Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that controls cell motility and survival downstream of integrin receptors. FAK expression and activity are elevated during breast and ovarian cancer progression and this is associated with a poor clinical prognosis. Small molecule FAK inhibitors (FAK-I) block breast and ovarian tumor progression through a novel mechanism that is associated with the apoptosis under anchorage-deprived conditions. Metastatic cells can grow as anchorage-independent spheroids and we hypothesize that a spheroid micro-environment remains dependent on integrin- and FAK-associated signaling for survival. Here we show that intraperitoneal (ip) injection of murine ID8 ovarian carcinoma cells into mice, recovery of ascites-associated tumor cells (ID8ip) and growth ex vivo, yielded tumor cells with elevated levels of phosphorylated FAK (Y397 and Y576 phosphorylation), αvβ5 integrin, and osteopontin (OPN) matrix protein expression compared to parental ID8 cells. Analyses of paraffin-embedded breast and ovarian tumor sections revealed significantly higher pY397 FAK (p<0.05), β5 integrin (p<0.0001), and OPN expression (p<0.005) in stage II-III compared to stage I tumors. Treatment of ovarian ID8ip, human ovarian HEY carcinoma, or human MDA-MB-231 breast carcinoma cells with FAK-I inhibited cell growth, prevented FAK Y397 phosphorylation, reduced β5 integrin and OPN levels independent of effects on β1 or β3 integrins or changes in matrix proteins such as fibronectin. FAK-I impairs anchorage independent cell growth and orthotopic tumor growth but not growth of cells in plastic-adherent cell culture. Stable knockdown of either FAK or β5 integrin in HEY cells prevented anchorage-independent growth. Re-expression of wildtype or kinase-dead FAK within HEY cells verified the importance of FAK activity in promoting β5 integrin and OPN expression associated with enhanced tumor growth. Ongoing studies are focused on determining the molecular connections of FAK to the regulation of αvβ5 and OPN expression. Together, our studies support a novel role for a signaling loop involving OPN and αvβ5 integrin leading to FAK activation and reinforcement of OPN and β5 integrin expression within the spheroid and tumor micro-environment enhancing breast and ovarian cancer cell survival and tumor progression. Supported by Susan G. Komen for the Cure (KG111237) and NIH grant CA102310

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1254. doi:1538-7445.AM2012-1254