Combined Inhibition of the Ras Pathway and Autophagy as a Treatment Approach for Pancreatic Cancer

We recently determined that concurrent inhibition of autophagy, using the lysosomal inhibitor chloroquine (CQ), and of ERK, using a small molecule ERK inhibitor (ERKi), synergistically suppressed the growth of pancreatic ductal adenocarcinoma (PDAC) cell lines and patient xenograft-derived (PDX) organoids in vitro and PDX tumors in vivo (Bryant et al., 2019, Nat Med 25:628). Our findings, together with similar observations by McMahon, Kinsey and colleagues (Kinsey et al., 2019, Nat Med 25:620), provided the rationale for our initiation of a Phase I clinical trial evaluating the combination of MEKi (binimetinib; NCT04132505) or ERKi (LY3214996; NCT04386057) with hydroxychloroquine (HCQ) in PDAC. To extend these findings we performed a CRISPR/Cas-9 mediated genetic loss-of-function screen in the presence of CQ to determine additional sensitizers as well as mediators of resistance to autophagy inhibition. Top sensitizers included multiple facilitators of the DNA damage response, mTOR pathway components, and genes involved in the upstream regulation of the autophagy pathway. We validated the receptor tyrosine kinase IGF1R as both a potent sensitizer to HCQ, as well as a protein that exhibited compensatory phosphorylation upon HCQ treatment. Interestingly, while IGF1R inhibition induced autophagy alone, the induction was greatly enhanced in that presence of ERK or MEK inhibition. Accordingly, concurrent inhibition of IGF1R, ERK and autophagy induced cytotoxicity in PDAC cell lines and organoids. Furthermore, we identified PIKFYVE as a potent anti-autophagy target. Ongoing studies are aimed at comparing the effects of PIKFYVE inhibition to that of HCQ treatment in the presence and absence of ERK MAPK pathway inhibition. We conclude that concurrent suppression of multiple metabolic processes, to block compensatory rebound activities, will be needed for effective PDAC treatment.

Learning Objectives: 

1. Define the five current strategies for targeting RAS for cancer treatment.
2. Describe the how the mCherry-EGFP-LC3B reporter construct can be utilized to monitor autophagic flux.
3. Identify the four phases of the autophagic pathway and describe which phase is perturbed by chloroquine and the PIKfyve inhibitor, apilimod.