Human colon cancer HT-29 cell death responses to doxorubicin and Morus Alba leaves flavonoid extract

The mechanistic basis for the biological properties of Morus alba flavonoid extract (MFE) and chemotherapy drug of doxorubicin on human colon cancer HT-29 cell line death are unknown. The effect of doxorubicin and flavonoid extract on colon cancer HT-29 cell line death and identification of APC gene expression and PARP concentration of HT-29 cell line were investigated. The results showed that flavonoid extract and doxorubicin induce a dose dependent cell death in HT-29 cell line. MFE and doxorubicin exert a cytotoxic effect on human colon cancer HT-29 cell line by probably promoting or induction of apoptosis.

[Effect of triptolide on reversing hypermethylation of apc gene in Jurkat cells and its possible mechanisms]

This study was aimed to investigate the effect of traditional Chinese medicine, Triptolide (TPL) on reversing hypermethylation of antioncogene (apc gene) in acute lymphoblastic leukemia cell line Jurkat in vitro and to explore its mechanisms. The effects of TPL on cell growth, proliferation and cell cycle were detected by growth curve, MTT assay, colony formation test and flow cytometry, respectively. The effect of TPL on apc gene methylation of Jurkat cells was analyzed by nested methylation specific PCR; the expressions of apc gene, dnnt3a, dnmt3b mRNA were measured by RT-PCR; the protein expression of apc gene was detected by Western blot. The results showed that as compared with untreated control cells, the TPL of different concentrations could significantly inhibit growth and proliferation of Jurkat cells in dose-and time-dependent manners with IC₅₀ 19.7 ng/ml at 48 hours. All cytosines in CpG dinucleotides in untreated Jurkat cells had no changed, while all cytosines in Jurkat cells treated with TPL had been converted to thymidine suggesting the methylation of apc gene in Jurkat cells. The TPL could reverse hypermethylation of apc gene and induced the mRNA and protein expression of apc gene in dose-dependent manner. It is concluded that the small dose of TPL can obviously suppress the proliferation of Jurkat cells, activate and up-regulate the expression of apc gene through demethylation of apc gene resulting from DNMT and/or direct action, thereby inhibit the proliferation rate of Jurkat cells.

Rationale for, and design of, a clinical trial targeting polyamine metabolism for colon cancer chemoprevention

Polyamine metabolic genes are downstream targets of several genes commonly mutated in colon adenomas and cancers. Inhibitors of ornithine decarboxylase, such as difluoromethylornithine (DFMO), and agents that stimulate polyamine acetylation and export, such as non-steroidal anti-inflammatory drugs (NSAIDS), act at least additively to arrest growth in human cell models and suppress intestinal carcinogenesis in mice. These preclinical studies provided the rationale for colon cancer prevention trials in humans. A Phase IIb clinical study comparing the combination of DFMO and the NSAID sulindac versus placebo was conducted. Endpoints were colorectal tissue polyamine and prostaglandin E2 contents and overall toxicity to participants. Participants in the Phase IIb study served as a vanguard for a randomized, placebo-controlled prospective Phase III trial of the combination of DFMO and sulindac with the primary study endpoint the prevention of colon polyps. Seventy percent of participants will have completed the three years of treatment in December 2006.

Alterations of the Wnt signaling pathway during the neoplastic progression of Barrett's esophagus

