A Novel Redox-Sensitive Drug Delivery System Based on Trimethyl-Locked Polycarbonate

Stimuli-responsive polymer nanocarriers, capable of exploiting subtle changes in the tumor microenvironment for controlled drug release, have gained significant attention in cancer therapy. Notably, NAD(P)H: quinone oxidoreductase 1 (NQO1), found to be upregulated in various solid tumors, represents a promising therapeutic target due to its effective capability to enzymatically reduce trimethyl-locked (TML) benzoquinone structures in a physiological condition. In this study, a novel redox-sensitive carbonate monomer, MTC, was synthesized, and its amphiphilic block copolymers were prepared through ring-opening polymerization. By successfully self-assembling poly(ethylene glycol)-b-PMTC micelles, the model drug doxorubicin (DOX) was encapsulated with high efficiency. The micelles exhibited redox-responsive behavior, leading to rapid drug release. In vitro assessments confirmed their excellent biocompatibility and hemocompatibility. Furthermore, the inhibition of the NQO1 enzyme reduced drug release in NQO1-overexpressed cells but not in control cells, resulting in decreased cytotoxicity in the presence of NQO1 enzyme inhibitors. Overall, this study showcases the potential of MTC-based polycarbonate micelles to achieve targeted and specific drug release in the NQO1 enzyme-mediated tumor microenvironment. Therefore, the self-assembly of MTC-based polymers into nanomicelles holds immense promise as intelligent nanocarriers in drug delivery applications.

Artificial Kidney Capsule Packed with Mesenchymal Stem Cell-Laden Hydrogel for the Treatment of Rhabdomyolysis-Induced Acute Kidney Injury

Acute kidney injury (AKI) has emerged as a major public health problem affecting millions of people worldwide without specific and satisfactory therapies due to the lack of an effective delivery approach. In the past few decades, hydrogels present infinite potential in localized drug delivery, while their poor adhesion to moist tissue and isotropic diffusion character always restrict the therapeutic efficiency and may lead to unwanted side effects. Herein, we proposed a novel therapeutic strategy for AKI via a customizable artificial kidney capsule (AKC) together with a mesenchymal stem cell (MSC)-laden hydrogel. Specifically, an elastic capsule owning an inner chamber with the same size and shape as the kidney is designed and fabricated through three-dimensional (3D) modeling and printing, serving as an outer wrap for kidney and cell-laden hydrogels. According to the in vitro experiment, the excellent biocompatibility of gelatin-based hydrogel ensures viability and proliferation of MSCs. In vivo mice experiments proved that this concept of AKC-assisted kidney drug delivery could efficiently reduce epithelial cell apoptosis and minimize the damage of the renal tubular structure for mice suffering AKI. Such a strategy not only provides a promising alternative in the treatment of AKI but also offers a feasible and versatile approach for the repair and recovery of other organs.

Amino acid derived biopolymers: Recent advances and biomedical applications

Over the past few years, amino acids (AA) have emerged as promising biomaterials for the synthesis of functional polymers. Owing to the diversity of functional groups in amino acids, various polymerization methods may be used to make a wide range of well-defined functional amino-acid/peptide-based optically active polymers with varying polymer lengths, compositions, and designs. When incorporated with chirality and self-assembly, they offer a wide range of applications and are particularly appealing in the field of drug delivery, tissue engineering, and biosensing. There are several classes of these polymers that include polyamides (PA), polyesters (PE), poly(ester-amide)s (PEA)s, polyurethanes (PU)s, poly(depsipeptide)s (PDP)s, etc. They offer the ability to control functionality, conjugation, crosslinking, stimuli responsiveness, and tuneable mechanical/thermal properties. In this review, we present the recent advancements in the synthesis strategies for obtaining these amino acid-derived bio-macromolecules, their self-assembly properties, and the wealth of prevalent applications.

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.

