Ablation of microvessels in vivo upon dimerization of iCaspase-9

Anti-angiogenic therapies based on targeted disruption of the tumor microvascular network have been proposed for cancer treatment. Inhibitors of the endothelial cell pro-survival pathway mediated by VEGF were shown to activate caspases and cause microvascular regression, but the efficacy of this strategy can be hindered by the engagement of redundant survival pathways. Alternatively, if direct activation of an apical pro-apoptotic caspase is sufficient to disrupt microvessels in vivo, such a strategy could potentially override upstream endothelial cell survival inputs and disrupt tumor neovascular networks. Here, we fused caspase-9 to a mutated FKBP12 domain to express an inducible caspase-9 molecule (iCaspase-9) that can be activated by a cell-permeable dimerizer drug, and transduced this construct into primary endothelial cells. We found that drug-induced dimerization of iCaspase-9 is sufficient to activate endogenous caspase-3 and trigger apoptosis even when endothelial cells are treated with the pro-survival factors VEGF or bFGF. A single intraperitoneal injection of the dimerizer drug induced apoptosis of endothelial cells expressing iCaspase-9 and elimination of human microvessels engineered in immunodeficient mice. These results demonstrate that the activation of iCaspase-9 disrupts microvessels in vivo, and suggest a novel anti-angiogenic strategy based on the expression and controlled activation of an inducible death gene in neovascular endothelial cells.