Aberrant activation of the Wnt signaling pathway has been reported during neoplastic progression in Barrett's esophagus (BE). However, mutations in APC and CTNNB1 genes were rarely observed. In this study, expression pattern of Wnt ligands, Frizzled receptors and APC, as well as the methylation status of the APC, SFRP1 and SFRP2 promoter genes were investigated in normal esophageal mucosa and in preneoplastic and neoplastic lesions of BE patients. Promoter methylation of APC was found in all BE samples and in 95% of esophageal adenocarcinomas (EAC). Full methylation of APC correlated with lack of expression. In EAC, nuclear translocation of beta-catenin was observed regardless of the expression of APC. WNT2 expression was higher in dysplasia and EAC than in BE, with 20/26 (77%) of the EAC showing high expression of WNT2. SFRP1 methylation occurred in all BE samples and in 96% of EAC, while SFRP2 was methylated in 73% of the normal squamous esophageal mucosa samples. In conclusion, (1) alterations of key regulators of the Wnt signaling are frequent in the pathogenesis of BE; (2) the APC and SFRP1 genes are inactivated by promoter methylation in BE; (3) the WNT2 gene is upregulated along the progression from low-grade dysplasia to EAC.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces genetic changes in murine intestinal tumours and cells with ApcMin mutation

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is one of the mutagenic heterocyclic amines derived from cooked meat. In previous animal studies, spontaneous tumour formation in B6(Min/+) mice was associated with somatic loss of the wild-type Apc+ allele by loss of the entire chromosome 18 or by recombination. The objective of this study was to examine genetic changes caused by PhIP-exposure in a mouse intestinal cell line and in tumours from hybrid mice by keeping track of the chromosomes carrying the two Apc alleles. We transformed the SV40 T-immortalised intestinal epithelial cell line IMCE, derived from the B6(Min/+) mice by exposure to N-OH-PhIP, and studied the effect on Apc status and chromosome 18. Eighteen transformed cultures were obtained and all of them had retained the Apc+ allele. Five of seven transformed cultures were tumorigenic after implantation in nude mice. Chromosomal analysis of these five cultures and the parent IMCE cell line showed that the IMCE cells were near-tetraploid with an average of 77 chromosomes/cell, while the tumorigenic cell cultures were all triploid to hyper-triploid with a range of 61-69 chromosomes/cell. The number of copies of chromosome 18 was about four in the IMCE line and this copy number was retained in the transformed lines derived from IMCE. Changes in chromosome 18 and Apc during tumour development in vivo were examined in spontaneously formed and PhIP-induced intestinal tumours from two hybrid mice strains, i.e. B6(Min/+) - a murine FAP model - crossed with either AKR/J or A/J. We evaluated the allelic status of Apc, and the heterogenic microsatellite markers D18Mit19 and D18Mit4, located at the upper and lower ends of chromosome 18, respectively. In tumours from untreated animals, instability in the D18Mit19 and Apc was observed. Upon PhIP exposure, the B6(Min/A+) hybrid mouse tumours differed distinctly in genetic profile from those obtained from untreated animals and we detected three genetically different tumour groups, all of which had apparently retained Apc+. One group had allelic balance between the Apc(Min) and Apc+, the second had allelic imbalance between the Apc and D18Mit4 alleles, indicative of chromosomal stability in the first group and instability in the lower end of chromosome 18 in the second group, respectively. The third group showed variable allelic status of the three markers. A similar change in genetic profile was also seen in intestinal tumours of PhIP-exposed B6(Min/AKR+) hybrid mice, but it was less pronounced. Chromosomal breaks and/or recombinational events could be alternative explanations for the observed allelic imbalances in chromosome 18 markers in intestinal tumours from PhIP-exposed mice.

Leptin, insulin-like growth factor-1, and insulin-like growth factor-2 are mitogens in ApcMin/+ but not Apc+/+ colonic epithelial cell lines

