Ashok Kumar Pandurangan

Potential Targets for Prevention of Colorectal Cancer: a Focus on PI3K/Akt/mTOR and Wnt Pathways

Colorectal cancer (CRC) is one of the most common cancers in many parts of the world. Its development is a multi-step process involving three distinct stages, initiation that alters the molecular message of a normal cell, followed by promotion and progression that ultimately generates a phenotypically altered transformed malignant cell. Reports have suggested an association of the phosphoinositide-3-kinase (PI3K)/Akt pathway with colon tumorigenesis. Activation of Akt signaling and impaired expression of phosphatase and tensin homolog (PTEN) (a negative regulator of Akt) has been reported in 60-70% of human colon cancers and inhibitors of PI3K/Akt signaling have been suggested as potential therapeutic agents. Around 80% of human colon tumors possess mutations in the APC gene and half of the remainder feature β-catenin gene mutations which affect downstream signaling of the PI3K/Akt pathway. In recent years, there has been a great focus in targeting these signaling pathways, with natural and synthetic drugs reducing the tumor burden in different experiment models. In this review we survey the role of PI3K/Akt/mTOR and Wnt signaling in CRC.

Sphingosine-1-phosphate lyase downregulation promotes colon carcinogenesis through STAT3-activated microRNAs

Growing evidence supports a link between inflammation and cancer; however, mediators of the transition between inflammation and carcinogenesis remain incompletely understood. Sphingosine-1-phosphate (S1P) lyase (SPL) irreversibly degrades the bioactive sphingolipid S1P and is highly expressed in enterocytes but downregulated in colon cancer. Here, we investigated the role of SPL in colitis-associated cancer (CAC). We generated mice with intestinal epithelium-specific Sgpl1 deletion and chemically induced colitis and tumor formation in these animals. Compared with control animals, mice lacking intestinal SPL exhibited greater disease activity, colon shortening, cytokine levels, S1P accumulation, tumors, STAT3 activation, STAT3-activated microRNAs (miRNAs), and suppression of miR-targeted anti-oncogene products. This phenotype was attenuated by STAT3 inhibition. In fibroblasts, silencing SPL promoted tumorigenic transformation through a pathway involving extracellular transport of S1P through S1P transporter spinster homolog 2 (SPNS2), S1P receptor activation, JAK2/STAT3-dependent miR-181b-1 induction, and silencing of miR-181b-1 target cylindromatosis (CYLD). Colon biopsies from patients with inflammatory bowel disease revealed enhanced S1P and STAT3 signaling. In mice with chemical-induced CAC, oral administration of plant-type sphingolipids called sphingadienes increased colonic SPL levels and reduced S1P levels, STAT3 signaling, cytokine levels, and tumorigenesis, indicating that SPL prevents transformation and carcinogenesis. Together, our results suggest that dietary sphingolipids can augment or prevent colon cancer, depending upon whether they are metabolized to S1P or promote S1P metabolism through the actions of SPL.

Chemopreventive sphingadienes downregulate Wnt signaling via a PP2A/Akt/GSK3β pathway in colon cancer

Sphingadienes (SDs) derived from soy and other natural sphingolipids are cytotoxic to colon cancer cells via an Akt-dependent mechanism and reduce adenoma formation in Apc(Min/+) mice. Wnt signaling is fundamental to colon carcinogenesis and is the basis for spontaneous tumorigenesis in Apc(Min/+) mice and patients with familial adenomatous polyposis. In the present study, we investigated the impact of SDs on Wnt signaling. Oral SD administration reduced levels of active β-catenin and Wnt targets c-Myc and cyclin D1 in Apc(Min/+) mouse intestinal tissues. Colon cancer cells treated with SDs exhibited reduced Wnt transcriptional activity, as well as reduced nuclear β-catenin localization and subsequent reduction in active-β-catenin levels. Further, we observed a decrease in phosphorylated (inactive) GSK3β in SD-treated mice and colon cancer cells. Expression of constitutively active myristoylated-Akt or inactivation of GSK3β using LiCl attenuated SD-mediated inhibition of Wnt transcriptional activity and active-β-catenin levels. SDs exhibited additive effects with inhibitors of the phosphatidylinositol-3-kinase/Akt/mTOR pathway to induce cytotoxicity. Further, a combination regime of SDs and low-dose rapamycin decreased visible polyps in Apc(Min/+) mice and reduced the levels of Wnt target gene expression and mTOR target activation. SD-mediated inhibition of Akt and Wnt pathways and cytotoxicity in colon cancer cells was dependent upon the activity of protein phosphatase 2A, as shown by reversal of these effects by pretreatment with okadaic acid or calyculin A. Our cumulative findings indicate that SDs inhibit Wnt signaling through a protein phosphatase 2A/Akt/GSK3β-dependent mechanism that may contribute to their chemopreventive effects in intestinal tumorigenesis.

