Biological dosimetry dose-response curves for residents living near nuclear power plants in South Korea.

The purpose of this study was to establish the dose-response curves for biological dosimetry of the Dong Nam Institute of Radiological and Medical Sciences to monitor radiation exposure of local residents in the vicinity of the nuclear power plant. The blood samples of five healthy volunteers were irradiated with gamma ray, and each sample was divided equally for analysis of chromosomal aberrations by Giemsa staining and three-color fluorescence in situ hybridization painting of the triplet (chromosomes #1, #2, and #4). The results of chromosomal aberrations followed the Poisson distribution in all individual and averaged data which include inter-individual variation in radiation susceptibility. Cytogenetics Dose Estimate Software version 5.2 was used to fit the dose-response curve and to determine the coefficients of linear-quadratic equations. The goodness of fit of the curves and statistical significance of fitted α and ß-coefficients were confirmed in both Giemsa-based dicentric analysis and FISH-based translocation analysis. The coefficients calculated from the five-donor average data were almost identical in both of the analyses. We also present the results that the dose-response curve for dicentric chromosomes plus fragments could be more effective for dose estimation following low-dose radiation accidents.

Ionizing Radiation Selectively Increases CXC Ligand 10 Level via the DNA-Damage-Induced p38 MAPK-STAT1 Pathway in Murine J774A.1 Macrophages.

Ionizing radiation (IR) is an important means of tumor treatment in addition to surgery and drugs. Attempts have been made to improve the efficiency of radiotherapy by identifying the various biological effects of IR on cells. Components of the tumor microenvironment, such as macrophages, fibroblasts, and vascular endothelial cells, influence cancer treatment outcomes through communication with tumor cells. In this study, we found that IR selectively increased the production of CXC motif chemokine ligand 10 (CXCL10), which is emerging as an important biomarker for determining the prognosis of anticancer treatments, without changing the levels of CXCL9 and CXCL11 in murine J774A.1 macrophages. Pretreatment with KU55933, an ataxia telangiectasia mutated (ATM) kinase inhibitor, significantly inhibited IR-induced CXCL10 production. In contrast, pretreatment with N-acetyl-cysteine or glutathione, a reactive oxygen species scavenger, did not inhibit IR-induced CXCL10 production. Further, we attempted to identify the intracellular molecular target associated with the IR-induced increase in CXCL10 secretion by J774A.1 macrophages. IR phosphorylated p38 mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 1 (STAT1) in J774A.1 macrophages, and p38 MAPK and STAT1 were involved in CXCL10 via IR using pharmacological inhibitors (SB203580 and fludarabine, respectively) and the siRNA technique.

Dicentric chromosome assay using a deep learning-based automated system.

The dicentric chromosome assay is the "gold standard" in biodosimetry for estimating radiation exposure. However, its large-scale deployment is limited owing to its time-consuming nature and requirement for expert reviewers. Therefore, a recently developed automated system was evaluated for the dicentric chromosome assay. A previously constructed deep learning-based automatic dose-estimation system (DLADES) was used to construct dose curves and calculate estimated doses. Blood samples from two donors were exposed to cobalt-60 gamma rays (0-4 Gy, 0.8 Gy/min). The DLADES efficiently identified monocentric and dicentric chromosomes but showed impaired recognition of complete cells with 46 chromosomes. We estimated the chromosome number of each "Accepted" sample in the DLADES and sorted similar-quality images by removing outliers using the 1.5IQR method. Eleven of the 12 data points followed Poisson distribution. Blind samples were prepared for each dose to verify the accuracy of the estimated dose generated by the curve. The estimated dose was calculated using Merkle's method. The actual dose for each sample was within the 95% confidence limits of the estimated dose. Sorting similar-quality images using chromosome numbers is crucial for the automated dicentric chromosome assay. We successfully constructed a dose-response curve and determined the estimated dose using the DLADES.

Involvement of the p38 MAPK-NLRC4-Caspase-1 Pathway in Ionizing Radiation-Enhanced Macrophage IL-1ß Production.

