(259b) Heterogeneous Antibody Presentation within Lipid Microdomains for Enhanced Binding of Liposomes to Injured Endothelium

Neutrophils, a type of leukocyte, are localized to inflamed endothelium via a process that includes rolling, adhesion, arrest, and transmigration. This process is regulated by the upregulation of endothelial leukocyte adhesion molecule-1 (E-selectin) and intercellular adhesion molecule-1 (ICAM-1) in response to pro-inflammatory stimuli, such as the cytokine interleukin-1α (IL-1 α). Current methods that target endothelial cells (ECs) do not account for the organization of E-selectin and ICAM-1, which co-localize in detergent-insoluble lipid domains. We propose to mimic the neutrophil-EC interaction by designing vehicles that mirror the antibody presentation in lipid rafts as a novel strategy to target inflamed endothelium. In our previous work, we demonstrated that immunoliposomes with higher ligand mobility had increased cellular binding by more than 4-fold. In addition, we have shown that disruption of lipid raft formation by addition of the cholesterol depleting agent, methyl-beta-cyclodextrin, inhibits binding. We hypothesized that liposomes displaying anti-ICAM-1 and anti-ELAM-1 localized in gel phase (Lβ) lipid microdomains may increase cellular binding. Giant unilamellar vesicles (GUVs) and small unilamellar vesicles (SUVs) containing 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP, C18:1, Tm ~0 °C), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC, C18:0, Tm = 55 °C) and cholesterol were prepared. Varying the molar ratios of unsaturated and saturated lipids resulted in separation of the lipid phases and formation of lipid microdomains. Binding of SUVs containing microdomains bearing different densities of anti-ICAM-1 and anti-ELAM-1 to ECs were evaluated. Increased cellular binding of liposomes displaying the antibodies localized on lipid microdomains was demonstrated. These results show a direct correlation between a heterogeneous antibody presentation and an increase in endothelial cell targeting efficiency.