Sustained-release delivery of octreotide from biodegradable polymeric microspheres

A Novel System for Fabricating Microspheres with Microelectromechanical System-Based Bioprinting Technology

Objective and Impact Statement: The microspheres were widely utilized in the field of life sciences, and we have developed an innovative microelectromechanical system (MEMS)-based bioprinting technology (MBT) system for the preparation of the microspheres. The microspheres can be automatically and high-throughput produced with this cutting-edge system. Introduction and Methods: This paper mainly introduced a novel, efficient, and cost-effective approach for the microsphere fabrication with the MBT system. In this work, the whole microsphere production equipment was built and the optimal conditions (like concentration, drying temperature, frequency, and voltage) for generating uniform hydroxypropyl cellulose-cyclosporine A (HPC-CsA) and poly-l-lactic acid (PLLA) microspheres were explored. Results: Results demonstrated that the optimal uniformity of HPC-CsA microspheres was achieved at 2% (w/v) HPC-CsA mixture, 45 °C (drying temperature), 1,000 Hz (frequency), and 25 V (voltage amplitude). CsA microspheres [coefficient of variation (CV): ~9%] are successfully synthesized, and the drug encapsulation rate was 84.8%. The methodology was further used to produce PLLA microspheres with a diameter of ~2.55 μm, and the best CV value achieved 6.84%. Conclusion: This investigation fully highlighted the integration of MEMS and bioprinting as a promising tool for the microsphere fabrication, and this MBT system had huge potential applications in pharmaceutical formulations and medical aesthetics.

Terpenes from Cannabis sativa induce antinociception in a mouse model of chronic neuropathic pain via activation of adenosine A 2A receptors

ABSTRACT

Terpenes are small hydrocarbon compounds that impart aroma and taste to many plants, including Cannabis sativa . A number of studies have shown that terpenes can produce pain relief in various pain states in both humans and animals. However, these studies were methodologically limited and few established mechanisms of action. In our previous work, we showed that the terpenes geraniol, linalool, β-pinene, α-humulene, and β-caryophyllene produced cannabimimetic behavioral effects via multiple receptor targets. We thus expanded this work to explore the potential antinociception and mechanism of these Cannabis terpenes in a mouse model of chronic pain. We first tested for antinociception by injecting terpenes (200 mg/kg, IP) into male and female CD-1 mice with mouse models of chemotherapy-induced peripheral neuropathy (CIPN) or lipopolysaccharide-induced inflammatory pain, finding that the terpenes produced roughly equal antinociception to 10 mg/kg morphine or 3.2 mg/kg WIN55,212. We further found that none of the terpenes produced reward as measured by conditioned place preference, while low doses of terpene (100 mg/kg) combined with morphine (3.2 mg/kg) produced enhanced antinociception vs either alone. We then used the adenosine A 2A receptor (A 2A R) selective antagonist istradefylline (3.2 mg/kg, IP) and spinal cord-specific CRISPR knockdown of the A 2A R to identify this receptor as the mechanism for terpene antinociception in CIPN. In vitro cAMP and binding studies and in silico modeling studies further suggested that the terpenes act as A 2A R agonists. Together these studies identify Cannabis terpenes as potential therapeutics for chronic neuropathic pain and identify a receptor mechanism for this activity.

Exploring the relationship between bulk Young's Modulus of materials and milling efficiency during wet bead milling of pharmaceutical compounds

Wet bead milling (WBM) is one of the main approaches for manufacturing long acting injectable (LAI) suspensions, wherein the particle size of an Active Pharmaceutical Ingredient (API) is reduced in a liquid vehicle via grinding. A common challenge observed during WBM is long milling time to achieve target particle size, resulting in poor milling efficiency. The objective of this work was to identify potential API attributes predictive of milling efficiency during WBM. In this study, physical and mechanical properties of nine APIs were characterized. Formulations with these APIs were manufactured using WBM. Bulk Young's Modulus was identified to have a significant influence on the rate of particle attrition. The rank order of Young's Moduli of the APIs was consistent with that of milling efficiency, estimated by an empirical function defined in this study called Milling Resistance (ϕ), representing the holistic impact of milling time, tip speed, bead loading, and batch to chamber volume ratio. The identification of such intrinsic material properties, which provide an early evaluation of potential manufacturing risks, is beneficial to product development, as these assessments can be performed with limited quantities of materials and help identify and design out scale-up challenges.

