Abstract 3291: Macrophages and granulocytes promote the malignant glioma phenotype

Abstract

Abstract Solid tumors, including glioblastoma, contain large populations of both malignant and non-malignant cells. The tumor microenvironment contains a multitude of different cell types and recent evidence supports the role of CD45+ bone marrow cells such as vascular modulating macrophages. Tumor associated macrophages accumulate in hypoxic or necrotic regions of human tumors where they release VEGF. Recent studies have demonstrated that the number of M2-skewed macrophages (CD163+/CD204+) in human tumors correlates with glioma grade, cell proliferation and microvascular density. Myeloid cells including macrophages and granulocytes are thought to promote the malignant phenotype of many solid tumor types but little is known about their influence on glioma biology. To evaluate the impact of macrophages and granulocytes on the malignant phenotype, we used co-culture experiments to determine the influence of these cells on glioma cytokine and angiogenic factor release, glioma cell invasion and proliferation, and resistance to chemotherapy. Mouse macrophages or granulocytes (ATCC) were cultured alone or together with U87 or glioma stem cells using a Boyden chamber to maintain cell separation. Conditioned media and RNA were evaluated for expression of both mouse and human chemokine expression using ELISA and quantitative PCR. Co-culture resulted in a significant increase in macrophage VEGF-A, CXCL1, HGF, VEGF-C and PlGF expression and granulocyte IGF1, FGF, CCL11, VEGF-C and VEGF-D compared to baseline suggesting that myeloid cell-glioma crosstalk may promote VEGF-A-independent angiogenesis in glioma tumors. Co-culture promoted glioma cell expression of PDGF, CCL11, CXCL9, and INF-β. We next evaluated the impact of myeloid cells on glioma invasion. At baseline, U87 demonstrates minimal transwell migration in vitro and does not invade normal brain in vivo. When co-cultured, macrophages and granulocytes significantly increased U87 in vitro transwell migration compared to control. Finally, serum free media incubated for 48 hours with mouse macrophages or granulocytes was used as growth medium for U87 cells. Using a SRB cell proliferation assay, conditioned media from granulocytes but not macrophages increased glioma proliferation compared to controls. Conditioned media from both macrophages and neutrophils reduced the sensitivity of glioma cells to temozolomide in vitro. These results suggest that both macrophages and granulocytes may play an important role in promoting glioma angiogenesis, invasion and resistance to chemotherapy. However, granulocytes were more effective in promoting glioma proliferation. Targeting myeloid cells may be an effective approach to inhibiting the glioma malignant phenotype. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3291. doi:10.1158/1538-7445.AM2011-3291