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HER3 exerts resistance against epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), resulting in tumor relapse in lung cancers. Previously, we have demonstrated that EGFR induces HER3 overexpression and that contributes to the formation of cancer stem-like tumorspheres. However, the cellular mechanism of EGFR in regulating HER3 expression was obscure. We hypothesized that EGFR-downstream STAT3 participates in HER3 expression since STAT3 contributes to cancer stemness and surviving EGFR-TKIs. First, RNAseq was used to uncover the potential genes involving in formation of lung cancer HCC827-derived stem-like tumorspheres. EGFR-positive lung cancer cell lines (HCC827, A549, H1975) were individually treated with a panel containing 172 compounds which targeting to stem cell-associated genes in order to searching potential agents against EGFR-positive lung cancers. In addition, gene knockdown and RNAseq were used for investigating the molecular mechanism of STAT3 on regulating tumor progression and survival of lung cancers. We found that BBI608, a STAT3 inhibitor, was a potential therapeutic agent specifically reducing the cell viability of EGFR-positive lung cancers. Interestingly, the inhibitory effects caused by BBI608 were similar with that derived from YM155, an ILF3 inhibitor, both compounds reduced G9a-mediated HER3 expression. We, furthermore, demonstrated that STAT3 upregulated G9a to silence miR-145-5p for exacerbating HER3 expression in this study. In conclusion, this study figured out the potential cellular function of STAT3 in EGFR-positive lung cancers. We also evaluated that BBI608 was potential to eradicate EGFR-positive lung cancers and demonstrated that STAT3 regulated expression of HER3, indicating that STAT3 was a reliable therapeutic target against EGFR-TKI-resistant lung cancers. Note: This abstract was not presented at the meeting. Citation Format: Chun-Chia Cheng, Ya-Wen Chiang, Ken-Hong Lim, Jungshan Chang, Ai-Sheng Ho, Yi-Fang Chang. STAT3 represses miR-145-5p to exacerbate HER3 expression for surviving EGFR-TKIs in lung cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3028.

Objectives: YM155, an inhibitor of interleukin enhancer-binding factor 3 (ILF3), significantly suppresses cancer stemness property, implying that ILF3 contributes to cell survival of cancer stem cells. However, the molecular function of ILF3 inhibiting cancer stemness remain unclear. This study aimed to uncover the potential function of ILF3 involving in cell survival of epidermal growth factor receptor (EGFR)-positive lung stem-like cancer, and investigate the potential role to improve the efficacy of anti-EGFR therapeutics. Materials and Methods: The regulated association of EGFR and ILF3 was investigated at first. ILF3 was knockdowned and RNAseq was utilized to search for the putative genes regulated by ILF3. Meanwhile, HCC827- and A549-derived cancer stem-like cells were used to investigate the role of ILF3 in the formation of cancer stem-like tumorspheres. Results: We found that EGFR induced ILF3 expression, and YM155 reduced EGFR expression. The knockdown of ILF3 reduced not only EGFR expression in mRNA and protein levels, but also cell proliferation in vitro and in vivo, demonstrating that ILF3 was an oncoprotein contributing to cancer cell survival. Moreover, the knockdown and inhibition of ILF3 by shRNA and YM155, respectively, reduced the formation and survival of HCC827- and A549-derived tumorspheres through inhibiting HER3/ERBB3 expression, and synergized the therapeutic efficacy of afatinib, a tyrosine kinase inhibitor, against EGFR-positive A549 lung cells. Conclusion: This study demonstrated that ILF3 played an oncogenic role maintaining the EGFR-mediated cellular pathway as a therapeutic target to improve the therapeutic efficacy of afatinib. Therefore, we suggested that YM155, an ILF3 inhibitor, was potential for utilization in cancer therapy against the EGFR-positive cancers. Citation Format: Chun-Chia Cheng, Kuei-Fang Chou, Cheng-Wen Wu, Nai-Wen Su, Cheng-Liang Peng, Ying-Wen Su, Jungshan Chang, Ai-Sheng Ho, Huan-Chau Lin, Caleb Gon-Shen Chen, Yu-Cheng Chang, Ken-Hong Lim, Yi-Fang Chang. EGFR-mediated interleukin enhancer-binding factor 3 contributes to formation and survival of cancer stem-like tumorspheres through regulating HER3/ERBB3 expression as a therapeutic target against EGFR-positive non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3060.

Cancer stem cells survive and lead to tumor recurrence in tumor therapeutic treatments. Lung cancer cells highly express epidermal growth factor receptor (EGFR), which is critical for tumor progression. We hypothesized that EGFR may play a pivotal role in the induction of cancer stemness cells (CSCs). The aim of this study attempted to investigate the molecular mechanism of EGFR-mediated cancer stemness, and to discover the potent therapeutic agents. A high expression level of cancer stemness markers, ALDH1, CD133, Oct4, and Nanog was observed in tumorspheres derived from HCC827. External EGF further elevated the expression of Oct4 in HCC827 cells. Moreover, chemical inhibition and genetic knockdown of EGFR reduced the Oct4 expression and also tumorsphere formation. We found that inhibitors targeting to EGFR (afatinib), ILF3 (YM155), and G9a (UNC0642) are potential to reduce the formations of tumorspheres. The results revealed that EGFR triggered the formation of tumorspheres through elevating the activations of G9a-mediated stemness genes. In addition, YM155 effectively inhibited tumor growth and formation of tumorspheres as an anti-lung cancer agent blocking the EGFR-G9a cell initiating program pathway. This study demonstrated that EGFR participated in maintain of cancer stemness property through expressing ILF3 and G9a expressions. YM155 inhibited the EGFR-G9a stemness pathway, and reduced the formation of tumorspheres as a potent anti-lung cancer agent. Citation Format: Chun-Chia Cheng, Jungshan Chang, Huan-Chau Lin, Ai-Sheng Ho, Ken-Hong Lim, Chun-Chao Chang, Yi-Fang Chang, Cheng-Wen Wu. EGFR induces ILF3 and G9a expressions to maintain Oct4-mediated stemness property in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 934. doi:10.1158/1538-7445.AM2017-934