Crosslinked triblock copolymeric micelle for redox-responsive drug delivery

Advances in PEG-based ABC terpolymers and their applications

ABC terpolymers are a class of very important polymers because of their expansive molecular topologies and extensive architectures. As block A, poly(ethylene glycol) (PEG) is one of the most principal categories owing to good biocompatibility and wide commercial availability. More importantly, the synthetic approaches of ABC terpolymers using PEG as a macroinitiator are facile and varied. PEG-based ABC terpolymers from design and synthesis to applications are highlighted in this review. Linear, 3-miktoarm, and cyclic polymers as the architecture are separated. The synthetic approaches of PEG-based ABC terpolymers mainly include the sequential polymerization or coupling of polymers. PEG-based ABC terpolymers have wide applications in the fields of drug carriers, gene vectors, templates for the fabrication of inorganic hollow nanospheres, and stabilizers of metal nanoparticles.

Interface crosslinked mPEG-b-PAGE-b-PCL triblock copolymer micelles with high stability for anticancer drug delivery

The stability of polymeric micelles is a key property for anticancer drug delivery. In this study, a novel amphiphilic triblock copolymer, methoxy poly(ethylene glycol)-b-poly(allyl glycidyl ether)-b-poly(ε-caprolactone) (mPEG-b-PAGE-b-PCL), with different hydrophobic lengths was designed and synthesized using the combination of two successive ring-opening polymerizations. The products were characterized using ¹H NMR and gel permeation chromatography (GPC). The triblock copolymers could self-assemble into micelles to encapsulate doxorubicin (DOX). The diameter of the DOX-loaded micelles increased from 63 to 92 nm with increasing PCL block length in the copolymer composition. The interface of the mPEG-b-PAGE-b-PCL micelles was crosslinked by a thiol-ene reaction with 1,4-butanedithiol. The stability, drug release and in vitro cytotoxicity of the DOX-loaded micelles were studied. The results showed that the DOX-loaded micelles could be effectively endocytosed by cancer cells and have good antitumor efficacy. In addition, the crosslinked micelles (CLMs) had better tumor accumulation than the noncrosslinked micelles (NCLMs) after intravenous injection using the lipophilic dye DiR.

Chitosan-based advanced materials for docetaxel and paclitaxel delivery: Recent advances and future directions in cancer theranostics

Paclitaxel (PTX) and docetaxel (DTX) are key members of taxanes with high anti-tumor activity against various cancer cells. These chemotherapeutic agents suffer from a number of drawbacks and it seems that low solubility in water is the most important one. Although much effort has been made in improving the bioavailability of PTX and DTX, the low bioavailability and minimal accumulation at tumor sites are still the challenges faced in PTX and DTX therapy. As a consequence, bio-based nanoparticles (NPs) have attracted much attention due to unique properties. Among them, chitosan (CS) is of interest due to its great biocompatibility. CS is a positively charged polysaccharide with the capability of interaction with negatively charged biomolecules. Besides, it can be processed into the sheet, micro/nano-particles, scaffold, and is dissolvable in mildly acidic pH similar to the pH of the tumor microenvironment. Keeping in mind the different applications of CS in the preparation of nanocarriers for delivery of PTX and DTX, in the present review, we demonstrate that how CS functionalized-nanocarriers and CS modification can be beneficial in enhancing the bioavailability of PTX and DTX, targeted delivery at tumor site, image-guided delivery and co-delivery with other anti-tumor drugs or genes.

Logic-Based Delivery of Site-Specifically Modified Proteins from Environmentally Responsive Hydrogel Biomaterials

The controlled presentation of proteins from and within materials remains of significant interest for many bioengineering applications. Though "smart" platforms offer control over protein release in response to a single external cue, no strategy has been developed to trigger delivery in response to user-specified combinations of environmental inputs, nor to independently control the release of multiple species from a homogenous material. Here, a modular semisynthetic scheme is introduced to govern the release of site-specifically modified proteins from hydrogels following Boolean logic. A sortase-mediated transpeptidation reaction is used to generate recombinant proteins C-terminally tethered to gels through environmentally sensitive degradable linkers. By varying the connectivity of multiple stimuli-labile moieties within these customizable linkers, YES/OR/AND control of protein release is exhaustively demonstrated in response to one and two-input combinations involving enzyme, reductant, and light. Tethering of multiple proteins each through a different stimuli-sensitive linker permits their independent and sequential release from a common material. It is expected that these methodologies will enable new opportunities in tissue engineering and therapeutic delivery.

