Facile construction of dual-bioresponsive biodegradable micelles with superior extracellular stability and activated intracellular drug release

Nanoparticle-mediated metronomic chemotherapy in cancer: A paradigm of precision and persistence

Current methods of cancer therapy have demonstrated enormous potential in tumor inhibition. However, a high dosage regimen of chemotherapy results in various complications which affect the normal body cells. Tumor cells also develop resistance against the prescribed drugs in the whole treatment regimen increasing the risk of cancer relapse. Metronomic chemotherapy is a modern treatment method that involves administering drugs at low doses continuously, allowing the drug sufficient time to take its effect. This method ensures that the toxicity of the drugs is to a minimum in comparison to conventional chemotherapy. Nanoparticles have shown efficacy in delivering drugs to the tumor cells in various cancer therapies. Combining nanoparticles with metronomic chemotherapy can yield better treatment results. This combination stimulates the immune system, improving cancer cells recognition by immune cells. Evidence from clinical and pre-clinical trials supports the use of metronomic delivery for drug-loaded nanoparticles. This review focuses on the functionalization of nanoparticles for improved drug delivery and inhibition of tumor growth. It emphasizes the mechanisms of metronomic chemotherapy and its conjunction with nanotechnology. Additionally, it explores tumor progression and the current methods of chemotherapy. The challenges associated with nano-based metronomic chemotherapy are outlined, paving the way for prospects in this dynamic field.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Stimuli-responsive drug delivery systems triggered by intracellular or subcellular microenvironments

Drug delivery systems (DDS) triggered by local microenvironment represents the state-of-art of nanomedicine design, where the triggering hallmarks at intracellular and subcellular levels could be employed to exquisitely recognize the diseased sites, reduce side effects, and expand the therapeutic window by precisely tailoring the drug-release kinetics. Though with impressive progress, the DDS design functioning at microcosmic levels is fully challenging and underexploited. Here, we provide an overview describing the recent advances on stimuli-responsive DDSs triggered by intracellular or subcellular microenvironments. Instead of focusing on the targeting strategies as listed in previous reviews, we herein mainly highlight the concept, design, preparation and applications of stimuli-responsive systems in intracellular models. Hopefully, this review could give useful hints in developing nanoplatforms proceeding at a cellular level.

Nanoimmunoengineering strategies in cancer diagnosis and therapy

Cancer immunotherapy strategies in combination with engineered nanosystems have yielded beneficial results in the treatment of cancer and their application is increasing day by day. The pivotal role of stimuli-responsive nanosystems and nanomedicine-based cancer immunotherapy, as a subsidiary discipline in the field of immunology, cannot be ignored. Today, rapid advances in nanomedicine are used as a platform for exploring new therapeutic applications and modern smart healthcare management strategies. The progress of nanomedicine in cancer treatment has confirmed the findings of immunotherapy in the medical research phase. This study concentrates on approaches connected to the efficacy of nanoimmunoengineering strategies for cancer immunotherapies and their applications. By assessing improved approaches, different aspects of the nanoimmunoengineering strategies for cancer therapies are discussed in this study.

PEGylated Doxorubicin Prodrug-Forming Reduction-Sensitive Micelles With High Drug Loading and Improved Anticancer Therapy

Significant efforts on the design and development of advanced drug delivery systems for targeted cancer chemotherapy continue to be a major challenge. Here, we reported a kind of reduction-responsive PEGylated doxorubicin (DOX) prodrug via the simple esterification and amidation reactions, which self-assembled into the biodegradable micelles in solutions. Since there was an obvious difference in the reduction potentials between the oxidizing extracellular milieu and the reducing intracellular fluids, these PEG-disulfide-DOX micelles were localized intracellularly and degraded rapidly by the stimulus to release the drugs once reaching the targeted tumors, which obviously enhanced the therapeutic efficacy with low side effects. Moreover, these reduction-sensitive micelles could also physically encapsulate the free DOX drug into the polymeric cargo, exhibiting a two-phase programmed drug release behavior. Consequently, it showed a potential to develop an intelligent and multifunctional chemotherapeutic payload transporter for the effective tumor therapy.

Black phosphorus assisted polyionic micelles with efficient PTX loading for remotely controlled release and synergistic treatment of drug-resistant tumors

Nanomedicines have been widely used in the effective delivery of chemotherapeutic drugs due to their advantages such as increasing the half-life of drugs, selectively targeting tumor tissues, and thus reducing systemic toxicity. However, the low drug entrapment rate and the difficulty of real-controlled release at tumor sites hinder their further clinical translations. Here we have developed biodegradable polyionic micelles (PD-M) to facilitate black phosphorus (BP) encapsulation (PD-M@BP) for improved drug loading. With the introduction of BP, PTX-loaded PD-M@BP (PD-M@BP/PTX) with sizes of 124-162 nm exhibited superior encapsulation efficiency over 94% and excellent colloidal stability. Meanwhile, PD-M well protected BP from fast degradation to show the good photothermal performance under near-infrared (NIR) irradiation, thus achieving the remotely controlled fast PTX release due to micelle core melting and dissociation, accompanied by the synergistic photothermal tumor therapy. The in vivo results demonstrated that the PD-M@BP/PTX nanosystem not only realized significant inhibition of multi-drug resistant (MDR) cervical tumors (HeLa/PTXR tumor) by remote NIR-regulation, but also reduced the potential damage of chemotherapeutic drugs to the whole body, rendering these hybrid nanosystems as great tools to treat MDR tumors synergistically.

