(699f) Analyzing Cancer as a Metabolic Disease Using 13C Metabolic Flux Analysis to Decipher Pathway Regulation

During carcinogenesis tumor cells undergo a metabolic transformation to fuel their aggressive growth in the body. Unique changes in energetic and biosynthetic pathway fluxes enable cancer cells to better utilize substrates in their microenvironment but offer novel therapeutic targets as well. Here we have conducted metabolic flux analysis (MFA) using stable isotopic tracers to characterize the role of key metabolic pathways in supplying carbon precursors and energy-redox equivalents for cell growth. Using 13C glucose and glutamine tracers we identified elevated fluxes within central carbon metabolism in A549 cells. Significant levels of reductive carboxylation were detected in MFA experiments, and experimental modeling of lipogenesis using isotopomer spectral analysis (ISA) indicated this pathway was the preferred route of glutamine carbon to fatty acid synthesis in tumor cells. By using shRNA to knockdown isocitrate dehydrogenase expression in the cytosolic or mitochondrial compartments, we demonstrate the major enzyme responsible for this flux is IDH1. Ample expression of this enzyme is necessary for cells to proliferate in vitro. Furthermore, oncogenic mutations and signals from the microenvironment direct cells to modulate this flux, indicating that reductive carboxylation plays a role in tumorigenesis. These results highlight the utility of 13C MFA in elucidating the metabolic phenotype of tumor cells and identifying potential drug targets for cancer.