Receptor-interacting protein kinase-3 (RIP3 or RIPK3) is an essential part of the cellular machinery that executes "programmed" or "regulated" necrosis. Here we show that programmed necrosis is activated in response to many chemotherapeutic agents and contributes to chemotherapy-induced cell death. However, we show that RIP3 expression is often silenced in cancer cells due to genomic methylation near its transcriptional start site, thus RIP3-dependent activation of MLKL and downstream programmed necrosis during chemotherapeutic death is largely repressed. Nevertheless, treatment with hypomethylating agents restores RIP3 expression, and thereby promotes sensitivity to chemotherapeutics in a RIP3-dependent manner. RIP3 expression is reduced in tumors compared to normal tissue in 85% of breast cancer patients, suggesting that RIP3 deficiency is positively selected during tumor growth/development. Since hypomethylating agents are reasonably well-tolerated in patients, we propose that RIP3-deficient cancer patients may benefit from receiving hypomethylating agents to induce RIP3 expression prior to treatment with conventional chemotherapeutics.

Identification of small molecules that safely inhibit cancer progression is critical for cancer therapeutics. Saponins exhibit cytostatic and cytotoxic activity against various cancer cells, but the mechanism is not well understood. Here, we investigated whether saponin D (designated SB365), an active component isolated from Pulsatilla koreana, could inhibit the progression of hepatocellular carcinoma (HCC) and considered its mechanism. SB365 strongly suppressed the growth of HCC cells in a dosedependent manner and induced apoptosis by increasing the proportion of sub G1 apoptotic cells from 8% to 21% through induction of expression of Bax and cleaved caspase-3. In addition, SB365 exhibited potent anti-angiogenic activity and decreased the expression of hypoxia-inducible factor-1a (HIF-1a) and vascular endothelial growth factor, a key molecule for angiogenesis. Furthermore, SB365 suppressed the tube formation and migration of HUVEC, as well as in vivo neovascularization in a mouse Matrigel plug assay. In vivo study showed that SB365 significantly inhibited tumor growth in an HCC xenograft model, inducing apoptosis by increasing the expression of the cleaved caspase-3 and DNA fragmentation. The expressions of vascular endothelial growth factor and CD34 in the tumor tissue were decreased by SB365 treatment. In examining its mechanism, SB365 was found to effectively suppress the phosphorylation of PI3K downstream factors, such as Akt, mTOR and p70S6K both in vitro and in vivo. Our study demonstrates that SB365 not only induces apoptosis but also inhibits cell growth and angiogenesis through modulation of the PI3K/Akt/mTOR pathway in human HCC. We suggest that SB365 may be a new chemotherapeutic candidate against

Hepatic stellate cells (HSCs) are the primary source of matrix components in liver disease such as fibrosis. Phosphatidylinositol 3-kinase (PI3K) signaling in HSCs has been shown to induce fibrogenesis. In this study, we evaluated the anti-fibrotic activity of a novel imidazopyridine analogue (HS-173) in human HSCs as well as mouse liver fibrosis. HS-173 strongly suppressed the growth and proliferation of HSCs and induced the arrest at the G2/M phase and apoptosis in HSCs. Furthermore, it reduced the expression of extracellular matrix components such as collagen type I, which was confirmed by an in vivo study. We also observed that HS-173 blocked the PI3K/Akt signaling pathway in vitro and in vivo. Taken together, HS-173 suppressed fibrotic responses such as cell proliferation and collagen synthesis by blocking PI3K/Akt signaling. Therefore, we suggest that this compound may be an effective therapeutic agent for ameliorating liver fibrosis through the inhibition of PI3K signaling.

SB365, Pulsatilla saponin D isolated from the root of Pulsatilla koreana, has exhibited potential beneficial effects as a chemopreventive agent for critical health conditions including cancer. However, the molecular mechanisms underlying the activity of SB365 remain unknown. Here, we examined anticancer efficacy of SB365 against gastric cancer and its mechanism of action. SB365 effectively inhibited the growth of gastric cancer cells. Its apoptotic effect was accompanied by increased evidence of cleaved caspase-3 and poly(ADP ribose) polymerase. To elucidate the anticancer mechanism of SB365, we used an array of 42 different receptor tyrosine kinases (RTKs). Of the 42 different phospho-RTKs, SB365 strongly inhibited expression of activated c-mesenchymal-epithelial transition factor (c-Met) in gastric cancer cells. Also, the activation of the c-Met signal cascade components, including Akt and mammalian target of rapamycin, was inhibited by SB365 in a dose-dependent manner. In angiogenesis studies, SB365 inhibited tube formation in hepatocyte growth factor (HGF)-induced human umbilical vein endothelial cells and suppressed microvessel sprouting from the rat aortic ring, ex vivo, and blood vessel formation in the Matrigel plug assay in mice. In xenograft animal models, SB365 significantly delayed tumor growth in a dose-dependent manner. In tumor tissue, SB365 suppressed c-Met signaling, proliferation and angiogenesis and induced apoptosis. These findings suggest that SB365 docks at an allosteric site on c-Met and thereby targets c-Met signaling pathway, cell growth/angiogenesis inhibition and apoptosis induction. Therefore, SB365 may be a novel drug candidate for the treatment of gastric cancer.

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