Stimuli-responsive nanoparticles based on poly acrylic derivatives for tumor therapy

Serve side effects caused by discriminate damage of chemotherapeutic drugs to normal cell and cancer cells remain a main obstacle in clinic. Hence, continuous efforts have been made to find ways to effectively enhance drug delivery and reduce side effects. Recent decades have witnessed impressive progresses in fighting against cancer, with improved understanding of tumor microenvironment and rapid development in nanoscale drug delivery system (DDS). Nanocarriers based on biocompatible materials provide possibilities to improve antitumor efficiency and minimize off-target effects. Among all kinds of biocompatible materials applied in DDS, polymeric acrylic derivatives such as poly(acrylamide), poly(acrylic acid), poly(N-isopropylacrylamide) present inherent biocompatibility and stimuli-responsivity, and relatively easy to be functionalized. Furthermore, nanocarrier based on polymeric acrylic derivatives have demonstrated high drug encapsulation, improved uptake efficiency, prolonged circulation time and satisfactory therapeutic outcome in tumor. In this review, we aim to discuss recent progress in design and development of stimulus-responsive poly acrylic polymer based nanocarriers for tumor targeting drug delivery.

Stimuli-Responsive Aliphatic Polycarbonate Nanocarriers for Tumor-Targeted Drug Delivery

Nanoparticles based on amphiphilic copolymers with tunable physicochemical properties can be used to encapsulate delicate pharmaceutics while at the same time improving their solubility, stability, pharmacokinetic properties, reducing immune surveillance, or achieving tumor-targeting ability. Those nanocarriers based on biodegradable aliphatic polycarbonates are a particularly promising platform for drug delivery due to flexibility in the design and synthesis of appropriate monomers and copolymers. Current studies in this field focus on the design and the synthesis of new effective carriers of hydrophobic drugs and their release in a controlled manner by exogenous or endogenous factors in tumor-specific regions. Reactive groups present in aliphatic carbonate copolymers, undergo a reaction under the action of a stimulus: e.g., acidic hydrolysis, oxidation, reduction, etc. leading to changes in the morphology of nanoparticles. This allows the release of the drug in a highly controlled manner and induces a desired therapeutic outcome without damaging healthy tissues. The presented review summarizes the current advances in chemistry and methods for designing stimuli-responsive nanocarriers based on aliphatic polycarbonates for controlled drug delivery.

pH-Sensitive and Long-Circulation Nanoparticles for Near-Infrared Fluorescence Imaging-Monitored and Chemo-Photothermal Synergistic Treatment Against Gastric Cancer

Gastrectomy is the primary therapeutic option for gastric cancer. Postoperative treatment also plays a crucial role. The strategy to improve the postoperative prognosis of gastric cancer requires a combined system that includes a more efficient synergistic treatment and real-time monitoring after surgery. In this study, photothermal-chemotherapy combined nanoparticles (PCC NPs) were prepared via π-π stacking to perform chemo-photothermal synergistic therapy and continuous imaging of gastric cancer. PCC NPs had a spherical morphology and good monodispersity under aqueous conditions. The hydrodynamic diameter of PCC NPs was 59.4 ± 3.6 nm. PCC NPs possessed strong encapsulation ability, and the maximum drug loading rate was approximately 37%. The NPs exhibited extraordinary stability and pH-response release profiles. The NPs were rapidly heated under irradiation. The maximum temperature was close to 58°C. PCC NPs showed good biocompatibility both in vitro and in vivo. Moreover, the NPs could effectively be used for in vivo continuous monitoring of gastric cancer. After one injection, the fluorescent signal remained in tumor tissues for nearly a week. The inhibitory effect of PCC NPs was evaluated in a gastric cancer cell line and xenograft mouse model. Both in vitro and in vivo evaluations demonstrated that PCC NPs could be used for chemo-photothermal synergistic therapy. The suppression effect of PCC NPs was significantly better than that of single chemotherapy or photothermal treatment. This study lays the foundation for the development of novel postoperative treatments for gastric cancer.

Biodegradable pH-responsive micelles loaded with 8-hydroxyquinoline glycoconjugates for Warburg effect based tumor targeting

Biodegradable triblock copolymer poly(ethylene glycol)-b-polycarbonate-b-oligo([R]-3-hydroxybutyrate) was prepared via metal-free ring-opening polymerization of ketal protected six-membered cyclic carbonate followed by esterification with bacterial oligo([R]-3-hydroxybutyrate) (oPHB). Amphiphilic triblock copolymer self-organizes into micelles with a diameter of ~25 nm. Acid-triggered hydrolysis of ketal groups to two hydroxyl groups causes an increase in hydrophilicity of the hydrophobic micelle core, resulting in the micelles swell and drug release. oPHB was added as core-forming block to increase the stability of prepared micelles in all pH (7.4, 6.4, 5.5) studied. Doxorubicin and 8-hydroxyquinoline glucose- and galactose conjugates were loaded in the micelles. In vitro drug release profiles in PBS buffers with different pH showed that a small amount of loaded drug was released in PBS at pH 7.4, while the drug was released much faster at pH 5.5. MTT assay showed that the blank micelles were non-toxic to different cell lines, while glycoconjugates-loaded micelles, showed significantly increased ability to inhibit the proliferation of MCF-7 and HCT-116 cells compared to free glycoconjugates. The glycoconjugation of anti-cancer drugs and pH-responsive nanocarriers have separately shown great potential to increase the tumor-targeted drug delivery efficiency. The combination of drug glycoconjugation and the use of pH-responsive nanocarrier opens up new possibilities to develop novel strategies for efficient tumor therapy.

