Preparation, characterization, and in vitro evaluation of 1- and 4-month controlled release orntide PLA and PLGA microspheres

Development and Characterization of Olanzapine Loaded Poly(lactide-co-glycolide) Microspheres for Depot Injection: In vitro and In vivo Release Profiles

Purpose:

The purpose of this study was to develop a new PLGA based microsphere formulation aimed to release the olanzapine for the period of one month which will result in increased compliance.

Methods:

Microspheres loaded with olanzapine were prepared using oil in water emulsion and solvent evaporation technique. The microspheres were characterized by surface morphology, shape, size, bulk density, encapsulation efficiency, and Fourier transform infrared spectrometry. In vitro release studies were performed in phosphate buffer at 37°C and in vivo studies were conducted on male Sprague- Dawley rats.

Results:

The morphological results indicated that microspheres produced were having a smooth surface, spherical shape and the size in the range from 9.71 to 19.90 μm mean diameter. Encapsulation efficiency of olanzapine loaded microspheres was in the range of 78.53 to 96.12% and was affected by changing the ratio of lactic to glycolic acid in copolymer PLGA. The properties of PLGA and other formulation parameters had a significant impact on in vitro and in vivo release of drug from microspheres. In vitro release kinetics revealed that release of drug from microspheres is by both non-Fickian diffusion and erosion of PLGA polymer. In vivo data indicated an initial burst release and then sustained release depending on properties of PLGA, microsphere size, and bulk density.

Conclusion:

This study indicates that microsphere formulations developed with PLGA (75:25) and PLGA (85:15) have provided a sufficient steady release of drug for at least 30 days and can be potential candidates for 30-day depot injection drug delivery of olanzapine.

Soybean Lecithin-Mediated Nanoporous PLGA Microspheres with Highly Entrapped and Controlled Released BMP-2 as a Stem Cell Platform

Injectable polymer microsphere-based stem cell delivery systems have a severe problem that they do not offer a desirable environment for stem cell adhesion, proliferation, and differentiation because it is difficult to entrap a large number of hydrophilic functional protein molecules into the core of hydrophobic polymer microspheres. In this work, soybean lecithin (SL) is applied to entrap hydrophilic bone morphogenic protein-2 (BMP-2) into nanoporous poly(lactide-co-glycolide) (PLGA)-based microspheres by a two-step method: SL/BMP-2 complexes preparation and PLGA/SL/BMP-2 microsphere preparation. The measurements of their physicochemical properties show that PLGA/SL/BMP-2 microspheres had significantly higher BMP-2 entrapment efficiency and controlled triphasic BMP-2 release behavior compared with PLGA/BMP-2 microspheres. Furthermore, the in vitro and in vivo stem cell behaviors on PLGA/SL/BMP-2 microspheres are analyzed. Compared with PLGA/BMP-2 microspheres, PLGA/SL/BMP-2 microspheres have significantly higher in vitro and in vivo stem cell attachment, proliferation, differentiation, and matrix mineralization abilities. Therefore, injectable nanoporous PLGA/SL/BMP-2 microspheres can be potentially used as a stem cell platform for bone tissue regeneration. In addition, SL can be potentially used to prepare hydrophilic protein-loaded hydrophobic polymer microspheres with highly entrapped and controlled release of proteins.

Characterization, Stability and Biological Activity In Vitro of Cathelicidin-BF-30 Loaded 4-Arm Star-Shaped PEG-PLGA Microspheres

BF-30 is a single chain polypeptide of an N-segment with an α-helix from cathelicidin gene encoding, and it contains 30 amino acid residues, with a relative molecular mass and isoelectric point of 3637.54 and 11.79, respectively. Cathelicidin-BF-30 was entrapped in four-arm star-shaped poly(ethylene glycol-b-dl-lactic acid-co-glycolic acid) block copolymers (4-arm-PEG-PLGA) by a double-emulsion solvent-evaporation method. Three release phases of cathelicidin-BF-30loaded 4-arm-PEG-PLGA microspheres were observed, including an initial burst-release phase, followed by a lag phase with minimal drug release and finally a secondary zero-order release phase. The delivery system released BF-30 over more than 15 days in vitro. Furthermore, the material for preparing the microspheres has good biocompatibility and biodegradability. Additionally, based on the drug resistance of food pathogenic bacteria, the antibacterial effects of BF-30 on Shigella dysenteriae CMCC 51105 (Sh. dysenteriae CMCC 51105), Salmonella typhi (S. typhi) and Staphylococcus aureus (S. aureus) as well as the stability of the in vitro release of the BF-30-loded microspheres were studied. The α-helix secondary structure and antibacterial activity of released BF-30 were retained and compared with native peptide. These BF-30 loaded microspheres presented <10% hemolysis and no toxicity for HEK293T cells even at the highest tested concentration (150 μg/mL), indicating that they are hemocompatible and a promising delivery and protection system for BF-30 peptide.

