Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Matrices
Reexamination Certificate
2000-12-15
2004-06-01
Page, Thurman K. (Department: 1653)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Matrices
C424S489000, C424S484000
Reexamination Certificate
active
06743446
ABSTRACT:
BACKGROUND
Since the concept of protein or drug delivery from polymers was first introduced, research efforts have focused on developing polymer formulations that would be widely applicable for delivery of biologically active agents, such as proteins, peptides, oligonucleotides, DNA, low molecular weight drugs and vaccine antigens. Efforts to this end have intensified recently since hundreds of recombinant proteins and other biotechnological drugs and vaccine antigens are in the pipeline for FDA approval, and the current method of protein delivery generally requires injections on a daily basis. Frequent dosing is clinically undesirable due to patient discomfort, psychological distress, and poor compliance for administering self-injections. To reduce injection frequency, peptide and protein drugs are encapsulated in biodegradable polymers, which are processed into a form that is easily administered through a syringe needle. Current preparations on the market for the delivery of small peptides can reduce the frequency of injections to once every 1-3 months depending on the size and dose of the polymer implant. This incubation time, for which a large globular protein must remain encapsulated in the polymer at physiological temperature, poses significant challenges to retain both the structural integrity and the biological activity of the protein.
Two injectable polymer configurations are currently used to deliver peptides and proteins: spherical particles on the micrometer scale (~1-100 &mgr;m), which are commonly referred to as “microspheres”, and single cylindrical implants on the millimeter scale (~0.8-1.5 mm in diameter), which we term “millicylinders”. Both configurations are prepared from the biocompatible copolymer class, poly(lactide-co-glycolide) (PLGA) commonly used in resorbable sutures, and each configuration has distinct advantages and disadvantages.
Once injected into the body, these polymer implants slowly release the biologically active agents, thereby providing desirable levels of the agent over a prolonged period of time. Because of its safety, FDA approval and biodegradability, the poly(lactide-co-glycolides) (PLGAs) are the most common polymer class used for preparing biodegradable delivery systems for biologically active agents. Unfortunately, the microenvironment in PLGA surrounding the encapsulated agent can become highly acidic, causing many of these agents to lose their biological activity. Accordingly, it is desirable to modify the methods that are currently used to prepare polymeric delivery systems which liberate acids during biodegradation, such as PLGA, and to thereby produce a polymeric implant that is capable of releasing the biologically active agent over a prolonged period of time and maintaining the stability of the biologically active agent that is retained in the delivery system during nonenzymatic hydrolysis, hereinafter referred to as “biodegradation” of such a system. Such methods would also be useful for preparing implants that are made from polymers that contain acid that slowly dissolves and lowers the pH of the microenvironment surrounding the encapsulated agent
SUMMARY OF THE INVENTION
The present invention provides new methods for reducing or inhibiting the irreversible inactivation of water-soluble biologically active agents in biodegradable polymeric delivery systems which are designed to release such agents over a prolonged period of time, such as PLGA delivery systems. In accordance with the present invention, it has been discovered that, in many instances, the acids that are produced during biodegradation of PLGA can induce an irreversible inactivation or instability of biologically active agents, such as for example proteins, drugs, oligonucleotides and vaccine antigens. It has also been determined that the addition of certain antacids, such as for example MgOH
2
, to the system will not significantly reduce the acid-induced instability of the biologically active unless the polymer is prepared in a manner which results in the formation of an interconnected network of pores within the polymer. It has also been discovered that the acid-induced instability of biologically active agents encapsulated in PLGA delivery can be inhibited or significantly reduced by preparing PLGA delivery systems whose microclimate, i.e. the pores where the active agent resides, uniformly or homogenously maintain a pH of between 3 and 9, preferably between 4 and 8, more preferably between 5 and 7.5 during biodegradation. Depending on the size of the delivery system, i.e., the weight average particle diameter and the initial bulk permeability of the polymer, this result is achieved by (a) incorporating a water-soluble carrier into the delivery system, (b) incorporating a select basic additive (or antacid) into the delivery system, (c) incorporating both a water soluble carrier and a select basic additive into the delivery system, (d) adding a pore forming molecule for increasing the rate of release of low molecular weight monomers and oligomers into the delivery system, (e) using a PLGA polymer with reduced glycolide content, i.e. PLGA with from 100% to 75% lactide and 0 to 25% glycolide) (f) using a microencapsulation method that yields a more extensive pore-network, e.g. oil-in-oil emulsion-solvent extraction as opposed to water-in-oil-in water-solvent evaporation method, and (g) combinations thereof.
The present invention also relates to PLGA delivery systems prepared by the present method. Such delivery systems have a low porosity (e.g. <50%) and a uniform morphology (e.g. spherical or cylindrical usually with smooth or uniformly rough surfaces, and when particulate, all particles are similar in external and internal appearance under the scanning electron microscope. In addition, the PLGA delivery systems of the present invention have a low initial burst release (e.g. <50% of the drug is released during the 1st hour of biodegradation) Most importantly, during biodegradation, the present PLGA delivery systems maintain a relatively homogenous microclimate pH greater than 3 and less than 9, preferably greater than 4 and less than 8, more preferably greater than 5 and less than 7.5, so that less than 15% of the combined released and residual encapsulated test protein bovine serum albumin forms nonconvalent, water-insoluble aggregates when incubated in a physiological buffer solution for 4 weeks at 37° C.
In certain embodiments, the PLGA delivery system comprises bone morphogenetic protein-2, vincristine sulfate, fibroblast growth factor, or tissue plasminogen activator.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides methods of preparing PLGA delivery systems which stabilize the soluble biologically active agents that are encapsulated therein. As used herein, the term stabilize refers to an improvement in the stability of the encapsulated agent, which is necessary to approach or achieve a stable state. A stable biologically active agent as used herein refers to a biologically active agent such as a protein, peptide, oligonucleotide, low-molecular weight drug, or vaccine antigen that retains at least 80%, preferably 90%, of its original structure and/or biological activity during its release from the PLGA delivery system. During biodegradation of PLGA delivery systems, soluble agents often undergo acid-induced irreversible instability. Such instability may result from noncovalent aggregation of the agent, peptide-bond hydrolysis, deamidation, isomerization, covalent aggregation, deformylation, depurination, etc. Each of these acid-induced physical or chemical alterations can be monitored using standard techniques known in the art. For example, aggregation can be monitored by loss of solubility, SDS-PAGE, and or size-exclusion chromatography.
The methods of the present invention also provide controlled release PLGA delivery systems. As used herein, controlled release means the release kinetics are engineered into the system such that the agent is released in a manner controlled by the system itself or its surroundings, preferably
Bentz Hanne
Hubbell Jeffrey A.
Jiang Wenlei
Kang Jichao
Schwendeman Steven P.
Calfee Halter & Griswold LLP
Fubara Blessing
Page Thurman K.
The Ohio State University Research Foundation
LandOfFree
Methods for stabilizing biologically active agents... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods for stabilizing biologically active agents..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods for stabilizing biologically active agents... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3352684