Mechanistic dissection and inhibitor targeting of autophagy in RAS driven cancers

Title: Mechanistic dissection and inhibitor targeting of autophagy in RAS driven cancers
PI: Kirsten L. Bryant, PhD
Description/Abstract
Autophagy is a self-degradation process whereby cells can orderly clear defective organelles and recycle
macromolecules as a nutrient source. Autophagy is elevated and essential for the tumorigenic growth of KRAS-
mutant pancreatic ductal adenocarcinoma (PDAC), providing the rationale for clinical evaluation of the autophagy
inhibitor hydroxychloroquine (HCQ) for PDAC. Disappointingly, when used as monotherapy or in combination
with standard of care, HCQ has shown limited to no clinical efficacy for PDAC. We recently determined that the
treatment of PDAC with inhibitors of the key KRAS effector pathway, the RAF-MEK-ERK mitogenic activated
protein kinase (MAPK) cascade, unexpectedly caused further elevation of autophagy, rendering PDAC acutely
dependent on this process, and hypersensitive to autophagy inhibition. We determined that ERK inhibition
impaired other critical processes that then led to compensatory upregulation of autophagy. Our findings, together
with essentially identical conclusions by another independent co-published study, have led to the initiation of
clinical trials evaluating either MEK (trametinib, binimetinib) or ERK (LY3214996) inhibitor in combination with
HCQ for metastatic KRAS-mutant PDAC. While early observations from compassionate use of this combination
support a significant clinical impact, our preliminary studies support our premise that we can improve upon this
therapy. We propose two aims to further advance autophagy inhibition as an anti-RAS therapeutic approach.
HCQ is a lysosome inhibitor and consequently not selective for autophagy. We hypothesize that inhibitors of the
proteins upstream in the autophagy pathway, will synergize with HCQ and more potently and durably inhibit the
autophagy pathway. Additionally, a comprehensive evaluation of the effect of inhibition of each individual node
of the autophagy pathway on flux in the context of an autophagy-addicted cancer such as PDAC has not been
performed. Thus, we will determine the effect of individual and combined inhibition of different nodes of the
autophagic pathway on autophagic flux (Aim 1). Our Aim 2 studies are based on our recent observation that
PDAC cells upregulate macropinocytosis in response to sustained inhibition of the RAS ERK MAPK pathway.
We hypothesize that the upregulation of macropinocytosis facilitates resistance to both RAS- and autophagy-
targeted therapeutics. We will characterize the mechanistic signaling underlying macropinocytic upregulation as
well as evaluate RAS inhibitor resistant cells to determine whether upregulated macropinocytic activity is a driver
of resistance. In summary, our studies will enhance our understanding of regulation of nutrient scavenging
pathways in PDAC and aid in the development of novel combination therapies to target autophagy and
macropinocytosis for the treatment of KRAS-mutant cancers.

Grant Number: 4R37CA251877-06
NIH Institute/Center: NIH
Principal Investigator: Kirsten Bryant