Investigating the electrostatic complexation of BCNO nanoparticles with a stimuli-responsive double hydrophilic graft copolymer

Abstract

The co-assembly of nanoparticles within double hydrophilic block copolymers (DHBC) via electrostatic complexation is a novel approach for the development of stimuli-responsive nanodrugs with improved bioavailability, biocompatibility, intracellular uptake, and therapeutic efficacy. This study investigated the co-assembly of boron carbon oxynitride (BCNO) nanoparticles within an acid-labile polyethylene glycol-graft-polyethyleneimine (PEG-g-PEI) DHGC as a promising boron nanodrug for boron neutron capture therapy (BNCT). First, BCNO nanoassemblies are prepared by mixing the charged-neutral graft copolymer of PEG-g-PEI into a dispersion of negatively charged BCNO nanoparticles. The BCNO nanoparticles and DHGC complex were characterized using various techniques, including dynamic light scattering, zeta potential, and transmission electron microscopy (TEM). Additionally, this study investigated the change in the hydrodynamic size and zeta potential of the DHGC/BCNO nanoparticle complexation over a wide range of mixing ratios (VBCNO/VDHGC). The results revealed that the BCNO nanoassemblies formed a stable aqueous dispersion at all mixing ratios investigated in this work. In addition, the size and surface charge of the BCNO nanoassemblies can be systematically modulated by adjusting the mixing ratio, molecular weight of the charged segment, ionic strength, and pH of the solution. TEM analysis revealed that the BCNO nanoassemblies formed at a high mixing ratio exhibited polydispersed size and irregular morphologies. With decreasing mixing ratio, the size of the BCNO nanoassemblies decreased, and the cluster exhibited a spherical morphology. In addition, an increase in the molecular weight of the charged PEI segment (10,000, 60,000, and 270,000 g/mole) of the DHGC resulted in the formation of larger BCNO aggregates. Lastly, the stability and pH-responsive behavior of the BCNO nanoassemblies were investigated at pH of 6.9, 6.0, and 5.0. Under mildly acidic conditions, the Schiff base bond cleaved, which resulted in the disassembly of the BCNO aggregates into smaller clusters with a spherical morphology. The DHGC@BCNO nanoassemblies exhibited an exceptional intracellular boron uptake of 627 ng-B/104 cells in MDA-MB-231 triple-negative breast cancer cells. In comparison, cells treated with bare BCNO nanoparticles and [10B]BPA small molecular boron drug demonstrated intracellular boron uptake of only 125 ng-B/104 cells and 17 ng-B/104 cells, respectively. The study highlights the potential of electrostatic colloidal co-assembly as a synthetic tool for developing hybrid nanomaterials with remarkable intracellular boron loading. This represents a significant step towards the development of an efficacious boron drug for boron neutron capture therapy (BNCT).