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SUPPLEMENTARY DATA. 7 figures, figure legends and supplementary methods Suppl. Fig. 1. TGF-ß1 pretreatment induces G1 arrest. Suppl. Fig. 2. TGF-ß1 pretreatment protects cells from low dose IR-induced apoptosis, regardless of p21. Suppl. Fig. 3. Smad2 and Smad3 are required for TGF-ß1-mediated suppression of low dose IR-induced apoptosis. Suppl. Fig. 4. TGF-ß1-mediated suppression of IR-induced DSBs is not observed immediately after ?-irradiation. Suppl. Fig. 5. TGF-ß1 pretreatment reduces chromosome breakage. Suppl. Fig. 6. Vectors used for in vivo NHEJ assay. Suppl. Fig. 7. TGF-ß1 pretreatment promotes the nuclear retention of NHEJ proteins.

Clinical efficacy of immune checkpoint blockade is often enhanced by their co-administration with immunogenic chemotherapy. Here a novel chemo-immunotherapy combination is reported that successfully overcomes the immunosuppressive tumor microenvironment to elicit an effective anti-tumor immune response. The CD47-SIRPα innate immune checkpoint was blocked by surface engineering human ferritin with a SIRPα variant, and this FHSIRPα efficiently inhibited the “don’t-eat-me” signal of cancer cells, thereby enhancing cancer cell phagocytosis in a colon carcinoma (CT26) model in immunocompetent mice. Doxorubicin prodrug, EMC-DEVD-S-DOX, that binds to circulating albumin following intravenous administration showed enhanced half-life, and the active drug was released via caspase-3 at tumor site following radiation treatment. Radiation-induced apoptosis of cancer cells resulted in release of active drug doxorubicin and upregulation of CD47 on cancer cell surface, sensitizing cancer cells to FHSIRPα treatment. The induction of immunogenic cell death (ICD) by the prodrug was confirmed in vitro by upregulation of calreticulin, translocation of HMGB1 and increased release of chaperone proteins in CT26.CL25 mouse colon cancer cells by flow cytometric analysis and confocal microscopy. The ICD effect of the prodrug correlated well in vivo and increased phagocytosis of tumor cells by antigen-presenting cells (APCs) in immunocompetent mice as analyzed by flow cytometry of tumor tissue and draining lymph nodes. Tumor infiltrates analyzed by flow cytometry also showed enrichment of APCs; and T cell-mediated elimination of immunogenic tumors was confirmed by the tumor-specific activation of T cells ex vivo as detected by secretion of IFNγ. Whereas FHSIRPα monotherapy showed modest tumor growth inhibition, combination with a doxorubicin prodrug resulted in effective inhibition of tumor growth by 95.2% (p Citation Format: Na Kyeong Lee, Jeong Uk Choi, Jung Je Park, Ji-Hyun Seo, Mi Ra Kim, Hyo Won Chang, Sang Yoon Kim, In-San Kim, Youngro Byun. Nanocage therapeutics FHSIRPα mediating immune checkpoint blockade awakens immunity against cancer with an albumin-binding caspase-cleavable doxorubicin prodrug EMC-DEVD-S-DOX [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2251.