Long-term delivery of protein therapeutics

INTRODUCTION

Proteins are effective biotherapeutics with applications in diverse ailments. Despite being specific and potent, their full clinical potential has not yet been realized. This can be attributed to short half-lives, complex structures, poor in vivo stability, low permeability, frequent parenteral administrations and poor adherence to treatment in chronic diseases. A sustained release system, providing controlled release of proteins, may overcome many of these limitations.

AREAS COVERED

This review focuses on recent development in approaches, especially polymer-based formulations, which can provide therapeutic levels of proteins over extended periods. Advances in particulate, gel-based formulations and novel approaches for extended protein delivery are discussed. Emphasis is placed on dosage form, method of preparation, mechanism of release and stability of biotherapeutics.

EXPERT OPINION

Substantial advancements have been made in the field of extended protein delivery via various polymer-based formulations over last decade despite the unique delivery-related challenges posed by protein biologics. A number of injectable sustained-release formulations have reached market. However, therapeutic application of proteins is still hampered by delivery-related issues. A large number of protein molecules are under clinical trials, and hence, there is an urgent need to develop new methods to deliver these highly potent biologics.

Preparation, characterization, in vitro release and degradation of cathelicidin-BF-30-PLGA microspheres

Cathelicidin-BF-30 (BF-30), a water-soluble peptide isolated from the snake venom of Bungarus fasciatus containing 30 amino acid residues, was incorporated in poly(D,L-lactide-co-glycolide) (PLGA) 75∶25 microspheres (MS) prepared by a water in oil in water W/O/W emulsification solvent extraction method. The aim of this work was to investigate the stability of BF-30 after encapsulation. D-trehalose was used as an excipient to stabilize the peptide. The MS obtained were mostly under 2 µm in size and the encapsulation efficiency was 88.50±1.29%. The secondary structure of the peptide released in vitro was determined to be nearly the same as the native peptide using Circular Dichroism (CD). The ability of BF-30 to inhibit the growth of Escherichia coli was also maintained. The cellular relative growth and hemolysis rates were 92.16±3.55% and 3.52±0.45% respectively.

Release of a wound-healing agent from PLGA microspheres in a thermosensitive gel

The purpose of this research was to develop a topical microsphere delivery system in a thermosensitive 20% poloxamer 407 gel (Pluronic F127) to control release of KSL-W, a cationic antimicrobial decapeptide, for a period of 4-7 days for potential application in combat related injuries. KSL-W loaded microsphere formulations were prepared by a solvent extraction-evaporation method (water-oil-water), with poly (D,L-lactic-co-glycolic acid) (PLGA) (50 : 50, low-weight, and hydrophilic end) as the polymeric system. After optimization of the process, three formulations (A, B, and C) were prepared with different organic to water ratio of the primary emulsion while maintaining other components and manufacturing parameters constant. Formulations were characterized for surface morphology, porous nature, drug loading, in vitro drug release, and antimicrobial activity. Microspheres containing 20% peptide with porous surfaces and internal structure were prepared in satisfactory yields and in sizes varying from 25 to 50 μm. Gels of 20% Pluronic F127, which were liquid at or below 24.6°C and formed transparent films at body temperature, were used as carriers for the microspheres. Rheological studies showed a gelation temperature of 24.6°C for the 20% Pluronic F127 gel alone. Gelation temperature and viscosity of formulations A, B, and C as a function of temperature were very close to those of the carrier. A Franz diffusion cell system was used to study the release of peptide from the microspheres suspended in both, phosphate-buffered saline (PBS) and a 20% Pluronic F127 gel. In vitro release of greater than 50% peptide was found in all formulations in both PBS and the gel, and in one formulation there was a release of 75% in both PBS and the gel. Fractions collected from the release process were also tested for bactericidal activity against Staphylococcus epidermidis using the broth microdilution method and found to provide effective antimicrobial activity to warrant consideration and testing in animal wound models for treating combat-related injuries.

Preparation, Characterization, and In Vivo Evaluation of Olanzapine Poly(D,L-lactide-co-glycolide) Microspheres

The aim of this study was to prepare injectable depot formulations of Olanzapine using four poly(D,L-lactide-co-glycolide) (PLGA) polymers of varying molecular weight and copolymer composition, and evaluate in vivo performance in rats. In vivo release profiles from the formulations were governed chiefly by polymer molecular weight and to a lesser extent, copolymer composition. Formulations A and B, manufactured using low molecular weight PLGA and administered at 10 mg/kg dose, released drug within 15 days. Formulation C, prepared from intermediate molecular weight PLGA and administered at 20 mg/kg dose, released drug in 30 days, while Formulation D, manufactured using a high molecular weight polymer and administered at 20 mg/kg dose, released drug in 45 days. A simulation of multiple dosing at 7- and 10-day intervals for Formulations A and B revealed that steady state was achieved within 7-21 days and 10-30 days, respectively. Similarly, simulations at 15-day intervals for Formulations C and D indicated that steady state levels were reached during days 15-45. Overall, steady state levels for 7-, 10-, or 15-day dosing ranged between 45 and 65 ng/mL for all the formulations, implying that Olanzapine PLGA microspheres can be tailored to treat patients with varying clinical needs.

