Abstract LB-210: IL-6 promotes stemness of cancer stem cells and may contribute to radiation resistance of non-small cell lung cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Lung cancer is the leading cause of cancer-related deaths among both men and women. Long-term survival of lung cancer patients remains low despite aggressive therapies including surgery, radiation, and chemotherapy. Ionizing radiation (IR) is the standard therapy for patients diagnosed with localized unresectable non-small cell lung cancer (NSCLC). However local tumor control by standard fractionated radiotherapy (RT) remains poor due to tumor resistance to IR. Accumulating evidences have indicated that cancer stem cells (CSCs, also known as cancer initiating cells) exist as a very minor population in NSCLC tumors, which are composed of heterogeneous cell populations. Our laboratory and others found that CSC population increases upon irradiation, which may contribute to radiation resistance. The role of IL-6 in NSCLC progression has been suggested since high IL-6 levels were detected in sera of lung cancer patients, but not detectable in most patients with benign lung diseases. However, the exact mechanism by which IL-6 influences lung cancer progression and its role in CSCs mediated radioresistance remain unresolved. Methods: We isolated CD133+ CSC population from 3 NSCLC cell lines (NSCLC-CSCs) and studied the role of IL-6 in CD133+ CSCs growth by treating cells with IL-6. In addition, we manipulated IL-6 expression levels in the IL-6 expressing A549 and H157 cells by the knockdown of IL-6 using lentiviral infection system carrying IL-6siRNA and isolated CD133+ cells for further analyses. The growth and stem cell marker expressions of these CSCs, IL-6 treated or non-treated, or IL-6 expressing or knocked down cells upon irradiation were then investigated. The differences in the activation of signaling pathways and neuroendocrine differentiation were also studied. Results and Conclusions: We found that IL-6 increased self-renewal of NSCLC-CSCs significantly and thereby increased NSCLC-CSC population. We also found that IL-6 increased stemness of the isolated CD133+ CSCs when CD133+ cells were treated with IL-6. More importantly, when we irradiated the CD133+ CSCs isolated from the IL-6 knocked down and scramble control A549 cells, we found that the CSCs isolated from the IL-6 knocked down cells exhibited lower survival than the CSCs of control cells. Therefore, we suggest that IL-6 may contribute to NSCLC-CSCs mediated-radioresistance via (i) direct triggering radioresistance, and (ii) increasing self-renewal and stemness of the survived CSCs. Mechanistic dissection studies revealed that the increased self-renewal of CSCs by IL-6 is due to the activation of the hedgehog signaling and the increased expression of bcl-2, while the IL-6 mediated increase of radioresistance is due to the activation of neuroendocrine differentiation, Stat 3 signaling pathway, and increased expression of bcl-2. Citation Format: Yuhchyau Chen, Ying Tsai, Jong-Wei Hsu, Shan-Zhou Duan, Peter Keng, Soo Ok Lee. IL-6 promotes stemness of cancer stem cells and may contribute to radiation resistance of non-small cell lung cancer. [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-210. doi:10.1158/1538-7445.AM2014-LB-210