Targeting Keratin 17 in Pancreatic Cancer: A Novel Rewired Pathway of Nucleotide Metabolism that Drives Chemoresistance

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is characterized by two molecular subtypes, of which the basal‐like subtype is associated with the worst survival and is highly resistant to the first‐line chemotherapy. We previously reported that keratin 17 (K17), a signature gene in basal‐like subtype, is a novel negative‐prognostic and predictive biomarker, whose overexpression results in resistance to Gemcitabine (Gem) and 5‐fluorouracil, the major chemotherapeutic agents in standard‐of‐care treatments, and leads to shortened patient survival. Here, we set out to uncover the mechanisms of chemoresistance and explore targeted therapies for K17‐expressing PDAC. We hypothesized that K17 reprograms cancer metabolism and leads to therapeutic resistance. 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, for drug‐testing, metabolomic and mechanistic studies. 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. Interestingly, K17‐expressing cells are more sensitive to a compound that targets de novo pyrimidine biosynthesis. Based on previous findings that K17 enters nucleus to regulate gene expression, weexplored 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 in K17 that is required for metabolic reprogramming. Importantly, mice bearing tumors with the deletion of the chromatin remodeling domain in K17 survived significantly longer than those with tumors expressing wild type K17. We are now performing ATAC‐seq, ChIP‐Seq and RNA‐Seq to understand how this domain alters pyrimidine biosynthesis. In summary, we identified a novel pathway of chemoresistance that could result in developing a biomarker‐based personalized therapy.