We have found that tumor-associated macrophages (TAMs) isolated from metastatic tumors displayed a predominant M2 phenotype. Preclinical studies show that M2-polarized TAMs forge an immunosuppressive microenvironment at metastatic niches to facilitate colonization. Colony-stimulating factor 1 receptor (CSF-1R) signaling is known to regulate the survival and maintenance of M2 TAMs, suggesting targeting CSF-1R might have therapeutic potential in halting cancer progression. To this end, we developed an orally active and selective small-molecule CSF-1R inhibitor EI-1071.

Experimental procedures: EI-1071 was evaluated in kinase and cell-based bioassays, including macrophage proliferation and osteoclast differentiation. In vivo activity was verified using murine syngeneic models of colorectal cancer and breast cancer. EI-1071 was administered individually or in combination with an anti-PD1 antibody. Tumor infiltrating leucocytes were profiled using flow cytometric analysis.

Results: EI-1071 exhibited nanomolar potency for inhibition of CSF-1R but not other 453 kinases tested. In cell-based bioassays, EI-1071 inhibited CSF-1R activity in human monocytes/macrophages, AML-5 leukemia, MNFS-60 leukemia, and human osteoclasts. In preclinical studies, EI-1071 displayed a favorable ADME properties, including hepatocyte stability, high Caco-2 permeability, and pharmacokinetic profiles. Oral administration of EI-1071 reduced TAM infiltration in the MC38 colorectal cancer and EMT6 breast cancer models. Moreover, EI-1071 dosed with an anti-PD-1 antibody showed further enhanced antitumor activity in vivo .

Conclusions: Preclinical characterization of EI-1071 demonstrated that it is a potent and selective CSF-1R inhibitor and has a favorable drug like properties for further clinical evaluation. Therefore, EI-1071 is undergoing IND-enabling activities for the First-In-Human (FIH) Phase 1 study.

Citation Format: Hung-Kai Chen, Huey-Wen Hsiao, Li-Ming Lu, Chih-Lun Hsiao, Yin-Ping Wang, Jing-Yi Huang, Chu-Bin Liao, Shao-Zheng Peng, Daw-Tsun Shih. A potent and selective cfms inhibitor EI-1071 inhibits CSF1R signaling and regulates the tumor-associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 343.