Abstract 5700: Increasing efficacy of iBET-151, a small molecule inhibitor of BET protein in combination with paclitaxel in gastric cancer

Abstract

Abstract Epigenetic dysregulation is a common characteristic of cancers, including gastric cancer (GC), which contributes to the development and progression of GC. BRD4 is one of the leaders for epigenetic regulation and is known to regulate the expression of oncogenes such as c-MYC, BCL-2, and CDK4. In a previous study, we evaluated the efficacy of iBET-151 in a large panel of GC cell lines and xenograft mouse models. We found that iBET-151 showed a modest growth-inhibitory effect in GC cells. Recent report showed, lowering the expression of BCL-2 and BCL-xL, which are the targets of BRD4, induces sensitivity to paclitaxel, frequently used antimitotic agent in GC. Therefore, we evaluate iBET-151 plus paclitaxel as a new combination treatment regimen for GC. The synergistic effect and possible mechanisms of iBET-151 with paclitaxel were evaluated in 49 GC cell lines or 10 GC organoids using cell proliferation assay, flow cytometry, western blotting, colony formation, and migration assays. We found that the addition of iBET-151 increased the sensitivity to paclitaxel alone treatment from 15% to 50% in approximately 70% (34/49) of GC cells. iBET-151 plus paclitaxel significantly promoted cell-cycle arrest at G1 or G2/M phase and increased sub-G1 phase and cleaved PARP expression, which correlates to increased cell death. Also, combined treatment suppressed c-Myc, Bcl-2, and Bcl-xL expression in AGS, YCC-1, YCC-32, and YCC-34. We found BET proteins were overexpressed in most patient-derived GC organoids whereas c-Myc, BCL-2, and BCL-xL were expressed at variable levels. We observed that there was a synergistic growth inhibition in 6 out of 10 (60%) organoids. The data suggests iBET-151 and paclitaxel have a synergistic effect not only in GC cell lines but also in GC organoids. In summary, our data show the combination of iBET-151 and paclitaxel resulted in markedly higher anti-tumor effects compared with either treatment alone for GC. With further studies to validate the efficacy and biomarker explorations, the combination of iBET-151 and paclitaxel represents a promising therapeutic strategy in GC. Citation Format: Sun Kyoung Kang, Sang Woo Cho, Woo Sun Kwon, Tae Soo Kim, Hyun Cheol Chung, Sun Young Rha. Increasing efficacy of iBET-151, a small molecule inhibitor of BET protein in combination with paclitaxel in gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5700.