Abstract P6-11-06: VS-6063 (defactinib) and VS-4718 reduce cancer stem cells in models of breast cancer: Implications for clinical trials in the neoadjuvant setting
Authors: Kolev Vihren N , McDermott Sean , Wicha Max , Pachter Jonathan A , Xu Qunli , Weaver David T 
Published: May 2015

Abstract
Cancer stem cells (CSCs) are an underlying cause of tumor progression and metastasis. In breast cancer, CSCs can be identified by Aldehyde Dehydrogenase 1 (ALDH) or CD44-high/CD24-low expression. Neoadjuvant chemotherapy has been shown to lead to an increase in CSCs in locally advanced breast cancer (Alamgeer et al., 2014, Br. Can. Res. R14). In addition, the presence of CSCs in residual axillary disease is associated with a significantly worse prognosis following neoadjuvant chemotherapy and surgery (Sakakibara et al. 2011, Cancer 3899, 2011). Currently, there are no approved therapies that effectively target and kill CSCs. VS-6063 and VS-4718 are orally bioavailable small molecules that kill cancer stem cells through the inhibition of Focal Adhesion Kinase (FAK). Both VS-6063 and VS-4718 have demonstrated preferential targeting of CSCs in preclinical models and are currently in clinical development.
Here we report that VS-6063 and VS-4718 effectively kill CSCs in multiple models of breast cancer. In an ex vivo model, biopsies from human breast tumors were obtained and cultured as primary explants within 24 hours of surgery. The primary explants were incubated with VS-6063, VS-4718 or paclitaxel for 4 days. Treatment with either VS-6063 or VS-4718 decreased the proportion of CSCs in contrast to paclitaxel. VS-6063 and VS-4718 diminished the self-renewal capacity of primary cultures from established TNBC patient-derived xenografts as measured by tumorsphere assays. In a MDA-MB-231 mouse xenograft model, treatment with VS-6063 decreased CSC more than 6-fold in an in vivo limiting dilutions assay. Similarly, using an imaging-based 4T1-luciferase TNBC orthotopic model, both VS-6063 and VS-4718 diminished the size of metastatic nodules within two weeks.
CSCs are readily detectable in primary breast cancers at surgery, yet methods to detect these populations are still developing. A multiplex assay for the CSC markers, ALDH1, CD44 and CD24, was explored with biopsies of primary tumor and matched lymph node, and primary tumors taken pre- and post-neoadjuvant chemotherapy. Consistent with previously reported data, elevated levels of ALDH were observed at higher levels post-treatment, and in lymph nodes. In addition, zones of ALDH+ and CD44-high/CD24-low tumor cells can be mapped with the multiplex assay for the potential detection of CSCs in breast cancer biopsies.
In summary, VS-6063 and VS-4718 diminish the CSC subpopulation in vitro, ex vivo and in xenograft models using a number of functional and biomarker assays. This critical subpopulation of CSCs is detectable in residual tumor following neoadjuvant therapy. Potentially, multiplex assays of CSC markers will be an improved means to monitor CSCs in clinical specimens. CSC-targeted agents such as VS-6063 or VS-4718 should be clinically tested in the neoadjuvant setting to potentially delay time to relapse and improve patient outcome.
Citation Format: Vihren N Kolev, Sean McDermott, Max Wicha, Jonathan A Pachter, Qunli Xu, David T Weaver. VS-6063 (defactinib) and VS-4718 reduce cancer stem cells in models of breast cancer: Implications for clinical trials in the neoadjuvant setting [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-11-06.