Luteolin, a Bioflavonoid Inhibits Colorectal Cancer through Modulation of Multiple Signaling Pathways: A Review

Luteolin, 3, 4, 5,7-tetrahydroxyflavone, belongs to a group of naturally occurring compounds called flavonoids that are found widely in the plant kingdom. It possesses many beneficial properties including antioxidant, anti- inflammatory, anti-bacterial, anti-diabetic and anti-proliferative actions. Colorectal cancer (CRC) is a leading cause of cancer related deaths worldwide. Many signaling pathways are deregulated during the progression of colon cancer. In this review we aimed to analyze the protection offered by luteolin on colon cancer. During colon cancer genesis, luteolin known to reduce oxidative stress thereby protects the cell to undergo damage in vivo. Wnt/β-catenin signaling, deregulated during neoplastic development, is modified by luteolin. Hence, luteolin can be considered as a potential drug to treat CRC.

EFFECT OF LUTEOLIN ON THE LEVELS OF GLYCOPROTEINS DURING AZOXYMETHANE-INDUCED COLON CARCINOGENESIS IN MICE

Luteolin (LUT), a bioflavonoid has been used as a chemopreventive agent world-wide against chemically induced cancer. Hence we designed an experiment to assess chemopreventive action of LUT on lipid peroxidation (LPO) and glycoconjugates in azoxymethane (AOM)-induced colon carcinogenesis. Colon cancer was induced by 15 mg/body kg. body weight of AOM and administration of LUT (at the dose of 1.2 mg/kg. body weight) was till end of the study. Analysis of lipid peroxidative end products such as protein carbonyl (PC), malonadehyde (MDA) and conjucated dienes (CD) demonstrated significant increase in in AOM-induced animals with reduction by LUT (p<0.05) . Increased levels of glycoconjugates such as hexose, hexosamine, sialic acid, fucose and mucoprotein were analyzed in serum and colon tissues examined histopathologically by periodic acid Schiffs (PAS) staining were also reversed by LUT l(p<0.05) . The secondary marker of colon cancer mucin depleted foci (MDF) was assessed in control and experimental group of animals. A characteristic increase of MDF was observed in AOM- induced colon cancer animals. Treatment with LUT decreased the incidence of MDF. These results suggest that LUT alters the expression of glycoconjugates and suppress colon cancer. Hence, we speculate that LUT can be used as a chemopreventive agent to treat colon cancer.

Luteolin, a bioflavonoid inhibits Azoxymethane-induced colorectal cancer through activation of Nrf2 signaling.

Abstract Colorectal cancer (CRC) is now perceived as a multistep process characterized by the accumulation of genetic alterations in oncogenes and tumor suppressor genes. Plant-derived compounds are receiving considerable attention for their potential role in reducing cancer risk. Luteolin, a bioflavonoid present in many fruits and vegetables, possesses antioxidant, anti-inflammatory and antiproliferative properties. This study was designed to investigate the possible role of luteolin administration on Phase 1 and 2 enzymes and NF-E2-related factor 2 (Nrf2)/keap1 pathway. Male Balb/C mice were divided into four groups: normal control, Azoxymethane (AOM)-induced, AOM-induced and luteolin treated, normal control treated with luteolin. CRC was induced by administration of AOM (15u2009mg/kg body weight) intraperitoneally (i.p.) once a week for three weeks. Luteolin administration (1.2u2009mg/kg body weight/day) significantly alleviated Phase1 enzymes in colon and liver, it increased the levels of phase 2 enzymes. Luteolin modulates the expressions of GST-α, µ and also the expression of Nrf2. Collectively, results of our hypothesis show that luteolin is a novel candidate for treating CRC.

Dietary cocoa protects against colitis‐associated cancer by activating the Nrf2/Keap1 pathway

Colorectal cancer (CRC) is the third most common malignancy in males and the second most common cancer worldwide. Chronic colonic inflammation is a known risk factor for CRC. Cocoa contains many polyphenolic compounds that have beneficial effects in humans. The objective of this study is to explore the antioxidant properties of cocoa in the mouse model of azoxymethane (AOM)/dextran sulfate sodium (DSS)-induced colitis-associated cancer, focusing on the activation of Nrf2 signaling. Mice were treated with AOM/DSS and randomized to receive either a control diet or a 5 and 10% cocoa diet during the study period. On day 62 of the experiment, the entire colon was processed for biochemical and histopathological examination and further evaluations. Increased levels of malondialdehyde (MDA) were observed in AOM/DSS-induced mice; however, subsequent administration of cocoa decreased the MDA. Enzymatic and nonenzymatic antioxidants, such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, were decreased in the AOM/DSS mice. Cocoa treatment increases the activities/levels of enzymatic and nonenzymatic antioxidants. Inflammatory mediators, such as inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, were elevated during AOM/DSS-induction, and treatment with 5 and 10% cocoa effectively decreases the expression of iNOS and COX-2. The NF-E2-related factor 2 and its downstream targets, such as NQO1 and UDP-GT, were increased by cocoa treatment. The results of our study suggest that cocoa may merit further clinical investigation as a chemopreventive agent that helps prevent CAC.