Morphological Transitions of Photoresponsive Vesicles from Amphiphilic Polypeptoid Copolymers for Controlled Release

Photoresponsive polymers have attracted increasing interest for a variety of applications. Here, we report a family of photoresponsive polypeptoid-based copolymer poly(ethylene glycol)-b-poly(N-(S-(o-nitrobenzyl)-thioethyl) glycine)-co-poly(N-(2-phenylethyl) glycine) (PEG-b-PNSN-co-PNPE) synthesized by the controlled ring-opening polymerization (ROP) technique. The key feature of the design is to incorporate both o-nitrobenzyl group moiety to offer the photoresponsive property and phenethyl residues to tune the structural and amphiphilic property of the system. We demonstrate that the cleavage degree of the o-nitrobenzyl group can reach to 100% upon UV-irradiation. With delicate design, a photoresponsive vesicle-to-sphere transition has been observed that facilitates the release of the encapsulants. This work provides a facile approach to prepare a type of photoresponsive polymers with tunable properties for drug delivery.

Alginate-based hydrogels as drug delivery vehicles in cancer treatment and their applications in wound dressing and 3D bioprinting

Hydrogels are a three-dimensional and crosslinked network of hydrophilic polymers. They can absorb a large amount of water or biological fluids, which leads to their swelling while maintaining their 3D structure without dissolving (Zhu and Marchant, Expert Rev Med Devices 8:607-626, 2011). Among the numerous polymers which have been utilized for the preparation of the hydrogels, polysaccharides have gained more attention in the area of pharmaceutics; Sodium alginate is a non-toxic, biocompatible, and biodegradable polysaccharide with several unique physicochemical properties for which has used as delivery vehicles for drugs (Kumar Giri et al., Curr Drug Deliv 9:539-555, 2012). Owing to their high-water content and resembling the natural soft tissue, hydrogels were studied a lot as a scaffold. The formation of hydrogels can occur by interactions of the anionic alginates with multivalent inorganic cations through a typical ionotropic gelation method. However, those applications require the control of some properties such as mechanical stiffness, swelling, degradation, cell attachment, and binding or release of bioactive molecules by using the chemical or physical modifications of the alginate hydrogel. In the current review, an overview of alginate hydrogels and their properties will be presented as well as the methods of producing alginate hydrogels. In the next section of the present review paper, the application of the alginate hydrogels will be defined as drug delivery vehicles for chemotherapeutic agents. The recent advances in the application of the alginate-based hydrogels will be describe later as a wound dressing and bioink in 3D bioprinting.

UV-responsive cyclic peptide progelator bioinks

We describe cyclic peptide progelators which cleave in response to UV light to generate linearized peptides which then self-assemble into gel networks. Cyclic peptide progelators were synthesized, where the peptides were sterically constrained, but upon UV irradiation, predictable cleavage products were generated. Amino acid sequences and formulation conditions were altered to tune the mechanical properties of the resulting gels. Characterization of the resulting morphologies and chemistry was achieved through liquid phase and standard TEM methods, combined with matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS).

cRGD-decorated biodegradable polytyrosine nanoparticles for robust encapsulation and targeted delivery of doxorubicin to colorectal cancer in vivo

