Abstract 5083: Dual targeting of the type 1 insulin-like growth factor receptor and its ligands as an effective anti-angiogenic strategy.
Authors: Bid Hemant K. , London Cheryl A. , Gao Jin , Zhong Haihong , Hollingsworth Robert H. , Houghton Peter J. 
Published: August 2014

Abstract
Background. Several childhood sarcomas, exhibit autocrine or paracrine growth through secretion of insulin-like growth factors 1 and 2 (IGF-1, IGF-2) and signaling through the Type 1 receptor (IGF-1R). In some childhood sarcoma xenografts IGF-1R antibodies dramatically decrease VEGF transcription and have potential anti-angiogenic activity. However, tumor-derived IGF-2 results in intrinsic resistance to IGF-1R-targeted antibodies, and continued tumor angiogenesis. We evaluated the anti-angiogenic activity of a ligand-binding antibody (MEDI-573) alone or in combination with IGF-1 receptor-binding antibodies as a potential strategy for effectively suppressing angiogenesis in pediatric sarcomas.
Methods. IGF-stimulated signaling was monitored by increased Akt phosphorylation in sarcoma and human vascular endothelial (HUVEC) cells. Effects on angiogenesis were determined in vitro by capillary tube formation in HUVECs and in vivo using a VEGF-stimulated Matrigel assay followed by assay of hemoglobin and CD34 immunostaining.
Results. The IGF-ligand binding antibody MEDI-573 suppressed Akt phosphorylation induced by exogenous IGF-1 and IGF-2 in sarcoma cells. Receptor binding antibodies, MAB391 and CP1-B02, suppressed IGF-1-stimulated phosphorylation of Akt, but not that induced by IGF-2. Both receptor-binding antibodies suppressed VEGF-induced HUVEC tube formation in vitro, but this was abrogated by exogenous IGF-2. MEDI-573 inhibited VEGF-stimulated HUVEC proliferation and tube formation in vitro, but did not inhibit angiogenesis in vivo, probably because MEDI-573 binds murine IGF-1 with low affinity. However, in vitro the anti-angiogenic activity of MEDI-573 was also circumvented by human recombinant IGF-1. The combination of receptor-binding and ligand-binding antibodies completely suppressed VEGF-stimulated proliferation of vascular endothelial cells in the presence of IGF-1 and IGF-2, and prevented ligand-induced phosphorylation of IGF-1R/IR receptors. Further, combining receptor-binding and ligand-binding antibodies completely suppressed VEGF-driven angiogenesis in a mouse model where Matrigel plugs containing both IGF-1 and IGF-2 were incorporated with VEGF.
Conclusions. Our previous study showed that IGF-2 produced by tumor cells in the microenvironment could circumvent the anti-angiogenic effects of IGF-1 receptor binding antibodies. In contrast, IGF-1 was able to overcome the anti-angiogenic effect of the IGF-ligand binding antibody, MEDI-573. Our current study demonstrates that combining receptor and ligand binding antibodies effectively suppresses VEGF-stimulated angiogenesis in vitro and in a mouse model. Studies are ongoing to evaluate this therapeutic strategy using pediatric sarcoma xenograft models with characterized IGF expression. (Supported by grants CA77776, CA23099 and MedImmune).
Citation Format: Hemant K. Bid, Cheryl A. London, Jin Gao, Haihong Zhong, Robert H. Hollingsworth, Peter J. Houghton. Dual targeting of the type 1 insulin-like growth factor receptor and its ligands as an effective anti-angiogenic strategy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5083. doi:10.1158/1538-7445.AM2013-5083