Search

Phenformin (Phen), a potent activator of AMPK, is effective against some resistant cancers. This study evaluated the inhibition of proliferation, migration, invasion, and angiogenesis by Phen in aggressive cancer cells and investigated the underlying mechanism of the inhibition. Cholangiocarcinoma (CCA) KKU-156 and KKU-452 cells were used in this study. The results showed that Phen suppressed cell proliferation and induced apoptosis in both cells. Phen suppressed migration and invasion of cancer cells in wound healing and transwell chamber assays, respectively. The effects were associated with depletions of glutathione (GSH) and decreased glutathione redox ratio which represents cellular redox state. The redox stress was linked with the loss of mitochondrial transmembrane potential, as evaluated by JC-1 assay. The effect of Phen on angiogenesis was performed using HUVEC cultured cells. Phen alone did not affect tube formation of HUVEC cells. However, conditioned media from CCA cell cultures treated with Phen suppressed the tube-like structure formation. The antitumor effect of Phen was associated with AMPK activation and suppression of mTOR phosphorylation, HIF-1A, and VEGF protein expression. In conclusion, Phen inhibits cell proliferation, migration, invasion, and angiogenesis probably through AMPK-mTOR and HIF-1A-VEGF pathways. Phen may be repurposed as chemoprevention of cancer.

Phenethyl isothiocyanate (PEITC) is a potential cancer prevention agent that is found in cruciferous vegetables. Previous studies have shown that the effect of PEITC-induced cell death declines rapidly after administration. The metabolic fate of PEITC is modulated by glutathione S-transferases (GST). In this study, we investigated whether GST activity modulates PEITC-induced cytotoxicity on cholangiocarcinoma (CCA) cells. The sensitivity of KKU-M214 and KKU-100 cells to PEITC was associated with GST activity. Two GST inhibitors, ethacrynic acid (EA) and cibacron blue, potentiated the cytotoxic effect of PEITC in CCA cells. PEITC-induced glutathione (GSH) depletion and redox stress, whereas EA itself or in combination with PEITC did not alter GSH redox status. The enhanced cytotoxic effect of EA may be due to inhibition of GST activity. This idea was validated by using siRNA directed against GSTP1 mRNA in KKU-M214 cells, and GSTP1 and GSTT1 mRNA in KKU-100 cells. These GST isoforms were abundantly expressed in the cell lines. Knockdown of GSTs in CCA cell lines potentiated the cytotoxic effect of PEITC. The present study shows that the antitumor effect of PEITC was potentiated by the suppression of GST activity. The inhibition of GST could be a crucial strategy to potentiate chemotherapeutic effect of PEITC on CCA.

Nuclear factor erythroid 2-related factor 2 (Nrf2), a key transcription factor regulating antioxidant, cytoprotective, and metabolic enzymes, plays important roles in drug resistance and proliferation in cancer cells. The present study was aimed to examine the expression of Nrf2 in connection with chemotherapeutic drug sensitivity on cholangiocarcinoma (CCA) cells. The basal levels of Nrf2 protein in cytosol and nuclear fractions of CCA cells were determined using Western blot analysis. Nrf2 mRNA expression of KKU-M156 and KKU-100 cells, representatives of low and high-Nrf2-expressing CCA cells, were silenced using siRNA. After knockdown of Nrf2, the sensitivity of those cells to the cytotoxicity of cisplatin (Cis) was enhanced in association with the increased release of AIF and downregulation of Bcl-xl in both cells. Also, knockdown of Nrf2 suppressed the replicative capability of those cells in colony-forming assay and enhanced their sensitivity to antiproliferative activity of Cis and 5-fluorouracil. The chemosensitizing effect was associated with the suppressed expression of Nrf2-regulated and Cis-induced antioxidant and metabolic genes including NQO1, HO-1, GCLC, TXN, MRP2, TKT, and G6PD. In cell cycle analysis, Nrf2 knockdown cells were arrested at G0/G1 phase and combination with Cis increased the accumulation of cells at S phase. The suppression of KKU-M156 cell proliferation was associated with the downregulation of cyclin D1 and increased level of p21. Inhibition of Nrf2 could be a novel strategy in enhancing antitumor activity of chemotherapeutic agent in control of resistant cancer.

Phenethyl isothiocyanate (PEITC) is a natural isothiocyanate with anticancer activity against many drug-resistant cancer cells. A body of evidence suggests that PEITC enhances oxidative stress leading to cancer cell death. Cholangiocarcinoma (CCA) is an aggressive bile duct cancer with resistance to chemotherapeutic drugs. PEITC rapidly kills KKU-100 CCA cells with concurrent induction of cellular glutathione depletion, superoxide formation, and loss of mitochondrial transmembrane potential. The loss was associated with increased Bax and decreased Bcl-xl proteins followed by the release of cytochrome c and the activation of caspase-9 and -3. Although TEMPOL could prevent superoxide formation, it did not prevent the disruption of glutathione (GSH) redox, mitochondrial dysfunction, and cell death. On the other hand, N-acetylcysteine could prevent the events and cell death. It was concluded that disruption of GSH redox but not superoxide formation may be an initial step leading to mitochondrial injury. PEITC could be a promising chemopreventive agent for CCA.

