Abstract 1567: Anti-cancer effect of Mps1 inhibitor in gastric cancer
Authors: Seo Kim Eun , Kwon Woo Sun , Soo Kim Tae , Park Juin , Cho Sang Woo , Kim Sunghwan , Chung Hyun Cheol , Rha Sun Young 
Published: April 2023

Abstract
Mps1/TTK is a key regulator of the spindle assembly checkpoint (SAC), a mitotic mechanism necessary for appropriate chromosomal alignment and segregation. SAC inactivation induced by Mps1 inhibition generates lethal genomic instability in actively dividing cancer cells. Mps1 inhibition is expected to have therapeutic potential as a molecular target in gastric cancer(GC) because Mps1 expression is higher in GC than in normal gastric tissue. In this study, we aim to investigate the efficacy and biological mechanism of a novel Mps1 inhibitor, compound-9 (J. Med. Chem. 2021, 64, 6985) in GC cell lines.
61 GC cell lines were used in this study. According to TCGA molecular subtype, 2 cell lines are EBV type, 4 cell lines are MSI-H type, 31 cell lines are CIN type, and 24 cell lines are GS type. The genomic and molecular status of the cell cycle and SAC-related factors were profiled using Whole Exome Sequencing (WES) and RNA sequencing. Endogenous Mps1 protein expression level was detected by immunoblotting. The sensitivity of the Mps1 inhibitor was evaluated by cell viability assay. IC50 values were determined by the CalcuSyn software and cell lines were classified as a sensitive (IC50 &lt;100 nM), moderate (100 nM &lt; IC50 &lt;10 μM), and resistant (IC50 &gt; 10 μM) group.
As a result of the Mps1 inhibitor sensitivity screening, 34% of the cell lines (21/61) were sensitive, 38% were moderate (23/61) and 28% were resistant (17/61). Compared to the TCGA subtype, EBV was 50% (1/2), MSI-H was 75% (3/4), CIN was 42% (13/31), and GS was 16.7% (4/23) sensitive to Mps1 inhibitor. Interestingly, MSI-H type cell lines (n=3), which have mononucleotide repeat (cMNR) mutations, were sensitive. According to molecular genomic profiling, DNA damage repair (DDR)-related genetic alterations were found in 27/61 (44.2%) of cell lines but were not associated with Mps1 inhibitor susceptibility. The sensitivity to Mps1 inhibitors correlates with mRNA expression of the SAC silencing molecule PPP1CA(PPP1CA) and the Mps1 downstream molecule MAD1(MAD1L1), but not with Mps1(TTK). PPP1CA (p&lt;0.5) and MAD1L (p&lt;0.05) mRNA expression levels were lower in the sensitive group than in the resistance group. Moreover, we observed that endogenous Mps1 protein expression levels varied regardless of the sensitivity of the Mps1 inhibitor. Further studies are ongoing to evaluate the underlying mechanisms.
Our data suggest that gastric cancer is sensitive to the Mps1 inhibitor, resulting in cell growth suppression. It may provide new potent treatment options for GC patients.
Citation Format: Kim Eun Seo, Woo Sun Kwon, Kim Tae Soo, Juin Park, Sang Woo Cho, Sunghwan Kim, Hyun Cheol Chung, Sun Young Rha. Anti-cancer effect of Mps1 inhibitor in gastric cancer [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 1567.