846.7 - Targeting ligand surface density controls both complement activation and targeting efficiency of immunoliposomes

Jia Nong (University of Pennsylvania), Patrick Glassman (University of Pennsylvania), Zhicheng Wang (University of Pennsylvania), Oscar Marcos-Contreras (University of Pennsylvania), Jacob Brenner (University of Pennsylvania), Vladimir Muzykantov (University of Pennsylvania)

Coupling monoclonal antibodies (mAb) and their derivatives to the surface of nanoparticles is a widely tested strategy to improve the specificity and magnitude of targeting to specific organs and cells. However, immediately after intravascular injections, nanoparticles are opsonized by many proteins, including complement protein C3.  Opsonization promotes two undesirable processes that limit the utility of nanoparticles: 1) rapid elimination by phagocytes and 2) an anaphylactoid syndrome known as complement activation-related pseudoallergy (CARPA), which manifests as capillary leak, hemolysis, hypotension, and can be catastrophic to critically ill patients.  These processes can be further enhanced by the Fc region of coupled mAbs, which enhances both recognition by phagocytes via FcγRs and complement activation, making antibody-targeted nanoparticle a “double-edged sword”.  In order to maximize the potential of targeted nanoparticles, CARPA must be minimized, while drug delivery is maintained. In this study, we investigated the effect of antibody coating density on complement activation, side effect, and targeting efficacy of targeted nanoparticles. Incubation of immunoliposomes with a range of mAb coating density with mouse serum revealed that C3a release (a marker of complement activation) was correlated with coating density (Fig A).  Following intravenous injection, increasing mAb coating density on liposomes promoted hemoconcentration (Fig B), increased numbers of white blood cells in circulation (Fig C), and increased liposome clearance by the liver (Fig C).  Liposomes that were coated with a mAb recognizing vascular cell adhesion molecule were injected into mice to study their blood and tissue pharmacokinetics.  Liposomes with a lower coating density had delayed clearance from the blood and, as a result, improved delivery to the target tissue (brain) (Figure D).  Future studies will elucidate the role of Fc receptors on liposome biodistribution, as well as the safety and efficacy of drug-loaded immunoliposomes coated with different densities of targeting ligands.



Immunoliposomes were conjugated with various amount of mAb on the surface. (A) C3a production after incubating immunoliposomes with naive mouse serum; (B) Hematocrit of naive mice IV injected with immunoliposomes; (C) Circulating monocytes and neutrophils amount in the whole blood and liver biodistribution of naive mice injected with immunoliposomes; (D) Blood and tissue pharmacokinetics of immunoliposones in TNF-alpha challenged mice. Mean±SEM; n=3; *p < 0.05 using one-way ANOVA