Abstract 723: Dual inhibition of MDM2 and p38 MAPK signaling is a potential therapeutic strategy in esophageal squamous cell carcinoma
Authors: Roy Souvick , Garg Rachana , Wang David , Goel Ajay 
Published: June 2022

Abstract
Background: Esophageal squamous cell carcinoma (ESCC) is one of the most common lethal malignancies. Despite recent advances in treatment, the overall 5-year survival rate remains low, primarily due to late diagnosis, acquired resistance to therapy, and distant metastases. Hence, development of novel therapeutic strategies is required to improve patient outcomes. The MDM2 gene is amplified in some patients with ESCC, frequently decreasing the tumor suppressive function of p53. In addition, 40-60% of ESCC tumors exhibit p53 mutations. Missense mutations within the p53 gene cause its overexpression and subsequent activation of p38 MAPK signaling. In this study, we aimed to investigate the effect of combining a p38 MAPK inhibitor and an MDM2 antagonist as a potential therapeutic strategy in ESCC.
Methods: To determine the synergistic anti-tumor activity of the MDM2 antagonist siremadlin (HDM-201) and the p38 MAPK inhibitor Ralimetinib dimesylate (LY2228820), we performed cell viability, colony formation, apoptosis, and cell cycle analysis in ESCC cell lines. Next, we evaluated the anti-tumor activity of HDM-201 and LY2228820 in a xenograft mouse model. Finally, we performed siRNA mediated silencing of p53 to assess its functional role in the MDM2 antagonist-induced activation of p38 MAPK signaling and its ability to modulate the DNA damage response (DDR) by measuring ROS status and phosphorylation of H2AX.
Results: HDM-201 exerted cytotoxic effects in p53-mutated ESCC cells in a dose-dependent manner and activated the p38 MAPK signaling pathway. These results prompted us to combine the p38 MAPK inhibitor LY2228820 with HDM-201 and evaluate this novel treatment strategy in a p53-mutant pre-clinical model of ESCC. We observed that HDM-201 and LY2228820 acted synergistically to decrease cell viability (p&lt;0.01) and colony formation (p&lt;0.01), as well as induction of apoptosis (p&lt;0.01) and G2/M phase cell cycle arrest (p&lt;0.01). The xenograft animal model confirmed our in vitro findings wherein the combined treatment exerted more potent anti-tumor activity (p&lt;0.05). We also observed that silencing of p53 promoted resistance towards the MDM2 antagonist and did not induce apoptosis, highlighting that a functional p53 is required for inducing apoptosis after combined treatment. Furthermore, we observed that the combined treatment promoted ROS induced oxidative stress (p&lt;0.01) and promoted DNA double strand breaks (DSBs) as evidenced by increased phosphorylation of H2AX (p&lt;0.01), highlighting its potential as an effective therapeutic strategy.
Conclusion: We provide novel pre-clinical evidence that inhibition of p38 MAPK signaling can augment the anti-tumor activity of an MDM2 antagonist in p53-mutant human tumor models of ESCC.
Citation Format: Souvick Roy, Rachana Garg, David Wang, Ajay Goel. Dual inhibition of MDM2 and p38 MAPK signaling is a potential therapeutic strategy in esophageal squamous cell carcinoma [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 723.