Pancreatic ductal adenocarcinoma (PDA) is a leading cause of cancer-related mortality in the United States. Unfortunately, both genomic and transcriptomic analyses of PDA have failed to identify therapeutically relevant targets. Combination chemotherapy remains the standard of care for the majority of patients who present with locally advanced or metastatic disease, resulting in a median overall survival of less than one year. PDA has been subclassified into 2-4 transcriptional subsets, which can be defined by their unique epigenetic states rather than a specific genetic profile. Of these subsets, the quasi-mesenchymal (QM) subtype is characterized by the worst prognosis, thus highlighting the importance of identifying new therapeutic avenues for QM PDA. The short- term goals of this proposal are to elucidate the genetic or epigenetic mechanisms regulating QM PDA subtype determination and to leverage that understanding toward the development of targeted therapies for QM disease. Our preliminary data suggest PDA may downregulate a novel epigenetic regulator and tumor suppressor in PDA in order to achieve this more aggressive QM PDA phenotype, while at the same time rendering tumor cells more sensitive to specific targetable therapies. This epigenetic regulator, a histone deacetylase called sirtuin 6 (SIRT6), was recently shown to act as a potent tumor suppressor in genetically engineered mouse models (GEMMs) of PDA, and inversely correlates with poor prognosis in patient samples. However, how SIRT6 is downregulated in PDA and its role in regulating PDA subtypes remains unknown. Here we propose three specific aims: (1) To identify novel mechanisms of SIRT6 downregulation in PDA; (2) To determine the functional role of SIRT6 in regulating PDA subtypes; and (3) To develop novel therapeutic approaches for this QM subset of PDA tumors. To accomplish these aims, we will apply a combination of cytogenetics, high- throughput sequencing, genetic gain of function and loss of function approaches and pharmaceutical interventions to a robust panel of molecularly characterized PDA GEMMs, human PDA cell lines and patient- derived xenografts from the NCI Patient-Derived Models Repository. Our approach also takes advantage of an innovative class of targeted therapeutics, which bind covalently to a specific residue on their target protein in order to achieve greater inhibition and specificity. The long-term goal of our work is to transform the clinical paradigm for this cancer from combination chemotherapy, toward a precision medicine-based approach utilizing predictive biomarkers to tailor more effective and less toxic therapies for PDA patients.
Pancreatic ductal adenocarcinoma (PDA) can be classified into quasi-mesenchymal (QM) and classical subtypes, but the genetic or epigenetic mechanisms driving subtype determination in PDA remain poorly understood. Our preliminary data suggests that loss of the histone deacetylase and PDA tumor suppressor gene Sirtuin 6 (SIRT6) may act an epigenetic switch that drives the more aggressive QM phenotype, while at the same time rendering PDA cells highly dependent on a specific targetable pathway. This proposal aims to elucidate mechanisms of SIRT6 downregulation in QM PDA, explore SIRT6 as a critical regulator of PDA subtype determination, and leverage this knowledge for the preclinical development of novel targeted therapies in this disease.