Macrophages are abundant immune cells in the tumor microenvironment and are crucial in regulating tumor malignancy. We previously reported that ionizing radiation (IR) increases the production of interleukin (IL)-1ß in lipopolysaccharide (LPS)-treated macrophages, contributing to the malignancy of colorectal cancer cells; however, the mechanism remained unclear. Here, we show that IR increases the activity of cysteine-aspartate-specific protease 1 (caspase-1), which is regulated by the inflammasome, and cleaves premature IL-1ß to mature IL-1ß in RAW264.7 macrophages. Irradiated RAW264.7 cells showed increased expression of NLRC4 inflammasome, which controls the activity of caspase-1 and IL-1ß production. Silencing of NLRC4 using RNA interference inhibited the IR-induced increase in IL-1ß production. Activation of the inflammasome can be regulated by mitogen-activated protein kinase (MAPK)s in macrophages. In RAW264.7 cells, IR increased the phosphorylation of p38 MAPK but not extracellular signal-regulated kinase and c-Jun N-terminal kinase. Moreover, a selective inhibitor of p38 MAPK inhibited LPS-induced IL-1ß production and NLRC4 inflammasome expression in irradiated RAW264.7 macrophages. Our results indicate that IR-induced activation of the p38 MAPK-NLRC4-caspase-1 activation pathway in macrophages increases IL-1ß production in response to LPS.

Resveratrol analogue, HS-1793, inhibits inflammatory mediator release from macrophages by interfering with the TLR4 mediated NF-κB activation.

Resveratrol is known to have anti-inflammatory properties. However, high-dose resveratrol is required for optimal anti-inflammatory effects. HS-1793 is a derivative designed to be metabolically stable and more effective than resveratrol. We tested whether HS-1793 also has anti-inflammatory activity. HS-1793 effectively inhibited the mRNA and protein expression of lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in macrophages. Therefore, the production of nitric oxide (NO) and prostaglandin E2 (PGE2) was significantly attenuated. In addition, HS-1793 completely suppressed the production of inflammatory cytokines enhanced by LPS treatment along with a decrease in Toll-like receptor 4 (TLR4) expression. At the same time, the expression of myeloid differentiation factor 88 (MyD88), IL-1 receptor-associated kinase 1 (IRAK1), and TNF receptor-associated factor 6 (TRAF6) signaling molecules and the nuclear translocation of nuclear factor kappa B (NF-κB)/p65 were also downregulated. We conclusively suggest that HS-1793 also exhibits anti-inflammatory properties by effectively inhibiting TLR4-mediated NF-κB activation.

Enhancement of Radiosensitivity by DNA Hypomethylating Drugs through Apoptosis and Autophagy in Human Sarcoma Cells.

The targeting of DNA methylation in cancer using DNA hypomethylating drugs has been well known to sensitize cancer cells to chemotherapy and immunotherapy by affecting multiple pathways. Herein, we investigated the combinational effects of DNA hypomethylating drugs and ionizing radiation (IR) in human sarcoma cell lines both in vitro and in vivo. Clonogenic assays were performed to determine the radiosensitizing properties of two DNA hypomethylating drugs on sarcoma cell lines we tested in this study with multiple doses of IR. We analyzed the effects of 5-aza-dC or SGI-110, as DNA hypomethylating drugs, in combination with IR in vitro on the proliferation, apoptosis, caspase-3/7 activity, migration/invasion, and Western blotting using apoptosis- or autophagy-related factors. To confirm the combined effect of DNA hypomethylating drugs and IR in our in vitro experiment, we generated the sarcoma cells in nude mouse xenograft models. Here, we found that the combination of DNA hypomethylating drugs and IR improved anticancer effects by inhibiting cell proliferation and by promoting synergistic cell death that is associated with both apoptosis and autophagy in vitro and in vivo. Our data demonstrated that the combination effects of DNA hypomethylating drugs with radiation exhibited greater cellular effects than the use of a single agent treatment, thus suggesting that the combination of DNA hypomethylating drugs and radiation may become a new radiotherapy to improve therapeutic efficacy for cancer treatment.

Ginsenoside-Rp1 inhibits radiation-induced effects in lipopolysaccharide-stimulated J774A.1 macrophages and suppresses phenotypic variation in CT26 colon cancer cells.

This study investigated the inhibitory effect of ginsenoside-Rp1 (G-Rp1) on the ionizing radiation (IR)-induced response in lipopolysaccharide (LPS)-stimulated macrophages and its effects on the malignancy of tumor cells. G-Rp1 inhibited the activation of IR-induced DNA damage-related signaling molecules and thereby interfered with the IR-increased production of nitric oxide (NO) and interleukin (IL)-1ß. The inhibitory effect of G-Rp1 increased the survival rate of mice inoculated with CT26 colon cancer cells by suppressing the phenotypic variation of tumor cells induced by conditioned medium obtained from IR- and LPS-treated J774A.1 macrophages.

