Design of Hollow Hyaluronic Acid Cylinders for Sustained Intravitreal Protein Delivery.

A hollow cylinder intravitreal implant was developed to achieve sustained release of protein to the retina for the treatment of retinal diseases. Hollow cylinders were fabricated by molding and cross-linking hyaluronic acid, the major component of the vitreous humor. Hollow cylinders were filled with a concentrated protein solution, and the properties of the cylinder walls were tested. Cross-linked hyaluronic acid hydrogels with swelling degrees as low as 2.7 were achieved as a means to extend the release of protein. Hollow cylinders were capable of releasing an antigen-binding fragment for over 4 months at a maximum release rate of 4 µg per day. Protein release from hollow cylinders was modeled using COMSOL Multiphysics® software, and diffusion coefficients between 1.0 × 10-11 and 3.0 × 10-11 cm2/s yielded therapeutically effective levels of protein. Cylinders with a 1 mm outer radius were capable of loading >1 mg of protein while releasing at least 2.5 µg a day for over 4.5 months. Although smaller cylinders facilitate intravitreal placement, decreasing the cylinder radius severely limited drug loading. Design of hollow cylinder intravitreal implants must balance high drug loading to reduce device size with control of the diffusion coefficient to sustain protein release.

Thermogelling properties of purified poloxamer 407.

Poloxamers are triblock copolymers with a center block of hydrophobic polypropylene oxide (PPO) flanked by two hydrophilic polyethyleneoxide (PEO) blocks. Among this family of copolymers, poloxamer 407 is a non-ionic surfactant with reversible gelation properties above a particular polymer concentration and a particular temperature. Easy preparation of poloxamer 407 based sterile injectable formulations have made this copolymer a good candidate for drug delivery, specifically when controlled release of the drug is required. Previously, the applications of compendial poloxamer 407 preparations were demonstrated; however, low viscosity, poor elasticity, and sol-to-gel transition temperature (Tsol-gel) over a wide temperature range were observed. A purification process was introduced to eliminate impurities and low molecular weight copolymer molecules from the compendial poloxamer 407 resulting in higher viscosity values with Tsol-gel in a narrow temperature range. Here, poloxamer 407 was purified based on the proposed process and the rheological and analytical evaluation of the purified poloxamer 407 was conducted and compared to unpurified, compendial poloxamer 407. Then, the impact of poloxamer 407 concentration on gel formation was evaluated. For drug delivery applications, the effect of relevant buffer salts and the effect of addition of ethanol to the poloxamer 407 solutions were rheologically evaluated.

Thermosensitive Gel-Based Formulation for Intratumoral Delivery of Toll-Like Receptor 7/8 Dual Agonist, MEDI9197.

Toll-like receptor (TLR) agonists TLR 7/8, MEDI9197, is a imidazoquinoline analogue that can be used for cancer immunotherapy based on its efficacy toward a variety of tumors. Systemic administration of TLR agonists results in stimulation of the immune system throughout the entire body causing undesirable side effects. To minimize these adverse events, local administration of TLR agonists including intratumoral (IT) delivery has been introduced. Here, a poloxamer 407 thermogel formulation for IT delivery of a TLR 7/8 dual agonist, MEDI9197, is described in which the combination of the aqueous thermogel and the ethanolic TLR 7/8 dual agonist, MEDI9197, solution leads to precipitated drug particles within the gel. The in vitro release profile showed an initial burst followed by sustained release. A B16-OVA mouse tumor model was used to assess the in vivo pharmacokinetics, efficacy, and systemic cytokine and chemokine (cytokine) production of the poloxamer 407-based thermogel formulation. The pharmacokinetic evaluation showed that the agonist level within the tumor was reduced by ∼70% over 14 days while serum agonist levels indicated an initial burst at the 6-h time point followed by a drop in serum drug levels over the 14 days of the experiment. The tumor growth inhibition, survival, and serum cytokines for post-IT injection of the poloxamer 407 formulation showed that it slowly released TLR 7/8 agonist, MEDI9197, resulting in more efficacious tumor growth inhibition compared with control groups. In addition, the cytokine levels in circulation indicated that a dose increase led to a decrease in the serum inflammatory and interferon-inducible cytokines levels. This observation could be due to a reduction of drug diffusion and escape from the tumor site due to the precipitation of the drug inside the tumor leading to sustained release. IT delivery of TLR 7/8 dual agonist, MEDI9197, via a thermosensitive gel-based formulation was efficacious and could offer an alternate method of local drug delivery.

