One-Step "Click Chemistry"-Synthesized Cross-Linked Prodrug Nanogel for Highly Selective Intracellular Drug Delivery and Upregulated Antitumor Efficacy

Construction of Peptide-Lipoic Acid Cationic Polymers with Redox Responsiveness and Low Toxicity for Gene Delivery

As gene therapy continues to evolve, the development of safe and effective cationic polymer carriers is critical. In this work, three polymers have been prepared by ring-opening polymerization on the basis of peptide-lipoic acid monomers. By adjusting the sequence of the peptides, redox-responsive cationic polymers with different positive charge numbers were obtained, as well as investigating their performance as gene carriers. The results showed that the polymers complexed with negatively charged genes by electrostatic interaction and successfully transported the genes into the cells, additionally degrading and releasing the genes under glutathione (GSH) conditions. Furthermore, the polymers as gene carriers in different cell lines demonstrated lower cytotoxicity, with an excellent cell survival rate of 8 times higher than the "gold standard" polyethylenimine (PEI) at the same concentration. In vitro transfection experiments showed that the polymers successfully released and transfected genes into cells, demonstrating their immense potential in gene therapy.

CuAAC ensembled 1,2,3-triazole linked nanogels for targeted drug delivery: a review

Copper(i) catalyzed alkyne azide cycloaddition (CuAAC), the quintessential example of 'click chemistry', provides an adaptable and adequate platform for the synthesis of nanogels for sustained drug release at targeted sites because of their better biocompatibility. The coupling of drugs, carried out via various synthetic routes including CuAAC, into long-chain polymeric forms like nanogels has exhibited considerable assurance in therapeutic advancements and intracellular drug delivery due to the progression of water solubility, evacuation of precocious drug release, and improved upthrust of the pharmacokinetics of the nanogels, thereby rendering them as better and efficient drug carriers. The inefficiency of drug transmission to the target areas due to the resistance of complex biological barriers in vivo is a major hurdle that impedes the therapeutic translation of nanogels. This review compiles the data of nanogels synthesized specifically via CuAAC 'click' methodology, as scaffolds for targeted drug delivery and their assimilation into nanomedicine. In addition, it elaborates the ability of CuAAC to graft specific moieties and conjugating biomolecules like proteins and growth factors, onto orthogonally functionalized polymer chains with various chemical groups resulting in nanogels that are not only more appealing but also more effective at delivering drugs, thereby enhancing their site-specific target approach and initiating selective therapies.

Biomedicine Innovations and Its Nanohydrogel Classifications

As one of the most cutting-edge and promising polymer crosslinked network nanoparticle systems. Polymer nano-sized hydrogels (nanogels) have been a hot topic in the biomedical field over the last few decades. Due to their unique characteristics, which include their relatively high drug encapsulation efficiency, ease of preparation, high tunability, low toxicity, high stability in serum and responsive behavior to a range of stimuli to facilitate drug release. Nanogels are thought to be the next generation of drug delivery systems that can completely change the way that drug delivery systems have an impact on patients' lives. Nanogels have demonstrated significant potential in a variety of fields, including chemotherapy, diagnosis, organ targeting, and delivery of bioactive molecules of different dimensions. However, the lack of substantial clinical data from nanogels becomes one of the major barriers to translating the nanogel concept into a practical therapeutic application for many disease conditions. In addition, nanogel safety profiles have been the major concern that hinders it advancement to the clinical trial phase. This review aims to emphasize the unique properties of nanogels as delivery systems for a variety of bioactive molecules over other nano-delivery systems. Also, this review attempts to give insight into the recent progress in nanogels as a carrier in the field of nanomedicine to overcome complex biological barriers. Relevant scientific data and clinical rationale for the development and the potential use of nanogel as a carrier for targeted therapeutic interventions are discussed. Finally, the concluding points of this review highlight the importance of understanding the long-term toxicity profile of nanogel within the biological system to fully understand their biocompatibility.

Clickable Polysaccharides for Biomedical Applications: A Comprehensive Review

Recent advances in materials science and engineering highlight the importance of designing sophisticated biomaterials with well-defined architectures and tunable properties for emerging biomedical applications. Click chemistry, a powerful method allowing specific and controllable bioorthogonal reactions, has revolutionized our ability to make complex molecular structures with a high level of specificity, selectivity, and yield under mild conditions. These features combined with minimal byproduct formation have enabled the design of a wide range of macromolecular architectures from quick and versatile click reactions. Furthermore, copper-free click chemistry has resulted in a change of paradigm, allowing researchers to perform highly selective chemical reactions in biological environments to further understand the structure and function of cells. In living systems, introducing clickable groups into biomolecules such as polysaccharides (PSA) has been explored as a general approach to conduct medicinal chemistry and potentially help solve healthcare needs. De novo biosynthetic pathways for chemical synthesis have also been exploited and optimized to perform PSA-based bioconjugation inside living cells without interfering with their native processes or functions. This strategy obviates the need for laborious and costly chemical reactions which normally require extensive and time-consuming purification steps. Using these approaches, various PSA-based macromolecules have been manufactured as building blocks for the design of novel biomaterials. Clickable PSA provides a powerful and versatile toolbox for biomaterials scientists and will increasingly play a crucial role in the biomedical field. Specifically, bioclick reactions with PSA have been leveraged for the design of advanced drug delivery systems and minimally invasive injectable hydrogels. In this review article, we have outlined the key aspects and breadth of PSA-derived bioclick reactions as a powerful and versatile toolbox to design advanced polymeric biomaterials for biomedical applications such as molecular imaging, drug delivery, and tissue engineering. Additionally, we have also discussed the past achievements, present developments, and recent trends of clickable PSA-based biomaterials such as 3D printing, as well as their challenges, clinical translatability, and future perspectives.