Prospects of pharmaceuticals and biopharmaceuticals loaded microparticles prepared by double emulsion technique for controlled delivery

Several methods and techniques are potentially useful for the preparation of microparticles in the field of controlled drug delivery. The type and the size of the microparticles, the entrapment, release characteristics and stability of drug in microparticles in the formulations are dependent on the method used. One of the most common methods of preparing microparticles is the single emulsion technique. Poorly soluble, lipophilic drugs are successfully retained within the microparticles prepared by this method. However, the encapsulation of highly water soluble compounds including protein and peptides presents formidable challenges to the researchers. The successful encapsulation of such compounds requires high drug loading in the microparticles, prevention of protein and peptide degradation by the encapsulation method involved and predictable release, both rate and extent, of the drug compound from the microparticles. The above mentioned problems can be overcome by using the double emulsion technique, alternatively called as multiple emulsion technique. Aiming to achieve this various techniques have been examined to prepare stable formulations utilizing w/o/w, s/o/w, w/o/o, and s/o/o type double emulsion methods. This article reviews the current state of the art in double emulsion based technologies for the preparation of microparticles including the investigation of various classes of substances that are pharmaceutically and biopharmaceutically active.

Materials for pharmaceutical dosage forms: molecular pharmaceutics and controlled release drug delivery aspects

Controlled release delivery is available for many routes of administration and offers many advantages (as microparticles and nanoparticles) over immediate release delivery. These advantages include reduced dosing frequency, better therapeutic control, fewer side effects, and, consequently, these dosage forms are well accepted by patients. Advances in polymer material science, particle engineering design, manufacture, and nanotechnology have led the way to the introduction of several marketed controlled release products and several more are in pre-clinical and clinical development.

Reverse Micelle-Based Microencapsulation of Oxytetracycline Hydrochloride into Poly-d,l-Lactide-co-Glycolide Microspheres

The objectives of this study were to solubilize oxytetracycline hydrochloride (HCl) in reverse micelles to prepare poly-d,l-lactide-co-glycolide (PLGA) microspheres and to explore parameters affecting its encapsulation efficiency. Oxytetracycline HCl was dissolved in the reverse micelles consisting of cetyltrimethylammonium bromide, water, and ethyl formate. A PLGA polymer was then dissolved in the reverse micellar solution, and a modified solvent quenching procedure was carried out to prepare PLGA microspheres. Encapsulation efficiencies of oxytetracycline HCl ranged from 2.3 +/- 0.2 to 24.9 +/- 4.6%, depending on experimental conditions. Important parameters affecting its encapsulation efficiency included the amounts of water used to prepare the reverse micelles and PLGA polymer. With regard to microsphere morphology, the reverse micellar process produced the microspheres with smooth and pore-free surfaces. In particular, their internal matrices did not possess hollow cavities that were frequently observed when a typical double emulsion technique was used to make microspheres. In summary, it was possible to encapsulate oxytetracycline HCl into PLGA microspheres via the ethyl formate-based reverse micellar technique. We also anticipate that the use of ethyl formate could avoid environmental and human toxicity issues associated with methylene chloride.

Local controlled drug delivery to the brain: mathematical modeling of the underlying mass transport mechanisms

The mass transport mechanisms involved in the controlled delivery of drugs to living brain tissue are complex and yet not fully understood. Often the drug is embedded within a polymeric or lipidic matrix, which is directly administered into the brain tissue, that is, intracranially. Different types of systems, including microparticles and disc- or rod-shaped implants are used to control the release rate and, thus, to optimize the drug concentrations at the site of action in the brain over prolonged periods of time. Most of these dosage forms are biodegradable to avoid the need for the removal of empty remnants after drug exhaustion. Various physical and chemical processes are involved in the control of drug release from these systems, including water penetration, drug dissolution, degradation of the matrix and drug diffusion. Once the drug has been released from the delivery system, it has to be transported through the living brain tissue to the target site(s). Again, a variety of phenomena, including diffusion, drug metabolism and degradation, passive or active uptake into CNS tissue and convection can be of importance for the fate of the drug. An overview is given of the current knowledge of the nature of barriers to free access of drug to tumour sites within the brain and the state of the art of: (i) mathematical modeling approaches describing the physical transport processes and chemical reactions which can occur in different types of intracranially administered drug delivery systems, and of (ii) theories quantifying the mass transport phenomena occurring after drug release in the living tissue. Both, simplified as well as complex mathematical models are presented and their major advantages and shortcomings discussed. Interestingly, there is a significant lack of mechanistically realistic, comprehensive theories describing both parts in detail, namely, drug transport in the dosage form and in the living brain tissue. High quality experimental data on drug concentrations in the brain tissue are difficult to obtain, hence this is itself an issue in testing mathematical approaches. As a future perspective, the potential benefits and limitations of these mathematical theories aiming to facilitate the design of advanced intracranial drug delivery systems and to improve the efficiency of the respective pharmacotherapies are discussed.

