Cationic Cell Penetrating Peptides: Characterization of Transport Properties in Epithelial Cells and Their Utilization as Delivery Systems for Protein and Peptide Drugs

The recent interest in cationic cell penetrating peptide (CPPs) stems from their potential utility as non-invasive drug delivery platforms. These peptides are short sequences consisting mostly of arginine or lysine residues including the Tat peptide, Antp peptide and different oligomers of arginine and lysine. By conjugating CPPs to a wide range of impermeable cargo, their intracellular delivery has shown to be increased in different types of cells by a less defined mechanism of transduction. Despite their versatility, few studies have focused on their application for transcellular delivery. Considering that the original protein from which the cationic CPPs are derived, HIV-1 Tat protein, is able to exit the infected cell and internalize into neighbouring cells, it is conceivable that CPPs can enter into differentiated epithelial cells from the apical domain and exit on the basolateral domain. If this is true, they can also ferry impermeable cargo across the epithelial cells, thus aid in overcoming one of the notorious barriers for oral and pulmonary delivery of proteins and peptides. This hypothesis was tested by investigating the transport of CPPs in alveolar epithelial cells and also by conjugating CPPs to a peptide and a protein drug intended for oral and pulmonary delivery respectively. The results presented in this thesis show that CPPs can be transported across alveolar epithelial cells without severely compromising cellular integrity. Additionally, oligoarginine conjugated to protein drug, e.g., insulin, can facilitate the transport of insulin in vitro across alveolar epithelial cells by a transcellular pathway and can enhance insulin transport in vivo when delivered into the lungs of diabetic rats. However, conjugating oligoarginine to a peptide drug, desmopressin, improved in vitro transport marginally but did not have any beneficial effect when delivered orally. From this work, the potential for CPPs as delivery systems for transcellular transport of proteins, especially through the pulmonary route, is realized.