A Study of Glutathione-Responsive Dual-Drug-Loaded Nanoparticles in Anti-Osteosarcoma Treatment

We connected polyglutamic acid and methotrexate (MTX) through disulfide bonds to prepare glutathione-responsive nanoparticles (MTX NPs) and encapsulated doxorubicin (DOX) to obtain dual drug-loaded NPs (DOX/MTX NPs) (Fig. 1). The appearance of the carbonyl stretching vibration peak at approximately 1640 cm−1 in the results of the infrared spectrum proved the successful synthesis of three kinds of nanoparticles (NPs) with different feeding ratios. The particle sizes of NPs with different feeding ratios were 100–200 nm, and the encapsulation of DOX slightly increased the size, while the surface charge was always negative. The release of MTX at 10 mM glutathione (GSH) was as high as 91.45%, and that of DOX was 89.44%, suggesting that the breakage of disulfide bonds leads to the disintegration of NPs. The results of the cell experiment showed that the encapsulation of DOX effectively increased toxicity and side effects in 143B cells and significantly induced cell apoptosis, and the inhibition of the migration rate increased as the feeding ratio increased. In animal experiments, DOX/MTX NPs significantly induced tumor cell apoptosis and inhibited cell proliferation and tumor growth. The nanoparticles had excellent tumor-targeting properties. Tumor-targeted NPs with the combined action of the two drugs provided a good strategy for the efficient and precise treatment of osteosarcoma.

Recent Advances in Poly(α-L-glutamic acid)-Based Nanomaterials for Drug Delivery

Poly(α-L-glutamic acid) (PGA) is a class of synthetic polypeptides composed of the monomeric unit α-L-glutamic acid. Owing to their biocompatibility, biodegradability, and non-immunogenicity, PGA-based nanomaterials have been elaborately designed for drug delivery systems. Relevant studies including the latest research results on PGA-based nanomaterials for drug delivery have been discussed in this work. The following related topics are summarized as: (1) a brief description of the synthetic strategies of PGAs; (2) an elaborated presentation of the evolving applications of PGA in the areas of drug delivery, including the rational design, precise fabrication, and biological evaluation; (3) a profound discussion on the further development of PGA-based nanomaterials in drug delivery. In summary, the unique structures and superior properties enables PGA-based nanomaterials to represent as an enormous potential in biomaterials-related drug delivery areas.

Advances in the Novel Nanotechnology for the Targeted Tumor Therapy by the Transdermal Drug Delivery

Despite modern medicine advances greatly, cancer remains a serious challenge to world health for which effective methods of treatment have hardly been developed yet. However, throughout the recent years, the rapid-developing nanotechnology has provided a new outlook of cancer therapy by transdermal drug delivery. By disrupting the stratum corneum, drugs are delivered through the skin and navigated to the tumor site by drug delivery systems such as nanogels, microneedles, etc. The superiorities include the improvement of drug pharmacokinetics as well as reduced side effects. This paper reviews the reported novel development of transdermal drug delivery systems for targeted cancer therapy. Advanced techniques for penetrating the skin will be discussed as well.

Exploring the potential of polypeptide–polypeptoide hybrid nanogels for mucosal delivery

By chain extension of polysarcosine with phenylalanine and cystine, nanogels are formed. The nanogels facilitate the transport of dyes across an artificial mucus coated membrane and their release by reductive bond cleavage.

Dually Cross-Linked Core-Shell Structure Nanohydrogel with Redox-Responsive Degradability for Intracellular Delivery

A redox-responsive nanocarrier is a promising strategy for the intracellular drug release because it protects the payload, prevents its undesirable leakage during extracellular transport, and favors site-specific drug delivery. In this study, we developed a novel redox responsive core-shell structure nanohydrogel prepared by a water in oil nanoemulsion method using two biocompatible synthetic polymers: vinyl sulfonated poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate)-polyethylene glycol-poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate) triblock copolymer, and thiolated hyaluronic acid. The influence on the nanohydrogel particle size and distribution of formulation parameters was investigated by a three-level full factorial design to optimize the preparation conditions. The surface and core-shell morphology of the nanohydrogel were observed by scanning electron microscope, transmission electron microscopy, and further confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy from the standpoint of chemical composition. The redox-responsive biodegradability of the nanohydrogel in reducing environments was determined using glutathione as reducing agent. A nanohydrogel with particle size around 250 nm and polydispersity index around 0.1 is characterized by a thermosensitive shell which jellifies at body temperature and crosslinks at the interface of a redox-responsive hyaluronic acid core via the Michael addition reaction. The nanohydrogel showed good encapsulation efficiency for model macromolecules of different molecular weight (93% for cytochrome C, 47% for horseradish peroxidase, and 90% for bovine serum albumin), capacity to retain the peroxidase-like enzymatic activity (around 90%) of cytochrome C and horseradish peroxidase, and specific redox-responsive release behavior. Additionally, the nanohydrogel exhibited excellent cytocompatibility and internalization efficiency into macrophages. Therefore, the developed core-shell structure nanohydrogel can be considered a promising tool for the potential intracellular delivery of different pharmaceutical applications, including for cancer therapy.