The malignancy of liver cancer cells is increased by IL-4/ERK/AKT signaling axis activity triggered by irradiated endothelial cells.

The malignant traits involved in tumor relapse, metastasis and the expansion of cancer stem-like cells are acquired via the epithelial-mesenchymal transition (EMT) process in the tumor microenvironment. In addition, the tumor microenvironment strongly supports the survival and growth of malignant tumor cells and further contributes to the reduced efficacy of anticancer therapy. Ionizing radiation can influence the tumor microenvironment, because it alters the biological functions of endothelial cells composing tumor vascular systems. However, to date, studies on the pivotal role of these endothelial cells in mediating the malignancy of cancer cells in the irradiated tumor microenvironment are rare. We previously evaluated the effects of irradiated endothelial cells on the malignant traits of human liver cancer cells and reported that endothelial cells irradiated with 2 Gy reinforce the malignant properties of these cancer cells. In this study, we investigated the signaling mechanisms underlying these events. We revealed that the increased expression level of IL-4 in endothelial cells irradiated with 2 Gy eventually led to enhanced migration and invasion of cancer cells and further expansion of cancer stem-like cells. In addition, this increased level of IL-4 activated the ERK and AKT signaling pathways to reinforce these events in cancer cells. Taken together, our data indicate that ionizing radiation may indirectly modulate malignancy by affecting endothelial cells in the tumor microenvironment. Importantly, these indirect effects on malignancy are thought to offer valuable clues or targets for overcoming the tumor recurrence after radiotherapy.

Irradiated endothelial cells modulate the malignancy of liver cancer cells.

The tumor microenvironment is closely associated with tumor malignancy, and includes tumor relapse and metastasis trigged by epithelial-mesenchymal transition (EMT), which leads to the expansion of cancer stem-like cells. Radiotherapy is known to acutely and persistently affect changes in this tumor microenvironment by altering the vascular functions of tumor endothelial cells. However, the precise role of endothelial cells in tumor malignancy following treatment with irradiation has not been completely elucidated. The present study investigated the differences in malignant behavior of liver cancer cells in response to irradiated endothelial cells. To achieve this, a co-cultivation system was established to identify the potential role of endothelial cells in malignant liver cancer cells using medium conditioned with endothelial cells. It was observed that the medium conditioned by endothelial cells when irradiated with a single dose (2 Gy), greatly increased the migratory and invasive properties of liver cancer cells, as well as inducing mesenchymal markers, and enhancing the sphere-forming ability of liver cancer cells, The mRNA levels of genes regulating the self-renewal of cancer stem cells were increased in liver cancer cells by treatment with medium conditioned with endothelial cells. However, neither the medium conditioned by endothelial cells irradiated with fractionated doses (2 Gy × 3; 2 Gy/day for 3 days) or with a single dose (6 Gy) greatly influenced the malignancy of liver cancer cells. In conclusion, the data obtained by the present study indicated that 2 Gy irradiation of endothelial cells influenced the increase in tumor malignancy in liver cancer cells. Furthermore, the distinct differences in the indirect effects of ionizing radiation on tumor malignancy may provide valuable information for the improvement in the efficacy of radiotherapy.

Downregulation of UHRF1 increases tumor malignancy by activating the CXCR4/AKT-JNK/IL-6/Snail signaling axis in hepatocellular carcinoma cells.

UHRF1 (ubiquitin-like, with PHD and RING finger domains 1) plays a crucial role in DNA methylation, chromatin remodeling and gene expression and is aberrantly upregulated in various types of human cancers. However, the precise role of UHRF1 in cancer remains controversial. In this study, we observed that hypoxia-induced downregulation of UHRF1 contributes to the induction of the epithelial-mesenchymal transition (EMT) in hepatocellular carcinoma cells. By negatively modulating UHRF1 expression, we further showed that UHRF1 deficiency in itself is sufficient to increase the migratory and invasive properties of cells via inducing EMT, increasing the tumorigenic capacity of cells and leading to the expansion of cancer stem-like cells. Epigenetic changes caused by UHRF1 deficiency triggered the upregulation of CXCR4, thereby activating AKT and JNK to increase the expression and secretion of IL-6. In addition, IL-6 readily activated the JAK/STAT3/Snail signaling axis, which subsequently contributed to UHRF1 deficiency-induced EMT. Our results collectively demonstrate that UHRF1 deficiency may play a pivotal role in the malignant alteration of cancer cells.

