Despite advances in cardiovascular care, atherosclerosis remains the leading cause of mortality in the United States and worldwide. A vast majority of cardiovascular events such as stroke or myocardial infarction result from rupture or erosion of vulnerable atherosclerotic plaques. These plaques are characterized by high and active macrophage content. Current imaging modalities including magnetic resonance (MR) imaging characterize anatomic and structural features of the plaque rather than its content. Macrophage-specific delivery of gadolinium-based contrast agents (GBCAs) that are often used in cardiovascular MR imaging to enhance contrast between tissues will allow early detection of vulnerable plaques and risk stratification of vulnerable patients. This will also minimize the GBCA dose, thus diminishing the adverse effects of GBCAs. Recently, high density lipoproteins (HDLs) were suggested as delivery nanocarriers for GBCAs. However, unmodified HDL are not normally uptaken by macrophages and require addition of targeting molecules. The approach we are taking to target GBCA-HDL to macrophages involves a naturally occurring oxidation of the major protein of HDL, apolipoprotein (apo) A-I, and eliminates the need for targeting moieties. The long-term objective of the proposed project is to develop a novel approach to early detection and evaluation of vulnerable plaques. In Phase I of this project, we generated and characterized GBCA-HDL formulations that contain oxidized apo A-I, confirmed their target-binding activity in vitro, and demonstrated their specific uptake by intraplaque macrophages in a mouse model of atherosclerosis using in vivo MR imaging and histology. We also generated fully functional GBCA-HDL using synthetic oxidized apo A-I peptides in place of native human apo A-I. This simplifies development of the commercial product and allows to avoid potential clinical and regulatory pitfalls. In Phase II, we propose to more broadly screen GBCA-HDL that contain synthetic oxidized apo A-I peptides, identify the leads and develop the easy-to-scale-up synthetic methodology to allow for clinical-scale manufacture of these agents in liquid and lyophilized form, validate imaging efficacy of the leads in mouse and rabbit models of atherosclerosis, and perform pharmacokinetic, biodistribution and single-dose toxicology studies in two species. A follow-up work will include validation of imaging efficacy of the lead candidates in a porcine model of atherosclerosis, further optimization of the lead formulations and the technology of their manufacture, and the more detailed safety and pharmacokinetic studies required for IND submission. Upon completion of these activities, an IND application will be submitted for clinical testing of GBCA-HDL-enhanced MR in the context of atherosclerosis and coronary artery disease.
Atherosclerosis is the major cause of cardiovascular disease, the number one leading cause of death worldwide. The proposed research will result in the development of novel imaging techniques that could substantially improve early diagnosis and treatment of atherosclerosis, allowing for diagnosis before symptoms occur, identification of those individuals with higher risk, and for monitoring response to treatment.