Dong-Hoon Jin

Increased expression of ATG10 in colorectal cancer is associated with lymphovascular invasion and lymph node metastasis.

Background Autophagy has paradoxical and complex functions in cancer development, and autophagy-related genes (ATG) are key regulators in autophagy. Until now, more than 30 different ATG proteins have been identified in yeast, and their mammalian counterparts also have been reported. Although the roles of a few ATG proteins in cancer have been characterized, the role of ATG10 is almost completely unknown. Methodology/Principal Findings To investigate the clinicopathological role of ATG10 in colorectal cancer, we analyzed ATG10 expression in colorectal cancer tissues and cell lines. Protein expression analysis showed that ATG10 is highly increased in colorectal cancer (tissue - 18/37 cases, 48%; cell line –8/12 cell lines, 66%). Immunohistochemical analysis with clinicopathological features indicated a strong association of the up-regulation of ATG10 with tumor lymph node metastasis (pu200a=u200a0.005) and invasion (p<0.001). Moreover, both 5-year disease free survival and overall survival rates of patients bearing tumors that did not express ATG10 were significantly higher than those of patients bearing ATG10-expressing tumors (pu200a=u200a0.012). Conclusion/Significance Increased expression of ATG10 in colorectal cancer is associated with lymphovascular invasion and lymph node metastasis indicating that ATG10 may be a potential prognostic maker in colorectal cancer.

Enhanced antitumor activity of vitamin C via p53 in Cancer cells

Ascorbate is an important natural antioxidant that can selectively kill cancer cells at pharmacological concentrations. Despite its benefit, it is quite difficult to predict the antitumor effects of ascorbate, because the relative cytotoxicity of ascorbate differs between cancer cell lines. Therefore, it is essential to examine the basis for this fundamental disagreement. Because p53 is activated by DNA-damaging stress and then regulates various cellular conditions, we hypothesized that p53 can sensitize cancer cells to ascorbate. Using isogenic cancer cells, we observed that the presence of p53 can affect ascorbate cytotoxicity, and also reactivation of p53 can make cancer cells sensitive to ascorbate. p53-dependent enhancement of ascorbate cytotoxicity is caused by increased reactive oxygen species generation via a differentially regulated p53 transcriptional network. We also found that transcriptionally activated p53 was derived from MDM2 ubiquitination by ascorbate and subsequently its signaling network renders cancer cells more susceptible to oxidative stress. Similar to the p53 effect on in vitro ascorbate cytotoxicity, inhibition of tumor growth is also stronger in p53-expressing tumors than in p53-deficient ones in vivo. This is the first observation that ascorbate cytotoxicity is positively related to p53 expression, activating its transcriptional network to worsen intracellular oxidative stress and consequently enhancing its cytotoxicity. Based on our study, reactivation of p53 may help to achieve more consistent cytotoxic effects of ascorbate in cancer therapies.

The MEK1/2 inhibitor AS703026 circumvents resistance to the BRAF inhibitor PLX4032 in human malignant melanoma cells.

Background:Although inhibitors of the proto-oncogene BRAF have shown excellent antitumor activity against malignant melanoma, their efficacy is limited by the development of acquired drug resistance, a process in which reactivation of MAP kinase (MEK) is known to play an important role. In this study, we evaluated the efficacy of AS703026, a new MEK inhibitor, in BRAF inhibitor–resistant melanoma cell lines. Methods:Two melanoma cells lines, RPMI-7951 and SK-MEL5, harboring an activating mutation of BRAF (V600E) were treated with the BRAF inhibitor PLX4032 to select a BRAF inhibitor–resistant cell line for further study. Cell viability assay was determined with MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay and trypan blue exclusion method; apoptosis assay was performed by annexin-V staining. Knockdown of BRAF was investigated by small interfering RNA. Results:RPMI-7951 cells exhibited an increased sensitivity to combined treatment with PLX4032 and AS703026 compared to either drug alone. Consistent with this, the combination of PLX4032 and AS703026 significantly induced apoptosis, whereas each drug used alone did not, as demonstrated by a flow cytometric analysis of annexin-V/propidium iodide–stained cells and Western blot analysis of cleaved caspase-3. Notably, immunoblot analyses also showed a depletion of phosphorylated-ERK with combined drug treatment. In addition, AS703026 synergized with small interfering RNA–mediated downregulation of BRAF to produce results similar to those of combined treatment with PLX4032 and AS703026. Conclusions:Our results suggest that combined treatment with AS703026 and a BRAF inhibitor overcomes the resistance to BRAF inhibitors in malignant melanoma cells harboring a mutant form of BRAF.

