TGF-ß and Hypoxia/Reoxygenation Promote Radioresistance of A549 Lung Cancer Cells through Activation of Nrf2 and EGFR.

Although many studies have examined the roles of hypoxia and transforming growth factor- (TGF-) ß separately in the tumor microenvironment, the effects of simultaneous treatment with hypoxia/reoxygenation and TGF-ß on tumor malignancy are unclear. Here, we investigated the effects of redox signaling and oncogenes on cell proliferation and radioresistance in A549 human lung cancer cells in the presence of TGF-ß under hypoxia/reoxygenation conditions. Combined treatment with TGF-ß and hypoxia activated epidermal growth factor receptor (EGFR) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a redox-sensitive transcription factor. Interestingly, Nrf2 knockdown suppressed the effects of combined treatment on EGFR phosphorylation. In addition, blockade of EGFR signaling also suppressed induction of Nrf2 following combined treatment with hypoxia and TGF-ß, indicating that the combined treatment induced positive crosstalk between Nrf2 and EGFR. TGF-ß and hypoxia/reoxygenation increased the accumulation of reactive oxygen species (ROS), while treatment with N-acetyl-l-cysteine abolished the activation of Nrf2 and EGFR. Treatment with TGF-ß under hypoxic conditions increased the proliferation of A549 cells compared with that after vehicle treatment. Moreover, cells treated with the combined treatment exhibited resistance to ionizing radiation (IR), and knockdown of Nrf2 increased IR-induced cell death under these conditions. Thus, taken together, our findings suggested that TGF-ß and hypoxia/reoxygenation promoted tumor progression and radioresistance of A549 cells through ROS-mediated activation of Nrf2 and EGFR.

Induction of galectin-1 by TGF-ß1 accelerates fibrosis through enhancing nuclear retention of Smad2.

Fibrosis is one of the most serious side effects in cancer patients undergoing radio-/ chemo-therapy, especially of the lung, pancreas or kidney. Based on our previous finding that galectin-1 (Gal-1) was significantly increased during radiation-induced lung fibrosis in areas of pulmonary fibrosis, we herein clarified the roles and action mechanisms of Gal-1 during fibrosis. Our results revealed that treatment with TGF-ß1 induced the differentiation of fibroblast cell lines (NIH3T3 and IMR-90) to myofibroblasts, as evidenced by increased expression of the fibrotic markers smooth muscle actin-alpha (α-SMA), fibronectin, and collagen (Col-1). We also observed marked and time-dependent increases in the expression level and nuclear accumulation of Gal-1. The TGF-ß1-induced increases in Gal-1, α-SMA and Col-1 were decreased by inhibitors of PI3-kinase and p38 MAPK, but not ERK. Gal-1 knockdown using shRNA decreased the phosphorylation and nuclear retention of Smad2, preventing the differentiation of fibroblasts. Gal-1 interacted with Smad2 and phosphorylated Smad2, which may accelerate fibrotic processes. In addition, up-regulation of Gal-1 expression was demonstrated in a bleomycin (BLM)-induced mouse model of lung fibrosis in vivo. Together, our results indicate that Gal-1 may promote the TGF-ß1-induced differentiation of fibroblasts by sustaining nuclear localization of Smad2, and could be a potential target for the treatment of pulmonary fibrotic diseases.

Niclosamide enhances ROS-mediated cell death through c-Jun activation.

