Abstract 2279: Anti-VEGF but not VEGF receptor inhibitor therapy prolongs survival and blocks myeloid cell recruitment to orthotopic glioblastoma
Authors: de Groot John F. , Piao Yuji 
Published: February 2011

Abstract
The growth of glioblastoma tumors depends on the formation of new blood vessels. VEGF is the best-known and most potent regulator of angiogenesis and recent clinical trials in glioma with small-molecule inhibitors of VEGFR and the VEGF antibody bevacizumab have shown promising results. In addition to promoting angiogenesis, VEGF and PlGF are potent myeloid cell chemokines known to be important for attracting VEGFR1+ monocytes to glioma tumors. Recent experimental evidence suggests that elimination of VEGFR1 signaling in bone marrow-derived cells significantly decreases glioma growth and vascularization, suggesting that VEGFR1-expressing myeloid cells play an important role in sustaining glioma angiogenesis.
In the present study we evaluated the effect of anti-VEGF and VEGFR inhibitor therapy on animal survival and on the infiltration of CD11b+ myeloid cells into orthotopic glioma tumors. Following orthotopic implantation of 5 × 105 U87 cells, animals were treated with bevacizumab (Avastin, Genentech, “anti-VEGF”), sunitinib (Sutent, Pfizer), or the combination of bevacizumab plus sunitinib and followed for survival (n=8-12 per group). Sunitinib monotherapy did not prolong animal survival compared to control. Bevacizumab significantly prolonged survival but the combination of bevacizumab plus sunitinib was superior with a median survival of 63.5 days compared to 46.5 days for bevacizumab alone (p=0.048). Separate animal cohorts (n=6) were sacrificed at 4 and 6 weeks for collection of peripheral blood and tumor. Whole blood was analyzed and infiltrated myeloid cells were isolated from tumor using a Miltenyi Biotech dissociation kit and evaluated using a FACSCanto flow cytometer. Acquired data was analyzed with FloJo software with gate analysis designed to remove debris. U87 tumors recruited a large number of CD11b+/F4/80+ macrophages into tumor compared to normal brain without tumor. At 4 weeks, bevacizumab treated mice had significantly lower numbers of infiltrated CD11b+/F4/80+ myeloid cells compared to sunitinib treated and untreated controls. Monocyte/macrophage infiltration was not blocked by VEGFR inhibitor treatment suggesting that anti-VEGF therapy is better able to decrease accumulation of tumor macrophages. At the time of tumor progression during continuous bevacizumab therapy (6 weeks), there was a dramatic and significant increase in the numbers of infiltrated Gr1+/CD11b+ cells.
These results suggest that the benefit of anti-VEGF therapy in this orthotopic glioma model is associated with a decrease in the recruitment and infiltration of CD11b+/F4/80+ cells into tumor. Neither a decrease in myeloid cell recruitment nor a survival benefit was observed in VEGFR inhibitor treated mice. Tumor progression during continuous anti-VEGF therapy is associated with an increase in Gr1+/Cd11b+ cell infiltration.
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 2279.