Abstract LB524: Discovery of highly selective RON kinase inhibitors

RON is a receptor tyrosine kinase of the MET proto-oncogene family, known as macrophage stimulating 1 receptor (MST1R) that recognizes macrophage-stimulating protein (MSP). RON has been known to be highly expressed in several epithelial tumors, promoting tumor progression and metastasis, and on macrophages surface, facilitating M2-like phenotype polarization of tumor-associated macrophages (TAM) to impair anti-tumor functions of CD8+ T cells. Although pharmacological inhibition of RON kinase has received attention from many research groups, monoclonal antibody drug showed a limited clinical efficacy due to RON variant of receptor region. Because the structure homology of kinase domain between RON and MET is 80%, discovery of RON-specific small molecule inhibitor is considered to be highly challenging to achieve. At first, we discovered a lead compound with about 50-fold of RON selectivity against MET kinase. Our medicinal chemistry efforts elevated RON/MET selectivity up to 500~10,000-fold (IC50 = 1~50 nM in RON enzyme assay), and the target specificity was proved through a panel assay of 372 kinases (Reaction Biology Corp.). A series of compounds effectively modulated p-RON and downstream signals (e.g. p-ERK and p-AKT) in MDA-MB-453, and inhibited cell proliferation of Ba/F3 cell-line engineered with human RON kinase. Significant anti-tumor effects were shown in syngeneic mouse models compared to a control group after oral administration, and studies related to immuno-oncology are ongoing in in-vitro or ex-/in-vivo assay systems. In conclusion, we have identified RON selective small molecule inhibitors that will be useful to figure out the biology following RON selective inhibition against MET kinase, and to validate the translational potential of RON kinase as a therapeutic target for human diseases including cancer. Citation Format: Young Jin Ham, GyeongHwan Kim, Juhyun Lee, Jaeyoung Lee, Min Kyung Kim, Sunhong Kim, Woosook Kim, Han Byoul Kim, Sung Woong Jang, Hee Dong Park, Seonguk Jeon, Seok-Joo Kim, Joongheui Cho, Jungjoon Kim, Hong bin Yoon, Youngshin Kwak. Discovery of highly selective RON kinase inhibitors [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 LB524.