過去研究指出三氧化二砷能藉由產生活性氧物種（ROS）誘發癌細胞發生細胞凋亡。但是有些癌細胞對三氧化二砷具有抗性，雖然提高三氧化二砷的劑量可以提高細胞對三氧化二砷的敏感性，但劑量一提高就不是臨床上可接受的範圍。而臨床上也常使用放射線治療合併化學藥物來增加治療癌症的效果。因此本研究的主要目的為利用低劑量游離輻射來促進三氧化二砷誘發前脊髓淋巴癌細胞U-937細胞產生細胞凋亡之機制探討。實驗結果發現單獨處理低劑量放射線（4Gy）會造成細胞週期G2/M phase的停滯並且在12小時達到最高之後慢慢下降。合併處裡所造成的細胞內ROS的上升、細胞存活率的下降、增加細胞週期G2/M phase的停滯、增加細胞發生細胞凋亡及粒線體膜電位的下降都較單獨處理放射線或三氧化二砷的效果好。並且合併處理會延長G2/M phase的停滯時間。以上結果可知，合併處理會造成細胞抗增生的效果是藉由增加G2/M phase及細胞凋亡的比例。這表示合併處理可藉由增加細胞內ROS的上升及粒線體膜電位的下降而增強細胞發生細胞凋亡。

Recent studies indicated that arsenic trioxide (ATO) may lead to cancer cells apoptosis via production of intracellular reactive oxygen species（ROS）.Resistance against ATO-induced cytotoxicity was found in several cancer cell lines. Although those resistant cancer cell lines can still be rendered apoptosis by higher doses of ATO; however, these dose are not practical in the clinical setting. The combined treatment（irradiation and chemotherapeutic）is commonly used in clinical cancer therapy. The aim of current study is to investigate the mechanisms of combined treatment of low dose irradiation and ATO-enhanced apoptotic cell death in U-937 cells which is a ATO-resistant cancer cell line. The cytotoxicity effect of combined treatment is more effective than irradiation or arsenic trioxide alone. Combined treatment increased intracellular ROS levels、 reduced cells viability、 increased cell cycle G2/M phase arrest、increased apoptosis and reduced mitochondrial membrane potential（△Ψm）. Combined treatment also increased the G2/M phase arrest duration. IR in combination with ATO revealed an anti-cell proliferation effect in U-937 cells via increased G2/M proportion and apoptosis. These findings suggested that IR in combination with ATO could increase intracellular ROS level and decrease mitochondrial membrane potential, thereby enhancing apoptotic
cell death.

Ho SY, Huang PC, Guo HR, Chang WH, Chen RJ, Wei BL, Wu WJ, Tai C, Wang YJ. Mechanisms of apoptosis induction and cell cycle regulation in irradiated leukemia U937 cells and enhancement by arsenic trioxide. Radiat Res. 2006.

Yan H, Peng ZG, Wu YL, Jiang Y, Yu Y, Huang Y, Zhu YS, Zhao Q, Chen GQ. Hypoxia-simulating agents and selective stimulation of arsenic trioxide-induced growth arrest and cell differentiation in acute promyelocytic leukemic cells. Haematologica. 2005.

Lemarie A, Morzadec C, Merino D, Micheau O, Fardel O, Vernhet L. Arsenic trioxide induces apoptosis of human monocytes during macrophagic differentiation through nuclear factor-kappaB-related survival pathway down-regulation. J Pharmacol Exp Ther. 2006 Jan;316(1):304-14. Epub 2005.

McCollum G, Keng PC, States JC, McCabe MJ Jr. Arsenite delays progression through each cell cycle phase and induces apoptosis following G2/M arrest in U937 myeloid leukemia cells. J Pharmacol Exp Ther. 2005.

Tabellini G, Cappellini A, Tazzari PL, Fala F, Billi AM, Manzoli L, Cocco L, Martelli AM. Phosphoinositide 3-kinase/Akt involvement in arsenic trioxide resistance of human leukemia cells. J Cell Physiol. 2005.

Yi J, Yang J, He R, Gao F, Sang H, Tang X, Ye RD. Emodin enhances arsenic trioxide-induced apoptosis via generation of reactive oxygen species and inhibition of survival signaling. Cancer Res. 2004.

Yang J, Tang XM, Li H, Shi GY, Zhu P, Jin HF, Yi J. Emodin sensitizes HeLa cell to arsenic trioxide induced apoptosis via the reactive oxygen species-mediated signaling pathways. Shi Yan.Sheng Wu Xue Bao. 2003

Akao Y. Mizoguchi H. Kojima S. Naoe T. Ohishi N. Yagi K. Arsenic
induces apoptosis in B-cell leukaemic cell lines in vitro: activation of
caspases and down-regulation of Bcl-2 protein. British Journal of
Haematology. 102(4):1055-60, 1998.

