Biodegradable thermogelling hydrogel of P(CL-GL)-PEG-P(CL-GL) triblock copolymer: degradation and drug release behavior

A thermo-sensitive, injectable and biodegradable in situ hydrogel as a potential formulation for uveitis treatment

The thermo-sensitive hydrogels with high drug loading rate achieved sustained drug release over 2 weeks. Histopathological examination of retina confirmed the excellent biocompatibility and effective anti-inflammatory property of the hydrogel.

Novel Random Triblock Copolymers for Sustained Delivery of Macromolecules for the Treatment of Ocular Diseases

The objective of this study is to design, develop, and synthesize novel random triblock (RTB) copolymers for sustained delivery of macromolecules. RTB copolymers have not been utilized for the delivery of macromolecules for ocular diseases. RTB copolymers comprising of polyethylene glycol, glycolide, and ɛ-caprolactone blocks were synthesized and assessed for their molecular weights and purity using ¹H-NMR spectroscopy, gel permeation chromatography, FTIR (functionality), and XRD (crystallinity). No toxicity was observed when ocular cell lines were treated with RTB copolymers. These materials were applied for encapsulation of peptides and proteins (catalase, IgG, BSA, IgG Fab fragment, lysozyme, insulin, and octreotide) in nanoparticles. Particle size ranged from 202.41 ± 2.45 to 300.1 ± 3.11 nm depending on the molecular size and geometry of proteins/peptides. Polydispersity indices were between 0.26 ± 0.02 and 0.46 ± 0.07 respectively. Percentage entrapment efficiency and drug loading ranged from 83.44 ± 2.24 to 45.35 ± 5.53 and 21.56 ± 0.46 to 13.08 ± 1.35 respectively depending on molecular weights of peptides or proteins. A sustained in vitro release of macromolecule was observed over 3-month period. These results suggest that RTB copolymers may be suitable for sustained delivery systems for various macromolecules for different diseases including ocular diseases.

Evaluation of Intracameral Pentablock Copolymer Thermosensitive Gel for Sustained Drug Delivery to the Anterior Chamber of the Eye

PURPOSE

To investigate PTSgels (Pentablock copolymers) as an injectable formulation technology for sustained ocular drug delivery. Drug release profile, tolerability, and polymer degradation for one of the thermosensitive, biodegradable, and biocompatible compositions were investigated through intracameral (IC) injection in rabbits.

METHODS

New Zealand White rabbit eyes were injected IC (50 μL) with 100 μg near-infrared-immunoglobulin G (NIR-IgG) in balanced salt solution (BSS) or 20% PTSgel; or with PTSgel or BSS alone. Ocular irritation scoring, intraocular pressure (IOP), and corneal thickness (CT) measurement, as well as color and infrared photography, were performed for up to 28 days postinjection. Upon euthanasia at 7, 14, or 28 days, eyes underwent ex vivo imaging (Xenogen IVIS) followed by tissue fixation and histopathology.

RESULTS

IC injection of PTSgel (liquid at room temperature) was performed without difficulty using a 31G needle. The polymer quickly gelled in the IC space resulting in an inferior anterior chamber deposit. The tested PTSgel was well tolerated, with no significant changes in IOP or CT. Eyes injected with NIR-IgG in PTSgel had visible NIR-IgG through 9 days postinjection, and ex vivo imaging detected a strong NIR-IgG signal in the anterior chamber through day 28. The gel deposit steadily decreased in size over time and was nearly eliminated by 28 days.

CONCLUSIONS

The PTSgel released IgG for 28 days and was well tolerated. The polymer degraded in parallel with drug release. These results demonstrate the potential of intracameral PTSgel formulations for sustained delivery of biologic therapies to the ocular anterior segment.

Bactericidal Effect of Lauric Acid-Loaded PCL-PEG-PCL Nano-Sized Micelles on Skin Commensal Propionibacterium acnes

