Novel echogenic drug-immunoliposomes for drug delivery.

RATIONALE AND OBJECTIVES: We have developed novel echogenic immunoliposomes (ELIPs) that can be antibody-conjugated for the specific highlighting of atheroma and atheroma components. The utility of these agents for regional drug delivery has not been evaluated previously. We chose to use an antibiotic as the prototype drug. The concept that an infectious agent may affect the development and progression of atherosclerosis has stimulated trials on the use of antibiotics for coronary syndromes. However, these agents are given systemically with concomitant problems. Development of an agent for local drug delivery may obviate adverse effects and improve treatment efficacy. The aim of this study was to evaluate the potential of our ELIPs for drug incorporation and to demonstrate efficient drug delivery to cultured cells. METHODS: Azithromycin was incorporated into the ELIPs during development. Free drug was removed with a Sephadex G-50 column. Acoustic properties were evaluated using an intravascular ultrasound catheter and quantified by computer-assisted videodensitometry. Human umbilical arterial endothelial cells were infected with Chlamydia pneumoniae. Cells were treated with the drug-ELIP complexes, and infection-forming units were counted using fluorescence techniques. RESULTS: We were able to incorporate a drug into the ELIPs with retention of acoustic properties. The drug-ELIP complex demonstrated effective inhibition of microbial growth in endothelial cells (P < 0.001 vs. empty liposomes and control). CONCLUSIONS: We have developed a novel acoustic drug-liposomal agent that can deliver drugs to cultured cells. Although in vivo translation is required, this technique has potential for site-specific drug delivery.

Quantitative immunoblot assay for assessment of liposomal antibody conjugation efficiency.

Routine direct assessment of immunoglobulin (Ig)-liposome(lp) conjugation efficiency has been impeded by phospholipid interference with standard protein and immunoassay methods. Rabbit IgG conjugated to anionic liposomes was quantitated in immunoblots using computer image analysis techniques. Lp-coupled Ig was separated from free Ig by dialysis in disposable Spectra/Por units (MWCO 300 kDa). Differential Lowry protein assay (DLA) of the thiolated Ig reactant and the dialyzate provided an estimate of conjugation efficiency that was compared to the results of the immunoblot assay (IBA). The color response of Ig-lp in the IBA was about an order of magnitude greater than rabbit IgG alone, requiring the synthesis of an Ig-lp standard in which the Ig conjugation efficiency was assessed by radiotracer methodology. The use of the same standard in three colorimetric protein assays verified the accuracy of the IBA and demonstrated that the colorimetric assays could be employed to determine Ig-lp conjugation efficiency. In terms of sensitivity and specificity, however, the IBA is better suited for routine assessment of laboratory-scale Ig-lp conjugation efficiencies. The DLA was found to be an unsatisfactory measure of conjugation efficiencies because an interfering substance was apparently released by Ig-lp preparations.