P53 is an important biomarker in response to genotoxic stress, but it is also known to plays a key role in the regulation of metabolic homeostasis. The loss of p53 is a well-established contributor to the malignant transformation and glycolytic phenotype acquisition of cells during cancer development. However, the role of p53 in genotoxic therapy-induced metabolic shift in cancers remains unclear. Here, we attempted to elucidate how p53 participates in the glycolytic shift of head and neck cancer cell lines following irradiation. We established a stable radioresistant head and neck cancer cells (HN30-R; p53 wild type and UMSCC1-R; p53 null type) through cumulative irradiation and then analyzed their glucose metabolic profiles and mitochondria respiration. As a result, the metabolic analysis revealed no changes glycolysis of HN30-R cells, but UMSCC1-R cells exhibited increased glycolysis through increased glucose uptake and lactate production and glycolytic intermediates as well as related glycolytic enzymes, compared to UMSCC1 cells. Also, we confirmed that the mitochondrial respiration was reduced by the maximal respiration parameters of oxygen consumption rate (OCR) and that abnormal mitochondria were accumulated by electron microscopy in UMSCC1-R cells. Thus, UMSCC1-R cells exhibited an increased sensitivity to glycolysis-targeting drugs such a hexokinases inhibitor (2-deoxy-D-glucoes; 2-DG) and a lactate dehydrogenase-A inhibitor (AT101), but HN30-R cells did not shown any changes. Moreover, we identified that mitophagy limits glycolytic shift through the p53-dependent clearance of abnormal mitochondria. Taken together, these results suggest that p53 null type cells increased aerobic glycolysis to overcome the accumulation of abnormal mitochondria in radioresistnat cells. Conversely, p53 wild type cells inhibited the glycolytic shift by regulating a integrity through p53-dependent mitophagy. Thus, glycolysis-targeted drugs could be an alternative strategy for overcoming recurrent cancers after radiotherapy, and p53 status could be a biomarker for selecting participants for clinical trials. Citation Format: Hyo Won Chang, Ji Won Kim, Mi Ra Kim, Hae Yun Nam, Myungjin Lee, Won Hyeok Lee, Song Hee Kim, Da Seul Seong, Myung Woul Han, Jong Cheol Lee, Jung Je Park, Ji-hyun Seo, Seong Who Kim, Sang Yoon Kim. P53-dependent mitophagy controls glycolytic shift in radioresistant head and neck cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2405.

Acquired resistance to tamoxifen (TAM) is a serious therapeutic problem in breast cancer patients. Here, we found that TAM-resistant MCF-7 cells (TAMR-MCF-7 cells) produced higher levels of vascular endothelial growth factor (VEGF) than control MCF-7 cells. Molecular analyses using reporter genes and Western blots supported the involvement of c-Jun/activator protein-1 and hypoxia-inducible factor 1α in enhanced VEGF transcription in TAMR-MCF-7 cells. Pin1, a peptidyl prolyl isomerase, was consistently overexpressed in TAMR-MCF-7 cells, and c-Jun/activator protein-1–dependent VEGF transcription in TAMR-MCF-7 cells was almost completely inhibited by Pin1 siRNA and by the Pin1 inhibitor juglone. Chick chorioallantoic membrane assays confirmed that the increased angiogenic intensity of TAMR-MCF-7 cells was significantly suppressed by Pin1 inhibition. These results show that Pin1 overexpression is closely associated with VEGF-mediated angiogenesis and suggest that Pin1 is a potential therapeutic target of excessive angiogenesis in TAM-resistant breast cancer cases.[Mol Cancer Ther 2009;8(8):2163–71]

The presence of p53 mutation was associated with poor survival in various tumors. The involvement of p53 in apoptosis and cell-cycle control makes it a plausible biomarker of prognosis . Classifying TP53 mutations in HNSCC described disruptive TP53 mutation in either the L2 or L3 loop of the DNA binding domain, resulting in polarity change within the protein, or stop cordon. Disruptive TP53 mutation in HNSCC tumors predicts for locoregional recurrence, due to increased radioresistance via the inhibition of senescence. Senescence induction contributes to cancer therapy responses and is crucial for p53-mediated tumor suppression. However, whether p53 inactivation actively suppresses senescence induction has been unclear. Here, we found that overexpression CIP2A (cancerous inhibitor of protein phosphatase 2A) positively correlated with presence of p53 mutation in head and neck cancer and mediates radioresistance through suppression of radiation induced senescence. And we demonstrated that rapamycin could induce senescence via CIP2A downregulation and increase radiosensitivity in p53 disruptive mutation cell line. This is the first investigation to analyze the role of CI2A in resistance to the radiotherapy of head and neck cancer. As a consequence, a greater understanding of radioresistance mechanisms through our results in head and neck cancer with p53 mutation will enable the rational design of combination regimens and sequential treatment algorithms to improve clinical outcomes and points to the usefulness of CIP2A as a biomarker to predict clinical response to rapamycin in head and neck cancer. Citation Format: Song Hee Kim, Won hyeok Lee, Myung Jin Lee, Hyo Won Chang, Ji Won Kim, Mi Ra Kim, Jung Je Park, Myung Woul Han, Sang Yoon Kim. CIP2A can be a therapeutic target of rapamycin in radioresistant head and neck cancer with P53 mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5476. doi:10.1158/1538-7445.AM2017-5476

