Formation of drug-bearing vesicles in mixed colloids of bile salts and phosphatidylcholine

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors used small-angle neutron scattering to study drug interactions with mixed colloids of bile salt and phosphatidylcholine. Because the mixed colloids form liposomes spontaneously, this system is a model for drug-bile interactions that are important in understanding the efficacy of oral drug formulations and in advanced applications for liposome drug delivery systems. The authors studied particle formation in incorporation of enzymatic products formed in the gut and the effects of cholesteric drugs and taxol on vesicle formation. The studies show that particle morphology is not affected by inclusion of most cholesteric drugs and taxol, and is not affected by incorporation of the products of enzymatic action. The findings suggest that particle form is important for the physiological function of bile and they are beginning to show which drugs affect liposome formation

In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement

AbstractOBJECTIVESThe purpose of this study was to target acoustically reflective liposomes to atherosclerotic plaques in vivo for ultrasound image enhancement.BACKGROUNDWe have previously demonstrated the development of acoustically reflective liposomes that can be conjugated for site-specific acoustic enhancement. This study evaluates the ability of liposomes coupled to antibodies specific for different components of atherosclerotic plaques and thrombi to target and enhance ultrasonic images in vivo.METHODSLiposomes were prepared with phospholipids and cholesterol using a dehydration/rehydration method. Antibodies were thiolated for liposome conjugation with N-succinimidyl 3-(2-pyridyldithio) propionate resulting in a thioether linkage between the protein and the phospholipid. Liposomes were conjugated to antifibrinogen or anti–intercellular adhesion molecule-1 (anti–ICAM-1). In a Yucatan miniswine model, atherosclerosis was developed by crush injury of one carotid and one femoral artery and ingestion of a hypercholesterolemic diet. After full plaque development the arteries were imaged (20-MHz intravascular ultrasound catheter and 7.5-MHz transvascular linear probe) after injection of saline, unconjugated liposomes and antibody conjugated liposomes.RESULTSConjugated liposomes retained their acoustically reflective properties and provided ultrasonic image enhancement of their targeted structures. Liposomes conjugated to antifibrinogen attached to thrombi and fibrous portions of the atheroma, whereas liposomes conjugated to anti–ICAM-1 attached to early atheroma.CONCLUSIONSOur data demonstrate that this novel acoustic agent can provide varying targeting with different antibodies with retention of intravascular and transvascular acoustic properties

901–48 Antibody Conjugation of Acoustically Reflective Liposomes for Tissue Targeting

We have previously demonstrated the formulation of acoustic multilamellar liposomes that does not require gas entrapment. Successful antibody conjugation of liposomes, while retaining acoustic properties, could provide an ultrasonic contrast agent for the early detection of atherosclerosis, thrombi, and vegetations. We prepared liposomes from a (55: 10: 5: 30) molar mixture of egg phosphatidylcholine, 4-(p-maleimidophenyl)butyryl-phosphatidylethanolamine, dipalmitoyalphosphatidylglycerol, and cholesterol by hydration of the lipid film and sonication followed by freeze drying and resuspension. Human gamma globulin was thiolated for conjugation to the liposomes with N-succinimidyl 3-(2-pyridyldithio)propionate. Following reaction, the unbound antibody was removed by separation on a Sepharose 4B column. To determine acoustic properties, the conjugated preparation was imaged with a 20 mHz intravascular ultrasound catheter (Cardiovascular Imaging System, Sunnyvale, CA) and compared to water and our previously unconjugated liposomes.ResultsThis method allowed near complete conjugation of liposomes. The average liposomal size following antibody conjugation was 0.5μm.Gray Scale brightness (mean) and heterogeneity.Gray scaleWaterUnconjugatedConjugatedMean10.957.9*47.4*Heterogeneity4.5514.1215.45*p < 0.005 vs. waterMagnitude of brightness Δ vs. water in dB (20log[lipo/water]) was 14.5 for unconjugated and 12.7 for conjugated liposomes.We have demonstrated a method of antibody conjugation to liposomes that allows the liposomes to retain their acoustic reflectivity. This novel technique allows for target-specific in-vivo acoustic enhancement of pathologic vascular structures