Abstract C026: Concurrent inhibition of the RAS ERK-MAPK pathway and PIKfyve as a therapeutic strategy for pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized clinically by poor survival and mechanistically by KRAS- and autophagy-dependent growth. We and others previously demonstrated that inhibition of KRAS signaling via downstream inhibition of the RAF-MEK-ERK pathway enhanced autophagic flux and dependency of PDAC on autophagy. Furthermore, we demonstrated that concurrent treatment with the nonspecific autophagy inhibitor chloroquine (CQ) and ERK MAPK inhibitors synergistically blocked PDAC growth. These findings provided rationale for our initiation of Phase I/II clinical trials evaluating the combination of MEKi (binimetinib; NCT4132505) or ERKi (LY3214996; NCT04386057) with HCQ in PDAC. However, a limitation of this approach is that CQ/HCQ is limited in terms of specificity and potency. Thus, we aimed to identify alternative anti-autophagy strategies. We performed a CRISPR-Cas9 loss- of-function screen in PDAC cell lines that identified the lipid kinase PIKfyve as a growth- promoting gene. PIKfyve is a lipid kinase that is essential for the generation of PI(3,5)P2 and critical for the dynamic regulation of lysosomal recycling. Because PIKfyve has been implicated in regulation of autophagy in other cellular contexts, we evaluated the effects of PIKfyve inhibition on growth and autophagic flux in PDAC cell lines and tumors. We demonstrated that PIKfyve inhibition by the small molecule apilimod resulted in durable growth suppression, with much greater potency than CQ treatment. PIKfyve inhibition potently reduced autophagy as indicated by decreased autophagic flux and the robust accumulation of autophagy-related proteins. Additionally, PIKfyve inhibition resulted in the accumulation of LAMP1 positive vacuoles that exhibited impaired cargo degradation, likely due to a lack of required acidity. Next, we hypothesized that PIKfye inhibition would sensitize PDAC cells to RAS pathway inhibition. We demonstrated that PIKfyve inhibition blocked the compensatory increases in autophagic flux associated both with MEK inhibition and with direct RAS inhibition. Accordingly, combined inhibition of PIKfyve and either the RAS ERK-MAPK pathway or RAS itself showed robust growth suppression across a panel of KRAS-mutant PDAC models. Growth suppression was due, in part, to potentiated cell cycle arrest and induction of apoptosis following loss of IAP proteins. These findings implicate PIKfyve as an effective anti-autophagy target when paired with RAS or ERK-MAPK pathway inhibition in pre-clinical models of PDAC. Citation Format: Jonathan M DeLiberty, Mallory K Roach, Clint A Stalnecker, Ryan Robb, Elyse G Schechter, Noah L Pieper, Runying Yang, Scott Bang, Khalilah E Taylor, Kristina Drizyte-Miller, John P Morris IV, Channing J Der, Adrienne D Cox, Kirsten L Bryant. Concurrent inhibition of the RAS ERK-MAPK pathway and PIKfyve as a therapeutic strategy for pancreatic cancer [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 Suppl_2):Abstract nr C026.