Spindle assembly checkpoint (SAC) prevents mis-segregation of chromosome and allows accurate division in mitosis. Mps1 (also known as TTK) is one of the essential kinases for recruitment of SAC proteins after chromosome segregation. Failure of SAC induces chromosome instability, mitotic catastrophe, and ultimately apoptotic cell death and Mps1 is induced or activated in rapidly dividing tumor cells. Therefore, Mps1 has been considered an attractive anti-cancer drug target. VRN081569 is a potent type I kinase inhibitor of Mps1, which stabilizes Mps1 kinase domain in a closed conformation by forming a tight interface with its kinase domain. This structural stabilization appears to increase cellular potency for the induction of aneuploidy and apoptosis (~ 10 nM or less GI50 value). The loss of retinoblastoma tumor suppressor gene (Rb1), which is prevalent in advanced cancers, dysregulates cell cycle and promotes cell division. In particular, the resistance to CDK4/6 inhibitors has been reportedly mediated by loss of the Rb1 gene. We found that Rb1-negative cells express higher level of Mps1 than Rb1-positive cells and VRN081569 efficiently induce apoptosis of Rb1-negative Triple Negative Breast Cancer (TNBC) cell line MDA-MB-468 than Rb1-positive TNBC MDA-MB-231. Especially we confirmed that VRN081569 induces caspase 3/7 activity faster in Rb1-negative cells (~50-fold EC50 of caspase 3/7 activity compared to Rb1-positive cells), and cell cycle analysis has shown that our compound induces a dose-dependent dysregulation of mitosis, resulting in a decrease in the frequency of the G0/G1 phase, and also induces aneuploidy and apoptosis. Finally, we confirmed a combination effects with anti-microtubule agents BCL-2 inhibitor and PARP-1 inhibitor, suggesting that modulation of two different cellular processes may overcome the lack of single agent activity for TNBC.

Citation Format: Hong Ryul Jung, Yeonsil Kim, Haelee Kim, Ji-Hye Kwon, Dong-hyuk Seo, Jung Beom Son, Nam Doo Kim, Daekwon Kim, Sunghwan Kim. VRN08, a Selective Mps1 Kinase Inhibitor Induces Mitotic Catastrophe and Apoptosis Efficiently in Advanced Cancers Including Rb1-Deficient [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB119.