Inhibition of peptide acylation in PLGA microspheres with water-soluble divalent cationic salts

Peptide Acylation in Aliphatic Polyesters: a Review of Mechanisms and Inhibition Strategies

Biodegradable polyesters are widely employed in the development of controlled release systems for peptide drugs. However, one of the challenges in developing a polyester-based delivery system for peptides is the acylation reaction between peptides and polymers. Peptide acylation is an important factor that affects formulation stability and can occur during storage, in vitro release, and after drug administration. This review focuses on the mechanisms and parameters that influence the rate of peptide acylation within polyesters. Furthermore, it discusses reported strategies to minimize the acylation reaction.

Design of experiments approach for the development of a validated method to determine the exenatide content in poly(lactide-co-glycolide) microspheres

Due to the lack of pharmacopeia guidelines for injectable microspheres based on poly (D, L-lactide-co-glycolide) (PLGA), an internal method validation is a critical prerequisite for quality assurance. One of the essential issues of developing peptide-based drugs loaded PLGA microspheres is the precise determination of the amount of peptide drug entrapped in the microspheres. The aim of this study is the development and optimization of a method for measuring the drug content loading of PLGA microspheres using exenatide as a model peptide drug. Exenatide-loaded PLGA microspheres were prepared by a double emulsion solvent evaporation method. The extraction method to determine exenatide content in microspheres was optimized using Design of Experiments (DoE) approach. After the initial screening of six factors, using Fractional Factorial design (FFD), four of them, including type of organic solvent, buffer/organic solvent ratio (v/v), shaking time and pH, exhibited significant effects on the response, namely the exenatide loading, and a Box-Behnken design (BBD) was subsequently applied to obtain its optimum level. The optimum level for organic solvent volume, buffer/organic solvent ratio, shaking time, and pH were 4 ml, 1, 5.6 hrs, and pH 6, respectively. The exenatide content in microspheres under these conditions was 6.4 ± 0.0 (%w/w), whereas a value of 6.1% was predicted by the derived equation. This excellent agreement between the actual and the predicted value demonstrates that the fitted model can thus be used to determine the exenatide content.

Effects of water-soluble additive on the release profile and pharmacodynamics of triptorelin loaded in PLGA microspheres

A satisfactory drug release profile for gonadotropin-releasing hormone (GnRH) agonist drugs is high initial release followed by small amount of drug release per day. In the present study, three water-soluble additives (NaCl, CaCl₂ and glucose) were selected to improve the drug release profile of a model GnRH agonist drug-triptorelin from PLGA microspheres. The pore manufacturing efficiency of the three additives was similar. The effects of three additives on drug release were evaluated. Under the optimal initial porosity, the initial release amount of microspheres containing different additives was comparable, this ensured a good inhibitory effect on testosterone secretion in the early stage. For NaCl or CaCl₂ containing microspheres, the drug remaining in the microsphere depleted rapidly after the initial release. The testosterone concentration gradually returned to an uncontrolled level. However, for glucose containing microspheres, it was found that the addition of glucose could not only increase the initial release of the drug but also assist in the subsequent controlled drug release. A good and long-time inhibitory effect on testosterone secretion was observed in this formulation. The underlying cause why the incorporation of glucose delayed the subsequent drug release was investigated. SEM results showed that considerable pores in glucose containing microspheres were healed during the microspheres incubation. After thermal analysis, an obvious glass transition temperature (Tg) depression was observed in this formulation. As Tg decreased, polymer chains are able to rearrange at lower temperatures. This, morphologic change was reflected in the gradual closure of the pores, and is the likely reason that drug release slowed down after the initial release.HighlightsThe addition of glucose could not only increase the burst release of the drug but also delay the subsequent drug release.High initial burst and a sustained drug release helped obtain a good inhibitory effect on testosterone secretion.As Tg decreased, polymer chain was prone to rearrange. Morphologic change was reflected in the gradual closure of the pores. This was the reason that drug release slowed down after the initial burst.

In vitro degradation and erosion behavior of commercial PLGAs used for controlled drug delivery

Copolymers of lactic (or lactide) and glycolic (or glycolide) acids (PLGAs) are among the most commonly used materials in biomedical applications, such as parenteral controlled drug delivery, due to their biocompatibility, predictable degradation rate, and ease of processing. Besides manufacturing variables of drug delivery vehicles, changes in PLGA raw material properties can affect product behavior. Accordingly, an in-depth understanding of polymer-related "critical quality attributes" can improve selection and predictability of PLGA performance. Here, we selected 19 different PLGAs from five manufacturers to form drug-free films, submillimeter implants, and microspheres and evaluated differences in their water uptake, degradation, and erosion during in vitro incubation as a function of L/G ratio, polymerization method, molecular weight, end-capping, and geometry. Uncapped PLGA 50/50 films from different manufacturers with similar molecular weights and higher glycolic unit blockiness and/or block length values showed faster initial degradation rates. Geometrically, larger implants of 75/25, uncapped PLGA showed higher water uptake and faster degradation rates in the first week compared to microspheres of the same polymers, likely due to enhanced effects of acid-catalyzed degradation from PLGA acidic byproducts unable to escape as efficiently from larger geometries. Manufacturer differences such as increased residual monomer appeared to increase water uptake and degradation in uncapped 50/50 PLGA films and poly(lactide) implants. This dataset of different polymer manufacturers could be useful in selecting desired PLGAs for controlled release applications or comparing differences in behavior during product development, and these techniques to further compare differences in less reported properties such as sequence distribution may be useful for future analyses of PLGA performance in drug delivery.