The clinical success of nanomedicines demands on the development of simple biodegradable nanocarriers that can efficiently and stably encapsulate chemotherapeutics while quickly release the payloads into target cancer cells. Herein, we report that cRGD-decorated biodegradable polytyrosine nanoparticles (cRGD-PTN) boost encapsulation and targeted delivery of doxorubicin (DOX) to colorectal cancer in vivo. The co-assembly of poly(ethylene glycol)-poly(L-tyrosine) (PEG-PTyr) and cRGD-functionalized PEG-PTyr (mol/mol, 80/20) yielded small-sized cRGD-PTN of 70 nm. Interestingly, cRGD-PTN exhibited an ultra-high DOX encapsulation with drug loading contents ranging from 18.5 to 54.1 wt%. DOX-loaded cRGD-PTN (cRGD-PTN-DOX) was highly stable against dilution, serum, and Triton X-100 surfactant, while quickly released DOX in HCT-116 cancer cells, likely resulting from enzymatic degradation of PTyr. Flow cytometry, confocal microscopy and MTT assays displayed that cRGD-PTN-DOX was efficiently internalized into α_vβ₅ overexpressing HCT-116 colorectal cancer cells, rapidly released DOX into the nuclei, and induced several folds better antitumor activity than non-targeted PTN-DOX and clinically used liposomal DOX (Lipo-DOX). SPECT/CT imaging revealed strong tumor accumulation of ¹²⁵I-labeled cRGD-PTN, which was 2.8-fold higher than ¹²⁵I-labeled PTN. Notably, cRGD-PTN-DOX exhibited over 5 times better toleration than Lipo-DOX and significantly more effective inhibition of HCT-116 colorectal tumor than non-targeted PTN-DOX control, affording markedly improved survival rate in HCT-116 tumor-bearing mice with depleting side effects at 6 or 12 mg DOX equiv./kg. cRGD-PTN-DOX with great simplicity, robust drug encapsulation and efficient nucleic drug release appears promising for targeted chemotherapy of colorectal tumor.

Functional biodegradable polymers via ring-opening polymerization of monomers without protective groups

Biodegradable polymers are of current interest and chemical functionality in such materials is often demanded in advanced biomedical applications. Functional groups often are not tolerated in the polymerization process of ring-opening polymerization (ROP) and therefore protective groups need to be applied. Advantageously, several orthogonally reactive functions are available, which do not demand protection during ROP. We give an insight into available, orthogonally reactive cyclic monomers and the corresponding functional synthetic and biodegradable polymers, obtained from ROP. Functionalities in the monomer are reviewed, which are tolerated by ROP without further protection and allow further post-modification of the corresponding chemically functional polymers after polymerization. Synthetic concepts to these monomers are summarized in detail, preferably using precursor molecules. Post-modification strategies for the reported functionalities are presented and selected applications highlighted.

Facile Approach to Covalent Copolypeptide Hydrogels and Hybrid Organohydrogels

Crosslinking of tryptophan (Trp) containing copolypeptides with varying ratios of benzyl-l-glutamate (BLG) and Nα-(carbobenzyloxy)-l-lysine (Z-Lys) is achieved by the selective reaction with hexamethylene-bis-TAD (bisTAD). Conversion of the resulting organogels into biocompatible hydrogels by full BLG or Z-Lys deprotection is demonstrated. Moreover, diffusion controlled deprotection allows the design of macroscopic hybrid organohydrogels comprising hydrophilic as well as hydrophobic regions at a desired ratio and position. FTIR and SEM analysis confirm the coexistence of both hydrophilic and hydrophobic segments in one copolypeptide piece. Selective loading of hydrogel and organogel segments with hydrophilic and hydrophobic dyes, respectively, is observed on macroscopic amphiphilic gels and films. These materials offer significant potential as dual-loaded drug release gels as well as tissue engineering platforms.

Progress in Photo-Responsive Polypeptide Derived Nano-Assemblies

Stimuli-responsive polymeric materials have attracted significant attention in a variety of high-value-added and industrial applications during the past decade. Among various stimuli, light is of particular interest as a stimulus because of its unique advantages, such as precisely spatiotemporal control, mild conditions, ease of use, and tunability. In recent years, a lot of effort towards the synthesis of a biocompatible and biodegradable polypeptide has resulted in many examples of photo-responsive nanoparticles. Depending on the specific photochemistry, those polypeptide derived nano-assemblies are capable of crosslinking, disassembling, or morphing into other shapes upon light irradiation. In this mini-review, we aim to assess the current state of photo-responsive polypeptide based nanomaterials. Firstly, those 'smart' nanomaterials will be categorized by their photo-triggered events (i.e., crosslinking, degradation, and isomerization), which are inherently governed by photo-sensitive functionalities, including O-nitrobenzyl, coumarin, azobenzene, cinnamyl, and spiropyran. In addition, the properties and applications of those polypeptide nanomaterials will be highlighted as well. Finally, the current challenges and future directions of this subject will be evaluated.