Acne is the over growth of the commensal bacteria Propionibacterium acnes (P. acnes) on human skin. Lauric acid (LA) has been investigated as an effective candidate to suppress the activity of P. acnes. Although LA is nearly insoluble in water, dimethyl sulfoxide (DMSO) has been reported to effectively solubilize LA. However, the toxicity of DMSO can limit the use of LA on the skin. In this study, LA-loaded poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) micelles (PCL-PEG-PCL) were developed to improve the bactericidal effect of free LA on P. acnes. The block copolymers mPEG-PCL and PCL-PEG-PCL with different molecular weights were synthesized and characterized using ¹H Nuclear Magnetic Resonance spectroscopy (¹H NMR), Fourier-transform infrared spectroscopy (FT-IR), Gel Permeation Chromatography (GPC), and Differential Scanning Calorimetry (DSC). In the presence of LA, mPEG-PCL diblock copolymers did not self-assemble into nano-sized micelles. On the contrary, the average particle sizes of the PCL-PEG-PCL micelles ranged from 50⁻198 nm for blank micelles and 27⁻89 nm for LA-loaded micelles. The drug loading content increased as the molecular weight of PCL-PEG-PCL polymer increased. Additionally, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of free LA were 20 and 80 μg/mL, respectively. The MICs and MBCs of the micelles decreased to 10 and 40 μg/mL, respectively. This study demonstrated that the LA-loaded micelles are a potential treatment for acne.

Long-term delivery of protein therapeutics

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Formulation strategies for sustained release of proteins

Proteins constitute an increasing proportion of the drugs in development. The barriers to their entry into the blood stream and rapid clearance means that they often have to be injected several times a day, affecting patient compliance. This paper reviews the major technologies enabling the development of injectable sustained-release products and formulation strategies to maintain protein integrity and modify release rates. Whilst many injectable sustained-release products are on the market, these are all delivering small molecular weight drugs and peptides. This is due to the manufacturing processes that denature and degrade the proteins upon encapsulation and release into the body. Formulation strategies are discussed and a number of new technologies reviewed that are able to overcome the issues with conventional manufacturing processes. The reliance of many processes on organic solvents has prevented their application to the development of injectable sustained release protein products. The development of entirely solvent free and aqueous methods of manufacture of these products has meant that numerous sustained-release protein products are close to reaching the market.

Effect of hydrophobic and hydrophilic additives on sol-gel transition and release behavior of timolol maleate from polycaprolactone-based hydrogel

The objective of this work was to delineate the effect of hydrophilic and hydrophobic polymeric additives on sol-gel transition and release profile of timolol maleate (TM) from poly (ethylene glycol)-poly (ε-caprolactone)- poly (ethylene glycol) (PEG-PCL-PEG)-based thermosensitive hydrogel. Polycaprolactone (hydrophobic additive) and polyvinyl alcohol (PVA) (hydrophilic additive) reduced critical gel concentration of PEG-PCL-PEG triblock polymer. The effect of PCL on sol-gel transition was more pronounced than PVA. However, with PCL no statistically significant difference in release profile was observed. The effect of PVA on release profile was more pronounced, which reduced the cumulative percentage release of TM from 86.4±0.8% to 73.7±1.8% over 316 h. Moreover, cytotoxicity of the hydrogel was also investigated utilizing rabbit primary corneal epithelial culture cells. No significant cytotoxicity of hydrogel alone or in presence of additives was observed. So, polymeric additive strategy serves as a valuable tool for optimizing TM release kinetics from PEG-PCL-PEG hydrogel matrix.

Solution formulation development of a VEGF inhibitor for intravitreal injection

PF-00337210 is a potent, selective small molecule inhibitor of VEGFRs and has been under consideration for the treatment of age-related macular degeneration. An ophthalmic solution formulation intended for intravitreal injection was developed. This formulation was designed to maximize drug properties such that the formulation would precipitate upon injection into the vitreous for sustained delivery. As a parenteral formulation with additional constraints dictated by this specialized delivery route, multiple features were balanced in order to develop a successful formulation. Some of these considerations included low dosing volumes (≤0.1 mL), a limited repertoire of safe excipients for intravitreal injection, and the unique physical chemical properties of the drug. The aqueous solubility as a function of pH was characterized, buffer stressing studies to select the minimal amount of buffer were conducted, and both chemical and physical stability studies were executed. The selected formulation consisted of an isotonic solution comprised of PF-00337210 free base in a citrate-buffered vehicle containing NaCl for tonicity. The highest strength for regulatory toxicology studies was 60 mg/mL. The selected formulation exhibited sufficient chemical stability upon storage with no precipitation, and acceptable potency and recovery through an intravitreal dosing syringe. Formulation performance was simulated by precipitation experiments using extracted vitreous humor. In simulated injection experiments, PF-00337210 solutions reproducibly precipitated upon introduction to the vitreous so that a depot was formed. To our knowledge, this is the first time that a nonpolymeric in situ-forming depot formulation has been developed for intravitreal delivery, with the active ingredient as the precipitating agent.