Long-acting injectable formulation technologies: Challenges and opportunities for the delivery of fragile molecules

INTRODUCTION

The development of long acting injectables (LAIs) for protein and peptide therapeutics has been a key challenge over the last 20 years. If these molecules offer advantages due to their high specificity and selectivity, their controlled release may confer several additional benefits in terms of extended half-life, local delivery, and patient compliance.

AREA COVERED

This manuscript aims to give an overview of peptide and protein based LAIs from an industrial perspective, describing both approved and promising technologies (with exceptions of protein engineering strategies and devices), their advantages and potential improvements to aid their access to the market.

EXPERT OPINION

Many LAIs have been developed for peptides, with formulations on the market for several decades. On the contrary, LAIs for proteins are still far from the market and issues related to manufacturing and sterilization of these products still need to be overcome. In situ forming depots (ISFDs), whose simple manufacturing conditions and easy administration procedures (without reconstitution) are strong advantages, appear as one of the most promising technologies for the delivery of these molecules. In this regard, the approval of ELIGARD® in the early 2000's (which still requires a complex reconstitution process), paved the way for the development of second-generation, ready-to-use ISFD technologies like BEPO® and FluidCrystal®.

Changing the daily injection of glatiramer acetate to a monthly long acting product through designing polyester-based polymeric microspheres

Introduction: Glatiramer acetate (GA) is a newly emerged therapeutic peptide to reduce the frequency of relapses in multiple sclerosis (MS). Despite its good performance in controlling MS, it is not widely used due to daily or biweekly subcutaneous injections due to rapid degradation and body clearance. Therefore, implant design with sustained release leads to prolonged biological effects by gradually increasing drug exposure and protecting GA from rapid local degradation. Methods: Different emulsion methods, PLGA type, surfactant concentration, drug/polymer ratio, drying processes, stirring method, and other variables in preliminary studies modified the final formulation. The release kinetics were studied through mechanistic kinetic models such as zero-order, Weibull, Higuchi, etc. In this study, all challenges for easy scale-up, methodological detail, and a simple, feasible setup in mass production were discussed. Results: The optimized formulation was obtained by 1:6 drug/PLGA, 0.5% w/w polyvinyl alcohol, and 0.75% w/w NaCl in the external aqueous phase, 1:10 continuous phase to dispersed phase ratio, and without any surfactant in the primary emulsion. The final freeze-dried particles presented a narrow distributed size of 1-10 µm with 7.29% ± 0.51 drug loading and zero-order release behavior with appropriate regression correlation (R2 98.7), complete release, and only 7.1% initial burst release. Conclusion: Therefore, to achieve improvement in patient compliance through better and longer efficacy, designing the parenteral sustained release microspheres (MPSs) of this immune modulator is a promising approach that should be considered.

Recent Progress in Drug Release Testing Methods of Biopolymeric Particulate System

Biopolymeric microparticles have been widely used for long-term release formulations of short half-life chemicals or synthetic peptides. Characterization of the drug release from microparticles is important to ensure product quality and desired pharmacological effect. However, there is no official method for long-term release parenteral dosage forms. Much work has been done to develop methods for in vitro drug release testing, generally grouped into three major categories: sample and separate, dialysis membrane, and continuous flow (flow-through cell) methods. In vitro drug release testing also plays an important role in providing insight into the in vivo performance of a product. In vitro release test with in vivo relevance can reduce the cost of conducting in vivo studies and accelerate drug product development. Therefore, investigation of the in vitro–in vivo correlation (IVIVC) is increasingly becoming an essential part of particulate formulation development. This review summarizes the principles of the in vitro release testing methods of biopolymeric particulate system with the recent research articles and discusses their characteristics including IVIVC, accelerated release testing methods, and stability of encapsulated drugs.

PLGA/PLA-Based Long-Acting Injectable Depot Microspheres in Clinical Use: Production and Characterization Overview for Protein/Peptide Delivery

Over the past few decades, long acting injectable (LAI) depots of polylactide-co-glycolide (PLGA) or polylactic acid (PLA) based microspheres have been developed for controlled drug delivery to reduce dosing frequency and to improve the therapeutic effects. Biopharmaceuticals such as proteins and peptides are encapsulated in the microspheres to increase their bioavailability and provide a long release period (days or months) with constant drug plasma concentration. The biodegradable and biocompatible properties of PLGA/PLA polymers, including but not limited to molecular weight, end group, lactide to glycolide ratio, and minor manufacturing changes, could greatly affect the quality attributes of microsphere formulations such as release profile, size, encapsulation efficiency, and bioactivity of biopharmaceuticals. Besides, the encapsulated proteins/peptides are susceptible to harsh processing conditions associated with microsphere fabrication methods, including exposure to organic solvent, shear stress, and temperature fluctuations. The protein/peptide containing LAI microspheres in clinical use is typically prepared by double emulsion, coacervation, and spray drying techniques. The purpose of this review is to provide an overview of the formulation attributes and conventional manufacturing techniques of LAI microspheres that are currently in clinical use for protein/peptides. Furthermore, the physicochemical characteristics of the microsphere formulations are deliberated.