Radiotherapy is an effective treatment modality in the clinical treatment of cancers, and has been combined with chemotherapy in order to improve therapeutic efficacy. Therefore, we aimed to develop small molecules that enhance the cytotoxic effects of radiotherapy. In this study, we provide evidence that niclosamide is an effective radiosensitizer in non-small cell lung cancer cells. Using a cell-based high-throughput viability screen of 1040 compounds in combination with γ-ionizing radiation (IR), we found niclosamide, an FDA-approved antihelminthic agent, had a radiosensitizing effect on H1299 human lung cancer cells. Pretreatment with niclosamide enhanced IR- induced cell death of H1299 in a dose-dependent manner via apoptosis compared with IR or niclosamide alone. The combined treatment induced significantly more phosphorylation of p38 MAPK and c-Jun in H1299 cells than IR or niclosamide alone. Since IR induces apoptosis through generation of reactive oxygen species (ROS), hydrogen peroxide (H2O2) was employed as another ROS generator and we found that niclosamide also sensitized cells to H2O2. Niclosamide pretreatment also induced c-Jun and its phosphorylation in the presence of H2O2, thereby enhancing apoptosis. N-acetyl-L-cysteine (NAC) treatment abolished both cell death and c-Jun activation induced by the combination treatments. Knockdown of c-Jun also decreased PARP cleavage and clonogenic cell survival in niclosamide- and IR-treated H1299 cells. Our findings suggest that niclosamide could be a promising radiosensitizer in lung cancer patients through activation of the p38 MAPK-c-Jun axis.

An effective strategy for increasing the radiosensitivity of Human lung Cancer cells by blocking Nrf2-dependent antioxidant responses.

Radiotherapy and chemotherapeutic agents can effectively induce apoptosis through generation of reactive oxygen species (ROS). Cancer cells frequently express high levels of ROS-scavenging enzymes, which confer resistance to ROS-mediated cell death. Keap1 (Kelch-like ECH-associated protein 1) sequesters and promotes the degradation of the antioxidant response element-binding transcription factor Nrf2 (nuclear factor erythroid-2-related factor 2). In non-small-cell lung cancer (NSCLC) cell lines and NSCLC patients, Keap1 is often present as a biallelic mutant that results in constitutive activation of Nrf2 function, which contributes to cytoprotection against oxidative stress and xenobiotics. To identify small molecules that inhibit antioxidant responses and increase apoptotic death after radiotherapy, we screened a chemical library containing 8000 synthetic compounds using a cell-based luciferase assay system. 4-(2-Cyclohexylethoxy)aniline (IM3829) inhibited the increase in Nrf2-binding activity and expression of the Nrf2 target genes induced by treatment with tertiary butylhydroquinone or radiation. Combined treatment with IM3829 and radiation significantly inhibited clonogenic survival of H1299, A549, and H460 lung cancer cells. IM3829 significantly increased ROS accumulation in irradiated cells compared with cells exposed to radiation alone and led to apoptotic cell death, as confirmed by caspase-3 and PARP cleavage. In mice bearing H1299 or A549 lung cancer xenografts, IM3829 together with radiation inhibited tumor growth more effectively than radiation alone. Our findings suggest that IM3829 could be a promising radiosensitizer in lung cancer patients, particularly those with high expression of Nrf2.

Acriflavine enhances radiosensitivity of colon cancer cells through endoplasmic reticulum stress-mediated apoptosis.

Radiotherapy (RT) is one of the most effective tools in the clinical treatment of cancer. Because the tumor suppressor p53 plays a central role in radiation-mediated responses, including cell cycle-arrest and apoptosis, a number of studies have suggested that p53 could be a useful therapeutic target of anti-cancer agents. Accordingly, we sought to discover a new agent capable of increasing p53 activity. HCT116 colon cancer cells, containing wild-type p53, were stably transfected with a p53 responsive-luciferase (p53-Luc) reporter gene. A cell-based high-throughput screen of 7920 synthetic small molecules was performed in duplicate. Of the screened compounds, acriflavine (ACF) significantly increased p53-Luc activity in a concentration-dependent manner without causing toxicity. Pretreatment with ACF enhanced the induction of p53 protein expression and phosphorylation on serine 15 by γ-irradiation. Clonogenic assays showed that ACF pretreatment also potentiated radiation-induced cell death. The combination of irradiation and ACF treatment induced mitochondrial release of cytochrome c and significant activation of caspase-3 with PARP cleavage in colon cancer cells, demonstrating typical apoptotic cell death. Combined treatment with ACF and radiation increased the expression of Bax and Bad, while decreasing expression of Bcl-2. In addition, the ACF/radiation treatment combination induced endoplasmic reticulum (ER) stress responses mediated by IRE1α (inositol-requiring transmembrane kinase and endonuclease 1α), eIF-2α (eukaryotic initiation factor 2α), caspase-2/12, and CHOP (C/EBP homologous protein). The knockdown of IRE1α by siRNA inhibited the apoptotic cell death induced by ACF/radiation treatment. In vivo studies showed that combined treatment with ACF and radiation significantly inhibited the growth of tumors in colorectal cancer xenografted mice. These results indicate that ACF acts through p53-dependent mitochondrial pathways and ER stress signals, and could be a promising radiosensitizer.