The Advances in Phospholipids-Based Phase Separation Gels for the Sustained Release of Peptides, Proteins, and Chemotherapeutics

Implantable drug delivery systems formed upon injection offer a host of advantages, including localized drug administration, sustained release, minimized side effects, and enhanced patient compliance. Among the various techniques utilized for the development of in situ forming drug implants, solvent-induced phase inversion emerges as a particularly promising approach. However, synthetic polymer-based implants have been associated with undesirable effects arising from polymer degradation. In response to this challenge, a novel category of drug delivery systems, known as phospholipids-based phase separation gels (PPSGs), has emerged. These gels, characterized by their low initial viscosity, exhibit injectability and undergo rapid transformation into in situ implants when exposed to an aqueous environment. A typical PPSG formulation comprises biodegradable components, such as phospholipids, pharmaceutical oil, and a minimal amount of ethanol. The minimized organic solvents in the composition show good biocompatibility. And the relatively simple composition holds promise for industrial-scale manufacturing. This comprehensive review provides an overview of the principles and advancements in PPSG systems, with specific emphasis on their suitability as drug delivery systems for a wide range of active pharmaceutical ingredients (APIs), spanning from small molecules to peptides and proteins. Additionally, we explore the critical parameters and underlying principles governing the formulation of PPSG-based drug delivery strategies, offering valuable insights on optimization strategies.

Terpenes from Cannabis sativa Induce Antinociception in Mouse Chronic Neuropathic Pain via Activation of Spinal Cord Adenosine A2A Receptors

Terpenes are small hydrocarbon compounds that impart aroma and taste to many plants, including Cannabis sativa. A number of studies have shown that terpenes can produce pain relief in various pain states in both humans and animals. However, these studies were methodologically limited and few established mechanisms of action. In our previous work, we showed that the terpenes geraniol, linalool, β-pinene, α-humulene, and β-caryophyllene produced cannabimimetic behavioral effects via multiple receptor targets. We thus expanded this work to explore the efficacy and mechanism of these Cannabis terpenes in relieving chronic pain. We first tested for antinociceptive efficacy by injecting terpenes (200 mg/kg, IP) into male and female CD-1 mice with chemotherapy-induced peripheral neuropathy (CIPN) or lipopolysaccharide-induced inflammatory pain, finding that the terpenes produced roughly equal efficacy to 10 mg/kg morphine or 3.2 mg/kg WIN55,212. We further found that none of the terpenes produced reward as measured by conditioned place preference, while low doses of terpene (100 mg/kg) combined with morphine (3.2 mg/kg) produced enhanced antinociception vs. either alone. We then used the adenosine A2A receptor (A2AR) selective antagonist istradefylline (3.2 mg/kg, IP) and spinal cord-specific CRISPR knockdown of the A2AR to identify this receptor as the mechanism for terpene antinociception in CIPN. In vitro cAMP and binding studies and in silico modeling studies further suggested that the terpenes act as A2AR agonists. Together these studies identify Cannabis terpenes as potential therapeutics for chronic neuropathic pain, and identify a receptor mechanism in the spinal cord for this activity.

IVIVC of Octreotide in PLGA-Glucose Microsphere Formulation, Sandostatin® LAR

In vitro-in vivo correlation (IVIVC) analysis reveals a relationship between in vitro release and in vivo pharmacokinetic response of the drug of interest. Sandostatin LAR Depot (SLD) for endocrine tumors and acromegaly is a sustained-release formulation of octreotide, a cyclic oligomer of 8 amino acids, which prolongs therapeutic efficacy and enhances medication compliance of octreotide. Since the efficacy of SLD is dependent on the pharmacokinetic characteristics of octreotide released from a biodegradable matrix polymer, poly(lactide-co-glycolide)-glucose, of SLD, the IVIVC of SLD is critical for predicting an in vivo behavior of the octreotide. In this study, in vitro release of octreotide from SLD was investigated using the release test media each containing 0.02% or 0.5% surfactant and having different pH values of 7.4 and 5.5. In vivo pharmacokinetic profiles of SLD were determined by LC-MS/MS analysis of the systemic blood concentration of octreotide after the SLD injection to rodents. In IVIVC analysis, the Weibull model was adopted as a drug release model for biodegradable microsphere formulation. The IVIVC analyses revealed the in vitro release test condition of SLD with the highest IVIV correlation coefficient. By applying the in vitro release data to the model derived from the IVIVC analysis, pharmacokinetic parameters of SLD could be predicted with the prediction error of ± 10 ~ 15%. IVIVC analysis and pharmacokinetic prediction model of SLD in our study can be an efficient tool for the development of long-acting pharmaceutical dosage forms.

