Anales RANF

P.20 P.A METABOLIC IMMUNE CHECKPOINT: ADENOSINE IN BRAIN METASTASES TUMOR MICROENVIRONMENT A. Salamero Boix 1 , M. Schulz 1,2 , T. Alekseeva 1 , J. Zinke 3 , K. Niesel 1 , S. Stein 1 , F. Rödel 4 , P. Harter 3,5,6 , K. Plate 3,5,6 , L. Sevenich 1,5,6 1 Georg-Speyer-Haus, Institute for Tumor Biology and Experimental Therapy, Frankfurt am Main, Hessen, Germany 2 Faculty 15-Biological Sciences, Goethe University Frankfurt, Germany 3 Institute of Neurology, Edinger Institute, KGU Frankfurt, Germany 4 Department of Radiotherapy and Oncology, Goethe University Frankfurt, Germany, 5 Frankfurt Cancer Institute, Goethe University Frankfurt, Germany, 6 German Cancer Consortium (DKTK) and German Cancer Research Center (DKFZ), Heidelberg, Baden-Württemberg, Germany Brain metastases are the most common intracranial neoplasm in adults and represent the major cause of death in tumor patients. Given the fact that purines i.e. ATP and adenosine play key roles in neurotransmission and act as danger signals, we seek to understand the involvement of glial crosstalk in brain metastasis from different primary entities via adenosine and purinergic signaling and investigate how standard of care modulates this pathway. We observed cell-type specific expression of the key enzymes that convert purines to adenosine in a syngeneic breast-to-brain metastases model. While the cancer cells mainly expressed CD73, the myeloid compartment showed preferential expression of CD39. For functional analyses, we depleted tumor and/or stromal-cell derived CD73 or CD39 by CRISPR/Cas9 (for tumor cells) and knock-out mouse models (for stromal cells). In line with our data, we found no difference in brain metastases incidence and tumor growth in CD73 proficient and deficient mice if CD73 activity is unaffected in the tumor cells. Preliminary data indicate that genetic targeting of CD73 in the tumor and stromal compartment led to a delay in tumor onset, reduced growth rates and prolonged survival. However, in contrast to our genetic approaches, we found that CD73 pharmacological inhibition led to decreased median survival. Strikingly, the combination of CD73 inhibition with fractionated whole brain radiotherapy reverted this effect. Of clinical relevance is the observed expression of CD39, CD73, ADA, ADK, A2AR and A2BR in tumor cells and tumor-associated stromal cells in human brain metastases. Interestingly, A2BR expression inversely correlated with CD3, CD4 and CD8 infiltration, indicating that an adenosine driven environment might be implicated in establishing an immune suppressive environment. The long-term goal of this project is to interrogate if blockade of adenosine generating enzymes and adenosine receptors might establish a purine-driven pro-inflammatory environment that is more sensitive to standard of care treatment or immune therapies.