What is a liposome?

– Liposomes are artificially prepared spherical vesicles made of phospholipid bilayer.

Phospholipid Bilayer

Polar Head Groups

Three carbon glycerol

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Liposomes Formation

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TYPE SPECIFICATION

MLV Multilamellar large vesicles->0.5m

OLV Oligolamellar vesicles-0.1-1 m

UV Unilamellar vesicles (all size ranges)

SUV Small Unilamellar Vesicles- 20-100 nm

MUV Medium sized unilamellar vesicles

LUV Large unilamellar vesicles->100nm

GUV Giant unilamellar vesicles->1m

MV Multivesicular vesicles->1m

CLASSIFICATION OF LIPOSOMESBased on Structural Parameters

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REV Single or oligolamellar vesicles made by

reverse- phase evaporation method.

MLV_REV Multilamellar vesicles made by reverse-

phase evaporation method.

SPLV Stable plurilamellar vesicles

FATMLV Frozen and thawed MLV

VET Vesicles prepared by extrusion technique.

DRV Dehydration – rehydration method.

CLASSIFICATION OF LIPOSOMESBased on Method of Liposome Preparation

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Based upon Composition & Applications

CLASSIFICATION OF LIPOSOMES

Conventional liposomes(CL) Neutral or negatively charged

Phospholipids and cholestrol.

Fusogenic liposomes (RSVE) Reconstituted Sendai virus envelopes

pH sensitive liposomes Phospholipid such as PE or DOPE

with either CHEMS or OA

Cationic liposomes Cationic lipids with DOPE

Long circulatory stealth Neutral high Tc, cholestrol and 5- 10%

liposomes (LCL) of PEG - DSPE or GM1

Immuno-liposomes CL or LCL with attached monoclonal

antibody or recognition sequence

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Method of Preparation of Liposomes

Passive loading techniques Active loading techniques

Mechanical dispersion methodsSolvent dispersion methodsDetergent removal methods

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• Mechanical dispersion methods Lipid film hydration by hand shaking,non-hand shaking or freeze drying Microemulsification Sonication French pressure cell Membrane extrusion Dried reconstituted vesicles Freeze-thawed liposomes

• Solvent dispersion methods Ethanol injection Ether injection Double emulsion vesicles Reverse phase evaporation vesicles Stable plurilamellar vesicles

• Detergent removal methods Dialysis Column chromatography Dilution Reconstituted Sendai Virus enveloped vesicles

Method of Preparation of Liposomes

Passive Loading Techniques

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• In order to increase the surface area of dried lipid film and to facilitate instantaneous

hydration, the lipid is dried over a finely divided particulate support, such as powdered

sodium chloride, or sorbitol or other polysacharrides.

• These dried lipid coated particulates are called pro-liposomes.

• Pro-liposomes form dispersion of MLV’s on adding water into them, where support is

rapidly dissolved and lipid film hydrates to form MLV’s.

• This method also overcomes the stability problems of liposomes encountered during

the storage of dispersion, dry or frozen form.

• It is ideally suited for preparations where the material incorporates into lipid membrane.

Pro-Liposomes

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SONICATED UNILAMELLAR VESICLES (SUV’s)

Preparation of SUV’s from Bath/Probe Sonicator from MLV’s

Uses of Liposomes

Chelation therapy for treatment of heavy metal poisoning

Enzyme replacement

Diagnostic imaging of tumors

Study of membranes

Cosmetics

Drug Delivery

Liposome for Drug Delivery

• Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases.

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Drug Targeting

Modes of Liposome/Cell Interaction

Adsorption Endocytosis

Fusion Lipid transfer

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THERAPEUTIC APPLICATION OF LIPOSOMES

LIPOSOMES AS DRUG DELIVERY VEHICLES:

1. Enhanced drug solubilization (amphotericin B, minoxidil, paclitaxel,

cyclosporin),

2. Protection of sensitive drug molecules (cytosine arabinose,

ribozymes)

3. Enhanced intracellular uptake (anticancer, antiviral and antimicrobial

drugs).

4. Altered pharmacokinetics and biodistribution (prolonged or sustained

release of drugs with short circulatory half-lives).

5. Drugs delivered via liposomes may be protected from the actions of

metabolizing enzymes

6. Using liposomes as a drug deliverer allows potentially lower doses of drug to be used, reducing toxicity and side-effects.

Current liposomal drug preparations

Type of Agents ExamplesAnticancer Drugs

Anti bacterial

AntiviralDNA materialEnzymes

RadionuclideFungicidesVaccines

*Currently in Clinical Trials or Approved for Clinical Use

Malaria merozoite, Malaria sporozoiteHepatitis B antigen, Rabies virus glycoprotein

Amphotericin B*In-111*, Tc-99m

Hexosaminidase A Glucocerebrosidase, Peroxidase

Duanorubicin, Doxorubicin*, Epirubicin Methotrexate, Cisplatin*, CytarabinTriclosan, Clindamycin hydrochloride, Ampicillin, peperacillin, rifamicinAZTcDNA - CFTR*

CFTR

Gene TherapyDeliver cDNA of Cystic Fibrosis Transmembrane Conductance

Regulator (CFTR) to epithelial tissue of respiratory system

Fuse to cell membrane and incorporate cDNA into cell

Clinical trials - no significant change in symptoms

Now trying adeno associated virus

Cationic liposome

Doxil

Chemotherapy drug doxorubinAnemia, damage to veins and tissue at injection, decrease

platelet and WBC count.

Treats Kaposi’s sarcoma lesions or cancer tumorsModifications of liposome “stealth”

keeps doxorubin in blood for 50 hours instead of 20 minutes

concentrates at KS lesions and tumors

*Just approved by FDA*

Amphotericin B

Side effects: nephrotoxicity, chills, and fevers

Systemic fungal infections in immune compromised patients

Fungizone - AmB with deoxycholate

AmB - kills ergosterol-containing fungal cells, also kills cholesterol-containing human cells

No decrease in effectiveness of drug against fungi

Liposomal Formulation of AmB

Decrease in toxicity

Exact Mechanism of liposomes not understood

Cholesterol - only few %moles

Phospholipid:AmB ratio

DiffusionLipid transfer

AmB

Lipid

Problems with Liposomal Preparations of Drugs

$$$$

Fungizone $40.58 Amphotec $2334

Doxil $1200 per treatment, twice the cost of normal protocol of chemotherapy and drugs

Lack long term stability (short shelf life)

Freeze dry and pH adjustment

Low “Pay Load” - poor encapsulation

Physical and chemical instability

Polar drugs and drugs without opposite charge

Modifications

Possibility of new side effectsDoxil “hand and foot syndrome”

Problems continued

EfficacyCFTR

Studies with insulin show that liposomes may be an effective way to package proteins and peptides for use

Clinical Trials for several liposomal formulations More studies on the manipulation of liposomes

Future

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Thank You