Impact of octreotide counterion nature on the long-term stability and release kinetics from an in situ forming depot technology

The generation of acylated impurities has represented an important hurdle in the development of long acting injectables for therapeutic peptides using biocompatible polymers with a polyester moiety. We investigated here an in situ forming depot (ISFD) technology that uses polyethylene glycol - polyester copolymers and a solvent exchange mechanism to promote depot formation. This technology has shown promise in formulating small molecules as well as therapeutic proteins. In the present work, using the well-known somatostatin analog octreotide acetate (OctAc) as a model molecule, we evaluated this delivery platform to release therapeutic peptides. Peptide acylation was found to be pronounced in the formulation, while it was very limited once the depot was formed and during the release process. The octreotide acylation pattern was fully characterized by LC-MS/MS. Moreover, it was demonstrated that exchanging the acetate anion with more hydrophobic counterions like pamoate or lauryl sulfate allowed to greatly improve the peptide stability profile, as well as the formulation release performance. Finally, the in vivo evaluation through pharmacokinetics studies in rat of these new octreotide salts in ISFD formulations showed that octreotide was quantifiable up to four weeks post-administration with a high bioavailability and an acceptable initial burst.

Characterization of attributes and in vitro performance of exenatide-loaded PLGA long-acting release microspheres

Bydureon® (Bdn) is a once-weekly injectable long-acting release (LAR) product for adults with type 2 diabetes based on PLGA microspheres encapsulating the glucagon like peptide (GLP-1) analog, exenatide. Despite its widespread use in type 2 diabetes treatment, little information has been published concerning the physical-chemical aspects and exenatide stability in this product. Here, we developed and validated methods to evaluate attributes and performance of Bdn such as particle size/size distribution and residual levels of moisture and organic solvent(s). The reverse engineering of the exenatide LAR was also performed to identify and quantify principal components in the product. Stability-indicating UPLC and LC-MS methods were applied to characterize exenatide degradation (such as oxidation, deamidation and acylation products) during in vitro release evaluation. The 55-μm volume-median Bdn microspheres slowly released the exenatidein vitroover two months with a very low initial burst release to avoid unwanted side effects. Residual organic solvent levels (methylene chloride, ethanol, heptane, and silicon oil) also met the USP criteria. Peptide acylation was the most prominent peptide reaction during both encapsulation and in vitro release, and the acylated peptide steadily increased during release relative to parent exenatide, becoming the most abundant peptide species extracted from the microspheres at later release stages. The presence of peptide impurities during the release period, which are not extractable in the polymer and likely insoluble in water, might be one potential cause for immunogenicity. Further evaluation will be needed to confirm this hypothesis. Release of peptide was minimal over the first 2 weeks before the microspheres steadily released peptide for more than 28 days. The rigorous technical approach discussed in this paper may provide critical information for both companies and the FDA for developing generic exenatide-PLGA formulations and other important PLGA microsphere products.

Synthesis and Biological Application of Polylactic Acid

Over the past few decades, with the development of science and technology, the field of biomedicine has rapidly developed, especially with respect to biomedical materials. Low toxicity and good biocompatibility have always been key targets in the development and application of biomedical materials. As a degradable and environmentally friendly polymer, polylactic acid, also known as polylactide, is favored by researchers and has been used as a commercial material in various studies. Lactic acid, as a synthetic raw material of polylactic acid, can only be obtained by sugar fermentation. Good biocompatibility and biodegradability have led it to be approved by the U.S. Food and Drug Administration (FDA) as a biomedical material. Polylactic acid has good physical properties, and its modification can optimize its properties to a certain extent. Polylactic acid blocks and blends play significant roles in drug delivery, implants, and tissue engineering to great effect. This article describes the synthesis of polylactic acid (PLA) and its raw materials, physical properties, degradation, modification, and applications in the field of biomedicine. It aims to contribute to the important knowledge and development of PLA in biomedical applications.

Proton Oriented-"Smart Depot" for Responsive Release of Ca2+ to Inhibit Peptide Acylation in PLGA Microspheres

PURPOSE

The purpose of this study was to characterize and detail the mechanism of a smart Ca²⁺ release depot (Ca₃(PO₄)₂) about its ability for sustainable inhibition on peptide acylation within PLGA microspheres.

METHODS

The octreotide acetate release and acylation kinetics were analyzed by RP-HPLC. Changes of Ca²⁺ concentration and adsorption behavior were determined by a Calcium Colorimetric Assay Kit. The inner pH changes were delineated by a classic pH sensitive probe, Lysosensor yellow/ blue® dextran. Morphological changes of microspheres, adsorption between polymer and additive, transformation of Ca₃(PO₄)₂ were characterized using SEM, FTIR and SSNMR separately.