Bridging the gap between fundamental research and product development of long acting injectable PLGA microspheres

INTRODUCTION

Long acting Injectable PLGA microspheres have gained more and more interest and attention in the field of life cycle management of pharmaceutical products due to their biocompatibility and biodegradability. So far, a multitude of trial-and-error experiments at lab scale have been used for establishing the correlation relationship between critical process parameters, critical material attributes and critical quality attributes. However, few published studies have elaborated on the development of PLGA microspheres from an industrial perspective.

AREAS COVERED

In this review, the scale-up feasibility of translational technologies of PLGA microspheres manufacturing have been evaluated. Additionally, state-of-the-art of technologies and facilities in PLGA development have been summarized. Meanwhile, the industrial knowledge matrix of PLGA microspheres development and research are establishing which provide comprehensive insight for understanding properties of PLGA microspheres as controlled/sustained release vehicle.

EXPERT OPINION

There is still big gap between fundamental research in academic institute and product development in pharmaceuticals. Therefore, the difference and connection between them should be identified gradually for better understanding of PLGA microspheres development.

Glycosylated Ang-(1-7) MasR Agonist Peptide Poly Lactic-co-Glycolic Acid (PLGA) Nanoparticles and Microparticles in Cognitive Impairment: Design, Particle Preparation, Physicochemical Characterization, and In Vitro Release

Heart failure (HF) causes decreased brain perfusion in older adults, and increased brain and systemic inflammation increases the risk of cognitive impairment and Alzheimer’s disease (AD). Glycosylated Ang-(1-7) MasR agonists (PNA5) has shown improved bioavailability, stability, and brain penetration compared to Ang-(1-7) native peptide. Despite promising results and numerous potential applications, clinical applications of PNA5 glycopeptide are limited by its short half-life, and frequent injections are required to ensure adequate treatment for cognitive impairment. Therefore, sustained-release injectable formulations of PNA5 glycopeptide are needed to improve its bioavailability, protect the peptide from degradation, and provide sustained drug release over a prolonged time to reduce injection administration frequency. Two types of poly(D,L-lactic-co-glycolic acid) (PLGA) were used in the synthesis to produce nanoparticles (≈0.769−0.35 µm) and microparticles (≈3.7−2.4 µm) loaded with PNA5 (ester and acid-end capped). Comprehensive physicochemical characterization including scanning electron microscopy, thermal analysis, molecular fingerprinting spectroscopy, particle sizing, drug loading, encapsulation efficiency, and in vitro drug release were conducted. The data shows that despite the differences in the size of the particles, sustained release of PNA5 was successfully achieved using PLGA R503H polymer with high drug loading (% DL) and high encapsulation efficiency (% EE) of >8% and >40%, respectively. While using the ester-end PLGA, NPs showed poor sustained release as after 72 h, nearly 100% of the peptide was released. Also, lower % EE and % DL values were observed (10.8 and 3.4, respectively). This is the first systematic and comprehensive study to report on the successful design, particle synthesis, physicochemical characterization, and in vitro glycopeptide drug release of PNA5 in PLGA nanoparticles and microparticles.

Journey to the Market: The Evolution of Biodegradable Drug Delivery Systems

Biodegradable polymers have been used as carriers in drug delivery systems for more than four decades. Early work used crude natural materials for particle fabrication, whereas more recent work has utilized synthetic polymers. Applications include the macroscale, the microscale, and the nanoscale. Since pioneering work in the 1960’s, an array of products that use biodegradable polymers to encapsulate the desired drug payload have been approved for human use by international regulatory agencies. The commercial success of these products has led to further research in the field aimed at bringing forward new formulation types for improved delivery of various small molecule and biologic drugs. Here, we review recent advances in the development of these materials and we provide insight on their drug delivery application. We also address payload encapsulation and drug release mechanisms from biodegradable formulations and their application in approved therapeutic products.

