Novel Therapy for Diabetic PAD Monitored With Dual Isotope Multimodality Imaging

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 DESCRIPTION (provided by applicant): Symptomatic peripheral arterial disease (PAD) is a disabling condition in diabetes that can lead to leg ulcers, amputation, and death. There are currently no effective drug therapies for symptomatic PAD leaving surgical revascularization and interventional catheter based approaches and these can fail leading to limb loss. Developing novel therapies to treat PAD and to image response to therapy represents an unmet need. Advanced Glycation End products (AGEs) are produced by the nonenzymatic binding of glucose to proteins. AGEs bind a receptor (RAGE) to initiate pathways that play important roles in accelerating the development and progression of vascular disease in diabetes and by inhibiting the angiogenic response to limb ischemia. We developed a monoclonal anti-RAGE antibody for imaging and have shown in diabetic and hyperlipidemic mice and pigs that RAGE is expressed diffusely in vascular tissue of hindlimbs. We have also used imaging to confirm that knocking out RAGE restores the normal response to tissue hypoxia imposed by femoral artery ligation. We hypothesized that if our antibody is a blocking antibody it may have potential as a therapeutic agent for PAD and consequently performed confirmatory experiments in cell culture of vascular smooth muscle cells to document blocking properties. Using imaging confirmed by immunohistology we showed in diabetic mice with femoral artery ligation pretreated with antibody vs. saline greater angiogenesis at 5 days and improved blood flow at 24 days in the ischemic hind limb of antibody treated mice compared to placebo treated mice. In this grant application we propose a large animal treatment trial using dual isotope multimodality imaging to document response to therapy. Purpose bred diabetic Yucatan minipigs will receive either antibody or non-immune IgG for 2 months. After one month, catheter based unilateral femoral artery occlusion (FAO) will be performed in these pigs plus additional age matched and weight matched non-diabetic Yucatan minipigs. At 24 h (acute insult) and 28 days (healing) after FAO 201Tl hybrid SPECT/CT imaging will be performed for limb skeletal muscle perfusion and CT angiography for large vessel anatomy. At day 7 after FAO hybrid SPECT/CT imaging will be performed with 99mTc scVEGF-PEG-DOTA (scV/Tc) a novel probe that targets VEGF receptors 1 and 2 and shown in preliminary experiments in mice to track angiogenesis in limb ischemia. Regional hindlimb muscle perfusion will be quantified from uptake of thallium-201 for early and late time points and regional limb angiogenesis from uptake of scV/Tc probe for day 7. We expect that the reduction in perfusion defects from day 1 to 28 will be greater in the antibody treated compared to placebo treated pigs and the magnitude of this change will relate to the quantitative uptake of scV/Tc at day 7 and to the collateral vessel score at day 28. The result of the proposed work has the potential to serve as justification for further development of the antibody and this dual isotope multimodality imaging approach towards a clinical trial.