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In cardiovascular and cerebrovascular biology, control of thrombosis and the coagulation cascade in ischemic stroke, myocardial infarction, and other coagulopathies is the focus of significant research around the world. Ischemic stroke remains one of the largest causes of death and disability in developed countries. Preventing thrombosis and protecting vessel patency is the primary goal. However, utilization of the body’s natural coagulation cascades as an approach for targeted destruction of abnormal, disease-associated vessels and tissues has been increasing over the last 30 years. This vascular targeting approach, often termed “vascular infarction”, describes the deliberate, targeted delivery of a thrombogenic effector to diseased blood vessels with the aim to induce localized activation of the coagulation cascade and stable thrombus formation, leading to vessel occlusion and ablation. As systemic delivery of pro-thrombotic agents may cause consternation amongst traditional stroke researchers, proponents of the approach must suitably establish both efficacy and safety to take this field forward. In this review, we describe the evolution of this field and, with a focus on thrombogenic effectors, summarize the current literature with respect to emerging trends in “coaguligand” development, in targeted tumor vessel destruction, and in expansion of the approach to the treatment of brain vascular malformations.

Radiation-induced bystander effects (RIBEs) are detected in cells that are not irradiated but receive signals from treated cells. The present study explored these bystander effects in a U87MG multicellular tumour spheroid model. A medium transfer technique was employed to induce the bystander effect, and colony formation assay was used to evaluate the effect. Relative changes in expression of BAX, BCL2, JNK and ERK genes were analysed using RT-PCR to investigate the RIBE mechanism. A significant decrease in plating efficiency was observed for both bystander and irradiated cells. The survival fraction was calculated for bystander cells to be 69.48% and for irradiated cells to be 34.68%. There was no change in pro-apoptotic BAX relative expression, but anti-apoptotic BCL2 showed downregulation in both irradiated and bystander cells. Pro-apoptotic JNK in bystander samples and ERK in irradiated samples were upregulated. The clonogenic survival data suggests that there was a classic RIBE in U87MG spheroids exposed to 4 Gy of X-rays, using a medium transfer technique. Changes in the expression of pro- and anti-apoptotic genes indicate involvement of both intrinsic apoptotic and MAPK pathways in inducing these effects.

Endothelial cells are highly sensitive to ionizing radiation, and exposure leads to multiple adaptive changes. Remarkably, part of this response is the translocation of normally intracellular proteins to the cell surface. It is unclear whether this ectopic expression has a protective or deleterious function, but, regardless, these surface-exposed proteins may provide unique discriminatory targets for radiation-guided drug delivery to vascular malformations or tumor vasculature. We investigated the ability of an antibody–thrombin conjugate targeting mitochondrial PDCE2 (E2 subunit of pyruvate dehydrogenase) to induce precision thrombosis on irradiated endothelial cells in a parallel-plate flow system. Click-chemistry was used to create antibody–thrombin conjugates targeting PDCE2 as the vascular targeting agent (VTA). VTAs were injected into the parallel-plate flow system with whole human blood circulating over irradiated cells. The efficacy and specificity of fibrin-thrombus formation was assessed relative to non-irradiated controls. The PDCE2-targeting VTA dose-dependently increased thrombus formation: minimal thrombosis was induced in response to 5 Gy radiation; doses of 15 and 25 Gy induced significant thrombosis with equivalent efficacy. Negligible VTA binding or thrombosis was demonstrated in the absence of radiation or with non-targeted thrombin. PDCE2 represents a unique discriminatory target for radiation-guided drug delivery and precision thrombosis in pathological vasculature.