The Design Of Cationic Amphipathic Anti-Cancer Peptides Based On KLA And The Studies On Their Anti-Cancer Mechanisms

Cancer treatment by conventional radiotherapy and chemotherapy is hindered by toxic side effects and the frequent development of multi-drug resistance by cancer cells. Exploiting new forms of anti-cancer drugs with high efficiency and low toxicity, changing the interaction method of anti-cancer drugs, thus completely cure cancer is still the trend of current anti-cancer research. In recent years,a new kind of therapy based on the cationic biological active peptide become the focus of anti-cancer research. Cationic amphipathic peptides(CAPs) are a class of membrane-active peptides with low molecular weight, high portion of cationic and hydrophobic amino acids. Many cationic amphipathic peptides could cause distability of cell membrane and subsequent cell death. The cationic and hydrophobic characteristics of these peptides give them high affinity to cancer cell membrane,making them a new candidate of anti-cancer drugs.Firstly, in this thesis, we give a brief introduction of characteristics malignant tumor and cationic amphipathic peptides, review the mechanism and application of cationic amphipathic peptides. Then we give an introduction of an anti-cancer peptide with low cell uptake efficiency KLA and some optimizations on this peptide. Then review factors that affect peptide biological activity,providing reference for artificial design of anti-cancer peptides. Then we present the main research work on KLA-based anti-cancer peptide design, biophysical properties and anti-cancer mechanism studies in two parts. Through modification of KLA on amino acid levels, we obtained a series of peptides with high anti-cancer effect, and then thoroughly studied the relationship of biophysical properties, structures and functions of petides, clarified their different anti-cancer mechanisms.In this work we find that by substitution of alanine(A)with leucine(L) residues, enhanced cytotoxicities were observed in both lysine(K) and arginine(R) series of peptides. KL-rich or RL-rich peptides with intact amphipathic helical interface could form lipid-induced helices and form micelles in solution. They accumulate on cell membranes and cause instant membrane lysis likely through transmembrane pores formation. Rearranging residue positions to minimize hydrophobicity can cause great decrease of cytotoxicity to KL-rich peptide but not to RL-rich peptides. Interestingly, a hydrophobicity minimized RL-rich peptide 4(RL2)(RLLRLLRLRRLLRL-NH2) displayed a different mode of interaction with cells. It can penetrate cell membrane and progressively induce cell stress-triggered caspase-3-dependent apoptosis. In this model peptide system, we show that synergies among factors of hydrophobicity, hydrophobicity and K/R composition determine the distinct mode of action of cationic hydrophobic peptides. Hydrophobicity-reduced, arginine-rich hydrophobic peptides may represent a new class of peptide therapeutics for future design and development.