Combination of isoliquiritigenin and tumor necrosis factor-related apoptosis-inducing ligand induces apoptosis in colon cancer HT29 cells

<p><b>OBJECTIVES</b>Isoliquiritigenin is a chalcone derivative with potential in cancer chemoprevention. Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent, some cancer cells are resistant to TRAIL treatment. Current studies have tried to overcome TRAIL-resistant cancer cells. Here, we show for the first time that isoliquiritigenin overcomes TRAIL resistance in colon cancer HT29 cells.</p><p><b>METHODS</b>HT29 cells were treated with isoliquiritigenin and/or TRAIL, and apoptosis induction was detected by flow cytometry and fluorescence microscopy. Protein expression relating to the TRAIL pathway was analyzed by Western blotting.</p><p><b>RESULTS</b>A single treatment with isoliquiritigenin scarcely induced apoptosis in HT29 cells. Combined treatment with suboptimal concentrations of isoliquiritigenin and TRAIL markedly induced apoptosis, however. The effect was blocked by a pan-caspase inhibitor and a caspase-3, 8, 9, or 10 inhibitor, suggesting that the combination facilitates caspase-dependent apoptosis. Furthermore, the apoptosis induced by isoliquiritigenin and TRAIL was blocked by a dominant negative form of the TRAIL receptor. This result indicates that the combined effect is caused by specific interaction between TRAIL and its receptors. Isoliquiritigenin increased the amount of DR5 protein among TRAIL receptors. Isoliquiritigenin did not significantly increase levels of the Bcl-2 family proteins Bcl-2, Bcl-xL, and BAX.</p><p><b>CONCLUSIONS</b>Our results suggest that isoliquiritigenin has the potential to overcome resistance to TRAIL in cancer cells and its chemopreventive effects may depend on TRAIL function.</p>

INK4 Family -A promising target for 'gene-regulating chemoprevention' and 'molecular-targeting prevention' of cancer

Inactivation of the p16(INK4a) gene is one of the most frequent defects that contribute to oncogenesis in human cancer, since it is a tumor-suppressor gene. Therefore, functional restoration of p16(INK4a) is one of the most effective methods for cancer prevention. We proposed the concept of 'gene-regulating chemoprevention' and 'molecular-targeting prevention' of cancer, which assumes that transcriptional regulation by drugs on tumor-suppressor genes or functionally similar genes to the tumor-suppressor genes contributes to the prevention of human malignancies. The p16(INK4a) homologs p15(INK4b), p18(INK4c) and p19(INK4d) have been recently identified, and these four members constitute the INK4 family of proteins. All directly bind to cyclin D-cyclin dependent kinase (CDK) 4/6 and are therefore specific inhibitors of these complexes. We recently showed that histone deacetylase (HDAC) inhibitors, promising chemopreventive and chemotherapeutical agents, induce p15(INK4b) and p19(INK4d) gene expression and cause growth arrest, suggesting that both genes are important molecular targets for HDAC inhibitors. Furthermore, we found that 12-O-tetradecanoylphorbol-13-acetate (TPA), which is widely used as a tumor promoter and protein kinase C activator, promotes human cancer cell growth through the down-regulation of p18(INK4c) gene expression. This suggests that a mouse two-stage carcinogenesis model using TPA might partially represent the most common human carcinogenesis pathway related to RB. Our results suggest that the INK4 family consists of attractive and promising molecular targets for the 'gene-regulating chemoprevention' and 'molecular-targeting prevention' of cancer.

INK4 Family\\---A Promising Target for \lqGene-Regulating Chemoprevention\rq and \lqMolecular-Targeting Prevention\rq of Cancer---

Inactivation of the p16INK4a gene is one of the most frequent defects that contribute to oncogenesis in human cancer, since it is a tumor-suppressor gene. Therefore, functional restoration of p16INK4a is one of the most effective methods for cancer prevention. We proposed the concept of ‘gene-regulating chemoprevention’ and ‘molecular-targeting prevention’ of cancer, which assumes that transcriptional regulation by drugs on tumor-suppressor genes or functionally similar genes to the tumor-suppressor genes contributes to the prevention of human malignancies. The p16INK4a homologs p15INK4b, p18INK4c and p19INK4d have been recently identified, and these four members constitute the INK4 family of proteins. All directly bind to cyclin D-cyclin dependent kinase (CDK) 4/6 and are therefore specific inhibitors of these complexes. We recently showed that histone deacetylase (HDAC) inhibitors, promising chemopreventive and chemotherapeutical agents, induce p15INK4b and p19INK4d gene expression and cause growth arrest, suggesting that both genes are important molecular targets for HDAC inhibitors. Furthermore, we found that 12-O-tetradecanoylphorbol-13-acetate (TPA), which is widely used as a tumor promoter and protein kinase C activator, promotes human cancer cell growth through the down-regulation of p18INK4c gene expression. This suggests that a mouse two-stage carcinogenesis model using TPA might partially represent the most common human carcinogenesis pathway related to RB. Our results suggest that the INK4 family consists of attractive and promising molecular targets for the ‘gene-regulating chemoprevention’ and ‘molecular-targeting prevention’ of cancer.