Effect of the covalent modification of horseradish peroxidase with poly(ethylene glycol) on the activity and stability upon encapsulation in polyester microspheres

Encapsulation of proteins in polyester microspheres by coacervation methods frequently causes protein inactivation and aggregation. Furthermore, an often-substantial amount of the encapsulated proteins is released within the first 24 h from the microspheres. To overcome these problems poly(ethylene glycol) (PEG) was employed as excipient and protein-modifying agent. The model protein horseradish peroxidase (HRP) was chemically modified or co-lyophilized with PEG of differing molecular weights, namely PEG(5000), PEG(20000), and PEG(40000). The lyophilized preparations were encapsulated in poly(D,L-lactide-co-glycolic) acid (PLGA) microspheres by a coacervation method. Covalent modification of HRP with PEG increased the encapsulation efficiency (EE) from 83% to about 100% while PEG when used as an excipient reduced the EE. Encapsulation caused aggregation of ca. 5% of non-modified HRP and the residual specific activity was only 57%. Covalent modification with PEG reduced HRP aggregation to less than 1% and improved its residual activity to more than 95%. When PEG was used as excipient similar results were found with respect to a reduction in encapsulation-induced aggregation, but no more than 80% of residual activity was obtained even for the best formulation after encapsulation. It was also found that covalent modification of HRP with PEG substantially reduced the unwanted initial "burst" release observed during the initial 24 h of in vitro release from about 70% to 23%. Furthermore, HRP activity and stability were also improved during in vitro release for HRP-PEG conjugates. The data show that covalent modification of proteins with PEG might be useful to improve protein stability during coacervation encapsulation and subsequent release as well as to increase EE and reduce the burst release.

Methods to assess in vitro drug release from injectable polymeric particulate systems

This review provides a compilation of the methods used to study real-time (37 degrees C) drug release from parenteral microparticulate drug delivery systems administered via the subcutaneous or intramuscular route. Current methods fall into three broad categories, viz., sample and separate, flow-through cell, and dialysis techniques. The principle of the specific method employed along with the advantages and disadvantages are described. With the "sample and separate" technique, drug-loaded microparticles are introduced into a vessel, and release is monitored over time by analysis of supernatant or drug remaining in the microspheres. In the "flow-through cell" technique, media is continuously circulated through a column containing drug-loaded microparticles followed by analysis of the eluent. The "dialysis" method achieves a physical separation of the drug-loaded microparticles from the release media by use of a membrane, which allows for sampling without interference of the microspheres. With all these methods, the setup and sampling techniques seem to influence in vitro release; the results are discussed in detail, and criteria to aid in selection of a method are stated. Attempts to establish in vitro-in vivo correlation for these injectable dosage forms are also discussed. It would be prudent to have an in vitro test method for microparticles that satisfies compendial and regulatory requirements, is user friendly, robust, and reproducible, and can be used for quality-control purposes at real-time and elevated temperatures.

A model-dependent approach to correlate accelerated with real-time release from biodegradable microspheres

The purpose of this study was to determine the feasibility of applying accelerated in vitro release testing to correlate or predict long-term in vitro release of leuprolide poly(lactide-co-glycolide) microspheres. Peptide release was studied using a dialysis technique at 37 degrees C and at elevated temperatures (50 degrees C-60 degrees C) in 0.1M phosphate buffered saline (PBS) pH 7.4 and 0.1M acetate buffer pH 4.0. The data were analyzed using a modification of the Weibull equation. Peptide release was temperature dependent and complete within 30 days at 37 degrees C and 3 to 5 days at the elevated temperatures. In vitro release profiles at the elevated temperatures correlated well with release at 37 degrees C. The shapes of the release profiles at all temperatures were similar. Using the modified Weibull equation, an increase in temperature was characterized by an increase in the model parameter, alpha, a scaling factor for the apparent rate constant. Complete release at 37 degrees C was shortened from approximately 30 days to 5 days at 50 degrees C, 3.5 days at 55 degrees C, 2.25 days at 60 degrees C in PBS pH 7.4, and 3 days at 50 degrees C in acetate buffer pH 4.0. Values for the model parameter beta indicated that the shape of the release profiles at 55 degrees C in PBS pH 7.4 (2.740) and 50 degrees C in 0.1M acetate buffer pH 4.0 (2.711) were similar to that at 37 degrees C (2.677). The E(a) for hydration and erosion were determined to be 42.3 and 19.4 kcal/mol, respectively. Polymer degradation was also temperature dependent and had an E(a) of 31.6 kcal/mol. Short-term in vitro release studies offer the possibility of correlation with long-term release, thereby reducing the time and expense associated with long-term studies. Accelerated release methodology could be useful in the prediction of long-term release from extended release microsphere dosage forms and may serve as a quality control tool for the release of clinical or commercial batches.

