Abstract C047: Improving the efficacy of dual ERK-MAPK and autophagy inhibition as a therapeutic strategy for pancreatic ductal adenocarcinoma
Authors: DeLiberty Jonathan M. , Roach Mallory K. , Pieper Noah L. , Drizyte-Miller Kristina , Schechter Elyse G. , Yang Runying , Der Channing J. , Cox Adrienne D. , Stalnecker Clint A. , Bryant Kirsten L. 
Published: January 2024

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is characterized by KRAS- and autophagy-dependent growth. We and others recently demonstrated that inhibition of KRAS signaling through targeting the RAF-MEK-ERK kinase cascade resulted in further reliance on autophagy. We found that targeting this increased reliance on autophagy with the autophagy inhibitor hydroxychloroquine (HCQ)/chloroquine (CQ) together with MEK or ERK inhibition (MEKi, ERKi) synergistically blocked PDAC growth. These findings provided rationale for our initiation of Phase I/II clinical trials evaluating the combination of MEKi (binimetinib; NCT04132505) or ERKi (LY3214996; NCT04386057) with HCQ in PDAC. However, a limitation of this approach is that HCQ/CQ are not specific or potent autophagy inhibitors. Thus, we sought to identify a more efficacious autophagy inhibition strategy. To this end, we performed a CRISPR-Cas9 mediated genetic loss-of-function screen in PDAC cells to identify other targetable mediators of autophagy. We identified PIKfyve, a lipid kinase critical for the recycling dynamics of lysosomes, as an essential autophagy-related gene in PDAC cells. PIKfyve inhibition by the clinical candidate inhibitor apilimod resulted in potent reduction of autophagic flux and growth. Additionally, PIKfyve inhibition induced intracellular vacuolization. These PIKfyve-regulated vacuoles stained positive for the lysosomal marker, LAMP1, and exhibited reduced acidity and impaired cargo degradation. Importantly, PIKfyve inhibition prevented the increased autophagic flux we observed when we inhibited MEK with the clinical stage MEKi, mirdametinib. As a result, co-targeting MEK and PIKfyve led to synergistic impairment of PDAC cell proliferation. Similar results were observed following dual inhibition of KRAS and PIKfyve. We found the synergistic growth inhibition was due in part to a substantial induction of apoptosis unique to combination treatment. We then tested the combination of MEKi and PIKfyvei in a panel of patient derived PDAC organoids and observed a robust synergistic reduction in viability, suggesting this may be an efficacious therapeutic strategy for PDAC treatment. Future work includes in vivo studies, currently underway, to determine the efficacy of single agent PIKfyve inhibition, as well as efficacy studies assessing combined MEKi and PIKfyvei in orthotopic mouse models of PDAC. Taken together, these findings implicate PIKfyve as an effective anti-autophagy target when paired with RAS or ERK-MAPK pathway inhibition in pre-clinical models of pancreatic cancer.
Citation Format: Jonathan M. DeLiberty, Mallory K. Roach, Noah L. Pieper, Kristina Drizyte-Miller, Elyse G. Schechter, Runying Yang, Channing J. Der, Adrienne D. Cox, Clint A. Stalnecker, Kirsten L. Bryant. Improving the efficacy of dual ERK-MAPK and autophagy inhibition as a therapeutic strategy for pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C047.