Abstract 2302: Preclinical evaluation of CDK4/6 inhibitor and biomarker exploration in gastric cancer

Dysregulation of cell cycle is a hallmark of cancer and the p16 INK4a -CDK4/6-Rb pathway is often disrupted in many types of cancer including gastric cancer. Inhibition of CDK4/6 in cancer cells has become a promising therapeutic strategy, but not tested in gastric cancer. In this study, we investigated the effect of abemaciclib (LY2835219), a dual inhibitor of CDK4 and CDK6, and identified potential biomarkers in 49 gastric cancer cell lines. The cytotoxicity of abemaciclib was assessed by CCK-8 assay. For exploration of predictive biomarkers, status of single nucleotide variants (SNVs) and copy number variations (CNVs) were analyzed by whole exome sequencing (WES). Also, RNA and protein expression levels of cell cycle related molecules were determined by RNA sequencing and Western Blot, respectively. In TCGA study (The Cancer Genome Atlas, Nature 2017) approximately 37% of stomach adenocarcinoma patients have defects in the p16 INK4a -CDK4/6-Rb pathway (143/388patients); notable signatures include alterations of p16 INK4a (14%), Rb1 (7%), CDK4 (4%), CDK6 (8%), cyclinD1 (6%), and cyclinE1 (12%). In our 49 gastric cancer cell lines, we confirmed 25 cell lines have defects in this pathway (51%) including alterations of p16 INK4a (38%), Rb1 (10%), CDK6 (8%), cyclinD1 (4%), and cyclinE1 (2%). Based on the sensitivity of abemaciclib, we could divide 49 gastric cancer cell lines into: sensitive (IC 50 50 ≥0.5uM, 21/49cell lines) groups with the cut off 0.5uM which was determined by clinically achievable concentration from phase I trial. As a result of relation analysis between protein expression and sensitivity of abemaciclib, p16 INK4a deletion did not correlate with sensitivity. Then, correlation analysis between sensitivity and RNA expressions of p16 INK4a -CDK4/6-Rb pathway related genes were determined. Significant correlations were found in p16 INK4a (r=0.4783, p=0.0016), Rb1 (r=-0.3206, p=0.0410), and cyclinE1 (r=0.5378, p=0.0003) whereas not in cyclinD1, CDK4, and CDK6. Protein expression levels of p16 INK4a and cyclinD1 were not related to sensitivity of abemaciclib. In addition, with reproduction of the GDSC (Genomics of Drug Sensitivity in Cancer) information, focal recurrent copy number alterations of regions of chromosome 9p24.3-p21.1 (cnaPANCAN144) were correlated with CDK4/6 inhibitor sensitivity. Among ninety-one genes within these regions, 16 genes from cnaPANCAN144 were correlated with sensitivity of abemaciclib (p≤0.05). Our results indicate that abemaciclib is a potential therapeutic agent for gastric cancer and demonstrate that RNA expressions of p16 INK4a , Rb1, and cyclinE1 would be predictive biomarkers based on molecular genetic profiling. Citation Format: Hyun Joo Bae, Woo Sun Kwon, Hyun Jeong Kim, Sun Kyoung Kang, Inhye Jeong, Tae Soo Kim, Hyun Cheol Chung, Sun Young Rha. Preclinical evaluation of CDK4/6 inhibitor and biomarker exploration in gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2302.