Nanogels: A novel approach in antimicrobial delivery systems and antimicrobial coatings

The implementation of nanotechnology to develop efficient antimicrobial systems has a significant impact on the prospects of the biomedical field. Nanogels are soft polymeric particles with an internally cross-linked structure, which behave as hydrogels and can be reversibly hydrated/dehydrated (swollen/shrunken) by the dispersing solvent and external stimuli. Their excellent properties, such as biocompatibility, colloidal stability, high water content, desirable mechanical properties, tunable chemical functionalities, and interior gel-like network for the incorporation of biomolecules, make them fascinating in the field of biological/biomedical applications. In this review, various approaches will be discussed and compared to the newly developed nanogel technology in terms of efficiency and applicability for determining their potential role in combating infections in the biomedical area including implant-associated infections.

Stimuli-responsive polypeptides for controlled drug delivery

Controlled drug delivery systems, which could release loaded therapeutics upon physicochemical changes imposed by physiological triggers in the desired zone and during the required period of time, offer numerous advantages over traditional drug carriers including enhanced therapeutic effects and reduced toxicity. A polypeptide is a biocompatible and biodegradable polymer, which can be conveniently endowed with stimuli-responsiveness by introducing natural amino acid residues with innate stimuli-responsive characteristics or introducing responsive moieties to its side chains using simple conjugating methods, rendering it an ideal biomedical material for controlled drug delivery. This feature article summarizes our recent work and other relevant studies on the development of polypeptide-based drug delivery systems that respond to single or multiple physiological stimuli (e.g., pH, redox potential, glucose, and hypoxia) for controlled drug delivery applications. The material designs, synthetic strategies, loading and controlled-release mechanisms of drugs, and biomedical applications of these stimuli-responsive polypeptides-based drug delivery systems are elaborated. Finally, the challenges and opportunities in this field are briefly discussed.

Polypeptides-Drug Conjugates for Anticancer Therapy

Polypeptides are an important class of biodegradable polymers that have been widely used in drug delivery field. Owing to the controllable synthesis and robust side chain-functionalization ability, polypeptides have long been ideal candidates for conjugation with anticancer drugs. The chemical conjugation of anticancer drugs with polypeptides, termed polypeptides-drug conjugates, has demonstrated several advantages in improving pharmacokinetics, enhancing drug targeting, and controlling drug release, thereby leading to enhanced therapeutic outcomes with reduced side toxicities. This review focuses on the recent advances in the design and preparation of polypeptides-drug conjugates for enhanced anticancer therapy. Strategies for conjugation of different types of drugs, including small-molecule chemotherapeutic drugs, proteins, vascular disrupting agents, and gas molecules, onto polypeptides backbone are summarized. Finally, the challenges and future perspectives on the development of innovative polypeptides-drug conjugates for clinical cancer treatment are also presented.

Covalently Crosslinked Hydrogels via Step-Growth Reactions: Crosslinking Chemistries, Polymers, and Clinical Impact

Hydrogels are an important class of biomaterials with the unique property of high-water content in a crosslinked polymer network. In particular, chemically crosslinked hydrogels have made a great clinical impact in past years because of their desirable mechanical properties and tunability of structural and chemical properties. Various polymers and step-growth crosslinking chemistries are harnessed for fabricating such covalently crosslinked hydrogels for translational research. However, selecting appropriate crosslinking chemistries and polymers for the intended clinical application is time-consuming and challenging. It requires the integration of polymer chemistry knowledge with thoughtful crosslinking reaction design. This task becomes even more challenging when other factors such as the biological mechanisms of the pathology, practical administration routes, and regulatory requirements add additional constraints. In this review, key features of crosslinking chemistries and polymers commonly used for preparing translatable hydrogels are outlined and their performance in biological systems is summarized. The examples of effective polymer/crosslinking chemistry combinations that have yielded clinically approved hydrogel products are specifically highlighted. These hydrogel design parameters in the context of the regulatory process and clinical translation barriers, providing a guideline for the rational selection of polymer/crosslinking chemistry combinations to construct hydrogels with high translational potential are further considered.

Polypeptide-based drug delivery systems for programmed release

Recent years have seen increasing interests in the use of ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs) to prepare synthetic polypeptides, a class of biocompatible and versatile materials, for various biomedical applications. Because of their rich side-chain functionalities, diverse hydrophilicity/hydrophobicity profiles, and the capability of forming stable secondary structures, polypeptides can assemble into a variety of well-organized nano-structures that have unique advantages in drug delivery and controlled release. Herein, we review the design and use of polypeptide-based drug delivery system derived from NCA chemistry, and discuss the future perspectives of this exciting and important biomaterial area that may potentially change the landscape of next-generation therapeutics and diagnosis. Given the high significance of precise control over release for polypeptide-based systems, we specifically focus on the versatile designs of drug delivery systems capable of programmed release, through the changes in the chemical and physical properties controlled by the built-in molecular structures of polypeptides.

Synthesis of Nanogels: Current Trends and Future Outlook

Nanogels represent an innovative platform for tunable drug release and targeted therapy in several biomedical applications, ranging from cancer to neurological disorders. The design of these nanocarriers is a pivotal topic investigated by the researchers over the years, with the aim to optimize the procedures and provide advanced nanomaterials. Chemical reactions, physical interactions and the developments of engineered devices are the three main areas explored to overcome the shortcomings of the traditional nanofabrication approaches. This review proposes a focus on the current techniques used in nanogel design, highlighting the upgrades in physico-chemical methodologies, microfluidics and 3D printing. Polymers and biomolecules can be combined to produce ad hoc nanonetworks according to the final curative aims, preserving the criteria of biocompatibility and biodegradability. Controlled polymerization, interfacial reactions, sol-gel transition, manipulation of the fluids at the nanoscale, lab-on-a-chip technology and 3D printing are the leading strategies to lean on in the next future and offer new solutions to the critical healthcare scenarios.

