(194d) An Ex Vivo Human Plaque Model for the Design of Amphiphilic Nanoparticle-Based Therapeutics for the Management of Atherosclerosis

Cardiovascular disease is the leading cause of death in the developed world, affecting more than 80 million people in the United States alone. This condition is largely caused by atherosclerosis, the formation of atheromatous lesions within the arterial walls, which is self-perpetuated through a low-level inflammatory response. The formation of atherosclerotic plaques is initiated by oxidation of low density lipoprotein (oxLDL) which triggers inflammation from endothelial cells. Monocytes are recruited to inflamed areas, which then differentiate into macrophages that can phagocytose resident oxLDL. OxLDL uptake via macrophages is unregulated, mediated by scavenger receptors (CD36 and SRA), and ultimately leads to foam cell formation and narrowing of the artery. Current strategies for treating this disease are limited in their ability to specifically delivery therapeutics to the site of lesions or lesion prone regions and cannot prevent further uncontrolled uptake of oxLDL. While statins prevent synthesis of LDL in the liver, they are unable to clear LDL introduced to the body via other pathways. Recently, our laboratories have identified a novel class of biomaterials containing a mucic acid backbone with lauryl side chains bound to polyethylene glycol (M12PEG), termed nanolipoblockers (NLBs). When formulated into micelles, these NLBs are able to bind to cells, macrophages and endothelial, via scavenger receptors and inhibit the uptake of oxLDL. They have also been shown to have a strong association with pre-inflamed cells, suggesting that these bioactive materials can accumulate at lesion sites. While the micellar formulation has strong therapeutic potential, serum containing conditions limit its bioactivity; thus, a more stable nanoparticle (NP) formulation has been established with superior bioactivity in serum containing conditions. NPs are fabricated via a flash nanoprecipitation process and contain the amphiphilic, M12PEG, shell and a hydrophobic core. This formulation enables the delivery of hydrophobic compounds with low water solubility to inflamed tissues.

In this work, we developed a novel ex vivo human carotid plaque model to evaluate bioactivity of a library of NPs comprised of a M12PEG amphiphilic shell and different hydrophobic cores.  Hydrophobic cores investigated include the bioactive M12, anti-inflammatory vitamin E, and a combination of both bioactives.  Using the ex vivo plaque model and primary human monocyte derived macrophages (hMDMs), bioactivity was assessed by evaluating the ability of the NPs to become internalized, inhibit oxLDL uptake, and reduce inflammation. The NPs were found to readily associate with hMDMs and the human plaques, even after a short 5 min incubation (similar exposure time to treatments administered via balloon catheter). This strong association within cellular regions of the plaque provides a feasible system for targeted drug delivery and enhanced therapeutic potential. All NP formulations demonstrated successful inhibition of oxLDL uptake at the site of lesions proving the therapeutic potential of these NPs. Additionally, the vitamin E and M12/vitamin E core NP formulations exhibited the lowest inflammatory gene expression, which were significantly less than that caused by oxLDL alone. In conclusion, this ex vivo human carotid plaque model has provided a novel method to test cardiovascular therapeutics on clinically relevant specimens. Employing this platform we have identified and optimized a novel NP-based therapeutic delivery system which will facilitate the management of inflammation and lipid accumulation at the site of atherosclerotic lesions.