Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase which mediates integrin and growth factor receptor signaling to regulate tumor growth, metastasis and angiogenesis. FAK is also required for the proliferation/survival of cancer stem cells (CSCs). Protein tyrosine kinase 2 (PYK2) is the most closely related protein kinase to FAK, sharing 60% amino acid identity in the kinase domain and a similar role in cellular signaling pathways. Several lines of evidence suggest that dual targeting of FAK and PYK2 should confer greater antitumor efficacy than an agent which only inhibits FAK. Inhibition of tumor angiogenesis or mammary stem cells by FAK inhibition can be bypassed by PYK2 activity, suggesting advantages of dual FAK/PYK2 inhibition. Accordingly, a critical role of PYK2 in CSC regulation and NSCLC patients’ prognosis has recently been reported (Kuang et al. 2013, Br J Cancer). Furthermore, preclinical data suggest that PYK2 inhibition can prevent growth of metastatic tumor cells in bone. Results of PYK2 knockout in mice suggest that PYK2 inhibition is likely to be well tolerated. Based on the observation of reduced macrophage infiltration in PYK2 knockout mice, we investigated effects of PYK2 inhibition on tumor-associated macrophages (TAMs). Abundance of TAMs has been correlated with poor prognosis in multiple cancer types including mesothelioma and breast cancer. Defactinib is a potent and orally active inhibitor of FAK kinase activity. Preliminary clinical activity has been observed in a Phase 1 single agent trial and in an ongoing trial in combination with paclitaxel in patients with ovarian cancer. We find that in addition to potent FAK inhibition, defactinib also inhibits PYK2 kinase activity with nanomolar potency in both biochemical enzymatic and cellular autophosphorylation assays. Using both pharmacological FAK inhibitors and FAK siRNA, we have previously demonstrated that FAK inhibition effectively reduces CSCs. We report here that dual targeting of FAK and PYK2 by defactinib may more effectively suppress CSCs than inhibition of FAK alone. We find that differentiated THP-1 macrophages release IL-6 and IL-8, and these cytokines increase the proportion of ALDH-positive CSCs in mesothelioma and breast cancer cell lines. Defactinib dose-dependently inhibited production of IL-6 and IL-8, whereas a FAK-only reference inhibitor had no effect on these cytokines. Furthermore, in MM87 mesothelioma and MDA-MB-231 breast cancer xenograft models, defactinib substantially reduced the number of F4/80-positive TAMs in the tumors. These data support a model in which TAMs release IL-6 and IL-8 in a PYK2-dependent manner. Dual inhibition of FAK and PYK2 by defactinib effectively decreases both the presence of TAMs in tumors and the ability of TAMs to release cytokines that stimulate CSC proliferation and survival, and may therefore provide the opportunity for more durable clinical response than inhibition of FAK alone.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B283.

Citation Format: Jennifer E. Ring, Vihren N. Kolev, Irina M. Shapiro, Quentin G. Wright, Joseph R. Testa, Mahesh V. Padval, Qunli Xu, Jonathan A. Pachter. Defactinib (VS-6063) targets cancer stem cells directly and through inhibition of tumor-associated macrophages and cytokine production. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B283.