Abstract 4390: Non-coding RNAs in EGFR therapy resistance in breast cancer

Abstract

Abstract The purpose of this study is to identify novel mechanisms of resistance to epidermal growth factor receptor (EGFR) targeted therapies. The initial success of EGFR targeted therapies such as gefitinib and lapatinib has been confounded by intrinsic or acquired therapy resistance. Emerging data, including our studies, show drug-induced dysregulation of non-coding RNAs (ncRNAs) that may downregulate multiple effectors of chemoresistance by transcriptional or post-transcriptional regulation. To investigate the role of ncRNAs in regulation of EGFR therapy resistance, we created syngeneic therapy sensitive and resistant breast cancer (BC) cell lines by exposing therapy sensitive SKBR3 and BT-474 cells to different concentrations of gefitinib or lapatinib. Differentially expressed ncRNAs in resistant and sensitive cells were identified from quantitative RT-PCR analysis and their targets detected by Western blot. A long ncRNA (lncRNA) that we have named Colon Cancer Associated Transcript 2 (CCAT2) (Ling et al., Genome Res. 2013, 23:1446-61) was downregulated in EGFR/HER2 therapy resistant BC cells. The microRNA miR -221/222 was upregulated in parallel with decreased CCAT2. Increased miR-221/222 and decreased miR-200 family have been associated with cancer malignancy and epithelial to mesenchymal transition (EMT), a hallmark of therapy resistance. Accordingly, miR-200a was downregulated in EGFR therapy resistant BC cells. miR-200 family plays an important role in suppression of EMT by downregulation of zinc finger E-box binding homeobox (Zeb)1/2 and β-catenin. Zeb 1/2 are negative regulators of E-cadherin, and β-catenin is a potent pro-cancer transcriptional activator in the absence of an E-cadherin axis. Results show upregulation of Zeb1, β-catenin and its transcriptional effector c-Myc, and stem cell-like marker CD44, while E-cadherin was downregulated in the E-cadherin positive BT-474 cells. We also found downregulation of miR-221/222 targets, PTEN and APAF1, in the SKBR3 resistant variants, which is consistent with the upregulation of miR-221/222 expression. In conclusion, this data suggest that downregulation of CCAT2 and miR-200 family, and upregulation of miR-221/222 contributes to EGFR targeted therapy resistance. Therefore, targeting these ncRNAs maybe a viable alternative to overcoming therapy resistance in BC. Citation Format: Luis D. Borrero-García, Linette Castillo-Pichardo, Roxana S. Redis, George A. Calin, Suranganie Dharmawardhane. Non-coding RNAs in EGFR therapy resistance in breast 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 4390. doi:10.1158/1538-7445.AM2014-4390