Reversible Cross-Linked Mixed Micelles for pH Triggered Swelling and Redox Triggered Degradation for Enhanced and Controlled Drug Release

Good stability and controlled drug release are important properties of polymeric micelles for drug delivery. A good candidate for drug delivery must have outstanding stability in a normal physiological environment, followed with low drug leakage and side effects. Moreover, the chemotherapeutic drug in the micellar core should also be quickly and "on-demand" released in the intracellular microenvironment at the tumor site, which is in favor of overcoming multidrug resistance (MDR) effects of tumor cells. In this work, a mixed micelle was prepared by the simple mix of two amphiphilic copolymers, namely PCL-SS-P(PEGMA-co-MAEBA) and PCL-SS-PDMAEMA, in aqueous solution. In the mixed micelle's core-shell structure, PCL blocks were used as the hydrophobic core, while the micellar hydrophilic shell consisted of two blocks, namely P(PEGMA-co-MAEBA) and PDMAEMA. In the micellar shell, PEGMA provided hydrophilicity and stability, while MAEBA introduced the aldehyde sites for reversible crosslinking. Meanwhile, the PDMAEMA blocks were also introduced in the micellar shell for pH-responding protonation and swelling of the micelle. The disulfide bonds between the hydrophobic core and hydrophilic shell had redox sensitive properties. Reversible cross-linked micelles (RCLMs) were obtained by crosslinking the micellar shell with an imine structure. RCLMs showed good stability and excellent ability against extensive dilution by aqueous solution. In addition, the stability in different conditions with various pH values and glutathione (GSH) concentrations was studied. Then, the anticancer drug doxorubicin (DOX) was selected as the model drug to evaluate drug entrapment and release capacity of mixed micelles. The in vitro release profiles indicated that this RCLM had controlled drug release. In the simulated normal physiological environment (pH 7.4), the drug release of the RCLMs was restrained obviously, and the cumulative drug release content was only 25.7 during 72 h. When it came to acidic conditions (pH 5.0), de-crosslinking of the micelles occurred, as well as protonation of PDMAEMA blocks and micellar swelling at the same time, which enhanced the drug release to a large extent (81.4%, 72 h). Moreover, the drug release content was promoted further in the presence of the reductant GSH. In the condition of pH 5.0 with 10 mM GSH, disulfide bonds broke-up between the micelle core and shell, followed by shedding of the shell from the inner core. Then, the micellar disassembly (degradation) happened based on the de-crosslinking and swelling, and the drug release was as high as 95.3%. The MTT assay indicated that the CLSMs showed low cytotoxicity and good biocompatibility against the HepG2 cells. In contrast, the DOX-loaded CLSMs could efficiently restrain the proliferation of tumor cells, and the cell viability after 48 h incubation was just 13.2%, which was close to that of free DOX. This reversible cross-linked mixed micelle with pH/redox responsive behaviors is a potential nanocarrier for chemotherapy.

Synthesis and evaluation of cationic polymeric micelles as carriers of lumbrokinase for targeted thrombolysis

To achieve targeted thrombolysis, a targeted delivery system of lumbrokinase (LK) was constructed using RGDfk-conjugated hybrid micelles. Based on the specific affinity of RGDfk to glycoprotein complex of GPⅡb/Ⅲa expressed on the surface of membrane of activated platelet, LK loaded targeted micelles (LKTM) can be delivered to thrombus. The hybrid micelles were composed of polycaprolactone-block-poly (2-(dimethylamino) ethyl methacrylate) (PCL-PDMAEMA), methoxy polyethylene glycol-block- polycaprolactone (mPEG-PCL) and RGDfk conjugated polycaprolactone-block- polyethylene glycol (PCL-PEG-RGDfk). PCL-PDMAEMA was synthesized via ring open polymerization (ROP) and atom transfer radical polymerization (ATRP). PCL-PEG-RGDfk was synthesized via ROP and carbodiimide chemistry. The prepared LKTM was characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Colloidal stability assay showed the prepared LKTM was stable. Biocompatibility assay was performed to determine the safe concentration range of polymer. The assay of fluorescent distribution in vivo demonstrated that LKTM can be efficiently delivered to thrombi in vivo. Thrombolysis in vivo indicated the thrombolytic potency of LKTM was optimal in all groups. Notably, the laboratory mice treated with LKTM exhibited a significantly shorter tail bleeding time compared to those treated with LK or LK-loaded micelles without RGDfk, which suggested that the targeted delivery of LK using RGDfk-conjugated hybrid micelles effectively reduced the bleeding risk.

Dual-targeting nanoparticles with core-crosslinked and pH/redox-bioresponsive properties for enhanced intracellular drug delivery

Multifunctional nanoparticles (NPs) with high blood-stability, tumor-targeting ability, and stimuli-bioresponsive drug release behaviors are urgently demanded. Herein, folic acid (FA) and galactose (GAL) functionalized, core-crosslinked NPs (CC NPs) with dual-targeting and pH/redox-bioresponsive properties were developed based on amphiphilic FA-poly(6-O-methacryloyl-d-galactopyranose)-b-poly[2-(diisopropylamino) ethyl methacrylate-co-pyridyl disulfide methylacrylate] [FA-PMAgGP-b-P(DPA-co-PDEMA), termed as FA-PMgDP] block copolymers, and then investigated for facilitated hepatoma-targeting delivery of doxorubicin (DOX). A series of PMgDP copolymers were synthesized though two-step RAFT copolymerization followed by acid-induced acetal deprotection reaction. Their well-defined chemical structures and compositions were characterized by ¹H NMR and gel permeation chromatography. Nano-sized, non-crosslinked PMgDP NPs (PMgDP NC NPs) with sizes of less than 25 nm in aqueous solution were self-assembled via the solvent exchange method, and PMgDP CC NPs were readily prepared in the presence of dithiothreitol. The drug-loading content of PMgDP CC NPs was up to 15.8% and its entrapment efficiency was 89.0%. In normal physiological conditions, 11.6% of DOX was released from DOX-loaded PMgDP CC NPs at 25 h, whereas in analogous intracellular microenvironment, 95.5% was released at 11 h owing to the acid-induced protonation of tertiary amine and reductive cleavage of disulfide bond in the hydrophobic core. In a cellular uptake study, FA and GAL-mediated, active, dual-targeted DOX-loaded FA-PMgDP CC NPs showed a 3.54-fold increase in cellular uptake efficiency to HepG2 cells compared to that of shown by single GAL-targeted, DOX-loaded PMgDP NC NPs. Results of in vitro cytotoxicity study showed that blank FA-PMgDP CC NPs exhibited good biocompatibility, whereas dual-targeting DOX-loaded FA-PMgDP CC NPs increased cell apoptosis. Therefore, the above results indicated that the well-constructed FA-PMgDP CC NPs with multi-synergistic effect may serve as new nanocarriers in the field of precise hepatoma-targeting drug delivery.