Nanogels Capable of Triggered Release

This chapter provides an overview of soft and environmentally sensitive polymeric nanosystems, which are widely known as nanogels. These particles keep great promise to the area of drug delivery due to their high biocompatibility with body fluids and tissues, as well as due to their ability to encapsulate and release the loaded drugs in a controlled manner. For a long period of time, the controlled drug delivery systems were designed to provide long-termed or sustained release. However, some medical treatments such as cancer chemotherapy, protein and gene delivery do not require the prolonged release of the drug in the site of action. In contrast, the rapid increase of the drug concentration is needed for gaining the desired biological effect. Being very sensitive to surrounding media and different stimuli, nanogels can undergo physico-chemical transitions or chemical changes in their structure. Such changes can result in more rapid release of the drugs, which is usually referred to as triggered drug release. Herein we give the basic information on nanogel unique features, methods of sensitive nanogels preparation, as well as on main mechanisms of triggered release. Additionally, the triggered release of low-molecular drugs and biomacromolecules are discussed.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

pH-Sensitive nanogels for drug delivery in cancer therapy

Compared to normal tissue, solid tumors exhibit a lower pH value. Such pH gradient can be used to design pH-sensitive nanogels for selective drug delivery. The acid-sensitive elements in the nanogel cause it to swell/degrade rapidly, followed by rapid drug release.

Robust and smart polypeptide-based nanomedicines for targeted tumor therapy

Nanomedicines based on synthetic polypeptides are among the most versatile and advanced platforms for tumor therapy. Notably, several polypeptide-based nanodrugs are currently under human clinical assessments. The previous (pre)clinical studies clearly show that dynamic stability (i.e. stable in circulation while destabilized in tumor) of nanomedicines plays a vital role in their anti-tumor performance. Various strategies have recently been developed to design dynamically stabilized polypeptide-based nanomedicines by e.g. crosslinking the nanovehicles with acid, reactive oxygen species (ROS), glutathione (GSH), or photo-sensitive linkers, inter-crosslinking between vehicles and drugs, introducing π-π stacking or lipid-lipid interactions in the nanovehicles, chemically conjugating drugs to vehicles, and forming unimolecular micelles. Interestingly, these robust and smart nanodrugs have demonstrated improved tumor targetability, anti-tumor efficacy, as well as safety profiles in different tumor models. In this review, representative strategies to robust and smart polypeptide-based nanomedicines for targeted treatment of varying malignancies are highlighted. The exciting development of dynamic nanomedicines will foresee further increasing clinical translation in the future.

Injectable Click Chemistry-based Bioadhesives for Accelerated Wound Closure

Tissue adhesives play a vital role in surgical processes as a substitute for sutures in wound closure. However, several existing tissue adhesives suffer from cell toxicity, weak tissue-adhesive strength, and high cost. In this study, by taking advantage of the fast and specific inverse-demand Diels-Alder cycloaddition reaction, a series of bioadhesives were produced by employing copper-free click chemistry pair trans-cyclooctene (TCO) /tetrazine (Tz) in chitosan. The gelation time of the bioadhesives can be optimized to be less than 2 minutes, which meets the need for surgical wound closure in practice. By adding 4-arm polyethylene glycol propionaldehyde (PEG-PALD) as a co-crosslinker, the adhesive strength of the bioadhesives was optimized to be 2.3 times higher than that of the conventional fibrin glue. Moreover, by adjusting the amount of the co-crosslinker, the swelling ratio and pore size of the chitosan bioadhesives can be tuned to fit the need of drug encapsulation and cell seeding. The chitosan bioadhesives possess no significant in vitro cytotoxicity. Using a mice skin incision wound model, we found that the chitosan bioadhesives were able to close the wound faster and promote wound healing process than the fibrin glue. In conclusion, our results support that the innovative click-chemistry based bioadhesives have been developed with improved physical and biological properties for surgical wound closures. STATEMENT OF SIGNIFICANCE: The manuscript describes a new group of click chemistry-based chitosan bioadhesives fabricated by reacting copper-free click chemistry pair trans-cyclooctene/tetrazine with co-crosslinker PEG-PALD. The new bioadhesives possess the properties of simple preparation, injectability, fast gelation, a minimal cytotoxicity, strong adhesive strength to tissue, and enhanced wound healing responses. This innovative strategy may draw interests of readers from the field of biomaterials, drug delivery, surgical device, and translational medicine.

Using Polypeptide Bearing Furan Side Chains as a General Platform to Achieve Highly Effective Preparation of Smart Glycopolypeptide Analogue-Based Nano-Prodrugs for Cancer Treatment

Although several synthetic polypeptide-based nano-prodrugs (NPDs) have entered clinical trials for cancer treatment, achieving a highly effective production of the NPDs for clinical translation remains a challenge. Herein, we develop a typical preparation of pH/glutathione (GSH) dual-responsive glycopolypeptide analogue NPDs having a high drug capsulation/loading efficiency of ca. 93% and ca. 27% even based on ring-opening polymerization (ROP) of a novel and general furan-containing N-carboxyanhydride (NCA) monomer, which facilitates the Diels-Alder (D-A) side-chain functionalization by maleimide modified chemotherapy drug without using any reactive additives. High reactivity of the D-A reaction resulting in the high preparation efficiency of the NPDs is confirmed by ¹H NMR and density functional theory (DFT) calculations. The self-assembled properties as well as the dual-responsiveness of the NPDs are systemically studied by particle size and zeta potential assay, transmission electron microscopy and drug-delivery dynamics. The cell uptake mechanism, intracellular drug distribution, in vitro/vivo antitumor activity evaluations and the main organ damages of the NPDs are all investigated. Our work can provide a good solution to solve the inefficient fabrication of the smart synthetic polypeptide-based micelles for cancer treatment by following this general and sophisticated platform.

