Ahn Na Koo

Tumor accumulation and antitumor efficacy of docetaxel-loaded core-shell-corona micelles with shell-specific redox-responsive cross-links.

A robust core-shell-corona micelle bearing redox-responsive shell-specific cross-links was evaluated as a carrier of docetaxel (DTX) for cancer therapy. The polymer micelles of poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-phenylalanine) (PEG-PLys-PPhe) in the aqueous phase provided the three distinct functional domains: the PEG outer corona for prolonged circulation, the PLys middle shell for disulfide cross-linking, and the PPhe inner core for DTX loading. The shell cross-linking was performed by the reaction of disulfide-containing cross-linkers with Lys moieties in the middle shells. The shell cross-linking did not change the micelle size or the spherical morphology. The shell cross-linked micelles exhibited enhanced serum stability. The DTX release from the DTX-loaded disulfide cross-linked micelles (DTX-SSCLM) was facilitated by increasing the concentration of glutathione (GSH). At an intracellular GSH level, DTX release was facilitated due to the reductive cleavage of the disulfide cross-links in the shell domains. The in vivo tissue distribution and tumor accumulation of the DTX-SSCLM that were labeled with a near-infrared fluorescence (NIRF) dye, Cy5.5, were monitored in MDA-MB231 tumor-bearing mice. Non-invasive real-time optical imaging results indicated that the DTX-SSCLM exhibited enhanced tumor specificity due to the prolonged stable circulation in blood and the enhanced permeation and retention (EPR) effect compared with the DTX-loaded non-cross-linked micelles (DTX-NCLM). The DTX-SSCLM exhibited enhanced therapeutic efficacy in tumor-bearing mice compared with free DTX and DTX-NCLM. The domain-specific shell cross-linking that is described in this work may serve as a useful guidance for enhancing the antitumor therapeutic efficacy of various polymer micelles and nano-aggregates.

Ketal Cross-Linked Poly(ethylene glycol)-Poly(amino acid)s Copolymer Micelles for Efficient Intracellular Delivery of Doxorubicin

A biocompatible, robust polymer micelle bearing pH-hydrolyzable shell cross-links was developed for efficient intracellular delivery of doxorubicin (DOX). The rationally designed triblock copolymer of poly(ethylene glycol)-poly(L-aspartic acid)-poly(L-phenylalanine) (PEG-PAsp-PPhe) self-assembled to form polymer micelles with three distinct domains of the PEG outer corona, the PAsp middle shell, and the PPhe inner core. Shell cross-linking was performed by the reaction of ketal-containing cross-linkers with Asp moieties in the middle shells. The shell cross-linking did not change the micelle size and the spherical morphology. Fluorescence quenching experiments confirmed the formation of shell cross-linked diffusion barrier, as judged by the reduced Stern-Volmer quenching constant (K(SV)). Dynamic light scattering and fluorescence spectroscopy experiments showed that shell cross-linking improved the micellar physical stability even in the presence of micelle disrupting surfactants, sodium dodecyl sulfate (SDS). The hydrolysis kinetics study showed that the hydrolysis half-life (t(1/2)) of ketal cross-links was estimated to be 52 h at pH 7.4, whereas 0.7 h at pH 5.0, indicating the 74-fold faster hydrolysis at endosomal pH. Ketal cross-linked micelles showed the rapid DOX release at endosomal pH, compared to physiological pH. Confocal laser scanning microscopy (CLSM) showed that ketal cross-linked micelles were taken up by the MCF-7 breast cancer cells via endocytosis and transferred into endosomes to hydrolyze the cross-links by lowered pH and finally facilitate the DOX release to inhibit proliferation of cancer cells. This ketal cross-linked polymer micelle is promising for enhanced intracellular delivery efficiency of many hydrophobic anticancer drugs.

Catechol-functionalized adhesive polymer nanoparticles for controlled local release of bone morphogenetic protein-2 from titanium surface.

