Recent advances in development of imine-based acid-degradable polymeric nanoassemblies for intracellular drug delivery

Design, Synthesis, and Acid-Responsive Disassembly of Shell-Sheddable Block Copolymer Labeled with Benzaldehyde Acetal Junction

Smart nanoassemblies degradable through the cleavage of acid-labile linkages have attracted significant attention because of their biological relevance found in tumor tissues. Despite their high potential to achieve controlled/enhanced drug release, a systematic understanding of structural factors that affect their pH sensitivity remains challenging, particulary in the consruction of effective acid-degradable shell-sheddable nanoassemblies. Herein, the authors report the synthesis and acid-responsive degradation through acid-catalyzed hydrolysis of three acetal and ketal diols and identify benzaldehyde acetal (BzAA) exhibiting optimal hydrolysis profiles in targeted pH ranges to be a suitable candidate for junction acid-labile linkage. The authors explore the synthesis and aqueous micellization of well-defined poly(ethylene glycol)-based block copolymer bearing BzAA linkage covalently attached to a polymethacrylate block for the formation of colloidally-stable nanoassemblies with BzAA groups at core/corona interfaces. Promisingly, the investigation on acid-catalyzed hydrolysis and disassembly shows that the formed nanoassemblies meet the criteria for acid-degradable shell-sheddable nanoassemblies: slow degradation at tumoral pH = 6.5 and rapid disassembly at endo/lysosomal pH = 5.0, while colloidal stability at physiological pH = 7.4. This work guides the design principle of acid-degradable shell-sheddable nanoassemblies bearing BzAA at interfaces, thus offering the promise to address the PEG dilemma and improve endocytosis in tumor-targeting drug delivery.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB+). Irradiation by red/NIR light allowed for efficient excitation of MB+ and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

AIE luminogen labeled polymeric micelles for biological imaging and chemotherapy

In this study, an amphiphilic polymer FA-CS-DBA-CHO with aggregation-induced emission (AIE) feature was prepared by introducing 4-(diphenylamino)benzaldehyde derivative (DBA-CHO), imine bond and folic acid (FA) to the molecular structure of chitosan (CS). The amphiphilicity drove the polymer to self-assemble into micelles, and paclitaxel (PTX) could be solubilized in the hydrophobic core. Due to the excellent AIE effect, FA-CS-DBA-CHO exhibited strong cellular imaging capability. The pH-sensitive imine bond in the polymer allowed for accurate drug release in acidic environment. Both in vitro and in vivo studies demonstrated that the PTX-loaded FA-CS-DBA-CHO micelles could significantly inhibit the growth of tumor cells but without any notable toxicity. This micellar system was excellent carrier for bioimaging and chemotherapeutic drug delivery.

Metformin-Mediated Fast Charge-Reversal Nanohybrid for Deep Penetration Piezocatalysis-Augmented Chemodynamic Immunotherapy of Cancer

Immune checkpoint blockade (ICB) therapy still suffers from insufficient immune response and adverse effect of ICB antibodies. Chemodynamic therapy (CDT) has been demonstrated to be an effective way to synergize with ICB therapy. However, a low generation rate of reactive oxygen species and poor tumor penetration of CDT platforms still decline the immune effects. Herein, a charge-reversal nanohybrid Met@BF containing both Fe3O4 and BaTiO3 nanoparticles in the core and Metformin (Met) on the surface was fabricated for tumor microenvironment (TME)- and ultrasound (US)-activated piezocatalysis-chemodynamic immunotherapy of cancer. Interestingly, Met@BF had a negative charge in blood circulation, which was rapidly changed into positive when exposed to acidic TME attributed to quaternization of tertiary amine in Met, facilitating deep tumor penetration. Subsequently, with US irradiation, Met@BF produced H2O2 based on piezocatalysis of BaTiO3, which greatly enhanced the Fenton reaction of Fe3O4, thus boosting robust antitumor immune response. Furthermore, PD-L1 expression was inhibited by the local released Met to further augment the antitumor immune effect, achieving effective inhibitions for both primary and metastatic tumors. Such a combination of piezocatalysis-enhanced chemodynamic therapy and Met-mediated deep tumor penetration and downregulation of PD-L1 provides a promising strategy to augment cancer immunotherapy.

