Abstract 4249: NGR-TNF, a novel direct-acting vascular targeting agent, does not induce “cytokine-rebound” recruitment of pro-angiogenic bone-marrow derived cells

Abstract

Abstract NGR-TNF, presently in advanced clinical development, is a direct-acting vascular targeting agent coupling the CNGRCG peptide (NGR), homing to angiogenic blood vessels, and tumour necrosis factor alpha (TNF). In order to further elucidate the mechanism of action, we investigated whether NGR-TNF mobilizes bone-marrow derived cells (BMDCs) and growth factors. Herein, treatment with either certain chemotherapy drugs at maximum tolerated dose (e.g. paclitaxel, cyclophosphamide, 5-FU), vascular-disrupting agents (VDAs; e.g. fosbretabulin, Oxi4503), or local irradiation can rapidly induce mobilization and subsequent tumor homing of proangiogenic BMDCs, such as circulating endothelial progenitor cells (CEPs), CD11b/Tie-2-expressing monocytes (TEMs), CD11b+Gr1+ neutrophils and myeloid-derived suppressor cells (MDSCs), and CD11b+F4/80+ macrophages. Increase in several growth factors and chemokines, such as SDF-1, G-CSF as well as osteopontin, contribute to the mobilization of BMDCs that colonize the tumour site and induce angiogenesis and rapid tumor regrowth. Lewis lung carcinoma (LLC) cells were subcutaneously implanted into immunocompetent C57BL/6J mice or into GFP+ bone marrow-chimeric mice, obtained by transplanting into lethally irradiated C57BL/6J mice bone marrow cells from UBI-GFP/BL6 donors. Blood was obtained 4 or 24 hours after treatment with either NGR-TNF, VDA, an anti-VEGFR2/flk-1 antibody or saline, by either cardiac puncture or retro-orbital sinus bleeding. Using flow cytometry (LSRII), CEPs were defined as CD45-/CD13+/flk-1+/CD117+/7AAD-, TEMs as CD45+/CD11b+/Tie2+/flk-1+ and MDSCs as CD45+/CD11b+/Gr1+ cells. Levels of circulating growth factors were assessed by ELISAs. When administrated at low doses (optimal biological dose), comparable to doses being used in clinical trials, NGR-TNF causes a decrease of tumor blood vessels density and induces apoptosis of tumor cells and tumor endothelial cells in vivo. It is worth noting that, unlike the above-mentioned treatments, NGR-TNF fails to mobilize or recruit to the tumor site different subtypes of pro-angiogenic BMDCs nor induces growth factors. Therefore, low doses of NGR-TNF exert an antitumor activity without inducing reactive a pro-angiogenic host response, which is likely an important feature for preventing/overcoming resistance and for designing combination therapeutic strategies. 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 4249. doi:10.1158/1538-7445.AM2011-4249