V. G. Deepagan

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 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.

ROS-generating TiO2 nanoparticles for non-invasive sonodynamic therapy of cancer

The non-invasive photodynamic therapy has been limited to treat superficial tumours, primarily ascribed to poor tissue penetration of light as the energy source. Herein, we designed a long-circulating hydrophilized titanium dioxide nanoparticle (HTiO2 NP) that can be activated by ultrasound to generate reactive oxygen species (ROS). When administered systemically to mice, HTiO2 NPs effectively suppressed the growth of superficial tumours after ultrasound treatments. In tumour tissue, the levels of proinflammatory cytokines were elevated several fold and intense vascular damage was observed. Notably, ultrasound treatments with HTiO2 NPs also suppressed the growth of deeply located liver tumours at least 15-fold, compared to animals without ultrasound treatments. This study provides the first demonstration of the feasibility of using HTiO2 NPs as sensitizers for sonodynamic therapy in vivo.

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.

Long-Circulating Au-TiO2 Nanocomposite as a Sonosensitizer for ROS-Mediated Eradication of Cancer

Although sonodynamic therapy (SDT) has emerged as a potential alternative to conventional photodynamic therapy, the low quantum yield of the sonosensitizer such as TiO2 nanoparticles (NPs) is still a major concern. Here, we have developed hydrophilized Au-TiO2 nanocomposites (HAu-TiO2 NCs) as sonosensitizers for improved SDT. The physicochemical properties of HAu-TiO2 NCs were thoroughly studied and compared with their counterparts without gold deposition. Upon exposure of HAu-TiO2 NCs to ultrasound, a large quantity of reactive oxygen species (ROS) were generated, leading to complete suppression of tumor growth after their systemic administration in vivo. Overall, it was evident that the composites of gold with TiO2 NPs significantly augmented the levels of ROS generation, implying their potential as SDT agents 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.

In situ diselenide-crosslinked polymeric micelles for ROS-mediated anticancer drug delivery

Stimuli-responsive micelles have emerged as the drug carrier for cancer therapy since they can exclusively release the drug via their structural changes in response to the specific stimuli of the target site. Herein, we developed the in situ diselenide-crosslinked micelles (DCMs), which are responsive to the abnormal ROS levels of tumoral region, as anticancer drug carriers. The DCMs were spontaneously derived from selenol-bearing triblock copolymers consisting of polyethylene glycol (PEG) and polypeptide derivatives. During micelle formation, doxorubicine (DOX) was effectively encapsulated in the hydrophobic core, and diselenide crosslinks were formed in the shell. The DCMs maintained their structural integrity, at least for 6 days in physiological conditions, even in the presence of destabilizing agents. However, ROS-rich conditions triggered rapid release of DOX from the DOX-encapsulating DCMs (DOX-DCMs) because the hydrophobic diselenide bond was cleaved into hydrophilic selenic acid derivatives. Interestingly, after their systemic administration into the tumor-bearing mice, DOX-DCMs delivered significantly more drug to tumors (1.69-fold and 3.73-fold higher amount compared with their non-crosslinked counterparts and free drug, respectively) and effectively suppressed tumor growth. Overall, our data indicate that DCMs have great potential as drug carriers for anticancer therapy.

Biostable and bioreducible polymersomes for intracellular delivery of doxorubicin

To minimize the premature drug release of nanocarriers, we have developed chemically cross-linked bioreducible polymersomes (CLPMs) that can specifically release the drug inside cancer cells. Polymersomes were prepared using poly(ethylene glycol)-b-poly(lysine)-b-poly(caprolactone), a biocompatible triblock copolymer. To chemically cross-link the polymersomes, the primary amine of the triblock copolymer was reacted with a disulfide-containing cross-linker. Doxorubicin (DOX) was chosen as a model anti-cancer drug, and was effectively encapsulated into the CLPMs. The drug-loaded polymersomes greatly retarded the release of DOX under physiological conditions (pH 7.4), whereas the release rate of DOX increased remarkably in the presence of 10 mM glutathione, mimicking an intracellular environment. Microscopic observation showed that DOX-loaded CLPMs could effectively deliver the drug into an intracellular level of SCC7 cancer cells, leading to high cytotoxicity. These observations suggest that CLPMs are promising nanocarriers for intracellular DOX delivery.

A PEGylated hyaluronic acid conjugate for targeted cancer immunotherapy

ABSTRACT The cell‐free approach to foreignizing tumor cells with non‐self antigens has received increasing attention as a method to induce cytotoxic T lymphocyte (CTL)‐mediated immunological rejection of tumors, because the clinical translation of the conventional CTL‐based cancer immunotherapies has been limited by a complicated manufacturing process and autotransplantation. In this study, we prepared matrix metalloproteinase 9 (MMP9)‐responsive polymeric conjugates consisting of PEGylated hyaluronic acid (HA) as the targeting moiety and ovalbumin (OVA) as the model foreign antigen. The MMP9‐cleavable linker was introduced between PEG and the HA backbone to facilitate the detachment of the PEG corona from the conjugate at the tumor site. From the in vitro cellular uptake study, it was revealed that the conjugate was effectively taken up by the CD44‐expressing TC‐1 cancer cells in the presence of MMP9 via receptor‐mediated endocytosis. When the conjugate was systemically administered into the tumor‐bearing mice with endogenous OVA‐specific CTLs, the tumor growth was markedly inhibited, which was attributed to the significant antigen presentation on the tumor cells. Overall, the MMP9‐responsive conjugates bearing foreign antigens might have the potential as an alternative to CTL‐based cancer immunotherapeutics. Graphical abstract Figure. No caption available.

Intracellularly Activatable Nanovasodilators To Enhance Passive Cancer Targeting Regime

Conventional cancer targeting with nanoparticles has been based on the assumed enhanced permeability and retention (EPR) effect. The data obtained in clinical trials to date, however, have rarely supported the presence of such an effect. To address this challenge, we formulated intracellular nitric oxide-generating nanoparticles (NO-NPs) for the tumor site-specific delivery of NO, a well-known vasodilator, with the intention of boosting EPR. These nanoparticles are self-assembled under aqueous conditions from amphiphilic copolymers of poly(ethylene glycol) and nitrated dextran, which possesses inherent NO release properties in the reductive environment of cancer cells. After systemic administration of the NO-NPs, we quantitatively assessed and visualized increased tumor blood flow as well as enhanced vascular permeability than could be achieved without NO. Additionally, we prepared doxorubicin (DOX)-encapsulated NO-NPs and demonstrated consequential improvement in therapeutic efficacy over the control groups with considerably improved DOX intratumoral accumulation. Overall, this proof of concept study implies a high potency of the NO-NPs as an EPR enhancer to achieve better clinical outcomes.