Dinesh Thapa

NRF2 blockade suppresses colon tumor angiogenesis by inhibiting hypoxia-induced activation of HIF-1α

Transcription factor NRF2 is an important modifier of cellular responses to oxidative stress. Although its cytoprotective effects are firmly established, recent evidence suggesting important roles in cancer pathobiology has yet to be mechanistically developed. In the current study, we investigated the role of NRF2 in colon tumor angiogenesis. Stable RNAi-mediated knockdown of NRF2 in human colon cancer cells suppressed tumor growth in mouse xenograft settings with a concomitant reduction in blood vessel formation and VEGF expression. Similar antiangiogenic effects of NRF2 knockdown were documented in chick chorioallantoic membrane assays and endothelial tube formation assays. Notably, NRF2-inhibited cancer cells failed to accumulate HIF-1α protein under hypoxic conditions, limiting expression of VEGF and other HIF-1α target genes. In these cells, HIF-1α was hydroxylated but pharmacological inhibition of PHD domain-containing prolyl hydroxylases was sufficient to restore hypoxia-induced accumulation of HIF-1α. Mechanistic investigations demonstrated that reduced mitochondrial O(2) consumption in NRF2-inhibited cells was probably responsible for HIF-1α degradation during hypoxia; cellular O(2) consumption and ATP production were lower in NRF2 knockdown cells than in control cells. Our findings offer novel insights into how cellular responses to O(2) and oxidative stress are integrated in cancer cells, and they highlight NRF2 as a candidate molecular target to control tumor angiogenesis by imposing a blockade to HIF-1α signaling.

Dietary Resveratrol prevents development of high-grade prostatic intraepithelial neoplastic lesions: Involvement of SIRT1/S6K axis

SIRT1 (mammalian ortholog of the yeast silent information regulator 2) is a NAD-dependent histone deacetylase belonging to the multigene family of sirtuins. Anecdotal and epidemiologic observations provide evidence for beneficial effects of the calorie restriction mimetic resveratrol (RES), a SIRT1 activator in preventing cardiovascular diseases and cancer. Although SIRT1 possesses both tumorigenic and antitumorigenic potential, the molecular mechanisms underlying SIRT1-mediated tumor progression or inhibition are poorly understood. In this study, we investigated the role of SIRT1 in multiple human prostate cancer cell lines and prostate-specific PTEN knockout mouse model using resveratrol. Androgen-independent prostate cancer cell lines (C42B, PC3, and DU145) express higher levels of SIRT1 than androgen-responsive (LNCaP) and nontumorigenic prostate cells (RWPE-1). Resveratrol enhanced this expression without any significant effect on SIRT1 enzymatic activity. Inhibition of SIRT1 expression using shRNA enhanced cell proliferation and inhibited autophagy by repressing phosphorylation of S6K and 4E-BP1. These biologic correlates were reversed in the presence of resveratrol. Analysis of prostates from dietary intervention with resveratrol showed a significant reduction in prostate weight and reduction in the incidence of high-grade prostatic intraepithelial neoplastic (HGPIN) lesions by approximately 54% with no significant change in body weight. Consistent with the in vitro findings, resveratrol intervention in the PTEN knockout mouse model was associated with reduction in the prostatic levels of mTOR complex 1 (mTORC1) activity and increased expression of SIRT1. These data suggest that SIRT1/S6K-mediated inhibition of autophagy drives prostate tumorigenesis. Therefore, modulation of SIRT1/S6K signaling represents an effective strategy for prostate cancer prevention. Cancer Prev Res; 6(1); 27–39. ©2012 AACR.

Clotrimazole Ameliorates Intestinal Inflammation and Abnormal Angiogenesis by Inhibiting Interleukin-8 Expression through a Nuclear Factor-κB-Dependent Manner