Engineered in-situ depot-forming hydrogels for intratumoral drug delivery.

Chemotherapy is the traditional treatment for intermediate and late stage cancers. The search for treatment options with minimal side effects has been ongoing for several years. Drug delivery technologies that result in minimal or no side effects with improved ease of use for the patients are receiving increased attention. Polymer drug conjugates and nanoparticles can potentially offset the volume of drug distribution while enhancing the accumulation of the active drug in tumors thereby reducing side effects. Additionally, development of localized drug delivery platforms is being investigated as another key approach to target tumors with minimal or no toxicity. Development of in-situ depot-forming gel systems for intratumoral delivery of immuno-oncology actives can enhance drug bioavailability to the tumor site and reduce systemic toxicity. This field of drug delivery is critical to develop given the advent of immunotherapy and the availability of novel biological molecules for treating solid tumors. This article reviews the advances in the field of engineered in-situ gelling platforms as a practical tool for local delivery of active oncolytic agents to tumor sites.

Structure, size, and solubility of antigen arrays determines efficacy in experimental autoimmune encephalomyelitis.

Presentation of antigen with immune stimulating "signal" has been a cornerstone of vaccine design for decades. Here, the antigen plus immune "signal" of vaccines is modified to produce antigen-specific immunotherapies (antigen-SITs) that can potentially reprogram the immune response toward tolerance of an autoantigen. The codelivery of antigen with a cell adhesion inhibitor using Soluble Antigen Arrays (SAgAs) was previously shown to slow or halt experimental autoimmune encephalomyelitis (EAE), a murine form of multiple sclerosis (MS). SAgAs are comprised of a hyaluronic acid backbone with cografted intercellular cell adhesion molecule-1 ligand derived from αL-integrin (CD11a237-246, "LABL") and an encephalitogenic epitope peptide of proteolipid protein (PLP139-151, "PLP"). Here, the physical characteristics of the carrier were investigated to evaluate how structure, size, and solubility drive the immune response when treating EAE. A bifunctional peptide (small, soluble), SAgAs (large, soluble), and PLGA nanoparticles (large, insoluble) all displaying PLP and LABL in equimolar ratios were compared. Maximum EAE suppression was achieved with coincident display of both peptides on a soluble construct.

Hyaluronic acid colloidal gels as self-assembling elastic biomaterials.

Hyaluronic acid (HA) is a naturally occurring biodegradable polymer with a variety of applications in medicine. The use of HA as a filler or scaffold for regenerating tissues often requires improving the elastic properties of HA. This is conventionally accomplished via chemical crosslinking, which might require the generation of toxic free radicals. Although the mechanical properties of the resulting gel material can be tuned, these types of materials are static and susceptible to mechanical failure. The aim of this study was to develop a colloidal system for scaffold fabrication that is held together by physical interactions between HA nanoparticles. HA nanoparticles composed of 17 kDa HA suspended in water at different concentrations (15%, 30%, and 45% w/v, respectively) formed a stable three-dimensional (3D) colloidal gel as a result of physical entanglement of free polymer chains on the surfaces of nanoparticles. The swelling ratio, shear moduli (G), compressive failure properties, and viscosity of colloidal gels were concentration dependent. The colloidal gels also were found to exhibit dynamic and recoverable properties, thus suggesting that these "self-associating colloids" offer characteristics distinct arising from crosslinked polymers or high concentration colloids.

Hyaluronic acid nanoparticles titrate the viscoelastic properties of viscosupplements.

Hyaluronic acid (HA) is a glycosaminoglycan with diverse biomedical applications including viscosupplementation of synovial fluid for the treatment osteoarthritis. Current HA viscosupplements such as Synvisc, Orthovisc, and Hyalgan have shown positive effects of reducing pain and improving joint function. The therapeutic efficacy, however, is highly transient, and these viscous fluids suffer from poor injectability. HA nanoparticles were found to modify the rheological properties of a model of the HA viscosupplement Orthovisc. Nanoparticles were successfully synthesized from 17 and 1500 kDa HA. Nanoparticle suspensions of HA were studied at different concentrations and in blends with the model viscosupplement. Nanoparticles made from 1500 kDa HA reduced the viscosupplement viscosity and elasticity to a much greater degree than nanoparticles made from 17 kDa HA. The difference in the nanoparticle effect on viscoelasticity suggested that nanoparticles made from 17 kDa HA may have dangling surface polymers that facilitated interactions with HA in solution. This hypothesis was supported by the greater compressibility of 17 kDa nanoparticles as determined by ultrasonic vibrational spectroscopy. Rheological investigations showed that the viscoelasticity of viscosupplements could be discretely titrated by modulating the concentration and type of HA nanoparticle additive (hard sphere or hairy). Thus, the injectability of viscosupplements may be enhanced while maintaining high elasticity.

