Using shape effects to target antibody-coated nanoparticles to lung and brain endothelium

Abstract

Vascular endothelium offers a variety of therapeutic targets for the treatment of cancer, cardiovascular diseases, inflammation, and oxidative stress. Significant research has been focused on developing agents to target the endothelium in diseased tissues. This includes identification of antibodies against adhesion molecules and neovascular expression markers or peptides discovered using phage display. Such targeting molecules also have been used to deliver nanoparticles to the endothelium of the diseased tissue. Here we report, based on in vitro and in vivo studies, that the specificity of endothelial targeting can be enhanced further by engineering the shape of ligand-displaying nanoparticles. In vitro studies performed using microfluidic systems that mimic the vasculature (synthetic microvascular networks) showed that rod-shaped nanoparticles exhibit higher specific and lower nonspecific accumulation under flow at the target compared with their spherical counterparts. Mathematical modeling of particle-surface interactions suggests that the higher avidity and specificity of nanorods originate from the balance of polyvalent interactions that favor adhesion and entropic losses as well as shear-induced detachment that reduce binding. In vivo experiments in mice confirmed that shape-induced enhancement of vascular targeting is also observed under physiological conditions in lungs and brain for nanoparticles displaying anti-intracellular adhesion molecule 1 and anti-transferrin receptor antibodies.

Keywords: SMN; biodistribution; cylinder; drug delivery; morphology.

Fig. 1.

Forces acting on particles under flow. (A) Schematic of particles interacting with a wall under flow. (B) Scanning electron micrographs of polystyrene spheres and (C) elongated particles stretched from the 200-nm spheres. Scale bar, 1 μm. (D) RBE4-laden SMN.

Fig. 2.

Attachment of particles on OVA-coated SMNs. Quantification of attachment of particles coated with IgG [spheres (IgG-S) or rods (IgG-R)] or anti-OVA [spheres (OVA-mAb-S) or rods (OVA-mAb-R)] at various shear rates at the inlet region (A) and at the bifurcation (B) of the device. (C) Adhesion ratios of nanorods (■) and nanospheres (●) for specific antibodies (OVA-mAb)/nonspecific antibodies (IgG). (D) Adhesion ratios of OVA-mAb–coated particles (■) and IgG-coated particles (●) for nanorods and nanospheres, respectively.

Fig. 3.

Attachment of particles to endothelial cells under flow. (Top) Bright-field images showing RBE4 cells in SMNs to which particles have attached/internalized: (A) ICAM-mAb-rods, (B) ICAM-mAb-spheres, (C) IgG-rods, and (D) IgG-spheres. (Middle) Fluorescent images corresponding to the bright-field images from the top row. The images in the middle row show particles attaching/internalizing in RBE4 cells in the SMNs. (Bottom) Zoomed-in views of corresponding images from the fluorescence images from the middle row.

Fig. 4.

In vivo biodistribution of particles. (A) Bar graph representing percentage of injected dosage per gram of organ (%ID/g) for ICAM-mAb coated rods (black), ICAM-mAb-coated spheres (dark grey), IgG-coated rods (light gray) and IgG-coated spheres (white). (B) Ratio of ICAM-mAb–coated particles to IgG-coated particles for rods (black) and spheres (gray). (C) Lung/liver accumulation of nanoparticles for IgG- or ICAM-mAb–coated spheres and rods. (D) Ratio of TfR-mAb–coated rods to spheres; the graph highlights the higher nanorod accumulation in all organs, except liver (n = 3–5 for all in vivo experiments).