Histone deacetylase inhibitors -Promising agents for 'gene-regulating chemoprevention' and 'molecular-targeting prevention' of cancer-

One of the best approaches against cancer is prevention. Inactivation of the p53 or p16(INK4a) genes has been extensively reported in most human cancer cells. Both p53 and p16(INK4a) function as tumor suppressors. Therefore, functional restoration of these molecules is considered to be one of the most useful methods for cancer prevention and therapy. We have proposed a concept termed 'gene-regulating chemoprevention and chemotherapy' regarding the above pathway. This concept assumes that transcriptional regulation by drugs on tumor-suppressor genes, downstream target genes or functionally similar genes (for example, family genes) of the tumor-suppressor genes would contribute to the prevention of human malignancies. Histone deacetylase (HDAC) inhibitors have been shown to be potent inducers of growth arrest, differentiation and apoptotic cell death. Previously, we demonstrated that HDAC inhibitors, such as sodium butyrate and trichostatin A (TSA), transcriptionally induce the cyclin-dependent kinase inhibitor p21(WAF1/Cip1), a downstream target gene of p53, in a p53-independent manner. Furthermore, we have recently shown that HDAC inhibitors activate Gadd45, another downstream target gene of p53, and p19(INK4d), a gene functionally similar to p16(INK4a). Our results, taken together with previous findings, suggest that HDAC inhibitors may be one of the most attractive and promising agents for 'gene-regulating chemoprevention' and 'molecular-targeting prevention' of cancer.

Histone Deacetylase Inhibitors ---Promising Agents for \lqGene-Regulating Chemoprevention\rq and \lqMolecular-Targeting Prevention\rq of Cancer---

One of the best approaches against cancer is prevention. Inactivation of the p53 or p16INK4a genes has been extensively reported in most human cancer cells. Both p53 and p16INK4a function as tumor suppressors. Therefore, functional restoration of these molecules is considered to be one of the most useful methods for cancer prevention and therapy. We have proposed a concept termed ‘gene-regulating chemoprevention and chemotherapy’ regarding the above pathway. This concept assumes that transcriptional regulation by drugs on tumor-suppressor genes, downstream target genes or functionally similar genes (for example, family genes) of the tumor-suppressor genes would contribute to the prevention of human malignancies. Histone deacetylase (HDAC) inhibitors have been shown to be potent inducers of growth arrest, differentiation and apoptotic cell death. Previously, we demonstrated that HDAC inhibitors, such as sodium butyrate and trichostatin A (TSA), transcriptionally induce the cyclin-dependent kinase inhibitor p21WAF1/Cip1, a downstream target gene of p53, in a p53-independent manner. Furthermore, we have recently shown that HDAC inhibitors activate Gadd45, another downstream target gene of p53, and p19INK4d, a gene functionally similar to p16INK4a. Our results, taken together with previous findings, suggest that HDAC inhibitors may be one of the most attractive and promising agents for ‘gene-regulating chemoprevention’ and ‘molecular-targeting prevention’ of cancer.

Quercetin enhances tumorigenicity induced by N-ethyl-N'-nitro-N-nitrosoguanidine in the duodenum of mice

Quercetin, a flavonoid, widely distributed in many fruits and vegetables, is well known to have an antitumor effect despite its mutagenicity. In this study, we examined the effect of dietary quercetin on duodenum-tumorigenicity of mice induced by a chemical carcinogen, N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Eight-week-old male C57BL/6 mice were divided into 4 groups; ENNG without quercetin (group A), ENNG with 0.2% quercetin (group B), ENNG with 2% quercetin (group C), and 2% quercetin without ENNG (group D). ENNG was given in drinking water for the first 4 weeks, and thereafter quercetin was given in a mixed diet. At week 20, the average number of duodenal tumors per mouse was significantly higher in group C (mean±SE, 7.26±1.75, p<0.05) than in group A (2.32±0.31). The size of the duodenal tumors increased significantly in group B (1.79±0.09 mm, p<0.001) compared with group A (1.43±0.09 mm). In contrast, no duodenal tumor was induced in group D. The present findings suggest that excessive intake of quercetin occasionally is a risk factor for carcinogenesis of some specific organs such as the upper intestine.

Quercetin Enhances Tumorigenicity Induced by N-Ethyl-N'-Nitro-N-Nitrosoguanidine in the Duodenum of Mice*

Quercetin, a flavonoid, widely distributed in many fruits and vegetables, is well known to have an anti-tumor effect despite its mutagenicity. In this study, we examined the effect of dietary quercetin on duodenum-tumorigenicity of mice induced by a chemical carcinogen, N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Eight-week-old male C57BL/6 mice were divided into 4 groups; ENNG without quercetin (group A), ENNG with 0.2% quercetin (group B), ENNG with 2% quercetin (group C), and 2% quercetin without ENNG (group D). ENNG was given in drinking water for the first 4 weeks, and thereafter quercetin was given in a mixed diet. At week 20, the average number of duodenal tumors per mouse was significantly higher in group C (mean±SE, 7.26±1.75, p<0.05) than in group A (2.32±0.31). The size of the duodenal tumors increased significantly in group B (1.79±0.09 mm, p<0.001) compared with group A (1.43±0.09 mm). In contrast, no duodenal tumor was induced in group D. The present findings suggest that excessive intake of quercetin occasionally is a risk factor for carcinogenesis of some specific organs such as the upper intestine.