Abstract 4604: Effect of CDK 4/6 inhibition on anti-angiogenesis effect in gastric cancer
Authors: Cho Sang Woo , Kwon Woo Sun , Kim Tae Soo , Park Juin , Kim Eun Seo , Chung Hyun Cheol , Rha Sun Young 
Published: April 2023

Abstract
Angiogenesis, a hallmark of cancer, is a phenomenon in which new blood vessels are created from existing blood vessels. As the tumor grows, they secrete ligands such as vascular endothelial growth factor (VEGF). Therefore, anti-tumor effect could be achieved by preventing tumor-associated angiogenesis. In previous reports, CDK4/6 has been acknowledged to regulate VEGF transcription in addition to cell cycle regulation. There are few studies explaining the angiogenesis-related effects of CDK4/6 inhibitors in gastric cancer (GC). In this study, we aim to verify the anti-angiogenesis effect through CDK4/6 inhibition. First, we confirmed proliferation and angiogenesis in endothelial cells. Next, the change in VEGF expression induced by CDK4/6 inhibitor in GC cell lines was investigated. In-vitro angiogenesis research was conducted using human umbilical vein endothelial cells (HUVEC). Abemaciclib was used as a CDK4/6 inhibitor. To determine the efficacy of abemaciclib, HUVEC was treated with abemaciclib for 3 days and cell viability was assessed by CCK-8 assay. IC50 value was determined by the CalcuSyn software. Furthermore, tube formation assay, wound healing assay, cell cycle analysis and SA-β-gal assay were performed to explore effect of abemaciclib on HUVEC. VEGF-A expression was evaluated by ELISA. First, we identified direct anti-angiogenesis effect of abemaciclib on HUVEC. The IC50 value was 1.28 μM. At clinically achievable concentrations of abemaciclib (Cmax, 0.5 μM), HUVEC only showed a 20% growth inhibition. Abemaciclib did not suppress tube formation and migratory potential of HUVECs. However, abemaciclib induced a G1 arrest in HUVEC after 0.5 μM abemaciclib treatment for 24hr. To ensure whether the increase in the number of G1 phase cells is due to senescence, SA-β-gal assay was performed. The levels of SA-β-gal-positive cell staining in abemaciclib-treated group were higher than control, suggesting that abemaciclib induced cell senescence on HUVEC. While our results suggested that CDK4/6 inhibitor did not show direct anti-angiogenic effect on endothelial cells, we studied indirect anti-angiogenesis effect of abemaciclib in GC cell lines through regulation of VEGF transcription. Conditioned media of 49 GC cell lines had a wide range of VEGF secretion ranged from 0.146 to 22.676 ng/mL. (ave. 4.07 ng/mL). We have set the cut off of secreted VEGF as 10 ng/mL, at which angiogenesis can be induced. There were four cell lines (4/49, 8.2%) whose VEGF concentrations were more than the angiogenesis-inducing VEGF concentration (10 ng/mL). Interestingly, 3 of these 4 GC cell lines demonstrated a decrease in VEGF secretion, following 0.5 μM abemaciclib treatment. In conclusion, we did not observe inhibition of angiogenesis in HUVEC. However, CDK4/6 inhibition can cause senescence in HUVEC, inhibit tumor growth, and indirectly induce anti-angiogenic effects in gastric cancer.
Citation Format: Sang Woo Cho, Woo Sun Kwon, Tae Soo Kim, Juin Park, Eun Seo Kim, Hyun Cheol Chung, Sun Young Rha. Effect of CDK 4/6 inhibition on anti-angiogenesis effect 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 4604.