Antagonism of the mu-delta opioid receptor heterodimer enhances opioid antinociception by activating Src and calcium/calmodulin-dependent protein kinase II signaling

ABSTRACT

The opioid receptors are important regulators of pain, reward, and addiction. Limited evidence suggests the mu and delta opioid receptors form a heterodimer (MDOR), which may act as a negative feedback brake on opioid-induced analgesia. However, evidence for the MDOR in vivo is indirect and limited, and there are few selective tools available. We recently published the first MDOR-selective antagonist, D24M, allowing us to test the role of the MDOR in mice. We thus cotreated CD-1 mice with D24M and opioids in tail flick, paw incision, and chemotherapy-induced peripheral neuropathy pain models. D24M treatment enhanced oxymorphone antinociception in all models by 54.7% to 628%. This enhancement could not be replicated with the mu and delta selective antagonists CTAP, naltrindole, and naloxonazine, and D24M had a mild transient effect in the rotarod test, suggesting this increase is selective to the MDOR. However, D24M had no effect on morphine or buprenorphine, suggesting that only specific opioids interact with the MDOR. To find a mechanism, we performed phosphoproteomic analysis on brainstems of mice. We found that the kinases Src and CaMKII were repressed by oxymorphone, which was restored by D24M. We were able to confirm the role of Src and CaMKII in D24M-enhanced antinociception using small molecule inhibitors (KN93 and Src-I1). Together, these results provide direct in vivo evidence that the MDOR acts as an opioid negative feedback brake, which occurs through the repression of Src and CaMKII signal transduction. These results further suggest that MDOR antagonism could be a means to improve clinical opioid therapy.

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.

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.

Challenges of peptide and protein drug delivery by oral route: Current strategies to improve the bioavailability

Advancement in biotechnology provided a notable expansion of peptide and protein therapeutics, used as antigens, vaccines, hormones. It has a prodigious potential to treat a broad spectrum of diseases such as cancer, metabolic disorders, bone disorders, and so forth. Protein and peptide therapeutics are administered parenterally due to their poor bioavailability and stability, restricting their use. Hence, research focuses on the oral delivery of peptides and proteins for the ease of self-administration. In the present review, we first address the main obstacles in the oral delivery system in addition to approaches used to enhance the stability and bioavailability of peptide/protein. We describe the physiochemical parameters of the peptides and proteins influencing bioavailability in the systemic circulation. It encounters, many barriers affecting its stability, such as poor cellular membrane permeability at the GIT site, enzymatic degradation (various proteases), and first-pass hepatic metabolism. Then describe the current approaches to overcome the challenges mentioned above by the use of absorption enhancers or carriers, structural modification, formulation and advance technology.

Preparation of long-acting microspheres loaded with octreotide for the treatment of portal hypertensive

The purpose of this study was to optimize the preparation method of injectable Octreotide microspheres. To explore the correlation between the solvent system and the general properties of microspheres to reduce burst release and enable them to be used for portal hypertension. Octreotide microspheres were prepared by modified double emulsion solution evaporation method after optimizing preparation conditions. The results showed that Octreotide microspheres had a particle size of 57.48 ± 15.24 μm, and the initial release was significantly reduced. In vitro release and in vivo pharmacokinetic data indicated that Octreotide was released stably within 1200 h. The effects on portal vein pressure, liver tissue morphology and other related indexes were observed after administration. As obvious results, injection of Octreotide microspheres could significantly reduce portal vein pressure and reduce the portal vein lumen area in experimental cirrhotic portal hypertensive rats. The optimized Octreotide PLGA microsphere preparation has been proved to have a good effect on PHT in vivo after detecting aminotransferase (AST) and alanine aminotransferase (ALT) activity, liver tissue hydroxyproline (Hyp) content, serum and liver tissue malondialdehyde (MDA) levels, plasma prostacyclin (PGI₂) levels, and liver tissue tumor necrosis factor (TNFα) content. In addition, serum and liver tissue superoxide dismutase (SOD) activity and liver tissue glutathione (GSH) content, plasma thromboxane (TXA₂), serum nitric oxide (NO), liver tissue nitric oxide synthase (NOS), and plasma and liver tissue endothelin (ET) were significantly increased.

