Design And Synthesis Of Novel Chimeric Peptide-amphiphiles For Cancer Therapy

Peptides have been widely used for gene and drug delivery due to their inherent bioactivity, biodegradability and well biocompatibility. Because of the specific bioactivity of peptides, peptide-based gene and drug delivery systems could achieve improved gene transfection efficiency, enhanced drug targeting property and reduced side-effect, etc. On the basis of numerous previous research works, we designed and prepared series of novel chimeric peptide-amphiphiles for cancer therapy. The achievements of these amphiphilic peptides in tumor targeting, inhibition of cancer cells and solid tumor growth indicate a promising avenue of clinical cancer therapy.In chapter 1, the recent progress in peptides and polypeptides as gene and drug carriers, and used for drug modification were reviewed. The mechanism and characteristics of some bioactive peptides were also introduced. Finally, the prospect of peptides in cancer treatments was proposed.In chapter 2, two kinds of arginine-rich amphiphilic lipopeptides with hydrophobic aliphatic tails (C12GR8GDS, LP1 and C18GR8GDS, LP2) were designed and synthesized as functional gene vectors. With hydrophobic tail modification, these amphiphilic lipopeptides could bind DNA more efficiently and form stable spherical complexes in comparison with the control peptide (AcGR8GDS, P1). Moreover, the size and zeta potential results demonstrated the charge density and stability of the vector/DNA complexes could be improved with the increasing length of the aliphatic tails. In vitro transfection experiments showed that LP1 and LP2 could induce much higher gene expression level (luciferase expression) as compared with P1. Due to the incorporation of arginine-glycine-aspartic acid (RGD) sequences which could be specifically recognized by integrinsαvβ3 and avβ5 over-expressed on cancer cells, these lipopeptides could be specifically recognized by cancer cells, i.e. LP1 and LP2 exhibited relatively higher transfection efficiency in HeLa cell line than that of P2 (C18R8) and P3 (R8) without RGD sequence. While the transfection efficiencies of LP2 and P2 were similar in 293T cells. Lipopeptides exhibited very low cell cytotoxicity in both HeLa and 293T cell lines even at high concentration.In chapter 3, a surfactant-like tetra-tail amphiphilic peptide, [(C18)2K]2KR8GRGDS was designed and synthesized for targeted drug delivery. The resulting peptide-amphiphile, consisting of four hydrophobic aliphatic tails and a hydrophilic peptide head group, was able to self-assemble into nanosized micelles in aqueous medium at low concentration. Ibuprofen and doxorubicin (DOX) was loaded into peptide micelles as model hydrophobic drugs respectively, and the sustained release behavior was observed. Due to the incorporation of targeted arginine-glycine-aspartic acid (RGD) sequences and cell-penetrating peptide (CPP) residue octaarginine (R8), the micelles could be recognized specifically by cancer cells, as well as transport through the cell membrane efficiently. The observation of laser-scanning confocal microscopy confirmed effective cellular uptaking of porphyrin-loaded peptide micelles. Furthermore, the porphyrin-loaded micelles exhibited low dark toxicity and high phototoxicity against cancer cells, indicating the powerful potential for effective photodynamic therapy. Combined with the low cytotoxicity of the peptide against both HeLa and 293T cell lines, the surfactant-like peptide developed in this study may be promising in clinical application for targeted drug delivery.In Chapter 4, a novel amphiphilic prodrug was synthesized though conjugating a dual ligands chimeric peptide (AcGRGDSR8-ADDA-OH) with an anti-cancer drug doxorubicin (DOX). After modification by hydrophilic peptide residue, the solubility of this hydrophobic drug in physiological environment (pH 7.4) was increased effectively. And this amphiphilic prodrug was able to self-assemble into stable spherical nanoparticles with the DOX moiety as hydrophobic core in aqueous medium. As a result, the stability of the drug was improved, and the cytotoxicity of doxorubicin was decreased significantly as well. From the data we obtained, the half maximal inhibitory concentration (IC50) of prodrug against HeLa and COS7 cells increased 8-and 22-fold respectively as compared with doxorubicin in molar amount, and leading to the increase of difference between cancer cell and normal cell during the therapeutic procedure. Beacause of the presence of hydrophilic peptide shell, doxorubicin could be released in tumor cells and cause cell apoptosis with the enzymetic hydrolysis of peptide segment. Due to the promotion of dual ligands including cell-penetrating peptide (R8) and RGD moiety, the prodrug could be uptaken by tumore cells specifically, which was demonstrated by laser-scanning confocal microscopy observation. The chemotherapy results of solid tumor against nude mice model of human cervix cancer indicated that the prodrug could maintain favorable curative effect with very low side-effect compared with doxorubicin during the therapeutic process. This kind of mutli-functional chimeric peptide modified prodrug characteristics with high effectiveness and low toxicity may be promising in clinical treatment of cancer and solid tumors.