Injectable, Shear-Thinning, Self-Healing, and Self-Cross-Linkable Benzaldehyde-Conjugated Chitosan Hydrogels as a Tissue Adhesive

Benzaldehyde-conjugated chitosan (CH-CBA) was synthesized by a coupling reaction between chitosan (CH) and carboxybenzaldehyde (CBA). The pH-sensitive self-cross-linking can be achieved through the Schiff base reaction. The degree of substitution (DS) of CH-CBA was controlled at 1.4-12.7% by optimizing the pH and reagent stoichiometry. The dynamic Schiff base linkages conferred strong shear-thinning and self-healing properties to the hydrogels. The viscosity of the 2 wt/v % CH-CBA hydrogel decreased from 5.3 × 107 mPa·s at a shear rate of 10-2 s-1 to 2.0 × 103 mPa·s at 102 s-1 at pH 7.4. The CH-CBA hydrogel exhibited excellent biocompatibility in vitro and in vivo. Moreover, the hydrogel adhered strongly to porcine small intestine, colon, and cecum samples, comparable to commercial fibrin glue, and exhibited effective in vivo tissue sealing in a mouse cecal ligation and puncture model, highlighting its potential as a biomaterial for application in tissue adhesives, tissue engineering scaffolds, etc.

Advance Progress in Assembly Mechanisms of Carrier-Free Nanodrugs for Cancer Treatment

Nanocarriers have been widely studied and applied in the field of cancer treatment. However, conventional nanocarriers still suffer from complicated preparation processes, low drug loading, and potential toxicity of carriers themselves. To tackle the hindrance, carrier-free nanodrugs with biological activity have received increasing attention in cancer therapy. Extensive efforts have been made to exploit new self-assembly methods and mechanisms to expand the scope of carrier-free nanodrugs with enhanced therapeutic performance. In this review, we summarize the advanced progress and applications of carrier-free nanodrugs based on different types of assembly mechanisms and strategies, which involved noncovalent interactions, a combination of covalent bonds and noncovalent interactions, and metal ions-coordinated self-assembly. These carrier-free nanodrugs are introduced in detail according to their assembly and antitumor applications. Finally, the prospects and existing challenges of carrier-free nanodrugs in future development and clinical application are discussed. We hope that this comprehensive review will provide new insights into the rational design of more effective carrier-free nanodrug systems and advancing clinical cancer and other diseases (e.g., bacterial infections) infection treatment.

Visible Light-ATRP Driven by Tris(2-Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA500 ) in water is enabled using CuBr2 with tris(2-pyridylmethyl)amine (TPMA) as a ligand under blue or green-light irradiation without requiring any additional reagent, such as a photo-reductant, or the need for prior deoxygenation. Polymers with low dispersity (Đ = 1.18-1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co-catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr]+ absorbs light.

Metal-based nanomaterials and nanocomposites as promising frontier in cancer chemotherapy

Cancer is a disease associated with complex pathology and one of the most prevalent and leading reasons for mortality in the world. Current chemotherapy has challenges with cytotoxicity, selectivity, multidrug resistance, and the formation of stemlike cells. Nanomaterials (NMs) have unique properties that make them useful for various diagnostic and therapeutic purposes in cancer research. NMs can be engineered to target cancer cells for early detection and can deliver drugs directly to cancer cells, reducing side effects and improving treatment efficacy. Several of NMs can also be used for photothermal therapy to destroy cancer cells or enhance immune response to cancer by delivering immune-stimulating molecules to immune cells or modulating the tumor microenvironment. NMs are being modified to overcome issues, such as toxicity, lack of selectivity, increase drug capacity, and bioavailability, for a wide spectrum of cancer therapies. To improve targeted drug delivery using nano-carriers, noteworthy research is required. Several metal-based NMs have been studied with the expectation of finding a cure for cancer treatment. In this review, the current development and the potential of plant and metal-based NMs with their effects on size and shape have been discussed along with their more effective usage in cancer diagnosis and treatment.