Polypeptide self-assemblies: nanostructures and bioapplications

Polypeptide copolymers can self-assemble into diverse aggregates. The morphology and structure of aggregates can be varied by changing molecular architectures, self-assembling conditions, and introducing secondary components such as polymers and nanoparticles. Polypeptide self-assemblies have gained significant attention because of their potential applications as delivery vehicles for therapeutic payloads and as additives in the biomimetic mineralization of inorganics. This review article provides an overview of recent advances in nanostructures and bioapplications related to polypeptide self-assemblies. We highlight recent contributions to developing strategies for the construction of polypeptide assemblies with increasing complexity and novel functionality that are suitable for bioapplications. The relationship between the structure and properties of the polypeptide aggregates is emphasized. Finally, we briefly outline our perspectives and discuss the challenges in the field.

Amino acid-derived stimuli-responsive polymers and their applications

The recent advances achieved in the study of various stimuli-responsive polymers derived from natural amino acids have been reviewed.

Improved Photodynamic Therapy Efficacy of Protoporphyrin IX-Loaded Polymeric Micelles Using Erlotinib Pretreatment

Photodynamic therapy (PDT) has attracted widespread attention in recent years as a noninvasive and highly selective approach for cancer treatment. We have previously reported a significant increase in the 90-day complete response rate when tumor-bearing mice are treated with the epidermal growth factor receptor (EGFR) inhibitor erlotinib prior to PDT with the photosensitizer benzoporphyrin-derivative monoacid ring A (BPD-MA) compared to treatment with PDT alone. To further explore this strategy for anticancer therapy and clinical practice, we tested whether pretreatment with erlotinib also exhibited a synergistic therapeutic effect with a nanocarrier containing the clinically relevant photosensitizer protoporphyrin IX (PpIX). The PpIX was encapsulated within biodegradable polymeric micelles formed from the amphiphilic block copolymer poly(ethylene glycol)-polycaprolactone (PEG-PCL). The obtained micelles were characterized systematically in vitro. Further, an in vitro cytotoxicity study showed that PDT with PpIX loaded micelles did exhibit a synergistic effect when combined with erlotinib pretreatment. Considering the distinct advantages of polymeric nanocarriers in vivo, this study offers a promising new approach for the improved treatment of localized tumors. The strategy developed here has the potential to be extended to other photosensitizers currently used in the clinic for photodynamic therapy.

Triggered Copolypeptide Hydrogel Degradation Using Photolabile Lysine Protecting Groups

We have prepared a new l-lysine-based N-carboxyanhydride monomer containing a photolabile o-nitrobenzyloxycarbonyl protecting group. This monomer was used to prepare poly(l-lysine)-block-poly(oNB-l-lysine) block copolypeptides that formed hydrogels with tunable physical properties and the capability to be degraded by UV irradiation. In these materials, the oNB-lysine residues were found to be excellent surrogates for the hydrophobic residues typically used to form block copolypeptide hydrogels, thus adding functionality without adversely altering self-assembly characteristics. Upon irradiation, full cleavage of the o-nitrobenzyloxycarbonyl groups was observed, resulting in dissolution of the product, poly(l-lysine), and complete hydrogel disruption. When dye molecules were entrapped in the hydrogels, photolysis resulted in release and mixing of these molecules with the surrounding media.

