Abstract B006: Targeting keratin 17-mediated metabolic reprogramming of de novo pyrimidine biosynthesis as a novel strategy to overcome chemoresistance in pancreatic cancer
Authors: Pan Chun-Hao , Tseng Robert , Horowitz Michael , Sira Md Afjalus , Chen Bo , Donnelly Katie L. , Leiton Cindy V. , Marchenko Natalia , Singh Pankaj K. , Shroyer Kenneth R. , Escobar-Hoyos Luisa F. 
Published: November 2022

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer death. We previously reported that keratin 17 (K17) is a negative prognostic and predictive biomarker, whose overexpression confers the resistance to chemotherapies. Here, we investigated the mechanisms of chemoresistance and tumor-specific vulnerabilities that can be exploited for the development of novel targeted therapies for K17-expressing PDAC. We hypothesized that K17 reprograms cancer metabolism and leads to therapeutic resistance. To test this, we manipulated the expression of K17 in multiple in vitro and in vivo models of PDAC, spanning human and murine PDAC cells and orthotopic xenografts. Unbiased metabolomic studies in isogenic PDAC models identified several key metabolic pathways that are upregulated in the presence of K17, including glycolysis, purine biosynthesis, and pyrimidine biosynthesis. We demonstrate that K17 increases pyrimidine biosynthesis, a pathway that has been linked to chemoresistance. Patient dataset analysis revealed that K17 expression and enzymes involved in pyrimidine, but not purine, de novo biosynthesis are associated with shorter patient survival. To address how altered nucleotide biosynthesis contributes to chemoresistance, we performed drug-response experiments with exogenous nucleosides. We found that deoxycytidine (dC) and deoxythymidine (dT) are sufficient to promote resistance to Gemcitabine (a dC analog) and 5-fluorouracil (a dT analog), respectively. To further evaluate therapeutic opportunity by targeting K17-dependent pyrimidine biosynthesis, we tested compounds that inhibit individual nucleotide biosynthetic pathways. We found that K17-expressing cells were more sensitive to Brequinar, a specific inhibitor of dihydroorotate dehydrogenase (DHODH), the rate-limiting enzyme in de novo pyrimidine biosynthetic pathway. Targeting DHODH by siRNA or by Brequinar had synergistic effects when combined with Gemcitabine in inhibiting cell viability of K17-positive cells, revealing a druggable pathway dependency for K17-positive tumors. Currently, we are testing the combination of Brequinar and Gemcitabine in our animal models. Overall, we identified a novel pathway of chemoresistance and a target which could lead to the development of a biomarker-based therapy for K17-expressing PDAC.
Citation Format: Chun-Hao Pan, Robert Tseng, Michael Horowitz, Md Afjalus Sira, Bo Chen, Katie L. Donnelly, Cindy V. Leiton, Natalia Marchenko, Pankaj K. Singh, Kenneth R. Shroyer, Luisa F. Escobar-Hoyos. Targeting keratin 17-mediated metabolic reprogramming of de novo pyrimidine biosynthesis as a novel strategy to overcome chemoresistance in pancreatic cancer [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 B006.