Colon cancer: genomics and apoptotic events

An intermittent approach for cancer chemoprevention

Cancer chemoprevention approaches generally use long-term, continuous treatment, which can produce major preventive effects but which can also have unexpected serious adverse events. This raises the question of whether intermittent dosing schedules might reduce toxicity while retaining benefit, a concept that we call short-term intermittent therapy to eliminate premalignancy (SITEP). Recent preclinical studies support a novel SITEP approach whereby short-term, intermittent therapy eliminates premalignant cells via apoptosis that is induced by synthetic lethal interactions. Synthetic lethality allows personalized, selective elimination of premalignant clones without harming normal cells. This Opinion article provides a detailed discussion of the principle, method and future development of the SITEP approach.

Dietary selenomethionine increases exon-specific DNA methylation of the p53 gene in rat liver and colon mucosa

The regulation of site-specific DNA methylation of tumor suppressor genes has been considered as a leading mechanism by which certain nutrients exert their anticancer property. This study was to investigate whether selenium (Se) affects the methylation of globe genomic DNA and the exon-specific p53 gene. Three groups of rats (n = 6-7/group) were fed the AIN-93G basal diet supplemented with 0 [Se deficient (D)], 0.15 [Se adequate (A)], or 4 mg [Se supranutritional (S)] (Se as l-selenomethionine)/kg diet for 104 d, respectively. Rats fed the A or S diet had greater plasma and liver glutathione peroxidase activity, liver thioredoxin reductase activity, and plasma homocysteine concentration than those fed the D diet. However, compared with the A diet, rats fed the S diet did not further increase these Se-dependent enzyme activities or homocysteine concentration. In contrast, Se concentrations in kidney, liver, gastrocnemius muscle, and plasma were increased in a Se-dose-dependent manner. Interestingly, rats fed the S diet had significantly less global liver genomic DNA methylation than those fed the D diet. However, the S diet significantly increased the methylation of the p53 gene (exons 5-8) but not the β-actin gene (exons 2-3) DNA in liver and colon mucosa compared with those fed the D diet. Taken together, long-term Se consumption not only affects selenoprotein enzyme activities, homocysteine, tissue Se concentrations, and global genomic DNA methylation but also increases exon-specific DNA methylation of the p53 gene in a Se-dose-dependent manner in rat liver and colon mucosa.

Apoptosis inducing effect of plumbagin on colonic cancer cells depends on expression of COX-2

Plumbagin, a quinonoid found in the plants of the Plumbaginaceae, possesses medicinal properties. In this study we investigated the anti-proliferative and apoptotic activity of plumbagin by using two human colonic cancer cell lines, HT29 and HCT15. IC50 of Plumbagin for HCT15 and HT29 cells (22.5 µM and 62.5 µM, respectively) were significantly different. To study the response of cancer cells during treatment strategies, cells were treated with two different concentrations, 15 µM, 30 µM for HCT15 and 50 µM, 75 µM for HT29 cells. Though activation of NFκB, Caspases-3, elevated levels of TNF-α, cytosolic Cytochrome C were seen in both HCT15 cells HT29 treated with plumbagin, aberrant apoptosis with decreased level of pEGFR, pAkt, pGsk-3β, PCNA and Cyclin D1was observed only in 15 µM and 30 µM plumbagin treated HCT15 and 75 µM plumbagin treated HT29 cells. This suggests that plumbagin induces apoptosis in both HCT15 cells and HT29 treated, whereas, proliferation was inhibited only in 15 µM and 30 µM plumbagin treated HCT15 and 75 µM plumbagin treated HT29 cells, but not in 50 µM plumbagin treated HT29 cells. Expression of COX-2 was decreased in 75 µM plumbagin treated HT29 cells when compared to 50 µM plumbagin treated HT29 cells, whereas HCT15 cells lack COX. Hence the observed resistance to induction of apoptosis in 50 µM plumbagin treated HT29 cells are attributed to the expression of COX-2. In conclusion, plumbagin induces apoptosis in colonic cancer cells through TNF-α mediated pathway depending on expression of COX-2 expression.

Quercetin enhances 5-fluorouracil-induced apoptosis in MSI colorectal cancer cells through p53 modulation

PURPOSE

Colorectal tumors (CRC) with microsatellite instability (MSI) show resistance to chemotherapy with 5-fluorouracil (5-FU), the most widely used pharmacological drug for CRC treatment. The aims of this study were to test the ability of quercetin (Q) and luteolin (L) to increase the sensitivity of MSI CRC cells to 5-FU and characterize the dependence of the effects on cells' p53 status.

METHODS

Two MSI human CRC-derived cell lines were used: CO115 wild type (wt) for p53 and HCT15 that harbors a p53 mutation. Apoptosis induction in these cells by 5-FU, Q and L alone, and in combinations was evaluated by TUNEL and western blot. The dependence of the effects on p53 was confirmed by small interference RNA (siRNA) in CO115 cells and in MSI HCT116 wt and p53 knockout cells.

