Angiogenesis plays a pivotal role in serious retinal and corneal eye diseases, including macular degeneration, diabetic retinopathy, and corneal neovascularization, and contributes to disease development in cancer, cardiovascular disease, and arthritis. Angiogenesis inhibitors that target vascular endothelial growth factor (VEGF) have been hailed as solutions to pathogenic angiogenesis. However, VEGF targeting can be accompanied by serious ocular and systemic side effects including disruption of wound healing, is complicated by breakthrough of alternate angiogenic pathways, and is not uniformly effective for all angiogenic disorders, particularly those affecting the cornea. There thus remains an outstanding need for alternate antiangiogenic therapies that can supplant or complement existing anti-VEGF approaches. We have discovered that CMG2, one of the two primary anthrax toxin receptors, has significant angiogenic effects. Administration of PASSSR (a nontoxic component of anthrax toxin that binds CMG2 with high affinity) inhibits both VEGF- and bFGF- dependent corneal neovascularization, and reduces both tumor growth and endothelial cell migration. The antiangiogenic effects of PASSSR reflect CMG2 targeting, since anti-CMG2 mAbs or soluble (circulating) CMG2 also inhibit corneal vessel growth, CMG2 knockdown endothelial cells show dramatically reduced cell migration that is PASSSR-insensitive, and CMG2 knockout mice show very high inhibition of corneal angiogenesis (80%) that is unchanged by treatment with PASSSR. Together, these data strongly indicate that CMG2 is a key player in angiogenesis, and that CMG2 antagonists can be highly effective angiogenesis inhibitors. Notably, CMG2- knockout and PASSSR-treated mice are generally healthy, indicating that unlike VEGF targeting, CMG2 targeting is likely not accompanied by serious systemic side effects. Here we propose phage display isolation of circular peptide CMG2 antagonists for inhibition of corneal neovascularization and other neovascularization disorders. Anti-angiogenic peptides will be isolated based on their ability to disrupt CMG2-PASSSR binding, a strategy that we have successfully used to identify other antiangiogenic CMG2 antagonists. Given the high structural homology of CMG2 to integrins and the significant number of known effective peptide integrin antagonists, we expect that effective peptide CMG2 antagonists exist and can be identified. Peptides identified by phage display will be evaluated in vitro with respect to CMG2 affinity, ex vivo with respect to inhibition of endothelial cell migration, and in vivo in the cornal micro-pocket assay, which directly measures corneal neovascularization and also models angiogenesis in general. Identified peptide CMG2 antagonists can be used as lead compounds or therapies for corneal neovascularization and other angiogenesis-related diseases, and will have key advantages over existing anti-VEGF therapies, including higher corneal efficacy and likely reduced systemic and ocular side effects. This work thus has significant potential for large impact on morbidity, mortality, and vision worldwide.
Angiogenesis plays a key role in serious eye diseases and cancer. Molecules that bind CMG2 inhibit angiogenesis. Given similarity of CMG2 to integrins and the large number of peptide integrin antagonists, we propose to identify antiangiogenic peptide CMG2 antagonists by phage display and validate their activity.