RESULTS

Before and after microspheres formulation, the property and effectiveness of Ca₃(PO₄)₂ were investigated. Compared with a commonly used calcium salt (CaCl₂), high encapsulation efficiency (96.56%) of Ca₃(PO₄)₂ guarantees lasting effectiveness. In an increasingly acidic environment that simulated polymer degradation, the poorly water-soluble Ca₃(PO₄)₂ could absorb protons and transform into the more and more soluble CaHPO₄ and Ca(H₂PO₄)₂ to produce sufficient Ca²⁺ according to severity of acylation. The corresponding Ca²⁺ produce capacity fully met the optimum inhibition requirement since the real-time adsorption sites (water-soluble carboxylic acids) inside the degrading microspheres were rare. A sustained retention of three switchable calcium salts and slow release of Ca²⁺ were observed during the microsphere incubation. FTIR results confirmed the long-term inhibition effect induced by Ca₃(PO₄)₂ on the adsorption between drug and polymer.

CONCLUSIONS

With the presence of the smart Ca²⁺ depot (Ca₃(PO₄)₂) in the microspheres, a sustainable and long-term inhibition of peptide acylation was achieved.

Nucleotide-binding oligomerization domain 1 (NOD1) modulates liver ischemia reperfusion through the expression adhesion molecules

BACKGROUND & AIMS

In liver transplantation, organ shortage leads to the use of marginal grafts that are more susceptible to ischemia-reperfusion (IR) injury. We identified nucleotide-binding oligomerization domain 1 (NOD1) as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in IR. Herein, we aimed to elucidate the role of NOD1 in IR injury, particularly focusing on its effects on the endothelium and hepatocytes.

METHOD

Nod1 WT and KO mice were treated with NOD1 agonists and subjected to liver IR. Expression of adhesion molecules was analyzed in total liver, isolated hepatocytes and endothelial cells. Interactions between PMNs and hepatocytes were studied in an ex vivo co-culture model using electron microscopy and lactate dehydrogenase levels. We generated NOD1 antagonist-loaded nanoparticles (np ALINO).

RESULTS

NOD1 agonist treatment increased liver injury, PMN tissue infiltration and upregulated ICAM-1 and VCAM-1 expression 20 hours after reperfusion. NOD1 agonist treatment without IR increased expression of adhesion molecules (ICAM-1, VCAM-1) in total liver and more particularly in WT hepatocytes, but not in Nod1 KO hepatocytes. This induction is dependent of p38 and ERK signaling pathways. Compared to untreated hepatocytes, a NOD1 agonist markedly increased hepatocyte lysis in co-culture with PMNs as shown by the increase of lactate dehydrogenase in supernatants. Interaction between hepatocytes and PMNs was confirmed by electron microscopy. In a mouse model of liver IR, treatment with np ALINO significantly reduced the area of necrosis, aminotransferase levels and ICAM-1 expression.

CONCLUSION

NOD1 regulates liver IR injury through induction of adhesion molecules and modulation of hepatocyte-PMN interactions. NOD1 antagonist-loaded nanoparticles reduced liver IR injury and provide a potential approach to prevent IR, especially in the context of liver transplantation.

LAY SUMMARY

Nucleotide-binding oligomerization domain 1 (NOD1) is as an important modulator of polymorphonuclear neutrophil (PMN)-induced liver injury, which occurs in ischemia-reperfusion. Here, we show that the NOD1 pathway targets liver adhesion molecule expression on the endothelium and on hepatocytes through p38 and ERK signaling pathways. The early increase of adhesion molecule expression after reperfusion emphasizes the importance of adhesion molecules in liver injury. In this study we generated nanoparticles loaded with NOD1 antagonist. These nanoparticles reduced liver necrosis by reducing PMN liver infiltration and adhesion molecule expression.

Complex sameness: Separation of mixed poly(lactide-co-glycolide)s based on the lactide:glycolide ratio

Poly (lactide-co-glycolide) (PLGA) has been used for making injectable, long-acting depot formulations for the last three decades. An in depth understanding of PLGA polymers is critical for development of depot formulations as their properties control drug release kinetics. To date, about 20 PLGA-based formulations have been approved by the U.S. Food and Drug Administration (FDA) through new drug applications, and none of them have generic counterparts on the market yet. The lack of generic PLGA products is partly due to difficulties in reverse engineering. A generic injectable PLGA product is required to establish qualitative and quantitative (Q1/Q2) sameness of PLGA to that of a reference listed drug (RLD) to obtain an approval from the FDA. Conventional characterizations of PLGA used in a formulation rely on measuring the molecular weight by gel permeation chromatography (GPC) based on polystyrene molecular weight standards, and determining the lactide:glycolide (L: G) ratio by ¹H NMR and the end-group by ¹³C NMR. These approaches, however, may not be suitable or sufficient, if a formulation has more than one type of PLGA, especially when they have similar molecular weights, but different L:G ratios. Accordingly, there is a need to develop new assay methods for separating PLGAs possessing different L:G ratios when used in a drug product and characterizing individual PLGAs. The current work identifies a series of semi-solvents which exhibit varying degrees of PLGA solubility depending on the L:G ratio of the polymer. A good solvent dissolves PLGAs with all L:G ratios ranging from 50:50 to 100:0. A semi-solvent dissolves PLGAs with only certain L:G ratios. Almost all semi-solvents identified in this study increase their PLGA solubility as the L:G ratio increases, i.e., the lactide content increases. This lacto-selectivity, favoring higher L:G ratios, has been applied for separating individual PLGAs in a given depot formulation, leading to analysis of each type of PLGA. This semi-solvent method allows a simple, practical bench-top separation of PLGAs of varying L:G ratios. This method enables isolation and identification of individual PLGAs from a complex mixture that is critical for the quality control of PLGA formulations, as well as reverse engineering for generic products to establish the Q1/Q2 sameness.