Impurity formation studies with peptide-loaded polymeric microspheres Part I. In vivo evaluation

The purpose of the present investigation was to assess the peptide related substances or impurities formed during incubation of drug loaded poly-(D,L-lactide-co-glycolide) (PLGA) and poly-(D,L-lactide) (PLA) microspheres under in vivo conditions. Sprague-Dawley rats were injected with separate batches of octreotide microspheres prepared by either an oil/water or oil/oil dispersion technique. At specified time points (days 14, 22, 30, and 41), animals were sacrificed and microsphere particles were recovered from the subcutaneous injection sites. The recovered particles were further extracted with 1:1 mixture of dimethylsulfoxide:dichloromethane for subsequent impurity analysis by HPLC and mass spectrometry. During incubation, the percentage purity of parent compound depended on the PLGA co-monomer ratio (e.g. 50:50, 85:15, and 100:0 glycolide:lactide ratios). After 41 days of incubation, for instance, octreotide area percentage by HPLC was determined to be approximately 47% for PLGA 50:50 microspheres, approximately 75% for PLGA 85:15 microspheres, and approximately 87% for PLA microspheres. Spectral analysis of particle extracts revealed the presence of peptide related substances with 58 m/z and 72 m/z units higher than the parent peptide m/z value. This indicated the presence of glycoyl and lactoyl covalent substitutions on the drug compound, resulting from chemical interaction between peptide amine groups and PLGA or PLA ester groups.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for quantitation and molecular stability assessment of insulin entrapped within PLGA nanoparticles

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was evaluated for both qualitative and quantitative analysis of insulin entrapped within poly(D,L-lactic-co-glycolic acid) nanoparticles. Quantitation was performed by adding an internal standard (arg-insulin) to defined and unknown sample solutions, in order to reduce point-to-point and sample-to-sample variability. The ratio of the peak height of insulin to the peak height of arg-insulin was plotted against the insulin concentration. In this way, an excellent linear relationship was found (R2 > 0.99). This method of quantitation was compared with classical UV spectroscopy and reverse-phase high-performance liquid chromatography measurements. All methods provided close final drug loading values for the insulin-loaded nanoparticle batches tested. Additionally, with respect to molecular stability, covalent insulin dimers were found only at trace levels in those nanoparticles. Compared with other methods, MALDI-TOF MS is a valuable tool for the characterization of proteins from nanoparticles, because no extensive extraction and complex sampling procedures are required.

Strategic approaches for overcoming peptide and protein instability within biodegradable nano- and microparticles

This paper reviews the major factors that are closely involved in peptide and protein degradation during the preparation of biodegradable nano- and microparticles. The various means usually employed for overcoming these obstacles are described, in order to bring to the fore the strategies for protein stabilization. Both processing and formulation parameters can be modified and are distinctly considered from a strategic point of view. We describe how partial or full protein stability retention within the carriers and during drug release might be achieved by individual or combined optimized strategies. Additionally, problems commonly encountered during protein quantification, stability determination and release are briefly reviewed. Artefacts that might occur during sampling and analytical procedures and which might hinder critical interpretation of results are discussed.

In vivo release kinetics of octreotide acetate from experimental polymeric microsphere formulations using oil/water and oil/oil processes

The purpose of the present study was to characterize the in vivo release kinetics of octreotide acetate from microsphere formulations designed to minimize peptide acylation and improve drug stability. Microspheres were prepared by a conventional oil/water (o/w) method or an experimental oil/oil (o/o) dispersion technique. The dosage forms were administered subcutaneously to a rat animal model, and serum samples were analyzed by radioimmunoassay over a 2-month period. An averaged kinetic profile from each treatment group, as a result, was treated with fractional differential equations. The results indicated that poly(l-lactide) microspheres prepared by the o/o dispersion technique provided lower area under the curve (AUC) values during the initial diffusion-controlled release phase, 7.79 ngxd/mL, versus 75.8 ngxd/mL for the o/w batch. During the subsequent erosion-controlled release phase, on the other hand, the o/o technique yielded higher AUC values, 123 ngxd/mL, versus 42.2 ngxd/mL for the o/w batch. The differences observed between the 2 techniques were attributed to the site of drug incorporation during the manufacturing process, given that microspheres contain both porous hydrophilic channels and dense hydrophobic matrix regions. An o/o dispersion technique was therefore expected to produce microspheres with lower incorporation in the aqueous channels, which are responsible for diffusion-mediated drug release.

