Self-assembled lipopeptide prodrug depot for sustained release: Design and synthesis of peptide glutamic acid dialkylamides, their self-assembly into tubules, and their stability to proteolytic degradation

Issues in traditional drug delivery, especially of lability of molecules such as peptides, are addressed in this thesis with a novel, model drug delivery system. Self-assembling properties of lipidated peptides are utilized to attain unique hollow cylindrical tubules and helices, called lipid tubules, which are explored as a depot for delivery of therapeutic peptides and other labile drugs. Because of the constant diameter of the crystalline microstructure geometry, it is proposed that the constituent monomeric lipopeptides will be released to the surrounding site of injection at a constant rate. In order for such sustained release of peptides at biological site to work, the peptide depot must be stable to proteolytic degradation.; Mono, di, tri, and tetra peptide glutamic acid dialkylamides with varying lipid chain lengths are synthesized, assembled into the high axial ratio microstructures (HARMs) of tubules and helices, and characterized. A larger headgroup peptide (decapeptide) glutamic acid dialkylamide containing a trypsin cleavage site was constructed, assembled into well-defined HARMs, and kinetics of hydrolysis by trypsin measured. The lipopeptide within the tightly packed crystalline bilayer array are shown to be virtually completely protected from hydrolysis by trypsin. The non-aggregated form of the lipopeptide is hydrolyzed by four orders of magnitude faster than the same lipopeptide in the microstructure array. Additionally, a novel facile method of tritio-acetylation of peptide, novel assay methods for lipopeptides, as well as a novel method for estimating critical aggregation concentration of low solubility amphiphiles are presented.; The lipopeptide tubule in the present study is a model peptide delivery system, where the headgroup peptide can be replaced by other therapeutic peptide or drug molecules, appropriate cleavage sites, and linkers. In addition, the lipid chain length can be varied to control the rates of drug release. The present demonstration of the stability of model peptide-drug depot to premature proteolytic degradation, combined with the ability of the HARMs, to provide controlled, sustained release is significant advance in developing rational and technologically advanced drug delivery system.