Encapsulation and stabilization of nerve growth factor into poly(lactic-co-glycolic) acid microspheres.

The development of a stable sustained-release formulation of recombinant human nerve growth factor (rhNGF) for the treatment of neuronal diseases is described. The protein was encapsulated into poly(lactic-co-glycolic) acid (PLGA) microspheres using a spray freeze drying technique. Liquid nitrogen and cold ethanol were used to spray-freeze-dry solid rhNGF that had been suspended in a solution of PLGA dissolved in ethyl acetate. When excipients such as sugar (trehalose), surfactant (pluronic F68), and poly(ethylene glycol) (PEG) were added to the PLGA formulation to protect rhNGF from degradation during spray freeze drying, the protein degraded via aggregation during in vitro release. The formation of an insoluble rhNGF-zinc complex prior to encapsulation into PLGA microspheres stabilized the protein during both microencapsulation and release. In this study, we have demonstrated that the addition of zinc acetate in a 1:12 rhNGF-to-zinc acetate molar ratio in a solid rhNGF formulation (4 mM sodium bicarbonate at pH 7.4) improves stability of rhNGF during release at 37 degrees C (physiological temperature). The stabilization may be due to rhNGF complexation with zinc to form stable aggregates. The PLGA formulation consisting of 10% rhNGF encapsulated in 12 kDa PLGA (50:50 lactide/glycolide) provided a continuous release of 14 days. The low initial burst (approximately 1%) and controlled-release rate were achieved by the addition of 3 or 6% solid zinc carbonate to the polymer phase during microencapsulation.

Comparison between light induced and chemically induced oxidation of rhVEGF.

PURPOSE: The primary objective of this study was to compare the effects of light-and chemical-induced oxidation of recombinant human vascular endothelial growth factor (rhVEGF) and the impact of these reactions on protein formulation. METHODS: A liquid formulation of rhVEGF was exposed to fluorescent light (2 x 10(4) lux for up to 4 weeks), hydrogen peroxide (H2O2), or t-butythydroperoxide (t-BHP) to induce oxidation of rhVEGF. All samples were then treated by tryptic digest and analyzed by reversed phase HPLC to determine the extent of oxidation. Chemically treated samples were also examined by near-UV and far-UV circular dichroism spectroscopy to determine the effect of oxidation on the structure of the protein. RESULTS: Exposure to light for 2 weeks resulted in 8 to 40% oxidation of all 6 methionine residues of rhVEGF (Met3 > Met18 > Met55 > Met78.81 > Met94). This amount of oxidation did not affect the binding activity of rhVEGF to its kinase domain receptor (KDR). Light exposure for 4 weeks increased metsulfoxide formation at Met3 and Met18 by an additional 16%, but did not affect the other residues. This oxidation decreased the receptor binding capacity to 73%. possibly due to the role of Met 18in receptor binding. Chemical oxidation of rhVEGF resulted in a greater extent of oxidation at all 6 methionines. Complete oxidation of Met3, Met18 and Met55 was observed after treatment with H2O2, while these residues underwent 40 to 60% oxidation after treatment with t-BHP. The receptor binding capacity was significantly reduced to 25% and 55% after treatment with H2O2 and t-BHP, respectively. After chemical oxidation, no changes in the secondary or tertiary structure were observed by far-UV and near-UV CD spectroscopy, respectively. CONCLUSIONS: Methionine residues with exposed surface areas greater than 65 A2 and sulfur surface areas greater than 16 A2 were most susceptible to oxidation. Chemical oxidation resulted in higher metsulfoxide formation and decreased binding activity of the protein to KDR than light-induced oxidation. The reduction in KDR binding was not caused by measurable conformational changes in the protein. Photooxidation was dependent on the amount of energy imparted to the protein, while the ability of t-BHP or H2O2 to react with methionine was governed by solvent accessibility of the methionine residues and steric limitations of the oxidizing agent. Significant chemical oxidation occurred on sulfurs with minimum surface areas of 16 A2, while increased photooxidation occurred as a function of increasing surface areas of solvent exposed sulfur atoms. Such differences in the extent of oxidation should be considered during protein formulation since it may help predict potential oxidation problems.

Development of poly-(D,L-lactide--coglycolide) microsphere formulations containing recombinant human vascular endothelial growth factor to promote local angiogenesis.

