Characterization of INCB081776, a potent and selective dual AXL/MER kinase inhibitor

Tyro-3, Axl, and Mer constitute the TAM family of receptor tyrosine kinases (RTKs), which are amplified, translocated, or over-expressed in numerous types of human cancer. These RTKs play important roles in tumor growth, survival, cell adhesion and migration as well as drug resistance. In addition, it has been shown that both AXL and MER are critical regulators of innate immunity, phagocytosis, and immune-suppressive activity. Therefore targeting both AXL and MER kinases may not only impact the growth, survival and malignant progression of neoplastic cells directly, but also has the potential to restore and enhance host immunity against cancers. INCB081776 is a potent inhibitor of AXL and MER that exhibits selective pharmacological activity and enhanced anti-tumor immune activity. In biochemical assays, INCB081776 potently inhibited the kinase activity of recombinant AXL/MER enzymes and was highly selective against a panel of 192 kinases (IC 50 = 0.61±0.31 nM and 3.17±1.97 nM against AXL and MER, respectively). INCB081776 is greater than 30 fold selective against TYRO3. Selectivity against TYRO3 is important as retinal toxicity associated with loss of the Mer gene appears to be modulated by TYRO3 in mice. In cellular assays, INCB081776 effectively blocked auto-phosphorylation of AXL or MER including BAF3 cells transfected with constitutively active AXL or MER, AXL in H1299 tumor cells, or MER kinase in G361 tumor cells, with low nanomolar IC 50 values. In addition, INCB081776 inhibited activation of MER kinase in primary human macrophages with low nanomolar IC 50 potency. More importantly, in an in vitro functional assay, INCB081776 partially reversed M2 macrophage-mediated suppression of T cell proliferation, and increased IFN-γ in co-cultured macrophages and T cells. In vivo, INCB081776 administration to H1299 tumor-bearing mice dose-dependently inhibited the phosphorylation in tumors. Consistent with the proposed mechanism of action, INCB081776 potently inhibited tumor growth in immunocompetent mice, but not in immunodeficient mice, demonstrating that a functional immune system is important for activity. Treatment was associated with dose-related increases in the percent of tumor-infiltrating effector CD4+ and CD8+ T cells, as well as macrophages with the M1 phenotype. In addition, INCB081776 decreased the percentage of intratumoral M2 macrophages and monocytic myeloid-derived suppressor cell (M-MDSC) immune cell populations. In the 4T1 model, combining INCB081776 with anti-PD-L1 resulted in synergistic anti-tumor effects compared to either single agent. Collectively, these preclinical data support the hypothesis and potential therapeutic utility of INCB081776 as an immunotherapeutic agent capable of enhancing tumor immune surveillance mechanisms in cancer patients as a single agent and when combined with therapies mediating immune PD-L1 checkpoint blockade. Citation Format: Margaret Favata, Kerri Lasky, Yvonne Lo, Patricia Feldman, Jun Li, Yaoyu Chen, Christina Stevens, Min Ye, Hui Wang, Ke Liu, Richard Wynn, Yanlong Li, Jennifer Harris, Robert Landman, Yu Li, Xiaozhao Wang, Chunhong He, Yun-Long Li, Chu-Biao Xue, Wenqing Yao, Jonathan Rios-Doria, Zhenhai Gao, Maryanne Covington, Xuesong M. Liu, Holly Koblish, Peggy Scherle. Characterization of INCB081776, a potent and selective dual AXL/MER kinase inhibitor [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 3759.