Carnitine sensitizes TRAIL-resistant cancer cells to TRAIL-induced apoptotic cell death through the up-regulation of Bax.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor family with apoptosis-inducing activity. Given that TRAIL selectively induces cell death in various tumors but has little or no toxicity to normal cells, TRAIL agonists have been considered as promising anti-cancer therapeutic agents. However, the resistance of many primary tumors and cancer cells to TRAIL poses a challenge. In our present study, we found that carnitine, a metabolite that transfers long-chain fatty acids into mitochondria for beta-oxidation and modulates protein kinase C activity, sensitizes TRAIL-resistant cancer cells to TRAIL. Combination of carnitine and TRAIL was found to synergistically induce apoptotic cell death through caspase activation, which was blocked by a pan caspase inhibitor, but not by an inhibitor of autophagy or an inhibitor of necrosis. The combination of carnitine and TRAIL reversed the resistance to TRAIL in lung cancer cells, colon carcinoma cells, and breast carcinoma cells. We further demonstrate that carnitine, either alone or in combination with TRAIL, enhances the expression of the pro-apoptotic Bcl-2 family protein, Bcl-2-associated X protein (Bax). The down-regulation of Bax expression by small interfering RNA reduced caspase activation when cells were treated with TRAIL, and experiments with cells from Bax knockout mice confirmed this result. Taken together, our current results suggest that carnitine can reverse the resistance of cancer cells to TRAIL by up-regulating Bax expression. Thus, a combined delivery of carnitine and TRAIL may represent a new therapeutic strategy to treat TRAIL-resistant cancer cells.

A receptor tyrosine kinase inhibitor, Tyrphostin A9 induces cancer cell death through Drp1 dependent mitochondria fragmentation.

Mitochondria dynamics controls not only their morphology but also functions of mitochondria. Therefore, an imbalance of the dynamics eventually leads to mitochondria disruption and cell death. To identify specific regulators of mitochondria dynamics, we screened a bioactive chemical compound library and selected Tyrphostin A9, a tyrosine kinase inhibitor, as a potent inducer of mitochondrial fission. Tyrphostin A9 treatment resulted in the formation of fragmented mitochondria filament. In addition, cellular ATP level was decreased and the mitochondrial membrane potential was collapsed in Tyr A9-treated cells. Suppression of Drp1 activity by siRNA or over-expression of a dominant negative mutant of Drp1 inhibited both mitochondrial fragmentation and cell death induced by Tyrpohotin A9. Moreover, treatment of Tyrphostin A9 also evoked mitochondrial fragmentation in other cells including the neuroblastomas. Taken together, these results suggest that Tyrphostin A9 induces Drp1-mediated mitochondrial fission and apoptotic cell death.

Combined treatment with vitamin C and sulindac synergistically induces p53- and ROS-dependent apoptosis in human colon cancer cells.

Sulindac has anti-neoplastic properties against colorectal cancers; however, its use as a chemopreventive agent has been limited due to toxicity and efficacy concerns. Combinatorial treatment of colorectal cancers has been attempted to maximize anti-cancer efficacy with minimal side effects by administrating NSAIDs in combination with other inhibitory compounds or drugs such as l-ascorbic acid (vitamin C), which is known to exhibit cytotoxicity towards various cancer cells at high concentrations. In this study, we evaluated a combinatorial strategy utilizing sulindac and vitamin C. The death of HCT116 cells upon combination therapy occurred via a p53-mediated mechanism. The combination therapeutic resistance developed in isogenic p53 null HCT116 cells and siRNA-mediated p53 knockdown HCT116 cells, but the exogenous expression of p53 in p53 null isogenic cells resulted in the induction of cell death. In addition, we investigated an increased level of intracellular ROS (reactive oxygen species), which was preceded by p53 activation. The expression level of PUMA (p53-upregulated modulator of apoptosis), but not Bim, was significantly increased in HCT116 cells in response to the combination treatment. Taken together, our results demonstrate that combination therapy with sulindac and vitamin C could be a novel anti-cancer therapeutic strategy for p53 wild type colon cancers.

Bay 61-3606 Sensitizes TRAIL-Induced Apoptosis by Downregulating Mcl-1 in Breast Cancer Cells.

Breast cancer cells generally develop resistance to TNF-Related Apoptosis-Inducing Ligand (TRAIL) and, therefore, assistance from sensitizers is required. In our study, we have demonstrated that Spleen tyrosine kinase (Syk) inhibitor Bay 61–3606 was identified as a TRAIL sensitizer. Amplification of TRAIL-induced apoptosis by Bay 61–3606 was accompanied by the strong activation of Bak, caspases, and DNA fragmentation. In mechanism of action, Bay 61–3606 sensitized cells to TRAIL via two mechanisms regulating myeloid cell leukemia sequence-1 (Mcl-1). First, Bay 61–3606 triggered ubiquitin-dependent degradation of Mcl-1 by regulating Mcl-1 phosphorylation. Second, Bay 61–3606 downregulates Mcl-1 expression at the transcription level. In this context, Bay 61–3606 acted as an inhibitor of Cyclin-Dependent Kinase (CDK) 9 rather than Syk. In summary, Bay 61–3606 downregulates Mcl-1 expression in breast cancer cells and sensitizes cancer cells to TRAIL-mediated apoptosis.