Exogenous vitamin C triggered structural changes of redox-activated dual core-crosslinked biodegradable nanogels for boosting the antitumor efficiency

Premature leakage of drugs during blood circulation and slow drug release at the tumor site are two major challenges that nanocarriers have to overcome to achieve successful cancer therapy. Herein, a dual core-crosslinked, redox-sensitive polymeric nanogel (sDL) was constructed by the self-assembly of two star-shaped amphiphilic copolymers (4sP(EG-b-LLA)-N₃, 4sP(EG-b-DLA)-N₃) in the presence of a redox-sensitive crosslinker (d-ss-Bu), where hydrophilic polyethylene glycol (PEG) was used as the shell and the functional hydrophobic poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) were used as the dual crosslinked core via stereocomplex formation and chemical interactions. The dual core-crosslinked structure of the nanogels allowed for almost 2-fold enhanced doxorubicin (DOX)-loading capacity, favorable structural stability to restrict the premature leakage of therapeutic drug and smaller particle size to accelerate the internalization efficiency compared to non-crosslinked nanocarriers. Furthermore, exogenous vitamin C (Vc) can trigger the breakage of redox-sensitive bonds to accelerate drug release from nanogels for improved in vitro antitumor efficacy. Notably, in vivo near-infrared imaging showed that the highly stable DOX-loaded sDL efficiently aggregated at the tumor site. Sequential administration of DOX-loaded sDL and Vc exhibited the highest tumor inhibition effect without associated systemic toxicity compared to the corresponding single injection of Vc or DOX-loaded sDL control groups for in vivo studies, indicating that exogenous administration of Vc can synergistically impact the release of DOX from sDL. Therefore, the developed nanogels proved to be promising smart carriers for achieving precise tunable-stability in response to relevant environments and the combination of Vc to activate reduction-sensitive drug delivery is a promising approach to maximize the therapeutic efficacy.

Hypoxia-Responsive Polypeptide Nanoparticles Loaded with Doxorubicin for Breast Cancer Therapy

Microenvironments of various solid tumors are characterized by hypoxia. Herein, we report a novel nanoparticle that can selectively release loaded drugs in hypoxic environments. The nanoparticle was prepared using a hypoxia-responsive amphiphilic polymer in aqueous media. The polymer was synthesized by conjugating a hydrophobic small molecule, 4-nitrobenzyl (3-azidopropyl) carbamate, to the side chains of an mPEG-PPLG copolymer. Doxorubicin (DOX) could be loaded into the nanoparticles with a high efficiency of 97.8%. The generated drug-loaded micellar nanoparticles (PPGN@DOX) presented hypoxia-sensitive drug release behavior in vitro. Meanwhile, PPGN@DOX could be effectively internalized by 4T1 cells and could release DOX into the cell nuclei under hypoxic conditions. The in vitro anticancer results suggested that PPGN@DOX presented superior tumor cell-killing ability compared with free DOX in hypoxic environments. Furthermore, PPGN@DOX prolonged the blood circulation time and improved the biological distribution of DOX, resulting in increased antitumor outcomes and reduced side effects in vivo. Overall, the present work demonstrates that hypoxia-responsive nanoparticles have great application potential in the treatment of hypoxic tumors.

Celastrol Self-Stabilized Nanoparticles for Effective Treatment of Melanoma

Background

Celastrol (CEL), a triterpene extracted from the Chinese herb tripterygium wilfordii, has been reported to have profound anticancer activities. However, poor water solubility and high side toxicities have severely restricted the clinical applications of CEL.

Purpose

We proposed a facile “in situ drug conjugation-induced self-assembly” strategy to prepare CEL-loaded nanoparticles (CEL-NPs) that exhibited enhanced antitumor activity against melanoma.

Methods

First, the CEL was chemically conjugated onto a methoxyl poly(ethylene glycol)-b-poly(L-lysine) (mPEG-PLL) backbone, resulting in the conversion of the double hydrophilic mPEG-PLL polymer into an amphiphilic polymer prodrug, mPEG-PLL/CEL. The obtained mPEG-PLL/CEL could self-assemble into stable micelles in aqueous solution due to the hydrophobic association of CEL moieties in the side chains and the possible electrostatic interaction between the carboxyl group in CEL and the residue amine group in the PLL segment. Thus, the obtained mPEG-PLL/CEL nanoparticles were named CEL self-stabilized nanoparticles (CEL-NPs), which were then characterized by dynamic light scattering and transmission electron microscopy. Furthermore, the antitumor effects of the CEL-NPs were investigated by an MTT assay in vitro and in a B16F10 tumor-bearing mice model.

Results

The CEL-NPs exhibited sustained drug release behavior and were effectively endocytosed by B16F10 cells. Furthermore, the in vivo antitumor evaluation demonstrated that the CEL-NPs had remarkably higher tumor growth inhibition rates and lower systemic side effects than free CEL.