NQO1-induced activation of AMPK contributes to cancer cell death by oxygen-glucose deprivation.

Oxygen and glucose deprivation (OGD) due to insufficient blood circulation can decrease cancer cell survival and proliferation in solid tumors. OGD increases the intracellular [AMP]/[ATP] ratio, thereby activating the AMPK. In this study, we have investigated the involvement of NQO1 in OGD-mediated AMPK activation and cancer cell death. We found that OGD activates AMPK in an NQO1-dependent manner, suppressing the mTOR/S6K/4E-BP1 pathway, which is known to control cell survival. Thus, the depletion of NQO1 prevents AMPK-induced cancer cell death in OGD. When we blocked OGD-induced Ca(2+)/CaMKII signaling, the NQO1-induced activation of AMPK was attenuated. In addition, when we blocked the RyR signaling, the accumulation of intracellular Ca(2+) and subsequent activation of CaMKII/AMPK signaling was decreased in NQO1-expressing cells under OGD. Finally, siRNA-mediated knockdown of CD38 abrogated the OGD-induced activation of Ca(2+)/CaMKII/AMPK signaling. Taken together, we conclude that NQO1 plays a key role in the AMPK-induced cancer cell death in OGD through the CD38/cADPR/RyR/Ca(2+)/CaMKII signaling pathway.

Downregulation of UHRF1 promotes EMT via inducing CXCR4 in human cancer cells.

Activation of epithelial-mesenchymal transition (EMT) is important for malignant tumor progression exhibiting migratory and invasive properties. UHRF1 (ubiquitin-like, with PHD and RING finger domains 1), as an epigenetic regulator, plays a crucial role in DNA CpG methylation, chromatin remodeling and gene expression. Many studies demonstrated that UHRF1 is aberrantly expressed in various types of human cancer. However, the precise role of UHRF1 in human cancers remains highly controversial. In the present study, we found that downregulation of UHRF1 enhances the migratory and invasive properties of human cancer cells by inducing EMT, and that the CXCR4 signaling pathway is strictly necessary for UHRF1 deficiency-mediated induction of EMT. Downregulation of UHRF1 induced the expression of the EMT-regulating transcription factors, Zeb1, Slug and Snail and then led to decreased protein level of E-cadherin, and increased protein level of N-cadherin and vimentin, including increased migratory and invasive properties of human cancer cells. In addition, siRNA targeting of Zeb1 or Snail effectively attenuated UHRF1 deficiency-induced EMT, but siRNA targeting of Slug did not, indicating that Zeb1 and Snail play key roles in this event. Moreover, downregulation of UHRF1 induced the expression of CXCR4 in HepG2 cells. siRNA targeting of CXCR4 greatly suppressed the UHRF1 deficiency-induced EMT, as evidenced by a reversal of expression patterns of Snail and Zeb1, and by reduced migratory and invasive properties of HepG2 cells. In conclusion, our results demonstrate that downregulation of UHRF1 contributes to the induction of EMT in human cancer cells via the activation of CXCR4 signaling pathway. Our observation also suggests that UHRF1 may play a pivotal role in suppressing the malignant alteration of cancer cells.

Epigenetics meets radiation biology as a new approach in cancer treatment.

Cancer is a disease that results from both genetic and epigenetic changes. In recent decades, a number of people have investigated the disparities in gene expression resulting from variable DNA methylation alteration and chromatin structure modification in response to the environment. Especially, colon cancer is a great model system for investigating the epigenetic mechanism for aberrant gene expression alteration. Ionizing radiation (IR) could affect a variety of processes within exposed cells and, in particular, cause changes in gene expression, disruption of cell cycle arrest, and apoptotic cell death. Even though there is growing evidence on the importance of epigenetics and biological processes induced by radiation exposure in various cancer types including colon cancer, specific epigenetic alterations induced by radiation at the molecular level are incompletely defined. This review focuses on discussing possible IR-mediated changes of DNA methylation and histone modification in cancer.

NQO1 prevents radiation-induced aneuploidy by interacting with Aurora-A.

