Hazard-free microencapsulation for structurally delicate agents, an application of stable aqueous-aqueous emulsion

Abstract

This invention provides method for sustained release delivery of structurally delicate agents such as proteins and peptides. Using unique emulsion system (Stable polymer aqueous-aqueous emulsion), proteins and peptides can be microencapsulated in polysacchride glassy particles under a condition free of any chemical or physical hazard such as organic solvents, strong interfacial tension, strong shears, elevated temperature, large amount of surfactants, and cross-linking agents. Proteins loaded in these glassy particles showed strong resistance to organic solvents, prolonged activity in hydrated state, and an excellent sustained release profile with minimal burst and incomplete release when being further loaded in degradable polymer microspheres. This invention provides a simple yet effective approach to address all the technical challenges raised in sustained release delivery of proteins.

Description

CROSS REFERENCE OF RELATED APPLICATION [0001] This application claims priority of U.S. Ser. No. 60 / 384,971, filed Jun. 3, 2002, and U.S. Ser. No. 60 / 418,100, filed Oct. 11, 2002, the contents of which are incorporated by reference here into this application. [0002] Throughout this application, various references are referred to. Disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.FIELD OF THE INVENTION [0003] The present invention demonstrates a novel method for preparing a novel particulate glassy system which effectively preserve structure / activity of proteins peptides, DNA, liposomes and live viruses during formulation process, storage, and application. BACKGROUND OF THE INVENTION [0004] Due to the impermeability and short half-life, most of protein therapeutics require frequent injection. To reduce injection frequency, development of sustained...

AI Technical Summary

Benefits of technology

[0012] A major difficulty that delayed development of sustained release or non-invasive protein formulations is that proteins are denatured during the formulation process. To prevent protein denature, a formulation process must be free of (or proteins must be protected from) the chemical physical hazards discussed above. In achieving this objective, however, properties and functions of the final product such as particle size and shape, release profile, loading efficiency, prolonged activity at the site of release and so forth should not be compromised. It is also preferred that the manufacture process can be easy, reproducible and environmentally friendly.

[0014] First, fragile biological agents such as proteins can be loaded into the dispersed phase of the stable polymer aqueous-aqueous emulsion system (24) under a condition free of any chemical or physical hazard. A uniform size distribution of the droplets can be achieved by a conventional emulsification process under appropriate shear stress and low interfacial tension (due to the aqueous-aqueous nature). Then the system can be freeze-dried to dry powder in which the polymer droplets converted to glassy particles of uniform sizes (1-5 um in diameter). Once the glassy particles are formed, the structure of the loaded are preserved and protected. Due to its hydrophilicity and high glassy transition temperature, the system offers strong resistance to organic solvents as well as resistance to ambient temperature and moisture (in terms of protein activity retention). The bio-agents-loaded AqueSpheres can therefore be used for inhalation drug delivery (based on their size range) or subjected to further formulation process with biodegradable hydrophobic polymers for sustained release.

[0016] Bioactivity of the proteins loaded in AqueSpheres was retained after contacted with organic solvents and after microencapsulation process as assayed in cell proliferation (Example 5, 6, and 7), indicating that conformation of proteins were well protected in the glassy matrix of polysaccharide. In addition, the activity retention of proteins after miroencapsuleted in PLGA microspheres (Example 7) suggests high encapsulation efficiency.

[0017] The most challenging task in developing sustained release protein dosage forms is to ensure protein activity in a hydrated state at physiological temperature (21). Hydration and temperature elevation will increase the mobility of proteins and lower the energy barrier for protein hydrolysis, aggregation and conformation change. With the present technology, proteins loaded in AqueSpheres showed prolonged activity in a hydrated state at 37° C. (Example 8). Recombinant human erythropoietin (rhEPO) which has in vivo half life of 8.5 hrs and in vitro half life of a day showed a half life of a week under a hydrated condition when loaded in AqueSpheres (Example 8). The AqueSphere matrix formed a viscous phase surrounding the proteins so that limited protein mobility and the chance for proteins to contact with each other and other species (the degradable polymer and enzymes).

[0018] Burst effect, defined as rapid release of considerable amount of loadings in the initial period of administration, is another common problem in developing sustained release dosage forms of protein drugs. Burst effect is found for both injectable implants and microsphere formulations, although the causes may be different. Accompanying with burst effect is incomplete release that part of the proteins loaded strongly interact with the polymer matrix and are not able to release in the required period. Having proteins pre-encapsulated in AqueSpheres prior to loading into degradable polymers can effectively prevent burst effect, and at the same time, reduce the portion of incomplete release (Example 9).

[0019] Moreover, AqueSpheres helps to reduce local acidity generated by polymer degradation. Local acidity is another cause believed for protein denaturation during release period. AqueSpheres form inter-connected channels when being hydrated in degradable polymer matrix that their viscous nature limits diffusion of macromolecular proteins but permeable to small molecular buffers. This nature allow the local acidity be buffered in the sustained release process. In addition, the surface modifier (sodium alginate) itself possesses significant buffer effect.

Problems solved by technology

A major difficulty that delayed development of sustained release or non-invasive protein formulations is that proteins are denatured during the formulation process.

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