The obese state is associated with elevated circulating levels of insulin, insulin-like growth factors (IGF), and leptin. Research is contradictory regarding the role of these elevated growth factors in colon cancer risk. We hypothesized that colonic epithelial cells that were Apc deficient (ApcMin/+) but not those expressing wild-type Apc (Apc+/+) would experience a hyperproliferative and antiapoptotic phenotype when exposed to these growth factors. This hypothesis was addressed using two nontumorigenic murine colonic epithelial cell lines with distinct Apc genotypes: Apc+/+ YAMC cells and ApcMin/+ IMCE cells. Cells were treated for 48 hours with various concentrations of leptin (0.001-50 ng/mL), IGF-1 (0.1-200 ng/mL), or IGF-2 (0.1-600 ng/mL). In YAMC cells, leptin caused a significant decrease in cell proliferation (P < 0.01) compared with controls due to induction of caspase activity and apoptosis. In contrast, in the IMCE cells, leptin induced a 75% increase in cell proliferation compared with controls (P < 0.0001). IGF-1 and IGF-2 also induced 50% greater proliferation in the IMCE cells (P < 0.001) compared with controls. Cotreatment of IMCE cells with leptin and either IGF-1 or IGF-2 induced greater proliferation than either growth factor alone (P < 0.0001). IMCE cell proliferation caused by leptin only treatment was associated with activation of p42/44 mitogen-activated protein kinase (MAPK), p38 MAPK, and nuclear factor-kappaB nuclear translocation but not with MAPK kinase or Janus-activated kinase/signal transducers and activators of transcription activation. These data provide the first evidence that leptin may interact with IGFs to promote survival and expansion of colonic epithelial cells that were Apc deficient (ApcMin/+) but not those expressing wild-type Apc (Apc+/+).

Epigenetic modification regulates both expression of tumor-associated genes and cell cycle progressing in human colon cancer cell lines: Colo-320 and SW1116

The aim of this study is to assess the effects of DNA methylation and histone acetylation, alone or in combination, on the expression of several tumor-associated genes and cell cycle progression in two established human colon cancer cell lines: Colo-320 and SW1116. Treatments with 5-aza-2-deoxycytidine (5-aza-dC) and trichostatin A, alone or in combination, were applied respectively. The methylation status of the CDKN2A promoter was determined by methylation-specific PCR, and the acetylated status of the histones associated with the p21WAF1 and CDKN2A genes was examined by chromatin immunoprecipitation. The expression of the CDKN2A, p21WAF1, p53, p73, APC, c-myc, c-Ki-ras and survivin genes was detected by real-time RT-PCR and RT-PCR. The cell cycle profile was established by flow cytometry. We found that along with the demethylation of the CDKN2A gene promoter in both cell lines induced by 5-aza-dC alone or in combination with TSA, the expression of both CDKN2A and APC genes increased. The treatment of TSA or sodium butyrate up-regulated the transcription of p21WAF1 significantly by inducing the acetylation of histones H4 and H3, but failed to alter the acetylation level of CDKN2A-associated histones. No changes in transcription of p53, p73, c-myc, c-Ki-ras and survivin genes were observed. In addition, TSA or sodium butyrate was shown to arrest cells at the G1 phase. However, 5-aza-dC was not able to affect the cell cycle progression. In conclusion, regulation by epigenetic modification of the transcription of tumor-associated genes and the cell cycle progression in both human colon cancer cell lines Colo-320 and SW1116 is gene-specific.

Promoter Methylation Inhibits APC Gene Expression by Causing Changes in Chromatin Conformation and Interfering with the Binding of Transcription Factor CCAAT-Binding Factor

