Abstract 1444: TPX-0022, a potent MET/SRC/CSF1R inhibitor that modulates the tumor immune microenvironment in preclinical models

Abstract Within the tumor microenvironment (TME), CSF1R (colony stimulating factor 1 receptor) signaling plays a pivotal role in recruitment and enrichment of M2 tumor-associated macrophages (TAM) that dampen the anti-tumor immune response and promote tumor progression. Although CSF1R inhibitors have shown promise in the clinic, tumor cells and TAMs can bypass CSF1R inhibition and expand M2 TAMs through other growth factor receptors, such as MET (hepatocyte growth factor receptor) to confer resistance to targeted therapies and immune checkpoint inhibitors. Through autocrine signaling pathways, CSF1R and MET activation in tumors contribute to tumor invasiveness and metastasis. Therefore, inhibitors that target both CSF1R and MET, such as TPX-0022 (a compact macrocyclic inhibitor of MET/SRC/CSF1R), may more effectively suppress CSF1R mediated signaling in tumor cells and the stroma. In the current study, the role of TPX-0022 in the anti-tumor immune response is evaluated in the context of both normal immune cells and immunocompetent syngeneic murine models. TPX-0022 blocks both HGF and CSF1 mediated signaling and proliferation of MET and CSF1R dependent cell lines. In the MC-38 syngeneic model, TPX-0022 treatment repolarized TAMs towards M1 anti-tumorigenic macrophages, increased CD8 T cells, and inhibited tumor growth. In a mixed lymphocyte reaction assay, we demonstrated that pretreatment of macrophages with TPX-0022 enhances macrophage function in driving the activation and proliferation of CD8 T cells. Furthermore, TPX-0022 treatment of anti-C3/CD28 and or SIINFEKL peptide stimulated murine T cells had no deleterious effects on T cell activation and proliferation. Additionally, TPX-0022 enhanced T cell cytotoxic function towards cancer cells in a dose-dependent manner. Detailed analysis of the TME in CT-26 animals treated with TPX-0022 showed a significant reduction in TAMs, rebalancing both immunosuppressive Treg and M2 macrophages towards anti-tumorigenic CTL (CD8+ CD69+ GnzB+) and M1 macrophages. The combination of TPX-0022 and a PD-1 antibody resulted in significant downregulation of pro-tumorigenic cytokines IL-10, IP-10, IL-1β, and HGF, without impacting the anti-tumor cytokine IFN-γ. In the MC-38 model, TPX-0022 demonstrated single-agent activity and a trend to enhanced efficacy in combination with a PD-1 antibody. Taken together, the preclinical data demonstrates that the MET/SRC/CSF1R inhibitor TPX-0022 can reprogram tumor associated macrophages as well as support antigen presentation and activation of T cells within the TME. A TPX-0022 combination with a PD-1 therapy yielded more anti-tumor activity than single agent treatments. Together, the in vitro and in vivo preclinical data provide a mechanistic rationale for the potential utility of TPX-0022 in combination with immune checkpoint inhibitors. Citation Format: Vikas K. Goel, Wei Deng, Dayong zhai, Nathan V. Lee, Ana Parra, Brion W. Murray. TPX-0022, a potent MET/SRC/CSF1R inhibitor that modulates the tumor immune microenvironment in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1444.