 and GSTT1), sulfotransferase (SULT1A1 and SULT1A2), N-acetyl transferase 2 (NAT2), NAD(P)H:quinone oxidoreductase (NQO1), methylenetetrahydrofolate reductase (MTHFR), and microsomal epoxide hydrolase (EPHX1) genes. Matched case-control analysis identified alleles associated with higher colorectal cancer risk as carriage of CYP1A1*2C (OR = 2.15, 95% CI 1.36-3.39) and homozygosity for GSTM1*2/*2 (OR = 1.53, 95% CI 1.16-2.02). In contrast, inheritance of the CYP2A6*2 (OR = 0.51, 95% CI 0.28-1.06), CYP2C19*2 (OR = 0.72, 95% CI 0.52-0.98) and the EPHX1(His113) alleles were associated with reduced cancer risk. We found no association with colorectal cancer risk with NAT2 genotype or any of the other polymorphic genes associated with the metabolism and disposition of heterocyclic amine carcinogens. This data suggests that heterocyclic amines do not play an important role in the aetiology of colorectal cancer but that exposure to other carcinogens such as polycyclic aromatic hydrocarbons may be important determinants of cancer risk.