Radiotherapy is a well-established therapeutic modality used in treatment of many cancers. However, radioresistance remains a serious obstacle to successful treatment. Radioresistance can cause local recurrence and distant metastases in some patients after treatment by radiation. Thus, special emphasis has been given to the discovery of effective radiosensitizers. EphA3 receptors functions contribute to tumor development, modulating cell-cell adhesion, invasion, neo-angiogenesis, tumor growth and metastasis. However, the role of EphA3 in radioresistance remains to be elucidated. Here, we established the stable radioresistant head and neck cancer cell line (AMC HN3R cell line) and identified that EphA3 was overexpressed predominantly in the AMC HN3R cancer cell line through DNA microarray, real time PCR and Western blotting. Additionally, we identified that EphA3 was overexpressed in recurred laryngeal cancer specimen after radiation therapy. And we found that EphA3 mediated the tumor invasiveness and migration and EMT (epithelial mesenchymal transition) related protein expression in AMC HN3R cancer cell line. To investigate the role of EphA3 in modulating the radiosensitivity, we observed the change of survival fraction after transfection EphA3 siRNA. And we found that inhibition of EphA3 enhances radiosensitivity in AMC HN 3R cell line. In conclusion, these results suggest that EphA3 is overexpressed in radioresistant head and neck cancer and can play a crucial role in development radioresistance in head and neck cancers through regulation of EMT pathway. Citation Format: Myung Woul Han, Song Hee Kim, Hyo Won Chang, Hae Yun Nam, Myungjin Lee, Gui Chul Kim, Yoon sun Lee, Mi Ra Kim. EphA3 maintains radioresistance in head and neck cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1170.

Conventional chemotherapy requires therapy holiday due to their toxic adverse effects. However, the therapy holiday has been allowing cancer cell to relapse and caused secondary metastasis to occur in other tissue. On the contrast, metronomic maintenance chemotherapy (MMC) treats anticancer drugs frequently to reduce the adverse effects from normal tissues by maintaining low concentration in the blood. In this context, an oral route is more suitable for MMC than a parenteral route. Our oral delivery system that uses electrochemical property of bile acid derivatives increases bioavailability of doxorubicin (DOX) from below 5% to 26% by eluding p-gp. The antitumor studies showed that 5mg/kg/day oral DOX complex inhibited 70% of tumor volume in C3H mice model bearing SCC7 tumor. The H&E staining of intestines and liver and the blood analysis proved that there were no histological and hematological toxicities. In addition, low dose of the DOX complex affects cell cycle regulation to arrest cancer cells. The concentration of 10nM, 30nM of DOX restricted the cell cycle at checkpoints in G1 phase of MCF-7 cells which are p-53 wild type and checkpoints in G2-M phase of MDA-MB 231 cells which are p-53 disruptive type. When MK8776, a inhibitor of cell cycle checkpoints, is treated with the low concentration of DOX, the cancer cells went through apoptosis or senescence depending on a type of cancer. In conclusion, our oral delivery of doxorubicin can offer safe and effective chemotherapy. Note: This abstract was not presented at the meeting. Citation Format: Seho Kweon, Foyez K.A. Mahmud, Hyo Won Chang, Have Yoon Nam, Mi Ra Kim, Jung Je Park, Youngro Byun, Sang Yoon Kim. Oral delivery of doxorubicin using bile enhancer for metronomic maintenance chemotherapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5351. doi:10.1158/1538-7445.AM2015-5351

