Click Chemistry for Biofunctional Polymers: From Observing to Steering Cell Behavior

Click chemistry has become one of the most powerful construction tools in the field of organic chemistry, materials science, and polymer science, as it offers hassle-free platforms for the high-yielding synthesis of novel materials and easy functionalization strategies. The absence of harsh reaction conditions or complicated workup procedures allowed the rapid development of novel biofunctional polymeric materials, such as biopolymers, tailor-made polymer surfaces, stimulus-responsive polymers, etc. In this review, we discuss various types of click reactions─including azide-alkyne cycloadditions, nucleophilic and radical thiol click reactions, a range of cycloadditions (Diels-Alder, tetrazole, nitrile oxide, etc.), sulfur fluoride exchange (SuFEx) click reaction, and oxime-hydrazone click reactions─and their use for the formation and study of biofunctional polymers. Following that, we discuss state-of-the-art biological applications of "click"-biofunctionalized polymers, including both passive applications (e.g., biosensing and bioimaging) and "active" ones that aim to direct changes in biosystems, e.g., for drug delivery, antiviral action, and tissue engineering. In conclusion, we have outlined future directions and existing challenges of click-based polymers for medicinal chemistry and clinical applications.

Chitosan-coated PLA/poloxamer nanoparticles stimulate immunologic cancer cell death and synergistic chemo-immunotherapeutic efficacy

Cancer, a key factor in declining global life expectancy, has driven the integration of chemotherapy and immunotherapy to address multidrug resistance and influence the tumor microenvironment. We developed a novel vaccine delivery carrier, a chitosan-coated polylactic acid/poloxamer nanoparticle (CPP NP), designed to co-encapsulate an anticancer drug and antigen without any chemical conjugation process, enabling effective and synergistic cancer chemo-immunotherapy. The CPP NP achieved synergistic efficacy through paclitaxel (PTX), an immunogenic cell death-inducing chemotherapeutic agent; ovalbumin (OVA), which promotes dendritic cell maturation; and enhanced cellular uptake facilitated by chitosan. The PTX and OVA-loaded CPP NPs (PTX/OVA@CPP NPs) were stable in PBS for four weeks and resuspended well after lyophilization without any cryoprotectants. Moreover, PTX and OVA from the NPs exhibited a sustained release rate and pH-responsive release pattern within different cellular microenvironments. Importantly, PTX@CPP NPs exhibited much higher anticancer efficacy across various cancer cell lines, even multidrug-resistant cells, compared to free PTX and PTX@PP NPs without the chitosan coating. In antigen-presenting cells, OVA@CPP NPs led to higher IL-2 secretion and cellular uptake compared to free OVA and OVA@PP NPs. Furthermore, in a tumor-bearing mouse model, PTX/OVA@CPP NPs exhibited strong synergistic tumor suppression and triggered OVA antigen-specific responses, promoting an antitumor immune response. These findings demonstrate that PTX/OVA@CPP NPs show potential as new chemo-immunotherapeutic agents for effective cancer treatment.

Homeostatic growth of dynamic covalent polymer network toward ultrafast direct soft lithography

Soft lithography is a complementary extension of classical photolithography, which involves a multistep operation that is environmentally unfriendly and intrinsically limited to planar surfaces. Inspired by homeostasis processes in biology, we report a self-growth strategy toward direct soft lithography, bypassing conventional photolithography and its limitations. Our process uses a paraffin swollen light responsive dynamic polymer network. Selective light exposure activates the network locally, causing stress imbalance. This drives the internal redistribution of the paraffin liquid, yielding controllable formation of microstructures. This single-step process is completed in 10 seconds, does not involve any volatile solvents/reactants, and can be adapted to three-dimensional complex surfaces. The living nature of the network further allows sequential growth of hierarchical microstructures. The versatility and efficiency of our approach offer possibilities for future nanotechnologies beyond conventional microfabrication techniques.