Separation and identification of acylated leuprorelin inside PLGA microspheres

Studies have shown that the N-terminus and lysine side residue of peptides are prone to acylation in poly(d,l-lactide-co-glycolide) (PLGA) microspheres. Peptides such as leuprorelin lack a free N-terminus or lysine and only contain serine, arginine, and tyrosine as nucleophilic residues. The purpose of this study was to detect potential acylation impurities and determine their corresponding acylation sites in commercial leuprorelin-loaded PLGA microspheres. Commercial samples from three vendors were selected as targets for our study. The high-performance liquid chromatography (HPLC) conditions of the European Pharmacopoeia were used to separate and collect impurities. HPLC-tandem mass spectrometry (HPLC-MS/MS) was applied to confirm both the structure and acylation sites of the impurities. Our study demonstrated that impurities originating from both degradation of microspheres and synthesis of leuprorelin were well separated and identified using these HPLC conditions. HPLC-MS/MS analysis of acylated leuprorelin showed that diglycoyl, lactoyl-glycoyl, dilactoyl, and monolactoyl groups were conjugated to serine in leuprorelin-loaded PLGA microspheres. This is the first report showing serine to be the acylation site in peptide-loaded PLGA microspheres. Separation and identification of acylated leuprorelin derivatives will assist in minimising acylation and guiding the development of quality control for commercial leuprorelin-loaded PLGA microspheres.

Reverse Engineering the 1-Month Lupron Depot®

The 1-month Lupron Depot® (LD) encapsulating water-soluble leuprolide in poly(lactic-co-glycolic acid) (PLGA) microspheres is a benchmark product upon which modern long-acting release products are often compared. Despite expiration of patent coverage, no generic product for the LD has been approved in the USA, likely due to the complexity of components and manufacturing processes involved in the product. Here, we describe the reverse engineering of the LD composition and important product attributes. Specific attributes analyzed for microspheres were as follows: leuprolide content by three methods; gelatin content, type, and molecular weight distribution; PLGA content, lactic acid/glycolic acid ratio, and molecular weight distribution; mannitol content; in vitro drug release; residual solvent and moisture content; particle size distribution and morphology; and glass transition temperature. For the diluent, composition, viscosity, and specific gravity were analyzed. Analyzed contents of the formulation and the determined PLGA characteristics matched well with the official numbers stated in the package insert and those found in literature, respectively. The gelatin was identified as type B consistent with ~ 300 bloom. The 11-μm volume-median microspheres in the LD slowly released the drug in vitro in a zero-order manner after ~ 23% initial burst release. Very low content of residual moisture (< 0.5%) and methylene chloride (< 1 ppm) in the product indicates in-water drying is capable of removing solvents to extremely low levels during manufacturing. The rigorous approach of reverse engineering described here may be useful for development of generic leuprolide-PLGA microspheres as well as other new and generic PLGA microsphere formulations.

Inhibition of Octreotide Acylation Inside PLGA Microspheres by Derivatization of the Amines of the Peptide with a Self-Immolative Protecting Group

Acylation of biopharmaceuticals such as peptides has been identified as a major obstacle for the successful development of PLGA controlled release formulations. The purpose of this study was to develop a method to inhibit peptide acylation in poly(d,l-lactide-co-glycolide) (PLGA) formulations by reversibly and temporarily blocking the amine groups of a model peptide (octreotide) with a self-immolative protecting group (SIP), O-4-nitrophenyl-O'-4-acetoxybenzyl carbonate. The octreotide with two self-immolative protecting groups (OctdiSIP) on the N-terminus and lysine side chain was synthesized by reaction of the peptide with O-4-nitrophenyl-O'-4-acetoxybenzyl carbonate, purified by preparative RP-HPLC and characterized by mass spectrometry. Degradation studies of OctdiSIP in aqueous solutions of different pH values showed that protected octreotide was stable at low pH (pH 5) whereas the protecting group was eliminated at physiological pH, especially in the presence of an esterase, to generate native octreotide. OctdiSIP encapsulated in PLGA microspheres, prepared using a double emulsion solvent evaporation method, showed substantial inhibition of acylation as compared to the unprotected octreotide: 52.5% of unprotected octreotide was acylated after 50 days incubation of microspheres in PBS pH 7.4 at 37 °C, whereas OctdiSIP showed only 5.0% acylation in the same time frame. In conclusion, the incorporation of self-immolative protection groups provides a viable approach for inhibition of acylation of peptides in PLGA delivery systems.