Fenton-reaction-stimulative nanoparticles decorated with a reactive-oxygen-species (ROS)-responsive molecular switch for ROS amplification and triple negative breast cancer therapy

P@P/H NPs were rapidly disintegrated in response to ROS, and this further enhanced ROS level in tumor cells via the Fenton reaction.

Programmed pH/reduction-responsive nanoparticles for efficient delivery of antitumor agents in vivo

To bypass the biological barriers during the drug delivery process, it is desirable to develop smart nanoparticles (NPs) with flexible physical and chemical properties. In this study, a programmed NP delivery system with a pH-triggered detachable PEG layer and a lactobionic acid (Lac)-modified reduction-responsive core was developed to address the "PEG dilemma" and provide an on-demand intracellular release of doxorubicin (DOX). The positively charged DOX-loaded lactobionic acid-chitosan-lipoic acid (DOX/LCL) NPs were prepared and coated with a negatively charged dimethylmaleic acid-PEG-chitosan (PEG-CS-DA) layer to obtain a prolonged circulation time and improve the tumor-targeting effect. After reaching the tumor tissues through a targeted delivery effect, the surface charge of the PEG-CS-DA layer was reversed from negative to positive because of the trigger by the acidic microenvironment (pH 6.8), thus leading to the detachment of the PEG layer. The exposure of positive charges and the active targeting ligand enhanced cellular uptake and facilitated penetration into tumor tissues. Subsequently, the rapid release and diffusion of DOX into the nuclei was triggered by the intracellular high concentration of glutathione, thus leading to cell apoptosis. In conclusion, these programmed pH/reduction-responsive NPs provide a promising strategy for the delivery of antitumor agents in vivo. STATEMENT OF SIGNIFICANCE: In this study, novel programmed pH/reduction-responsive NPs were developed for the delivery of DOX in vivo. These NPs were coated with a negatively charged PEG layer to improve the serum stability and tumor target effect. The PEG layer detached because of the trigger by tumor acidic microenvironment (pH 6.8), thus leading to the exposure of positive charges and the active targeting ligand, which enhanced cellular uptake and facilitated penetration into tumor tissues. Subsequently, the rapid release of DOX was triggered by the intracellular high concentration of glutathione, thereby resulting in enhanced cytotoxicity. These programmed pH/reduction-responsive NPs provide a promising strategy for the delivery of antitumor agents in vivo.

Polytyrosine nanoparticles enable ultra-high loading of doxorubicin and rapid enzyme-responsive drug release

Despite the great significance of clinically viable nanovehicles, very few of them exhibit stability and high anticancer drug loading with fast intracellular drug release. Herein, we report that polytyrosine nanoparticles (PTNs) self-assembled from poly(ethylene glycol)-b-poly(l-tyrosine) block copolymer enable the ultra-high loading and rapid enzyme-responsive release of doxorubicin (DOX). Notably, PTNs achieve a remarkably high DOX loading of 63.1 wt% likely due to the existence of strong π-π stacking between polytyrosine and DOX, as shown by UV-vis analysis. Additionally, PTNs present a high docetaxel loading of 17.5 wt%. Furthermore, PTNs exhibit good colloidal stability in 10% FBS, but are quickly de-stabilized by proteinase K. Interestingly, ca. 90% of DOX is released under 6 U mL-1 proteinase K in 24 h or in RAW 264.7 cells in 8 h. The DOX-loaded PTNs display efficient delivery and release of DOX in both RAW 264.7 cells and HCT-116 human colorectal cancer cells, achieving a better in vitro antiproliferative effect than the clinically used liposomal DOX formulation. Thus, these polytyrosine nanoparticles appear to be a potentially viable platform for the controlled delivery of anthraquinone anticancer agents.

Novel block glycopolymers prepared as delivery nanocarriers for controlled release of bortezomib

To explore block glycopolymers as novel polymeric delivery nanocarriers for anticancer drug bortezomib (BTZ), three types of block glycopolymers, poly(ethylene glycol)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PGAMA20), poly(ethylene glycol)-block-poly(styrene)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PS50-b-PGAMA20), and poly(ethylene glycol)-block-poly(2-(diethyl amino) ethyl methacrylate)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PDEA50-b-PGAMA20), were synthesized via atom transfer radical polymerization (ATRP) using a PEG-based ATRP macroinitiator. Three glycopolymers possess the capacity to load BTZ via pH-induced dynamic covalent bonding and/or hydrophobic interaction with their specific self-assembly behaviors, and PEG113-b-PS50-b-PGAMA20 carrier maintains the sustain release behavior of BTZ due to the stable micellar structure; PEG113-b-PDEA50-b-PGAMA20 carrier realizes the abrupt release at pH 5.5 by collapse of micellar structure, while PEG113-b-PGAMA20 carrier exhibits the fastest release at studied solution pHs. This study would provide a light to develop novel block glycopolymer carrier for the delivery of anticancer drug bearing boronic acid groups. Graphical abstractᅟᅟ.

