Abstract 2334: Anti-angiogenic activity of anthrax lethal toxin using the mouse retina as a model system

Abstract

Abstract Our laboratory has previously shown that inhibition of MKK pathways by anthrax lethal toxin (LeTx) inhibits tumor growth and angiogenesis, reduces VEGF secretion, and results in rapid cessation of blood flow to tumors in melanoma and sarcoma xenograft model systems. To gain insight into the anti-angiogenic nature of LeTx, we utilized both developmental and pathological models of vascularization in the murine retina. By immunoblotting and immunofluorescence microscopy we observed that MAPK activation occurs in a spatially and temporally regulated manner during retinal vascular development. Intravitreal administration of LeTx caused an early delay in retinal vascular development followed by the formation of abnormal vascular tufts that co-stained with phosphorylated MAPK in the outer retinal region. Using a model of oxygen-induced retinopathy, western analysis revealed that MAPK activation preceded the onset of hypoxia and development of neovascularization in this model system. Intravitreal injection of LeTx during hypoxia resulted in a persistent lack of development and progression of all pathologic aspects of neovascularization, while having minimal effect on macrophage recruitment. VEGF levels remained at an elevated level even with the persistent lack of neovascular growth and continued hypoxic environment, implying a VEGF-independent mechanism for the effects of MKK inhibition. Additionally, immature retinal vasculature during normal development was persistently destroyed following MAPK inhibition, while mature vessels from adult animals were unaffected. Our studies not only reveal that MKK signaling plays a key role in retinal angiogenesis but also that perturbation of MKK signaling by LeTx can profoundly alter vascular morphogenesis. The persistent destruction of immature vessels during normal vascular development in the retina and in the model of oxygen-induced retinopathy suggests an extreme sensitivity of immature vessels to MKK signaling inhibition. Since MKK inhibition prevents oxygen-induced retinopathy by a mechanism independent of the VEGF-targeting strategies, this approach may be used in conjunction with existing strategies utilizing VEGF inhibitors to prevent pathologic angiogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2334. doi:1538-7445.AM2012-2334