Curcumin, a major component from tumeric and well-known dietary spice, possesses various pharmacological effects. The cancer chemoprevention effect is suggested to act through its pro-oxidant property. The study was to clarify effects of curcumin on cholangiocarcinoma cells, a cancer of the bile duct that refractory to chemotherapeutic drugs. We examined time-course of oxidant formation in relation to antitumor and the adaptive antioxidant response of the cells. Curcumin induced antiproliferation and apoptosis in KKU-M214 CCA cells with concentration- and time- dependent manners. The antiproliferative effect of curcumin was observed at concentrations as low as 3 microM and was not necessarily associated with oxidative stress, while induction of apoptosis required significant production of superoxide anion, suppression of cellular redox and collapse of mitochondrial transmembrane potential. Western blot analysis showed a temporal relationship between the suppression of nuclear NF-kappaB with Bcl-XL protein levels. Up-regulation of p53 and Bax was associated with marked oxidative stress and apoptosis. Curcumin also induced Nrf2 protein expression with up-regulation of gamma-glutamylcysteine ligase mRNA and increased cellular antioxidant, glutathione. The study suggests that curcumin could be developed into an effective chemoprevention against CCA., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Aim: To investigate whether dicoumarol, a potent inhibitor of NAD(P)H quinone oxidoreductase-1 (NQO1), potentiates gemcitabine to induce cytotoxicity in cholangiocarcinoma cells (CCA) and the role of reactive oxygen generation in sensitizing the cells., Methods: Four human cell lines with different NQO1 activity were used; the human CCA cell lines, KKU-100, KKU-OCA17, KKU-M214, and Chang liver cells. NQO1 activity and mRNA expression were determined. The cells were pretreated with dicoumarol at relevant concentrations before treatment with gemcitabine. Cytotoxicity was determined by staining with fluorescent dyes. Oxidant formation was examined by assay of cellular glutathione levels and reactive oxygen species production by using dihydrofluorescein diacetate. Measurement of mitochondrial transmembrane potential was performed by using JC-1 fluorescent probe. Western blotting analysis was performed to determine levels of survival related proteins., Results: Dicoumarol markedly enhanced the cytotoxicity of gemcitabine in KKU-100 and KKU-OCA17, the high NQO1 activity and mRNA expressing cells, but not in the other cells with low NQO1 activity. Dicoumarol induced a marked decrease in cellular redox of glutathione in KKU-100 cells, in contrast to KKU-M214 cells. Dicoumarol at concentrations that inhibited NQO1 activity did not alter mitochondrial transmembrane potential and production of reactive oxygen species. Gemcitabine alone induced activation of NF-kappaB and Bcl-(XL) protein expression. However, gemcitabine and dicoumarol combination induced increased p53 and decreased Bcl-(XL) levels in KKU-100, but not in KKU-M214 cells., Conclusion: NQO1 may be important in sensitizing cells to anticancer drugs and inhibition of NQO1 may be a strategy for the treatment of CCA.

Purpose: The aim of this study was to evaluate the effect of inflammation on NAD(P)H: quinone oxidoreductase-1 (NQO1), the xenobiotic metabolizing and antioxidant enzyme protecting cells against electrophiles and reactive oxygen species in biliary cancer (cholangiocarcinoma) cells., Methods: Human cholangiocarcinoma cell line, KKU-OCA17 and HeLa Chang liver cells were treated with inflammatory cytokine combinations (interferon-gamma, interleukin-1beta and tumor necrosis factor-alpha) for 48 h before NQO1 activity was assayed. Oxidant status was examined by assays of formation of nitric oxide (NO) and superoxide, and glutathione (GSH) levels. Expression of NQO1 was assessed by a reverse transcription and polymerase chain reaction. Effects of S-nitroso-glutathione (GSNO) were examined if the effects of inflammatory cytokines could be mimicked by nitric oxide donor., Results: NQO1 activity in KKU-OCA17 and HeLa Chang liver cells was suppressed by cytokine combination. Cytokines induced formation of NO and suppression of redox ratios of GSH and glutathione disulfide (GSSG). GSNO produced the similar effects as cytokines on KKU-OCA17, in contrast, GSNO induced increase of NQO1 activity in HeLa Chang liver cells. The treatment of cytokines or GSNO suppressed expression of NQO1 in KKU-OCA17 and HeLa Chang liver cells., Conclusions: Inflammatory cytokines induced oxidative stress and this is associated with suppression of NQO1, whereas may contribute to differential susceptibility of biliary epithelial cells to chemical-induced cytotoxicity and carcinogenesis.