Recent Advances in the Application of ATRP in the Synthesis of Drug Delivery Systems

Advances in atom transfer radical polymerization (ATRP) have enabled the precise design and preparation of nanostructured polymeric materials for a variety of biomedical applications. This paper briefly summarizes recent developments in the synthesis of bio-therapeutics for drug delivery based on linear and branched block copolymers and bioconjugates using ATRP, which have been tested in drug delivery systems (DDSs) over the past decade. An important trend is the rapid development of a number of smart DDSs that can release bioactive materials in response to certain external stimuli, either physical (e.g., light, ultrasound, or temperature) or chemical factors (e.g., changes in pH values and/or environmental redox potential). The use of ATRPs in the synthesis of polymeric bioconjugates containing drugs, proteins, and nucleic acids, as well as systems applied in combination therapies, has also received considerable attention.

Dynamic Imine Bonding Facilitates Mannan Release from a Nanofibrous Peptide Hydrogel

Recently, there has been increased interest in using mannan as an immunomodulatory bioconjugate. Despite notable immunological and functional differences between the reduced (R-Man) and oxidized (O-Man) forms of mannan, little is known about the impact of mannan oxidation state on its in vivo persistence or its potential controlled release from biomaterials that may improve immunotherapeutic or prophylactic efficacy. Here, we investigate the impact of oxidation state on the in vitro and in vivo release of mannan from a biocompatible and immunostimulatory multidomain peptide hydrogel, K2(SL)6K2 (abbreviated as K2), that has been previously used for the controlled release of protein and small molecule payloads. We observed that O-Man released more slowly from K2 hydrogels in vitro than R-Man. In vivo, the clearance of O-Man from K2 hydrogels was slower than O-Man alone. We attributed the slower release rate to the formation of dynamic imine bonds between reactive aldehyde groups on O-Man and the lysine residues on K2. This imine interaction was also observed to improve K2 + O-Man hydrogel strength and shear recovery without significantly influencing secondary structure or peptide nanofiber formation. There were no observed differences in the in vivo release rates of O-Man loaded in K2, R-Man loaded in K2, and R-Man alone. These data suggest that, after subcutaneous injection, R-Man naturally persists longer in vivo than O-Man and minimally interacts with the peptide hydrogel. These results highlight a potentially critical, but previously unreported, difference in the in vivo behavior of O-Man and R-Man and demonstrate that K2 can be used to normalize the release of O-Man to that of R-Man. Further, since K2 itself is an adjuvant, a combination of O-Man and K2 could be used to enhance the immunostimulatory effects of O-Man for applications such as infectious disease vaccines and cancer immunotherapy.

Tumor Targeting and pH-Sensitive Inclusion Complex Based on HP-β-CD as a Potential Carrier for Paclitaxel: Fabrication, Molecular Docking, and Characterization

In this study, a tumor-targeting and pH-sensitive inclusion complex based on the host-guest recognition between the chitosan and folic acid grafted HP-β-CD (FA-CS-CD) and stearic acid modified 2-benzimidazolemethanol (BM-SA) was designed and fabricated for the controlled delivery of paclitaxel (PTX). Through the combination of computational simulations and experiments, the interaction between FA-CS-CD, BM-SA, and PTX was investigated, and the optimized preparation method was obtained. For the optimized PTX-loaded FA-CS-CD/BM-SA inclusion complex, the particle size and zeta potential were 146 nm and +15.4 mV, respectively. In vitro drug release study revealed the pH-triggered drug release behavior of the inclusion complex. Both in vitro and in vivo evaluations demonstrated that the PTX-loaded FA-CS-CD/BM-SA inclusion complex exhibited enhanced antitumor efficiency and minimized systemic toxicity. This system might be a promising carrier for PTX.

pH-triggered cancer-targeting polymers: From extracellular accumulation to intracellular release

