Thavasyappan Thambi

Bioreducible Block Copolymers Based on Poly(Ethylene Glycol) and Poly(γ-Benzyl L-Glutamate) for Intracellular Delivery of Camptothecin

Poly(ethylene glycol)-b-poly(γ-benzyl L-glutamate)s bearing the disulfide bond (PEG-SS-PBLGs), which is specifically cleavable in intracellular compartments, were prepared via a facile synthetic route as a potential carrier of camptothecin (CPT). Diblock copolymers with different lengths of PBLG were synthesized by ring-opening polymerization of benzyl glutamate N-carboxy anhydride in the presence of a PEG macroinitiator (PEG-SS-NH(2)). Owing to their amphiphilic nature, the copolymers formed spherical micelles in an aqueous condition, and their particle sizes (20-125 nm in diameter) were dependent on the block length of PBLG. Critical micelle concentrations of the copolymers were in the range 0.005-0.065 mg/mL, which decreased as the block length of PBLG increased. CPT, chosen as a model anticancer drug, was effectively encapsulated up to 12 wt % into the hydrophobic core of the micelles by the solvent casting method. It was demonstrated by the in vitro optical imaging technique that the fluorescence signal of doxorubicin, quenched in the PEG-SS-PBLG micelles, was highly recovered in the presence of glutathione (GSH), a tripeptide reducing disulfide bonds in the cytoplasm. The micelles released CPT completely within 20 h under 10 mM GSH, whereas only 40% of CPT was released from the micelles in the absence of GSH. From the in vitro cytotoxicity test, it was found that CPT-loaded PEG-SS-PBLG micelles showed higher toxicity to SCC7 cancer cells than CPT-loaded PEG-b-PBLG micelles without the disulfide bond. Microscopic observation demonstrated that the disulfide-containing micelle could effectively deliver the drug into nuclei of SCC7 cells. These results suggest that PEG-SS-PBLG diblock copolymer is a promising carrier for intracellular delivery of CPT.

Hypoxia-responsive polymeric nanoparticles for tumor-targeted drug delivery

Hypoxia is a condition found in various intractable diseases. Here, we report self-assembled nanoparticles which can selectively release the hydrophobic agents under hypoxic conditions. For the preparation of hypoxia-responsive nanoparticles (HR-NPs), a hydrophobically modified 2-nitroimidazole derivative was conjugated to the backbone of the carboxymethyl dextran (CM-Dex). Doxorubicin (DOX), a model drug, was effectively encapsulated into the HR-NPs. The HR-NPs released DOX in a sustained manner under the normoxic condition (physiological condition), whereas the drug release rate remarkably increased under the hypoxic condition. From in vitro cytotoxicity tests, it was found the DOX-loaded HR-NPs showed higher toxicity to hypoxic cells than to normoxic cells. Microscopic observation showed that the HR-NPs could effectively deliver DOX into SCC7 cells under hypoxic conditions. In vivo biodistribution study demonstrated that HR-NPs were selectively accumulated at the hypoxic tumor tissues. As consequence, drug-loaded HR-NPs exhibited high anti-tumor activity in vivo. Overall, the HR-NPs might have a potential as nanocarriers for drug delivery to treat hypoxia-associated diseases.

Bioreducible shell-cross-linked hyaluronic acid nanoparticles for tumor-targeted drug delivery.

The major issues of self-assembled nanoparticles as drug carriers for cancer therapy include biostability and tumor-targetability because the premature drug release from and nonspecific accumulation of the drug-loaded nanoparticles may cause undesirable toxicity to normal organs and lower therapeutic efficacy. In this study, we developed robust and tumor-targeted nanocarriers based on an amphiphilic hyaluronic acid (HA)-polycaprolactone (PCL) block copolymer, in which the HA shell was cross-linked via a bioreducible disulfide linkage. Doxorubicin (DOX), chosen as a model anticancer drug, was effectively encapsulated into the nanoparticles with high drug loading efficiency. The DOX-loaded bioreducible HA nanoparticles (DOX-HA-ss-NPs) greatly retarded the drug release under physiological conditions (pH 7.4), whereas the drug release rate was markedly enhanced in the presence of glutathione, a thiol-containing tripeptide capable of reducing disulfide bonds in the cytoplasm. Furthermore, DOX-HA-ss-NPs could effectively deliver the DOX into the nuclei of SCC7 cells in vitro as well as to tumors in vivo after systemic administration into SCC7 tumor-bearing mice, resulting in improved antitumor efficacy in tumor-bearing mice. Overall, it was demonstrated that bioreducible shell-cross-linked nanoparticles could be used as a potential carrier for cancer therapy.

