The study of the impact of autophagy on the radiosensitivity and treatment outcome of cancer

• Main Authors: Hsien-Chun, 曾顯群
• Other Authors: 周芬碧教授
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/52301579297583171894

博士 === 中山醫學大學 === 生化暨生物科技研究所 === 99 === The only curative modality for treatment of primary hepatocellular carcinoma is complete surgical removal. However, few patients can receive complete surgical resection because of frequent late stage at diagnosis. For the treatment of unresectable hepatocellular carcinoma at diagnosis, there are several treatment modalities such as: transarterial chemoembolization (TACE)、intratumoral alcohol injection、radiofrequency ablation (RFA)、biological therapy、chemotherapy and 3-D conformal radiotherapy. In this study, 3-methyladenine (3-MA), an autophagy inhibitor, was investigated for its potential to enhance radio-sensitivity under radio-resistant conditions both in vitro and in vivo. Hep3B and HepG2 cells were used to examine the radioresistance of liver cancer cells. The results show that Hep3B cells respond to irradiation with increased apoptotic cell death and that HepG2 is radio-resistant due to the IR-induced autophagy, as verified by DNA fragmentation, electron microscopy, acidic vesicular organelle formation, and Western blot analysis. Application of IR with 3-MA to inhibit autophagy simultaneously suppressed the expression of LC3 and enhanced cell death. The tumor xenograft model in nude mice verified the synergistic cytotoxic effect of 3-MA and IR, which resulted in significant repression of tumor growth. The results demonstrate that IR-induced autophagy provides a self-protective mechanism against radiotherapy in HepG2 cells. In addition, 3-MA enhances the cytotoxicity of IR in cell models and suppresses tumor growth in animal models. Based on these results, application of 3-MA, or other autophagy inhibitors, could be used as an adjuvant for radiotherapy when radio-resistance develops as a result of autophagy response. Recent studies indicate the existence of CSCs（cancer stem cells）as the main cause of treatment failure and cancer relapse. In our study a total of 34 rectal cancer patients with neoadjuvant chemoradiotherapy and surgery were enrolled. Collection of the cancer tissues including biopsy specimens and surgical specimens was sent for immunohistochemical staining of CD133 ( a cancer stem cell marker) and p62 ( an autophagy marker ). Their reading and grading was executed by two pathologists. Our result showed that high expression of CD133 was correlated to poor patient’s disease-free survival. The expression of p62 marker has no effect on survival. Our data showed TRG4 was significantly related to DFS, but not to OS. Our study demonstrated that IR induced autophagy in HepG2 cells, which contributed to its resistance to radiation. Combination of 3-MA and IR enhanced the cytotoxicity of HepG2 cells. This may be adopted as a new strategy in considering the radiotherapy of liver cancer. A more effective treatment should be developed to eradicate cancer stem cells. It is our future goal to search a new effective biomarker to predict the treatment response of cancer since p62 expression fails to be relevant to survival. It is also important to determine if there is any potential to target autophagy signaling in the elimination of cancer stem cells.