Self-Assembling Ionic Polyphosphazenes and Their Biomedical Applications

Intracellular Delivery of Active Proteins by Polyphosphazene Polymers

“…Since PZ polymers interact with proteins and other molecules (e.g., lipids, polysaccharides, etc.) via non-covalent electrostatic and hydrogen bonding [ 27 , 28 , 34 ], it is expected that these polymers would interact with such elements on the cell surface, facilitating protein delivery. Interestingly, in studies to determine the mechanism of interaction with cells, it was observed that both avidin and polymer pre-incubated with cells and present during the treatment with polymer/protein complexes decreased uptake of the complex by cells, with avidin exerting a more acute influence ( Figure 4 A).…”

“…Other delivery systems that have been investigated for their ability to non-covalently assemble into supramolecular complexes broadly applicable across different protein cargo types are cationic polymers functionalized with guanidium [ 24 ], polymeric protein transduction domain mimics (PTDMs) [ 25 ], fluoroamphiphilic polymers [ 26 ], Pep-1 [ 13 ], CPP adaptors [ 11 ], which have been found to be efficient for in vitro cytosolic delivery using reporter molecules. Of particular note is that the polymer:cargo ratio for this PZ delivery system ranged from 2:1 to 2.5:1, significantly higher than CPPs that use a 10:1 CPP:cargo ratio [ 12 ], and most other systems designed to carry proteins, are not aimed for intracellular delivery [ 4 , 27 , 55 ]. Therefore, these PZ polymers will add to a very narrow repertoire of polymers that can spontaneously self-assemble with a number of different types of cargo such as peptides, proteins and antibodies, using a simple mixing protocol, and deliver them to different cell types.…”

“…Hence, while a number of strategies are available to achieve intracellular delivery of proteins, the development of a non-covalent approach that can provide sufficient therapeutic load without affecting protein structure or activity, can be adapted to a variety of cargo and cell types, and can avoid cytotoxicity are limited [ 11 , 12 , 13 , 24 , 25 , 26 ], warranting the development of other delivery systems. Water-soluble polyphosphazenes (PZs) are hybrid organic-inorganic polyelectrolyte-type polymers that are attaining increasing recognition as multifunctional drug delivery vehicles [ 27 , 28 , 29 ]. Their unique macromolecular structure consists of an alternating phosphorus and nitrogen backbone and organic side groups, which provides for hydrolytic degradability under physiological conditions [ 30 ] and enables self-assembly with macromolecular drugs, including proteins, and some biological targets through non-covalent interactions [ 27 , 31 , 32 , 33 , 34 ].…”

“…Water-soluble polyphosphazenes (PZs) are hybrid organic-inorganic polyelectrolyte-type polymers that are attaining increasing recognition as multifunctional drug delivery vehicles [ 27 , 28 , 29 ]. Their unique macromolecular structure consists of an alternating phosphorus and nitrogen backbone and organic side groups, which provides for hydrolytic degradability under physiological conditions [ 30 ] and enables self-assembly with macromolecular drugs, including proteins, and some biological targets through non-covalent interactions [ 27 , 31 , 32 , 33 , 34 ]. PZ polymers have been formulated mostly as vaccine adjuvants [ 35 ] or in supramolecular assemblies including micelles, nanoparticles, hydrogels etc., hence they are flexible systems with multiple applications accorded by adjusting the side groups for different applications [ 36 ].…”

“…One of the most important design features of these polymers is their excellent solubility in aqueous solutions at near physiological pH [ 31 , 32 ]. PZ polymers are miscible with water in a broad range of ratios and form clear, low viscosity solutions at concentrations ranging from 0.1 to 2 mg/mL, at which they have been used as injectable formulations [ 27 , 35 ]. We have shown these hydrolytically degradable carriers facilitate uptake of protein cargo by cells in culture, in particular, avidin used as a model protein [ 31 , 33 ].…”