Gene therapy Lecture 8

What is a liposome? ◦ Spherical vesicles with a phospholipid bilayer Hydrophilic Hydrophobic

Uses of Liposomes Chelation therapy for treatment of heavy metal poisoning Enzyme replacement Diagnostic imaging of tumors Study of membranes Drug/Gene Delivery

Liposome with DNA or Drug

Entry into the cell A liposome has an aqueous solution core surrounded by a hydrophobic membrane, in the form of a lipid bilayer. Hydrophilic solutes dissolved in the core cannot readily pass through the bilayer. Hydrophobic chemicals associate with the bilayer. A liposome can be hence loaded with hydrophobic and/or and hydrophilic molecules. To deliver the molecules to a site of action, the lipid bilayer can fuse with the cell membrane, thus delivering the liposome contents. Thus preparation of liposomes in a solution of DNA or drugs (which would normally be unable to diffuse through the membrane) they can be (indiscriminately) delivered past the lipid bilayer.

Entry into the cell

Nano-liposomes Composition: Nano-Liposomes are made up of lipids, most of which occur naturally within the body. Size and stability: Typically nanometers,Nano- Liposomes are stable in blood, circulate well, and easily enter tumor cells to deliver their payloads, destroying cancer cells. Active ingredients: both water-loving (hydrophilic) and water-hating (hydrophobic) compounds can be loaded into NanoLiposomes. Protection: Actives are stored either within the liposomal core or lipid bilayer, preventing degradation during circulation. Delivery: NanoLiposomes are stable during circulation and release payloads intracellularly following membrane fusion. Targeting: NanoLiposomes can be targeted through size and surface charge, or a wide range of targeting materials can be attached to the surface.

Cationic Liposome Cationic liposomes are structures that are made of positively charged lipids and are increasingly being researched for use in gene therapy due to their favourable interactions with negatively charged DNA and cell membranes. They can be administered efficiently, safely, and repeatedly for direct gene transfer for the treatment of human diseases. An ideal cationic liposome is capable of targeting tumor vessels and tumor cells.

Current liposomal drug preparations Type of AgentsExamples Anticancer Drugs Anti bacterial Antiviral DNA material Enzymes Radionuclide Fungicides Vaccines *Currently in Clinical Trials or Approved for Clinical Use Malaria merozoite, Malaria sporozoite Hepatitis B antigen, Rabies virus glycoprotein Amphotericin B* In-111*, Tc-99m Hexosaminidase A Glucocerebrosidase, Peroxidase Duanorubicin,Doxorubicin*, Epirubicin Methotrexate, Cisplatin*, Cytarabin Triclosan, Clindamycin hydrochloride, Ampicillin, peperacillin, rifamicin AZT cDNA - CFTR*

Doxil Chemotherapy drug doxorubin Anemia, damage to veins and tissue at injection, decrease platelet and WBC count, toxic to the body Treats cancer tumors Modifications of liposome “stealth” keeps doxorubin in blood for 50 hours instead of 20 minutes concentrates at KS lesions and tumors *approved by FDA in 2000*

Problems with Liposomal Preparations of Drugs Price 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

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