Increased interleukin (IL)-8 plays an important role not only in activation and recruitment of neutrophils but also in inducing exaggerated angiogenesis at the inflamed site. In the present study, we investigated the fact that clotrimazole (CLT) inhibits intestinal inflammation, and the inhibitory action is mediated through suppression of IL-8 expression. In the trinitrobenzene sulfonic acid (TNBS)-induced rat colitis model, CLT dose-dependently protected from the TNBS-induced weight loss, colon ulceration, and myeloperoxidase activity increase. In the lesion site, CLT also suppressed the TNBS-induced angiogenesis, IL-8 expression, and nuclear factor (NF)-κB activation. In a cellular model of colitis using tumor necrosis factor (TNF)-α-stimulated HT29 colon epithelial cells, treatment with CLT significantly suppressed TNF-α-mediated IL-8 induction and NF-κB transcriptional activity revealed by a luciferase reporter gene assay. Furthermore, cotreatment with CLT and pyrrolidine dithiocarbamate, a NF-κB inhibitor, synergistically reduced the NF-κB transcriptional activity as well as IL-8 expression. In an in vitro angiogenesis assay, CLT suppressed IL-8-induced proliferation, tube formation, and invasion of human umbilical vein endothelial cells. The in vivo angiogenesis assay using chick chorioallantoic membrane also showed that CLT significantly inhibited the IL-8-induced formation of new blood vessels. Taken together, these results suggest that CLT may prevent the progression of intestinal inflammation by not only down-regulating IL-8 expression but also inhibiting the action of IL-8 in both colon epithelial and vascular endothelial cells during pathogenesis of intestinal inflammation.

Clotrimazole ameliorates intestinal inflammation and abnormal angiogenesis by inhibiting IL-8 expression through a NF-κB-dependent manner

Increased interleukin (IL)-8 plays an important role not only in activation and recruitment of neutrophils but also in inducing exaggerated angiogenesis at the inflamed site. In the present study, we investigated the fact that clotrimazole (CLT) inhibits intestinal inflammation, and the inhibitory action is mediated through suppression of IL-8 expression. In the trinitrobenzene sulfonic acid (TNBS)-induced rat colitis model, CLT dose-dependently protected from the TNBS-induced weight loss, colon ulceration, and myeloperoxidase activity increase. In the lesion site, CLT also suppressed the TNBS-induced angiogenesis, IL-8 expression, and nuclear factor (NF)-κB activation. In a cellular model of colitis using tumor necrosis factor (TNF)-α-stimulated HT29 colon epithelial cells, treatment with CLT significantly suppressed TNF-α-mediated IL-8 induction and NF-κB transcriptional activity revealed by a luciferase reporter gene assay. Furthermore, cotreatment with CLT and pyrrolidine dithiocarbamate, a NF-κB inhibitor, synergistically reduced the NF-κB transcriptional activity as well as IL-8 expression. In an in vitro angiogenesis assay, CLT suppressed IL-8-induced proliferation, tube formation, and invasion of human umbilical vein endothelial cells. The in vivo angiogenesis assay using chick chorioallantoic membrane also showed that CLT significantly inhibited the IL-8-induced formation of new blood vessels. Taken together, these results suggest that CLT may prevent the progression of intestinal inflammation by not only down-regulating IL-8 expression but also inhibiting the action of IL-8 in both colon epithelial and vascular endothelial cells during pathogenesis of intestinal inflammation.

Grifola frondosa water extract alleviates intestinal inflammation by suppressing TNF-|[alpha]| production and its signaling

TNF-α is a major cytokine involved in inflammatory bowel disease (IBD). In this study, water extract of Grifola frondosa (GFW) was evaluated for its protective effects against colon inflammation through the modulation of TNF-α action. In coculture of HT-29 human colon cancer cells with U937 human monocytic cells, TNF-α-induced monocyte adhesion to HT-29 cells was significantly suppressed by GFW (10, 50, 100 µg/ml). The reduced adhesion by GFW correlated with the suppressed expression of MCP-1 and IL-8, the major IBD-associated chemokines. In addition, treatment with GFW significantly suppressed TNF-α-induced reactive oxygen species production and NF-κB transcriptional activity in HT-29 cells. In differentiated U937 monocytic cells, LPS-induced TNF-α production, which is known to be mediated through NF-κB activation, was significantly suppressed by GFW. In an in vivo rat model of IBD, oral administration of GFW for 5 days (1 g/kg per day) significantly inhibited the trinitrobenzene sulfonic acid (TNBS)-induced weight loss, colon ulceration, myeloperoxidase activity, and TNF-α expression in the colon tissue. Moreover, the effect of GFW was similar to that of intra-peritoneal injection of 5-aminosalicylic acid (5-ASA), an active metabolite of sulfasalazine, commonly used drug for the treatment of IBD. The results suggest that GFW ameliorates colon inflammation by suppressing production of TNF-α as well as its signaling through NF-κB leading to the expression of inflammatory chemokines, MCP-1 and IL-8. Taken together, the results strongly suggest GFW is a valuable medicinal food for IBD treatment, and thus may be used as an alternative medicine for IBD.

