P-01.12 Impact of glutamate metabolism and its inhibition on melanoma development and immune cells

<h3>Background</h3> Tumor immunity is negatively regulated by metabolites in the tumor tissue. Metabolic reprogramming impacts the activation and maturation of dendritic cells (DC). We work on the transgenic melanoma mouse model tg(Grm1)EPv which spontaneously develops melanoma due to overexpression of the metabotropic glutamate receptor 1 (Grm1) in melanocytes. This aberrant glutamate metabolism drives melanoma formation also in patients, however the effects on immune cell function is poorly understood. Thus, we study the metabolic changes in progressing tg(Grm1)EPv melanoma and their possible effects on DC and T cell responses. <h3>Materials and Methods</h3> We performed analysis of myeloid subsets in tumors and draining lymph nodes during tumor progression with multicolor flow cytometry. Metabolic screening of the tg(Grm1)EPv mice at different disease stages with LC-MS technology and glutamate release assays were done to understand metabolic alterations upon tumor development. Interference with glutamate metabolism was tested in vitro on melanoma cell lines and in vivo in tumor-bearing mice to investigate tumor cell behavior and subsequent effects on immune cells. <h3>Results</h3> The characterization of DC subtypes during tumor progression demonstrated a decrease in conventional DC type 2 (cDC2) and LC, whereas cDC1 were unchanged. All DC subtypes displayed a more immunosuppressive phenotype with tumor growth. Metabolic measurements revealed a shift towards glutamate/glutamine, a shift from Glucose/Pyruvate to Lactate during glycolysis and a decrease in ATP. This data is supported by RNA sequencing results showing an increased expression of enzymes involved in glutamate metabolism and glycolysis. These changes indicate a Warburg effect, disruption of the respiratory chain, and metabolic changes in the tumor microenvironment that are advantageous for the tumor cells and unfavorable for DC. Glutamate pathway inhibition with Buthionine sulphoximine (BSO) induced ferroptotic cell death in Grm1-positive melanoma cells in vitro. Current investigations with BSO for treatment of tumors in tg(Grm1)EPv mice point at slower tumor growth combined with infiltration of immune cells suggesting immunogenic cell death by interference with glutamate metabolism. <h3>Conclusions</h3> The interference with glutamate metabolism could represent a novel therapeutic strategy for cancer patients however the effects on immune cells need further investigation. Thus, combination therapy with inhibitors of the glutamate pathway might improve response rates in melanoma patients in future. S. Dieckmann: None. C.H. Tripp: None. H. Strandt: None. F. Hornsteiner: None. A. Schäfer: None. H. Oberacher: None. J. Wölk: None. N. Hermann-Kleiter: None. P. Stoitzner: None.