As an important regulator in Wnt-signaling pathway, the APC gene is involved in apoptosis and cell cycle arrest. The loss of APC function is observed in most familial adenomatous polyposis-associated and sporadic colorectal cancer. APC gene is frequently inactivated by DNA mutations. However, hypermethylation in APC gene promoter was also observed in different cancers. In this study, by analyzing the methylation status of APC promoter in 22 colorectal cancer cell lines with different APC expression levels, we identified Regions A and B in the promoter, where the methylation of CpG sites was invariably correlated with the loss of gene expression. By nuclease accessibility assay, we also observed a correlation between the closed chromatin conformation in APC promoter and loss of gene expression. When the nonexpressing cell lines were treated with a DNA methyltransferase inhibitor, 5-Aza-2'-Deoxycytidine, the APC expression in these cells was induced, CpG sites were demethylated, and closed chromatin conformation was opened. However, when these cell lines were treated with a histone deacetylase inhibitor, Trichostatin A, no significant changes in APC expression, methylation status, and chromatin conformation were observed. Using transient transfection assay, a CCAAT box located in Region B was identified, which was involved in up-regulation of APC expression. Methylation of CpG sites around the CCAAT box resulted in a significant inhibition in the gene expression. The specific binding of a transcription factor CCAAT-binding factor (CBF) to the CCAAT box was determined by electrophoretic mobility shift analysis. The binding was inhibited after CpG sites close to the CCAAT box were methylated, indicating that DNA methylation can silence gene expression through interfering with the binding of transcription factors to the promoter. The biological function of CBF in APC gene regulation was further indicated by the decrease of luciferase activities in cells cotransfected with a plasmid carrying APC promoter/luciferase gene and a plasmid expressing dominant negative CBF mutant. In summary, methylation of CpG sites around CCAAT box in APC promoter inhibits the gene expression by changing the chromatin conformation and interfering with the binding of transcription factor CBF to CCAAT box.

Effects of cyclooxygenase-2 inhibitor NS-398 on APC and c-myc expression in rat colon carcinogenesis induced by azoxymethane

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been reported to protect against the development of colon cancer; however, the mechanism(s) by which NSAIDs exert their effects is still unclear. The aim of this study was to examine the effects of NSAIDs on the expression of the tumor suppressor APC gene and the c-myc oncogene in the colons of rats treated with a colon-specific carcinogen, azoxymethane (AOM).

METHODS

Gene expression levels were estimated by a reverse transcription (RT)-competitive polymerase chain reaction (PCR) method.

RESULTS

The group of rats simultaneously administered AOM and NS-398, a cyclooxygenase (COX)-2 inhibitor, showed a significant reduction in the number of preneoplastic lesions of colon cancer compared with that in the group of rats treated with AOM alone. Furthermore, the APC expression level in the group of rats treated with both AOM and NS-398 was significantly greater than that in the group of rats treated with AOM alone; this result for APC gene expression was reconfirmed by the immunohistochemical staining of APC protein. In addition, c-myc mRNA expression was clearly decreased in the group of rats treated with both AOM and NS-398 compared with the level in the group of rats treated with AOM alone.

CONCLUSIONS

Our data thus indicate that NS-398 causes an increase in APC expression and a decrease in c-myc expression.

Expression of COX-2 and Wnt pathway genes in adenomas of familial adenomatous polyposis patients treated with meloxicam

BACKGROUND

Familial adenomatous polyposis (FAP) is an autosomal, dominantly inherited predisposition to colorectal cancer caused by germline mutations within the adenomatous polyposis coli (APC) gene, a key member of the Wnt signalling pathway. A new class of non-steroidal anti-inflammatory drugs (NSAIDs), the specific cyclooxygenase 2 (COX-2) inhibitors, have recently been applied for the treatment of FAP patients.

PATIENTS AND METHODS

The expressions of the Wnt members and targets APC, c-myc, cyclin D1 and COX-2, as measured by real-time quantitative RT-PCR, have been evaluated in fresh samples of normal colorectal mucosa and matched adenoma tissue of six unrelated FAP patients before and after treatment with meloxicam.

RESULTS

A significant up-regulation of COX-2 in adenomas after treatment with meloxicam was found. Furthermore, in adenomas, a down-regulation of APC after treatment and a tight correlation of the expressions of the two Wnt targets, c-myc and cyclin D1, in both stages of treatment were observed.

CONCLUSION

A feedback loop mediated by the peroxisome proliferator-activated receptor (PPAR) gamma is discussed as being responsible for the up-regulation of COX-2

Cyclooxygenase-2: a novel target for cancer chemotherapy?