Although preclinical animal studies have demonstrated the utility of recombinant human vascular endothelial growth factor (rhVEGF) in promoting neovascularization in regions of ischemia, rhVEGF systemic administration did not provide clinical benefit to patients in recent placebo-controlled Phase II clinical trials. The amount of rhVEGF localized in the ischemic region after systemic administration is minimal and does not persist for more than 1 day. A greater persistence of rhVEGF at the region of ischemia may provide an increased angiogenesis with the eventual formation of patent blood vessels to restore nourishment to the tissues. We sought to develop a formulation of rhVEGF in poly(D,L-lactide--co-glycolide) (PLG) microspheres that would provide a continuous local delivery of intact protein. A stable formulation of rhVEGF for encapsulation contained a small amount of a stabilizing sugar, trehalose. Addition of excess trehalose increased the rate of release from the PLG. In addition, PLG with free acid end groups appeared to retard the initial release of rhVEGF by associating with it through ionic interactions at the positively charged heparin binding domain. rhVEGF was released continuously for 21 days with a very low (less than 10%) initial burst. The released rhVEGF aggregated and hydrolyzed over time and lost heparin affinity but not receptor affinity. The compression molding of rhVEGF PLG microspheres into disks yielded formulations with a low initial release and a lag of 10 days followed by complete release. The PLG microsphere formulations were assessed in the corneal implant model of angiogenesis and generated a dose-dependent angiogenic response. These formulations were also administered intravitreally and subretinally, generating local neovascularization comparable to the human disease states, vitroretinopathy and age-related macular degeneration, respectively. The rhVEGF PLG formulations may increase local angiogenesis without systemic side effects and may also be useful in the development of ocular disease models.

Sustained release of recombinant human insulin-like growth factor-I for treatment of diabetes.

Recombinant human insulin-like growth factor-I (rhIGF-I) was found to improve glycemic control and enhance insulin sensitivity in patients with a syndrome of severe insulin resistance. Therefore, the protein may be considered as an alternative therapy in the treatment of diabetes when the patients become insensitive to insulin treatment. Because the protein was administered twice per day in the clinical trials, a sustained release polylactic-co-glycolic acid (PLGA) formulation for rhIGF-I with low initial burst (<20%), maximum possible protein loading (15-20%) and a continuous release of 1-2 weeks may provide greater patient convenience and compliance. The protein was encapsulated in PLGA for sustained release using a spray freeze-drying technique. Formulation parameters such as protein loading, polymer end group, and the presence of zinc carbonate were studied for their effects on in vitro release of rhIGF-I from PLGA microspheres. As the protein loading was increased, the initial burst increased. Due to the hydrophilic properties of the polymers, rhIGF-I encapsulated in unblocked PLGA (free acid end groups) gave a lower initial burst and a more steady-state release profile than the blocked PLGA (hydrocarbon end groups) with the same protein loading and PLGA molecular weight. At 15% w/w protein loading, the addition of 6% w/w zinc carbonate as a protein release modifier to the unblocked PLGA (12 kDa) decreased the initial burst of rhIGF-I. Therefore, a formulation consisting of 15% rhIGF-I and 6% zinc carbonate in 12 kDa, unblocked 50:50 PLGA can provide the required release characteristics in vitro. Rat studies revealed that rhIGF-I in this formulation was released in vivo at a rate which was comparable to that observed in vitro. These studies demonstrate the potential for a sustained release, 14-day formulation for rhIGF-I.

Intraocular pharmacokinetics and safety of a humanized monoclonal antibody in rabbits after intravitreal administration of a solution or a PLGA microsphere formulation.

Poly(lactic-co-glycolic) acid (PLGA) bioresorbable microspheres are used for controlled-release drug delivery and are particularly promising for ocular indications. The objective of the current study was to evaluate the pharmacokinetics and safety of a recombinant human monoclonal antibody (rhuMAb HER2) in rabbits after bolus intravitreal administration of a solution or a PLGA-microsphere formulation. On Day 0, forty-eight male New Zealand white rabbits (2.3-2.6 kg) were immobilized with intramuscular ketamine/xylazine, and the test materials were injected directly into the vitreous compartment. Group 1 animals received rhuMAb HER2 in 50:50 lactide: glycolide PLGA microspheres; Group 2 animals received rhuMAb HER2 in solution (n = 24/group). The dose for each eye was 25 microg (50 microl). After dosing, animals were sacrificed at 2 min, and on 1, 2, 4, 7, 14, 23, 29, 37, 44, 50, and 56 days (n = 2/timepoint/group). Safety assessment included direct ophthalmoscopy, clinical observations, body weight, and hematology and clinical chemistry panels. At necropsy, vitreous and plasma were collected for pharmacokinetics and analysis for antibodies to rhuMAb HER2, and the vitreal pellet (Group 1) was prepared for histologic evaluation. All animals completed the study per protocol-both treatments were well tolerated, and no suppurative or mixed inflammatory cell reaction was observed in the vitreal samples (Group 1) at any of the time points examined. Antibodies to rhuMAb HER2 were detected in plasma samples by Day 7 in both treatment groups, but infrequently in vitreous samples. There were no safety implications associated with this immune response. The in vitro characterization of the PLGA microspheres provided reasonable projections of the in vivo rhuMAb HER2 release kinetics (Group 1). The total amount of antibody that was released was similar in vitro (25.9%) and in vivo (32.4%). RhuMAb HER2 (Group 2) was cleared slowly from the vitreous compartment, with initial and terminal half-lives of 0.9 and 5.6 days, respectively. The volume of distribution approximated the vitreous volume in a rabbit eye.

