Studies On The Lung Cancer Cell Death Induced By Radiotherapy Combined With Chemotherapy And Related Mechanisms

Radiation therapy and chemotherapy is one of effective treatments to lung cancer, through a variety of signaling pathways ionizing radiation and chemotherapy drugs can induce tumor cells death. The research about apoptosis has more thorough and perfect, but autophagy, type II programmed cell death, the role played by much dispute in this process. in physiological condition, through autophagy cells can degrade damaged, aging and loss of function long life protein, organelles, and realize material and energy recycle, is a kind of cell survival mechanism. But when the outside stimulus too large or time is too long, through the process of autophagy material excessive degradation will lead to programmed cell death. It reports that in human lung cancer cell A549 and H460 ionization radiation can cause autophagy, using autophagy inducer or joint ionizing radiation can increase cytotoxicity effect of radiation.In early research the role of ionizing radiation and chemotherapy drugs is more in inducing apoptosis induced or from the cell level of autophagy. However, in non-small cell lung cancer tumors xenograft, and the role of autophagy and its relationship with apoptosis have not been reported.In vitro using MDC staining and cellular immune fluorescence technology, autophagy is detected in non-small cell lung cancer cell lines A549 after ionizing radiation (F=7.0,P <0.05). And in vivo Lewis lung carcinoma model in mice was conducted to evaluate the effect of different radiotherapy program(conventional fractionated irradiation combined with cisplatin group (combined group), conventional fractionated irradiation group, hyperfractionated radiation group, radiation alone group and the control group),and immunohistochemical method was used to detect autophagy and apoptosis related gene expression changes. Compared with control, autophagic dots increase clearly in 2Gy and 8 Gy in 16h and 24h.In addition, cytotoxic can be detect after cisplatin treatment using MTT assay.In vivo, the animals model verified the synergistic cytotoxic effect of ciaplatin and irradiation resulting in a substantial shrinkage of tumor volume(F=12.47,P<0.001). Immunohistochemistry staining showed an increased proportion of DRAM,PI3Kâ…¢,BECLIN1 and LC3â…¡-positive cells(F=7.885,p<0.001;F=19.79, p<0.001; F=3.509, p<0.05,F= 34.04, p<0.001), and an BCL-2 and p-AKT decreased proportion(F=23.87,p<0.001;F= 54.52, p<0.001), demonstrating that cisplatin enhanced radiosensitivity via autophagy. In addition the increased apoptosis protein expression p21 (F=83.87, p<0.001)were also found in conventional fractionated irradiation group and hyperfractionated radiation group, ciaplatin in combination with radiation compared with control. But BAX and MDM2 have no significant change.It showed apoptosis enhancement on ciaplatin in combination with radiation have inhibition tumor effect. Our report suggests that induction of autophagy through combined cisplatin and radiotherapy is a potential therapeutic strategy in patients with non-small cell lung cancer.