Self-porating polymersomes of PEG–PLA and PEG–PCL: hydrolysis-triggered controlled release vesicles

Controlled release polymer vesicles are prepared using hydrolysable diblock copolymers of polyethyleneglycol-poly-l-lactic acid (PEG-PLA) or polyethyleneglycol-polycaprolactone (PEG-PCL). Encapsulation studies with a common anti-cancer agent, doxorubicin, show loading comparable to liposomes. Rates of encapsulant release from the hydrolysable vesicles are accelerated with an increased proportion of PEG but are delayed with a more hydrophobic chain chemistry (i.e. PCL). Rates of release also rise linearly with the molar ratio of degradable copolymer blended into membranes of a non-degradable, PEG-based block copolymer (PEG-polybutadiene (PBD)). With all compositions, in both 100 nm and giant vesicles, the average release time (from hours to days) reflects a highly quantized process in which any given vesicle is either intact and retains its encapsulant, or is porated and slowly disintegrates. Poration occurs as the hydrophobic PLA or PCL block is hydrolytically scissioned, progressively generating an increasing number of pore-preferring copolymers in the membrane. Kinetics of this evolving detergent mechanism overlay the phase behavior of amphiphiles with transitions from membranes to micelles allowing controlled release.

DNA delivery from photocrosslinked PEG hydrogels: encapsulation efficiency, release profiles, and DNA quality

Sustained DNA delivery from polymer matrices provides a means for enhanced and prolonged gene therapy; however, limitations exist with respect to tailoring the DNA release profiles and maintaining the quality of the encapsulated DNA over time. To address these issues, PEG-based macromolecular monomers were photopolymerized to produce hydrogels with various degradation rates to control the DNA release profiles. Photocrosslinked PEG-based hydrogels were designed that released DNA for periods of 6-100 days with either nearly linear or delayed burst release profiles. Plasmid DNA was released primarily in the relaxed and supercoiled forms, and the released DNA showed high biological activity in plated cell cultures. The addition of both chemical and physical protective agents helped preserve the supercoiled form of the plasmid DNA during photoencapsulation (up to 75% compared to non-encapsulated plasmid controls), thereby enhancing the biological activity of the released DNA.

Assessment of fertility in male rats after extended chemical castration with a GnRH antagonist

The purpose of this study was to assess whether male rats whose testosterone levels were suppressed to castration levels (<0.5 ng/mL) for a 1-year period by the sustained delivery of orntide acetate, a GnRH antagonist, would return to fertility (ie, produce offspring) after serum testosterone returned to control levels. Male rats comprising a treatment group (orntide microspheres, dose = 27 mg/kg/y), a vehicle control group, and a control group of proven male breeders were used. For the treatment and vehicle control groups, serum orntide and testosterone levels were monitored at periodic intervals for 14 months from the initiation of treatment. After serum testosterone levels returned to vehicle control levels and orntide serum levels were no longer discernible for the treated group, each of the animals was housed with 2 drug-naive, female, proven breeders. All the breeder females produced offspring with the exception of 1 female housed with a male rat from the treatment group and the 2 females housed with a single male rat from the vehicle control group. The mean size and weight of the litters from each group were not statistically different. Further, fertility of the offspring from each group was assessed. The male and female offspring studied were all shown to be fertile. The results suggest that lack of fertility due to testosterone suppression in male rats is reversible after cessation of treatment with the GnRH analog, orntide.

Amphiphilic copolymers of epsilon-caprolactone and gamma-substituted epsilon-caprolactone. Synthesis and functionalization of poly(D,L-lactide) nanoparticles