Bright and Stable Near-Infrared Pluronic-Silica Nanoparticles as a Contrast Agent for in vivo Optical Imaging

Near-infrared (NIR) fluorescent nanostructured materials have emerged as novel contrast agents for non-invasive bioimaging. Here we report a class of polymer-silica nanoparticles doped with a NIR fluorescent dye prepared through a facile one-pot strategy. Hydrophobic NIR fluorescent dyes such as IR 780 iodide could be easily encapsulated into the micellar core by self-assembly of amphiphilic triblock copolymer Pluronic F127. When subsequently adding silane in aqueous solution, nanoparticles with a cross-linked core and a hydrophilic PEG shell were formed. The structure of the as-obtained nanoparticles was confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The nanoparticles exhibited a well-defined spherical structure with a mean diameter of approximately 30 nm, and excellent monodispersity and stability in aqueous solution. In addition, the photo-stability of IR 780 was significantly improved by encapsulation into the nanoparticles. In vitro MTT assay with cell lines HEK293 and A431 demonstrated that the IR 780 loaded nanoparticles (termed as IR780@NPs) were biocompatible. In vivo sentinel lymph node imaging revealed that the fluorescent intensity and retention time of the IR780@NPs were clearly superior to its constituent free dye, making it amenable to in vivo bioimaging. Further in vivo tumor imaging indicated that IR780@NPs have a longer retention time and much higher accumulation on the tumor site compared to free dye after intravenous administration. Overall this hydrophilic NIR fluorescent contrast agent exhibits excellent photophysical characteristics and low cytotoxicity, and holds a strong promise for a variety of applications including bioimaging and therapy.

A Nanoplatform with Precise Control over Release of Cargo for Enhanced Cancer Therapy

The development of a nanocarrier delivery system having both sufficient stability in blood circulation and a rapid drug release profile at target sites remains a major challenge in cancer therapy. Here, a multifunctional star-shaped micellar system with a precisely spatiotemporal control of releasing encapsulated agents is developed by mixing a photoinitiated crosslinking amphiphilic copolymer with a phenylboronic acid (PBA)-functionalized redox-sensitive amphiphilic copolymer for the first time. The combination of the functional polymers effectively resolves the contradiction that the micellar system cannot release the rapid drug release in cells when it possesses an extreme stability that is often required in blood circulation. In this system, the inner core polymers are photo-crosslinked, endowing a stable micelle matrix structure; the end groups of the hydrophilic segments are decorated with PBA ligands, providing an active targeting ability; disulfide bonds in the micellar matrix impart a redox-responsive trigger for the prompt intracellular release of drugs. As a result, with a relatively low DOX dosage (2 mg kg(-1) per injection) the in vivo antitumor effect on H22-bearing BALB/c mice shows that the micelles have a high therapeutic efficacy against solid tumors while minimal side effects against normal tissues.

Synthesis, self-assembly, and photocrosslinking of fullerene-polyglycerol amphiphiles as nanocarriers with controlled transport properties

In this work, we report a new, simple, gram-scale method for synthesizing water-soluble fullerene-polyglycerol amphiphiles (FPAs) that self-assemble into partially and fully crosslinked nanoclusters with the ability to controllably transport hydrophobic and hydrophilic agents.

Crosslinked polymeric self-assemblies as an efficient strategy for photodynamic therapy on a 3D cell culture

Polymeric crosslinked self-assemblies based on poly(ethyleneoxide-b-ε-caprolactone) have been synthesized. They are shown to be more efficient vectors for photodynamic therapy compared to uncrosslinked systems.

Thermo/redox/pH-triple sensitive poly(N-isopropylacrylamide-co-acrylic acid) nanogels for anticancer drug delivery

