Pilot: Targeting De Novo and Salvage Nucleotide Synthesis with FASN/ATR Inhibition to Enhance Radiation Therapy Reponses

Radioresistance in metastatic, progressive gastroenteropancreatic neuroendocrine tumors (GEP-NETs) is a major factor leading to the failure of peptide receptor radiotherapy (PRRT) and poor prognosis in NET patients. The mechanism of primary and acquired radiation resistance to radionuclide therapy in NETs is poorly understood and the contribution of lipid biogenesis and nucleotide metabolism in radiation resistance are not known. Fatty acid synthase (FASN), a key enzyme of de novo lipid biogenesis, is significantly overexpressed in the majority of cancer tissues and associated with a poor prognosis. We hypothesize that FASN activity is essential for NADP-NADPH turnover and de novo nucleotide synthesis. In addition, we propose to disrupt supply of nucleotides from nucleotide salvage pathway though ATR inhibition. The current application proposes a comprehensive research plan to determine role of FASN in de novo nucleotide synthesis and determine how simultaneous inhibition of both de novo nucleotide synthesis and nucleotide salvage pathway inhibition disrupts DNA repair and enhances therapeutic activity of radiation therapy. Therefore, in Aim 1, we will elucidate the role of palmitate synthesis on NADP-NADPH turnover and nucleotide de novo synthesis. We will test the hypothesis that FASN inhibition results in disruption of NADP-NADPH turnover and inhibition of de novo nucleotide synthesis. Using targeted metabolomics, we will delineate how de novo palmitate flux alters intermediates of nucleotide metabolism. Furthermore, our preliminary data suggests that simultaneous inhibition of de novo nucleotide synthesis with FASN inhibition and nucleotide salvage pathway can enhance effect of radiation therapy in patients that receive targeted radiotherapy. Therefore, in Aim 2, we will evaluate in preclinical models of NET metastasis effect of FASN and ATR inhibition on radiation therapy in NET metastasis. I will utilize most advanced pre-clinical imaging models and models of NET metastasis for drug combination evaluations. These models will be used in conjunction with state-of-the-art approaches, including Stable Isotope-Resolved Metabolomics (SIRM) to evaluate the effect of FASN downregulation or overexpression on cancer metabolism. I anticipate that the proposed work will identify a subset of NET patients who would benefit from targeted FASN inhibition and further advance our understanding of the role of FASN in NET that would potentially lead to the development of novel therapeutic strategies to treat this disease. After collecting preliminary data from this collaborative study, we will submit an R01 application where we will test and translate the proposed methods to NET patients undergoing radiation/combination therapy Shared Resource Facilities utilized: Biospecimen and Tissue Procurement, Biostatistics and Bioinformatics, Metabolism Core, Imaging Core Shared Resource Facilities 1