Abstract A39: FAK inhibitors VS-6063 and VS-4718 preferentially target ovarian cancer stem cells
Authors: Kolev Vihren N. , Wright Quentin G. , Vidal Christian M. , Tam Winnie F. , Pavdal Mahesh V. , Xu Qunli , Pachter Jonathan A. 
Published: August 2014

Abstract
Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that orchestrates cell signaling through integrins and growth factor receptors and plays important roles in tumorigenesis. Amplification and overexpression of FAK have been observed in aggressive human cancers including ovarian and breast cancers. VS-6063 and VS-4718 are potent, selective, and orally active FAK inhibitors. In a Phase 1 clinical trial, VS-6063 was well tolerated and demonstrated preliminary clinical activity. In addition, we have demonstrated that VS-6063 can be combined with paclitaxel and preliminary signs of clinical activity, including CA-125 reduction to normal levels, were observed with this combination in patients with ovarian cancer. VS-4718 was shown to inhibit tumor growth and metastasis in preclinical tumor models including an ovarian cancer xenograft model and is currently under evaluation in a Phase 1 clinical trial. We have shown previously that inhibition of FAK preferentially targets cancer stem cells in breast cancer models. We extended these studies and report here that the FAK inhibitors VS-6063 and VS-4718 effectively abrogate cancer stem cells (CSCs) in ovarian cancer models.
VS-4718 and VS-6063 were first evaluated in several orthogonal cancer stem cell assays in vitro. Treatment of OVCAR-8 or TOV-21G human ovarian cancer cells with these FAK inhibitors in matrigel reduced the percentage of Aldefluor+ CSCs and attenuated tumorsphere forming efficiency. Accordingly, in a side population (SP) assay assessing CSCs by Hoechst dye exclusion, these FAK inhibitors reduced SP CSCs in the OVCAR-5 ovarian cancer cell line. Similar effects were observed with the breast cancer cell lines SUM159 and MDA-MB-231. In direct contrast, the standard-of-care cytotoxic agents, paclitaxel and carboplatin, increased the percentage of CSCs, indicating that these agents do not effectively target CSCs. Importantly, combination of VS-6063 or VS-4718 with cytotoxic agents attenuated the enrichment of CSCs caused by cytotoxic agents as measured by the Aldefluor assay and in vivo tumor initiating potential. To assess drug effects on tumor-initiating capability, the clearest arbiter of CSC activity, TOV-21G cells were pre-treated in vitro with various compounds and 1,000 of the resulting cells were injected into immunodeficient mice. VS-4718 alone or VS-4718 in combination with paclitaxel prevented tumor initiation, while paclitaxel alone did not reduce tumor initiation, suggesting that treatment with VS-4718 could effectively eliminate tumor initiating CSCs. Furthermore, ex vivo treatment of primary human ovarian cancer tissue with VS-4718 or VS-6063 also reduced the percentage of CSCs as assessed by CD24hi/CD117hi CSC markers and the Aldefluor assay.
In addition to targeting CSCs, we also observed that FAK inhibitors enhanced the activity of paclitaxel to reduce bulk tumor cells both in vitro and in vivo.
In summary, our data indicate that the FAK inhibitors VS-6063 and VS-4718 preferentially target cancer stem cells and enhance the activity of paclitaxel. These results provide rationale for the clinical development of Verastem's FAK inhibitors for the treatment of ovarian cancer.
Citation Format: Vihren N. Kolev, Quentin G. Wright, Christian M. Vidal, Winnie F. Tam, Mahesh V. Pavdal, Qunli Xu, Jonathan A. Pachter. FAK inhibitors VS-6063 and VS-4718 preferentially target ovarian cancer stem cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A39.