Aneuploidy is the most common characteristic of human cancer cells. It also causes genomic instability, which is involved in the initiation of cancer development. Various lines of evidence indicate that nicotinamide adenine dinucleotide(P)H quinone oxidoreductase 1 (NQO1) plays an important role in cancer prevention, but the molecular mechanisms underlying this effect have not yet been fully elucidated. Here, we report that ionizing radiation (IR) induces substantial aneuploidy and centrosome amplification in NQO1-deficient cancer cells, suggesting that NQO1 plays a crucial role in preventing aneuploidy. NQO1 deficiency markedly increased the protein stability of Aurora-A in irradiated cancer cells. Small interfering RNA targeting Aurora-A effectively attenuated IR-induced centrosome amplification concerned with aneuploidy in NQO1-deficient cancer cells. Furthermore, we found that NQO1 specifically binds to Aurora-A via competing with the microtubule-binding protein, TPX2 (targeting protein for Xklp2), and contributes to the degradation of Aurora-A. Our results collectively demonstrate that NQO1 plays a key role in suppressing IR-induced centrosome amplification and aneuploidy through a direct interaction with Aurora-A.

Radio-sensitivities and angiogenic signaling pathways of irradiated normal endothelial cells derived from diverse human organs.

The purpose of the present investigation was to study the effects of ionizing radiation on endothelial cells derived from diverse normal tissues. We first compared the effects of radiation on clonogenic survival and tube formation of endothelial cells, and then investigated the molecular signaling pathways involved in endothelial cell survival and angiogenesis. Among the different endothelial cells studied, human hepatic sinusoidal endothelial cells (HHSECs) were the most radio-resistant and human dermal microvascular endothelial cells were the most radio-sensitive. The radio-resistance of HHSECs was related to adenosine monophosphate-activated protein kinase and p38 mitogen-activated protein kinase-mediated expression of MMP-2 and VEGFR-2, whereas the increased radio-sensitivity of HDMECs was related to extracellular signal-regulated kinase-mediated generation of angiostatin. These observations demonstrate that there are distinct differences in the radiation responses of normal endothelial cells obtained from diverse organs, which may provide important clues for protection of normal tissue from radiation exposure.

The radiosensitivity of endothelial cells isolated from human breast cancer and normal tissue in vitro.

We developed a novel method for harvesting endothelial cells from blood vessels of freshly obtained cancer and adjacent normal tissue of human breast, and compared the response of the cancer-derived endothelial cells (CECs) and normal tissue-derived endothelial cells (NECs) to ionizing radiation. In brief, when tissues were embedded in Matrigel and cultured in endothelial cell culture medium (ECM) containing growth factors, endothelial cells grew out of the tissues. The endothelial cells were harvested and cultured as monolayer cells in plates coated with gelatin, and the cells of 2nd-5th passages were used for experiments. Both CECs and NECs expressed almost the same levels of surface markers CD31, CD105 and TEM-8 (tumor endothelial marker-8), which are known to be expressed in angiogenic endothelial cells, i.e., mitotically active endothelial cells. Furthermore, both CECs and NECs were able to migrate into experimental wound in the monolayer culture, and also to form capillary-like tubes on Matrigel-coated plates. However, the radiation-induced suppressions of migration and capillary-like tube formations were greater for CECs than NECs from the same patients. In addition, in vitro clonogenic survival assays demonstrated that CECs were far more radiosensitive than NECs. In summary, we have developed a simple and efficient new method for isolating endothelial cells from cancer and normal tissue, and demonstrated for the first time that endothelial cells of human breast cancer are significantly more radiosensitive than their normal counterparts from the same patients.

Novel histone deacetylase inhibitor CG200745 induces clonogenic cell death by modulating acetylation of p53 in cancer cells.

Histone deacetylase (HDAC) plays an important role in cancer onset and progression. Therefore, inhibition of HDAC offers potential as an effective cancer treatment regimen. CG200745, (E)-N(1)-(3-(dimethylamino)propyl)-N(8)-hydroxy-2-((naphthalene-1-loxy)methyl)oct-2-enediamide, is a novel HDAC inhibitor presently undergoing a phase I clinical trial. Enhancement of p53 acetylation by HDAC inhibitors induces cell cycle arrest, differentiation, and apoptosis in cancer cells. The purpose of the present study was to investigate the role of p53 acetylation in the cancer cell death caused by CG200745. CG200745-induced clonogenic cell death was 2-fold greater in RKO cells expressing wild-type p53 than in p53-deficient RC10.1 cells. CG200745 treatment was also cytotoxic to PC-3 human prostate cancer cells, which express wild-type p53. CG200745 increased acetylation of p53 lysine residues K320, K373, and K382. CG200745 induced the accumulation of p53, promoted p53-dependent transactivation, and enhanced the expression of MDM2 and p21(Waf1/Cip1) proteins, which are encoded by p53 target genes. An examination of CG200745 effects on p53 acetylation using cells transfected with various p53 mutants showed that cells expressing p53 K382R mutants were significantly resistant to CG200745-induced clonogenic cell death compared with wild-type p53 cells. Moreover, p53 transactivation in response to CG200745 was suppressed in all cells carrying mutant forms of p53, especially K382R. Taken together, these results suggest that acetylation of p53 at K382 plays an important role in CG200745-induced p53 transactivation and clonogenic cell death.

