Abstract 2384: Role of bone marrow derived progenitor cells in intracranial tumor neovascularization

Abstract

Abstract Background: Glial tumors are the most common and lethal adult brain tumor and the histopathological hallmark of their malignant transformation is vascular proliferation. Hence novel strategies to target tumor vascularity are continuously being explored in hopes to improve patient outcomes. More recent interest is focused on the role of bone marrow derived precursors cells (BMDCs) in tumor neovascularization. Whether BMDC differentiate into endothelial cells (EC) or perivascular support cells (PVC) is controversial and whether it is tumor type or tumor stage dependent remains unknown. Finally, impact of ionizing radiation (IR) on recruitment, migration and differentiation of BMDCs in brain tumor vasculature has not been examined. Methods: Animal Models: Bone marrow (BM) of NOD/SCID mice were stably reconstituted with BM derived from green-fluorescent protein (GFP) transgenic mice. Subsequently, brain tumor xenografts in an intracranial window chamber model (ICW) were generated using U87 glioma cells engineered to stably express mCherry fluorochrome. In-vivo imaging: Two-photon laser microscopy (2PLM) was used to obtain longitudinal real-time in-vivo images of the tumor cells, tumor vasculature and allow tracing of the circulating GFP+BMDCs in the ICW model. Mice were imaged daily for 20-30 days following cell implantation or following completion of RTx. Radiation Therapy (RTx): In order to examine the effects of IR, U87-mCherry tumors were treated with hemicranial irradiation at two regimens, 3×2Gy or 3×5Gy. U87-mCherry+RTx arm was compared to RTx alone or U87-mCherry alone. Brain Tumor Analysis: Mice were sacrificed in accordance with animal care protocol, using perfusion fixation and brains collected for correlative immunohistochemical (IHC) analysis. Results: Within 24 hours following tumor cell implantation GFP+ BMDCs can be seen circulating intravascularily and lining the vessel wall. 7d post implantation there is a decrease in GFP+BMDCs within vessels whilst cells migrating, differentiating and integrating outside the vessel lumen increases. IHC and 2PLM analysis identified three distinct GFP+ cells evolving over time: 1) circulating cells in vascular lumen in decreasing quantity, 2) supporting cells intimately encasing vessel walls that are smooth muscle cells or PVCs and 3) infiltrating cells within tumor microenvironment that are macrophages and micrglia. Control animals demonstrated a temporary recruitment of GFP+BMDCs to the injection site with no differentiation into cellular processes. Conclusion: Our results are the first to examine the real-time dynamic contribution of BMDC to glioma vasculature in-vivo. We demonstrate that BMDC differentiate to form macrophages and vascular support structures in the tumor microenvironment, with limited contribution to ECs. Ongoing work focuses on understanding alterations in response to IR and molecular regulators of BMDC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2384.