Liposomes were discovered in 1961 by Alec D. Bangham who was studying
phospholipids and blood clotting, and since then they became very versatile
tools in biology, biochemistry and medicine.
Liposomes are nano size artificial vesicles of spherical shape that can be
produced from natural phospholipids and cholesterol. Bangham discovered
that phospholipids combined with water immediately forms a bi-layered
sphere because one end of each molecule is water soluble, while the opposite
end is water insoluble (see Figure bellow).
Liposomes are broadly classified by their structure
- Multilamellar liposomes: Spherically concentric multilamellar (many
bilayers) structures
- Unilamellar liposomes: Spherical concentric unilamellar (one bilayer)
structures
The properties of liposomes in addition to the general properties of
surfactants those make them useful for different applications are
- Structural stability on dilution
- Varying permeability of the bilayer to different molecules.
- Ability to entrap both water soluble and insoluble substances and
deliver them into desired environments.
The size, lamellarity (unilamellar or multilamellar) and lipid composition of
the bilayers influence many of the important properties like the fluidity,
permeability, stability and structure -these can be controlled and customized
to serve specific needs. The properties are also influenced by external
parameters like the temperature, ionic strength and the presence of certain
molecules nearby.
Liposomes is extensively studied for encapsulation of drugs. When lipid self
assemble to liposomes water-soluble drugs will be trapped inside the
liposomal cavity; fat-soluble drugs are incorporated within phospholipid bi-
layer. The lipid bilayer of the liposome can fuse with other bilayers (e.g. cell
membrane), thus delivering the liposome contents.
Liposomal formulations are the first NanoPharmaceuticals introduced to
market, Doxil® PEGylated liposomal formulation for doxorubicin is the first
product based on liposomes. Theses liposomes are called as “Stealth”
liposomes with size <200nm which are long circulation with hydrophilic
(PEG) surface. These long circulating liposomes found to target to tumour
tissue by a mechanism known as enhanced permeation and retention (EPR).
Hence liposomal formulation of doxorubicin considerably reduced the cardio-
toxicity of drug. Many lipososmal products are under various phases of
clinical trials, here is the table showing some of product which are in market:
Alza
Biomira Inc
Elan
Endovasc
Gilead
Inex Pharmaceuticals
NeoPharm
Recoly N.V.
Telik
Tibotec Therapeutics
Transaveinc
Genzyme
Lipoid
NOF Corp
Northern Lipids
Phospholipid GmbH
| Product |
Drug |
Company |
| Doxil |
Doxorubicin |
ALZA |
| DaunoXome |
Doxorubicin |
Gilead Sciences |
| Ambisome |
Amphotericin B |
Gilead Sciences |
| Amphotec |
Amphotericin B |
ALZA |
| Abelect |
Amphotericin B |
ELAN |
Induction of cancer cell-specific apoptosis by folate-labeled cationic
liposomes NEW
Journal of Controlled Release, 2006, 111, 325-332
Investigating the uptake and intracellular fate of pH-sensitive liposomes by
flow cytometry and spectral bio-imaging
Journal of Controlled Release, 2006, 110, 490-504.
Gadolinium-loaded liposomes allow for real-time magnetic resonance imaging
of convection-enhanced delivery in the primate brain
Experimental Neurology, 2005, 196, 381-389.
Neuroblastoma targeting by c-myb-selective antisense oligonucleotides
entrapped in anti-GD(2) immunoliposome: immune cell-mediated anti-tumor
Cancer Letters, 2005, 228, 181-186.
Spray-freeze-dried liposomal ciprofloxacin powder for inhaled aerosol drug
delivery
International. Journal of Pharmaceutics., 2005, 305, 180-185.
Patent Watch
Combined chemo-immunotherapy with liposomal drugs and cytokines
Gabizon et al., USPT 6,787,132, September 7, 2004.
Liposome composition and method for administration of a radiosensitizer
Uster , et al., USPT 6,818,227, November 16, 2004.
Enteric-coated proliposomal formulations for poorly water soluble drugs
Betageri, USPT 6,759,058, July 6, 2004.
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