Abstract 3535: Simultaneous inhibition of Axl and MerTK enhances anti-PDL1 efficacy and creates a pro-inflammatory tumor immune microenvironment in head and neck cancer
Authors: Kostecki Kourtney L. , Iida Mari , Wiley Anne L. , Hong Seungpyo , Salgia Ravi , Harari Paul M. , Wheeler Deric L. 
Published: June 2022

Abstract
The tyrosine kinase receptors Axl and MerTK, known for their role on macrophages in regulating clearance of apoptotic cells, are highly overexpressed in head and neck cancer (HNC). Previous studies in our laboratory have shown that Axl is a critical driver of survival, proliferation, metastasis, and therapeutic resistance in HNC, and that MerTK is functionally redundant to Axl. In this study, we investigated the cooperative role of Axl and MerTK in creating an immunologically cold tumor immune microenvironment (TIME) by targeting both receptors simultaneously with a small molecule inhibitor of Axl and MerTK (INCB081776). Because Axl and MerTK are expressed on both macrophages and HNC cancer cells, we examined the effect of INCB081776 treatment on each cell type. In macrophages, Axl and MerTK signaling leads to M2-type polarization, an anti-inflammatory state that leads to the resolution of inflammation and, in cancer settings, promotes tumor growth. Our experiments suggest that treatment with INCB081776 can reduce M2 polarization and increase M1-type polarization, a pro-inflammatory state that promotes inflammation and tumor cell killing. Next, to determine the efficacy of INCB081776 on HNC cancer cells, mouse oral cancer (MOC) tumors were implanted in syngeneic mice and treated with INCB081776 alone or in combination with a monoclonal antibody against PDL1 (anti-PDL1), thereby mimicking current standard-of-care immune checkpoint inhibitor treatment. The results showed a marked effect of INCB081776 single-agent treatment on MOC tumor growth and an increase in several pro-inflammatory cell types (M1 macrophages, CD8+ T cells, total infiltrating leukocytes), suggesting that INCB081776 treatment can create an immunologically hot TIME. Further, in-depth analysis of tumor infiltrating leukocytes following INCB081776 treatment in both immunologically hot (MOC1) and cold (MOC2) HNC tumors suggested that INCB081776 has a greater effect in cold tumors. In cold tumors, levels of pro-inflammatory cells (CD8+ T cells, M1 macrophages, etc.) increased, and levels of anti-inflammatory cells (M2 macrophages, regulatory T cells, etc.) decreased, both to a greater extent than in hot tumors. Finally, the combination of INCB081776 and anti-PDL1 was superior to either treatment alone in slowing tumor growth. Together, these studies indicate that INCB081776 cooperates with anti-PDL1 in a syngeneic mouse model of HNC to slow tumor growth and create a pro-inflammatory environment, especially in immunologically cold tumors, thereby highlighting the potential clinical benefit of this therapeutic combination.
Citation Format: Kourtney L. Kostecki, Mari Iida, Anne L. Wiley, Seungpyo Hong, Ravi Salgia, Paul M. Harari, Deric L. Wheeler. Simultaneous inhibition of Axl and MerTK enhances anti-PDL1 efficacy and creates a pro-inflammatory tumor immune microenvironment in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3535.