HGG-02. METABOLIC TARGETING OF HIGH-GRADE GLIOMAS WITH MTAP LOSS

Malignant transformation of pediatric glioma is often associated with homozygous deletion of CDKN2A. With CDKN2A loss, MTAP which is in the same chromosomal location, 9p21, is homozygously deleted in a majority of HGGs and some LGGs. The MTAP gene codes for methylthioadenosine phosphorylase (MTAP) protein which plays an important role in methionine salvage pathway. Absence of MTAP results in accumulation of 5’-methylthioadenosine (MTA), de novo purine synthesis, and tumor cell dependency on protein arginine methyltransferase 5 (PRMT5) and its substrate provider, methionine adenosyltransferase II alpha (MAT2A). We hypothesize that drugs targeting PRMT5, MAT2A, and de novo purine synthesis, in combination with drugs targeting hyper-activated RAS/MAPK pathway, will be effective in inhibiting MTAP-null glioma growth. Patient-derived glioma cells were validated for MTAP loss using genome sequencing, RNA sequencing and western blot. MTA accumulation caused by MTAP loss was validated through high-performance liquid chromatography. Cells were subjected to monotherapy and combination drug therapy with PRMT5, MAT2A and de novo purine synthesis inhibitors, in addition to drugs targeting RAS/MAPK signaling pathway. Additionally, MTAP-null (MTAP(null)) in vivo models are being developed.We show accumulation of MTA in MTAP(null) cells compared to MTAP-wild type (MTAP(WT)) cells, caused by loss of MTAP that cleaves MTA to adenine and 5-methylthioribose-1-phosphate (MTR). Accumulation of MTA makes MTAP(null) glioma cells more sensitive to MAT2A inhibitor AG-270 in comparison to MTAP(WT) cells. Additionally, dual-drug therapies involving MTA and AG-270 result in additive effect on MTAP(null )cells and antagonistic effect on MTAP(WT) cells. De novo purine synthesis inhibitor and drugs targeting the RAS/MAPK pathways also exhibited cell growth inhibition of MTAP(null) cells. Overall, metabolic targeting of HGGs bearing CDKN2A/MTAP loss is indispensable for targeted therapy and for minimizing toxicity towards surrounding normal cells lacking similar mutations.