Optimizing Zinc-HisTag Coordination Remote Loading of Proteins in PLGA Microspheres

Metal-HisTag coordination remote loading (MHCRL) of proteins in PLGA microspheres was previously developed to provide a useful tool for discovery and preclinical development of controlled release protein formulations. Here we describe optimization of MHCRL, including (1) reducing thermal stress, (2) decreasing the complexity and duration of the procedure, (3) increasing loading capacity, (4) increasing the penetration depth of protein, and (5) improving the release profile. Directly encapsulating ZnCO₃as a Zn²⁺source for HisTag coordination, rather than remotely loading Zn²⁺, increased the Zn content ∼6-fold. Microspheres with directly encapsulated ZnCO₃more deeply encapsulated green fluorescent protein and more efficiently encapsulated human serum albumin at protein loading solutions concentrations ≥ 100 μg/mL than remotely loaded Zn²⁺microspheres. Tributyl acetylcitrate plasticized microspheres in terms of decreasingT_g, but led to a decrease in protein encapsulation efficiency. As such, the plasticizer was not deemed useful. The loading/healing cycles were reduced in time and temperature from 48h/42h at 43°C to 2h/6h at 37°C while maintaining strong encapsulation efficiency, resulting in significantly improved protein stability. Immunoreactive protein was slowly released for months following a modest burst release. The improved microspheres and shorter, low-temperature encapsulation could be a valuable asset to drug discovery scientists interested in controlled release of delicate and/or costly biologic candidates.

Preparation of siRNA-PLGA/Fab'-PLGA mixed micellar system with target cell-specific recognition

Small interfering RNAs (siRNAs) are susceptible to nucleases and degrade quickly in vivo. Moreover, siRNAs demonstrate poor cellular uptake and cannot cross the cell membrane because of its polyanionic characteristics. To overcome these challenges, an intelligent gene delivery system that protects siRNAs from nucleases and facilitates siRNA cellular uptake is required. We previously reported the potential of siRNA-poly(D,L-lactic-co-glycolic acid; PLGA) micelles as an effective siRNA delivery tool in a murine peritoneal dissemination model by local injection. However, there was no effective formulation for siRNA delivery to target cells via intravenous injection. This study aimed to prepare siRNA-PLGA/Fab'-PLGA mixed micelles for siRNA delivery to target floating cells and evaluate its formulation in vitro. As the target siRNA protein in CEMx174, CyclinB1 levels were significantly reduced when siRNA-PLGA/Fab'-PLGA mixed micelles were added to cells compared with siRNA-PLGA micelles. siRNA-PLGA/Fab'-PLGA mixed micelles have high cell permeability and high target cell accumulation by endocytosis because flow cytometry detected labeling micelles in target cells. This study supports siRNA-PLGA/Fab'-PLGA mixed micelles as an effective siRNA delivery tool. This formulation can be administered systemically in dosage form against target cells, including cancer metastasis or blood cancer.

Enhancing the anticancer efficacy of a LL-37 peptide fragment analog using peptide-linked PLGA conjugate micelles in tumor cells

LL-37, a well-known antimicrobial human peptide, is a cationic peptide that provides an important antimicrobial defense mechanism in damaged skin. Accumulating evidence indicates that LL-37 also displays an anticancer effect in colon cancer, gastric cancer, hematologic malignancy and oral squamous cell carcinoma. However, anticancer activity of LL-37 peptide fragment analogs has not been reported. Poor intercellular translocation may be one of the causes for this lack of observed anticancer activity. In this study, a LL-37 peptide fragment analog with cysteine at the N-terminus was conjugated with the biodegradable polymer, lactic acid/glycolic acid copolymer (PLGA), using the thiol group of cysteine. The purpose of this study was to improve the cell permeability of the peptide using a micellar system and then evaluate the anticancer activity. Cell proliferation, migration, and invasion assays were performed to evaluate the anticancer activity in four cancer cell lines with high metastasis, HM-1, B16/BL6, HeLa, and HepG2. The LL-37 fragment peptide analog-linked PLGA conjugate was shown to effectively inhibit cell proliferation, migration, and invasion and had increased cell permeability in all the cancer cell lines, compared with the peptide alone. These results suggested that LL-37 fragment peptide analog (CKR12)-linked PLGA conjugate micelles could be useful in the development of cancer therapeutics.

Developing a Model for a siRNA Delivery System by Cancer Implantation into Zebrafish Circulation

In recent decades, zebrafish (Danio rerio) has become a major in vivo model for the evaluation of drug efficacies and toxicities. In the field of drug delivery research, zebrafish larvae are a suitable model for the use of fluorescent-labeled chemicals, nanoparticle, liposome, or micelle-mediated delivery systems because of their transparent body wall. In the current chapter, we describe the method to perform micelle-based siRNA delivery using cancer cells implanted into the circulation of zebrafish.

Modification of Three-Phase Drug Release Mode of Octreotide PLGA Microspheres by Microsphere-Gel Composite System

In order to obtain sustained release of biodegradable microspheres, the purpose of this study was to design and characterize an injectable octreotide microsphere-gel composite system. The octreotide microspheres were prepared by phase separation method, which used PLGA as a carrier material, dimethyl silicone oil as a phase separation reagent, and n-heptane-Span 80 as a hardener. In addition, we used poloxamer 407 (PL 407) and poloxamer 188 (PL 188) as the thermosensitive gel matrix material. The composite system was obtained by scattering octreotide microspheres in a poloxamer gel. In vitro data showed that the release time of the composite system could last for about 50 days. Because of the blocking and control actions of the poloxamer gel, the initial burst release was significantly reduced and the plateau phase was eliminated. Pharmacokinetic data showed that the burst release of the composite system was significantly less than that of the microspheres, i.e., Cmax1 was reduced by about half. From day 2 to day 50, higher plasma concentration levels and more stable drug release behavior were exhibited. In addition, the good biocompatibility of the composite system in vivo was also demonstrated by hematoxylin-eosin (HE) staining. Therefore, the octreotide microsphere-gel composite system will be a new direction for hydrophilic polypeptide/protein-loaded sustained release dosage forms with high pharmacological activity.

Preparation and Characterization of Itraconazole- or Miconazole-Loaded PLGA Microspheres

The purpose of this study was to prepare poly(lactide-co-glycolide) (PLGA) microspheres (MS) loaded with itraconazole (ITCZ) or miconazole (MCZ) under different evaporation temperatures (25 or 40°C) using an oil-in-water emulsion solvent evaporation method in order to evaluate the initial burst release of drug. Loading efficiencies were comparatively good and the diameters of prepared drug-loaded PLGA MS were around 20 µm in all formulations. The release rates of ITCZ-PLGA MS prepared at 40°C showed a significantly restricted release profile compared with the corresponding ITCZ-PLGA MS prepared at 25°C. This difference in release rate of ITCZ was thought to be caused by the self-healing effect of PLGA, as the glass transition temperature of PLGA is around 40°C. With respect to the MCZ-PLGA MS, the initial burst release was similar in formulations prepared at both 25 and 40°C. Scanning electron microscope results suggested that the initial burst release was due to the localization of MCZ on the surface of MCZ-PLGA MS at higher concentrations. Differential scanning calorimetry measurements suggested complete amorphization of MCZ in MCZ-PLGA MS, whereas crystalline ITCZ was detected in the ITCZ-PLGA MS. This complete amorphization of MCZ is considered to be one of the reasons for the initial burst release.