Abstract C160: HMPL-653, a highly potent and selective CSF-1R inhibitor, targeting both tumor cells and tumor microenvironment
Authors: Hu Jia , Ge Liang , Zhang Hui , Jiang An , Yu Juntao , Xue Weifang , Wang Jian , Sai Yang , Yang Na , Qing Weiguo , Ren Yongxin , Shi Michael , Su Weiguo 
Published: December 2023

Abstract
Background: Colony stimulating factor 1 receptor (CSF-1R) and its ligand CSF-1 (CSF-1R/CSF-1) signaling regulates the function and survival of tumor-associated macrophages (TAM), which are involved in tumor progression and suppression of anti-tumor immunity. Moreover, activation of CSF-1R/CSF-1 axis including CSF-1 fusions or CSF-1R activating mutations has also been implicated in the pathogenesis of certain tumors such as tenosynovial giant cell tumor and histiocytic neoplasms. HMPL-653 is a highly potent and selective CSF-1R small molecule inhibitor, discovered and being currently developed in phase I clinical trial (NCT05277454) by HUTCHMED.
Methods: The inhibition on CSF-1R kinase was determined using Z-LYTE™ kinase assay. The selectivity of HMPL-653 was assessed against a panel of 413 kinases by Eurofins. Cellular target inhibition on phosphorylation of CSF-1R (p-CSF-1R) was detected by ELISA. In vitro cell viability was measured by CCK-8 assay. Multiple CSF-1/CSF-1R driven tumor models in Nu/Nu nude mice were applied to determine the anti-tumor activity of HMPL-653 as a single agent. To demonstrate the immunoregulatory effect of HMPL-653, a murine tumor model, B16F10, was established in C57BL/6J mice, and the combination regimen, HMPL-653 plus PCP (poly (I:C)+CpG+anti-PD-1) was evaluated.
Results: HMPL-653 strongly inhibited CSF-1R kinase with IC50 of 5 nM, showing &gt;7-fold potency than that of the approved CSF-1R inhibitor pexidartinib (IC50=39 nM). And the selectivity profiling in 413 kinase panels revealed that HMPL-653 was highly potent only against CSF-1R, indicating a lower off-target risk than paxidatinib reported. HMPL-653 potently inhibited CSF-1 stimulated p-CSF-1R in THP-1 cells with IC50 of 5 nM. In CSF-1/CSF-1R-dependent cell lines, M-NFS-60 (mouse myelogenous leukemia) and three cell lines stably expressed BCR-CSF-1R or CSF-1R mutations (Ba/F3-BCR-CSF-1R, Ba/F3-CSF-1RW450-E456del, and Ba/F3-CSF-1RY546-K551del), HMPL-653 significantly down regulated p-CSF-1R and its downstream signaling p-ERK and p-AKT. As a consequence, HMPL-653 robustly inhibited the cell viability of above cell models (IC50s: 3~40 nM). Besides the direct anti-tumor effect, HMPL-653 also demonstrated strong inhibition on macrophage survival and M2 macrophage polarization, indicating a potential effect on targeting tumor microenvironment. In vivo, oral administration of HMPL-653 induced remarkable and dose-dependent anti-tumor efficacies in M-NFS-60 ascites model and subcutaneous tumor models harboring above mentioned CSF-1R alterations. And the PK/PD analysis revealed that the anti-tumor effect correlated well with p-CSF-1R inhibition. Moreover, HMPL-653 significantly improved the anti-tumor activity of PCP regimen in B16F10 model by reducing TAMs including M2 macrophages and increasing the ratio of M1/M2 macrophages.
Conclusion: HMPL-653 is a highly potent and selective CSF-1R small molecule inhibitor which targets both CSF-1/CSF-1R-dependent tumors and tumor associated macrophages, warranting further clinical evaluation.
Citation Format: Jia Hu, Liang Ge, Hui Zhang, An Jiang, Juntao Yu, Weifang Xue, Jian Wang, Yang Sai, Na Yang, Weiguo Qing, Yongxin Ren, Michael Shi, Weiguo Su. HMPL-653, a highly potent and selective CSF-1R inhibitor, targeting both tumor cells and tumor microenvironment [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C160.