Extended release microparticle-in-gel formulation of octreotide: Effect of polymer type on acylation of peptide during in vitro release

Polymeric microparticles (MPs)-in-gel formulations for extended delivery of octreotide were developed. We investigated influence of polymer composition on acylation of octreotide and kinetics of release during in vitro release from biodegradable polymeric formulations. Polycaprolactone (PCL), polylactic acid (PLA), polyglycolic acid (PGA) and polyethylene glycol (PEG) based triblock (TB≈PCL10k-PEG2k-PCL10k) and pentablock (PBA≈PLA3k-PCL7k-PEG2k-PCL7k-PLA3k and PBB≈PGA3k-PCL7k-PEG2k-PCL7k-PGA3k) polymers were investigated. Octreotide was encapsulated in MPs using methanol-oil/water emulsion solvent evaporation method. The particles were characterized for size, morphology, encapsulation efficiency, drug loading and in vitro release. Release samples were subjected to HPLC analysis for quantitation and HPLC-MS analysis for identification of native and chemically modified octreotide adducts. Entrapment efficiency of methanol-oil/water method with TB, PBA and PBB polymers were 45%, 60%, and 82%, respectively. A significant fraction of released octreotide was acylated from lactide and glycolide based PBA (53%) and PBB (92%) polymers. Substantial amount of peptide was not released from PBB polymers after 330 days of incubation. Complete release of octreotide was achieved from TB polymer over a period of 3 months with minimal acylation of peptide (13%). PCL based polymers resulted in minimal acylation of peptide and hence may be suitable for extended peptide and protein delivery. Conversely, polymers having PLA and PGA blocks may not be appropriate for peptide delivery due to acylation and incomplete release.

Reversible hydrophobic ion-paring complex strategy to minimize acylation of octreotide during long-term delivery from PLGA microparticles

Acylation of peptide has been reported for a number of peptides and proteins during release from polymers comprising of lactide and glycolide. We hypothesize that reversible hydrophobic ion-pairing (HIP) complex may minimize octreotide acylation during release. Sodium dodecyl sulfate (SDS), dextran sulfate A (DSA, Mw 9-20 kDa) and dextran sulfate B (DSB, Mw 36-50 kDa) were selected as ion-pairing agents to prepare reversible HIP complex with octreotide. Complexation efficiency was optimized with respect to the mole ratio of ion-pairing agent to octreotide to achieve 100% complexation of octreotide. Dissociation studies suggested that DSA-octreotide and DSB-octreotide complexes dissociate completely at physiological pH in presence of counter ions unlike SDS-octreotide complex. DSA-octreotide and DSB-octreotide complex encapsulated PLGA microparticles (DSAMPs and DSBMPs) were prepared using the S/O/W emulsion method. Entrapment efficiencies for DSAMPs and DSBMPs were 74.7±8.4% and 81.7±6.3%, respectively. In vitro release of octreotide was performed by suspending MPs in gel. A large fraction of peptide was released in chemically intact form and <7% was acylated from DSAMPs and DSBMPs in gel over 55 days. Therefore, HIP complexation could be a viable strategy to minimize acylation of peptides and proteins during extended release from lactide and glycolide based polymers.

Improved poly(d,l-lactide-co-1,3-trimethylene carbonate)6 copolymer microparticle vehicles for sustained and controlled delivery of bioactive basic fibroblast growth factor

A novel, biocompatible and biodegradable six-arm branched copolymer poly(d,l-lactide)-co-(1,3-trimethylene carbonate)6 has been synthesized and fabricated as a porous microparticle with an oil-in-water single emulsion method. Poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles were further conjugated with heparin by 1-ethyl-3-3-dimethylamino-propylcarbodiimide/ N-hydroxysuccinimide chemistry and characterized using 1H-nuclear magnetic resonance and scanning electron microscopy. The heparin-loading capacity of poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles was identified as 213 ± 6 pmol/mg-particle determined with toluidine blue method. The resultant binding efficiency and release profile of basic fibroblast growth factor which is bound on heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles were quantitatively analyzed by enzyme-linked immunosorbent assay. Thus, the developed poly(d,l-lactide-co-1,3-trimethylene carbonate)6 porous microparticles presented superior capacity of growth factor cargo as 1965 ± 117 pg basic fibroblast growth factor per mg-microparticles and displayed a sustained release profile over 4 weeks with quite low initial burst. Additionally, the viability of dissociated basic fibroblast growth factor was confirmed with methylthiazolyltetrazolium quantitative assay along with in vitro culturing model of rodent neural stem cell. Collectively, our results demonstrate that heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 microparticles attained controllable and sustained delivery of bioactive basic fibroblast growth factor for 4 weeks with significantly reduced burst release. The present heparin–poly(d,l-lactide-co-1,3-trimethylene carbonate)6 porous microparticulate system could be potentially developed to foster a novel bioengineering platform for repair and regeneration of injured nervous system.

Identification and Assessment of Octreotide Acylation in Polyester Microspheres by LC-MS/MS

Purpose

Polyesters with hydrophilic domains, i.e., poly(d,l-lactic-co-glycolic-co-hydroxymethyl glycolic acid) (PLGHMGA) and a multiblock copolymer of poly(ε-caprolactone)-PEG-poly(ε-caprolactone) and poly(l-lactide) ((PC-PEG-PC)-(PL)) are expected to cause less acylation of encapsulated peptides than fully hydrophobic matrices. Our purpose is to assess the extent and sites of acylation of octreotide loaded in microspheres using tandem mass spectrometry analysis.

Methods

Octreotide loaded microspheres were prepared by a double emulsion solvent evaporation technique. Release profiles of octreotide from hydrophilic microspheres were compared with that of PLGA microspheres. To scrutinize the structural information and localize the actual modification site(s) of octreotide, liquid chromatography ion-trap mass spectrometry (LC-ITMS) was performed on the acylated adducts.

