Design, synthesis, and characterization of amphiphilic molecules for biomedical applications (2016)

Amphiphilic molecules, comprised of both hydrophilic and hydrophobic domains, have been extensively developed and investigated for various biomedical applications. In this dissertation, polymeric and small molecular weight amphiphiles were rationally designed and utilized as atherosclerotic therapeutics, antimicrobials, and liposome stabilizing agent. Atherosclerosis, a leading cause of mortality in developed countries, is characterized by the buildup of oxidized low-density lipoprotein (oxLDL) within the vascular intima, unregulated oxLDL uptake by macrophages, and ensuing formation of arterial plaque. Amphiphilic macromolecules (AMs) comprised of a branched hydrophobic domain and a hydrophilic poly(ethylene glycol) (PEG) tail have shown promising anti-atherogenic effects through direct inhibition of oxLDL uptake by macrophages. In this study, five AMs with controlled variations were evaluated for their micellar and structural stability in the presence of serum and lipase, respectively, to develop underlying structure-atheroprotective activity relations. In parallel, molecular dynamics simulations were performed to explore the AM conformational preferences within an aqueous environment. Notably, AMs with ether linkages between the hydrophobic arms and sugar backbones demonstrated enhanced degradation stability and storage stability, and also elicited enhanced anti-atherogenic bioactivity. Additionally, AMs with increased hydrophobicity elicited increased atheroprotective bioactivity in the presence of serum. These studies provide key insights for designing more serum-stable polymeric micelles as prospective cardiovascular nanotherapies. The rapid emergence of antibiotic-resistant bacteria and lack of efficacious treatments have prompted extensive research in development of novel antimicrobial agents. Inspired by the unique membrane-targeting mechanism of naturally occurring antimicrobial peptides (AMPs), two series of cationic amphiphiles (CAms) were strategically designed with hydrophilic head groups and non-polar domains segregated to opposite sides of the amphiphilesâ€™ backbone, known as a facially amphiphilic conformation. This orientation has been determined to be critical to elicit membrane-lytic properties. The CAms self-assembled into supramolecular nanostructures above their respective critical micelle concentrations (CMCs) upon direct dissolution. By systematically tuning the hydrophobicity, CAms with optimized compositions exhibited potent activity against both Gram-positive and Gram-negative bacteria as well as displaying negligible hemolytic activity. Scanning electron microscope and transmission electron microscope images revealed the morphology and ultrastructure changes of bacterial membranes induced by CAm treatment and further attested to their membrane-disrupting mechanism. Additionally, an all-atom molecular dynamics simulation was employed to understand the CAm-membrane interaction on a molecular level. This study shows that these CAms can serve as viable scaffolds for rationally designing the next generation of AMP mimics as effective antimicrobials to combat drug-resistant pathogens. Sterically stabilized liposomes have been widely used as long-circulating delivery vehicles. They are typically prepared with poly(ethylene glycol)- (PEG-) modified lipids, where the lipid portion is inserted in the lipid bilayers as an anchor and the hydrophilic PEG coats the surface to prevent liposome aggregation and rapid clearance in vivo. However, these steric protection effects are compromised upon systemic administration due to low retention of PEGylated lipids within liposome membranes upon dilution. Bolaamphiphiles (bolas), comprised of two hydrophilic head groups connected by a hydrophobic domain, can predominantly adopt a membrane-spanning configuration that confers robust bilayer retention. Hence, a series of PEG-bolas were developed to increase retention in the lipid bilayer, presumably leading to enhanced integrity of the PEG protective layer, and thus improved colloidal and biological stability (i.e., phagocytosis by macrophages) of resulting liposome formulations. We hypothesized that PEG-bolas with a sufficiently long hydrophobic domain and rigid central group could preferentially extend across lipid bilayers. Liposomes stabilized by PEG-bolas comprised of a biphenyl core and twelve-carbon alkyl chain exhibited similar storage and biological stability compared to conventional PEGylated lipid stabilized liposomes, but with significantly improved retention upon dilution. In this thesis, bioinspired amphiphiles were rationally designed by mimicking key characteristics of relevant biological molecules. Through systematic structure-activity relationship studies, the physicochemical properties and bioactivity of amphiphiles can be optimized for specific applications.