Bioreducible polymersomes for intracellular dual-drug delivery†

Stimuli-sensitive polymersomes, composed of amphiphilic block copolymers, have emerged as a promising nanocarrier for triggered release of anticancer drugs. In this study, we synthesized a bioreducible, amphiphilic triblock copolymer based on poly(ethylene glycol)-b-poly(lysine)-b-poly(caprolactone) bearing a disulfide bond (PEG-b-PLys-SS-PCL). Owing to its unique amphiphilicity, the copolymer formed self-assembled polymersomes (256 nm diameter) under aqueous conditions. These polymersomes were stable in physiological solution (pH 7.4), whereas they readily disintegrated under a reductive environment similar to an intracellular condition. The polymersomes could simultaneously encapsulate the hydrophobic camptothecin (CPT) in their membrane and the hydrophilic doxorubicin·hydrochloride (DOX·HCl) in their aqueous cores. The polymersomes released the drugs in a sustained manner under physiological conditions (pH 7.4), whereas the drug release rates dramatically increased in a reductive environment at 10 mM glutathione. From in vitro cytotoxicity tests, it was found that dual drug-loaded polymersomes showed significantly higher cytotoxicity to SCC7 cancer cells than those with the single drug. These results suggest that the polymersomes bearing the bioreducible linker have high potential as carriers for intracellular dual-drug delivery.

Bioreducible Carboxymethyl Dextran Nanoparticles for Tumor-Targeted Drug Delivery

Bioreducible carboxymethyl dextran (CMD) derivatives are synthesized by the chemical modification of CMD with lithocholic acid (LCA) through a disulfide linkage. The hydrophobic nature of LCA allows the conjugates (CMD-SS-LCAs) to form self-assembled nanoparticles in aqueous conditions. Depending on the degree of LCA substitution, the particle diameters range from 163 to 242 nm. Doxorubicin (DOX), chosen as a model anticancer drug, is effectively encapsulated into the nanoparticles with high loading efficiency (>70%). In vitro optical imaging tests reveal that the fluorescence signal of DOX quenched in the bioreducible nanoparticles is highly recovered in the presence of glutathione (GSH), a tripeptide capable of reducing disulfide bonds in the intracellular compartments. Bioreducible nanoparticles rapidly release DOX when they are incubated with 10 mm GSH, whereas the drug release is greatly retarded in physiological buffer (pH 7.4). DOX-loaded bioreducible nanoparticles exhibit higher toxicity to SCC7 cancer cells than DOX-loaded nanoparticles without the disulfide bond. Confocal laser scanning microscopy observation demonstrate that bioreducible nanoparticles can effectively deliver DOX into the nuclei of SCC7 cells. In vivo biodistribution study indicates that Cy5.5-labeled CMD-SS-LCAs selectively accumulate at tumor sites after systemic administration into tumor-bearing mice. Notably, DOX-loaded bioreducible nanoparticles exhibit higher antitumor efficacy than reduction-insensitive control nanoparticles. Overall, it is evident that bioreducible CMD-SS-LCA nanoparticles are useful as a drug carrier for cancer therapy.

Synthesis and physicochemical characterization of reduction-sensitive block copolymer for intracellular delivery of doxorubicin

AbstractAn amphiphilic diblock copolymer bearing the reduction-sensitive linker, composed of poly(ethylene glycol) (PEG) and hydrophobic poly(γ-benzyl L-glutamate) (PBLG), was prepared as the potential carrier of doxorubicin (DOX) via a facile synthetic method in the presence of a shell-sheddable PEG macroinitiator (PEG-SS-NH2). Owing to its amphiphilic nature, the copolymer (PEG-SS-PBLG) formed spherical micelles (137 nm in diameter) in aqueous conditions. The micelles were stable under the physiologic condition (pH 7.4) and were readily cleaved in the presence of glutathione (GSH), a tripeptide reducing the disulfide bond in the cytoplasm of the cell. DOX, chosen as a model anticancer drug, was effectively encapsulated into the hydrophobic core of the micelle with high loading efficiency (>75%). The micelle released DOX completely within 18 h at 10 mM GSH mimicking the intracellular condition, whereas only 34% of the drug was released from the micelle at 2 μM GSH. In vitro cytotoxicity tests revealed that DOX-loaded reduction-sensitive micelles are more toxic to SCC7 cells than reduction-insensitive control micelles. These results suggest that PEG-SS-PBLG is the promising carrier for the intracellular delivery of DOX.