RESULTS

CO115 p53-wt cells are more sensitive to 5-FU than the p53-mutated HCT15. The combination treatment of 5-FU with L and Q increased apoptosis with a significant effect for Q in CO115. Both flavonoids increased p53 expression in both cell lines, an effect particularly remarkable for Q. The significant apoptotic enhancement in CO115 incubated with Q plus 5-FU involved the activation of the apoptotic mitochondrial pathway. Importantly, knockdown of p53 by siRNA in CO115 cells and p53 knockout in HCT116 cells totally abrogated apoptosis induction, demonstrating the dependence of the effect on p53 modulation by Q.

CONCLUSION

This study suggests the potential applicability of these phytochemicals for enhancement 5-FU efficiency in MSI CRC therapy, especially Q in p53 wt tumors.

HOXB7 as a prognostic factor and mediator of colorectal cancer progression

PURPOSE

This study was to investigate the clinicopathologic significance and potential role of HOXB7 in the development and progression of colorectal cancer (CRC).

EXPERIMENTAL DESIGN

The relationship between HOXB7 expression and clinical characteristics of CRC was analyzed in 224 paraffin-embedded archived CRC specimens by immunohistochemistry (IHC). The effects of HOXB7 on cell growth and proliferation, as well as on tumorigenesis, were examined both in vitro and in vivo, using MTT assay, colony formation assay, cell cycle analysis, soft agar assay, and tumorigenesis in nude mice. Western blotting and real-time reverse transcriptase-PCR were performed to examine the impact of HOXB7 on the PI3K/Akt and MAPK signaling pathways.

RESULTS

HOXB7 protein level was significantly correlated with advanced Dukes stage (P < 0.001), T stage (P = 0.012), distant metastasis (P = 0.042), higher proliferation index (P = 0.007) and poor survival of patients (P = 0.005). Enforced expression of HOXB7 in CRC cell lines significantly enhanced cell growth, proliferation and tumorigenesis. Conversely, knockdown of HOXB7 caused an inhibition of cell growth, proliferation, and tumorigenesis. We also showed that HOXB7 accelerated G(0)-G(1) to S-phase transition concomitantly with upregulation of cyclin D1 and downregulation of p27Kip1. On the contrary, knockdown of HOXB7 caused G(1)-S-phase arrest, downregulation of cyclin D1 and upregulation of p27Kip1. Enforced expression of HOXB7 could enhance PI3K/AKT and MAPK pathway activity.

CONCLUSION

Our findings suggest that HOXB7 protein, as a valuable marker of CRC prognosis, plays an important role in the development and progression of human CRC.

CD86 +1057 G/A polymorphism and the risk of colorectal cancer

CD86 (B7-2), one of the costimulatory molecules on antigen-presenting cells, plays essential roles not only in autoimmunity and transplantation but also in tumor immunity. The purpose of this study was to investigate whether CD86 gene polymorphism was involved in predisposing an individual to colorectal cancer (CRC). The CD86 +1057 G/A polymorphism was genotyped by performing polymerase chain reaction-restriction fragment length polymorphism in 273 patients with CRC and 292 healthy controls. There were significant differences in the genotype and allele distribution of +1057 G/A polymorphism of the CD86 gene between cases and controls. The +1057 AA genotype was associated with a significantly increased risk of CRC when compared with the GG genotype (odds ratio [OR] = 2.16; 95% confidence interval [CI], 1.31-3.58). Using the G allele as a reference, a significant correlation was detected between the presence of the A allele and a risk of developing CRC (OR = 1.42; 95% CI, 1.12-1.80). Interestingly, the A allele in female patients with CRC was significantly higher than that in male patients after stratified analysis (OR = 1.49; 95% CI, 1.04-2.14). These data suggest that CD86 +1057G/A polymorphism may contribute to genetic susceptibility to CRC in a Chinese population.

PUMA suppresses intestinal tumorigenesis in mice

Defective apoptosis contributes to tumorigenesis, although the critical molecular targets remain to be fully characterized. PUMA, a BH3-only protein essential for p53-dependent apoptosis, has been shown to suppress lymphomagenesis. In this study, we investigated the role of PUMA in intestinal tumorigenesis using two animal models. In the azoxymethane (AOM)/dextran sulfate sodium salt model, PUMA deficiency increased the multiplicity and size of colon tumors but reduced the frequency of beta-catenin hotspot mutations. The absence of PUMA led to a significantly elevated incidence of precursor lesions induced by AOM. AOM was found to induce p53-dependent PUMA expression and PUMA-dependent apoptosis in the colonic crypts and stem cell compartment. Furthermore, PUMA deficiency significantly enhanced the formation of spontaneous macroadenomas and microadenomas in the distal small intestine and colon of APC(Min/+) mice. These results show an essential role of PUMA-mediated apoptosis in suppressing intestinal tumorigenesis in mice.