Conclusion

In summary, our present work not only demonstrates the generation of stable CEL-loaded nanoparticles for the efficient treatment of melanoma but also describes a general way to prepare drug self-stabilized nanomedicine for anticancer therapy.

An overview of nanogel-based vaccines

Introduction: The development of more efficacious vaccines, especially subunit vaccines administered via non-invasive routes, is a priority in vaccinology. Nanogels are materials that can meet the requirements to serve as efficient vaccine delivery vehicles (in terms of thermo-sensitivity, biocompatibility, and pH-responsiveness; among others); thus there is a growing interest in exploring the potential of nanogels for vaccine development. Areas covered: Herein, a critical analysis of nanogel synthesis methodologies is presented and nanogel-based vaccines under development are summarized and placed in perspective. Promising vaccine candidates based on nanogels have been reported for cancer, obesity, and infectious diseases (mainly respiratory diseases). Some of the candidates were administered by mucosal routes which are highly attractive in terms of simple administration and induction of protective responses at both mucosal and systemic levels. Expert opinion: The most advanced models of nanogel-based vaccines comprise candidates against cancer, based on cholesteryl pullulan nanogels evaluated in clinical trials with promising findings; as well as some vaccines against respiratory pathogens tested in mice thus far. Nonetheless, the challenge for this field is advancing in clinical trials and proving the protective potential in test animals for many other candidates. Implementing green synthesis approaches for nanogels is also required.

Quantitative and high drug loading of self-assembled prodrug with defined molecular structures for effective cancer therapy

Nanomedicines have made significant progress in the delivery of small molecular drugs, many challenges, however, still remain to be overcome, such as unsatisfactory drug loading, formulation instability, premature drug leakage, and poor blood circulation. Herein, an innovative glutathione (GSH)-sensitive amphiphilic dendritic prodrug with quantitative and high drug loading (>30 wt%) is reported. The multi-armed structure of prepared prodrug can self-assemble into nanoparticles in aqueous solution without the introduction of any organic solvents. The self-assembled prodrug nanoparticle is composed of the following key components: (i) polyethylene glycol (PEG) outer shell ensuring biocompatibility and prolonging blood circulation, (ii) prodrug inner core responding to GSH for triggered release of intact drug, (iii) multi-armed dendritic structure facilitating self-assembly and enhancing drug loading content, (iv) covalent drug conjugation avoiding drug leakage and improving stability, (v) defined chemical structures and quantitative drug loading easy for reproduction. Both in vitro and in vivo results show that these GSH-responsive prodrug nanoparticle exhibits significant inhibition of tumor cell growth, and is promising for efficient and safe chemotherapeutic delivery.

Temperature Responsive Nanoparticles Based on PEGylated Polyaspartamide Derivatives for Drug Delivery

The temperature responsive PEGylated polyaspartamide derivative, denoted as mPEG-PAAHP, was synthesized by the click reaction. FTIR and ¹H NMR were adopted to characterize and confirm the chemical structures of the obtained mPEG-PAAHPs. The temperature responsive behavior investigated by transmittance and dynamic light scattering showed that some of the obtained mPEG-PAAHPs exhibited obvious temperature responsiveness and could be used to prepare nanoparticles by quickly heating. Drug paclitaxel can be encapsulated into mPEG-PAAHP based nanoparticles with a high encapsulation efficiency up to 99% (corresponding to a drug loading content of around 9.9%). Dynamic light scattering results showed that the PTX-loaded nanoparticles had a mean size around 80 nm (PDI<0.2) and good stability in PBS with 150 mM ionic strength. In vitro cytotoxicity results showed that mPEG-PAAHP did not show any toxicity to HeLa cells, but the PTX-loaded nanoparticles based on mPEG-PAAHP exhibited obvious anti-cancer activity. Thus, the temperature responsive PEGylated polyaspartamide derivative mPEG-PAAHP may be a promising drug delivery system.

PEGylated Poly(α-lipoic acid) Loaded with Doxorubicin as a pH and Reduction Dual Responsive Nanomedicine for Breast Cancer Therapy

Disulfide-containing nanoparticles are promising vehicles for anticancer drug delivery. However, the preparation of disulfide-containing nanoparticles usually relies on complex synthetic procedures. In the present work, a PEGylated poly(α-lipoic acid) (mPEG-PαLA) copolymer was facilely synthesized and used for pH and reduction dual responsive drug delivery. Poly(α-lipoic acid) was prepared by thermal polymerization of α-lipoic acid without any catalyst or solvent and then conjugated with methoxy poly(ethylene glycol) to form the mPEG-PαLA copolymer. The obtained mPEG-PαLA copolymer was amphiphilic, which could self-assemble into nanoparticles (NPs) in aqueous solution. More interestingly, the mPEG-PαLA NPs showed high drug loading efficiency (87.7%) for the cationic drug doxorubicin (DOX). The DOX-loaded NPs (NPs-DOX) exhibited pH and reduction dual responsive drug release behaviors. Moreover, the flow cytometry analysis and confocal laser scanning microscopy confirmed that the drug-loaded nanoparticles could be efficiently internalized and subsequently release DOX in 4T1 cancer cells. As a result, the NPs-DOX displayed favorable antiproliferation efficacy in 4T1 cancer cells (measured by MTT assays). Furthermore, the NPs-DOX showed enhanced antitumor efficacy in a 4T1 tumor-bearing mice model with reduced side toxicities toward normal organs due to the prolonged circulation time and improved biodistribution in vivo. In other words, this work demonstrates that the PEGylated poly(α-lipoic acid) copolymer can be used as a biocompatible and stimuli-responsive nanocarrier for anticancer drug delivery, which may have potential clinical utility.