Heparin-based temperature-sensitive injectable hydrogels for protein delivery

Stimuli-sensitive injectable hydrogels, composed of biodegradable copolymers, have emerged as prominent candidate materials for the sustained delivery of therapeutic drugs. In this study, we developed a biodegradable and temperature-sensitive injectable hydrogel system based on heparin-bearing poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (Hep-PCLA) as the carrier system for lysozyme. Hep-PCLA conjugates are capable of undergoing temperature-induced sol-to-gel transitions in an aqueous solution. The gelation rate, mechanical strength, and viscosity of Hep-PCLA conjugates are controllably tunable by varying the graft density of PCLA copolymers to heparin. The gel window in which Hep-PCLA forms a gel covers the physiological conditions (37 °C), i.e., free flowing Hep-PCLA in aqueous solutions (25 °C) could form a hydrogel at body temperature. Using an in vitro cytotoxicity test, Hep-PCLA conjugates were found to be non-toxic to fibroblast cells, even at high concentrations. Lysozyme, chosen as a model protein, was effectively loaded into Hep-PCLA conjugates using ionic and hydrophobic interactions. The lysozyme-loaded conjugates readily formed a hydrogel when implanted in the back of Sprague-Dawley rats, and retarded the initial burst of lysozyme release, exhibiting sustained release. Our results show that biodegradable, temperature-sensitive injectable Hep-PCLA hydrogels can be used as sustained protein carriers.

Poly(ethylene glycol)-b-poly(lysine) copolymer bearing nitroaromatics for hypoxia-sensitive drug delivery.

UNLABELLED Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, an amphiphilic block copolymer, composed of poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block, was prepared for hypoxia-sensitive drug delivery. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition, implying high potential as a drug carrier for cancer therapy. STATEMENT OF SIGNIFICANCE Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, we developed a novel type of hypoxia-sensitive polymeric micelles (HS-PMs) that can specifically release the drug under the hypoxic conditions. HS-PMs were prepared using poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition. Overall, it is evident that the HS-PMs prepared in this study have the potential to effectively deliver hydrophobic drugs into the hypoxic cells involved in various intractable diseases.

Stimuli-Sensitive Injectable Hydrogels Based on Polysaccharides and Their Biomedical Applications

Stimuli-sensitive injectable polymeric hydrogels are one of the promising delivery vehicles for the controlled release of bioactive agents. In aqueous solutions, these polymers are able to switch sol-to-gel transitions in response to various stimuli including pH, temperature, light, enzyme and magnetic field. Therapeutic agents, including chemotherapeutic agents, protein drugs or cells, are easily mixed with the low-viscous polymer solution at room temperature. Therapeutic-agents-containing solutions are readily injected into target sites through syringe or catheter, which could form hydrogel depot and serve as bioactive molecules release carriers. In particular, they are convenient for in vivo injection in a minimally invasive manner. Owing to their ease of handling, hydrogel scaffolds encapsulated with a wide array of therapeutic agents including growth factors, cells or fillers have been used in regeneration or filling of the defect area. Therefore, injectable hydrogels found a variety of biomedical applications, such as drug delivery and tissue engineering. Here, we summarize the chemical designs and recent developments of polysaccharide-based injectable hydrogels, giving a special attention to hydrogels prepared using amphiphilic polysaccharides for biomedical applications. Advantages and future perspectives of polysaccharide-based injectable hydrogels are highlighted.

Poly(amino carbonate urethane)-based biodegradable, temperature and pH-sensitive injectable hydrogels for sustained human growth hormone delivery

In this study, a new pH-/temperature-sensitive, biocompatible, biodegradable, and injectable hydrogel based on poly(ethylene glycol)-poly(amino carbonate urethane) (PEG-PACU) copolymers has been developed for the sustained delivery of human growth hormone (hGH). In aqueous solutions, PEG-PACU-based copolymers existed as sols at low pH and temperature (pH 6.0, 23 °C), whereas they formed gels in the physiological condition (pH 7.4, 37 °C). The physicochemical characteristics, including gelation rate, mechanical strength and viscosity, of the PEG-PACU hydrogels could be finely tuned by varying the polymer weight, pH and temperature of the copolymer. An in vivo injectable study in the back of Sprague-Dawley (SD) rats indicated that the copolymer could form an in situ gel, which exhibited a homogenous porous structure. In addition, an in vivo biodegradation study of the PEG-PACU hydrogels showed controlled degradation of the gel matrix without inflammation at the injection site and the surrounding tissue. The hGH-loaded PEG-PACU copolymer solution readily formed a hydrogel in SD rats, which subsequently inhibited the initial hGH burst and led to the sustained release of hGH. Overall, the PEG-PACU-based copolymers prepared in this study are expected to be useful biomaterials for the sustained delivery of hGH.