Down-regulation of Bax-interacting factor-1 in colorectal adenocarcinoma

BACKGROUND

Bax-interacting factor-1 (Bif-1) protein is a member of the endophilin B family that plays a critical role in apoptosis, autophagy, and mitochondrial morphology. Loss of Bif-1 suppresses programmed cell death and promotes tumorigenesis. The connection of Bif-1 to colorectal cancer remains to be evaluated.

METHODS

To determine Bif-1 expression in human colorectal adenocarcinoma (CRC), the authors performed immunohistochemistry using stage-oriented cancer tissue microarrays containing 102 CRC samples of different stages and 38 samples of normal colorectal mucosa (NR). Formalin-fixed, paraffin-embedded core sections on the tissue array were immunostained using the avidin-biotin-peroxidase method and the anti-Bif-1 murine monoclonal antibody. Bif-1 staining was scored by 2 independent observers. To examine Bif-1 mRNA levels, the authors performed DNA microarray analysis of 205 CRC and 10 NR samples.

RESULTS

Bif-1 expression was negative in 22.5% (23 of 102) of CRCs. Moderate to strong Bif-1 staining was identified in 36.3% (37 of 102) of the tumors, and weak staining was noted in 41.2% (42 of 102). Twenty-six of 38 (68.4%) NR samples exhibited moderate to strong Bif-1 immunoreactivity, and none of them was negative. In 12 (31.6%) cases NR demonstrated weak Bif-1 stain. The mean (median) scores for CRCs and NR differed significantly: 3.2 (3.0) and 5.2 (6.0), respectively (P = .0003). The percentage of cases with negative expression also differed significantly between NR and CRC (P = .002). Decreased Bif-1 expression in CRCs was confirmed at the mRNA level by microarray analysis.

CONCLUSIONS

The authors report the down-regulation of Bif-1 during the transition from NR to CRC, a novel finding in agreement with the tumor suppressor function of Bif-1.

Natural polyphenols facilitate elimination of HT-29 colorectal cancer xenografts by chemoradiotherapy: a Bcl-2- and superoxide dismutase 2-dependent mechanism

Colorectal cancer is one of the most common malignancies worldwide. The treatment of advanced colorectal cancer with chemotherapy and radiation has two major problems: development of tumor resistance to therapy and nonspecific toxicity towards normal tissues. Different plant-derived polyphenols show anticancer properties and are pharmacologically safe. In vitro growth of human HT-29 colorectal cancer cells is inhibited ( approximately 56%) by bioavailable concentrations of trans-pterostilbene (trans-3,5-dimethoxy-4'-hydroxystilbene; t-PTER) and quercetin (3,3',4',5,6-pentahydroxyflavone; QUER), two structurally related and naturally occurring small polyphenols. I.v. administration of t-PTER and QUER (20 mg/kg x day) inhibits growth of HT-29 xenografts ( approximately 51%). Combined administration of t-PTER + QUER, FOLFOX6 (oxaliplatin, leucovorin, and 5-fluorouracil; a first-line chemotherapy regimen), and radiotherapy (X-rays) eliminates HT-29 cells growing in vivo leading to long-term survival (>120 days). Gene expression analysis of a Bcl-2 family of genes and antioxidant enzymes revealed that t-PTER + QUER treatment preferentially promotes, in HT-29 cells growing in vivo, (a) superoxide dismutase 2 overexpression ( approximately 5.7-fold, via specificity protein 1-dependent transcription regulation) and (b) down-regulation of bcl-2 expression ( approximately 3.3-fold, via inhibition of nuclear factor-kappaB activation). Antisense oligodeoxynucleotides to human superoxide dismutase 2 and/or ectopic bcl-2 overexpression avoided polyphenols and chemoradiotherapy-induced colorectal cancer elimination and showed that the mangano-type superoxide dismutase and Bcl-2 are key targets in the molecular mechanism activated by the combined application of t-PTER and QUER.

Association of the TP53 codon 72 polymorphism with colorectal cancer in a Chinese population

A TP53 gene polymorphism, resulting in an arginine (R) to proline (P) at codon 72 (TP53 R72P), has been associated with the susceptibility to various cancers. To better understand the role of this polymorphism in colorectal cancer etiology, we examined the association between TP53 R72P and colorectal cancer risk in 345 patients with colorectal cancer and 670 controls in a Chinese population. We observed that subjects with RP and PP genotypes had a 1.60-fold and a 2.37-fold increased risk for colorectal cancer, respectively. The 72P allele conferred a more pronounced increase in colorectal cancer risk among alcohol consumers (heterozygotes: OR = 3.01; homozygotes: OR = 4.71). The TP53 R72P polymorphism was not linked to tumor location, histologic grade, lymph node metastases, Dukes stage, p53 positivity, or age at diagnosis, but to tumor size. We conclude that the TP53 R72P polymorphism may contribute to the etiology of colorectal cancer in the Chinese population, particularly among alcohol consumers.