Hyperthermia improves therapeutic efficacy of doxorubicin carried by mesoporous silica nanocontainers in human lung cancer cells.

PURPOSE: We investigated the use of hyperthermia to improve the anti-cancer efficacy of doxorubicin (DOX)-loaded mesoporous silica nanocontainer Si-SS-CD-PEG. The hypothesis was that heat stimulates glutathione-mediated degradation of cyclodextrin gatekeeper, thereby causing the release of DOX from the carrier and DOX-induced cell death. MATERIALS AND METHODS: The release of DOX from DOX-loaded Si-SS-CD-PEG suspended in PBS containing glutathione (GSH) was studied by assessing the changes in DOX fluorescence intensity. The effect of heating at 42°C on the release of DOX from the intracellular carriers was determined with confocal microscopy. The extents of clonogenic and apoptotic cell death caused by DOX-loaded Si-SS-CD-PEG were determined. RESULTS: The release of DOX from DOX-loaded Si-SS-CD-PEG in PBS occurred only when GSH presented in the suspension, and heating at 42°C slightly increased the release of DOX from the carriers. Heating significantly elevated the GSH content in A549 cells and increased the release of DOX from the internalised carriers. Heating the cancer cells treated with the carriers at 42°C markedly increased the clonogenic death and apoptosis. The GSH content in A549 cells was greater than that in L-132 cells, and A549 cells were far more sensitive than L-132 cells to DOX-loaded Si-SS-CD-PEG at both 37°C and 42°C. CONCLUSIONS: Hyperthermia increased the GSH-mediated release of DOX from DOX-loaded Si-SS-CD-PEG. Furthermore, hyperthermia markedly elevated the GSH content in cancer cells, thereby increasing the release of DOX from the internalised carriers and potentiating the DOX-induced clonogenic and apoptotic cell death.

ß-lapachone significantly increases the effect of ionizing radiation to cause mitochondrial apoptosis via JNK activation in cancer cells.

BACKGROUND: ß-lapachone (ß-lap), has been known to cause NQO1-dependnet death in cancer cells and sensitize cancer cells to ionizing radiation (IR). We investigated the mechanisms underlying the radiosensitization caused by ß-lap. METHODOLOGY/PRINCIPAL FINDINGS: ß-lap enhanced the effect of IR to cause clonogenic cells in NQO1(+)-MDA-MB-231 cells but not in NQO1(-)-MDA-MB-231 cells. ß-lap caused apoptosis only in NQO1(+) cells and not in NQO1(-) cells and it markedly increased IR-induced apoptosis only in NQO1(+) cells. Combined treatment of NQO1(+) cells induced ROS generation, triggered ER stress and stimulated activation of ERK and JNK. Inhibition of ROS generation by NAC effectively attenuated the activation of ERK and JNK, induction of ER stress, and subsequent apoptosis. Importantly, inhibition of ERK abolished ROS generation and ER stress, whereas inhibition of JNK did not, indicating that positive feedback regulation between ERK activation and ROS generation triggers ER stress in response to combined treatment. Furthermore, prevention of ER stress completely blocked combination treatment-induced JNK activation and subsequent apoptotic cell death. In addition, combined treatment efficiently induced the mitochondrial translocation of cleaved Bax, disrupted mitochondrial membrane potential, and the nuclear translocation of AIF, all of which were efficiently blocked by a JNK inhibitor. Caspases 3, 8 and 9 were activated by combined treatment but inhibition of these caspases did not abolish apoptosis indicating caspase activation played a minor role in the induction of apoptosis. CONCLUSIONS/SIGNIFICANCE: ß-lap causes NQO1-dependent radiosensitization of cancer cells. When NQO1(+) cells are treated with combination of IR and ß-lap, positive feedback regulation between ERK and ROS leads to ER stress causing JNK activation and mitochondrial translocation of cleaved Bax. The resultant decrease in mitochondrial membrane leads to translocation of AIF and apoptosis.