Targeting FGFR Pathway in Human Hepatocellular Carcinoma: Expressing pFGFR and pMET for Antitumor Activity

The MET receptor tyrosine kinase, the receptor for hepatocyte growth factor (HGF), has been implicated in cancer growth, invasion, migration, angiogenesis, and metastasis in a broad variety of human cancers, including human hepatocellular carcinoma (HCC). Recently, MET was suggested to be a potential target for the personalized treatment of HCC with an active HGF–MET signaling pathway. However, the mechanisms of resistance to MET inhibitors need to be elucidated to provide effective treatment. Here, we show that HCC cells exhibit different sensitivities to the MET inhibitor PHA665752, depending on the phosphorylation status of FGFR. Treatment of cells expressing both phospho-FGFR and phospho-MET with the inhibitor PHA665752 did not cause growth inhibition and cell death, whereas treatment with AZD4547, a pan-FGFR inhibitor, resulted in decreased colony formation and cleavage of caspase-3. Moreover, silencing of endogenous FGFR1 and FGFR2 by RNAi of HCC cells expressing phospho-FGFR, phospho-FGFR2, and phospho-MET overcame the resistance to PHA665752 treatment. Treatment of primary cancer cells from patients with HCC expressing both phospho-FGFR and phospho-MET with PHA665752 did not induce cell death, whereas AZD4547 treatment induced cell death through the cleavage of caspase-3. In addition, treatment of cells resistant to PHA665752 with AZD4547 abrogated the activation of downstream effectors of cell growth, proliferation, and survival. On the basis of these results, we conclude that the FGFR pathway is critical for HCC survival, and that targeting this pathway with AZD4547 may be beneficial for the treatment of patients with HCC-expressing phospho-FGFR and phospho-MET. Mol Cancer Ther; 14(11); 2613–22. ©2015 AACR.

Corticotropin-releasing factor induces immune escape of cervical cancer cells by downregulation of NKG2D

Corticotropin-releasing factor (CRF), a coordinator of the bodys responses to stress, is found in various cancer tissues and cell lines. However, the exact abilities of CRF to manipulate natural killer (NK) cells during immune response have not been studied. NKG2D is an activating receptor that is expressed on most NK and CD8+ T cells. MHC class I-related chain A (MICA) and UL16-binding protein (ULBP) 1, 2 and 3 are well-known ligands for NKG2D. In the present study, we reported our findings regarding the role of CRF in cervical cancer cell survival. Human cervical cancer cell line, HeLa cells, had significantly higher intracellular expression of UL16-binding protein 2 (ULBP2) following CRF treatment but had only slightly increased surface expression of ULBP2. Notably, MMPi (pan-metalloproteases inhibitor) blocked the release of ULBP2 molecules from the surface of HeLa cells. Furthermore, incubating NK cells with culture supernatants from CRF-treated HeLa cells, which contained soluble NKG2D ligand, reduced NK cell activity by decreasing surface expression of NKG2D. Collectively, downregulation of NKG2D by CRF-induced soluble NKG2D ligand provides a potential mechanism by which cervical cancer cells escape NKG2D-mediated attack under stress conditions.

SAHA, an HDAC inhibitor, overcomes erlotinib resistance in human pancreatic cancer cells by modulating E-cadherin

Pancreatic cancer is one of the most lethal cancers and remains a major unsolved health problem. Less than 20xa0% of patients are surgical candidates, and the median survival for non-resected patients is approximately 3 to 4xa0months. Despite the existence of many conventional cancer therapies, few targeted therapies have been developed for pancreatic cancer. Combination therapy using erlotinib and gemcitabine is an approved standard chemotherapy for advanced pancreatic cancer, but it has marginal therapeutic benefit. To try to improve the therapeutic outlook, we studied the efficacy of another combination treatment and the relevance to E-cadherin in human pancreatic cancer cells. We treated two human pancreatic cancer cell lines with the histone deacetylase inhibitor (HDACi) SAHA. Interestingly, in these Panc-1 and Capan1 cells, we observed that the expression levels of E-cadherin and phosphorylated EGFR were gradually upregulated after treatment with SAHA. Furthermore, these cells underwent induced cell death after exposure to the combination treatment of SAHA and erlotinib. In Panc-1 cells, overexpression of E-cadherin activated the phosphorylation of EGFR and increased the cell sensitivity to erlotinib. In Capan1 cells, knocking down E-cadherin decreased the expression of phosphorylated EGFR, and these cells did not respond to erlotinib. Therefore, we demonstrated the efficacy of the combined treatment with SAHA and erlotinib in human pancreatic cancer cells, and we determined that the increased efficacy was due, at least in part, to the effects of SAHA on the expression of E-cadherin. Our studies suggest that E-cadherin may be a potent biomarker for pancreatic cancer.