Apoptosis in normal rectal mucosa, baseline adenoma characteristics, and risk of future adenomas

Low apoptosis in the normal rectal mucosa has been associated with colorectal adenomas in cross-sectional studies. It is unknown whether apoptosis can predict the occurrence of new adenomas. We evaluated whether apoptosis at baseline colonoscopy, as well as patient and adenoma characteristics, could predict future occurrence of adenomas. Study subjects were participants in the Diet and Health Study III, a cross-sectional study of adenoma risk factors between August 1998 and March 2000. At baseline, subjects underwent colonoscopy and provided normal rectal mucosal biopsies to evaluate apoptosis as well as information about diet and lifestyle. The present study includes 257 subjects who returned for follow-up colonoscopy between 2000 and 2005. Apoptosis, number of adenomas, size, and atypia at baseline colonoscopy were evaluated as predictors of new adenomas. Logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). At baseline, low apoptosis was significantly associated with increased risk of adenomas (P = 0.0001). Compared with those in the lowest tertile, subjects with high apoptosis were less likely to have an adenoma at follow-up (crude OR, 0.25; 95% CI, 0.09-0.65; adjusted OR, 0.29; 95% CI, 0.08-1.06). Having three or more adenomas at baseline was associated with increased risk of new adenomas (crude OR, 2.46; 95% CI, 1.14-5.31; adjusted OR, 3.74; 95% CI, 1.01-13.83). This study suggests that lower apoptosis is associated with increased risk of future adenoma development. If confirmed in larger studies, apoptosis could potentially be used to identify patients at highest risk for developing new adenomas.

Silibinin inhibits colorectal cancer growth by inhibiting tumor cell proliferation and angiogenesis

Herein, for the first time, we investigated in vivo efficacy and associated molecular biomarkers and mechanisms of a chemopreventive agent, silibinin, against human colorectal carcinoma (CRC) HT29 xenograft growth. Nude mice were implanted with HT29 cells and fed with vehicle (carboxymethyl cellulose or phosphatidylcholine) or 200 mg/kg/d dose of silibinin or 100 and 200 mg/kg/d doses of silybin-phytosome (5 days per week) for 32 days. Silibinin inhibited tumor growth that accounted for 48% (P = 0.002) decrease in tumor volume and 42% (P = 0.012) decrease in tumor weight at the end of the experiment without any adverse health effect. A stronger antitumor efficacy was observed with silybin-phytosome preparation. Silibinin decreased proliferation index by 40% (P < 0.001), increased apoptotic index by approximately 2-fold (P = 0.001), and reduced microvessel density by 36% (P = 0.001) in tumors. Antiproliferative and proapoptotic effects of silibinin were associated with down-regulation of extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt phosphorylation as well as cyclin D1 expression. Antiangiogenic effect of silibinin was coupled with a strong decrease in inducible nitric oxide synthase (NOS) and NOS3, cyclooxygenase-1 (COX-1) and COX-2, and hypoxia-inducing factor-1 alpha (HIF-1 alpha) and vascular endothelial growth factor (VEGF). These findings suggest in vivo antitumor efficacy of silibinin against CRC involving its antiproliferative, proapoptotic, and antiangiogenic activities. The inhibition of ERK1/2 and Akt signaling may account for antiproliferative and proapoptotic effects, whereas down-regulation of NOS, COX, HIF-1 alpha, and VEGF expression could lead to antiangiogenic effect of silibinin against CRC. Overall, potential use of silibinin against human CRC could be suggested.

Hsp70 response to 5-fluorouracil treatment in human colon cancer cell lines

BACKGROUND AND AIMS

Colorectal cancer is a common disease with high rate of mortality. Although there is evidence of some benefits of 5-fluorouracil (5-FU), the most commonly used drug in colon cancer therapy, it still remains unsatisfactory because of intrinsic or acquired drug resistance. Heat shock proteins (Hsps) synthesis can be increased by cellular insults, such as chemotherapy-induced damage. Inducible Hsp70 has been suggested to be involved in cytoprotection against apoptosis. In the present study, we investigated whether the content of Hsp70 is associated to 5-FU resistance.

METHODS

HT-29 and SNU-C4 human colon cancer cell lines were treated with 5-FU and their relative chemoresistance, and Hsp70 were determined.

RESULTS

Comparison of IC(50) values showed that the HT-29 cells were relatively resistant to 5-FU, whereas the SNU-C4 cells presented greater sensitivity to this drug. Further, 5-FU treatment leads to a hypodiploid population in HT-29 cells significantly lower compared to SNU-C4 cells. In the HT-29 cell line, 5-FU treatment promoted an increase of 5.5 times in Hsp70 concentration after 12 h. Then, within 24 h, the increase in Hsp70 levels was still about two times. In contrast, in the SNU-C4 cell line, 5-FU induced an increase of about two times in the Hsp70 content after 12 h and, after 24 h, did not significantly affect Hsp70 content.