Synthesis of next generation dual-responsive cross-linked nanoparticles and their application to anti-cancer drug delivery

Rare earth metal-mediated group transfer polymerisation enables the synthesis of previously inaccessible block copolymers of 2-vinylpyridine, diethyl vinylphosphonate and the new diallyl vinylphosphonate monomer. This precision polymerisation and the selective cross-linking of allyl side groups via thiol-ene click chemistry leads to the formation of well-defined dual-responsive nanoparticles. We demonstrate that these next generation nanocarriers are pH- and temperature-responsive and are capable of efficiently delivering doxorubicin into the nucleus of cancer cells. High anti-cancer activity could be demonstrated via cytotoxicity tests on breast cancer (MCF-7) and cervical cancer (HeLa) cells. These results validate this modular synthesis route as an ideal platform for the development of sophisticated nanocarriers for future drug delivery applications.

Disease-Triggered Drug Release Effectively Prevents Acute Inflammatory Flare-Ups, Achieving Reduced Dosing

For conditions with inflammatory flare-ups, fast drug-release from a depot is crucial to reduce cell infiltration and prevent long-term tissue destruction. While this concept has been explored for chronic diseases, preventing acute inflammatory flares has not been explored. To address this issue, a preventative inflammation-sensitive system is developed and applied to acute gout, a condition where millions of inflammatory cells are recruited rapidly, causing excruciating and debilitating pain. Rapid drug release is first demonstrated from a pH-responsive acetalated dextran particle loaded with dexamethasone (AcDex-DXM), reducing proinflammatory cytokines in vitro as efficiently as free drug. Then, using the air pouch model of gout, mice are pretreated 24 h before inducing inflammation. AcDex-DXM reduces overall cell infiltration with decreased neutrophils, increases monocytes, and diminishes cytokines and chemokines. In a more extended prophylaxis model, murine joints are pretreated eight days before initiating inflammation. After quantifying cell infiltration, only AcDex-DXM reduces the overall joint inflammation, where neither free drug nor a conventional drug-depot achieves adequate anti-inflammatory effects. Here, the superior efficacy of disease-triggered drug-delivery to prevent acute inflammation is demonstrated over free drug and slow-release depots. This approach and results promise exciting treatment opportunities for multiple inflammatory conditions suffering from acute flares.

Bioresponsive functional nanogels as an emerging platform for cancer therapy

INTRODUCTION

Bioresponsive nanogels with a crosslinked three-dimensional structure and an aqueous environment that undergo physical or chemical changes including swelling and dissociation in response to biological signals such as mild acidity, hyperthermia, enzymes, reducing agents, reactive oxygen species (ROS), and adenosine-5'-triphosphate (ATP) present in tumor microenvironments or inside cancer cells have emerged as an appealing platform for targeted drug delivery and cancer therapy.

AREAS COVERED

This review highlights recent designs and development of bioresponsive nanogels for facile loading and triggered release of chemotherapeutics and biotherapeutics. The in vitro and in vivo antitumor performances of drug-loaded nanogels are discussed.

EXPERT OPINION

Bioresponsive nanogels with an excellent stability and safety profile as well as fast response to biological signals are unique systems that mediate efficient and site-specific delivery of anticancer drugs, in particular macromolecular drugs like proteins, siRNA and DNA, leading to significantly enhanced tumor therapy compared with the non-responsive counterparts. Future research has to be directed to the development of simple, tumor-targeted and bioresponsive multifunctional nanogels, which can be either constructed from natural polymers with intrinsic targeting ability or functionalized with targeting ligands. We anticipate that rationally designed nanotherapeutics based on bioresponsive nanogels will become available for future clinical cancer treatment.

ABBREVIATIONS

AIE, aggregation-induced emission; ATP, adenosine-5'-triphosphate; ATRP, atom transfer radical polymerization; BSA, bovine serum albumin; CBA, cystamine bisacrylamide; CC, Cytochrome C; CDDP, cisplatin; CT, computed tomography; DC, dendritic cell; DiI, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate; DOX, doxorubicin; dPG, dendritic polyglycerol; DTT, dithiothreitol; EAMA, 2-(N,N-diethylamino)ethyl methacrylate; EPR, enhanced permeability and retention; GrB, granzyme B; GSH, glutathione tripeptide; HA, hyaluronic acid; HAase, hyaluronidases; HCPT, 10-Hydroxycamptothecin; HEP, heparin; HPMC, hydroxypropylmethylcellulose; LBL, layer-by-layer; MTX, methotrexate; NCA, N-carboxyanhydride; OVA, ovalbumin; PAH, poly(allyl amine hydrochloride); PBA, phenylboronic acid; PCL, polycaprolactone; PDEAEMA, poly(2-diethylaminoethyl methacrylate); PDGF, platelet derived growth factor; PDPA, poly(2-(diisopropylamino)ethyl methacrylate); PDS, pyridyldisulfide; PEG, poly(ethylene glycol); PEGMA, polyethyleneglycol methacrylate; PEI, polyethyleneimine; PHEA, poly(hydroxyethyl acrylate); PHEMA, poly(2-(hydroxyethyl) methacrylate; PNIPAM, poly(N-isopropylacrylamide); PMAA, poly(methacrylic acid); PPDSMA, poly(2-(pyridyldisulfide)ethyl methacrylate); PTX, paclitaxel; PVA, poly(vinyl alcohol); QD, quantum dot; RAFT, reversible addition-fragmentation chain transfer; RGD, Arg-Gly-Asp peptide; ROP, ring-opening polymerization; ROS, reactive oxygen species; TMZ, temozolomide; TRAIL, tumor necrosis factor-related apoptosis inducing ligand; VEGF, vascular endothelial growth factor.

