Abstract 516: Discovery and preclinical characterization of AMG 650, a first-in-class inhibitor of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers

Abstract Chromosomal instability (CIN) is a hallmark of human cancers and is caused by persistent errors in chromosome segregation during mitosis. Aggressive types of human cancer such as high-grade serous ovarian cancer and triple-negative breast cancer have elevated levels of CIN and frequently harbor TP53 gene alterations and are poorly served by current treatment options. These two CIN+ cancer types also share mutually exclusive genetic alterations in BRCA1 and CCNE1 cancer genes. KIF18A is a mitotic kinesin motor protein that localizes to the plus-end tips of kinetochore microtubule (MT) spindle fibers, where it regulates chromosome alignment during cell division. KIF18A is overexpressed in a subset of human cancers, and its elevated expression is associated with tumor aggressiveness. Recent reports provide compelling evidence that genetic ablation of KIF18A reduced the viability of CIN cancer cells (Marquis et al. Nature Com 2021, Quinton et al. Nature 2021, Cohen-Sharir et al. Nature 2021). Here, we report the discovery and preclinical characterization of AMG 650, a potent and selective inhibitor of KIF18A with a compelling anti-cancer profile distinct from other cell cycle and anti-mitotic drug targets. Structural insights gained by cryo-EM illustrate the unique binding mode of AMG 650 to an allosteric pocket at the interface of KIF18A motor α4 and α6 helices and α-tubulin. AMG 650 selectively inhibits KIF18A MT-ATPase motor activity (IC50 = 48 nM) and exhibits specificity against a panel of diverse motor proteins. In cells, AMG 650 is active at double-digit nM concentrations and phenocopies KIF18A genetic KD/KO dependencies across a panel of DNA-barcoded cancer cell lines. AMG 650 selectively activates the mitotic checkpoint resulting in multipolarity and apoptosis in breast and ovarian cancer cell lines enriched with CIN features. Notably, AMG 650 has minimal effects on proliferating human bone marrow mononuclear cells in culture at concentrations active on sensitive cancer cells (>100X window). In vivo, AMG 650 has low clearance, long half-life, and good oral bioavailability across preclinical species. In mice, oral administration of AMG 650 induces a dose-dependent pharmacodynamic response (pH3 mitotic marker) that is sustained for 24 hours in OVCAR-3 tumor model. Importantly, continuous once-daily dosing with AMG 650 shows robust anti-cancer activity with evidence of durable tumor regressions in a subset of human ovarian and breast CDX/PDX tumor models at well-tolerated doses. Lastly, the combination of AMG 650 with PARP inhibitor Olaparib enhances anti-cancer activity relative to single agent alone in BRCA1- and CCNE1-altered tumor models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via AMG 650, a first-in-class KIF18A inhibitor. Citation Format: Brian Belmontes, Jodi Moriguchi, Grace Chung, Jan Sun, Maria Stefania S. Ninniri, Kelly Hanestad, Kui Chen, John D. McCarter, Upendra P. Dahal, Sudipa Ghimire-Rijal, Yue Hao, Christopher P. Mohr, Xinchao Yu, Matthew G. Rees, Melissa Ronan, Jennifer Roth, Sheroy Minocherhomji, Jennifer R. Allen, Matthew P. Bourbeau, Paul E. Hughes, Nuria A Tamayo, Marc N. Payton. Discovery and preclinical characterization of AMG 650, a first-in-class inhibitor of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 516.