CONCLUSIONS

These data suggest that 5-FU induced Hsp70 synthesis in the HT-29 resistant cell line and that this Hsp70 accumulation could protect against 5-FU-induced apoptosis. Thus, Hsp70 protection against 5-FU-induced apoptosis might underlie colon cancer chemoresistance.

Modification of Gene Products Involved in Resistance to Apoptosis in Metastatic Colon Cancer Cells: Roles of Fas, Apaf-1, NFκB, IAPs, Smac/DIABLO, and AIF

BACKGROUND

Colon cancer becomes resistant to apoptosis as it acquires metastatic potential. SW480 and SW620 colon cancer cells were established from the same patient at different stages of tumor progression. The stage III colorectal cancer cell line (SW620) is more resistant to apoptosis. In the present report, we investigated the apoptotic gene products that might account for colon cancer evasion of immune attack and chemoradioresistance-induced apoptosis.

METHODS

SW480 and SW620 cells were used for this experiment. Type 1 apoptosis was induced by CH-11. Type 2 apoptosis was induced by cisplatin and ionizing radiation. Apoptosis was determined by caspase-3 activity and terminal deoxynucleotidyl transferase mediated dUTP nick end labeling. Gene products Fas, TRAIL, c-FLIP, Bid, BAX, Bcl-2, Bcl-xL, Apaf-1, nuclear factor-kappa B, Smac/DIABLO, apoptosis inducing factor, and the inhibitors of apoptosis were investigated by immunocytochemistry and Western blot analyses.

RESULTS

SW620 cell lines were more resistant to both Type 1 and Type 2 apoptosis induced by CH-11, cisplatin, and ionizing radiation, respectively. Examination of the extrinsic pathway demonstrated Fas receptor to be down-regulated in SW620. Apaf-1 was decreased in SW620 cells; while other members of the mitochondrial pathway including Bax, Bid, Bcl-xL, and Bcl-2 demonstrated minimal alterations of protein levels in both cell lines. Survivin and XIAP protein levels were increased in SW620 cells, which correlated with nuclear expression of nuclear factor-kappa B in SW620 cells but not SW480. Mitochondrial-released factors including Smac/DIABLO and apoptosis inducing factor were increased in SW480 cells.

CONCLUSIONS

SW620 cells have acquired genetic defects both in the intrinsic and extrinsic pathways of apoptosis, which may explain in part the ability of colon cancer cells to escape the immune system and to become chemoradioresistant. These genes may be potential targets for chemoradiosensitization in advanced colorectal cancer.

Acquisition of resistance to butyrate induces resistance to luminal components and other types of stress in human colon adenocarcinoma cells

Butyrate, naturally produced by anaerobic fermentation of diet-fiber, is the major nutrient of colonocytes and also an important regulator of colonic epithelium renewal and physiology. Other luminal components, such as bile acids or bacterial products, influence these processes. The model system we used to analyze the influence of several luminal stressors is composed of a previously established cell line resistant to the apoptotic effects of butyrate and their parental butyrate-sensitive cells. Viability of butyrate-resistant cells is unaffected by mild heat-shock (2h, 42 degrees C) and only slightly reduced by severe heat-shock (2h, 45 degrees C) in contrast to their butyrate-sensitive counterparts. The higher constitutive expression of HSP70 and HSP60 could contribute to this resistance. In addition, expression of HSP70 follows a different pattern after heat-shock in both cell lines. Butyrate-resistant cells are quite unaffected by treatment with deoxycholic acid but apoptosis is induced by chenodeoxycholic acid although to a lower extent than in butyrate-sensitive cells. These resistant cells are also less sensitive to lipopolysaccharide and show differences regarding the activation of ERK following osmotic stress. Thus, the cell model herein reported is a useful tool for investigating the molecular mechanisms of resistance to apoptosis, as well as to analyze specific targets for butyrate-resistant tumors.

Suppression of FHL2 expression induces cell differentiation and inhibits gastric and colon carcinogenesis

BACKGROUND AND AIMS

FHL2 (4-1/2 LIM protein 2) is an adapter and modifier in protein interactions that is expressed mainly in the heart and ovary. It functions in a cell type- or promoter-specific manner. The aims of this study were to examine its expression in gastrointestinal cancers and to determine its role in cell differentiation and tumorigenesis.

METHODS

FHL2 expression in cancerous and normal gastrointestinal cells was detected by reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. The effect of FHL2 suppression by both antisense and siRNA methods on cell differentiation and growth were evaluated in vitro and in vivo.

