Lendon G. Payne

Protein release from polyphosphazene matrices

Polyphosphazenes have been exploited as carriers for protein delivery due to versatility of molecular structures and sophisticated spectrum of chemical and physical properties. Ease of structural manipulations for this class of organometallic polymers allows efficient control over physico-chemical parameters of polyphosphazenes including their biodegradability and matrix permeability. Some polyphosphazenes offer additional advantages as protein delivery vehicles since microencapsulation of substrates in these systems can be achieved under remarkably mild physiological conditions. Because of these properties polyphosphazenes have tremendous potential as matrices for protein release as shown by studies both in vitro and in vivo.

Polymeric carriers for oral uptake of microparticulates.

Delivery of vaccine antigens by the oral route is plagued with challenges. Much of the research has focused on the development of microparticles as antigen carriers to the gastrointestinal (GIT) mucosa. Polymers, either natural or synthetic, have been the class of compounds most often investigated for their ability to form microparticles containing antigen. A great deal of research has been performed using model microparticles composed of polystyrene. From this work it has become clear that microparticles are taken up and translocated across the GIT epithelium. Antigen carrying microparticles generated from both hydrophobic and hydrophilic polymers are able to induce significant immune responses after oral immunization. Although very little systematic work on the effects of the physicochemical properties of the polymer composing the microparticles has been done, enough is known to conclude that the surface of the polymeric microparticle can be decisive in determining the overall uptake of the microparticles. Charge and the hydrophobic/hydrophilic balance of the polymer are important physicochemical characteristics that determine the value of the polymer as a microparticulate carrier. This review examines the properties of polymeric matrices that make them viable candidates as oral vaccine delivery vehicles.

Preparation of hydrogel microspheres by coacervation of aqueous polyphosphazene solutions

A new method of preparing ionically cross-linked polyphosphazene hydrogel microspheres which enables effective control over microsphere size distribution has been developed. The synthesized microspheres can be used in protein delivery and, especially, as vaccine delivery vehicles. A new technique utilizes the ability of aqueous solutions of poly[di(carboxylatophenoxy)phosphazene] (PCPP) to form coacervate microdroplets upon addition of sodium chloride. These microdroplets are then stabilized via polymer cross-linking with calcium ions. It was demonstrated that the method enables efficient microencapsulation of proteins. It was also shown that microsphere size can be controlled through the manipulation of microencapsulation conditions. The process is simple, highly reproducible and generates microspheres with a narrower microsphere size distribution, compared to the previous technologies.

Poly[di(carboxylatophenoxy)phosphazene] (PCPP) is a potent immunoadjuvant for an influenza vaccine.

The adjuvant activity of poly[di(carboxylatophenoxy)phosphazene] (PCPP) on the immunogenicity of formalin-inactivated influenza virions and commercial trivalent influenza vaccine was studied. Regardless of which antigen preparation is used, the addition of 100 micrograms PCPP enhances the HAI antibody response 10-fold over the levels elicited by the vaccine alone. Similarly, PCPP enhanced the IgM, IgG, and IgG1 ELISA antibody titers to influenza antigens at least 10-fold higher than the vaccine alone. In contrast, the IgG2a isotype titers were only enhanced about 2-fold. Immunization of aged mice (22 months old) with trivalent influenza vaccine alone did not sero-convert these mice as measured by HAI or ELISA whereas significant sero-conversion was achieved when mice were immunized with PCPP-formulated trivalent vaccine. The adjuvant activity of PCPP was shown to not be due to a site of injection depot effect. PCPP adjuvanticity was positively correlated to the molecular weight of the polymer.

Water-Soluble Phosphazene Polymers for Parenteral and Mucosal Vaccine Delivery

PCPP can be used in two different ways to potentiate an immune response. The soluble form of the polymer has been found to have immunoadjuvant activity. A single subcutaneous injection of polymer/influenza dramatically increases the ELISA, neutralizing, and HI antibodies to influenza virus compared to CFA. The polymer has also succeeded in dramatically increasing the amount of ELISA antibodies to TT. The antibody response elicited was predominantly of the IgG1 isotype. PCPP has also been used to generate micron-sized hydrogel microspheres through a process of divalent ion cross-linking of the polymer strands. These microspheres can induce significantly higher anti-TT serum IgG titers after a single intranasal immunization than TT alone.

Controlled release using ionotropic polyphosphazene hydrogels

Abstract Poly(bis(carboxylatophenoxy)phosphazene) (PCPP) forms hydrogels when treated in aqueous media with salts of divalent cations, such as calcium chloride. This system has potential as a material for the controlled release of drugs. To study the ability of the PCPP hydrogel matrix to release macromolecular substrates, 24-nm fluorescent polystyrene beads or proteins with varying molecular weights were encapsulated in polyphosphazene microspheres. The influence of polyphosphazene concentration and ionic crosslinker content on the outward diffusion of substrates and on microsphere morphology was investigated. In order to create a poly- L -lysine (PLL) outer membrane coating around the PCPP microspheres, the spheres were treated with PLL solution (single coating) or sequentially with PLL and PCPP solutions (double coating). The formation of these membranes (stable poly electrolyte complexes) strongly influences the permeability of the polyphosphazene microspheres and contributes to their stability in physiological saline solution. This enables liquefaction and swelling of the internal core of the microcapsules in saline solution via ion-exchange reactions with monovalent salts and chelating agents. Increasing the PLL molecular weight in the coating process results in a significant enhancement of the substrate release rate. It is possible that the mechanism of this process includes partial coating rupture without loss of bead coherence. The effect of microsphere coating on release profiles can be controlled by varying the molecular weights, the concentration of PLL and reaction times between PCPP microspheres and PLL.

Synthesis, Physico-Chemical Properties and Immunoadjuvant Activity of Water-Soluble Phosphazene Polyacids:

Mixed-substituted polyphosphazenes containing carboxylic acid and alkyl ether side groups were synthesized and characterized. Physicochemical properties of phosphazene polyacids in aqueous solutions were investigated as a function of copolymer structure and composition. The immunoadjuvant activity of polyphosphazenes was evaluated by studying the effect of copolymers on the immunogenicity of the influenza virus in mice. Synthesized polyphosphazenes demonstrated the ability to enhance the immune response as compared to the levels elicited by the vaccine alone.