Amphiphilic prodrug-decorated graphene oxide as a multi-functional drug delivery system for efficient cancer therapy

Graphene oxide (GO) has shown great potential in drug delivery. However, the aqueous stability, non-specific drug release and slow release rate are major problems of the GO-based drug delivery system. Herein, we for the first time integrate the dispersant, stabilizing agent and active targeting carrier into a novel drug delivery system based on GO/PP-SS-DOX nanohybrids. The redox-sensitive PP-SS-DOX prodrug was obtained by conjugating mPEG-PLGA (PP) with doxorubicin (DOX) via disulfide bond. PEG-FA provided active targeting property for the constructed drug delivery system, GO/PP-SS-DOX/PEG-FA. In this demonstrated system, PP-SS-DOX markedly increases the stability in physiological solutions of GO and guarantees the DOX release in the reductive environment (cancerous cells). And PEG-FA helps target to cancerous tissues and induces FR-mediated endocytosis. In vitro drug release exhibited the obvious reductive sensitivity and the cumulative release amount was up to 90%, while 40% in previous reports within 72 h. The in vitro cytotoxicity of targeting nanohybrids was significantly cytotoxic than that of non-targeting nanohybrids. In vivo results displayed that the as-prepared targeting nanohybrids showed efficacious antitumor effect while it had nearly no systemic adverse toxicity on B16 tumor-bearing mice. Therefore, the in vitro and in vivo results indicate that our constructed GO/PP-SS-DOX/PEG-FA drug delivery system is a promising carrier in cancer therapy.

In Situ Monitoring Intracellular Structural Change of Nanovehicles through Photoacoustic Signals Based on Phenylboronate-Linked RGD-Dextran/Purpurin 18 Conjugates

The stimuli-responsive polymeric nanocarriers have been studied extensively, and their structural changes in cells are important for the controlled intracellular drug release. The present work reported RGD-dextran/purpurin 18 conjugates with pH-responsive phenylboronate as spacer for monitoring the structural change of nanovehicles through ratiometric photoacoustic (PA) signal. Phenylboronic acid modified purpurin 18 (NPBA-P18) could attach onto the RGD-decorated dextran (RGD-Dex), and the resulting RGD-Dex/NPBA-P18 (RDNP) conjugates with different molar ratios of RGD-Dex and NPBA-P18 were prepared. When the moles of NPBA-P18 were equivalent to more than triple of RGD-Dex, the single-stranded RDNP conjugates could self-assemble into nanoparticles in aqueous solution due to the fairly strong hydrophobicity of NPBA-P18. The pH-responsive aggregations of NPBA-P18 were investigated by UV-vis, fluorescence, and circular dichroism spectra, as well as transmission electron microscope. Based on distinct PA signals between monomeric and aggregated state, ratiometric PA signal of I₇₅₀/I₇₁₀ could be presented to trace the structural change progress. Compared with RDNP single chains, the nanoparticles exhibited effective cellular internalization through endocytosis pathway. Furthermore, the nanoparticles could form well-ordered aggregates responding to intracellular acidic environment, and the resulting structural change was also monitored by ratiometric PA signal. Therefore, the noninvasive PA approach could provide a deep insight into monitoring the intracellular structural change process of stimuli-responsive nanocarriers.

Biocompatible Reduction and pH Dual-Responsive Core Cross-Linked Micelles Based on Multifunctional Amphiphilic Linear-Hyperbranched Copolymer for Controlled Anticancer Drug Delivery

Novel strategy has been developed for fabricating the biocompatible reduction and pH dual-responsive core cross-linked (CCL) micelles as drug delivery system (DDS) for the controlled anticancer drug delivery, via the atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) with N,N'-bis(acryloyl)cystamine (BACy) as cross-linker and a multifunctional amphiphilic linear-hyperbranched copolymer as macroinitiator, which was synthesized via the self-condensing vinyl copolymerization (SCVCP) of tBA and p-chloromethylstyrene (CMS) with a poly(ethylene glycol) (PEG) based initiator (mPEG-Br). The hydrolyzed core cross-linked (HCCL) micelles were obtained as DDS for doxorubicin (DOX) by hydrolysis the tBA units into acrylic acid (AA) ones. The in vitro release performance showed that higher GSH concentration and/or lower pH value would lead to a faster and more efficient DOX release, meaning their reduction and pH dual-responsiveness. Therefore, the proposed HCCL micelles are expected to be potential anticancer drug-carriers for tumor microenvironment responsive controlled delivery.

