Abstract 538: In vivo Imaging of Cathepsin Activity in Atherosclerosis With Customized Protease Nanosensors
In atherosclerosis, cathepsins digest the extracellular matrix of the fibrous cap and destabilize atheromata. Their function can be monitored with fluorescence molecular tomography (FMT) and activatable probes. To address two major constraints currently associated with imaging of murine atherosclerosis (lack of highly sensitive probes and absence of anatomical information), we compared protease sensors (PS) of variable size and pharmacokinetics and fused FMT datasets to computed tomography (FMT-CT). Fusion of FMT and CT was achieved with a multimodal imaging cartridge containing fiducial markers detectable by both modalities. A high-resolution CT angiography protocol accurately localized fluorescence to the aortic root of atherosclerotic apoE−/− mice (Figure⇓). To identify suitable sensors, we first modeled signal kinetics in-silico and then compared three probes with identical oligo-L-lysine cleavage sequences targeted by cathepsins: PS-5, 5nm in diameter containing 2 fluorochromes, PS-25, a 25nm version with an elongated lysine chain and PS-40, a polymeric nanoparticle. Serial FMT-CT showed fastest kinetics for PS-5 but surprisingly, highest fluorescence in lesions of the aortic root for PS-40 (FMT@24hrs, PS-5: 10.6 ± 2.2pmol, PS-25: 26.8 ± 4.4pmol, PS-40: 50.5 ± 5.8, p< 0.05). PS-40 robustly reported therapeutic effects of atorvastatin, corroborated by ex vivo imaging and qPCR for cathepsin B expression (p< 0.05). FMT-CT is a robust and observer-independent tool for non-invasive assessment of inflammatory murine atherosclerosis. Reporter containing nanomaterials may have unique advantages over small molecule agents for in vivo imaging.