(615a) To COIN a Term: Functional Composite Organic-Inorganic Nanoparticles (COINs) for Biomedical Applications

To
COIN a Term: Functional Composite Organic-Inorganic Nanoparticles (COINs) for
Biodistribution Analysis

Brian K. Wilson¹ and Robert K. Prud’homme¹

¹Princeton University, Princeton NJ, USA

Abstract

Nanoparticles
have received considerable attention as delivery vehicles for therapeutic,
diagnostic or mixed theranostic agents targeted against a wide variety of
disease conditions. Understanding the systemic biodistribution and the local
distribution (within tissues or sub-cellular compartments) are of interest for
understanding nanoparticle trafficking, uptake and targeting efficacy in vivo. Incorporating a tracer for the
nanoparticle vehicle itself allows quantification of both the nanoparticle distribution
and the releasable payload, for example a chemotherapeutic drug. Flash
NanoPrecipitation (FNP) provides an easy, scalable platform for producing
polymeric nanoparticles that encapsulate hydrophobic species in a core
stabilized by an amphiphilic block copolymer corona. Small, primary colloids of
rare earth metal oxides can be readily prepared with a hydrophobic surface
coating, enabling efficient encapsulation via
the FNP process. Producing rare earth metal oxide tagged nanoparticles is of
interest because of the inert nature of these oxides and the possible
multimodal quantification of their biodistribution by: mass spectrometry,
fluorescence microscopy and electron microscopy.

Rare earth
metals and their oxides (for example: europium, terbium and gadolinium) have
negligible endogenous background signal in
vivo, enabling quantification of bulk concentrations in digested tissue by
plasma mass spectrometry (ICP-MS). Furthermore, these rare earth metal oxide
colloids exhibit strong, element-characteristic fluorescence under electron
beam or ultraviolet irradiation, enabling them to be used as fluorescent probes
that display excellent stability and a lack of concentration-dependent quenching
behavior.  Lastly, the metal oxide
colloids provide a substantial degree of electron contrast, allowing for their
use as markers in TEM sections containing nanoparticles; the specific identity
of the metal can be determined by conventional elemental analysis methods such
as S/TEM EDX in situ.

Here we
demonstrate the synthesis of rare earth metal oxide colloid loaded polymeric
nanoparticles and their use in tracking biodistribution by ICP-MS and
fluorescence microscopy. Preparing the primary colloids with a small diameter
(< 5 nm) and a hydrophobic surface coating is critical for efficient
encapsulation and composite organic-inorganic nanoparticle (COIN) production.
Thermal decomposition synthesis from metal acetylacetonates and metal tris-oleates produces more uniform
colloids in the desired size range when compared to solution colloidal
precipitation methods. These primary metal oxide colloids can then be
encapsulated in poly(styrene) or poly(lactic acid) based nanoparticles
stabilized with a surface layer of poly(ethylene glycol) (PEG) to loadings of
at least ~50% weight and ~30% volume of the primary inorganic colloid. The free
ends of the PEG chains in the stabilizing corona can be modified with targeting
ligands to direct specific uptake of nanoparticles. We explore the use of folic
acid, cyclic RGDyK and internalizing iRGD ligands to target nanoparticles to KB and A549 tumor
lines, where bulk nanoparticle uptake is quantified by plasma mass
spectrometry. In vitro analysis of
nanoparticle cell binding and cellular distribution is performed using the
metal oxides as fluorescent markers in confocal microscopy.