Epidemiologic studies have documented a 40-50% reduction in incidence of colorectal cancer in individuals taking nonsteroidal antiinflammatory drugs (NSAIDs). Since NSAIDs are known to inhibit cyclooxygenases (COX-1, COX-2), the basic mechanism of their antitumor effects is conceivably the altered metabolism of arachidonic acid and, subsequently, prostaglandins (PGs). Although COX-2, the inducible isoform, is regularly expressed at low levels in colonic mucosa, its activity increases dramatically following mutation of the APC (adenomatous polyposis coli) gene suggesting that beta-catenin/T-cell factor mediated Wnt-signaling activity may regulate COX-2 gene expression. In addition, hypoxic conditions and sodium butyrate exposure may also contribute to COX-2 gene transcription in human cancers. The development of selective COX-2 inhibitors has made it possible to further evaluate the role of COX-2 activity in colorectal carcinogenesis. To date, at least five mechanisms by which COX-2 contributes to tumorigenesis and the malignant phenotype of tumor cells have been identified, including: (1) inhibition of apoptosis; (2) increased angiogenesis; (3) increased invasiveness; (4) modulation of inflammation/immuno-suppression; and (5) conversion of procarcinogens to carcinogens. A clear positive correlation between COX-2 expression and inhibition of apoptosis has been established, associated with increased PGE2 levels resulting in modulation of pro- and anti-apoptotic factors (e.g., bcl-2, MAKs/ras, caspase-3, Par-4). In terms of angiogenesis and invasiveness, COX-2 activity was found to increase the expression of growth factors (e.g., VDEG, PDGF, bFGF) and matrix metalloproteinases (MMPs). Since COX-2 inhibitors have been demonstrated to interfere with tumorigenesis and apoptosis, COX-2 and its gene product may be attractive targets for therapeutic and chemoprotective strategies in colorectal cancer patients. This may lead to new perspectives that by controlling the cancer phenotype, rather than attempting to eradicate all affected cells, may provide significant benefits to the cancer patient.

Sulindac and a cyclooxygenase-2 inhibitor, etodolac, increase APC mRNA in the colon of rats treated with azoxymethane

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to protect against the development of colon cancer. However, the mechanism(s) by which NSAIDs exert their effects is not clear.

AIMS

The aim of this study was to examine the effects of NSAIDs on mRNA expression of tumour suppressor adenomatous polyposis coli (APC) gene in rat colon mucosa.

METHODS

Starting at six weeks of age, three groups of rats (groups 1, 2, and 3) were treated with azoxymethane (AOM), a colon specific carcinogen, and another three groups (groups 4, 5, and 6) were not given AOM. Groups 2 and 3 were given 10 mg/kg of sulindac or etodolac, respectively, three times weekly during the experiment. Groups 4 and 5 were also given sulindac or etodolac, respectively, in the same manner as in groups 2 and 3. Group 6 (untreated control) was not given any agent (AOM or NSAIDs). At 10 weeks of age, preneoplastic lesions (aberrant crypt foci (ACF)) induced by AOM in the colon were counted, and the level of expression of APC mRNA in the colonic mucosa was estimated by the reverse transcription-competitive polymerase chain reaction method and northern blot analysis.

RESULTS

Mean occurrence of ACF in rats in groups 2 and 3 was reduced to approximately 50% of that in group 1. The level of APC mRNA expression in group 1 (AOM alone) was lower than that in group 6 (untreated control) (p<0.05); however, levels of APC mRNA expression in groups 2, 3, 4, and 5, to which NSAIDs had been administered, were significantly increased compared with levels in groups 1 and 6 (p<0.01).

CONCLUSIONS

Both sulindac and etodolac reduced the occurrence of ACF and induced an increase in APC mRNA in rat colon mucosa.