Redox Responsive Polymersomes for Enhanced Doxorubicin Delivery

In the present investigation, the potential of a novel, self-assembled, biocompatible, and redox-sensitive copolymer system with disulfide bond was explored for doxorubicin (DOX) delivery through polymersome nanostructures of ∼120 nm. The polymer system was synthesized with less steps, providing a high yield of 86%. The developed polymersomes showed admirable biocompatibility with high dose tolerability in vitro and in vivo. The colloidal stability of DOX-loaded polymersomes depicted a stable and uniform particle size over a period of 72 h. The cellular internalization of polymersomes was assessed in HeLa and MDA-MB-231 cell lines, where enhanced cellular internalization was observed. The dose-dependent cytotoxicity was observed for DOX-loaded polymersomes by MTT cytotoxicity assay in the above cell lines. The tumor suppression studies were assessed in Ehrlich ascites tumor (EAT) carrying Swiss albino mice, where polymersomes exhibited a 7.16-fold reduction in tumor volume correlated with control and 5.39-fold higher tumor inhibition capacity compared to conventional chemotherapy (free DOX treatment). The developed polymersomes gave safer insights concerning DOX associated toxicities by histopathology and serum biochemistry analysis. Thus, results focus on the potential of redox responsive polymersomes for efficacious and improved DOX therapy with enhanced antitumor activity and insignificant cardiotoxicity which can be translated to clinical settings.

Chemoenzymatic synthesis of dual-responsive graft copolymers for drug delivery: long-term stability, high loading and cell selectivity

A series of amphiphilic graft copolymers, poly(N-propargyldiethanolamine 4,4'-dithiodibutyionate)-graft-monomethoxy poly(ethylene glycol) (PPD-g-mPEG), were designed via a chemoenzymatic method for pH and reduced glutathione (GSH) dual-responsive drug delivery. The effects of percent grafting and molecular weights of mPEG on critical micelle concentration (CMC) values, size of micelles, drug loading and dual-response were tested. The graft copolymers could easily form homogeneous spherical micelles with appropriate sizes and zeta-potentials. The micelles of PPD-g-mPEG copolymers loaded doxorubicin (DOX) in high efficiency, and showed excellent stability under physiological conditions and synergetic dual-response to weakly acidic pH and GSH. In vitro experiments confirmed that the DOX-loaded micelles could be internalized into cancer cells efficiently and release DOX over time. Furthermore, cell cytotoxicity assays indicated that the graft copolymers were non-cytotoxic to both cancerous and normal cells while the DOX-loaded micelles greatly improved the selectivity ratios between HeLa cells and HL-7702 cells. DOX-loaded micelles also avoided hemolysis of red blood cells (RBCs) effectively compared with commercialized doxorubicin hydrochloride. All these demonstrated the potential of PPD-g-mPEG as a model to create more functional dual-responsive nanocarriers for controlled drug delivery.

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.

One-Pot Synthesis of pH/Redox Responsive Polymeric Prodrug and Fabrication of Shell Cross-Linked Prodrug Micelles for Antitumor Drug Transportation

Shell cross-linked (SCL) polymeric prodrug micelles have the advantages of good blood circulation stability and high drug content. Herein, we report on a new kind of pH/redox responsive dynamic covalent SCL micelle, which was fabricated by self-assembly of a multifunctional polymeric prodrug. At first, a macroinitiator PBYP- ss- iBuBr was prepared via ring-opening polymerization (ROP), wherein PBYP represents poly[2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane]. Subsequently, PBYP- hyd-DOX- ss-P(DMAEMA- co-FBEMA) prodrug was synthesized by a one-pot method with a combination of atom transfer radical polymerization (ATRP) and a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using a doxorubicin (DOX) derivative containing an azide group to react with the alkynyl group of the side chain in the PBYP block, while DMAEMA and FBEMA are the abbriviations of N, N-(2-dimethylamino)ethyl methacrylate and 2-(4-formylbenzoyloxy)ethyl methacrylate, respectively. The chemical structures of the polymer precursors and the prodrugs have been fully characterized. The SCL prodrug micelles were obtained by self-assembly of the prodrug and adding cross-linker dithiol bis(propanoic dihydrazide) (DTP). Compared with the shell un-cross-linked prodrug micelles, the SCL prodrug micelles can enhance the stability and prevent the drug from leaking in the body during blood circulation. The average size and morphology of the SCL prodrug micelles were measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The SCL micelles can be dissociated under a moderately acidic and/or reductive microenvironment, that is, endosomal/lysosomal pH medium or high GSH level in the tumorous cytosol. The results of DOX release also confirmed that the SCL prodrug micelles possessed pH/reduction responsive properties. Cytotoxicity and cellular uptake analyses further revealed that the SCL prodrug micelles could be rapidly internalized into tumor cells through endocytosis and efficiently release DOX into the HeLa and HepG2 cells, which could efficiently inhibit the cell proliferation. This study provides a fast and precise synthesis method for preparing multifunctional polymer prodrugs, which hold great potential for optimal antitumor therapy.

