tetraether macrocyclic lipid O O O OH OH OH O R 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 O O CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 PO 4 R 1 CH 3 OH Liposomes are spherical vesicles composed of a membrane surrounding an aqueous core. Liposomes are used for drug delivery (in the form of genes, peptides, vaccines, siRNA) due to their unique properties. As delivery agents, they are superior to free drugs in regards to antitumor activity, toxicity, therapeutic efficacy, drug resistance, and drug side effects. However, conventional liposomes have several handicaps; they can be rapidly removed from the circulation by body cells, by body enzymes, by stomach acid and by other components of the reticuloendothelial system (RES), which functions to recognize and destroy foreign substances. Stealth liposomes were engineered to help avoid detection by the RES. It was shown that by coating liposomes with polyethylene glycol (PEG), both stability and circulation half-life could be increased. Tetraether Archaeal Liposomes Parkson Lee-Gau Chong, Temple University School of Medicine, DMR Typical phospholipid found in conventional liposomes Drug in aqueous core Conventional Liposome A novel way to increase stability is to use liposomes composed of tetraether macrocyclic lipids isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius. These are called: Archaeosomes PLFE lipids form stable archaeosomes: lipids span entire lamellar structure membrane is one molecule thick show high thermal stability show unusually low proton permeability have tight, rigid lipid packing Archaeosomes are better: temperature stable pH stable resistant to mechanical stress, body enzymes, bile salts, serum proteins. S. acidocaldarius thrives at: o C and a pH of 2-3 A constituent of the S. acidocaldarius plasma membrane is polar lipid fraction E (PLFE). PLFE contains a mixture of bipolar tetraether lipids. These lipids have a pair of 40-carbon biphytanyl chains; each chain contains up to four cyclopentane rings. The number of cyclopentane rings in each chain increases as growth temperature increases.

We found that PLFE-based archaeosomes are remarkably stable against multiple autoclaving at pH 4-10 when compared to conventional liposomes. Stability was measured in terms of particle size, size distribution and vesicle morphology using dynamic light scattering and transmission electron microscopy This result adds one more reason for exploring bipolar tetraether archaeosomes as stable effective drug delivery vehicles. (Z 0 = size before autoclaving, Z 1, Z 2, Z 3 = size after first, second and third autoclaving; all particle sizes in nm) Autoclaving is a very effective decontamination method. The ability to maintain vesicle integrity after autoclaving would be a desirable feature for systemic use of liposomes. Conventional stealth liposomes before autoclaving average particle size ~200 nm PLFE archaeosomes after 6 cycles of autoclaving PLFE-based stealth archaeosomes before autoclaving Archael lipids; growth temp pHZ0Z0 Z1Z1 Z2Z2 Z3Z3 PLFE (65°C) PLFE (78°C) Conventional lipids used pHZ0Z0 Z1Z1 Z2Z2 Z3Z3 DMPC POPC >2000 Conventional stealth liposomes after 1 autoclaving average particle size ~1700 nm PLFE archaeosomes before autoclaving PLFE-based stealth archaeosomes after 6 cycles of autoclaving mm Micrograph of S acidocaldarius: liposome: Archaea tree: Tetraether Archaeal Liposomes Parkson Lee-Gau Chong, Temple University School of Medicine, DMR