Abstract 1634: Novel autophagy inhibitor ESK981 potentiates MEK inhibition cytotoxicity in pancreatic cancer
Authors: Cheng Caleb , Wisniewski Jasmine , Jackson Bailey , Bao Yi , Qiao Yuanyuan , Lyssiotis Costas A. , Chinnaiyan Arul M. 
Published: April 2023

Background Pancreatic Ductal Adenocarcinoma (PDAC) is extremely deadly with a dismal 5-year survival rate of only 11%. In PDAC, the overactive KRAS-MEK-ERK pathway is critical to maintaining metabolic homeostasis. Important recent work has shown that when MEK or ERK are inhibited, PDAC upregulates and becomes increasingly dependent on autophagy. Autophagy, the recycling of cellular material through lysosomal degradation, has already been previously established to be upregulated in and crucial to PDAC in order survive in its harsh microenvironment and allows PDAC to evade the immune system. Unfortunately, chloroquine (CQ), the only clinical-grade autophagy inhibitor tested in PDAC failed to improve patient survival in combination with chemotherapies in phase II trials. Recently, our lab reported a novel phase I-cleared multi-tyrosine kinase inhibitor ESK981 which disrupted autophagy and had substantial single agent efficacy in prostate cancer models. Given the importance of autophagy in PDAC and the ongoing clinical trials testing autophagy inhibitor CQ in combination with MEK/ERK inhibitors, this study aims to evaluate ESK981 as a therapeutic agent for PDAC, particularly its ability to potentiate MEK inhibitors’ antiproliferative effects in PDAC.

Methods and Results In mouse and human PDAC cell lines, we observed an accumulation of LC3A/B as well as P62 when treated with ESK981, suggesting a disruption of autophagic flux. To confirm an inhibition of autophagy, we used the GFP-LC3-RFP-LC3ΔG reporter system in Mia-Paca2 cells and saw that the GFP:RFP ratio was maintained near 1:1. To assess the effects of ESK981 on cell growth, we used Cell-Titer Glo assays which revealed that ESK981 suppresses proliferation of a panel of human and mouse PDAC cell lines at nanomolar concentrations. To further evaluate ESK981’s potential clinical applications, we evaluated ESK981’s ability to synergize with MEK inhibitor Trametinib. Using the GFP-LC3-RFP-LC3ΔG reporter system we saw that Trametinib decreased the GFP:RFP ratio as expected. When cells were pre-treated with ESK981, the ratio was increased, showing that ESK981 was able to block Trametinib-induced autophagic flux. Finally, using Cell-Titer Glo, we determined that ESK981 and Trametinib had a strong synergistic effect on suppressing cell proliferation (BLISS Score &gt;20) on mouse KPC line 7940B. Taken together, ESK981 is a promising autophagy inhibitor that shows strong anti-proliferative effects on both human and mouse PDAC cell lines as a single agent as well as in combination with Trametinib.

Citation Format: Caleb Cheng, Jasmine Wisniewski, Bailey Jackson, Yi Bao, Yuanyuan Qiao, Costas A. Lyssiotis, Arul M. Chinnaiyan. Novel autophagy inhibitor ESK981 potentiates MEK inhibition cytotoxicity in pancreatic 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 1634.