Abstract A32: GFAT: The crossroads of glucose and glutamine metabolism in pancreatic cancer
Authors: Halbrook Christopher J. , Kremer Daniel M. , Salamanca-Cardona Lucia , Keshari Kayvan R. , Lyssioitis Costas A. 
Published: December 2016

Due to a lack of early detection methods and effective treatment strategies, pancreatic cancer is slated to become the second leading cause of cancer related death in the United States. Pancreatic ductal adenocarcinoma (PDA), the most common type of pancreatic cancer, is initiated almost universally by mutations in the Kras oncogene. Kras mutations rewire metabolism in the cancer cells by enhancing nutrient capture and facilitating metabolic pathways that support survival and proliferation in the austere tumor microenvironment. Among these pathways, we have previously demonstrated that mutant Kras drives glucose flux into the hexosamine biosynthetic pathway (HBP) through upregulation of the rate limiting enzyme, glutamine fructose-6-phosphate transaminase (GFAT). The HBP plays a well-established role in the generation of the precursor substrates in glycosylation. In addition to this, GFAT has a less well appreciated facet, as it requires input from both glucose and glutamine (Gln). Specifically, GFAT deamidates the terminal nitrogen on Gln and releases glutamate, which can serve as an anaplerotic carbon source for the TCA cycle. Accordingly, GFAT sits at a nexus in the metabolism of the two canonical nutrients used by proliferating cells.

Previous work from our group demonstrated that GFAT1 knockdown in mouse PDA cells results in the inhibition of colony formation and decreased growth of subcutaneous xenografts in mice. These results combined with the nearly ubiquitous nature of Kras mutations in pancreatic cancer, strongly indicate that targeting the HBP by inhibition of GFAT could offer a powerful new avenue of treatment for PDA. Utilizing a Cas9/CRISPR approach to modulate GFAT expression in human PDA cells, we have generated cell lines which require the addition of downstream HBP metabolites to maintain cell viability. We have also found several cell lines in which the loss of GFAT expression appears to have no impact on cell viability, suggesting novel mechanisms of glucose and Gln metabolism in these cells. In addition to validating GFAT as a therapeutic option in PDAC, we have also explored the utility of the GFAT reaction as an imaging tool. To accomplish this, we have developed a method to monitor the conversion of Gln to glutamate by magnetic resonance spectroscopy using hyperpolarized glutamine. We further assessed the importance of GFAT in this conversion utilizing our GFAT-/- cell lines. Taken together, these results highlight the benefit of working to understand the complex nature of metabolic rewiring in pancreatic cancer cells, where a further understanding of these pathways may lead to more effective early detection and therapeutic options.

Citation Format: Christopher J. Halbrook, Daniel M. Kremer, Lucia Salamanca-Cardona, Kayvan R. Keshari, Costas A. Lyssioitis.{Authors}. GFAT: The crossroads of glucose and glutamine metabolism in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A32.