Abstract 3741: Cancer stem cell-like population from non-small cell lung cancer is preferentially suppressed by EGFR-TKIs.
Authors: Yang Fan , You Jiacong , Li Yang , Liao Jiayu , Zhou Qinghua 
Published: August 2014

Abstract
Lung cancer is the leading cause of death worldwide with a high metastasis rate. Non-small cell lung cancer accounts for 75-85% of lung cancers. Growing evidences show that some, if not all, tumors derive from a minor subpopulation of cancer cells, also known as cancer stem-like cells (CSCs), either retain or acquire the capacity for self-renewal and drug resistance. By the virtue of altered cell signaling pathways related to cell survival and/or apoptosis, CSCs are able to survive radiation or chemotherapeutic insults. Thus, the targeting of key signaling pathway(s) that is active in CSCs is very attractive therapeutic strategy to treating cancers. However, research has been hampered due to the lack of distinct molecular makers on CSCs. We take advantage of a rare subset of cells that can efflux the DNA binding dye out of the cell. These cells, called side population (SP) cells, are proved to be enriched with CSCs and have stem cell characteristics.
We evaluated the existence of SPs in PC-9 cells by staining them with Hoechst 33342. SP cells occupied 0.6-2.4% of the total cells in PC-9 cultures. It was noteworthy that the SP was completely eliminated in the presence of Verapamil. Consistent with our hypothesis that EGFR-TKIs regulate CSC, constitutive activation of EGFR increased the subpopulation almost 4.5-fold to 4.0%, whereas EGFR-TKI almost completely ablated it resulting in only 0.2% or 0.3% of the total cells. To understand the molecular mechanism(s) that EGF promote CSC population, the phosphorylation of EGFR at Tyr1068, AKT at Ser473 and ERK at Thr202/Tyr204 were investigated and they are all positive. More interestingly, EGFR/PI3K/AKT signaling inhibitors including Gefitinib, LY294002, U0126 and Erlotinib, significantly reduced the stem-like cancer cells. These results strongly suggested the importance of EGFR/PI3K/AKT as a potential target of eliminating CSCs. To verify that the effect of EGFR-TKIs on CSC phenotypes is mediated through β-catenin signaling, we used CSC-specific siRNAs to suppress β-catenin expression in PC-9 cells. A significant decrease in cancer stem-like cells was observed following β-catenin suppression. The treatment with Gefitinib dramatically reduced the tumor numbers and size in vivo xenograft model with PC9 cells. Although there were few SP cells (1.3% as detected) in Gefitinib-treated mice in the primary tumors, more discernible numbers of SP cells were detected in Cisplatin-treated (13.6%) or control-treated tumors (8.3%). Most notably, the reduction of SP cells by Gefitinib significantly reduced the migration capability. As a comparison, those primary culture cells derived from Cisplatin-treated tumors had an increased migration rate. Our discoveries raise an intriguing question of the role of β-catenin in acquired resistance of EGFR-TKIs-treated cancer stem cell-like population(s) and its potential as new treatment strategy for NSCLC in the future.
Citation Format: Fan Yang, Jiacong You, Yang Li, Jiayu Liao, Qinghua Zhou. Cancer stem cell-like population from non-small cell lung cancer is preferentially suppressed by EGFR-TKIs. [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 3741. doi:10.1158/1538-7445.AM2013-3741