We report on a novel surface functionalization approach to equip the titanium (Ti) surfaces with osteogenic properties. A key feature of the approach is the treatment of the Ti surfaces with Ti-adhesive nanoparticles that can stably load and controllably release bone morphogenetic protein-2 (BMP-2). Ti-adhesive nanoparticles were prepared by self-assembly of a catechol-functionalized poly(amino acid) diblock copolymer, catechol-poly(L-aspartic acid)-b-poly(L-phenylalanine) (Cat-PAsp-PPhe). The nanoparticles consist of Ti-adhesive peripheral catechol groups, anionic PAsp shells, and PPhe inner cores. Field-emission scanning electron microscopy (Fe-SEM) images showed that the Ti-adhesive nanoparticles could be uniformly immobilized on Ti surfaces. X-ray photoelectron spectroscopy (XPS) confirmed the successful anchoring of nanoparticles onto Ti surfaces. After surface immobilization of the nanoparticles, the static water contact angle of the Ti substrate decreased from 75.3° to 50.0° or 36.4°, depending on the surface nanoparticle. Fluorescence microscopic analysis showed that BMP-2 could be effectively incorporated onto the Ti surface with adhesive nanoparticles. BMP-2 was controllably released for up to 40 days. The Ti substrate functionalized with BMP-2-incorporated nanoparticles significantly promoted attachment, proliferation, spreading, and alkaline phosphatase (ALP) activity of human adipose-derived stem cell (hADSC). The catechol-functionalized adhesive nanoparticles may be applied to various medical devices to create surfaces for improved performance.

Fabrication of Porous PLGA Microspheres with BMP-2 Releasing Polyphosphate-Functionalized Nano-Hydroxyapatite for Enhanced Bone Regeneration

AbstractThis paper introduces a novel bone-regenerative scaffold that is based on the systematic combination of porous polymer microspheres, nano-hydroxyapatite, and bone morphogenetic protein-2 (BMP-2), where each component was rationally incorporated to express its intrinsic activity in bone tissue formation. Poly(lactide-co-glycolide) (PLGA) microspheres, with interconnected pore structures, were fabricated by a gas-forming method in a water-in-oil-in-water double emulsion and solvent evaporation process. Polyphosphate-functionalized nano-hydroxyapatite (PP-n-HAp) was employed as a main component and was immobilized on the pore surface of the PLGA microspheres to controllably incorporate and release BMP-2. The surface polyphosphate functionalities of PP-n-HAp enabled the stable chemical immobilization of nano-hydroxyapatite (n-HAp) on the amine-treated pore surface of the PLGA microspheres. Field-emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) confirmed the nano-level exposure of n-HAp on the pore surface of the PLGA microspheres. BMP-2 with a positive charge was bound at a high efficiency onto the anionic phosphates of surface-immobilized PP-n-HAp and was controllably released for approximately 1 month. The release rate was manipulated by adjusting the amount of loaded BMP-2. The osteogenic differentiation and proliferation of human adipose-derived stem cells (hADSCs) within the n-HAp/BMP-2-incorporated microspheres were monitored in a dynamic 3D cell culture system. Histological, immunohistochemical, and quantitative real-time polymerase chain reaction (PCR) analyses showed that the PP-n-HAp-immobilized surface promoted cell adhesion/proliferation and osteoconduction. With its osteoinductive property, the sustained release of BMP-2 further enhanced the bone tissue regenerative activity of the porous microspheres.

Calcium Carbonate Mineralized Nanoparticles as an Intracellular Transporter of Cytochrome c for Cancer Therapy.

A new intracellular delivery system based on an apoptotic protein-loaded calcium carbonate (CaCO3 ) mineralized nanoparticle (MNP) is described. Apoptosis-inducing cytochrome c (Cyt c) loaded CaCO3 MNPs (Cyt c MNPs) were prepared by block copolymer mediated in situ CaCO3 mineralization in the presence of Cyt c. The resulting Cyt c MNPs had a vaterite polymorph of CaCO3 with a mean hydrodynamic diameter of 360.5 nm and exhibited 60% efficiency for Cyt c loading. The Cyt c MNPs were stable at physiological pH (pH 7.4) and effectively prohibited the release of Cyt c, whereas, at intracellular endosomal pH (pH 5.0), Cyt c release was facilitated. The MNPs enable the endosomal escape of Cyt c for effective localization of Cyt c in the cytosols of MCF-7 cells. Flow cytometry showed that the Cyt c MNPs effectively induced apoptosis of MCF-7 cells. These findings indicate that the CaCO3 MNPs can meet the prerequisites for delivery of cell-impermeable therapeutic proteins for cancer therapy.