High Solubilization and Controlled Release of Paclitaxel Using Thermosponge Nanoparticles for Effective Cancer Therapy

Cancer, which is a leading cause of death, contributes significantly to reducing life expectancy worldwide. Even though paclitaxel (PTX) is known as one of the main anticancer drugs, it has several limitations, including low solubility in aqueous solutions, a limited dosage range, an insufficient release amount, and patient resistance. To overcome these limitations, we suggest the development of PTX-loaded thermosponge nanoparticles (PTX@TNP), which result in improved anticancer effects, via a simple nanoprecipitation method, which allows the preparation of PTX@TNPs with hydrophobic interactions without any chemical conjugation. Further, to improve the drug content and yield of the prepared complex, the co-organic solvent ratio was optimized. Thus, it was observed that the drug release rate increased as the drug capacity of PTX@TNPs increased. Furthermore, increasing PTX loading led to considerable anticancer activity against multidrug resistance (MDR)-related colorectal cancer cells (HCT 15), implying a synergistic anticancer effect. These results suggest that the solubilization of high drug amounts and the controlled release of poorly water-soluble PTX using TNPs could significantly improve its anticancer therapy, particularly in the treatment of MDR-p-glycoprotein-overexpressing cancers.

Data presenting the synthesis of three novel stimuli responsive hyperbranched polymers synthesised via RAFT polymerisation and the bio conjugation of folic acid

The data presented in this manuscript presents the characterisation spectra of three hyperbranched polymers as discussed in the paper “Folic Acid and Rhodamine Labelled pH Responsive Hyperbranched Polymers: synthesis, characterisation and cell uptake studies” [1]. Characterisation of polymers was performed via ¹H Nuclear Magnetic Resonance (¹H NMR) and Size Exclusion Chromatography (SEC). pH responsive characteristics were observed via Dynamic Light Scattering (DLS). The data for characterisation of folate conjugated hyperbranched polymer is presented as ¹H NMR, Ultra Violet Visible (UV-VIS) spectra and DLS measurements. Further data is presented detailing the experiments for the synthesis of monomers 2-propyl acrylic acid (PAA) and disulfide diacrylate (DSDA), with the full synthesis of folic acid-poly (ethylene glycol) (PEG) linker, rhodamine B ethylenediamine linker and bioconjugation reactions also detailed.

Recent Developments in the Area of Click-Crosslinked Nanocarriers for Drug Delivery

Click-crosslinking has been widely used for the fabrication of nanocarriers in recent years. Crosslinking can enhance the stability of nanocarriers that have served as an emerging platform for drug delivery to achieve cancer diagnosis and therapy. In crosslinking methods, click reactions have attracted increasing attention owing to their high reaction specificity and physiologically stable products. These reports on click-crosslinked nanocarriers are divided into four sections (nanogels, nanoparticles, micelles, and capsules) according to the types of nanocarriers. Click-crosslinked nanocarriers enhance the solubility of hydrophobic drugs and improve the efficacy of drug delivery owing to their good stability. Stimuli-responsive and targeted strategies can be introduced into click-crosslinked nanocarriers to enhance drug accumulation in tumors.

Reversible networks of degradable polyesters containing weak covalent bonds

The synthesis of reversible polyester networks based mainly on the Diels–Alder chemistry, alkene [2 + 2] cycloaddition or transesterification reactions and studies of their reversibility and its consequences are reviewed.

Recent advances in stimuli-responsive polymeric micelles via click chemistry

Stimuli-responsive polymeric micelles via click chemistry are divided into six major sections (temperature, light, ultrasound, pH, enzymes, and redox).

Advances in redox-responsive drug delivery systems of tumor microenvironment

With the improvement of nanotechnology and nanomaterials, redox-responsive delivery systems have been studied extensively in some critical areas, especially in the field of biomedicine. The system constructed by redox-responsive delivery can be much stable when in circulation. In addition, redox-responsive vectors can respond to the high intracellular level of glutathione and release the loaded cargoes rapidly, only if they reach the site of tumor tissue or targeted cells. Moreover, redox-responsive delivery systems are often applied to significantly improve drug concentrations in targeted cells, increase the therapeutic efficiency and reduce side effects or toxicity of primary drugs. In this review, we focused on the structures and types of current redox-responsive delivery systems and provided a comprehensive overview of relevant researches, in which the disulfide bond containing delivery systems are of the utmost discussion.