Fully biodegradable and surface-functionalized poly(D,L-lactide) (PLA) nanoparticles have been prepared by a co-precipitation technique. Novel amphiphilic random copolyesters P(CL-co-gammaXCL) were synthesized by controlled copolymerization of epsilon-caprolactone and epsilon-caprolactone substituted in the gamma-position by a hydrophilic X group, where X is either a cationic pyridinium (gammaPyCL) or a non-ionic hydroxyl (gammaOHCL). Nanoparticles were prepared by co-precipitation of PLA with the P(CL-co-gammaXCL) copolyester from a DMSO solution. Small amounts of cationic P(CL-co-gammaPyCL) copolymers are needed to quantitatively form stable nanoparticles (ca. 10 mg/ 100 mg PLA), although larger amounts of non-ionic P(CL-co-gammaOHCL) copolymers are needed (> or = 12.5 mg/ 100 mg PLA). Copolymers with a low degree of polymerization (ca. 40) are more efficient stabilizers, probably because of faster migration towards the nanoparticle-water interface. The nanoparticle diameter decreases with the polymer concentration in DMSO, e.g. from ca. 160 nm (16 mg/ml) to ca. 100 nm (2 mg/ml) for PLA/P(CL-co-gammaPyCL) nanoparticles. Migration of the P(CL-co-gammaXCL) copolyesters to the nanoparticle surface was confirmed by measurement of the zeta potential, i.e. ca. +65 mV for P(CL-co-gammaPCL) and -7 mV for P(CL-co-gammaOHCL). The polyamphiphilic copolyesters stabilize PLA nanoparticles by electrostatic or steric repulsions, depending on whether they are charged or not. They also impart functionality and reactivity to the surface, which opens up new opportunities for labelling and targeting purposes.

Preparation and Characterization of Temperature-Sensitive Poly(N-isopropylacrylamide)-b-poly(d,l-lactide) Microspheres for Protein Delivery

Temperature-sensitive diblock copolymers, poly(N-isopropylacrylamide)-b-poly(D,L-lactide) (PNIPAAm-b-PLA) with different PNIPAAm contents were synthesized and utilized to fabricate microspheres containing bovine serum albumin (BSA, as a model protein) by a water-in-oil-in-water double emulsion solvent evaporation process. XPS analysis showed that PNIPAAm was a dominant component of the microspheres surface. BSA was well entrapped within the microspheres, and more than 90% encapsulation efficiency was achieved. The in vitro degradation behavior of microspheres was investigated using SEM, NMR, FTIR, and GPC. It was found that the microspheres were erodible, and polymer degradation occurred in the PLA block. Degradation of PLA was completed after 5 months incubation in PBS (pH 7.4) at 37 degrees C. A PVA concentration of 0.2% (w/v) in the internal aqueous phase yielded the microspheres with an interconnected porous structure, resulting in fast matrix erosion and sustained BSA release. However, 0.05% PVA produced the microspheres with a multivesicular internal structure wrapped with a dense skin layer, resulting in lower erosion rate and a biphasic release pattern of BSA that was characterized with an initial burst followed by a nonrelease phase. The microspheres made from PNIPAAm-b-PLA with a higher portion of PNIPAAm provided faster BSA release. In addition, BSA release from the microspheres responded to the external temperature changes. BSA release was slower at 37 degrees C (above the LCST) than at a temperature below the LCST. The microspheres fabricated with PNIPAAm-b-PLA having a 1:5 molar ratio of PNIPAAm to PLA and 0.2% (w/v) PVA in the internal aqueous phase provided a sustained release of BSA over 3 weeks in PBS (pH 7.4) at 37 degrees C.

Biodegradable microspheres for protein delivery

In a very short time, since their emergence, the field of controlled delivery of proteins has grown immensely. Because of their relatively large size, they have low transdermal bioavailabilities. Oral bioavailability is generally poor since they are poorly absorbed and easily degraded by proteolytic enzymes in the gastrointestinal tract. Ocular and nasal delivery is also unfavorable due to degradation by enzymes present in eye tissues and nasal mucosa. Thus parenteral delivery is currently most demanding and suitable for delivery of such molecules. In systemic delivery of proteins, biodegradable microspheres as parenteral depot formulation occupy an important place because of several aspects like protection of sensitive proteins from degradation, prolonged or modified release, pulsatile release patterns. The main objective in developing controlled release protein injectables is avoidance of regular invasive doses which in turn provide patient compliance, comfort as well as control over blood levels. This review presents the outstanding contributions in field of biodegradable microspheres as protein delivery systems, their methods of preparation, drug release, stability, interaction with immune system and regulatory considerations.

Potential applications of polymeric microsphere suspension as subcutaneous depot for insulin

The objective of this investigation was to develop an injectable, depot-forming drug delivery system for insulin based on microparticle technology to maintain constant plasma drug concentrations over prolonged period of time for the effective control blood sugar levels. Formulations were optimized with two well-characterized biodegradable polymers namely, poly(DL-lactide-co-glycolide) and poly-epsilon-caprolactone and evaluated in vitro for physicochemical characteristics, drug release in phosphate buffered saline (pH 7.4), and evaluated in vivo in streptozotocin-induced hypoglycemic rats. With a large volume of internal aqueous phase during w/o/w double emulsion solvent evaporation process and high molecular weight of the polymers used, we could not achieve high drug capture and precise control over subsequent release within the study period of 60 days. However, this investigation revealed that upon subcutaneous injection, the biodegradable depot-forming polymeric microspheres controlled the drug release and plasma sugar levels more efficiently than plain insulin injection. Preliminary pharmacokinetic evaluation exhibited steady plasma insulin concentration during the study period. These formulations, with their reduced frequency of administration and better control over drug disposition, may provide an economic benefit to the user compared with products currently available for diabetes control.