Results

Hydrophilic microspheres showed less acylated adducts in comparison with PLGA microspheres. LC-MS/MS showed that besides the N-terminus and primary amine of lysine, the primary hydroxyl of the end group of octreotide was also subjected to acylation. Nucleophilic attack of the peptide can also occur to the carbamate bond presented in (PC-PEG-PC)-(PL) since 1,4-butanediisocyanate was used as the chain extender.

Conclusions

Hydrophilic polyesters are promising systems for controlled release of peptide because substantially less acylation occurs in microspheres based on these polymers. LC-ITMS provided detailed structural information of octreotide modifications via mass analysis of ion fragments.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-015-1685-3) contains supplementary material, which is available to authorized users.

Injectable controlled release depots for large molecules

Biodegradable, injectable depot formulations for long-term controlled drug release have improved therapy for a number of drug molecules and led to over a dozen highly successful pharmaceutical products. Until now, success has been limited to several small molecules and peptides, although remarkable improvements have been accomplished in some of these cases. For example, twice-a-year depot injections with leuprolide are available compared to the once-a-day injection of the solution dosage form. Injectable depots are typically prepared by encapsulation of the drug in poly(lactic-co-glycolic acid) (PLGA), a polymer that is used in children every day as a resorbable suture material, and therefore, highly biocompatible. PLGAs remain today as one of the few "real world" biodegradable synthetic biomaterials used in US FDA-approved parenteral long-acting-release (LAR) products. Despite their success, there remain critical barriers to the more widespread use of PLGA LARproducts, particularly for delivery of more peptides and other large molecular drugs, namely proteins. In this review, we describe key concepts in the development of injectable PLGA controlled-release depots for peptides and proteins, and then use this information to identify key issues impeding greater widespread use of PLGA depots for this class of drugs. Finally, we examine important approaches, particularly those developed in our research laboratory, toward overcoming these barriers to advance commercial LAR development.

One-step fabrication of agent-loaded biodegradable microspheroids for drug delivery and imaging applications

Non-spherical particles may offer advantages over conventional spherical systems for drug delivery applications. This work describes the fabrication of agent-loaded poly(lactic-co-glycolic acid) (PLGA) spheroids via the emulsion solvent evaporation (ESE) method. The versatility of this technique for loading a variety of therapeutics is demonstrated via loading of paclitaxel, bovine serum albumin, and cadmium sulfide nanoparticles into PLGA spheroids. The encapsulation efficiency for spheroids fabricated via oil-in-water (O/W) emulsions is highest at low aqueous phase surfactant concentrations while the encapsulation efficiency for spheroids made via water-in-oil-in-water (W/O/W) is highest at high aqueous phase surfactant concentrations and basic aqueous phase pH values. Particle aspect ratio polydispersity can be minimized via the use of high aqueous phase PVA concentration and pH. The ESE technique is an attractive alternative to recently described methods for fabrication of non-spherical particles due to its simplicity in setup, high particle yield and adaptability to a variety of biodegradable polymers and therapeutics.

Minimizing acylation of peptides in PLGA microspheres

The main objective of this study was to characterize and find mechanisms to prevent acylation of therapeutic peptides encapsulated in glucose-star poly(d,l-lactic-co-glycolic acid) (PLGA) microspheres. The effect of addition of divalent cation salts CaCl(2), MnCl(2) as well as carboxymethyl chitosan (CMCS) on inhibition of acylation of octreotide (Oct), salmon calcitonin (sCT), and human parathyroid hormone (hPTH) was evaluated. Peptide content and integrity inside the degrading microspheres was monitored by reversed-phase high performance liquid chromatography (HPLC) and mass spectrometry during release incubation under physiological conditions. The extent of peptide acylation was strongly inhibited in the formulations containing divalent cations and/or CMCS as excipients, although specific effects were dependent on the specific peptide and excipient combinations. Both inorganic cations improved stability of Oct and hPTH but not sCT. Addition of CMCS alone was ineffective. Combining inorganic cations with CMCS improved stability of Oct and sCT but it had no effect on hPTH stability. The operative stabilization mechanisms are consistent with blocking peptide-PLGA interactions by a) directly competing for PLGA interactions with dications and/or b) increasing peptide affinity in the stabilizer phase within PLGA pores. Hence, inorganic multivalent cations are general stabilizers against peptide acylation, the effect of which may be augmented in certain instances with addition of CMCS.

Reversible blocking of amino groups of octreotide for the inhibition of formation of acylated peptide impurities in poly(lactide-co-glycolide) delivery systems

The purpose of this study was to develop a novel method to inhibit the formation of acylated peptide impurities in poly(D,L-lactide-co-glycolide) (PLGA) formulations by reversely blocking the amino groups of octreotide with maleic anhydride (MA). Two mono-MA conjugates with different modification sites (N terminus and Lys residue) and di-MA conjugate of octreotide were prepared and isolated by reversed-phase high-performance liquid chromatography (RP-HPLC). The polymer interaction of peptides and the formation of acylated peptides were monitored by RP-HPLC. The stability of MA-octreotide conjugates in PLGA films was studied in 0.1 M phosphate buffer (pH 7.4) at 37°C. The conjugation of MA to octreotide substantially inhibited the interaction of peptide with PLGA polymer and the subsequent formation of acylated peptide impurities. The MA-octreotides were successfully converted to intact octreotide as pH drops by PLGA hydrolysis. In PLGA films, MA-octreotide also showed complete inhibition of peptide acylation. In conclusion, MA conjugation provides a viable approach for stabilizing peptides in PLGA delivery systems.

