Targetable PLGA microparticles and nanoparticles for the magnetic resonance imaging of atherosclerosis

Abstract

Atherosclerosis is a chronic disease characterized by the formation of plaque in hemodynamically unstable regions of arteries. The disease involves complicated molecular and cellular processes including inflammation, the immune system, low density lipoprotein, cytokines, and many other components. As such, the degree of disease is difficult to determine, and the clinical outcomes that stem from the disease are hard to predict. Current imaging techniques lack specificity for the plaques likely to cause clinical consequences such as heart attack or stroke. Consequently, a new and molecularly selective contrast agent formulation is necessary for accurate imaging of plaque and to aid in the determination of the correct patient-specific treatment. To that end, a stealth biodegradable particle was designed containing a high payload of contrast agent that is targetable to specific states of plaque development. The core material used in creation of the particle was the FDA-approved poly(lactide-co-glycolide) (PLGA), with carboxylic acid termini. The polymer was used in a modified water-in-oil-in-oil double emulsion method to form particles of sizes ranging from approximately 50 nm to 20 [mu]m, of near‐spherical shape, and with smooth surfaces. The PLGA particles were loaded with up to 30% Gd-DTPA, an FDA-approved contrast agent used with magnetic resonance imaging (MRI). As an adjunct, to enable visualization of individual particles in vitro, particles were alternatively loaded with rhodamine 6G, a fluorescent agent. The PLGA particles were surface functionalized with poly(ethylene glycol) (PEG) with a primary amine end group. The acid group of the PLGA and PEG-linked amine were coupled through an amide bond using carbodiimide chemistry. The presence of PEG on the surface of particles was confirmed using electron microscopy, 1H NMR, and zeta potential. The other end of the PEG chain terminated in a carboxylic acid that was subsequently used for coupling to a monoclonal antibody against the cell surface markers of inflammation and atherosclerosis, vascular cell adhesion molecule‐1 (VCAM‐1) and intercellular adhesion molecule-1 (ICAM-1). Particles with conjugated antibodies successfully attached to, entered, and distributed throughout cells in vitro.