Bone-regenerative activity of parathyroid hormone-releasing nano-hydroxyapatite/poly(L-lactic acid) hybrid scaffolds

We developed a bone-regenerative scaffold based on systematic combination of porous organic-inorganic hybrid scaffolds and recombinant human parathyroid hormone (rhPTH). The hybrid scaffold was fabricated by immobilization of polyphosphate-functionalized nano-hydroxyapatite (PP-n-HAp) on the surface of porous poly(L-lactic acid) (PLLA) scaffolds, which was followed by rhPTH loading on the polyphosphates of n-HAp surfaces. The surface polyphosphate functionalities of PP-n-HAp enabled the stable chemical immobilization of n-HAp on the amine-treated pore surface of the PLGA scaffolds. rhPTH with a positive charge was bound at a high efficiency of 98.1~99.5% onto the anionic polyphosphates of PP-n-HAp immobilized on PLLA surfaces and was sustainably released for up to 50 days. The release rate was manipulated by adjusting the amount of loaded rhPTH, and the release data were moderately fitted to the Higuchi’s diffusion model. Four types of scaffolds were tested in rabbit calvarias models (PLLA only, PP-n-HAp-PLLA, rhPTH (2 µg) loaded PP-n-HAp-PLLA, and rhPTH (10 µg) loaded PP-n-HAp-PLLA). After 5 weeks, rhPTH-loaded PP-n-HAp-PLLA (2 and 10 µg of rhPTH) displayed higher bone growth than the control (PLLA only) group. Nano-HAp and sustained release of rhPTH might be synergistically able to enhance the bone healing in the animal model.

Glutathione-mediated intracellular release of anti-inflammatory N-acetyl-L-cysteine from mesoporous silica nanoparticles

AbstractWe report on a smart mesoporous silica nanoparticle (MSN) that can trigger the release of anti-inflammatory N-acetyl-L-cysteine (NAC) within the intracellular environment. NAC was conjugated to the pore surfaces of MSNs through glutathione (GSH)-cleavable disulfide linkages. Solid-state nuclear magnetic resonance (NMR), Fourier-transform infrared (FTIR) spectroscopy, and Brunauer-Emmett-Teller (BET) analyses confirmed the successful NAC conjugation to the pore walls. The release of NAC from the NAC-conjugated MSN (MSN-NAC) could be controlled by adjusting the concentration of GSH regarding the release media. At an extracellular level of GSH (10 μM), the NAC release was greatly inhibited, whereas, at an intracellular level of GSH (2 mM), MSN-NAC facilitated the release of NAC. Confocal laser scanning microscopy (CLSM) studies showed that the NAC release was effectively triggered by intracellular GSH after uptake by BV-2 microglial cells. The MSN developed in this work may serve as the efficient intracellular carriers of NAC for the treatment of neuroinflammation.

Polymer therapeutics for treating cancer

Abstract: Bioactive polymers that can show direct or indirect effect in damaging cancer cells have attracted expanding interest in the pharmaceutical and biomedical fields, because they can play a major role in cytotoxicity for various cancer cells. The recent advances in this field of ‘polymer therapeutics’ have focused on two classes of bioactive polymers. One is the polyamine analogs that can inhibit cell growth and kill cancer cells. The other is the polymers that can eliminate multidrug resistance by inhibiting the function of P-glycoprotein (Pgp) and therefore indirectly enhance the anti-cancer efficacy of drugs in damaging cancer cells. Each class of polymers has unique mechanisms for cancer treatment and has been applied to treating a variety of cancers. This chapter deals with the background of the advent of ‘polymer therapeutics’ and a comprehensive review on the class of Pgp-inhibiting polymers as well as the polyamine analogs, structure–activity relationships, the mechanism for cytotoxicity, and their applications in cancer therapy.

Porous PLGA microspheres with BMP-2 releasing polyphosphate-functionalized nano-hydroxyapatite for enhanced bone regeneration

We report on bone-regenerative porous microspheres surface-decorated with polyphosphate-functionalized nano-hydroxyapatite (n-HAp) that can controllably release bone morphogenetic protein-2 (BMP-2). n-HAp was immobilized onto the pore surface of microspheres and could control the loading and the release of BMP-2.