Controlling ligand surface density optimizes nanoparticle binding to ICAM-1.

During infection, pathogens utilize surface receptors to gain entry into intracellular compartments. Multiple receptor-ligand interactions that lead to pathogen internalization have been identified and the importance of multivalent ligand binding as a means to facilitate internalization has emerged. The effect of ligand density, however, is less well known. In this study, ligand density was examined using poly(DL-lactic-co-glycolic acid) nanoparticles (PLGA NPs). A cyclic peptide, cLABL, was used as a targeting moiety, as it is a known ligand for intercellular cell adhesion molecule-1 (ICAM-1). To modulate the number of reactive sites on the surface of PLGA NPs, modified Pluronic with carboxyl groups and Pluronic with hydroxyl groups were combined in different ratios and the particle properties were examined. Utilizing a surfactant mixture directly affected the particle charge and the number of reactive sites for cLABL conjugation. The surface density of cLABL peptide increased as the relative amount of reactive Pluronic was increased. Studies using carcinomic human alveolar basal epithelial cells (A549) showed that cLABL density might be optimized to improve cellular uptake. These results complement other studies, suggesting that surface density of the targeting moiety on the NP surface should be considered to enhance the effect of ligands used for cell targeting.

"Soft" calcium crosslinks enable highly efficient gene transfection using TAT peptide.

PURPOSE: Typically, low molecular weight cationic peptides or polymers exhibit poor transfection efficiency due to an inability to condense plasmid DNA into small nanoparticles. Here, efficient gene delivery was attained using TAT/pDNA complexes containing calcium crosslinks. METHODS: Electrostatic complexes of pDNA with TAT or PEI were studied with increasing calcium concentration. Gel electrophoresis was used to determine DNA condensation. The morphology of the complexes was probed by transmission electron microscopy. Transfection efficiency was assessed using a luciferase reporter plasmid. The accessibility of phosphate and amine groups within complexes was evaluated to determine the effect of calcium on structure. RESULTS: TAT/pDNA complexes were condensed into small, 50-100 nm particles by optimizing the concentration of calcium. Complexes optimized for small size also exhibited higher transfection efficiency than PEI polyplexes in A549 cells. TAT and TAT complexes displayed negligible cytotoxicity up to 5 mg/mL, while PEI exhibited high cytotoxicity, as expected. Probing the TAT-Ca/pDNA structure suggested that calcium interacted with both phosphate and amine groups to compact the complexes; however, these "soft" crosslinks could be competitively disrupted to facilitate DNA release. CONCLUSION: Small and stable TAT-Ca/pDNA complexes were obtained via "soft" calcium crosslinks leading to sustained gene expression levels higher than observed for control PEI gene vectors. TAT-Ca/pDNA complexes were stable, maintaining particle size and transfection efficiency even in the presence of 10% of FBS. TAT-Ca complexes offer an effective vehicle offering potential for translatable gene delivery.

Particle size design of PLGA microspheres for potential pulmonary drug delivery using response surface methodology.

The large surface area, good vascularization, immense capacity for solute exchange and ultra-thinness of the alveolar epithelium are unique features of the lung facilitating systemic drug delivery via pulmonary administration. The efficacy and safety of many new and existing inhaled therapies may be enhanced through advanced controlled-release systems by using polymer particles. Poly (D,L-lactic-co-glycolic acid) (PLGA) is well known by its safety in biomedical preparations which has been approved for human use by the FDA. The optimum aerodynamic particle size distribution for most inhalation aerosols has generally been recognized to be in the range of 1-5 microns. PLGA microspheres, therefore, were prepared by a developed oil-in-oil solvent evaporation method and characterized. A four-factor, three levels Box-Behnken design was used for the optimization procedure with temperature, stirring speed, PLGA and surfactant concentration as independent variables. Particle size and polydispersity of microspheres were considered as dependent variables. PLGA microparticles were prepared successfully in desired size for pulmonary delivery by solvent evaporation method. It was found that the particle size of microspheres could be easily controlled. It was also proved that response surface methodology could efficiently be applied for size characterization and optimization of PLGA microparticles for pulmonary drug delivery.