Targeting atherosclerosis : nanoparticle delivery for diagnosis and treatment

Atherosclerosis is a type of arteriosclerosis, or hardening of the blood vessels that is due to the deposition of plaques in the vessel wall. Recently, it has become clear that not all plaques are the same and that those with large lipid, necrotic cores and thin fibrous caps can rupture and lead to acute events such as myocardial infarction, stroke, and death. Atherosclerosis is a complex disease that takes years to develop in humans and has been difficult to duplicate in an animal model. Two animal models of atherosclerosis were studied to determine if they could be used to identify novel targeting peptides for lesions that were vulnerable to rupture and a new animal model was developed to study the stabilization of vulnerable plaques. Phage display using T7 bacteriophage is a powerful technique both in vitro and in vivo to find peptides that specifically bind to various proteins and surfaces. The T7 phage vector was optimized to increase the circulation time of the phage by introducing two mutations into the tail proteins of the phage that decreased their uptake by the liver. Phage display was then used to test various peptides which bind to tumor vasculature in vivo to determine if they also bind to atherosclerotic plaques. One such peptide, CREKA, binds to clotted plasma proteins and was used to target atherosclerotic plaques in ApoE null mice fed a high fat diet. Subtle clotting that occurs on the luminal surface of atherosclerotic plaques, presents a novel target for nanoparticle-based diagnostics and therapeutics. We have developed multifunctional, modular micelles that contain a targeting element, a fluorophore and, when desired, a drug component in the same particle. The fluorescent micelles bind to the entire surface of the plaque and notably, concentrate at the shoulders of the plaque, a location that is prone to rupture. We also show that the targeted micelles deliver an increased concentration of the anticoagulant drug, hirulog, to the plaque when compared to untargeted micelle