TMET-35. ONE CARBON AND NUCLEOTIDE METABOLISM ARE NOVEL TARGETS IN PEDIATRIC BRAINSTEM TUMORS

Abstract

Abstract Diffuse intrinsic pontine glioma (DIPG) are inoperable tumors of the brainstem with no cure. The median survival of children with DIPG is less than 2 years and 5-year overall survival is only 1%. Genomic studies have identified recurrent mutations in histone H3, ACVR and TP53 genes in DIPG. However, there are still no breakthrough drug targets for DIPG. To better understand the disease biology and find new drug targets for DIPG, we recently performed joint pathway analysis of DIPG metabolites (untargeted metabolomics) and differentially expressed genes (RNAseq) relative to normal human neural stem cells. We discovered that specific enzymes of the de novo purine biosynthesis pathway (DNPB), serine synthesis and the associated and one-carbon (1C) metabolism are highly active and the most upregulated in DIPG tumors and cell lines. Gain and loss of function experiments as well as pharmacological studies indicated a mechanistic link between DIPG mutations and DNPB pathway and the dependence of DIPG cells on specific DNPB and 1C metabolism enzymes for in vitro and in vivo growth. The 1C pathway is crucial for rapidly proliferating malignant cells as it senses and regulates cellular nutrient status by allocating and cycling 1C-groups between different acceptor compounds. It controls synthesis of nucleotides, amino acids, glycogen and phosphoglyceride precursors, S-adenosylmethionine (SAM), glutathione and NADPH. Thus, besides dispensing carbon atoms it also regulates cellular epigenetic and redox status. An important carbon donor is serine which is synthesized from glucose at 3-phosphoglycerate step in glycolysis. Untargeted as well as carbon and nitrogen tracing experiments indicated large folate pools in DIPG cells that can serve as a buffer to potentially blunt antifolate therapy. Experiments are underway to understand the importance of the folate cycle in DIPG and design novel and translatable combination therapies for DIPG.