Abstract B057: KRAS mutant-specific protein interactions reveal mechanisms in pancreatic cancer tumorigenesis and metabolic regulation
Authors: Hobbs Guy Aaron , Burge Rachel , Linke Amanda , Sundararaj Kamala , O'Bryan John P. 
Published: November 2022

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is the third most deadly human cancer in the US with a five-year survival rate of 11%. KRAS is mutated in over 95% of PDAC patients and is a key driver of tumorigenesis. Despite the promise of targeted inhibition of the RAF-MEK-ERK MAPK signaling pathway, arguably the most critical KRAS-mediated signaling pathway, clinical trials targeting MEK/ERK signaling as a single-agent therapy have been unsuccessful, indicating the role of additional KRAS-specific signaling pathways. The most frequent KRAS mutations in PDAC are KRAS G12D (40%), KRAS G12V (33%) and KRAS G12R (17%). However, the KRAS G12R mutation is rare in lung and colorectal cancers (&lt;1%), suggesting the presence of KRAS mutant-specific signaling, which remains poorly understood. While mutagenic processes may drive the observed mutation frequency data, many studies have demonstrated that mutant KRAS protein signaling drives the overall observed mutational frequencies. In agreement with this observation, the KRAS Q61L mutant is predicted to occur in PDAC but is rarely detected in the patient population. Therein, we hypothesize that mutation-specific signaling promotes tumorigenesis and that determination of the KRAS mutant-specific interactomes that promote pancreatic tumorigenesis in KRAS G12R yet hinder oncogenic fitness in KRAS Q61L will provide insight into the development of KRAS mutation-selective therapies in PDAC. Thus, we used doxycycline-inducible KRAS constructs combined with BioID proximity labeling to determine the mutant-selective interactomes of four KRAS mutant proteins in an isogenic immortalized pancreatic cell line. While we detected significant overlap in effector signaling, numerous mutant-selective differences were detected, including pathways regulating endocytosis and autophagy. Interestingly, the PDAC tumor microenvironment has been shown to have limited nutrient availability, which promotes macropinocytosis, the nonselective uptake of proteins and molecules from extracellular spaces, and autophagy, a mode of cellular recycling, to promote tumor proliferation. To replicate this environment in cell culture, we utilized a minimal glucose medium supplemented with albumin, a large protein that is absorbed via macropinocytosis. We show that this altered cell culture medium preferentially drives increased macropinocytosis and resistance to MEK MAPK and autophagy inhibition in KRAS G12R-mutant PDAC. Furthermore, while KRAS G12R PDAC cell lines continue to proliferate in the absence of glucose, many KRAS G12D mutant PDAC cell lines fail to sustain proliferation. To determine alternative potential therapeutic vulnerabilities, we have performed an RNA sequencing screen in high and low glucose medium, which has exposed an increase in receptor tyrosine kinase signaling and a reprogramming of metabolic processes in the tricarboxylic acid cycle. These studies provide a rationale for the limited success of MEK/ERK therapies in the clinic and we propose novel treatment strategies for KRAS G12R PDAC patients with elevated macropinocytosis.
Citation Format: Guy Aaron Hobbs, Rachel Burge, Amanda Linke, Kamala Sundararaj, John P. O'Bryan. KRAS mutant-specific protein interactions reveal mechanisms in pancreatic cancer tumorigenesis and metabolic regulation [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B057.