Reduction-sensitive polymeric nanomedicines: An emerging multifunctional platform for targeted cancer therapy

The development of smart delivery systems that are robust in circulation and quickly release drugs following selective internalization into target cancer cells is a key to precision cancer therapy. Interestingly, reduction-sensitive polymeric nanomedicines showing high plasma stability and triggered cytoplasmic drug release behavior have recently emerged as one of the most exciting platforms for targeted delivery of various anticancer drugs including small chemical drugs, proteins, and nucleic acids. In vivo studies in varying tumor models reveal that these reduction-sensitive multifunctional nanomedicines outperform the currently used clinical formulations and reduction-insensitive counterparts, bringing about not only significantly enhanced tumor selectivity, accumulation and inhibition efficacy but also markedly reduced systemic toxicity and improved therapeutic index. In this review, we will highlight the cutting-edge advancement with a focus on in vivo performances as well as future perspectives on reduction-sensitive polymeric nanomedicines for targeted cancer therapy.

Glutathione-triggered dual release of doxorubicin and camptothecin for highly efficient synergistic anticancer therapy

An amphiphilic biodegradable prodrug (PLG-g-mPEG/CPT) was synthesized by conjugating disulfide-containing camptothecin (CPT) to poly(L-glutamic acid)-graft-methoxy poly(ethylene glycol) (PLG-g-mPEG) through esterification reaction. The amphiphilic prodrugs could self-assemble into micellar nanoparticles and encapsulate doxorubicin (DOX) in aqueous solution at pH 7.4. The treatment of the nanoparticles with reducing glutathione (GSH) at cytosolic concentration (10 mM) significantly promoted the in vitro dual release of DOX and CPT from the micelles. The results of flow cytometry (FCM) and confocal laser scanning microscopy (CLSM) manifested that the intracellular release of DOX and CPT from the micelles was enhanced by increasing the intracellular GSH level. Consistently, the MCF-7 cell killing mediated by the micelles was also intracellular GSH concentration-dependent. The low combination index (CI) value of < 0.3 demonstrated the high synergistic effect of DOX and CPT co-delivered by the nanoparticles in tumor cell killing. Therefore, this GSH-triggered dual release drug delivery system is a promising strategy for combination cancer therapy.

2,2'-Dithiodisuccinic acid-stabilized polyion complex micelles for pH and reduction dual-responsive drug delivery

In this work, a new kind of polyion complex (PIC) micelles with pH and reduction dual responsiveness was developed for effective intracellular drug delivery. The PIC micelles can be readily prepared by mixing a polycationic block polymer, methoxy poly(ethylene glycol)-b-poly(l-lysine) (mPEG-PLL), with a small molecule polyacid, 2, 2'-dithiodisuccinic acid (DTS) in aqueous media. The resultant PIC micelles are of uniform spherical shapes with hydrodynamic radii ranging from 65 to 75 nm based on different feeding ratios of mPEG-PLL and DTS. Interestingly, by using the small molecule polyacid DTS, the obtained PIC micelles show distinct pH-responsive disintegration in acid solution. Meanwhile, the PIC micelles were also assessed to be reduction-responsive due to the presence of disulfide bond in DTS. In view of these stimuli-responsive properties, the potential use of this PIC micelle as smart drug carrier was then investigated. Doxorubicin (DOX), a cationic anticancer drug, was loaded into the PIC micelles with high efficiency. In vitro drug release studies revealed that release of DOX from the PIC micelles was suppressed in neutral solutions due to the stable electrostatic interactions between PIC micelles and DOX, but could be accelerated in acidic solutions or under high GSH condition. Furthermore, flow cytometry and confocal laser scanning microscopy (CLSM) studies indicated that the DOX-loaded PIC micelles could be effectively internalized by MCF-7 human breast cancer cells and release the loaded DOX in intracellular environment. Consequently, the DOX-loaded PIC micelles were capable of inhibiting the proliferation of C26 murine colon cancer and MCF-7 human breast cancer cells in high efficiency, showing similar IC₅₀ values as free DOX. Thus, this biocompatible PIC micelle may be promising for intracellular drug delivery.

One-Step Synthesis of Targeted Acid-Labile Polysaccharide Prodrug for Efficiently Intracellular Drug Delivery

The therapeutic potential of the active targeting and acid-sensitive polysaccharide prodrug was investigated. The active targeting of polysaccharide prodrug was based on the specific interaction between cyclo(Arg-Gly-Asp-d-Phe-Lys) peptide (c(RGDfK)) and its receptor α_vβ₃ integrin overexpressed on the membrane of tumor cells. The cRGD-modified doxorubicin-conjugated hydroxyethyl starch (HES=DOX/cRGD) was synthesized via a one-step Schiff base reaction between oxidized HES, and DOX and c(RGDfK) that achieved an acid-accelerated drug release profile. The targeted polysaccharide prodrug self-assembled into micelle in aqueous environment with a moderate hydrodynamic diameter of 77.1 nm. All data in vitro indicated enhanced cell uptake and elevated cytotoxicity of HES=DOX/cRGD toward human malignant melanoma A375 cells compared with HES=DOX and DOX. Moreover, the smart prodrug also exhibited upregulated accumulation in the tumor, improved antitumor efficacy, and reduced systemic cytotoxicity in vivo. The cRGD-decorated acid-sensitive polysaccharide prodrug was advantageous in both antitumor efficacy and systemic security, showing great prospect in clinical application.

Polymerization-induced self-assembly of large-scale iohexol nanoparticles as contrast agents for X-ray computed tomography imaging

Fundamental research for CT imaging, in which iohexol nanoparticles (INPs) were synthesised using a one-pot strategy via polymerization-induced self-assembly (PISA).