Comparison of three in-situ gels composed of different oil types

A phospholipid-based phase separation in-situ gel (PPSG) system, which consists of phospholipids, medium chain oil (triglyceride) and ethanol as basic ingredients, has been previously developed in our lab. In addition, glycerol monooleate (monoglyceride) and glycerol dioleate (diglyceride) were also reported to be able to form liquid crystal gels. Monoglyceride, diglyceride and triglyceride have different degrees of hydroxyl substitution in glycerol and therefore different amphiphilic properties, which may cause different properties of gels composed of them. In this experiment, glycerol monooleate (GMO), glycerol dioleate (GDO) and glycerol trioleate (GTO) were selected to prepare three kinds of PPSGs. We systematically studied their in-vitro and in-vivo physicochemical properties and investigated their drug release behavior with octreotide (OCT) as the model drug. The results showed that PPSG composed of GTO (GTO-gel) had a different microstructure, a slower solvent diffusion speed and the less irritation to skin. In addition, the drug release result showed that the GTO-gel group had a lower initial release rate and a more stable release profile. All results above indicated that GTO-gel had a greater potential as a drug delivery system.

Release mechanisms of bovine serum albumin loaded-PLGA microspheres prepared by ultra-fine particle processing system

The ultra-fine particle processing system (UPPS) previously developed by our lab has been used to prepare various microparticulate formulations. Microspheres prepared by UPPS can achieve sustained release with a reduced initial burst compared to the microspheres prepared by the conventional water-in-oil-in-water (W/O/W) double emulsion technique. However, the in vitro drug release mechanism of the microspheres prepared by UPPS is still uninvestigated. This study aimed to investigate the mechanisms of bovine serum albumin (BSA) released from poly (D,L-lactic-co-glycolic acid) (PLGA) microspheres prepared by UPPS in comparison with microspheres prepared by the W/O/W double emulsion technique. The morphology, in vitro drug release, water uptake, and structural evolution of microspheres prepared by both techniques were evaluated. UPPS microspheres showed solid and compact internal structures without any pores or channels thereby exhibiting a reduced rate of water permeation in the release medium. In addition, the release of BSA in UPPS microspheres was mainly controlled by the erosion of the polymer matrix during the entire process, while BSA was released from W/O/W microspheres by both drug diffusion and matrix erosion. Moreover, the observed surface and internal structural evolution also confirmed their different release mechanisms. This work elaborates the release mechanism of PLGA microspheres prepared by UPPS and facilitates the design of microparticulate formulations. Graphical abstract.

Peptide-Based Therapeutics for Oncology

The development of peptide-based drugs, which are usually synthetic analogues of endogenous peptides, is currently one of the most topical directions in drug development. Among them, antitumor peptide-based drugs are of great interest. Anticancer peptides can be classified into three main groups based on their mechanism of action: inhibitory, necrosis-inducing and pro-apoptotic peptides. As an antitumor therapy, peptides are considered to have at least the same efficacy as chemotherapy or surgical treatment, but offer advantages in terms of safety and tolerability, given that chemotherapy is usually characterized by severe adverse effects, and surgery carries additional risks for patients. Short peptides have a number of benefits over other molecules. First, compared with full-length proteins and antibodies, short peptides are less immunogenic, more stable ex-vivo (prolonged storage at room temperature), and have better tumor or organ permeability. Moreover, the production of such short peptide-based drugs is more cost effective. Second, in comparison with small organic molecules, peptides have higher efficacy and specificity. Finally, due to the fact that the main products of peptide metabolism are amino acids, these drugs are usually characterized by lower toxicity. Short peptides have a highly selective mechanism of action, thereby demonstrating low toxicity. Furthermore, with the addition of different stabilizing structural modifications, as well as novel drug delivery systems, the peptide-based drugs are proving to be promising therapeutics for cancer mono- or polytherapy. However, challenges remain including that endogenous and synthetic peptide molecules can be oncogenic. Therefore, it is important to investigate whether peptides contribute to tumor growth. In order to answer such questions, numerous preclinical and clinical studies of peptide-based therapeutics are currently being conducted.

Development of Octreotide-Loaded Chitosan and Heparin Nanoparticles: Evaluation of Surface Modification Effect on Physicochemical Properties and Macrophage Uptake

