Studies Of The Targeted Delivery Process Of Peptide Modified Liposomes To Solid Tumors

Cancer is one the most serious lethal disease worldwide. Many factors can directly damage genes or combine with existing genetic faults of cells to cause malignancy. Systemic therapy, especially conventional cytotoxic drug therapy, had limited benefit for improving survival rate, due to toxic side effects, and frequently occurred multidrug resistance. To address these limitations, it's considered important to develop effective tumor targeting drug delivery systems.Tumor-targeted nanomedicines, including monoclonal antibody, polymer, micelle, nanoparticles and liposomes in clinical trial, are drug delivery systems being developed to improve drug accumulation in the tumor site, thereby enhancing drug levels, and/or to direct a drug away from those body sites that are particularly sensitive to the toxic effects of the drug. Liposomes, especially, are the main stream as sustained release drug delivery systems for the in vivo delivery of everything from small molecule therapeutics to nucleic acids. The main axes of liposomal nanocarriers include stealth liposomes which base on EPR effect to arrive the tumor site, ligand-mediated targeting liposome that increase the uptake of particles by the tumor cell, triggered release liposome using heat, ultrasound, light, or local triggers as remote triggers, and multi-functional, multi-component liposomal nanoparticles.However, clinical statistics show the targeted liposomes, though, can effectively gathering in the tumor site after the treatment, the increase in overall survival is modest in many cases. Therefore, a better understanding of the barriers that prevent efficacy and uniform delivery of nanoparticles into tumors is needed to develop strategies to improve treatment.Liposomes are artificial phospholipid vesicles, and one of the most well-investigated drug delivery carriers. Modification of the carrier surface properties and the content of the lipid bilayer can alter in vivo distribution dynamics for increased drug concentration in the target sites and less adverse effects in non-targeted tissues.In this study, we designed ligand modified tumor targeted liposome drug delivery system using EGFR as targets. GE11 is a peptide that has been shown to exhibit high binding affinity to EGFR-overexpressing tumor cells. It was used it in this study to decorate the surface of sterically stable PEGylated liposomes for targeting to EGFR-overexpressing tumor cells. The effect of liposome surface mole ratios of PEG-to-peptide on the targeting efficiency to EGFR- overexpressing tumor cells in vitro were investigated, as well as the possibilities of clearance by mononuclear phagocytes in circulation. To test the formulation stability of liposomes containing varying PEG and GE11, doxorubicin was loaded into liposomes to monitor the drug encapsulation stability and drug release profiles. The ?ndings suggested both PEG and GE11 surface densities were critical for targeted delivery properties. Ligand density affected drug loading capacity, formulation stability and eventually antitumor effects. Optimization of PEG-to-ligand ratio was important to achieve favorable therapeutic effect.We then examined in detail the pharmacokinetics, bio-distribution and antitumor effect of three selected formulations containing different surface densities: PEG/GE11(4:0),PEG/GE11(3.5:0.5),and PEG/ GE11(4:2). The data confirmed that GE11 decorated liposomes could significantly facilitate drug accumulation in SMMC7721 xenografts, and subsequently elicit improved therapeutic efficiency, compared to PEGylated liposomes. In order to study the detail distribution behavior of GE11-DLs in SMMC7721 xenografts, IHC and confocal microscopy methods were employed to exam the SMMC7721 tumor tissue. The different cell types and their contribution to the “tumor microenvironment” were investigated, including macrophages, tumor neoplastic epithelial cells. These stroma cells, as well as the extracellular matrix and various EGFR expression cells are all likely to affect the distribution of GE11 decorated liposomes in tumor. It was revealed that the receptor binding barrier might be detrimental to the permeability of GE11- targeting liposomes(GE11-TLs) in tumor tissues. Coadministration with collagenase or i RGD did not help to overcome the permeation barriers for GE11-TLs, in contrast to PEGylated liposomes(PLs). GE11-DLs were distributed mostly surrounding angiogenic vessels and specifically bound to EGFR-expressed stroma cells. The GE11 peptide contributed to ligand-mediated liposome uptake. It's maybe the destruction of “tumor microenviroment” caused by the cytotoxic effect on stroma cells that contributed mostly to the antitumor effect of GE11-DLs to SMMC7721 xenograft.This study had given us a better understanding of the biological and the(patho-) physiological principles of liposome mediated drug targeting. We hope the identification of barriers and obstacles of tumor-targeted drug delivery process will benefit the further development of strategies in the future.