Abstract PR10: Enhancing the effect of autophagy inhibition for pancreatic cancer treatment

Pancreatic ductal adenocarcinoma (PDAC) is characterized by KRAS- and autophagy-dependent tumorigenic growth. We determined the role of mutationally activated KRAS, found in ~95% of PDAC, in supporting autophagy. Surprisingly, acute KRAS suppression, which blocks proliferation, was associated with increased rather than decreased autophagic flux. Pharmacologic inhibition of ERK MAPK phenocopied the genetic silencing of KRAS and also increased autophagic flux. We speculated that the loss of ERK-driven metabolic processes may induce compensatory mechanisms to increase autophagy. Addressing a mechanism for ERK suppression-increased autophagy, we describe three mechanisms: 1) ERK inhibition-mediated increased transcription of autophagy and lysosomal genes, 2) ERK inhibitor-induced AMPK activation and suppression of mTOR signaling, and 3) ERK inhibition-facilitated decreased glycolytic flux. We then addressed whether ERK inhibition increased PDAC dependence on autophagy. Supporting this possibility, we found that cotreatment with the autophagy inhibitor chloroquine (CQ) synergistically enhanced ERK inhibitor-mediated antiproliferative activity. Similarly, genetic or pharmacologic inhibition of specific regulators of autophagy also enhanced ERK inhibitor activity. Encouraged by the synergistic relationship between ERK and autophagy inhibition, 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 mediators of the DNA damage response. One such sensitizing gene was CHEK1, which encodes the CHK1 serine/threonine kinase, required for checkpoint-mediated cell cycle arrest and activation of DNA repair in response to DNA damage. Accordingly, we showed that treatment with prexasertib, a clinical candidate CHK1 inhibitor, increased autophagic flux in PDAC cells and synergized with CQ to decrease PDAC cell proliferation and increase apoptosis. We conclude that concurrent suppression of multiple metabolic processes, to block compensatory rebound activities, will be needed for effective PDAC treatment. This abstract is also being presented as Poster B07. Citation Format: Kirsten L. Bryant, Jennifer E. Klomp, Ye S. Lee, Clint A. Stalnecker, Kajal R. Grover, A. Cole Edwards, Sen Peng, Mariaelena Pierobon, Emanuel F. Petricoin III, Nhan Tran, Alec C. Kimmelman, Adrienne D. Cox, Channing J. Der. Enhancing the effec