Abstract 3065: Erlotinib derivative, devoid of EGFR kinase inhibiting effect, induced apoptosis of triple-negative breast cancer cells through modulating Elk-1/CIP2A signaling pathway

Abstract

Abstract Background: Triple-negative breast cancer (TNBC), a subgroup of breast cancer, is characterized by its aggressive nature and poor prognosis. Therefore, the discovery and identification of new therapeutic molecule is currently one of urgent issues. Previous studies have suggested an oncoprotein, cancerous inhibitor of protein phosphatase 2A (CIP2A), is a potential therapeutic determinant that mediates the anti-cancer effects of several new agents. We have developed an erlotinib analogue TD-19 that is devoid of EGFR tyrosine kinase inhibition effect, and demonstrated its anti-tumor effects through the suppression of CIP2A-mediated pathway in non-small-cell lung cancer cells (J Pharmacol Exp Ther 2014). In this study, we tested the apoptotic effect of TD-19 in TNBC cells and examined the drug mechanism upstream of CIP2A. Methods: TNBC cell lines were used for in vitro studies. Cell viability was examined by MTT assay. Apoptosis was examined by flow cytometry and western blot. Signal transduction pathways in cells were assessed by western blot. In vivo efficacy of TD-19 was tested in nude mice with breast cancer xenografts. Results: TD-19 triggered significant apoptosis in MDA-MB-231, MDA-MB-468, MDA-MB-468 and BT-20 cell lines, as well as in non-TNBC cell lines (SK-BR3 and MCF-7). The induced apoptotic effects are associated with CIP2A and p-Akt downregulation in both dose- and time-dependent manners. Overexpression of CIP2A protected MDA-MB-468 from the induced apoptosis of TD-19. In addition, PP2A activity was increased in TD-19 treated MDA-MB-468 cells. Moreover, forskolin, a protein phosphatase 2A (PP2A) activator, enhanced the cell death induced by TD-19, whereas okadaic acid, a PP2A antagonist, attenuated the apoptosis. Mechanistically, we demonstrated that TD-19 downregulated CIP2A mRNA expression through affecting the total amount of Elk-1 in nucleus. Chromatin immunoprecipitation experiments showed TD-19 disturbed the binding of Elk-1 to the proximal CIP2A-promotor. Furthermore, TD-19 showed anti-tumor activity in mice bearing MDA-MB-468 xenograft tumors, and downregulated CIP2A as well as p-Akt in these xenografted tumors. Interestingly, combining TD-19 with cisplatin demonstrated enhanced anti-proliferative and apoptotic effects in association with CIP2A downregulation in vitro. Conclusions: Our results suggest that the novel erlotinib derivative (TD-19) induced apoptosis through inhibiting Elk1/CIP2A/PP2A/p-Akt signaling in TNBC cells. Pharmacological modulation of Elk-1/CIP2A signaling may be a therapeutic strategy for TNBC. (Supported by Yen Tjing Ling Medical Foundation (CI-104-07); MOST 104-2628-B-075-001-MY3; Yang-Ming Branch of Taipei City Hospital; and from the Ministry of Health and Welfare, Executive Yuan, Taiwan, MOHW104-TDU-B-211-124-001; and MOHW103TDU-212-114002). Citation Format: Ling-Ming Tseng, Yi-Ting Chen, Chun-Teng Huang, Pei-Yi Chu, Wan-Lun Wang, Chun-Yu Liu, Chung-Wai Shiau, Kuen-Feng Chen. Erlotinib derivative, devoid of EGFR kinase inhibiting effect, induced apoptosis of triple-negative breast cancer cells through modulating Elk-1/CIP2A signaling pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3065.