Multi-Target Approaches in Colon Cancer Chemoprevention Based on Systems Biology of Tumor Cell-Signaling

Kinome-wide analysis of the effect of statins in colorectal cancer

BACKGROUND

Epidemiological studies and meta-analyses show an association between statin use and a reduced incidence of colorectal cancer (CRC). We have shown that statins act on CRC through bone morphogenetic protein (BMP) signalling, but the exact cellular targets and underlying mechanism of statin action remain elusive. In this study, we set out to assess the influence of statins on global cancer cell signalling by performing an array-based kinase assay using immobilised kinase substrates spanning the entire human kinome.

METHODS

CRC cells with or without Lovastatin treatment were used for kinome analysis. Findings on kinome arrays were further confirmed by immunoblotting with activity-specific antibodies. Experiments in different CRC cell lines using immunoblotting, siRNA-mediated knockdown and treatment with specific BMP inhibitor Noggin were performed. The relevance of in vitro findings was confirmed in xenografts and in CRC patients treated with Simvastatin.

RESULTS

Kinome analysis can distinguish between non-specific, toxic effects caused by 10 µM of Lovastatin and specific effects on cell signalling caused by 2 µM Lovastatin. Statins induce upregulation of PTEN activity leading to downregulation of the PI3K/Akt/mTOR signalling. Treatment of cells with the specific BMP inhibitor Noggin as well as PTEN knockdown and transfection of cells with a constitutively active form of AKT abolishes the effect of Lovastatin on mTOR phosphorylation. Experiments in xenografts and in patients treated with Simvastatin confirm statin-mediated BMP pathway activation, activation of PTEN and downregulation of mTOR signalling.

CONCLUSIONS

Statins induce BMP-specific activation of PTEN and inhibition of PI3K/Akt/mTOR signalling in CRC.

Expression of cyclooxygenase-2 (COX-2) in pituitary tumours

BACKGROUND

Microvessel density in angiogenesis is regarded as a prognostic factor of tumour invasiveness, independent of cell proliferation. In recent studies of pituitary tumours, correlation between the expression of cyclooxygenase-2 (COX-2) and micro-vascularization density and microvessel surface density has been established. We studied the expression of COX-2 in different types of pituitary adenomas to determine the usefulness of COX-2 expression as a prognostic factor of tumour progression or recurrence in patients with hypophyseal tumours.

MATERIAL/METHODS

We retrospectively studied a group of 60 patients of mean age 46.7±17.6 (range, 18 to 85) years who underwent pituitary tumour surgery. Expression of COX-2, as determined by immunohistochemistry, was analyzed in relation to histopathology features of tumour, clinical symptoms, MR imaging and post-operative recurrence/progression of disease.

RESULTS

COX-2 was expressed in adenomas of 87% of patients, with a median index value of 57.5% [IQR=60.5]. Highest COX-2 expression was observed in hormonally inactive adenomas and gonadotropinomas and lowest in prolactinomas. We found no differences in COX-2 expression with respect to patient age, gender, tumour size, degree of tumour invasiveness, or whether tumours were immunopositive or immunonegative for pituitary hormones, nor have we found any relation between COX-2 expression and recurrence or progression of tumour size.

CONCLUSIONS

COX-2 does not appear to be a predictive factor for recurrence or progression of tumour size. Nevertheless, due to the observed relatively high expression of COX-2 in pituitary adenomas, further studies with COX-2 inhibitors are justified in these tumours.

Cancer chemoprevention by citrus pulp and juices containing high amounts of β-cryptoxanthin and hesperidin

β-Cryptoxanthin, a carotenoid, and hesperidin, a flavonoid, possess inhibitory effects on carcinogenesis in several tissues. We recently have prepared a pulp (CHRP) and citrus juices (MJ2 and MJ5) from a satsuma mandarin (Citrus unshiu Mar.) juice (MJ). They contain high amounts of β-cryptoxanthin and hesperidin. We have demonstrated that CHRP and/or MJs inhibit chemically induced rat colon, rat tongue, and mouse lung tumorigenesis. Gavage with CHRP resulted in an increase of activities of detoxifying enzymes in the liver, colon, and tongue rats'. CHRP and MJs were also able to suppress the expression of proinflammatory cytokines and inflammatory enzymes in the target tissues. This paper describes the findings of our in vivo preclinical experiments to develop a strategy for cancer chemoprevention of colon, tongue, and lung neoplasms by use of CHRP and MJs.

