Abstract 2282: Inhibition of vasculogenesis, but not angiogenesis, reduces tumor recurrence following irradiation

Abstract

Abstract Tumor blood vessels can derive from two sources: by angiogenesis, or the sprouting of endothelial cells from nearby blood vessels, and by vasculogenesis, which is produced by circulating cells. We have proposed that the radiation doses given in radiotherapy, will severely restrict local angiogenesis and thereby force tumor regrowth to rely on vasculogenesis. This involves the recruitment of proangiogenic circulating cells many of which are derived from the bone marrow. To investigate this hypothesis, we used the subcutaneously implanted FaDu human head and neck tumor and an orthotopic brain tumor using human U251 GBM cells. We found that local tumor irradiation induced the influx of bone marrow derived cells (BMDCs) in a dose-dependent manner into both tumor models with most of this increase reflecting influx of CD11b+ myelomonocytes. We postulated that this influx of BMDCs was stimulated by increased tumor hypoxia and HIF-1 levels caused by radiation damage to the tumor vasculature. To determine HIF-1 activity in real-time in our brain implanted U251 GBM, we stably expressed the HIF-1 reporter construct 5HRE-luc in U251 cells and showed that HIF-1 activity increased rapidly starting at about two weeks following 15 Gy, in parallel to the increase in tumor hypoxia that we observed at this time. To test our hypothesis that the increased HIF-1 levels were responsible for the increased influx of CD11b+ cells into the tumors, we used the HIF-1 inhibitor NSC-134754. When this was given daily for 2 weeks, starting immediately following irradiation, the increased tumor levels of CD11b+ monocytes observed after 15 Gy was abrogated. This treatment also prevented the regrowth of the irradiated tumors following irradiation. As a further test of our hypothesis we determined the effect of inhibiting the interaction of SDF-1 with its receptor CXCR4 using the clinically approved drug AMD3100, which we infused starting immediately following irradiation. This had no effect on the growth of unirradiated tumors in the brain but completely inhibited the recurrence of the irradiated tumors following either a single dose of 15 Gy or the more clinically relevant scheme of 5 daily doses of 2 Gy. Inhibition of angiogenesis with DC101 increased tumor growth delay but did not prevent tumor recurrences. We also showed that the recurrence of FaDu tumors locally irradiated with 20 Gy was prevented using a monoclonal neutralizing antibody against CD11b+ monocytes. This treatment did not increase the radiosensitivity of normal skin thereby providing a therapeutic gain. 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 2282.