Stimuli-responsive polymers are promising to achieve targeted delivery, improved stability during circulation, and controlled release of therapeutic and diagnostic agents. Among them, pH-responsive polymeric nanocarriers have attracted significant attention as pH varies in different body fluids (e.g., stomach, intestine, and colon) and intracellular organelles (e.g., endosome, lysosome, and mitochondria) to maintain homeostasis, while distinctive pH changes are also found in certain pathological states. For example, the extracellular environment of the tumor is acidic, which can be employed to drive selective delivery. During the internalization process, since most nanocarriers enter cells upon endocytosis where a drop of pH from 6.5 to 5.0 can occur from endosome to lysosome, pH-sensitive groups have been developed for enhanced cargo release. In this review, both non-covalent and covalent interactions responsive to pH changes are introduced, with a focus on the structure-property relationship and their applications in cancer targeting and endosomal escape.

Design and fabrication of chitosan-based AIE active micelles for bioimaging and intelligent delivery of paclitaxel

In this study, cetyl 4-formylbenzoate alkyl and 4-(2-hydroxyethoxy) benzophenonesalicylaldazide modified biotinylated chitosan (CS-BT-HBS-CB) featured with aggregation-induced emission (AIE) characteristic, active tumor-targeting ability and pH-responsive drug release property was designed and synthesized. The polymer was fabricated by introducing hydrophobic segment, tumor targeting ligand, acid-sensitive bond and AIE fluorophore to the backbone of chitosan. Due to its amphiphilicity, the polymer could self-assemble into micelles and encapsulate paclitaxel (PTX) to form PTX-loaded CS-BT-HBS-CB micelles. The mean size of the micelles was 167 nm, which was beneficial to the EPR effect. Moreover, with the help of above functional groups, the micelles exhibited excellent AIE effect, triggered drug release behavior by acidic condition, selective internalization by MCF-7 cells and excellent cellular imaging capability. In vivo studies revealed that the PTX-loaded CS-BT-HBS-CB micelles could enhance the antitumor efficacy with low systemic toxicity. This micellar system would be a potential candidate for cancer therapy and bioimaging.

Design of Smart Size-, Surface-, and Shape-Switching Nanoparticles to Improve Therapeutic Efficacy

Multiple biological barriers must be considered in the design of nanomedicines, including prolonged blood circulation, efficient accumulation at the target site, effective penetration into the target tissue, selective uptake of the nanoparticles into target cells, and successful endosomal escape. However, different particle sizes, surface chemistries, and sometimes shapes are required to achieve the desired transport properties at each step of the delivery process. In response, this review highlights recent developments in the design of switchable nanoparticles whose size, surface chemistry, shape, or a combination thereof can be altered as a function of time, a disease-specific microenvironment, and/or via an externally applied stimulus to enable improved optimization of nanoparticle properties in each step of the delivery process. The practical use of such nanoparticles in chemotherapy, bioimaging, photothermal therapy, and other applications is also discussed.

Targeted Delivery Methods for Anticancer Drugs

Simple Summary

The current main technological strategies for the delivery of anticancer drugs are discussed herein. This comprehensive review may help researchers design suitable delivery systems.

Abstract

Several drug-delivery systems have been reported on and often successfully applied in cancer therapy. Cell-targeted delivery can reduce the overall toxicity of cytotoxic drugs and increase their effectiveness and selectivity. Besides traditional liposomal and micellar formulations, various nanocarrier systems have recently become the focus of developmental interest. This review discusses the preparation and targeting techniques as well as the properties of several liposome-, micelle-, solid-lipid nanoparticle-, dendrimer-, gold-, and magnetic-nanoparticle-based delivery systems. Approaches for targeted drug delivery and systems for drug release under a range of stimuli are also discussed.

Synthesis of multiple stimuli-responsive degradable block copolymers via facile carbonyl imidazole-induced postpolymerization modification

A robust approach that centers on carbonyl imidazole chemistry was used to synthesize a triple-stimuli-responsive degradable block copolymer labeled with acetal, disulfide, and o-nitrobenzyl groups exhibiting acid, reduction, and light responses.