Chronic inflammatory mediators enhance prostate cancer development and progression

Chronic inflammation is postulated to influence prostate cancer progression. Preclinical studies have claimed that inflammatory mediators are involved in prostate cancer development and therefore suggested these as attractive targets for intervention. However, among the many pro-inflammatory mediators, there is no consensus regarding the identity of the primary one(s). In clinical studies, chronic inflammation has been found in prostate tumor specimens, and tissues resected for treatment of benign prostatic hyperplasia (BPH). Although collective evidence from molecular, experimental and clinical data suggests that inflammation can contribute or promote prostate carcinogenesis, an etiologic link has not yet been established. Moreover, the role of chronic inflammation in the onset of castration resistant and metastatic disease is unclear. Therefore it is important to open a dialog regarding recent findings on how chronic inflammatory mediators contribute to prostate cancer progression, and their usefulness to prevent disease progression. In this commentary, we assess the current literature with respect to chronic inflammation as a potential initiator and promoter of prostate carcinogenesis and discuss the prospects for its potential clinical applications.

Novel hexahydrocannabinol analogs as potential anti-cancer agents inhibit cell proliferation and tumor angiogenesis.

Both natural and synthetic cannabinoids have been shown to suppress the growth of tumor cells in culture and in animal models by affecting key signaling pathways including angiogenesis, a pivotal step in tumor growth, invasion, and metastasis. In our search for cannabinoid-like anticancer agents devoid of psychoactive side effects, we synthesized and evaluated the anti-angiogenic effects of a novel series of hexahydrocannabinol analogs. Among these, two analogs LYR-7 [(9S)-3,6,6,9-tetramethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol] and LYR-8 [(1-((9S)-1-hydroxy-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-2-yl)ethanone)] were selected based on their anti-angiogenic activity and lack of binding affinity for cannabinoid receptors. Both LYR-7 and LYR-8 inhibited VEGF-induced proliferation, migration, and capillary-like tube formation of HUVECs in a concentration-dependent manner. The inhibitory effect of the compounds on cell proliferation was more selective in endothelial cells than in breast cancer cells (MCF-7 and tamoxifen-resistant MCF-7). We also noted effective inhibition of VEGF-induced new blood vessel formation by the compounds in the in vivo chick chorioallantoic membrane (CAM) assay. Furthermore, both LYR analogs potently inhibited VEGF production and NF-κB transcriptional activity in cancer cells. Additionally, LYR-7 or LYR-8 strongly inhibited breast cancer cell-induced angiogenesis and tumor growth. Together, these results suggest that novel synthetic hexahydrocannabinol analogs, LYR-7 and LYR-8, inhibit tumor growth by targeting VEGF-mediated angiogenesis signaling in endothelial cells and suppressing VEGF production and cancer cell growth.

The anti-angiogenic and anti-tumor activity of synthetic phenylpropenone derivatives is mediated through the inhibition of receptor tyrosine kinases.

Abnormal angiogenesis plays a critical role in the pathogenesis of various diseases such as cancer and chronic inflammation. A variety of pro-angiogenic factors, including vascular endothelial growth factor (VEGF), exert their action through endothelial receptor tyrosine kinases (RTKs). The synthetic phenylpropenone derivatives, used in this study were the following: 1,3-diphenyl-propenone (DPhP), 3-phenyl-1-thiophen-2-yl-propenone (PhT2P), 3-phenyl-1-thiophen-3-yl-propenone (PhT3P) and 1-furan-2-yl-3-phenyl-propenone (FPhP). These derivatives were screened for their inhibitory effect on VEGF-induced angiogenesis in vitro using HUVECs and in vivo using chick chorioallantoic membrane (CAM). The order of anti-angiogenic activity was DPhP>FPhP>PhT3P>PhT2P. The most effective compound DPhP, also known as chalcone, showed weak VEGF receptor tyrosine kinase activity compared with the specific inhibitor, SU4312 (3-[[4-(dimethylamino)phenyl]methylene]-1,3-dihydro-2H-indol-2-one). However, DPhP also inhibited several other receptor tyrosine kinases including Tie-2, epithermal growth factor (EGF) receptor, EphB2, fibroblast growth factor (FGF) receptor 3 and insulin-like growth factor-1 (IGF-1) receptor, as revealed by a receptor tyrosine kinase array assay. In addition, the down-stream signaling, including ERK phosphorylation and NF-κB activation, after receptor activation was significantly inhibited by DPhP. Furthermore, in the HT29 human colon cancer cell-inoculated CAM assay, the tumor growth and tumor-induced angiogenesis was significantly inhibited by DPhP (10μg/ml). These results suggest that the simple flavonoid, DPhP (chalcone), has valuable potential as an antiangiogenic and anti-cancer agent, and its action is mediated through the inhibition of multi-target RTKs including VEGF receptor 2.

