Chapter 16
Downloaded by STANFORD UNIV GREEN LIBR on July 7, 2012 | http://pubs.acs.org Publication Date: March 9, 2006 | doi: 10.1021/bk-2006-0924.ch016
Using a Supercritical Fluid-Based Process: Application to Injectable Sustained-Release Formulations of Biomolecules 1,3
2
1
J . Richard , F . Deschamps , A . M. De Conti , and O . Thomas 1
2
Ethypharm, 194 Bureaux de la Colline, Saint-Cloud 92213, France Mainelab, 8 rue André Boquel, Angers 49100, France Permanent address: Serono International, Via di Valle Caia 22, I-00040 Ardea, Rome, Italy 2
The market development of fragile biomolecules such as recombinant proteins is impeded by the lack of an appropriate delivery method due to the proteins' poor oral bioavailability and short plasma half-life. Therefore, a strong need for a new microparticulate parenteral delivery system exists, allowing sustained release over weeks and preventing loss of protein activity during formulation and administration. Classical microencapsulation processes display major drawbacks related to the use of organic solvents and heat that can denaturate or cause aggregation of the proteins. Conversely, supercritical fluid (SCF)-based processes exhibit major advantages for designing and producing solvent-free microparticles with outstanding applications in the field of drug delivery. Special emphasis is given on the SCF-based process that we have recently developed to coat lyophilized protein particles with lipids, and obtain injectable sustained-release microparticles. Results concerning the physicochemical features of the microparticles produced, as well as the first in vivo pharmaco kinetic effects in animals are presented and discussed.
250
© 2006 American Chemical Society
In Polymeric Drug Delivery II; Svenson, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.
251
Downloaded by STANFORD UNIV GREEN LIBR on July 7, 2012 | http://pubs.acs.org Publication Date: March 9, 2006 | doi: 10.1021/bk-2006-0924.ch016
Introduction Therapeutic proteins are fragile biomolecules, which display a short plasma half-life after injection and cannot be administered by the oral route due to their poor stability in the gastrointestinal (GI) tract and their poor oral bioavailability. These proteins need an appropriate injectable delivery system to maintain therapeutic levels in the blood stream over long periods of time and hence avoid repeated injections, typically several times a week. Moreover, a sustainedrelease system is also expected to restrict the peak plasma concentration responsible for major clinical issues that are still unsolved. Microparticulate systems with specific physicochemical and size properties are currently developed and used for drug delivery. These microparticles consist of bio compatible polymers that contain drugs and can be administered to humans safely. Biodegradable polymers are commonly used to prepare injectable sustained-release delivery microparticles because they allow controlling the drug release profile by properly choosing their physicochemical features. These systems have been extensively investigated for their capability of achieving the release of therapeutically active proteins in a controlled way. Current methods for the preparation of protein-containing polymer microparticles are mainly based on emulsion-solvent extraction, phase separation or spray-drying. The main drawback of these techniques is the extensive use of organic solvents to either dissolve the polymer or induce phase separation and particle hardening. These solvents are suspected to be partly responsible for biological inactivation of the proteins incorporated in microspheres. Successful incorporation of proteins in poly(lactic-co-glycolic acid) (PLGA) copolymer microparticles has been reported with respect to loading and encapsulation efficiency, as well as microparticle size and morphology. However, protein instability in the polymer microparticles has been recognized as a major problem, resulting in incomplete release of native protein, which is denaturized or aggregated. Upon denaturation or aggregation, protein species become therapeutically inactive and may also induce side effects such as immunogenicity or toxicity, even i f there is only a low amount of degraded protein. Thus, development of new protein-loaded microparticle production processes should be focused on full preservation of the structure and biological activity of the native protein during preparation, storage and release. The use of supercritical fluids (SCF) for engineering of drug-loaded micro particles with or without limited use of organic solvents is a recent development. A SCF is a fluid whose pressure and temperature are higher than those at the critical point, that is, the end-point of the liquid-gas phase transition line, as it appears in a Pressure-Temperature phase diagram. Several features of SCF make them versatile and appropriate for production of drug-loaded polymer microparticles. SCF display some liquid-like properties such as a high density,
In Polymeric Drug Delivery II; Svenson, S.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.
252 and gas-like ones such as low viscosity and high diffusivity. The most important property of a SCF is its large compressibility near the critical point. This specific property leads to a fluid whose solvent power can be continuously tuned from that of a liquid to that of a gas applying small variations of pressure. C 0 is the most widely used SCF in pharmaceutical development and processing because of its low critical temperature (T = 31.1°C), its environmentally benign nature and other advantages. C 0 allows working at moderate temperatures and leaves no toxic residues since it turns back to its gas phase at ambient conditions. Due to its unique properties, C 0 is used routinely in large-scale operations for extraction of food ingredients. Many different approaches have been reported in the literature for the production of pure drug or drug-loaded microparticles, using an SCF either as a solvent for the drug and the polymer (RESS process), or as an anti-solvent (SAS, G A S , ASES, SEDS processes), or even as a swelling and plasticizing agent for the polymer (PGSS process) (1,2). In addition, coating processes of preformed solid drug microparticles have been recently developed in our laboratory to produce sustained-release microparticles of fragile bio molecules. These processes use SC or liquid C 0 either as a solvent or a nonsolvent for the coating material, which can be a solid lipid compound or a polymer (3,4). 2
c
2
Downloaded by STANFORD UNIV GREEN LIBR on July 7, 2012 | http://pubs.acs.org Publication Date: March 9, 2006 | doi: 10.1021/bk-2006-0924.ch016
2
2
Materials and Methods Materials Interferon a-2b (IFNa-2b) particles to be coated were produced by milling and sieving (