Controlled release of octreotide and assessment of peptide acylation from poly(D,L-lactide-co-hydroxymethyl glycolide) compared to PLGA microspheres

Purpose

To investigate the in vitro release of octreotide acetate, a somatostatin agonist, from microspheres based on a hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA).

Methods

Spherical and non-porous octreotide-loaded PLHMGA microspheres (12 to 16 μm) and loading efficiency of 60–70% were prepared by a solvent evaporation. Octreotide release profiles were compared with commercial PLGA formulation (Sandostatin LAR^®); possible peptide modification with lactic, glycolic and hydroxymethyl glycolic acid units was monitored.

Results

PLHMGA microspheres showed burst release (~20%) followed by sustained release for 20–60 days, depending on the hydrophilicity of the polymer. Percentage of released loaded peptide was high (70–90%); > 60% of released peptide was native octreotide. PLGA microspheres did not show peptide release for the first 10 days, after which it was released in a sustained manner over the next 90 days; > 75% of released peptides were acylated adducts.

Conclusions

PLHMGA microspheres are promising controlled systems for peptides with excellent control over release kinetics. Moreover, substantially less peptide modification occurred in PLHMGA than in PLGA microspheres.

Electronic Supplementary Material

The online version of this article (doi:10.1007/s11095-011-0517-3) contains supplementary material, which is available to authorized users.

Preparation and in-vitro/in-vivo evaluation of surface-modified poly (lactide-co-glycolide) fluorescent nanoparticles

OBJECTIVE

The aim was to develop biodegradable nanoparticles suitable for cellular delivery of chemotherapeutic drugs.

METHODS

Poly (lactide-co-glycolide) (PLGA) nanoparticles were prepared using a modified solvent evaporation method. Chitosan and calcium chloride were tested as surface modifiers. Coumarin-6 was incorporated into some formulations as a fluorescent marker.

KEY FINDINGS

The median size of the particles was between 400 nm and 7 microm, and scanning electron microscope pictures showed that the particles were smooth and spherical. The zeta potentials of the particles with and without surface modifier ranged between -25.7 mV and -7.0 mV, respectively. Fluorescence microscopy and flow cytometry (FACS) analysis showed that smaller surface-modified particles were efficiently internalised by neoplastic 4T1 cells. Image analysis of frozen tissue sections from Balb/c mice given nanoparticles via the tail vein showed that the particles were distributed preferentially into the lungs, followed by the liver, spleen, kidney and heart.

CONCLUSIONS

Chitosan-modified PLGA nanoparticles showed significant uptake by neoplastic 4T1 cells, and were distributed to several major organs frequently seen as sites of cancer metastasis in mice.

Chemotherapy with PLGA microspheres containing docetaxel decreases angiogenesis in human hepatoma xenograft

To investigate the antiangiogenic effect of sustained-release poly (lactic-co-glycolic acid) microspheres containing docetaxel (PMCD) in human hepatoma xenograft. PMCD were prepared by solvent evaporation method with an encapsulation efficiency of 98.7% and a release period of about 3 weeks in vitro. PMCD were intratumorally injected once for mice bearing a human hepatocellular carcinoma. On day 21 post-treatment, the inhibition rate of tumor growth was 72.7% in the high-dose group, indicating a significant antitumor activity. Meanwhile, excellent antiangiogenic effect was observed based on the contrast-enhanced ultrasonography as well as microvessel density determination. Additionally, the real-time fluorescence quantitative PCR revealed that the expressions of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and angiopoietin-2 (Ang2) genes were down-regulated significantly. Interstitial chemotherapy using PMCD was highly effective and safe for the treatment of the human hepatoma xenograft and that decreasing angiogenesis could be one of the most important mechanisms involved in the antitumor activity.

Hydrophilic polyester microspheres: effect of molecular weight and copolymer composition on release of BSA

Purpose

To study the release of a model protein, bovine serum albumin (BSA), from microspheres of an hydroxylated aliphatic polyester, poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA).

Methods

BSA-loaded microspheres were prepared by a double emulsion solvent evaporation method. The effect of copolymer composition and the molecular weight of the copolymer on in vitro release and degradation were studied. The integrity of the released BSA was studied by fluorescence spectroscopy and size exclusion chromatography (SEC).

Results

Microspheres prepared from PLHMGA with 50% hydroxymethyl glycolic acid (HMG) showed a burst release followed by a sustained release in 5–10 days. PLHMGA microspheres prepared from a copolymer with 35% and 25% HMG showed a sustained release of BSA up to 80% for 30 and 60 days, respectively. The release of BSA was hardly affected by the molecular weight of the polymer. Fluorescence spectroscopy and SEC showed that the released BSA preserved its structural integrity. Microspheres were fully degradable, and the degradation time increased from ~20 days to 60 days when the HMG content decreased from 50% to 25%.

Conclusions

Taking the degradation and release data together, it can be concluded that the release of BSA from PLHMGA microspheres is governed by degradation of the microspheres.