Optimization of Polyelectrolyte Complex Production: Implications of Molecular Characteristics on Physicochemical and Biological Properties

Abstract

This study focused on creating water-based, targeted, nanoparticulate polyelectrolyte complex (PEC) drug delivery vehicles. The polymeric structure of PECs allowed for integration of an anti-angiogenic, heparin binding peptide (TSP521) for cell-specific targeting to wound and tumor endothelia. Reaction environmental parameters dictate PEC physicochemical properties. Specifically, complexation between polyelectrolytes having significantly different molecular weights leads to formation of water-insoluble aggregates. Starting with this fact, similar and dissimilar molecular weight, five component PEC chemistries were applied and compared with and without ultrasonic dispergation. PEC formulations from precursors with similar, low molecular weights (LMW) yielded dispersions with suitable physicochemical characteristics verified by photon correlation spectroscopy and transmission electron microscopy. Similar, LMW PECs fabricated with dispergation exhibited pH-independent stability, validated by charge and size measurements. Process scale-up was assessed by mixing anions and cation streams in a Kenics static mixer. LMW PECs were prepared with iodinated proteins to address the effect of protein charge on entrapment and release in a simulated physiological environment. PECs could entrap proteins through intermolecular interactions and electrostatic forces. Unfortunately, incorporation was relatively low due to the weak amphipathic nature of the proteins. Release was controlled by non-Fickian diffusion. This platform was validated using human microvascular endothelial cells (HMVECs) with and without two TSP521 incorporation strategies: (1) passive core entrapment of a polyethylene glycol (PEG) conjugate and (2) direct peptide coupling to PEC amines. No toxicity was observed. Fluorescent labeling and flow cytometry was applied to characterize the binding and internalization mechanisms. PECs, without TSP521, bound cells through electrostatic interactions whereas macropinocytosis controlled the internalization. A flow cytometric, Scatchard analysis protocol was defined where peptide mediated interactions could be defined. Only PECs containing PEGylated TSP521 resulted in typical Scatchard behavior. Peptide presentation, through PEG, allowed PECs to interact with HMVECs through low affinity, heparan sulfate proteoglycans. This was the first Scatchard plot developed in the literature for nanoparticulate architectures and avoided radioactivity. A near-infrared fluorescent probe was incorporated into LMW PECs for biodistribution studies. LMW PECs were rapidly cleared from circulation as seen by whole animal imaging, excised organ fluorescence, and statistical analysis of the measured light fluxes.