Liposomes are ultra-micro spherical carrier preparations formed by lipid bilayers, and are typical representatives of nano-drug delivery systems. When amphiphilic molecules such as phospholipids are dispersed in the aqueous phase, the hydrophobic tails of the molecules gather together, and the hydrophilic heads are exposed in the aqueous phase to form closed vesicles with a bilayer structure. A variety of drugs of different polarities can be encapsulated in the water phase and bimolecular membrane in the vesicles. In addition, liposomes have good biocompatibility and can be normally metabolized. Therefore, liposomes have great potential for development as drug carriers.
The mechanism of action of the liposome drug delivery system can be divided into passive targeting, active targeting and biophysical targeting according to the different modes of action. The targeting of liposomes is mainly passive targeting. For example, using the particle size of liposomes to improve the aggregation of liposome drugs in tumor tissue is a manifestation of passive targeting; active targeting is a manifestation of passive targeting. It uses the specificity or selectivity of specific enzymes, antibodies, and ligands to modify them on the surface of drug-loaded liposomes to actively seek targets, thereby increasing the drug concentration at the target site; biophysical targeting is Using drug-loaded liposomes to carry special materials such as acids, bases, light-sensitive materials or magnetic materials at the same time, it is a kind of targeting that aggregates drugs to the action site. The liposome drug delivery system is mainly used in the fields of anti-tumor and anti-infection, and its mechanism of action mainly includes the following aspects.
Avoid Rapid Phagocytic Effects of the Reticuloendothelial System
The surface-modified liposome drug delivery system can avoid rapid phagocytosis by blood, liver, spleen, and other reticuloendothelial system (RES)-rich tissues or regions, and avoid rapid elimination of drug-loaded particles. When the surface of the drug-loaded liposomes is strongly hydrophobic, the liposomes are easily taken up by RES-rich tissues or regions such as blood, liver, and spleen, while when the surface of the drug-loaded liposomes is strongly hydrophilic, such as polyethylene glycol Diol-phospholipid derivative-modified (also known as PEGylation, pegylation) liposomes will not be rapidly cleared by RES in the blood, liver and spleen to achieve long-term circulation in the body, thereby increasing the accumulation of drugs in diseased tissues and improving treatment effect.
Penetration and Retention Enhancing Effects in Tumor Tissue
The enhanced penetration and retention effect (EPR effect) refers to the proliferation of blood vessels in solid tumor tissue, the wide space in the blood vessel wall, and the loose structure, which is conducive to the penetration and retention of liposome particles in the tumor tissue. The EPR effect promotes the selective distribution of liposome drug delivery systems in tumor tissues, thereby increasing the efficacy of drug-loaded liposomes and reducing systemic adverse reactions.
Tumor Cell Specific Binding Effect
By modifying the surface of the liposome with specific antibodies/ligands, the drug-loaded liposomes can be combined with specific antigens/receptors on the surface of tumor cells to play an active targeting role. At present, some receptors (such as integrin receptors, lectin receptors and folate receptors, etc.) are overexpressed in tumor tissues, and their corresponding ligands are used as targeting molecules to be modified on drug-loaded liposomes, which enables active targeted drug delivery of liposomes.
Block the Angiogenesis Effect of Tumor Tissue
Angiogenesis of tumor tissue provides abundant nutrients for tumor growth, therefore, blocking angiogenesis is an effective strategy in tumor therapy. Tumor tissue angiogenesis is regulated by a variety of molecules, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGFs), platelet-derived growth factor (PDGF), and matrix metalloproteinases (MMPs). During tumor treatment, these molecules may become targets of drug-loaded liposomes. At present, the main therapeutic measures to block angiogenesis include inhibiting endothelial cell proliferation and inhibiting VEGF.
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