Nutrient availability (i.e. diet) can affect metabolic pathways and determine the requirements of cancer cell metabolism to as large a degree as the metabolic genes that are reprogrammed in tumors. Previous work from us and others has shown that 1.) methionine availability affects one carbon cycle flux, DNA and histone methylation and thus epigenetic programming, 2.) dietary methionine restriction promotes metabolic health and extends insect and mammalian lifespan, two anti-cancer phenotypes, 3.) deletions of genes that affect methionine metabolism in tumors render them susceptible. Nevertheless, how this dietary factor (and diet in general) can influence cancer outcome is largely unknown. Our preliminary data shows that methionine restriction delays tumor growth in colorectal cancer patient derived xenograft (CRC PDX) models and sensitizes a genetically engineered mouse sarcoma model to radiation. These findings led us to propose an investigation to define the mechanisms underlying these phenotypes. We will consider the following aims. In aim 1 we seek to identify molecular determinants of sensitivity to methionine restriction. We will employ a metabolomics approach using a metabolite profiling platform and flux analysis method our laboratory has developed to investigate the metabolic changes in cancer cells that are induced by methionine restriction. We will next investigate the epigenetic role that methionine metabolism in tumor growth. The outcome will determine the metabolic and epigenetic adaptations that are modulated through dietary methionine metabolism. In aim 2, we will determine why the sarcomas are resistant to methionine restriction but respond to dietary methionine restriction and radiation in a synergistic manner. The outcome will define the metabolic and epigenetic mechanisms that occur in order to resist dietary manipulation of methionine metabolism but leads to a synergy effect of dietary methionine restriction and radiation. In aim 3, we will determine the role of methionine availability from diet in methylthioadenosine phosphorylase (MTAP)-deleted cancers. MTAP is an enzyme essential for the methionine salvage pathway and recent studies have shown that deletions in MTAP confer additional dependencies on methylation reactions. The outcome, using MTAP, dietary methionine, and methionine metabolism as a model system will characterize the metabolic interaction between dietary methionine and MTAP deletion and lead to a newfound understanding of the interaction between genetics and environment, particularly diet and nutrition in mediating cancer outcome.