Self-Stabilized Hyaluronate Nanogel for Intracellular Codelivery of Doxorubicin and Cisplatin to Osteosarcoma

Osteosarcoma is one of the most serious bone malignancies with rapid speed of deterioration and low survival rate in children and teenagers. Chemotherapy is an important treatment for osteosarcoma, while the conventional small-molecule therapeutics exhibit low efficacies and severe side effects in the clinic. Drug-delivery platforms based on nanotechnology, particularly for self-stabilized delivery platforms with prolonged blood circulation, enhanced intratumoral accumulation, improved antitumor efficacy, and diminished side effects, may break the deadlock on osteosarcoma chemotherapy. Here, a cisplatin (CDDP)-crosslinked hyaluronic acid (HA) nanogel (CDDPHANG) is prepared for effective delivery of doxorubicin (DOX) to treat osteosarcoma. Importantly, both DOX and CDDP have led clinically used antitumor drugs, and CDDP acts as a crosslinker and ancillary anticarcinogen to prevent the premature release of DOX and to achieve synergistic therapeutic performance. Because of the enhanced stability of the nanogel, this CDDP-crosslinked DOX-loaded nanomedicine (CDDPHANG/DOX) exhibits an obviously prolonged circulation time compared to free drugs. Moreover, after valid tumor accumulation, DOX and CDDP are synergistically delivered into the tumor cells and synchronously released into the intracellular acidic environment. Based on the synergistic apoptosis-inducing effects of DOX and CDDP, CDDPHANG/DOX reveals an evidently enhanced antitumor efficacy compared to free drugs and their combination, indicating its great prospects for the chemotherapy of osteosarcoma.

Endogenous pH-responsive nanoparticles with programmable size changes for targeted tumor therapy and imaging applications

Nanotechnology-based antitumor drug delivery systems, known as nanocarriers, have demonstrated their efficacy in recent years. Typically, the size of the nanocarriers is around 100 nm. It is imperative to achieve an optimum size of these nanocarriers which must be designed uniquely for each type of delivery process. For pH-responsive nanocarriers with programmable size, changes in pH (~6.5 for tumor tissue, ~5.5 for endosomes, and ~5.0 for lysosomes) may serve as an endogenous stimulus improving the safety and therapeutic efficacy of antitumor drugs. This review focuses on current advanced pH-responsive nanocarriers with programmable size changes for anticancer drug delivery. In particular, pH-responsive mechanisms for nanocarrier retention at tumor sites, size reduction for penetrating into tumor parenchyma, escaping from endo/lysosomes, and swelling or disassembly for drug release will be highlighted. Additional trends and challenges of employing these nanocarriers in future clinical applications are also addressed.

Bile Acid-Based Drug Delivery Systems for Enhanced Doxorubicin Encapsulation: Comparing Hydrophobic and Ionic Interactions in Drug Loading and Release

Doxorubicin (Dox) is a drug of choice in the design of drug delivery systems directed toward breast cancers, but is often limited by loading and control over its release from polymer micelles. Bile acid-based block copolymers present certain advantages over traditional polymer-based systems for drug delivery purposes, since they can enable a higher drug loading via the formation of a reservoir through their aggregation process. In this study, hydrophobic and electrostatic interactions are compared for their influence on Dox loading inside cholic acid based block copolymers. Poly(allyl glycidyl ether) (PAGE) and poly(ethylene glycol) (PEG) were grafted from the cholic acid (CA) core yielding a star-shaped block copolymer with 4 arms (CA-(PAGE- b-PEG)₄) and then loaded with Dox via a nanoprecipitation technique. A high Dox loading of 14 wt % was achieved via electrostatic as opposed to hydrophobic interactions with or without oleic acid as a cosurfactant. The electrostatic interactions confer a pH responsiveness to the system. 50% of the loaded Dox was released at pH 5 in comparison to 12% at pH 7.4. The nanoparticles with Dox loaded via hydrophobic interactions did not show such a pH responsiveness. The systems with Dox loaded via electrostatic interactions showed the lowest IC₅₀ and highest cellular internalization, indicating the pre-eminence of this interaction in Dox loading. The blank formulations are biocompatible and did not show cytotoxicity up to 0.17 mg/mL. The new functionalized star block copolymers based on cholic acid show great potential as drug delivery carriers.

pH and reduction-activated polymeric prodrug nanoparticles based on a 6-thioguanine-dialdehyde sodium alginate conjugate for enhanced intracellular drug release in leukemia

Synthesis schematics of DSA and 6-TG-DSA as well as processes of PPN self-assembly and its pH/GSH dual stimuli-response release of the conjugated 6-TG.

Reversible core-crosslinked nanocarriers with pH-modulated targeting and redox-controlled drug release for overcoming drug resistance

Herein, a pH and redox dual-sensitive core-crosslinked targeting nanocarrier was prepared and used for co-delivery of doxorubicin (DOX) and tariquidar (TQR). The nanocarrier not only had excellent stability but also prevented the leakage of the drug in the normal physiological environment efficiently. Meanwhile, the targeting function of nanocarriers could also be suppressed in the normal physiological environment, protecting nanocarriers from being captured by RAW264.7 cells. Under mild acidic conditions, the targeting function was regained, leading to an effective tumor cell uptake of the nanocarrier. Furthermore, reduction-responsive drug release would occur in the cytoplasm due to the collapse of the reduction-sensitive crosslinked structure in the nanocarrier. By means of ligand-receptor mediated endocytosis and TQR-mediated glycoprotein (P-gp) inhibition, the IC50 value of DOX to MCF-7/ADR cells reduced from more than 100 μg mL-1 to 8.55 μg mL-1, exhibiting great potential in overcoming drug resistance.