Lee JH, Park JW. The effect of alpha-phenyl-N-t-butylnitrone on ionizing radiation-induced apoptosis in U937 cells.
Free Radic Res. 2005

Charley MR. Tharp M. Locker J. Deng JS. Goslen JB. Mauro T. McCoy P. Abell E. Jegasothy B. Establishment of a human cutaneous T-cell lymphoma in C.B-17 SCID mice. J Invest Dermatol. 94(3):381-384, 1990.

Lee JH, Lee YM, Park JW. Regulation of ionizing radiation-induced apoptosis by a manganese porphyrin complex. Biochem Biophys Res Commun. 2005

Chun YJ. Park IC. Park MJ. Woo SH. Hong SI. Chung HY. Kim TH. Lee YS. Rhee CH. Lee SJ. Enhancement of radiation response in human cervical cancer cells in vitro and in vivo by arsenic trioxide (As2O3). FEBS Letters. 519(1-3):195-200, 2002.

Csapo Z. Keszler G. Safrany G. Spasokoukotskaja T. Talianidis I. Staub M. Sasvari-Szekely M. Activation of deoxycytidine kinase by
gamma-irradiation and inactivation by hyperosmotic shock in human lymphocytes. Biochemical Pharmacology. 65(12):2031-9, 2003.

Dai J. Weinberg RS. Waxman S. Jing Y. Malignant cells can be sensitized to undergo growth inhibition and apoptosis by arsenic trioxide through modulation of the glutathione redox system. Blood. 93(1):268-77, 1999.

Davison K. Cote S. Mader S. Miller WH. Glutathione depletion overcomes resistance to arsenic trioxide in arsenic-resistant cell lines. Leukemia. 17(5):931-40, 2003.

Davison K. Mann KK. Waxman S. Miller WH Jr. JNK activation is a
mediator of arsenic trioxide-induced apoptosis in acute promyelocytic leukemia cells. Blood. 103(9):3496-502, 2004.

Deng X. Hofmann ER. Villanueva A. Hobert O. Capodieci P. Veach DR. Yin X. Campodonico L. Glekas A. Cordon-Cardo C. Clarkson B. Bornmann WG. Fuks Z. Hengartner MO. Kolesnick R. Caenorhabditis elegans ABL-1 antagonizes p53-mediated germline apoptosis after ionizing irradiation. Nature Genetics. 36(8):906-12, 2004.

Dreher D. Junod AF. Role of oxygen free radicals in cancer development. European Journal of Cancer. 32( 1):30-8, 1996.

Estus S. Zaks WJ. Freeman RS. Gruda M. Bravo R. Johnson EM Jr. Altered gene expression in neurons during programmed cell death:
identification of c-jun as necessary for neuronal apoptosis. Journal of Cell Biology. 127(6 Pt 1):1717-27, 1994.

Flores ER. Tsai KY. Crowley D. Sengupta S. Yang A. McKeon F. Jacks T. p63 and p73 are required for p53-dependent apoptosis in response to DNA damage. Nature. 416(6880):560-4, 2002.

Cui ZG, Kondo T, Feril Jr LB, Waki K, Inanami O, Kuwabara M. Effects of antioxidants on X-ray- or hyperthermia-induced apoptosis in human lymphoma U937 cells.
Apoptosis. 2004.

Fulop GM. Phillips RA. The scid mutation in mice cause a general defect in DNA repair. Nature. 347(6292):479-482, 1990.

Park IC, Park MJ, Woo SH, Lee HC, An S, Gwak HS, Lee SH, Hong SI, Bae IJ, Seo KM, Rhee CH. Tetraarsenic oxide induces apoptosis in U937 leukemic cells through a reactive oxygen species-dependent pathway. Int J Oncol. 2003

Gupta S. Yel L. Kim D. Kim C. Chiplunkar S. Gollapudi S. Arsenic trioxide induces apoptosis in peripheral blood T lymphocyte subsets by inducing oxidative stress: a role of Bcl-2. Molecular Cancer Therapeutics. 2(8):711-9, 2003 .

Hengartner MO. The biochemistry of apoptosis.[see comment]. [Review] [75refs] Nature. 407(6805):770-6, 2000.

Huang XJ. Wiernik PH. Klein RS. Gallagher RE. Arsenic trioxide induces apoptosis of myeloid leukemia cells by activation of caspases. Medical Oncology. 16(1):58-64, 1999.

Huang SY. Chang CS. Tang JL. Tien HF. Kuo TL. Huang SF. Yao YT.Chou WC. Chung CY. Wang CH. Shen MC. Chen YC. Acute and chronic arsenic poisoning associated with treatment of acute
promyelocytic leukaemia. British Journal of Haematology. 103(4):1092-5, 1998 .

