Development and Analytical Characterization of Lipid-Based Nanoparticles

Abstract

Lipid-based nanoparticles are highly versatile platforms with extensive therapeutic applications. Despite rapid scientific advances in the past several decades, clinical translation of lipid nanoparticles remains challenging. Focusing on translational research of lipid nanoparticles, this thesis has two sections addressing preclinical formulation development and analytical methods on formulation characterization, respectively. The first section of the thesis, consisting of Chapters 2 and 3, focuses on the formulation optimization of synthetic high-density lipoproteins (sHDLs). sHDLs are a class of nanoparticles composed of ApoA-1 mimetic peptides and phospholipids mimicking the biofunctions of endogenous HDLs, including mediating cholesterol efflux, regulating endothelial functions, and resolving inflammation responses. To optimize the endothelial protective function of sHDLs, in Chapter 2, a vascular cell adhesion molecule 1 (VCAM-1) specific ligand was introduced on the surface of sHDLs to achieve an active targeting of activated endothelium. Indeed, these sHDLs demonstrated enhanced binding to the activated endothelium while inhibiting inflammatory responses and reducing leukocyte adhesion on inflamed endothelium. These data provided support as a stand-alone therapy or drug delivery carrier for inflammatory disease treatment. In Chapter 3, phosphatidylserine (PS), a bioactive lipid with intrinsic anti- inflammatory effects, was introduced in sHDL nanoparticles. This incorporation improved the sHDL stability and anti-inflammatory effects on LPS-activated macrophages without impairing the sHDL cholesterol efflux capacity and pharmacokinetic profile. Overall, the strategies developed in Chapters 2 and 3 may facilitate the optimization of sHDL functionalities to treat varieties of inflammatory diseases. The second section of the thesis, consisting of Chapters 4 and 5, focuses on developing analytical methods to ensure the successful formulation development, regulatory filing, and quality control of liposomal drug products. Chapter 4 examined the dialysis-based drug release assay which is commonly used to evaluate in vitro drug release kinetics of lipid nanoparticles. The analysis of the mass transfer process during dialysis assay revealed that due to the drug diffusional resistance of the dialysis membrane, the apparent drug release rate measured from the sampling compartment does not always accurately represent the actual drug release kinetics. To solve this problem, a series of mathematical models were developed to predict actual drug release kinetics from apparent drug release data and a calibration of the diffusional membrane resistance before release testing. The models not only enable the proper interpretation of the data from dialysis studies but also help to evaluate the dialysis methodology applied to in vitro drug release assays. In Chapter 5, a series of analytical methods were developed to characterize the key product attributes of a commercial multivesicular liposomal product, Exparel. The particle size, particle inner structure characteristics, drug and lipid contents, residual solvents, and pH of the product were characterized. In addition, a rotator-based, sample-and-separate in vitro drug release test was developed for formulation comparison and quality control purposes. The batch-to-batch variability of Exparel was examined by the established analytical methods. The knowledge derived from this chapter may facilitate the development of generic multivesicular liposomes.