Abstract C036: Vertical inhibition of the autophagy pathway enhances sensitization to RAS MAPK pathway inhibition in pancreatic ductal adenocarcinoma

Abstract PDAC growth is characterized by dependencies on both mutant KRAS signaling and autophagy. Our group and others previously demonstrated that inhibition of the RAF/MEK/ERK pathway in PDAC induces an increased dependence on autophagy, a metabolic nutrient scavenging process by which cellular components are recycled in times of nutrient stress. Combined inhibition of the ERK MAPK pathway and autophagy inhibited the growth of multiple preclinical models of PDAC. Based on these findings, combined ERK/MEK inhibition and hydroxychloroquine (HCQ) is currently under clinical evaluation (NCT03825289, NCT04386057). However, resistance to this combination has already been described. To identify sensitizers to CQ treatment, our lab performed a CRISPR-Cas9 mediated loss-of- function screen using an sgRNA library targeting genes associated with cancer signaling pathways. Surprisingly, we identified multiple autophagy related genes, indicating that concurrent inhibition of two nodes of the autophagy pathway may be a more effective method of inhibiting autophagy in PDAC. For example, we identified, PIK3C3, the gene that encodes for VPS34, a protein essential for the nucleation of autophagosomes, as a potential sensitizer to CQ treatment. Inhibition of VPS34 with the compound SAR405, resulted in both decreased autophagic flux and impaired proliferation. Additionally, VPS34 inhibition sensitized cells to CQ treatment, leading to further reduced proliferation. These results prompted us to hypothesize that inhibition of ULK1, a serine/threonine kinase critical for the initiation of autophagy, could also sensitize PDAC cells to CQ treatment. We found that ULK1 inhibition further reduced CQ-mediated anti-proliferative effects. Additionally, both ULK1 and VPS34 inhibitor treatment sensitized cells to PIKfyve inhibition with apilimod, a chemically and mechanistically distinct inhibitor of the termination phase of the autophagic pathway. Previous studies have indicated that autophagy inhibition alone is not a viable therapeutic avenue for the treatment of PDAC. Thus, we next determined whether vertical inhibition of the autophagy pathway improves the efficacy of combined inhibition of the RAS and autophagy pathway. We found that both VPS34 inhibition and ULK1 inhibition can decrease RAS inhibitor induced autophagic flux. Finally, vertical inhibition of the autophagic pathway via VPS34 inhibition and CQ sensitized PDAC cells to RAS inhibition to further reduce PDAC proliferation. Ongoing and future studies are aimed at elucidating the mechanism leading to decreased proliferation of combined anti-autophagy and RAS inhibitor therapies, as well as mechanistically understanding the effect of autophagy inhibition at multiple nodes on autophagic flux. Citation Format: Mallory K Roach, Jonathan M DeLiberty, Elyse G Schechter, Runying Yang, Noah L Pieper, Clint A Stalnecker, Kirsten L Bryant. Vertical inhibition of the autophagy pathway enhances sensitization to RAS MAPK pathway inhibition in pancreatic ductal adenocarcinoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr C036.