At present, most of the anticancer drugs are given parenterally, showing drug concentration above the maximum tolerable concentration (MTC) followed by rapid elimination from the plasma that causes enhanced side effects and lower efficacy. In contrast, low dose oral maintenance therapy may increase therapeutic efficacy by increasing the exposure time to cancer cells and also reduce the side effects by maintaining the drug concentration below MTC level. Pemetrexed is a folate antagonist approved for maintenance chemotherapy in lung cancer. However, a major limitation of Pemetrexed is the poor oral bioavailability which imposes IV administration. In this context, we have developed a physical complex of Pemetrexed with lysine conjugated deoxycholic acid (DCK) in water (mole ratio 1:2) for the purpose of oral delivery. The DSC thermogram of Pemetrexed/DCK complex showed the complex formation due to disappearance of exothermic and endothermic peaks from Pemetrexed. The pharmacokinetic studies of Pemetrexed/DCK were done in SD rats and analyzed by HPLC method. In antitumor study, low dose continuous oral therapy from 2.5 mg/kg to 20 mg/kg showed substantial tumor inhibition in SCC7 tumor bearing C3H mice. We also evaluated maintenance chemotherapy as oral Pemetrexed/DCK administration in A549 tumor bearing nude mice. We found that 5 mg/kg dose of oral Pemetrexed successfully inhibited tumor progression and also showed additional antitumor effects when given with Cisplatin as maintenance chemotherapy. In the context of oral anticancer drugs, we need to consider the toxicities in GI tracts (GIT). For this purpose, apoptosis in GI tracts and morphology of different organs were assessed by TUNEL and H&E staining. One month toxicity studies have been conducted in nude mice and we found that 5 mg/kg oral dose did not produce any abnormalities in hematological and serological parameters in mice having intact morphology of GI tracts. Our studies offer safe and effective oral maintenance chemotherapy of pemetrexed for cancer patients at home. Citation Format: Foyez Mahmud, Seho Kweon, Hyo Won Chang, Hae Yoon Nam, Mi Ra Kim, Jung Je Park, Sang Yoon Kim, Youngro Byun. Metronomic maintenance chemotherapy of orally active pemetrexed for effective treatment of lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4390. doi:10.1158/1538-7445.AM2015-4390

Introduction: Activating mutations of EGFR are well known as oncogenic driver mutations in lung adenocarcinoma. Currently, EGFR TKIs including Gefitinib and Erlotinib are used as the first line therapy in NSCLC patients harboring EGFR activating mutations. However, drug resistance caused by T790M mutation limits the efficacy of these 1st generation EGFR TKIs. Currently, some of the next generation EGFR TKIs are under investigation for the treatment of lung cancer patients having T790M mutation. In our current presentation, to obtain HM61713, an EGFR mutant selective inhibitor, as a clinical candidate and the evaluation of HM61713 for mutant EGFR cancer model will be introduced. Method: Novel analogues were designed and synthesized to find active compounds for the T790M mutation as well as EGFR activating mutations with good selectivity over wild- type EGFR. Finally, HM61713 was selected as a clinical candidate through multi-optimization processes including both in vitro and in vivo pharmacologcal studies. Results: HM61713 was designed as an irreversible kinase inhibitor having a Michael acceptor, which covalently binds to a cysteine residue near the kinase domain of mutant the EGFR. In a cell wash out test, HM61713 inhibited phospho-EGFR for a long duration with a half-life of over 24 hours. From in vitro study, HM61713 showed potent activities for H1975 (L858-T790M) and HCC827 (exon 19 del.) with GI50 values of 9.2 nM and 10 nM, respectively. Instead, it showed low potency for H358 (wild type EGFR NSCLC) with GI50 of 2,225 nM. In xenograft studies using H1975 and HCC827, HM61713 resulted in good efficacy without showing any side effects. Conclusion: HM61713 showed excellent in vitro and in vivo activities for H1975 harboring L858R-T790M mutation as well as HCC827 having exon 19 deletion mutation with selectivity over wild-type EGFR. Currently, HM61713 is undergoing phase I study (NCT01588145) for NSCLC patients after the failure of 1st generation EGFR TKIs in Korea. Citation Format: Kwang-Ok Lee, Mi Young Cha, Mira Kim, Ji Yeon Song, Jae-Ho Lee, Young Hoon Kim, Young-Mi Lee, Kwee Hyun Suh, Jeewoong Son. Discovery of HM61713 as an orally available and mutant EGFR selective inhibitor. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-100. doi:10.1158/1538-7445.AM2014-LB-100