The clinical application of doxorubicin (DOX), like other anticancer drugs, is limited by insufficient cellular uptake and the numerous drug resistance mechanisms existing in cells. The development of smart nanomaterials capable of carrying the drugs into the cells and of releasing them under the control of the microenvironment is an interesting approach that may increase the success of the anticancer drugs currently in use. Herein, we report an easy process to prepare biocompatible nanogels (NGs) with thermo/redox/pH-triple sensitivity, which are highly effective in the intracellular delivery of DOX. Redox-sensitive/degradable NGs (PNA-BAC) and nondegradable NGs (PNA-MBA) were prepared through in situ polymerization of N-isopropylacrylamide (NIPAM) and acrylic acid (AA) in the presence of sodium dodecyl sulfate (SDS) as a surfactant, using N,N'-bis(acryloyl)cystamine (BAC) as a biodegradable crosslinker or N,N'-methylene bisacrylamide (MBA) as a nondegradable crosslinker, respectively. After that, the cationic DOX drug was loaded into the NGs through electrostatic interactions, by simply mixing them in aqueous solution. Compared to nondegradable PNA-MBA NGs, PNA-BAC NGs not only presented a higher DOX drug loading capacity, but also allowed a more sustainable drug release behavior under physiological conditions. More importantly, PNA-BAC NGs displayed thermo-induced drug release properties and an in vitro accelerated release of DOX under conditions that mimic intracellular reductive conditions and acidic tumor microenvironments. The thermo/redox/pH multi-sensitive NGs can quickly be taken up by CAL-72 cells (an osteosarcoma cell line), resulting in a high DOX intracellular accumulation and an improved cytotoxicity when compared with free DOX and DOX-loaded nondegradable PNA-MBA NGs. The developed NGs can be possibly used as an effective platform for the delivery of cationic therapeutic agents for biomedical applications.

Reduction-sensitive amphiphilic copolymers made via multi-component Passerini reaction for drug delivery

One-step synthesis of amphiphilic polymers containing disulfide bond within the hydrophobic backbone was demonstrated via multi-component Passerini reaction. The obtained polymer was self-assembled into micelles in aqueous solution. Curcumin (CUR), an effective and safe anticancer agent, which was limited by its water insolubility and poor bioavailability, was loaded into the micelles as a model drug. The nanoscale polymeric micelles were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Faster intracellular CUR release was observed by confocal laser scanning microscopy (CLSM) in the HeLa cells pretreated with GSH than in the unpretreated ones. Micelles also loaded with NH2-BODIPY which was almost non-fluorescent and gave strong enhanced fluorescence under acid conditions. The phenomenon of the stronger enhanced fluorescence in the pretreated HeLa cells showed further that the obtained polymer was reduction-sensitive. In vitro MTT assays showed that the micelles were biocompatible and CUR-loaded micelles had higher cellular proliferation inhibition in contrast to free CUR toward HeLa cells. These results highlight the potential of using multi-component Passerini reaction to make functional copolymers as smart nanocarriers for drug delivery.

Biodegradable stimuli-responsive polypeptide materials prepared by ring opening polymerization

This tutorial review summarizes the most recent progress in stimuli-responsive polypeptides over the past decade.

Y-shaped block copolymer (methoxy-poly(ethylene glycol))2-b-poly(l-glutamic acid): preparation, self-assembly, and use as drug carriers

The nano polymer drugs based on Y-shaped block copolymer mPEG2-PGA show a great potential on the treatment for solid tumors.

Redox-responsive core cross-linked micelles based on cypate and cisplatin prodrugs-conjugated block copolymers for synergistic photothermal–chemotherapy of cancer

A synergistic effect of photothermal and chemotherapy of cancers was demonstrated using redox-responsive core cross-linked micelles fabricated from cypate and cisplatin prodrugs-conjugated block copolymers.

Thymine modified amphiphilic biodegradable copolymers for photo-cross-linked micelles as stable drug carriers

A photo-cross-linked micelle is synthesized via photodimerization of thymine moieties fabricated from amphiphilic block copolymers (mPEG-b-P(LA-co-MPT). The crosslinking behavior is monitored by UV-Vis spectra and (1) H NMR. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that cross-linked micelles had smaller sizes than their uncross-linked precursors. In vitro studies reveal that cross-linking of the micelle cores results in a slow drug release and faster cellular uptake in comparison with uncross-linked ones in MCF-7 and Hela cells. Moreover, the paclitaxel (PTX)-loaded core-cross-linked micelles exhibit similar anticancer efficacy as free PTX. This work provides a convenient tool for designing a more stable structure in the blood circulation to realize a controlled drug delivery.