Effect of osmotic pressure in the solvent extraction phase on BSA release profile from PLGA microspheres

This study investigated the influence of osmotic pressure in the organic solvent extraction phase on release profile of bovine serum albumin (BSA) from poly(lactide-co-glycolide) (PLGA) microspheres. BSA-loaded PLGA microspheres with a target load of 10% were prepared by a double emulsion phase separation method. All the microsphere batches were fabricated in the same conditions except that in the organic solvent (CH2Cl2) evaporation step. Different concentrations of NaCl (0, 1.8, and 3.6%) or sucrose (20%) were used to generate a range of osmotic pressures in the extraction aqueous phase. These microspheres were characterized for incorporation efficiency, surface and internal morphology, particle size, protein stability, and in vitro release. The microspheres were spherical with particle size ranging from 16.8 to 27.8 microns. Higher osmotic pressure resulted in a denser internal structure although similar nonporous surface morphology was observed with all batches. No significant difference in encapsulation efficiency existed from batch to batch (87-94%). Sodium dodecyl sulfate-polyamide gel electrophoresis showed that BSA integrity was well retained. The release profile of the batch prepared with only water as the continuous (solvent extraction) phase exhibited a 79% burst release in the first 24 hr followed by a plateau and then a little release after 21 days. In the presence of NaCl or sucrose, the burst effect significantly decreased with increase in osmotic pressure in the extraction aqueous phase, which was then followed by sustained release for 35 days. A mass balance was made when the release terminated. Therefore, in the organic solvent extraction and evaporation step, increasing the osmotic pressure in the aqueous phase both reduced the burst release from the microspheres and improved the subsequent sustained release profile.

Return to fertility after extended chemical castration with a GnRH antagonist

BACKGROUND

Antagonistic analogues of GnRH for the treatment of prostate cancer may be used clinically in persons for whom return to fertility after such treatment is important or desirable. The purpose of this study was, therefore, to evaluate the effects of a long term treatment with orntide, a GnRH antagonist, on testosterone levels and fertility in male rats.

METHODS

Two groups of male rats received either 120-day orntide microspheres (8.8 mg orntide/kg/120 days) or vehicle alone (control group). Serum orntide and testosterone levels in both groups were monitored at certain intervals for 9 months from the initiation of treatment. After recovery of normal serum testosterone levels in the treated animals, each rat was housed with two proven breeder, but drug-naive, females.

RESULTS

All mates of treated rats achieved pregnancy as rapidly as the mates of control rats although two of the control rats did not sire a litter with either female and one sired only one litter. The mean size of the litters of treated (12.3 offspring per litter) and control (10.6 offspring per litter) were similar. All offspring were grossly normal morphologically and behaviorally during the time to weaning.

CONCLUSIONS

These results suggest that lack of fertility due to testosterone suppression is reversible after cessation of treatment with this GnRH antagonist.

Evaluation of Orntide microspheres in a rat animal model and correlation to in vitro release profiles

Orntide acetate, a novel luteinizing hormone-releasing hormone (LHRH) antagonist, was prepared and evaluated in vivo in 30-day and 120-day sustained delivery formulations using a rat animal model. Orntide poly(d,l-lactide-co-glycolide) (PLGA) and poly(d,l- lactide) (PLA) microspheres were prepared by a dispersion method and administered subcutaneously in a liquid vehicle to rats at 2.2 mg Orntide/kg of body weight (30-day forms) or 8.8 mg Orntide/kg (120-day forms). Serum levels of Orntide and testosterone were monitored by radioimmunoassays, and a dose-response study at 4 doses (3, 2.25, 1.5, and 1.75 mg Orntide/kg) was conducted to determine the effective dose of Orntide. Microspheres with diameters between 3.9 and 14 micron were prepared. The onset and duration of testosterone suppression varied for different microsphere formulations and were influenced both by polymer properties and by microsphere characteristics. Microspheres prepared with 50:50 and 75:25 copolymers effectively sustained peptide release for 14 to 28 days, whereas an 85:15 copolymer and the PLA microspheres extended the pharmacological response for more than 120 days. Increase in drug load generally accelerated peptide release from the microspheres, resulting in higher initial serum levels of Orntide and shorter duration of the release. In general, apparent release was faster in vivo than under in vitro conditions. Orntide microspheres effectively suppressed testosterone in rats, providing rapid onset of release and extended periods of chemical castration. Testosterone suppression occurred immediately after microsphere administration without the initial elevation seen with LHRH superagonists.