Preventive inositol hexaphosphate extracted from rice bran inhibits colorectal cancer through involvement of Wnt/β-catenin and COX-2 pathways.

Nutritional or dietary factors have drawn attention due to their potential as an effective chemopreventive agent, which is considered a more rational strategy in cancer treatment. This study was designed to evaluate the effect of IP6 extracted from rice bran on azoxymethane- (AOM-) induced colorectal cancer (CRC) in rats. Initially, male Sprague Dawley rats were divided into 5 groups, with 6 rats in each group. The rats received two intraperitoneal (i.p.) injections of AOM in saline (15u2009mg/kg body weight) over a 2-week period to induce CRC. IP6 was given in three concentrations, 0.2% (w/v), 0.5% (w/v), and 1.0% (w/v), via drinking water for 16 weeks. The deregulation of the Wnt/β-catenin signaling pathway and the expression of cyclooxygenase (COX)-2 have been implicated in colorectal tumorigenesis. β-Catenin and COX-2 expressions were analysed using the quantitative RT-PCR and Western blotting. Herein, we reported that the administration of IP6 markedly suppressed the incidence of tumors when compared to the control. Interestingly, the administration of IP6 had also markedly decreased β-catenin and COX-2 in colon tumors. Thus, the downregulation of β-catenin and COX-2 could play a role in inhibiting the CRC development induced by IP6 and thereby act as a potent anticancer agent.

Allicin Alleviates Dextran Sodium Sulfate- (DSS-) Induced Ulcerative Colitis in BALB/c Mice

The objective of this study is to evaluate the effect of allicin (10u2009mg/kg body weight, orally) in an experimental murine model of UC by administering 2.5% dextran sodium sulfate (DSS) in drinking water to BALB/c mice. DSS-induced mice presented reduced body weight, which was improved by allicin administration. We noted increases in CD68 expression, myeloperoxidase (MPO) activities, and Malonaldehyde (MDA) and mRNA levels of proinflammatory cytokines, such as tumor necrosis factor- (TNF-) α, interleukin- (IL-) 1β, IL-6, and IL-17, and decrease in the activities of enzymic antioxidants such as superoxide dismutase (SOD), Catalase (CAT), Glutathione reductase (GR), and Glutathione peroxidase (GPx) in DSS-induced mice. However, allicin treatment significantly decreased CD68, MPO, MDA, and proinflammatory cytokines and increased the enzymic antioxidants significantly (P < 0.05). In addition, allicin was capable of reducing the activation and nuclear accumulation of signal transducer and activator of transcription 3 (STAT3), thereby preventing degradation of the inhibitory protein IκB and inducing inhibition of the nuclear translocation of nuclear factor (NF)-κB-p65 in the colonic mucosa. These findings suggest that allicin exerts clinically useful anti-inflammatory effects mediated through the suppression of the NF-κB and IL-6/p-STAT3Y705 pathways.

Gallic acid attenuates dextran sulfate sodium-induced experimental colitis in BALB/c mice

Gallic acid (GA) is a polyhydroxy phenolic compound that has been detected in various natural products, such as green tea, strawberries, grapes, bananas, and many other fruits. In inflammatory bowel disease, inflammation is promoted by oxidative stress. GA is a strong antioxidant; thus, we evaluated the cytoprotective and anti-inflammatory role of GA in a dextran sulfate sodium (DSS)-induced mouse colitis model. Experimental acute colitis was induced in male BALB/c mice by administering 2.5% DSS in the drinking water for 7 days. The disease activity index; colon weight/length ratio; histopathological analysis; mRNA expressions of IL-21 and IL-23; and protein expression of nuclear erythroid 2-related factor 2 (Nrf2) were compared between the control and experimental mice. The colonic content of malondialdehyde and the activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase activity were examined as parameters of the redox state. We determined that GA significantly attenuated the disease activity index and colon shortening, and reduced the histopathological evidence of injury. GA also significantly (P<0.05) reduced the expressions of IL-21 and IL-23. Furthermore, GA activates/upregulates the expression of Nrf2 and its downstream targets, including UDP-GT and NQO1, in DSS-induced mice. The findings of this study demonstrate the protective effect of GA on experimental colitis, which is probably due to an antioxidant nature of GA.