RESULTS

FHL2 expression was up-regulated in gastrointestinal cancer, compared with matched normal tissues. Stable transfection of gastric cancer cell line, AGS, and colon cancer cell line, Lovo, with antisense FHL2 induced lengthened or shuttle-shape morphologic changes with long or dendritic-like cytoplasmic processes and decreased the nuclear:cytoplasmic ratio. FHL2 antisense induced expressions of carcinoembryonic antigen and E-cadherin and the maturation of F-actin. Furthermore, FHL2 antisense inhibited the transcriptions of some oncogenes including cox-2, survivin, c-jun, and hTERT, and suppressed the promoter activity of activator protein-1 and hTERT. Suppression of FHL2 inhibited serum-dependent, anchorage-dependent and -independent cell growth, and suppressed de novo tumor formation in nude mice xenograft.

CONCLUSIONS

Suppression of FHL2 induces cell differentiation and inhibits tumorigenesis. Antisense or siRNA methods targeting FHL2 is a promising strategy for treatment of gastrointestinal cancers.

Colon cancer and the immune system: The role of tumor invading T cells

Colon cancer is still one of the leading causes of cancer death worldwide. Although the host immune system has been shown to react against tumor cells, mainly through tumor infiltrating lymphocytes and NK cells, tumor cells may utilize different ways to escape anti-tumor immune response. Tumor infiltration of CD8+ and CD4+ (T-bet+) effector T cells has been attributed to a beneficial outcome, and the enhancement of T cell activation through T cell receptor stimulation and co-stimulatory signals provides promising strategies for immunotherapy of colon cancer. Growing evidence supports a role for the Fas/FasL system in tumor immunology, although the mechanisms and consequences of FasL activation in colon cancer are not completely understood. In animal models, depletion of regulatory T cells (CD4+ CD25+ T cells) can enhance the anti-tumor immune response under certain conditions. Taken together, recent insights in the immune reaction against colon carcinoma have provided new approaches to immunotherapy, although much remains to be learned about the exact mechanisms.

Grape seed extract inhibits in vitro and in vivo growth of human colorectal carcinoma cells

PURPOSE

Accumulating evidences suggest the beneficial effects of fruit-and-vegetable consumption in lowering the risk of various cancers, including colorectal cancer. Herein, we investigated the in vitro and in vivo anticancer effects and associated mechanisms of grape seed extract (GSE), a rich source of proanthocyanidins, against colorectal cancer.

EXPERIMENTAL DESIGN

Effects of GSE were examined on human colorectal cancer HT29 and LoVo cells in culture for proliferation, cell cycle progression, and apoptosis. The in vivo effect of oral GSE was examined on HT29 tumor xenograft growth in athymic nude mice. Xenografts were analyzed by immunohistochemistry for proliferation and apoptosis. The molecular changes associated with the biological effects of GSE were analyzed by Western blot analysis.

RESULTS

GSE (25-100 microg/mL) causes a significant dose- and time-dependent inhibition of cell growth with concomitant increase in cell death. GSE induced G1 phase cell cycle arrest along with a marked increase in Cip1/p21 protein level and a decrease in G1 phase-associated cyclins and cyclin-dependent kinases. GSE-induced cell death was apoptotic and accompanied by caspase-3 activation. GSE feeding to mice at 200 mg/kg dose showed time-dependent inhibition of tumor growth without any toxicity and accounted for 44% decrease in tumor volume per mouse after 8 weeks of treatment. GSE inhibited cell proliferation but increased apoptotic cell death in tumors. GSE-treated tumors also showed enhanced Cip1/p21 protein levels and poly(ADP-ribose) polymerase cleavage.

CONCLUSIONS

GSE may be an effective chemopreventive agent against colorectal cancer, and that growth inhibitory and apoptotic effects of GSE against colorectal cancer could be mediated via an up-regulation of Cip1/p21.

In vitro models for the study of the effect of butyrate on human colon adenocarcinoma cells

The effect of butyrate has been analyzed on human colon adenocarcinoma cell lines with different properties regarding tumorigenicity, differentiation and resistance to apoptosis induced by this agent. Butyrate reduces cell proliferation, induces differentiation (according to alkaline phosphatase activity) and apoptosis, being these effects time- and concentration-dependent. The susceptibility to the cytotoxic effects of butyrate depends on the cell line considered and it is not directly related to tumorigenicity or differentiation. We show that 2mM butyrate treatment of non-tumorigenic BCS-TC2 cells for four days strongly influences the transcriptional activity, causing extensive modification in gene expression patterns (69 up-regulated and 109 down-regulated genes). Some of these genes are involved in the modulation of cell cycle progression, apoptosis and differentiation. We have analyzed the effect of butyrate in spontaneous or induced multicellular spheroids. The more stable spheroids (spontaneous or induced from butyrate-resistant cells) increase the resistance of cells to the effects of butyrate probably due to an impaired accessibility. This in vitro model could be useful to study the resistance of tumors to the effect of natural regulators (i.e. butyrate) as well as to develop and test new therapeutic approaches.