Octreotide (OCT) is a therapeutic peptide which is administered for the treatment of acromegaly. The purpose of this study was to design a new polyethylene glycol (PEG)-conjugated nanoparticle (PEG-NP) to overcome the short half-life and poor stability of OCT. The developed PEG-NPs were compared with non-PEGylated NPs with respect to their size, morphological characteristics, loading efficiency, release profile, and macrophage uptake. The OCT-loaded NPs and PEG-NPs were prepared by ionic complexion of chitosan (Cs) with either heparin (Hp) or PEGylated heparin (PEG-Hp). The chemical structure of PEG-Hp was confirmed by IR and proton nuclear magnetic resonance. Morphological analyses by scanning electron microscopy showed that NPs and PEG-NPs have a uniform shape. Dynamic laser scattering measurements indicated that hydrodynamic diameter of NPs and PEG-NPs were 222.5 ± 10.0 nm and 334.9 ± 6.7 nm, respectively. NPs and PEG-NPs had a positive zeta potential of about 32.5 ± 1.1 mv and 20.6 ± 2.4 mv, respectively. Entrapment efficiency was 61.4 ± 1.0% and 55.7 ± 2.4% for NPs and PEG-NPs, respectively. Compared with the NPs, the PEG-NPs exhibited a slower release profile. Subsequently, fluorescein isothiocyanate-labeled chitosanCs was synthesized and used to evaluate the stealth characteristic of PEG-NPs. In vitro macrophage uptake of fluorescently labeled NPs was measured by flow cytometry.

Long-acting intraocular Delivery strategies for biological therapy of age-related macular degeneration

As one of the leading causes of central vision loss in elderly population, worldwide cases of age-related macular degeneration (AMD) have seen a dramatic increase over the past several years. Treatment regimens for AMD, especially with biological agents, are complicated due to anatomical and physiological barriers, as well as administration of high doses and frequent regimens. Some clinical examples include monthly intravitreal administration of anti-VEGF antibody ranibizumab (Lucentis®) from Genentech and aflibercept (Eylea®) from Regeneron Pharmaceuticals. Long-acting sustained intraocular drug delivery provides promising solutions, such as Vitrasert® from Bausch & Lomb, an intravitreal biodegradable polymeric implant made from poly(D,L-lactic co glycolic acid) (PLGA), and can be used as a guiding reference to formulate sustained delivery systems. In this review, we discuss the anatomy and physiology of the eye, barriers to delivery, pathology of AMD, opportunities for biological therapeutics, and future prospects of intraocular delivery strategies that are in development for treatment of AMD.

Poly(lactic-co-glycolic acid) devices: Production and applications for sustained protein delivery

Injectable or implantable poly(lactic-co-glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow-release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion-based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein-laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high-throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion-based methods to emerging methods to fabricate protein-laden devices. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Peptide-Based Structures.

Injectable sustained release PLA microparticles prepared by solvent evaporation-media milling technology

The objective of this study was to develop agomelatine (AGM) intramuscular sustained release PLA microparticles by using solvent evaporation combined with wet milling technology. The final preparation had a regular and homogeneous particle size of approximately 35 µm, as measured by laser diffraction particle size analysis and scanning electron microscopy (SEM). The drug was confirmed to be within the carrier in an amorphous state through differential scanning calorimetry (DSC) and power X-ray diffraction (PXRD) experiments. Additionally, Fourier transform infrared spectroscopy (FT-IR) analysis was applied to confirm that there was hydrogen bonding between the drug and polymer at the molecular level. In vitro release experiments indicated that the drug could achieve long-term sustained release over the period of one month, with only a 3.07% burst release, due to the involvement of the polymer and removal of drug adsorbed on the surface during the wet grinding process. The dominant release mechanism was considered to be diffusion of the drugs in the initial period. Following this, with the hydrolysis of PLA to form a colloidal viscous layer, drug release is due to the combined effect of diffusion and erosion of the polymer matrix. Additionally, drug release behavior is closely related to the degradation mechanism of the polymer carrier. The results suggest that AGM could be developed as a potential delivery system for long-acting intramuscular administration with extensive application prospects.

Injectable Sustained-Release Depots of PLGA Microspheres for Insoluble Drugs Prepared by hot-Melt Extrusion

PURPOSE

Progesterone (PRG) was selected as a model drug to develop a long-acting injection system for poorly water-soluble drugs.

METHODS

Microspheres with high density-low porosity were prepared by hot-melt extrusion (HME) combined with wet-milling as the representative formulation, and a microcrystal suspension was also studied as a comparison. The morphology, particle size and distribution, polymorphism, drug distribution, density and porosity were characterized by scanning electron microscopy, laser diffraction particle size analyzer, power X-ray diffraction and DSC respectively. The in vivo performance of the different formulations within 7 days after intramuscular injection was evaluated in male SD rats.