Autophagy is frequently activated in radioresistant cancer cells. Rapamycin, mammalian target of rapamycin (mTOR) inhibitor, activates autophagy but enhances radiosensitivity. The mechanism of these actions by which such opposing functions coexist was investigated on radiation-resistant cancer cell lines (AMC-HN-9 and U-87) and the antitumor activity was evaluated in mice bearing xenografts of the cancer cells. Enhanced autophagic flux induced by radiation returned to untreated control levels. Treatment of the cancer cells with rapamycin leads to the potentiation and prolongation of radiation-induced autophagy, the increases in senescence-associated β-galactosidase activity, heterochromatin formation, and irreversible growth arrest. Furthermore, rapamycine resulted in a tumor regrowth delay and increased the level of β-galactosidase staining and the expression of heterochromatin markers in irradiated xenografts. These results suggest that even though autophagy is a survival mechanism in radioresistant cells, a persistent activation of autophagy by mTOR inhibitor induces premature senescence in these cells, eventually making the cells radiosensitive. Our data suggest a novel mechanism by which an inhibition of mTOR pathway increases autophagy but paradoxically increases radiosensitivity in radioresistant cancer cells. Citation Format: Hae Yun Nam, Myung Woul Han, Hyo Won Chang, Yoon Sun Lee, Myungjin Lee, Mi Ra Kim, Hyang Ju Lee, Ji Yung Jeoung, So Young Moon, Hyo Jung Kim, Sang Yoon Kim, Seong Who Kim. Rapamycin increases radiosensitivity of cancer cells by induction of premature senescence. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 81. doi:10.1158/1538-7445.AM2013-81

β-Catenin, a multifunctional protein involved in key molecule of Wnt signaling transduction, has been well known to regulate cell proliferation, differentiation, cell-cell adhesion, survival, and apoptosis as well as plays an important role in human tumorigenesis. Our previous report showed that Wnt/β-catenin pathway controls radiosensitivity of head and neck caner (HNC) cell via cyclooxygenase-2-mediated Ku expression. However, the specific molecular mechanisms of β-catenin in tumor cell survival and death are still not fully understood, so in the present study we attempted to elucidate the mechanism of cell death in HNC cell by studying how β-catenin silencing regulates cell death through KB1/AMPK signaling. We performed β-catenin knockdown in HNC cell by using small interfering RNA. Its effect on the cell viability was confirmed by observation of cell morphologic change, electron microscopy, MTT and FACS analysis. Also, we confirmed the expression of several proteins corresponding signal pathway by western blot analysis. β-catenin silencing significantly induced G1 cell-cycle arrest and also increased the expression of Bax and the active form of caspase-3, and decreased the expression of Bcl-2, demonstrating the sequential activation of apoptotic cascades following treatment with β-catenin siRNA in HNC cell. Interestingly, β-catenin silencing induced autophagy as well as apoptosis. We confirmed that the numbers of autophagic vacuoles and the expression of LC3-II increased in cells treated with β-catenin siRNA. This is probably because LKB1-dependent AMPK is activated by β-catenin silencing in HNC cell. Activated AMPK, in β-catenin silenced AMC-HN-3 cells, causes a G1 cell cycle arrest by phosphorylated p53 as well as inhibited protein synthesis by suppressing mTOR activity. Also, Treatment with LKB1 siRNA or compound C in AMC-HN-3 cells preserved cell viability against β-catenin silencing-induced cytotoxicity. Taken together, our data show that β-catenin silencing induces cell death through LKB1/AMPK signal, and as a result, apoptosis and autophagy are induced together in HNC cell, suggesting that a novel interaction between β-catenin and LKB1/AMPK signaling pathway occurs. Our study provides new insights into understanding the cellular and molecular mechanisms involving β-catenin silencing-induced cell death. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2283. doi:1538-7445.AM2012-2283

