P01.16MICROGLIA/MACROPHAGES AS CELLULAR TARGET OF NOVEL CXCR4 ANTAGONIST IN A GLIOMA MODEL

BACKGROUND: The CXCL12/CXCR4 signaling pathway has been recently described regulating proliferation, metastasis and angiogenesis in several solid tumors, including brain malignances and modulate the cross-talk between tumor and microenvironment. In gliomas recent studies demonstrated that tumor cells attracts surrounding microglia/macrophages into the tumour mass polarizing infiltrating microglia into an anti-inflammatory, immunosuppressive, proangiogenic phenotype (M2) that promote cancer growth, in this context CXCL12 acts as chemoattractant and contributes to suppress anti-tumor immunity, favoring the M2 phenotype polarization. Aim of this study was to evaluate the effects mediated by a novel CXCR4 antagonist, Peptide R, on tumor microenvironment in an orthotopic human glioblastoma multiforme (GBM) model. MATERIAL AND METHOD: Studies were performed using intracranial xenografts of U87MG GBM cells injected in CD1 nude mice. Peptide R (CNR and INT G. Pascale, Naples) (2mg/kg) was administered for 15-20 days since U87MG cells implantation. To evaluate glioma growth, tumor volume was assessed by magnetic resonance imaging (MRI) analyses, performed at 4.7 T. Confocal Laser Scanning Microscopy (CLSM) analyses on brain sections were conducted to analyze expression of markers identifying microglia/macrophages (CD11b, CD68) and markers associated to pro-inflammatory microglial phenotype (M1) or immunosuppressive phenotype (M2), respectively inducible nitric oxide synthase (iNOS) and Arginase-1 (Arg-1). Moreover we examined vascular endothelial growth factor, VEGF and endothelial marker expression (CD31). RESULTS: AND DISCUSSION: Confocal analyses of brain sections showed a modulation of reactivity and spatial distribution of microglia/macrophages in response to Peptide R, as detected by CD11b/CD68 double staining treatment. We reported a reduction in the number of CD11b+ cells recruited at the tumor-edge, together with an increased percentage of CD11b+ cells expressing iNOS, pro-inflammatory phenotype of microglia, in tumor core. At the same time, in peptide R-treated animals we observed reduced Arg-1 expression, by intratumoral endothelial structures, but not in CD11b + /Arg-1 cells. Furthermore Peptide R induced a drastic inhibition of VEGF and CD31 expression in tumor core. CONCLUSION: Our results showed that the new antagonist Peptide R induced alterations on tumor microenvironment favoring the acquisition of pro-inflammatory features in a GBM xenograft model creating a niche less favorable to the tumor growth. Modulation of CXCL12/CXCR4 axis in GBM may prove to be an important therapeutic strategy to interfere with the crosstalk between tumor and surrounding cellular microenvironment.