Jing Y. Dai J. Chalmers-Redman RM. Tatton WG. Waxman S. Arsenic trioxide selectively induces acute promyelocytic leukemia cell apoptosis via a hydrogen peroxide-dependent pathway. Blood. 94(6):2102-11, 1999.

Kaghad M. Bonnet H. Yang A. Creancier L. Biscan JC. Valent A. Minty A. Chalon P. Lelias JM. Dumont X. Ferrara P. McKeon F. Caput D. Monoallelically expressed gene related to p53 at 1p36, a region frequently deleted in neuroblastoma and other human cancers. Cell. 90(4):809-19, 1997.

Kawai K. Resetkova E. Enomoto T. Fornasier V.
Comparative studies in human thyroid xenografts in severe combined immunodeficient and nude mice. J. Clin. Endocrinol. Metab. 83(1):157-164, 1998.

Ko YC. A critical review of epidemiologic studies on black-foot disease. [Review] [10 refs] Journal of Uoeh. 8(3):339-53, 1986.

Kruszewski M. Wojewodzka M. Iwanenko T. Collins AR. Szumiel I.
Application of the comet assay for monitoring DNA damage in workers exposed to chronic low-dose irradiation. II. Base damage. Mutation Research. 416(1-2):37-57, 1998.

Kurki S. Latonen L. Laiho M. Cellular stress and DNA damage invoke temporally distinct Mdm2, p53 and PML complexes and
damage-specific nuclear relocalization. Journal of Cell Science. 116(Pt 19):3917-25, 2003.

Lee JH, Park JW. A manganese porphyrin complex is a novel radiation protector. Free Radic Biol Med. 2004

Lew YS. Kolozsvary A. Brown SL. Kim JH. Synergistic interaction with arsenic trioxide and fractionated radiation in locally advanced murine tumor. Cancer Research. 62(15):4202-5, 2002.

Schrijvers DM, Martinet W, De Meyer GR, Andries L, Herman AG, Kockx MM. Flow cytometric evaluation of a model for phagocytosis of cells undergoing apoptosis. J Immunol Methods. 2004.

Li YM. Broome JD. Arsenic targets tubulins to induce apoptosis in myeloid leukemia cells. Cancer Research. 59(4):776-80, 1999.

Ling YH. Jiang JD. Holland JF. Perez-Soler R. Arsenic trioxide produces polymerization of microtubules and mitotic arrest before apoptosis in human tumor cell lines. Molecular Pharmacology. 62(3):529-38, 2002
.

Lubaroff DM. Cohen MB. Schultz LD. Beamer WG. Survival of human prostate carcinoma, benign hyperplastic prostate tissues, and IL-2-activated lymphocytes in scid mice. Prostate. 27(1):32-41, 2004.

Ma BB. Bristow RG. Kim J. Siu LL. Combined-modality treatment of solidtumors using radiotherapy and molecular targeted agents. [Review] [209 refs] Journal of Clinical Oncology. 21(14):2760-76, 2003.

Martelli AM. Cappellini A. Tazzari PL. Billi AM. Tassi C. Ricci F. Fala F.Conte R. Casepase-9 is the upstream caspase activated by
8-methoxypsoralen and ultraviolet-A radiation treatment of Jurkat T
leukemia cells and normal T lymphocytes. Haematologica. 89(4):471-9, 2004.

Miller WH Jr. Schipper HM. Lee JS. Singer J. Waxman S. Mechanisms ofaction of arsenic trioxide. [Review] [119 refs] Review. Review, TutorialCancer Research. 62(14):3893-903, 2002.

Montemaggi P. Costamagna G. Dobelbower RR. Cellini N. Morganti AG.Mutignani M. Perri V. Brizi G. Marano P. Intraluminal brachytherapy in thetreatment of pancreas and bile duct carcinoma. International Journal of Radiation Oncology, Biology, Physics. 32(2):437-43, 1995.

Namgung U. Xia Z. Arsenite-induced apoptosis in cortical neurons is mediated by c-Jun N-terminal protein kinase 3 and p38
mitogen-activated protein kinase. Journal of Neuroscience.
20(17):6442-51, 2000.

Nathan CF. Root RK. Hydrogen peroxide release from mouse peritoneal macrophages: dependence on sequential activation and triggering. Journal of Experimental Medicine. 146(6):1648-62 1977.

Roboz GJ. Dias S. Lam G. Lane WJ. Soignet SL. Warrell RP Jr. Rafii S. Arsenic trioxide induces dose- and time-dependent apoptosis of endothelium and may exert an antileukemic effect via inhibition of angiogenesis. Blood. 96(4):1525-30, 2000.

Rojewski MT. Korper S. Thiel E. Schrezenmeier H. Depolarization of mitochondria and activation of caspases are common features of
arsenic(III)-induced apoptosis in myelogenic and lymphatic cell lines. Chemical Research in Toxicology. 17(1):119-28, 2004.

