Abstract B52: PTK6 inhibition as a novel strategy to reverse EMT and suppress metastasis of triple negative breast cancer

Abstract

Abstract Triple negative breast cancer (TNBC) poses clinical challenges due to intrinsic biological aggressiveness and lack of targeted therapies. Hypothesis: Protein tyrosine kinase 6 (PTK6) regulates epithelial-mesenchymal transition (EMT) of TNBC, as well as their growth and metastatic potential. We evaluated PTK6 as a promising therapeutic target to prevent metastases of TNBC. Experimental Procedures: Levels of PTK6 have prognostic significance; higher transcript levels are associated with poor outcomes for patients. We modulated the level of PTK6 in breast epithelial and TNBC cell lines, and determined effects on growth, migration, epithelial-mesenchymal transition and metastasis formation in vivo. Results: PTK6 promotes EMT; overexpression of kinase active PTK6 (Y447F) in non-transformed MCF10A cells promotes migration, suppresses expression of epithelial markers (E-cadherin, claudin-1), and increases expression of N-cadherin and fibronectin, markers of mesenchymal cells. Promotion of EMT is dependent on PTK6 kinase activity as overexpression of catalytically inactive PTK6 (K219M) failed to induce EMT. Downregulation of PTK6 in mesenchymal TNBC cells (human MDA-MB231 or murine MMTV-myc) restores epithelial properties and suppresses migration and growth in 3-D MatrigelTM cultures. PTK6 inhibition-induced E-cadherin expression is due to decreased expression of Snail, a transcriptional repressor of E-cadherin. PTK6 downregulation promotes the proteasome-dependent degradation of Snail protein, via a mechanism that is independent of GSK3β activity. PTK6 inhibition promotes anoikis of TNBC cells in vitro and prevents metastases in vivo; decreased metastasis formation is directly linked to PTK6-dependent regulation of EMT and E-cadherin levels. Conclusions: Our studies support PTK6 inhibition as a novel strategy to impair metastasis of TNBC cells via reversal of mesenchymal properties. The kinase dependency of EMT regulation by PTK6 highlight the potential for clinical translation of recently developed PTK6 kinase inhibitors as a therapeutic strategy for patients with triple negative breast cancers. Citation Format: Koichi Ito, Sun Hee Park, Hanna Y. Irie. PTK6 inhibition as a novel strategy to reverse EMT and suppress metastasis of triple negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B52.