Mutations of adenomatous polyposis coli and beta-catenin genes during progression of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine in rats

In the present study, we investigated mutations of the adenomatous polyposis coli (APC) and beta-catenin genes to clarify possible molecular mechanisms underlying development of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 weeks of age, were given 2000 ppm BHP in drinking water for 12 weeks and then maintained without further treatment until sacrifice at week 25 DNA was extracted from paraffin-embedded tissues, and PCR-single-strand conformation polymorphism analysis, followed by nucleotide sequencing, was performed. No APC mutations were detected in 17 hyperplasias, but 2 of 15 adenomas (13.3%) and 8 of 20 adenocarcinomas (40.0%) showed changes within exon 1 to the mutation cluster region in exon 15. For beta-catenin, no mutations were detected in 17 hyperplasias, but 3 of 15 adenomas (20.0%) and 5 of 20 adenocarcinomas (25.0%) had alterations within or flanking codons corresponding to important phosphorylation sites. Immunohistochemical staining showed beta-catenin protein localized in the cell membranes in the surrounding normal-appearing lung and 216 hyperplasias and localized mainly in the cytoplasm and/or nucleus in 10 of 37 adenomas (27.0%) and 21 of 40 adenocarcinomas (52.5%). These results suggest that the APC-beta-catenin-T-cell factor signaling pathway is involved in the acquisition of growth advantage from adenomas to adenocarcinomas in BHP-induced rat lung carcinogenesis.

Protein synthesis inhibitor-mediated stability of adenomatous polyposis coli mRNA levels in HCT-116 colon cancer cells

We examined the effect of a protein synthesis inhibitor, cycloheximide (CHX) on the adenomatous polyposis coli (APC) mRNA levels in HCT-116 colon cancer cell line. The HCT-116 cells were treated with different concentrations of CHX for 15 h. APC, p53 and beta-actin mRNA levels were determined by Northern blotting. Results showed that APC and beta-actin mRNA levels were significantly increased in a dose-dependent manner after CHX treatment. The p53 mRNA levels were moderately increased. The increase in APC mRNA levels after CHX treatment was due to increase in its stability instead of transcription. These results provide a model for CHX-induced APC mRNA stabilization and its implication in cell cycle arrest and cell survival studies.

Chemotherapy-induced nuclear alterations of morphologic and genomic characteristics in a human colon cancer grafted onto nude mice

PURPOSE

A human Dukes B colonic adenocarcinoma was grafted onto 40 nude mice. The mice were divided into four groups, one control and three representing experimental conditions. Animals in the three experimental groups received either adriamycin (ADR), 5-fluorouracil (5-FU), or camptothecin (CPT) over a 25-day period beginning 34 days after grafting. Control animals received saline on an identical schedule. Animals were killed 105 days after grafting.

METHODS

The effect of therapy was assessed by three techniques: 1) tumor size was periodically measured during the life of the animals, 2) modifications of APC, Ki-ras, and p53 genes were studied by polymerase chain reaction, dot-blot analysis, restriction analysis, and DNA sequencing, and 3) image cytometry of Feulgen-stained material was used to characterize 15 parameters describing morphometric, densitometric, and textural features of tumor nuclei.

RESULTS

When compared with controls, tumor growth (size) was maximally suppressed by treatment with CPT (P < or = 0.001). Growth was inhibited significantly by treatment with 5-FU (P < or = 0.01); no statistical difference in tumor size was observed between controls and animals treated with ADR. Modifications of APC, Ki-ras, and p53 genes were not observed; however, treatment did inhibit amplification of APC and p53 genes.

CONCLUSIONS

The 15 morphonuclear parameters were assessed to define populations of cell nuclei altered by chemotherapy. Although CPT maximally suppressed growth, it did not alter nuclear morphology when compared with controls. Treatment with either 5-FU or ADR resulted in nuclear morphologic alterations defined as distinct populations using multivariate analysis. Nonsupervised linear discriminant analysis was used to quantify the relative proportions of these populations. Four morphonuclear parameters were identified, which discriminated nuclei exposed to either ADR or 5-FU from controls.