Abstract 591: Development of Near-infrared Fluorescent Probe for Targeted Uptake by Atherosclerotic Plaque Macrophages

Abstract

Macrophages are a pivotal element in the development of atherosclerotic plaques and their polarization strongly affects plaque stability. Development of molecular imaging techniques to identify vulnerable plaques in atherosclerotic vessel walls will be a valuable diagnostic tool to assess patients` risk of myocardial infarction or stroke and to adjust therapy. Imaging of unstable plaques has so far been performed by using PET imaging agent [ 18 F] FDG. Fluorescence imaging using near-infrared fluorescent agents offers several advantages, as they are simple to use and minimally invasive. We have developed an activable near-infrared fluorescent probe using either peptide-linked ICG dye (indocyanine green) or free ICG as cargo in liposomes. The liposomes were labeled with phosphatidyl serine in order to trigger phagocytic uptake by macrophages. We have investigated the properties of our liposome probes in order to assess their suitability for screening of atherosclerosis risk patients in a wide array of different experimental models including cell culture and various animals (apoE -/- mice, WHHL rabbits and macaca fascicularis monkeys). Cell culture experiments using the human monocytic cell line THP-1 after differentiation into macrophages using the phorbol ester PMA and polarization of the macrophages by either LPS/IFNγ for M1 polarization or IL-4/ IL-13 for M2 polarization have shown considerable differences in uptake efficiency for the liposomes. M2 macrophages were found to show highest phagocytic activity while not polarized M0 were intermediate and M1 macrophages were least active. Polarization was confirmed by measuring known marker genes (TNFA, CCL3, MRC1) of macrophage polarization by RT-qPCR. In the animal studies we observed enrichment of ICG-labeled liposomes in atherosclerotic plaques of apoE -/- mice as well as WHHL rabbits. Macaca fascicularis experiments attempted to simulate final application in human subjects by detecting atherosclerotic plaques within the carotid aorta. Preliminary results indicate promising potential for liposome probes.