Abstract 1991: Vulnerability of platinum-resistant ovarian cancer to FAK inhibition
Authors: Osterman Carlos J. Diaz , Bean Lisa M. , Sulzmaier Florian J. , Taylor Kristin N. , Jiang Shulin A. , Tancioni Isabelle , Anderson Kristen , Jean Christine , Chen Xiao Lei , Kleinschmidt Elizabeth G. , Kolev Vihren N. , Weaver David T. , Pachter Jonathan A. , Connolly Denise C. , Molinolo Alfredo , Schlaepfer David D. 
Published: August 2018

Abstract
Platinum (CP)-resistant ovarian cancer (OC) has few effective treatment options. Adaptive chemotherapy resistance occurs in part through cancer stem cell (CSC) generation. Wnt/beta-catenin signaling is a driver of CSC survival via induction of gene expression, including aldehyde dehydrogenase (ALDH) enzymes. The gene for focal adhesion kinase (FAK) is commonly amplified in advance-stage OC and this is associated with decreased patient survival. How FAK is activated in OC and whether this is connected to CSC survival is unknown. Here, we find that FAK Y397 phosphorylation (a marker of FAK activation) is increased in non-necrotic Pax8-positive OC tumor tissue after neo-adjuvant chemotherapy compared to paired pre-treatment tumor biopsy samples. FAK activation occurs after CP plus paclitaxel treatment of xenograft tumors, within 60 min of CP treatment of OC cells, and FAK Y397 levels are constitutively-elevated in OC cells pre-adapted to exhibit elevated CP resistance. Pharmacological FAK inhibition (VS-4718, 0.1 µM) selectively prevented CP-resistant tumorsphere formation in vitro and combined with CP to promote cell apoptosis. Combinatorial VS-4718, CP, and paclitaxel chemotherapy exhibited additive inhibitory effects in preventing CP-resistant tumor growth in mice. VS-4718 monotherapy of tumor-bearing mice reduced tumor-associated ALDH activity and resulted in an 85-fold reduction in secondary tumors formed in limiting dilution assays. CRISPR-mediated FAK knockout in OVCAR3 cells combined with stable re-expression of FAK wildtype or a kinase-inactive FAK (K454R) mutant revealed that intrinsic FAK activity was essential for beta-catenin activation, ALDH-1A1 expression, and OVCAR3 tumorsphere growth. As activated constructs of beta-catenin but not YAP1 rescued FAK KO OVCAR3 phenotypes, these studies provide important insights into a FAK signaling linkage to beta-catenin in promoting CSC survival and adaptive resistance to CP chemotherapy. These studies provide the foundational support for a Phase I-II clinical trial for treatment of recurrent platinum-resistant ovarian cancer (NCT03287271) termed ROCKIF: Re-sensitization of carboplatin-resistant Ovarian Cancer by Kinase Inhibition of FAK. As FAK is activated in tumor cells surviving carboplatin-paclitaxel chemotherapy, co-targeting of this FAK/beta-catenin adaptive resistance pathway may expose a vulnerability of CP-resistant tumors.
Citation Format: Carlos J. Diaz Osterman, Lisa M. Bean, Florian J. Sulzmaier, Kristin N. Taylor, Shulin A. Jiang, Isabelle Tancioni, Kristen Anderson, Christine Jean, Xiao Lei Chen, Elizabeth G. Kleinschmidt, Vihren N. Kolev, David T. Weaver, Jonathan A. Pachter, Denise C. Connolly, Alfredo Molinolo, David D. Schlaepfer. Vulnerability of platinum-resistant ovarian cancer to FAK inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1991.