Intracranial delivery of recombinant nerve growth factor: release kinetics and protein distribution for three delivery systems.

PURPOSE: Three different polymeric delivery systems, composed of either poly(ethylene-co-vinyl acetate) (EVAc) or poly(lactide-co-glycolide) (PLGA), were used to administer recombinant human nerve growth factor (rhNGF) intracranially in rats. METHODS: The delivery systems were characterized with respect to release kinetics, both in the brain and in well-stirred buffer solutions. RESULTS: During incubation in buffered saline, the delivery systems released rhNGF in distinct patterns: sustained (EVAc), immediate (PLGA1) and delayed (PLGA2). One 10-mg delivery system was implanted in each rat and an ELISA technique was used to determine the amount of rhNGF in 1-mm coronal brain slices produced immediately after removal of the delivery system. High levels of rhNGF (as high as 60,000 ng in a brain slice of approximately 50 microliters) were recovered from the brain tissue at 1, 2, and 4 weeks after implantation. With all three delivery systems, the amount of rhNGF in each brain slice decreased exponentially with distance from the implant site: the distance over which concentration decreased by 10-fold was 2-3 mm for all delivery systems. When rhNGF release was moderate (10 to 200 ng rhNGF/day), the total amount of rhNGF in the brain increased linearly with release rate, suggesting an overall rate of rhNGF elimination of 0.4 hr-1 or a half-life of 1.7 hr. With higher release rates (500 to 50,000 ng rhNGF/day), total amounts of rhNGF in the brain were considerably higher than anticipated based on this rate of elimination. CONCLUSIONS: Polymeric controlled release can provide high, localized doses of rhNGF in the brain. All of the experimental data were consistent with penetration of rhNGF through the brain tissue with a diffusion coefficient approximately 8 x 10(-7) cm2/s, which is approximately 50% of the diffusion coefficient in water.

Development of a single-shot subunit vaccine for HIV-1. 5. programmable in vivo autoboost and long lasting neutralizing response.

The subunit vaccine for HIV-1, recombinant glycoprotein 120 (rgp120), was used as a model antigen to evaluate the potential for a pulsatile single immunization vaccine formulation consisting of poly(lactic-co-glycolic) acid (PLGA) microspheres. We designed rgp120 PLGA microsphere formulations that provide a pulse of rgp120 at 1 to 6 months (depending on the polymer) after administration, mimicking another immunization. In these studies, the in vitro pulse of rgp120 correlated well with the observed in vivo autoboost as measured by an increase in anti-gp120 antibodies in guinea pigs. The immune response to the rgp120 PLGA microsphere formulations was increased by adding the soluble form of the saponin-derived adjuvant, QS-21. The use of small microspheres, however, did not increase the humoral response to rgp120. A single immunization with rgp120 PLGA microspheres resuspended in soluble rgp120 and QS-21 elicited neutralizing antibody titers that were comparable to titers obtained from two immunizations of rgp120 and QS-21 at the same total dose. Administration of rgp120 PLGA microspheres in baboons resulted in high, long-lasting neutralizing antibody titers that were greater than repeated immunizations with soluble rgp120 and QS-21. These studies also indicated that a continuous release of QS-21 at the injection site may provide a greater immune response than a bolus injection. Overall, this work demonstrated that PLGA microsphere formulations may be designed to provide in vivo pulses of an antigen eliminating the need for repeated immunizations.

The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres.

PURPOSE: The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained. METHODS: rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C. RESULTS: rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH. CONCLUSIONS: rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.