Preparation of core-crosslinked linear-dendritic copolymer micelles with enhanced stability and their application for drug solubilisation

In this study we explore the preparation of core-crosslinked micelles of linear-dendritic methoxy-poly(ethylene glycol) (MPEG)-co-poly(ester-sulfide) (PES) polymers to improve the stability of such polymeric micelle systems against premature disintegration and drug release. A series of MPEG-PES copolymers were synthesised via stepwise reactions of acetylation and thiol-ene photoreaction. Surface tension measurement showed that the copolymers with ethenyl surface groups could self-associate in dilute aqueous solutions to form micelles. Crosslinking within the micelle cores in the presence of dithioerythritol (DTT) linker was initiated under UV radiation. The formation of core-crosslinked micelles was confirmed by HPLC in combination with charged aerosol detection (CAD). The copolymers were found to readily hydrolyse under acidic conditions due to the ester-containing dendrons. Drug solubilisation capacities of the micellar solutions were determined using griseofulvin as a poorly water-soluble model drug. The solubility of griseofulvin showed a 10-fold enhancement in 1% w/v micelle solution and increased with the concentration of the copolymers. Drug release studies indicated that a more sustained release of griseofulvin was achieved for the core-crosslinked micelles compared to the non-crosslinked micelles, attributable to greater stability of the crosslinked core structure. The findings of this study present a new pathway towards developing biodegradable polymeric nanocarriers.

Annexin V-Conjugated Mixed Micelles as a Potential Drug Delivery System for Targeted Thrombolysis

To alleviate the hemorrhagic side effect of thrombolysis therapy, a thrombus targeted drug delivery system based on the specific affinity of Annexin V to phosphatidylserine exposed on the membrane surface of activated platelet was developed. The amphiphilic and biodegradable biomaterial, polycaprolactone-block-poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate) (PCL-b-PDMAEMA-b-PHEMA (PCDH)) triblock polymer, was synthesized via ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP) to use as the nanocarriers of thrombolytic drug. In order to conjugate Annexin V to the polymer, PCDH was modified by succinic anhydride via ring-opening reaction to introduce the carboxyl group (PCDH-COOH). After preparation of PCDH/PCDH-COOH (9/1, m/m) mixed micelles, Annexin V was coupled with the micelles using carbodiimide chemistry. The blood clot lysis assay in vitro confirmed that lumbrokinase-loaded targeted micelles (LKTM) had stronger thrombolysis potency than free lumbrokinase (LK) and LK-loaded nontargeted micelles (LKM, P < 0.05). In vivo thrombolytic assay, multispectral, optoacoustic tomography (MSOT) was used to assess the target ability of LKTM. The results of MSOT images indicated the fluorescence intensity of the LKTM group located in the blood clot position were significantly stronger than the LKM group. A 5 mm of carotid artery containing blood clot was cut out 24 h later after administration to assess the degree of thrombolysis. The results of thrombolytic assay in vivo were consistent with the assay in vitro, which the differences between LK, LKM, and LKTM groups were both statistically significant. All the results of thrombolysis assays above proved that the capacity of thrombolysis in the LKTM group was optimal. It suggested that Annexin V-conjugated micelles will be a potential drug delivery system for targeted thrombolysis.

Redox and pH Dual Responsive Polymer Based Nanoparticles for In Vivo Drug Delivery

Responsive nanomaterials have emerged as promising candidates as drug delivery vehicles in order to address biomedical diseases such as cancer. In this work, polymer-based responsive nanoparticles prepared by a supramolecular approach are loaded with doxorubicin (DOX) for the cancer therapy. The nanoparticles contain disulfide bonds within the polymer network, allowing the release of the DOX payload in a reducing environment within the endoplasm of cancer cells. In addition, the loaded drug can also be released under acidic environment. In vitro anticancer studies using redox and pH dual responsive nanoparticles show excellent performance in inducing cell death and apoptosis. Zebrafish larvae treated with DOX-loaded nanoparticles exhibit an improved viability as compared with the cases treated with free DOX by the end of a 3 d treatment. Confocal imaging is utilized to provide the daily assessment of tumor size on zebrafish larva models treated with DOX-loaded nanoparticles, presenting sustainable reduction of tumor. This work demonstrates the development of functional nanoparticles with dual responsive properties for both in vitro and in vivo drug delivery in the cancer therapy.

Self-Assembly Assisted Fabrication of Dextran-Based Nanohydrogels with Reduction-Cleavable Junctions for Applications as Efficient Drug Delivery Systems

In order to overcome the key challenge in improving both fabrication efficiency and their drug delivery capability of anti-cancer drug delivery systems (ACDDS), here polyacrylic acid (PAA) grafted dextran (Dex) nanohydrogels (NGs) with covalent crosslinked structure bearing redox sensitive disulfide crosslinking junctions (Dex-SS-PAA) were synthesized efficiently through a one-step self-assembly assisted methodology (SAA). The Dex-SS-PAA were subsequently conjugated with doxorubicin through an acid-labile hydrazone bond (Dex-SS-PAA-DOX). The in vitro drug release behavior, anti-cancer effects in vivo, and biosafety of the as-prepared acid- and redox-dual responsive biodegradable NGs were systematically investigated. The results revealed that the Dex-SS-PAA-DOX exhibited pH- and redox-controlled drug release, greatly reduced the toxicity of free DOX, while exhibiting a strong ability to inhibit the growth of MDA-MB-231 tumors. Our study demonstrated that the Dex-SS-PAA-DOX NGs are very promising candidates as ACDDS for anti-cancer therapeutics.

Recent development of functional aliphatic polycarbonates for the construction of amphiphilic polymers

Functional aliphatic polycarbonates in the construction of amphiphilic polymers are summarized in seven categories (hydrophobic, hydrophilic, or/and functional unit).

Nanomaterial-based cancer immunotherapy

This review focuses on summarizing the existing work about nanomaterial-based cancer immunotherapy in detail.

A carbon based drug delivery system derived from a one-dimensional coordination polymer, doxorubicin loading and redox-responsive release

A redox-responsive drug delivery system has been fabricated through the modification of –S–S– bonds on coordination polymer derived mesoporous carbon nanoparticles with Ag as a “gatekeeper”.

