Trends in Pharmacological Sciences
ReviewLiposomes and nanoparticles: nanosized vehicles for drug delivery in cancer
Introduction
The application of innovative nanotechnologies to medicine – nanomedicine – has the potential to significantly benefit clinical practice, offering solutions to many of the current limitations in diagnosis, treatment and management of human disease. The diverse branches of nanomedicine include tissue regeneration [1], drug delivery [2] and imaging [3]. This review focuses on two nanotechnological drug delivery methods, liposomes and drug-conjugated nanoparticles.
Liposomes are closed spherical vesicles consisting of a lipid bilayer that encapsulates an aqueous phase in which drugs can be stored. The liposome diameter varies from 400 nm to 2.5 μm. Nanoparticles (NPs), which are particles ranging in size from 1 to 100 nm, exhibit unique physical and chemical properties that can be exploited for drug delivery by conjugation with drugs. Both these emerging nanoscale drug delivery systems can be used to improve current treatment regimens (Box 1).
High drug toxicity is a barrier to treatment because side effects limit the drug dosage that can be administered. This is best exemplified by cytotoxic cancer drugs. Although very effective in vitro, in human clinical use the drugs act indiscriminately on both cancerous and healthy tissues. Side effects can be both serious and unpleasant and range from nausea and hair loss to neuropathies, neutropenia and kidney failure. Therefore, drug non-specificity limits efficacy [4]. Box 2 details recent drugs and diseases under investigation for the use of nanoscale drug delivery.
This review outlines recent developments in the use of liposomes and NPs in the field of drug delivery for the treatment of cancer. An understanding of these new technologies is needed for the advancement of chemotherapy with higher efficacy and lower toxicity.
Section snippets
Advantages of nanoscale drug delivery systems
The ideal nanoscale drug delivery system ensures that the conjugated or bound drug–carrier complex arrives and acts preferentially at the selected target. Targeting of the drug–nanocarrier complex can be active, whereby the complex incorporates a ligand specific for the receptor or epitope of the target tissue (Table 1). In passive targeting, complexes diffuse and accumulate at sites with excessively leaky microvasculature, such as tumours and inflamed tissues, with normal endothelium being
Liposomes
The liposome bilayer can be composed of either synthetic or natural phospholipids. The predominant physical and chemical properties of a liposome are based on the net properties of the constituent phospholipids [11], including permeability, charge density and steric hindrance. The lipid bilayer closes in on itself due to interactions between water molecules and the hydrophobic phosphate groups of the phospholipids. This process of liposome formation is spontaneous because the amphiphilic
Conclusions and future direction
Liposomes and NPs are promising candidates for the development of drug delivery systems. Early experimental evidence, both clinically and preclinically, shows great potential for the widespread adoption of liposomes and NPs in cancer treatment. Their attractive properties include biocompatibility, low toxicity, lower clearance rates, the ability to target specific tissues and controlled release of drugs. They offer numerous advantages over conventional chemotherapy using free drug treatment, as
Acknowledgement
We would like to thank the EPSRC for financial support for the development of nanoparticles and nanomaterials for drug delivery and the NHIR for a (Neat) grant.
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