Redox-Sensitive Micelles Based on O,N-Hydroxyethyl Chitosan-Octylamine Conjugates for Triggered Intracellular Delivery of Paclitaxel

A redox-sensitive micellar system constructed from an O,N-hydroxyethyl chitosan-octylamine (HECS-ss-OA) conjugate with disulfide linkages between the hydrophobic alkyl chains and hydrophilic chitosan backbone was synthesized for triggered intracellular delivery of hydrophobic paclitaxel (PTX). In aqueous environments, conjugates formed micelles with high PTX loading (>30%). Mechanistically, the sensitivity of HECS-ss-OA micelles to reducing environments was investigated using the parameters of in vitro release and particle size. Intracellular release of nile red fluorescence alongside cytotoxicity studies further confirmed the potency of redox-sensitive micelles for intracellular drug delivery compared with redox-insensitive micelles. Additionally, an in vivo study confirmed the efficacy of PTX-loaded micelles in tumor-bearing mice with superior antitumor efficacy and diminished systemic toxicity when compared with the redox-insensitive micelles and a PTX solution. These results demonstrate the potential of redox-sensitive HECS-ss-OA micelles for intracellular trafficking of lipophilic anticancer drugs.

Preparation of pH and redox dual-sensitive core crosslinked micelles for overcoming drug resistance of DOX

When incubating the pH and redox dual-sensitive CCL/SS micelles with MCF-7/ADR cells, they could sufficiently overcome drug resistance to deliver DOX into MCF-7/ADR cells, leading to the apoptosis of tumor cells.

Reduction-sensitive polymeric nanocarriers in cancer therapy: a comprehensive review

Redox potential is regarded as a significant signal to distinguish between the extra-cellular and intra-cellular environments, as well as between tumor and normal tissues. Taking advantage of this physiological differentiation, various reduction-sensitive polymeric nanocarriers (RSPNs) have been designed and explored to demonstrate excellent stability during blood circulation but rapidly degrade and effectively trigger drug release in tumor cells. Therefore, this smart RSPN delivery system has attracted much attention in recent years, as it represents one of the most promising drug delivery strategies in cancer therapy. In this review, we will provide a comprehensive overview of RSPNs with various reducible linkages and functional groups up to date, including their design and synthetic strategies, preparation methods, drug release behavior, and their in vitro and in vivo efficacy in cancer therapy. In addition, dual- and triple-sensitive nanocarriers based on reducible disulfide bond-containing linkages will also be discussed.

Trigger responsive polymeric nanocarriers for cancer therapy

Conventional chemotherapy for the treatment of cancer has limited specificity when administered systemically and is often associated with toxicity issues. Enhanced accumulation of polymeric nanocarriers at a tumor site may be achieved by passive and active targeting. Incorporation of trigger responsiveness into these polymeric nanocarriers improves the anticancer efficacy of such systems by modulating the release of the drug according to the tumor environment. Triggers used for tumor targeting include internal triggers such as pH, redox and enzymes and external triggers such as temperature, magnetic field, ultrasound and light. While internal triggers are specific cues of the tumor microenvironment, external triggers are those which are applied externally to control the release. This review highlights the various strategies employed for the preparation of such trigger responsive polymeric nanocarriers for cancer therapy and provides an overview of the state of the art in this field.

Thiol-responsive gemini poly(ethylene glycol)-poly(lactide) with a cystine disulfide spacer as an intracellular drug delivery nanocarrier

Thiol-responsive gemini micelles consisting of hydrophilic poly(ethylene glycol) (PEG) blocks and hydrophobic polylactide (PLA) blocks with a cystine disulfide spacer were reported as effective intracellular nanocarriers of drugs. In the presence of cellular glutathione (GSH) as a reducing agent, gemini micelles gradually destabilize into monomeric micelles through cleavage of the cystine linkage. This destabilization of the gemini micelles changed their size distribution, with the appearance of small aggregates, and led to the enhanced release of encapsulated doxorubicin (DOX). The results obtained from cell culture via confocal laser scanning microscopy (CLSM) for cellular uptake, as well as cell viability measurements for anticancer efficacy suggest the potential of disulfide-based gemini polymeric micelles as controlled drug delivery carriers.