Butyrate induces profound changes in gene expression related to multiple signal pathways in bovine kidney epithelial cells

BACKGROUND

Global gene expression profiles of bovine kidney epithelial cells regulated by sodium butyrate were investigated with high-density oligonucleotide microarrays. The bovine microarray with 86,191 distinct 60mer oligonucleotides, each with 4 replicates, was designed and produced with Maskless Array Synthesizer technology. These oligonucleotides represent approximately 45,383 unique cattle sequences.

RESULTS

450 genes significantly regulated by butyrate with a median False Discovery Rate (FDR) = 0 % were identified. The majority of these genes were repressed by butyrate and associated with cell cycle control. The expression levels of 30 selected genes identified by the microarray were confirmed using real-time PCR. The results from real-time PCR positively correlated (R = 0.867) with the results from the microarray.

CONCLUSION

This study presented the genes related to multiple signal pathways such as cell cycle control and apoptosis. The profound changes in gene expression elucidate the molecular basis for the pleiotropic effects of butyrate on biological processes. These findings enable better recognition of the full range of beneficial roles butyrate may play during cattle energy metabolism, cell growth and proliferation, and possibly in fighting gastrointestinal pathogens.

Colon cancer and apoptosis

BACKGROUND

The implementation of new therapeutic options for the management of metastatic colon cancer mandates a revisit to apoptosis and its role in colon cancer tumorigenesis with an emphasis on the mechanisms leading to chemotherapeutic resistance and immune system evasion of colon cancer cells.

DATA SOURCES

Literature regarding molecular apoptosis mechanisms and the role of apoptosis in colon cancer progression are reviewed by this article.

CONCLUSION

Programmed cell death has rapidly emerged as a potential target for cancer treatment at various stages of tumor progression. Chemoprevention, immuno-regulation, and metastasis are prospective targets by which apoptotic mechanisms could be utilized in the prevention and management of tumorigenesis. Understanding how defects in the death receptor pathway of apoptosis permit colon cancer cells to escape the immune system would allow for treatment options whereby the body's immune system could again recognize and eliminate unwanted cells.

In vitro effects on polydextrose by colonic bacteria and caco-2 cell cyclooxygenase gene expression

A 4-stage colon simulator and a cell culture-based human intestinal epithelial function model were combined to study the effects of a soluble fiber, polydextrose (PDX), on intestinal microbes and mucosal functions relevant to the risk of colon cancer. We observed sustained degradation of PDX throughout the different stages of the model. The fermentation was characterized by gradual degradation of PDX, production of short-chain fatty acids, and no increasing in putrefactive markers. We observed less marked effects in the microbial densities. When we applied colon fermentation metabolites obtained from the simulators with PDX to Caco-2 colon cancer cell line, a significant dose-dependent decreasing effect on cyclooxygenase-2 (COX-2) and an increasing effect on COX-3 expression levels were observed. PDX concentration appeared not to have effect on the expression levels of COX-1. Overexpression of COX-2 and decreased expression of COX-1 have been suggested to be characteristics of colon cancer. The exact physiological role of COX-3, an intron-retaining splice variant of COX-1, is not known, but it is suspected to play a role in transcriptional regulation of COX-1 and COX-2. In vitro modulation of COX expression by colon microbial fermentation products of polydextrose offers an interesting starting point for further studies on possible risk-decreasing effect of PDX on the development of colon cancer.

Differentiation of androgen-independent prostate cancer PC-3 cells is associated with increased nuclear factor-kappaB activity

Recently, we have reported that inosine 5'-monophosphate dehydrogenase inhibitors, such as mycophenolic acid (MPA), induce the differentiation of PC-3 cells, which are derived from a human androgen-independent prostate cancer, into cells with a phenotype resembling maturing prostate secretory cells. Here, we describe such differentiation induced by the histone deacetylase inhibitor tributyrin. The maturation was defined by cytoplasmic vacuole production and induction of CD10, CD46, CD55, GRP78, keratin 17, and zinc-alpha-2-glycoprotein. To identify additional genes associated with tributyrin-induced PC-3 cell differentiation and to gain some insight into the mechanism that underlies this differentiation, we have, by means of microarray analyses, compared tributyrin-induced gene expression patterns with those of MPA, which initiates PC-3 cell differentiation by a dissimilar mode of action. We suggested that genes induced by both tributyrin and MPA would be most likely associated with differentiation rather than with the unique action of each particular inducer. Our results indicated that tributyrin or MPA induced the expression of a large number of common genes, including genes known or assumed to be NF-kappaB dependent. The NF-kappaB dependency of a group of these genes, which included the PC-3 cell differentiation marker keratin 17, was confirmed by using two common NF-kappaB activation inhibitors, Bay11-082 and TMB-8, and p65 subunit of NF-kappaB complex specific small interfering RNA. Taken together, our results implicate both NF-kappaB-dependent and NF-kappaB-independent genes in the processes leading to PC-3 cell differentiation induced by tributyrin and MPA.

