Defining Novel Redox Stress Mechanisms to Inhibit KRAS-driven Pancreatic Ductal Adenocarcinoma

Project Summary Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer deaths with a 5-year survival rate of 12%. Over 90% of PDAC is driven by oncogenic KRAS, however inhibitors targeting KRAS have been unsuccessful in the clinic thus far. Targeting oncogenic vulnerabilities is a key alternative approach. Oncogenic

RAS-generated reactive oxygen species (ROS) drives tumor progression through hyperactivation of proliferative, anti-apoptotic, and metastatic pathways. However, ROS can also trigger tumor suppressive outcomes through cellular damage. The nucleotide pool-cleansing 8-oxo-dGTPase MutT Homolog 1 (MTH1) is a critical redox

protective adaptation in RAS-driven tumor cells to overcome tumor-inhibitory ROS mediated consequences. MTH1 has been shown to prevent oncogene-induced oxidative stress and damage, and maintain high KRAS oncoprotein expression, associated ROS-driven oncogenic signaling, and tumorigenicity in lung cancer. Given

the importance of MTH1 in KRAS oncogenic biology and the fact that over 90% of PDAC is driven by oncogenic KRAS, I propose that MTH1 is similarly important in PDAC. In support of this idea, TCGA analysis revealed MTH1 expression is significantly higher in tumor tissue compared to normal tissue, and high MTH1 significantly

correlates with poor disease-free survival. The Rai lab reported 8-oxodGTPase activity is significantly elevated in patient PDAC tumor vs. normal tissue. Preliminary data show MTH1 loss reduces tumor burden in a subset of PKT cohorts, with lower burden associated with both reduced intratumoral EGFR expression and in cytokines

associated with an immunosuppressive tumor microenvironment (TME). When MTH1 is depleted via shRNA in PDAC cell lines, there is a significant decrease in proliferation associated with decreased total EGFR. Analysis of human PDAC tumor data through TIMER 2.0 shows intratumoral MTH1 expression significantly correlates

with infiltration of myeloid derived suppressor cells (MDSCs), suggesting high MTH1 expression supports and/or creates the immunosuppressive TME that make PDAC so difficult to treat. Therefor I hypothesize MTH1 is important for PDAC tumorigenesis through both tumor cell-intrinsic as well as previously-unappreciated

extrinsic mechanisms. To test this hypothesis, I will use our novel PKT mouse models with systemic and pancreas-specific MTH1 loss. Experiments proposed in Aim 1 will assess how systemic vs pancreas-specific MTH1 loss affects in vivo KRAS tumorigenesis; Aim 2 will independently ascertain how MTH1 regulates KRAS-

driven transformation and PDAC chemoresistance. Upon completion of these studies, we will establish novel mechanisms by which MTH1 regulates tumorigenesis thus filling a gap in the field regarding the link between MTH1 and KRAS in PDAC. Lastly, these aims have the potential to validate MTH1 as an alternative to targeting

oncogenic KRAS in PDAC patients which has been unsuccessful to date.