Glutathione responsive polymers and their application in drug delivery systems

Materials which respond to biological cues are the subject of intense research interest due to their possible application in smart drug delivery vehicles.

Surface charge switchable and core cross-linked polyurethane micelles as a reduction-triggered drug delivery system for cancer therapy

The core cross-linked polyurethane micelles with redox sensitive and pH-responsive surface charge switchable properties were prepared by using diisocyanates as crosslinkers and studied as anticancer drug carriers.

Facile preparation of pH/reduction dual-responsive prodrug nanohydrogels for tumor-specific intracellular triggered release with enhanced anticancer efficiency

Facile approach was developed for biocompatible and biodegradable pH/reduction dual-responsive nano-prodrug for tumor specific intracellular triggered release.

Preparation and antitumor evaluation of self-assembling oleanolic acid-loaded Pluronic P105/d-α-tocopheryl polyethylene glycol succinate mixed micelles for non-small-cell lung cancer treatment

Oleanolic acid (OA) is a triterpenoid found in various fruits and vegetables and used in traditional Chinese medicine. OA plays a crucial role in the treatment of several cancers, but poor water solubility, low permeability, and significant efflux have limited its widespread clinical use. Vitamin E-d-α-tocopheryl polyethylene glycol succinate (vitamin E-TPGS) and Pluronic P105 were used to improve the solubility and permeability and to decrease the efflux of OA. OA-loaded mixed micelles were prepared by ethanol thin-film hydration. The physicochemical properties of the micelles, including zeta potential, morphology, particle size, solubility, drug loading, and drug entrapment efficiency were characterized. OA release from micelles was slower than that from the free drug system. OA uptake by A549 non-small-cell lung cancer (NSCLC) cells was enhanced by the micelles. A tumor model was established by injecting A549 cells into nude mice. In vivo imaging showed that OA-micelles could accumulate in the tumors of nude mice. Additionally, smaller tumor size and increased expression of pro-apoptotic proteins were observed in OA-micelle-treated mice, indicating that OA-micelles are more effective than free OA in treating cancer. In vitro experiments were performed using two NSCLC cell lines (A549 and PC-9). Cytotoxicity evaluations showed that the half-maximal inhibitory concentrations of free OA and OA-micelles were 36.8±4.8 and 20.9±3.7 μM, respectively, in A549 cells and 82.7±7.8 and 56.7±4.7 μM, respectively, in PC-9 cells. Apoptosis assays revealed that the apoptotic rate of OA-micelle-treated A549 and PC-9 cells was higher than that of cells treated with the same concentration of free OA. Wound healing and transwell assays showed that migration and invasion were significantly suppressed in OA-micelle-treated cells. Immunofluorescence and Western blot analyses confirmed that the epithelial–mesenchymal transition was reversed in OA-micelle-treated cells. Mixed micelles are a promising nano-drug delivery system for lung cancer treatment.

Highly Stable Fluorinated Nanocarriers with iRGD for Overcoming the Stability Dilemma and Enhancing Tumor Penetration in an Orthotopic Breast Cancer

The stability dilemma and limited tumor penetration of nanocarriers in cancer chemotherapy remain two predominant challenges for their successful clinical translation. Herein, the pH-sensitive fluorocarbon-functionalized nanocarriers (SFNs) with a tumor-homing and penetrating peptide iRGD are reported to overcome the stability dilemma and enhance tumor accumulation and penetration in an orthotopic breast cancer. The highly stable SFNs with a low critical association concentration provide a safe and spacious harbor for hydrophobic drugs. Furthermore, the stimulus-responsive evaluation and in vitro drug release study show that the SFNs can balance intracellular dissociation for drug release and extracellular stability in the blood circulation. Additionally, the tumor penetration capacity has been dramatically enhanced in 3D multicellular spheroids, effectively affecting cells far from the periphery. This can be ascribed to the coadministration of iRGD having tumor-penetrating ability and fluorocarbon chains having good cell membrane permeability. The combination of SFNs and iRGD is a viable approach to assist drugs' effective accumulation in primary and metastasized tumor sites, significantly inhibiting the breast tumor growth and curbing lung and liver metastases in an orthotopic-tumor-bearing mouse model. Taken together, this pH-sensitive fluorinated nanosystem having excellent stability and tumor accumulation and penetration properties paves the way to combat cancer.

Facile construction of near-monodisperse and dual responsive polycarbonate mixed micelles with the ability of pH-induced charge reversal for intracellular delivery of antitumor drugs

A mixed strategy was used to construct size-adjustable, pH and redox dual-responsive, near-monodisperse and charge-conversional core-shell polycarbonate carriers. First, two kinds of random polycarbonates (PC(Arss-N2CH₃)) with different ratios of hydrophobic disulfide (Arss) and hydrophilic dimethylamine functional groups (N2CH₃) (relatively hydrophobic polycarbonate (BPC) with more disulfide groups and relatively hydrophilic polycarbonate (LPC) with more dimethylamine groups) were used to construct near-monodisperse core micelles in pH 7.4 PBS. Then, a negatively charged shell polymer, poly(ethylene glycol)-b-1,2-dicarboxylic-cyclohexene anhydride modified amino polycarbonate (PEG-PCDCA), bearing acid-labile β-carboxylic amides, was added to the core micelle solution to get the desired mixed micelle. The assembly process, pH induced charge-reversal, and dual-response abilities of the resultant mixed micelles were thoroughly studied using zeta potential and dynamic light scattering (DLS). Two model drugs, Nile red (NR) and doxorubicin (DOX), were successfully loaded into the micelle and could be released in response to dithiothreitol (DTT) and acidic conditions. Confocal microscopy indicated that the micelle system could achieve effective cellular uptake and DOX release in Hela cells. Moreover, the blank micelle and the drug-loaded mixed micelle showed slight and great cytotoxicity against Hela cells, respectively, indicating their significant potential in cancer therapy.