Native Chemical Ligation for Cross-Linking of Flower-Like Micelles

In this study, native chemical ligation (NCL) was used as a selective cross-linking method to form core-cross-linked thermosensitive polymeric micelles for drug delivery applications. To this end, two complementary ABA triblock copolymers having polyethylene glycol (PEG) as midblock were synthesized by atom transfer radical polymerization (ATRP). The thermosensitive poly isopropylacrylamide (PNIPAM) outer blocks of the polymers were copolymerized with either N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys), P(NIPAM- co-HPMA-Cys)-PEG-P(NIPAM- co-HPMA-Cys) (PNC) or N-(2-hydroxypropyl)methacrylamide-ethylthioglycolate succinic acid (HPMA-ETSA), P(NIPAM- co-HPMA-ETSA)-PEG-P(NIPAM- co-HPMA-ETSA) (PNE). Mixing of these polymers in aqueous solution followed by heating to 50 °C resulted in the formation of thermosensitive flower-like micelles. Subsequently, native chemical ligation in the core of micelles resulted in stabilization of the micelles with a Z-average of 65 nm at body temperature. Decreasing the temperature to 10 °C only affected the size of the micelles (increased to 90 nm) but hardly affected the polydispersity index (PDI) and aggregation number ( Nagg) confirming covalent stabilization of the micelles by NCL. CryoTEM images showed micelles with an uniform spherical shape and dark patches close to the corona of micelles were observed in the tomographic view. The dark patches represent more dense areas in the micelles which coincide with the higher content of HPMA-Cys/ETSA close to the PEG chain revealed by the polymerization kinetics study. Notably, this cross-linking method provides the possibility for conjugation of functional molecules either by using the thiol moieties still present after NCL or by simply adjusting the molar ratio between the polymers (resulting in excess cysteine or thioester moieties) during micelle formation. Furthermore, in vitro cell experiments demonstrated that fluorescently labeled micelles were successfully taken up by HeLa cells while cell viability remained high even at high micelle concentrations. These results demonstrate the potential of these micelles for drug delivery applications.

Core-crosslinked diblock terpolymer micelles – taking a closer look on crosslinking efficiency

We present an in-depth study on the crosslinking of diblock terpolymer micellar cores.

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

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

High drug loading and pH-responsive targeted nanocarriers from alginate-modified SPIONs for anti-tumor chemotherapy

To increase the accumulation of nanocarriers at the tumor site and reduce premature drug leakage, we fabricated alginate modified superparamagnetic iron oxide nanoparticles (SPIONs) with magnetic targeting capability for pH-responsive release of the anticancer drug doxorubicin (DOX) in tumor-cell microenvironments. The drug loading content (DLC) of SPION-4 was as high as 48.98% with a stable size of 135 nm, whereas the DLC of SPION-2 (amine-functionalized SPIONs as the control) was 7.58%. The in vitro release studies revealed that the acidic environment (pH 6.5 and pH 5.0) triggered the effective release of DOX from DOX-loaded SPION-4 twice and thrice as much as the neutral condition (pH 7.4) after 10.7 h, respectively. These nanocarriers exhibited good cytocompatibility towards both normal cells (LO2) and cancer cells (HepG2), but higher cytotoxicity against HepG2 cells for DOX-loaded SPION-4 than that against LO2 cells could be observed due to the effects of an additional magnet and the acidic microenvironment of cancer cells, which greatly improved the cellular uptake of magnetic nanoparticles and released more DOX in the cytoplasm and nucleus. The in vivo biodistribution and anti-tumor efficacy demonstrated that DOX-loaded SPION-4 under an external magnetic field could obviously increase the DOX concentration in tumor tissues to remarkably inhibit tumor growth and significantly reduce side effects of free DOX. Therefore, this work suggested that these SPION-4 nanoparticles may be a potential carrier to deliver chemotherapeutic agents in anti-tumor treatment.