Sakakibara T. Xu Y, Bumpers HL. Chen FA. Bankert RB. Arredondo MA.Edge SB. Repasky EA. Growth and Metastasis of Surgical Specimensof Human Breast Carcinomas in SCID Mice. Cancer J. Scl. Am.2(5):291-300, 1996.

Chen G, Zhu J, Shi X, Zhong H, Liu W, Jin X, Tang W, Li X, Ni J, Xiong S, Shen Z, Ma J, Zhang P, Zhang T, Claude G, Chen S, Chen L, Wang Z. Preliminary study on the arsenic trioxide-induced NB4 cell apoptosis and its molecular mechanisms]
Zhonghua Xue Ye Xue Za Zhi. 1997

Smith AH. Arroyo AP. Mazumder DN. Kosnett MJ. Hernandez AL. BeerisM. Smith MM. Moore LE. Arsenic-induced skin lesions among Atacameno people in Northern Chile despite good nutrition and centuries of exposure. Environmental Health Perspectives.
108(7):617-20, 2000.

Iwama K, Nakajo S, Aiuchi T, Nakaya K. Apoptosis induced by arsenic trioxide in leukemia U937 cells is dependent on activation of p38, inactivation of ERK and the Ca2+-dependent production of superoxide.Int J Cancer. 2001

Stadtman ER. Berlett BS. Fenton chemistry. Amino acid oxidation. Journalof Biological Chemistry. 266(26): 17201-11, 1991.

Stern JE. Li Y. Zhang W. Nitric oxide: a local signalling molecule controlling the activity of pre-autonomic neurones in the paraventricular nucleus of the hypothalamus. Acta Physiologica Scandinavica..177(1):37-42, 2003.

Sturlan S. Baumgartner M. Roth E. Bachleitner-Hofmann T.
Docosahexaenoic acid enhances arsenic trioxide-mediated apoptosis in arsenic trioxide-resistant HL-60 cells. Blood. 101(12):4990-7, 2003.

Suzuki YJ. Forman HJ. Sevanian A. Oxidants as stimulators of signal transduction. Free Radical Biology & Medicine. 22(1-2): 269-85, 1997.

Tanaka-Kagawa T. Hanioka N. Yoshida H. Jinno H. Ando M. Arsenite andarsenate activate extracellular signal-regulated kinases 1/2 by an epidermal growth factor receptor-mediated pathway in normal human keratinocytes. British Journal of Dermatology. 149(6):1116-27, 2003

Urashima M. Chen BP. Chen S. Pinkus GS. Bronson RT. Dedera DA. Hoshi Y. Teoh G. Ogata A. Treon SP. Chauhan D. Anderson KC. The development of a model for the homing of multiple myeloma cells to human bone marrow. Blood. 90(2):754-765, 1997.

Choi YJ, Park JW, Suh SI, Mun KC, Bae JH, Song DK, Kim SP, Kwon TK. Arsenic trioxide-induced apoptosis in U937 cells involve generation of reactive oxygen species and inhibition of Akt.
Int J Oncol. 2002

Winter WE. Maxwell GL. Tian C. Sobel E. Rose GS. Thomas G. CarlsonJW. Association of hemoglobin level with survival in cervical carcinomapatients treated with concurrent cisplatin and radiotherapy: a Gynecologic Oncology Group Study. Gynecologic Oncology. 94(2):495-501, 2004 .

Wu Q. Kirschmeier P. Hockenberry T. Yang TY. Brassard DL. Wang L. McClanahan T. Black S. Rizzi G. Transcriptional regulation during p21/WAF1/Cip1-induced apoptosis in human ovarian cancer cells. J. Biol. Chem. 277, 36329–36337.

Yi J. Yang J. He R. Gao F. Sang H. Tang X. Ye RD. Emodin enhances arsenic trioxide-induced apoptosis via generation of reactive oxygen species and inhibition of survival signaling. Cancer Research. 64(1):108-16, 2004.

Zheng Y. Shi Y. Tian C. Jiang C. Jin H. Chen J. Almasan A. Tang H. Chen Q. Essential role of the voltage-dependent anion channel (VDAC) in mitochondrial permeability transition pore opening and cytochrome c release induced by arsenic trioxide. Oncogene. 23(6):1239-47, 2004.

Yi J, Gao F, Shi G, Li H, Shi X, Tang X. Apoptosis susceptibility of tumor cells to arsenic trioxide and the inherent cellular level of reactive oxygen species. Chin Med J (Engl). 2002

Gao F, Yi J, Shi G, Li H, Shi X, Wang Z, Tang X. Ascorbic acid enhances the apoptosis of U937 cells induced by arsenic trioxide in combination with DMNQ and its mechanism. Zhonghua Xue Ye Xue Za Zhi. 2002.