The inhibitory effect of ginsan on TGF-ß mediated fibrotic process.

Transforming growth factor-beta (TGF-ß) plays a central role in the development of fibrosis by stimulating extracellular matrix accumulation, and signals either directly or indirectly through types I, II, and III (TßRI, II, and III) TGF-ß receptor complexes. Ginsan, a polysaccharide extracted from Panax ginseng, has multiple immunomodulatory effects. Here, we examine whether ginsan regulates the fibrogenic process by interfering with TGF-ß signaling pathways. TGF-ß treatment of murine or human normal lung fibroblasts enhanced the levels of several fibrotic markers, including smooth muscle alpha actin (α-SMA), collagen-1, and fibronectin. Interestingly, ginsan treatment either before or after TGF-ß administration led to significant reductions in all of α-SMA, collagen-1, and fibronectin expression levels. Ginsan not only inhibited phosphorylation of Smad2 and Smad3, but also attenuated pERK and pAKT signaling induced by TGF-ß. Moreover, ginsan restored TßRIII protein expression, which was significantly downregulated by TGF-ß, but reduced TßRI and TßRII protein levels. In a murine model of bleomycin (BLM)-induced pulmonary fibrosis, ginsan significantly suppressed accumulation of collagen, α-SMA, and TGF-ß. These data collectively suggest that ginsan acts as an effective anti-fibrotic agent in the treatment of pulmonary fibrosis by blocking multiple TGF-ß signaling pathways.

IM-412 inhibits transforming growth factor beta-induced fibroblast differentiation in human lung fibroblast cells.

Pulmonary fibrosis is a type of interstitial lung disease that causes progressive scarring in lung tissues. Although there have been many studies on fibrosis, there is no standard treatment for fibrotic disease. Thus, there is an urgent need for the development of effective anti-fibrotic drugs. Transforming growth factor beta (TGF-beta) is a major fibrotic mediator known to stimulate fibrosis. To identify small molecules that inhibit TGF-beta responses, we performed cell-based chemical screening using genetically engineered HEK293 reporter cells. Among 8000 chemical compounds containing biologically active natural products and synthetic or clinically used compounds, we found that 3-(2-chlorobenzyl)-1,7-dimethyl-1H-imidazo[2,1-f]purine-2,4(3H,8H)-dione (IM-412) significantly decreased TGF-beta stimulated reporter activity in a dose-dependent manner. In addition, IM-412 inhibited TGF-beta-induced expression of the fibrotic markers alpha-smooth muscle actin (alpha-SMA) and fibronectin, and collagen accumulation in CCD-18Lu human normal lung fibroblasts without cell cytotoxicity. IM-412 decreased Smad2 and -3 phosphorylation as well as JNK and ERK activity. Moreover, expression levels of TGF-beta receptor I (TbetaRI) and receptor II (TbetaRII) were down-regulated by IM-412 in a dose-dependent manner. Thus, our findings indicate that the small molecule IM-412 attenuated TGF-beta-mediated fibroblast differentiation through inhibition of the overall TGF-beta response and may be a promising novel agent for the treatment of pathological fibrotic conditions.