AbstractsBiology & Animal Science

Cationic Lytic Peptides as Drugs or Drug Carriers for Targeted Cancer Therapy

by Sheng Lu




Institution: University of Waterloo
Department:
Year: 2015
Keywords: cationic lytic peptide; drug delivery; nanotechnology; nanostructure; self-assembly; membrane selectivity
Record ID: 2061184
Full text PDF: http://hdl.handle.net/10012/9018


Abstract

Cationic lytic peptides (CLPs) have emerged as new anticancer agents with a new mode of action. This category of peptides is given the characteristics of overall positive charges and amphiphilicity, inducing cell death by disrupting integrity of cytoplasmic membranes or depolarizing mitochondrial membranes. Cationic lytic peptides show advantages to conventional chemotherapeutics in preferential killing of cancer cells and ability to avoid general mechanisms of multidrug resistance associated with cancer cells. The biocompatibility and the biodegradability of many CLPs are other advantages. These properties make CLPs promising therapeutics for cancer therapy. Although significant progress has been achieved over the past decade, high activity and high specificity towards cancer cells, as well as enhanced stability in serum, are still needed for clinical usage of CLPs. To address these issues, this thesis focuses on three aspects: a) the molecular mechanism of the preferential activity of CLPs on different lipid membranes, which is the main cause for the CLP selective cytotoxicity; b) stimuli-responsive design in CLPs for self-guided delivery; c) utilization of CLPs as delivery vehicles for the hydrophobic anticancer drug ellipticine (EPT). The last aspect is to take advantage of CLP’s capability to encapsulate hydrophobic compounds and deliver to cancerous cells. The studies include: (i) investigation of the CLP induced leakage on liposomes with various lipid compositions; (ii) characterization of the stimuli-responsive properties of the CLP and the properties of CLP-ellipticine complexes; (iii) evaluation of the selective cytotoxicity of the CLPs and CLP-ellipticine complexes on various cell lines; (iv) evaluation of the anticancer activity of CLPs in vitro and in vivo. The peptide C6, an 18-mer arginine-rich peptide, was found to adopt an amphiphilic helical conformation on 1-palmitoyl-2-oleoyl-3-sn-glycero-phosphocholine (POPC) membranes, and induce membrane leakage. The POPC liposome leakage and A549 cell death induced by C6 was shown in a concentration-dependent manner. The amount of C6 required to achieve a given level of membrane damage, as measured by efflux of fluorescent dye or cell mortality, increases linearly with lipid concentration or cell count. The hydrogen bonding between arginine residues of C6 and cholesterol-rich membrane was found to play an important role in the lytic activity of the peptide, as evidenced in both the leakage study and molecular dynamics analysis. The effect of hydrogen bonding was also observed in subsequent cytotoxicity studies performed on A549 (lung cancer cells with low cholesterol content), MCF-7 (breast cancer cells with high cholesterol content) and erythrocytes (abundant cholesterol in membranes). These results provide a new insight in tuning the activity of CLPs against cholesterol-rich membranes by modulation of hydrogen bonding. The peptide C6 was shown to possess moderate selectivity towards cancerous cells in vitro. By comparing the IC50…