Abstract 236: Pharmacological and genetic inhibition of FAK attenuates cancer stem cell function in vitro and in vivo.
Authors: Kolev Vihren , Wright Quentin , Vidal Christian , Shapiro Irina , Pavdal Mahesh , Keegan Mitchell , Xu Qunli , Pachter Jonathan 
Published: August 2014

Abstract
Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that orchestrates cell signaling through integrins and growth factor receptors. FAK has been implicated in multiple steps of carcinogenesis including tumor initiation, growth and metastasis. Amplification and overexpression of FAK have been observed in multiple aggressive human cancers including breast and ovarian. VS-4718 is a potent and selective FAK kinase inhibitor that was previously shown by us to exhibit preferential inhibitory activities on breast cancer stem cells. We have further extended our investigation of the role of FAK on cancer stem cells to other solid tumors and report here that pharmacological attenuation of FAK activity by VS-4718 or RNAi-mediated depletion of FAK exhibits preferential inhibitory effects on cancer stem cells.
To determine if FAK plays a role in the biology of cancer stem cells, we depleted FAK expression in breast, ovarian and mesothelioma cancer cell lines by RNAi. Our results indicated that shRNA-mediated knock-down of FAK inhibits tumorsphere formation in vitro. In parallel, VS-4718 was evaluated in a multitude of cancer stem cell assays both in vitro and in vivo. Pre-treatment of SUM159 cells with VS-4718 in matrigel reduced the percentage of ALDEFLUOR+ cancer stem cells and side population (SP). Similar effects were observed in ovarian cancer cell lines OVCAR-8 and OVCAR-5 where VS-4718 inhibited cancer stem cells as measured by multiple CSC assays. In an analogous fashion, VS-4718 also reduced the proportion of the ALDEFLUOR+ cells in H2052 human mesothelioma cells. In direct contrast, standard-of-care agents paclitaxel, carboplatin or pemetrexed increased the percentage of cancer stem cells, suggesting these agents do not effectively target cancer stem cells. Importantly combination of VS-4718 with standard-of-care agents attenuated chemotherapy-induced increases in the percentage of cancer stem cells in vitro in all three cancer models.
The in vivo effect of VS-4718 on cancer stem cells was evaluated in SUM159 and MDA-MB-231 human triple negative breast cancer xenograft models. Following systemic administration, VS-4718 significantly reduced the proportion of cancer stem cells in tumors as evidenced by decreases in the percentage of ALDEFLUOR+ cells and tumorsphere-forming efficiency relative to vehicle-treated tumors and significantly abrogated tumor-initiating capabilities of cancer cells in a limiting dilution re-implantation assay.
In summary, our results indicate the importance of FAK in the self-renewal of cancer stem cells in vitro and in vivo, and support the clinical development of FAK inhibitors to target cancer stem cells for the treatment of multiple cancers.
Citation Format: Vihren Kolev, Quentin Wright, Christian Vidal, Irina Shapiro, Mahesh Pavdal, Mitchell Keegan, Qunli Xu, Jonathan Pachter. Pharmacological and genetic inhibition of FAK attenuates cancer stem cell function in vitro and in vivo. [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 236. doi:10.1158/1538-7445.AM2013-236