RESULTS

The drug-loading rate of the microspheres could be as high as 40%. The average initial burst release of the microspheres (PLGA lactide:glycolide = 75:25) was only 6.7% much lower than that of the microsuspension (25.7%) and a sustained release was exhibited for at least 7 days. The release mechanism was speculated to be as follows. The microspheres are a drug depot with drug microcrystals in the PLGA matrix which is a layer by layer honeycomb structure.

CONCLUSIONS

Microspheres prepared by HME combined with wet-milling could achieve a long-term sustained release effect as a novel long-acting formulation strategy.

New therapeutic agents for acromegaly

The currently available somatostatin receptor ligands (SRLs) and growth hormone (GH) antagonists are used to control levels of GH and insulin-like growth factor 1 (IGF-1) in patients with acromegaly. However, these therapies are limited by wide variations in efficacy, associated adverse effects and the need for frequent injections. A phase III trial of oral octreotide capsules demonstrated that this treatment can safely sustain suppressed levels of GH and IGF-1 and reduce the severity of symptoms in patients with acromegaly previously controlled by injectable SRL therapy, with the added benefit of no injection-site reactions. Phase I and phase II trials of the pan-selective SRL DG3173, the liquid crystal octreotide depot CAM2029 and an antisense oligonucleotide directed against the GH receptor have shown that these agents can be used to achieve biochemical suppression in acromegaly and have favourable safety profiles. This Review outlines the need for new therapeutic agents for patients with acromegaly, reviews clinical trial data of investigational agents and considers how these therapies might best be integrated into clinical practice.

The influence of spray-drying parameters on phase behavior, drug distribution, and in vitro release of injectable microspheres for sustained release

For ternary solid dispersions, it is indispensable to characterize their structure, phase behavior, and the spatial distribution of the dispersed drug as this might influence the release profile and/or stability of these formulations. This study shows how formulation (feed concentration) and process (feed rate, inlet air temperature, and atomizing air pressure) parameters can influence the characteristics of ternary spray-dried solid dispersions. The microspheres considered here consist of a poly(lactic-co-glycolic acid) (PLGA) surface layer and an underlying polyvinylpyrrolidone (PVP) phase. A poorly soluble active pharmaceutical ingredient (API) was molecularly dispersed in this matrix. Differences were observed in component miscibility, phase heterogeneity, particle size, morphology, as well as API surface coverage for selected spray-drying parameters. Observed differences are likely because of changes in the droplet generation, evaporation, and thus particle formation processes. However, varying particle characteristics did not influence the drug release of the formulations studied, indicating the robustness of this approach to produce particles of consistent drug release characteristics. This is likely because of the fact that the release is dominated by diffusion from the PVP layer through pores in the PLGA surface layer and that observed differences in the latter have no influence on the release.

In vivo evaluation of different formulation strategies for sustained release injectables of a poorly soluble HIV protease inhibitor

At present no scientific rationale exists for selecting a particular enabling strategy to formulate a poorly water-soluble drug, although this is crucial as it will influence the in vivo performance of the resulting formulation. This study provides an insight into this complicated decision making process for a poorly soluble human immunodeficiency virus (HIV) protease inhibitor based upon in vivo test results. A formulation strategy based on the molecular dispersion of this active pharmaceutical ingredient (API) into a biphasic matrix consisting of water-insoluble poly(lactic-co-glycolic acid) (PLGA) and water-soluble polyvinylpyrrolidone (PVP) was evaluated. The long-term in vivo performance of this strategy was compared to that of other solubility enhancing approaches by evaluating exposure of the API in male Beagle dogs. Solid dispersions, based on a PLGA/PVP matrix, were compared to solid dispersions in a pure PLGA matrix. Additionally these solid dispersion strategies were compared to the strategy of particle size reduction by means of an API microsuspension. The in vivo performance of the various formulations over a period of 28days after intramuscular injection was evaluated by the observed initial burst release, plasma concentration-time profiles, time at which maximum plasma levels were reached and the estimated bioavailability. Compared to the other formulation strategies assessed, it was concluded that the addition of PVP in a PLGA matrix resulted in vivo in a more sustained release as well as a higher amount of drug released from the polymeric matrix. This was explained based on the structure of these binary PLGA/PVP matrices where the pore network originating from rapidly dissolving PVP plays a key role. Moreover, the results suggest that the API release from this type of formulation could be delayed by increasing the amount of PLGA in the formulation.