Abstract PO-023: Targeting a novel rewired pathway of nucleotide metabolism that drives chemoresistance in the most lethal molecular subtype of pancreatic cancer
Authors: Pan Chun-Hao , Otsuka Yuka , Sridharan BanuPriya , Woo Melissa , Leiton Cindy V. , Babu Sruthi , Gonçalves Mariana Torrente , Kawalerski Ryan R. , Bai Ji Dong K. , Moffitt Richard A. , Zhao Jiang , Chang David K. , Biankin Andrew V. , Duong Tim , Singh Pankaj K. , Scampavia Louis , Spicer Timothy , Shroyer Kenneth R. , Escobar-Hoyos Luisa F. 
Published: November 2020

Abstract
Pancreatic ductal adenocarcinoma (PDAC) includes two molecular subtypes, of which the basal-like subtype is associated with the shortest survival and is highly resistant to chemotherapy. The basal-like subtype is defined by a 25-gene signature; however, the role of these genes in promoting tumor aggression remains unexplored. Here, we set out to uncover the mechanisms of chemoresistance and explore targeted therapies for this subtype. We focused on studying an oncofetal antigen, keratin 17 (K17), which is the most overexpressed hallmark gene of the basal-like PDAC. We manipulated the expression of K17 and found that in multiple in vitro and in vivo models of PDAC, spanning human and murine PDAC cells and orthotopic xenografts, K17 expression resulted in a greater than two-fold increase in resistance to Gemcitabine (Gem) and 5-fluorouracil, the major chemotherapeutic agents in standard-of-care treatments. To uncover the mechanisms associated with K17-induced chemoresistance, we performed unbiased metabolomic studies in isogenic PDAC cell lines and found that compared to control cells, K17 increases intracellular levels of deoxycytidine (dC) by four-fold that promote Gem (dC analogue) resistance. Based on previous findings that K17 enters nucleus to regulate gene expression, we explored whether K17 triggers metabolic reprogramming at the transcriptional level and found that enzymes involved in pyrimidine biosynthesis are positively correlated with K17 expression in PDAC cells. Given that it is still poorly understood how K17 regulates gene expression, we performed domain-prediction analyses. We discovered and validated a novel chromatin remodeling domain on K17 that is required for metabolic reprogramming. We are now performing ChIP-Seq and RNA-Seq to understand how this domain alters pyrimidine biosynthesis. To identify small molecules that could target K17-expressing PDACs potentially by disrupting metabolic reprograming, we performed an unbiased high-throughput drug screen and found that Podophyllotoxin (PPT), a microtubule inhibitor, significantly and selectively killed K17-positive compared to K17-negative PDAC cells. In the clinic, another microtubule inhibitor, Paclitaxel (PTX), is used in combination with Gem as a first line chemotherapy. Surprisingly, when combined with Gem, PPT but not PTX, was synergistic in inhibiting the viability of K17-expressing PDAC cells and enhanced survival of mice bearing K17-expressing PDACs. Currently, we are exploring the role of PPT in regulating pyrimidine biosynthesis. In summary, we identified a novel pathway of chemoresistance and a compound that could result in developing a biomarker-based personalized therapy.
Citation Format: Chun-Hao Pan, Yuka Otsuka, BanuPriya Sridharan, Melissa Woo, Cindy V. Leiton, Sruthi Babu, Mariana Torrente Gonçalves, Ryan R. Kawalerski, Ji Dong K. Bai, Richard A. Moffitt, Jiang Zhao, David K. Chang, Andrew V. Biankin, Tim Duong, Pankaj K. Singh, Louis Scampavia, Timothy Spicer, Kenneth R. Shroyer, Luisa F. Escobar-Hoyos. Targeting a novel rewired pathway of nucleotide metabolism that drives chemoresistance in the most lethal molecular subtype of pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-023.