Inhibitory effects of clotrimazole on TNF-α-induced adhesion molecule expression and angiogenesis

Cell adhesion molecules play a pivotal role in chronic inflammation and pathological angiogenesis. In the present study, we investigated the inhibitory effects of clotrimazole (CLT) on tumor necrosis factor (TNF)-α-induced changes in adhesion molecule expression. CLT dose-dependently inhibited monocyte chemoattractant protein-1 (MCP-1), intercellular cell adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) expressions in TNF-α-stimulated HT29 colonic epithelial cells. This inhibitory action of CLT correlated with a significant reduction in TNF-α-induced adhesion of monocytes to HT29 cells, which was comparable to the inhibitory effects of anti-ICAM-1 and VCAM-1 monoclonal antibodies on monocyte-epithelial adhesion. These inhibitory actions of CLT were, at least in part, attributable to the inhibition of redox sensitive NF-κB activation, as CLT inhibited TNF-α-induced ROS generation as well as NF-κB nuclear translocation and activation in HT29 cells. Furthermore, the inhibition of TNF-α-induced monocyte adhesion was also mimicked by the specific NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC). Inflammatory mediators including TNF-α have known to promote angiogenesis, which in turn further contributes to inflammatory pathology. Therefore, we additionally evaluated whether CLT modulates TNF-α-induced angiogenesis using in vivo chick chorioallantoic membrane (CAM) assay. The CAM assay showed that CLT dose-dependently attenuated TNF-α-induced angiogenesis, and the effect was correlated with decreased inflammation of the CAM tissue. In conclusion, our results suggest that CLT can inhibit TNF-α-triggered expression of adhesion molecules, ICAM-1 and VCAM-1, and angiogenesis during inflammation.

Induction of p53-independent apoptosis by a novel synthetic hexahydrocannabinol analog is mediated via Sp1-dependent NSAID-activated gene-1 in colon cancer cells

Nonsteroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1) has received greater attention as a novel molecular target for anti-cancer therapeutics in recent years. We identified a novel synthetic hexahydrocannabinol analog, LYR-8 [(1-((9S)-1-hydroxy-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-2-yl)ethanone)], as a potent NAG-1 and apoptosis inducer in a panel of human cancer cells. LYR-8 did not possess any affinity for cannabinoid receptor CB(1) or CB(2), which eliminates the concern about potential psychoactive side effects. LYR-8 dramatically induced NAG-1 expression and apoptosis in HCT116 (wild-type p53) and HT29 (mutant p53) colon cancer cells. The NAG-1 expression by LYR-8 was not blocked by pifithrin-alpha, a specific p53 inhibitor, which was different from doxorubicin that induced p53-dependent NAG-1 transcriptional activity. The induction of NAG-1 promoter activity by LYR-8 was strongly correlated with increased Sp1 activation as noted in various luc-promoter activities. Furthermore, pretreatment with the specific Sp1 inhibitor mithramycin A completely reversed the LYR-8-induced NAG-1 expression in both HCT116 and HT29 cells. Knockdown of NAG-1 using siRNA significantly reversed LYR-8-induced cell death in both wild-type and mutant p53-expressing colon cancer cells. Furthermore, sensitization with NAG-1 inducer sulindac sulfide synergized LYR-8-induced cell death in both colon cancer cells. These results suggest that induction of NAG-1 via Sp1 activation is a promising therapeutic approach in cancer treatment, and that a novel compound like LYR-8 could be a potent chemotherapeutic agent for colon cancers including p53-mutated cancer.