Polysaccharide Nanoparticles for Efficient siRNA Targeting in Cancer Cells by Supramolecular pKa Shift.

Ying-Ming Zhang,Yu-Hui Zhang,Yu Liu,Yang Yang

doi:10.1038/srep28848

Abstract

Biomacromolecular pKa shifting is considered as one of the most ubiquitous processes in biochemical events, e.g., the enzyme-catalyzed reaction and protein conformational stabilization. In this paper, we report on the construction of biocompatible polysaccharide nanoparticle with targeting ability and lower toxicity by supramolecular pKa shift strategy. This was realized through a ternary assembly constructed by the dual host‒guest interactions of an adamantane-bis(diamine) conjugate (ADA) with cucurbit[6]uril (CB[6]) and a polysaccharide. The potential application of such biocompatible nanostructure was further implemented by the selective transportation of small interfering RNA (siRNA) in a controlled manner. It is demonstrated that the strong encapsulation of the ADA’s diammonium tail by CB[6] not only reduced the cytotoxicity of the nano-scaled vehicle but also dramatically enhanced cation density through an obvious positive macrocycle-induced pKa shift, which eventually facilitated the subsequent siRNA binding. With a targeted polysaccharide shell containing a cyclodextrin‒hyaluronic acid conjugate, macrocycle-incorporated siRNA polyplexes were specifically delivered into malignant human prostate PC-3 cells. The supramolecular polysaccharide nanoparticles, the formation of which was enabled and promoted by the complexation-assisted pKa shift, may be used as a versatile tool for controlled capture and release of biofunctional substrates.

Highlights

The states of protonation in solution, which can be quantitatively measured by the acidity constant of pKa, have critical relevance to our biomedical and physiological events1–4
The biodegradable cyclodextrin-tethered hyaluronic acid shell, which is recognized by hyaluronic acid receptors that are overexpressed on the surface of cancer cells, enhances the biocompatibility of the overall delivery system while ensuring targeting capability27,28
Besides the desirable targeting capability, the small interfering RNA (siRNA)-bound polyplexes, which are derived from the selective bimodal molecular recognition of the adamantane-bis(diamine) conjugate (ADA) with β-cyclodextrin (β-CD) and cucurbit[6]uril (CB[6]), exhibit higher transfection efficiency than that observed for the individual ammonium guest and conventional transfection reagents

Summary

Introduction

The states of protonation in solution, which can be quantitatively measured by the acidity constant of pKa, have critical relevance to our biomedical and physiological events. There is a general consensus that the binding process with nucleic acids always occurs via electrostatic interaction, which is ubiquitously practiced as the reliable noncovalent driving force owing to the inherently anionic property of naked nucleic acids25,26 This principle inspired us to hypothesize that a controlled nucleic acid binding may be realized by implementing the complexation-induced pKa shift strategy to adjust the acid−base equilibria in appropriate guests. It can be anticipated that the effective regulation of the pKa value of the amino group in ADA by host–guest complexation and the selective delivery of nucleic acids in target cells may enable practical applications of macrocycle-based non-viral vectors in gene therapy. Some relevant studies on protonation-directed gene silence and hyaluronic acid-based delivery systems have been separately reported, we report a quite simple and practical method to precisely adjust the cation density of polysaccharide nanoparticles by supramolecular pKa shift. To the best of our knowledge, this is the first example of implementing macrocycle-induced pKa shift concept in the selective transportation of nucleic acids

Methods

Results

Conclusion