Abstract 2205: CBT-102, an oral small molecule multi-kinase inhibitor, demonstrates favorable CSF-1R activity, offering means of controlling tumor associated macrophages

Background: The role of the tumor microenvironment (TME) in fostering the development of malignancies is prompting the pursuit of anticancer therapies that target its components as to opposed to the tumor itself. As part of their immune surveillance duties, immune cells form part of this microenvironment, and yet, cancer cells have devised means to downplay their tumoricidal capabilities. Colony stimulating factor 1 receptor (CSF-1R) may offer such a means of controlling tumor associated macrophages in the tumor microenvironment. Methods: The IC50 of CBT-102 against CSF1R was evaluated in both cell free system and cell based assays, where enzyme activity was evaluated with radiometric assay format, and cell growth inhibition was evaluated in the Ba/F3 hCSF1R cell line by the CellTiter-Glo (CTG) method. Further evaluation of CBT-102 IC50 was undertaken in M-NFS-60 syngeneic cell lines and human monocytes. In vivo studies of CBT-102 in combination with anti-PD1 antibody were performed in H22 and MC38 syngeneic models. Results: CBT-102 demonstrated a reproducible activity against CSF1R in a radiometric enzyme activity assay. Using engineered BaF3 hCSF1R cell lines, we demonstrated the IC50 value of CBT-102 was 0.588 µM compared to 1.333 µM of sulfatinib, a similar multi-kinase inhibitor, and 0.279 µM of GW2580, a more specific CSF1R kinase inhibitor. Similar studies conducted in M-NFS-60 cell lines and human monocyte also showed sub-micromolar activities of CBT-102. In vivo study combining CBT-102 with anti-PD1 antibody in syngeneic models demonstrated a favorable combination effect compared to each of the single agents. Conclusions: We demonstrated previously that CBT-102 effectively inhibits VEGFR and angiogenesis. The newly revealed mechanism of CBT-102, inhibiting CSF1R and macrophages, offers a promising dual mechanism of action in addition to targeting VEGFR and angiogenesis. Rational combination with check-point inhibitors (CPIs) may improve the efficacy of CBT-102 and broaden the impact of CPIs. Further studies may be needed to delineate the interplay among CBT-102’s different mechanisms and its impact in combination with CPIs. Citation Format: Elaine Liu, Lan Yang, Gavin Choy, Xiaoling Zhang, Tillman Pearce, Mamatha Reddy, Sanjeev Redkar, Qian Shi. CBT-102, an oral small molecule multi-kinase inhibitor, demonstrates favorable CSF-1R activity, offering means of controlling 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 2205.