Association of stem-like cells in gender-specific chemoprevention against intestinal neoplasia in MIN mouse

This study was undertaken to examine the gender-sensitivity and chemopreventive responsiveness of celecoxib on intestinal stem-like cells as a biomarker of colon carcino-genesis, using the MIN mouse model. Male and female MIN mice (6-7-weeks old) were randomized to either control diet or to a diet supplemented with celecoxib (1,500 ppm). The animals were euthanized ten weeks later and the intestines were flushed and opened longitudinally to assess tumor count. Small intestinal segments were formalin-fixed and tissue sections were subjected to immunohistochemical evaluation of DCAMKL1, a known marker of stem-like cells. We found that in animals receiving control (AIN 76A diet) alone, female MIN mice had a higher polyp count than males (52.32 ± 13.89 vs. 35.43 ± 16.05; p<0.0005). However, compared to control diet groups, celecoxib supplementation caused a larger reduction in the number of polyps in females than their male cohorts (6.38 ± 1.43 vs. 12.83 ± 6.74; a reduction of 88% in females to 64% in males). Significant differences (p=0.013) were observed in the number of DCAMKL1-stained cells in the crypts of the wild-type (WT) (10.01 ± 1.07 stem cells per high powered field; HPF) compared to the MIN mice (24.15 ± 8.08 stem cells per HPF), illustrating increased stem-like cells in animals that are more prone to neoplasia. DCAMKL1 labeled stem-like cells were equal in number in the male and female groups receiving the control AIN 76A diet alone (females, 25.73 stem-like cells/HPF); males, 24.15 stem-like cells/HPF). However, females showed a greater reduction in the number of DCAMKL1-labeled stem-like cells with celecoxib supplementation than the respective males (16.63 ± 4.23 vs. 21.56 ± 9.06; a reduction of 35.4% in females to 10.7% in males). We conclude that a higher number of stem-like cells in the uninvolved mucosa paralleled tumorigenesis and mirrored greater chemopreventive responsiveness of female MIN mice compared to males.

Phospho-sulindac (OXT-328) combined with difluoromethylornithine prevents colon cancer in mice

The nonsteroidal anti-inflammatory drug (NSAID) sulindac and the ornithine decarboxylase (ODC) antagonist difluoromethylornithine (DFMO), individually and together, are effective inhibitors of colon carcinogenesis. However, chronic use of sulindac is associated with significant side effects. We evaluated the chemopreventive efficacy of phospho-sulindac (P-S, OXT-328), an apparently safe derivative of sulindac, together with DFMO, in HT-29 human colon cancer xenografts. Nude mice were divided into four groups as follows: group 1 received vehicle (corn oil); group 2 received P-S (100 mg/kg/d) by oral gavage; group 3 received DFMO (2% in drinking water); and group 4 received P-S (100 mg/kg/d) by gavage plus DFMO (2% in drinking water; P-S/DFMO). Eighteen days after implantation, compared with controls, tumor volume was inhibited 65.9% by P-S, 52.9% by DFMO, and 70.9% by P-S/DFMO (P < 0.01 for all). P-S/DFMO reduced cell proliferation 27.1% and increased apoptosis 38.9% compared with controls (P < 0.05 for both). Compared with controls, P-S reduced the levels of thioredoxin-1 (Trx-1) and thioredoxin reductase (TrxR), whereas DFMO reduced polyamine content (putrescine and spermidine) and TrxR levels. Importantly, P-S/DFMO decreased putrescine and spermidine levels and the expression of Trx-1, TrxR, and cyclooxygenase (COX) 2. Of these molecular targets, TrxR most consistently correlated with tumor growth. Study results show that P-S/DFMO is an efficacious drug combination for colon cancer prevention and also show the safety of P-S, which may overcome the limiting side effects of conventional sulindac. P-S/DFMO has an intricate mechanism of action extending beyond polyamines and including the thioredoxin system, an emerging regulator of chemoprevention. P-S/DFMO merits further evaluation.

Coenzyme Q10 attenuated DMH-induced precancerous lesions in SD rats

Coenzyme Q10 (CoQ10) is known to be a compound with mitochondrial bioenergetic functions and antioxidant activity. In this study, we evaluated the effect of CoQ10 on the formation of aberrant crypt foci (ACF) induced by 1,2-dimethylhydrazine (DMH), DMH-induced leukocytic DNA damage and gene expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) by real-time PCR in colonic mucosa of male SD rats. The animals were divided into three groups and fed a casein-based high-fat and low fiber diet (100 g lard+20 g cellulose/kg diet) with or without CoQ10 (0.4 mg in soybean oil/kg BW/d, i.p.). One week after beginning the diets, the rats were subjected to 6 wk of treatment with DMH (30 mg/kg/wk, s.c.) and CoQ10 treatments continued over the entirety of the experimental period (59 d). Administration of CoQ10 resulted in reduction of ACF numbers, to 20% of the carcinogen control value. CoQ10 supplementation induced an antigenotoxic effect on DMH-induced DNA damage in the blood cells. Colonic mucosa of DMH-injected rats had significantly greater COX-2 and iNOS gene expression than those of control rats, while treatment with CoQ10 induced an inhibitory effect on over-expression of COX-2 and iNOS in colon tumors. Our results provide evidence that CoQ10 has a protective effect on the process of colon carcinogenesis, suppressing the development of preneoplastic lesions, possibly by modulating COX-2 and iNOS gene expression in colonic mucosa and DNA damage in leukocytes, suggesting that CoQ10 has chemotherapeutic activity.