Alpha-chaconine, a potato glycoalkaloid, induces apoptosis of HT-29 human colon cancer cells through caspase-3 activation and inhibition of ERK 1/2 phosphorylation

Although alpha-chaconine, one of the two major potato trisaccharide glycoalkaloids, have shown cytotoxic effects on human cancer cells, the exact mechanism of this action of alpha-chaconine is not completely understood. In this study, we found that alpha-chaconine induced apoptosis of HT-29 cells in a time- and concentration-dependent manner by using flow cytometric analysis. We also found that caspase-3 activity and the active form of caspase-3 were increased 12 h after alpha-chaconine treatment. Caspase inhibitors, N-Ac-DEVD-CHO and Z-VAD-fmk, prevented alpha-chaconine-induced apoptosis, whereas alpha-chaconine-induced apoptosis was potentiated by PD98059, an extracellular signal-regulated kinase (ERK) inhibitor. However, pretreatment of the cells with LY294002 and SB203580, inhibitors of PI3K and p38, respectively, BAPTA-AM, an intracellular Ca(2+) chelator, and antioxidants such as N-acetylcysteine (NAC) and Trolox had no effect on the alpha-chaconine-induced cell death. In addition, phosphorylation of ERK was reduced by the treatment with alpha-chaconine. Moreover, alpha-chaconine-induced caspase-3 activity was further increased by the pretreatment with PD98059. Thus, the results indicate that alpha-chaconine induces apoptosis of HT-29 cells through inhibition of ERK and, in turn, activation of caspase-3.

Xanthohumol induces apoptosis in cultured 40-16 human colon cancer cells by activation of the death receptor- and mitochondrial pathway

Xanthohumol (XN) is one of the major prenylflavonoids found in hop cones (Humulus lupulus L.). In this study, we investigated the cell growth inhibitory potential of XN on cultured human colon cancer cells. Cell proliferation was measured by sulforhodamine B staining. Poly(ADP-ribose)polymerase (PARP) cleavage, activation of caspases-3, -7, -8, and -9, and Bcl-2 family protein expression were detected by Western blot analyses. XN significantly reduced proliferation of the HCT 116-derived colon cancer cell line 40--16. Half-maximal inhibitory concentrations decreased from 4.1 microM after 24 h treatment to 3.6 and 2.6 microM after 48 and 72 h incubation, respectively. Treatment with 15 microM XN for 48 h and with 5 microM for 72 h led to the detection of the cleaved 89 kDa fragment of 116 kDa PARP as an indication of apoptosis induction. Concomitantly, we observed activation and cleavage of the effector caspases-3 and -7, induced by activation of the initiator caspases -8 and -9. Expression of anti-apoptotic Bcl-2 was down regulated when the cells were treated with XN for 48--72 h. We conclude that induction of apoptosis by downregulation of Bcl-2 and activation of the caspase cascade may contribute to the chemopreventive or therapeutic potential of XN.

Cyclin-dependent kinase inhibitors uncouple cell cycle progression from mitochondrial apoptotic functions in DNA-damaged cancer cells

DNA damage results in transcriptional induction of p53 target genes, including the cyclin-dependent kinase (CDK) inhibitor p21(Cip1) (CDKN1A) and the proapoptotic Bcl-2 family member p53 up-regulated modulator of apoptosis (PUMA). Depending on the cellular context, p21(Cip1) and PUMA mediate cell cycle arrest and apoptosis, respectively. By imposing cell cycle arrest at the expense of apoptosis, p21(Cip1) can sharply reduce the effectiveness of DNA-damaging anticancer agents in colorectal cancer cells. We investigated the link between cell cycle progression and the onset of apoptosis in DNA-damaged cells by analyzing the activation of the apoptotic cascade in p21(Cip1)-deficient HCT116 colorectal cancer cells. DNA damage induced a similar level of p53 activation and PUMA induction in p21(Cip1)-deficient cells compared with wild-type isogenic counterparts. p21(Cip1) did not act as a direct blocker of PUMA. However, only p21(Cip1)-deficient cells showed extensive cytochrome c release, mitochondrial membrane depolarization, and caspase activation. An increase in caspase activation occurred as these cells reached M-phase and incurred polyploidy. When ectopically expressed in p21(Cip1)-deficient HCT116 cells, p21(Cip1), its family member p27(Kip1), and the structurally unrelated CDK inhibitor p16(Ink4a) were similarly effective at causing cell cycle arrest and inhibiting DNA damage-induced apoptotic events such as cytochrome c release, mitochondrial membrane depolarization, and activation of the caspase cascade. These observations suggest that by blocking dysregulated cell cycle progression, CDK inhibitors can influence the sensitivity of the mitochondria to proapoptotic signals in DNA damage-induced cancer cells.