β1 integrin's aberrant expression has implicated a cancer progression and resistance to cytotoxic therapy. Moreover, cancer cells gained epithelial mesenchymal transition (EMT) features were more resistant to the detachment-induced cell death. In this regard, we investigated the mechanism by which β1-Integrin governs cell viability and verified whether the signaling pathway is associated with EMT features. Cancer cell lines from head and neck cancer patients (AMC-HN3 and AMC-HN9) and well-known EMT cancer, MDA-MB231, were used in this study. To determine whether three cell lines reveal the epithelial EMT features, EMT markers such as Snail, vimentin, fibronectin and E-cadherin were evaluated by western blot analysis and immunofluroscence. To knockdown β1 integrin signal, β1 integrin small interfering RNA (siRNA) was transiently transfected into all cell lines. The cell viability was examined by looking at the results of propidium iodide staining, MTT assay, changes in the mitochondrial membrane potential and cell morphology. MDA-MB231 and AMC-HN9 cells possessed EMT features whereas AMC-HN3 cells were not shown EMT phenotype. β1 integrin silencing cell increased the sub G1 from 1.0% to 29.8%, increased the percentage of cells losing their mitochondrial membrane potential from 5.3% to 65.9% as well as the number of fragmented mitochondria in AMC-HN3 cells. In contrast, MDA-MB231 cells showed more resistance to silencing of β1 integrin, lower cell death rate from 0.6% to 9.6% and less changes in the mitochondrial membrane potential from 4.34% to 34.51%. Interestingly, AMC-HN9 cells showed complete resistance to β1 integrin blocking even though FAK phosphorylation signaling was blocked in AMC-HN9 cells, same as AMC-HN3 cells, which is a different response from typical EMT featured cells. When AMC-HN9 cells were treated to inhibit β1 integrin and p53 separately, it showed no response to changes in the cellular morphology, viability and apoptosis-related signal pathway; however, when it was given the combined β1 integrin and p53, apoptosis occurred in the cell line. In this study, acquisition of the EMT features in cancer cells presented resistance to the β1 integrin inhibition. In addition, the activation of p53-p21 signaling pathway provided resistance to detachment-induced apoptosis in head and neck cancer cell line with EMT features. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1226. doi:10.1158/1538-7445.AM2011-1226

Based on our previous report showing that up-regulation of Ku70/Ku80 in AMC-HN9 (HN9) cells is required for cell-cycle re-entry and cell proliferation following irradiation, further study to investigate the mechanism by which β-catenin knockdown sensitizes the cells to irradiation have been conducted. β-Catenin, as a multifunctional protein involved in cadherin-mediated cell-cell adhesion and Wnt signaling transduction, have been well known to regulates cell growth and survival following radiation in various types of cancer cells. However, the molecular mechanisms by which β-catenin affects radiation sensitivity are still not fully understood, which led us to explore, with regard to regulation of Ku70/Ku80 expression, the molecular mechanism of the synergistic effects of β-catenin silencing and radiation combination in radio-resistant head and neck cancer cells. β-Catenin silencing using small interfering RNA(siRNA) down-regulated β-catenin expression up to 72 h both in membranous and nuclear fraction of HN9 cells. β-Catenin knockdown induced cell cycle arrest on G1 phase and thus decreased cell proliferation, but didn't cause any DNA damage response and cell death. Whereas expression of Ku70/Ku80 was up-regulated in HN9 cell following irradiation (4Gy), in the cells treated with combination of radiation and β-catenin siRNA, Ku70/Ku80 expression were dramatically decreased. In addition, when β-catenin silenced cells were exposed to single dose of radiation, irradiation-induced cell death was much more increased from 3.1% to 13% and accompanied with caspase-3 activation and PARP cleavage. Taken together, these results suggest that inhibition of Ku expression through β-catenin silencing is associated with its radio-sentitizing effect in HN9 cells and further studies to clarify the pathway linking β-catenin signaling and regulation of Ku70/Ku80 expression are warranted. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 508.