(584ak) Evaluating Nanodisks and Nanorods As Carriers for Targeting Diseased Endothelium in Physiological Blood Flows

Introduction:   The development of vascular-targeted carriers (VTC) for the
delivery of therapeutics could greatly improve the treatment of many human
diseases. Spherical nanoparticles are commonly used as potential drug carriers
due to their ability to easily navigate microvasculature and ease of
fabrication/drug loading. However, recent literature has shown that spherical
nanoparticles do not efficiently marginate and adhere
to the vascular wall in model blood vessels compared to larger micron sized
particles.^1,2 Therefore spherical nanoparticles may not be effective
as VTCs for drug delivery and diagnosis, particularly in targeting diseases
which affect medium/large blood vessels (M/LBV), such as atherosclerosis.
Recently, particle shape has received attention as a parameter that can be used
to improve the performance of VTCs. The purpose of this study is to examine the
hemodynamics of rod and disk-shaped particles of different aspect ratios
relative to spheres of equal volume both in vitro in human blood flow
under physiological conditions.

Materials and Methods:  Polystyrene
rod and disk-shaped particles were fabricated via a polymer film stretch method
previously described in literature.³ Rods, disks, and spherical
particles were conjugated with targeting molecules (sialyl
Lewis a, sLe^a) which bind to selectins.  The
differently shaped particles were tested for their margination
efficiency from blood flow both in vitro and
in vivo.  The particles explored ranged in
diameter from 0.5 – 2 μm (equivalent
spherical diameter; ESD, for rods and disks).

Vascular-targeted spheres, rods or disks at
a fixed concentration were mixed with RBC and saline flow buffer, and allowed
to flow over a layer of IL-1β activated human umbilical vein endothelial
cells (HUVEC) using a parallel plate flow chamber. Adhesion of VTCs from steady
blood flow from relatively low to relatively high shear rates (200-1000 s^-1)
was investigated. Since disturbed blood flow profiles are typical in areas of
vasculature where atherosclerosis tends to occur, particle adhesion pulsatile and
recirculatory blood flow profiles were also examined.  The adhesion of rods, disks and spheres
to the endothelium from blood flow was imaged/quantified using brightfield and fluorescence microscopy. Further, the
localization of these particles to the red blood cell free layer (RBC-FL) while
in flow was investigated using confocal microscopy.

Results and Discussion:  With
in vitro assays we find that rod-shaped microparticles
at a high aspect ratio have a higher binding efficiency to the HUVEC monolayer
from human blood flow than spheres of equivalent volume and targeting ligand
site density. Overall, adhesion was greatest for microparticles
with ESD=2 μm compared to those with smaller
volumes.  The improved adhesion
pattern for micron-sized rods was not due to better localization of rods to the
RBC-FL, as the confocal data showed equivalent levels of microrods/spheres
in the RBC-FL.  Adhesion of 500 nm
ESD spheres and rods was minimal; likely due to poor
localization to the RBC-FL.  While
rods with 500 nm ESD showed no improved adhesion compared to equivalent spheres, preliminary data suggests that equivalent
disk shaped particles display both better localization to the RBC-FL and
improved adhesion to the endothelium. 

Conclusions:   Our study shows that shape can be a very useful and tunable
parameter in the design of vascular-targeted carriers for imaging and treatment
of atherosclerosis and other diseases of M/LBVs.