The polymerization kinetics, oxidation-responsiveness, and in vitro anticancer efficacy of poly(ester-thioether)s

High-Molecular-Weight and Light-Colored Disulfide-Bond-Embedded Polyesters: Accelerated Hydrolysis Triggered by Redox Responsiveness

Disulfide bonds have attracted considerable attention due to their reduction responsiveness, but it is crucial and challenging to prepare disulfide-bond-based polyesters by melt polycondensation. Herein, the inherently poor thermal stability of the S-S bond in melting polycondensation was overcome. Moreover, poly(butylene succinate-co-dithiodipropionate) (PBSDi) with a light color and high molecular weights (Mn values up to 84.7 kg/mol) was obtained. These polyesters can be applied via melt processing with Td,5% > 318 °C. PBSDi10-PBSDi40 shows good crystallizability (crystallinity 56-38%) and compact lamellar thickness (2.9-3.2 nm). Compared with commercial poly(butylene adipate-co-terephthalate) (PBAT), the elevated mechanical and barrier performances of PBSDi make them better packaging materials. For the degradation behavior, the disulfide monomer obviously accelerates the enzyme degradation but has a weaker effect on hydrolysis. In 0.1 mol/L or higher concentrations of H2O2 solutions, the oxidation of disulfide bonds to sulfoxide and sulfone groups can be realized. This process results in a stronger nucleophilic attack, as confirmed by the Fukui function and DFT calculations. Additionally, the greater polarity and hydrophilicity of oxidation products, proved by noncovalent interaction analysis, accelerate the hydrolysis of polyesters. Moreover, glutathione-responsive breakage, from polymers to oligomers, is confirmed by an accelerated decline in molecular weight. Our research offers fresh perspectives on the effective synthesis of the disulfide polyester and lays a solid basis for the creation of high-performance biodegradable polyesters that degrade on demand.

ROS-responsive PEGylated ferrocene polymer nanoparticles with improved stability for tumor-selective chemotherapy and imaging

Ferrocene-based nanoparticles have garnered interest as reactive oxygen species (ROS)-responsive nanocarriers of anticancer drugs and imaging agents. However, their biomedical applications remain limited due to their poor physiological stability. PEGylation of nanocarriers improves their stability and biocompatibility. In this study, we aimed to develop novel PEG-ferrocene nanoparticles (PFNPs) with enhanced stability and ROS responsiveness for the delivery of paclitaxel (PTX) and imaging agents. PEGylation improved the stability of ferrocene nanoparticles, inhibiting their ROS-responsive destruction. Several PEG-ferrocene polymers containing different molar ratios of methacrylic acid and poly (ethylene glycol) methyl ether methacrylate was designed for optimization. ROS-responsive polymers with optimal monomer ratios were self-assembled into PFNPs with enhanced stability. The PFNPs distended, effectively releasing encapsulated PTX and imaging agents within 8 h in the presence of ROS. Furthermore, they remained stable, with no changes in their hydrodynamic diameters or polydispersity indexes after storage in an aqueous solution and biological buffer. The accumulation of PFNPs in a tumor model in vivo was 15-fold higher than a free dye. PTX-loaded PFNPs showed a substantial tumor-suppression effect, reducing tumor size to approximately 18% of that in the corresponding control group. These findings suggest a promising application of ROS-responsive PFNPs in tumor treatment as biocompatible nanocarriers of anticancer drugs and imaging agents.

Single-dose injectable nanovaccine-in-hydrogel for robust immunotherapy of large tumors with abscopal effect

Current cancer immunotherapy [e.g., immune checkpoint blockade (ICB)] only benefits small subsets of patients, largely due to immunosuppressive tumor microenvironment (TME). In situ tumor vaccination can reduce TME immunosuppression and thereby improve cancer immunotherapy. Here, we present single-dose injectable (nanovaccines + ICBs)-in-hydrogel (NvIH) for robust immunotherapy of large tumors with abscopal effect. NvIH is thermo-responsive hydrogel co-encapsulated with ICB antibodies and novel polymeric nanoparticles loaded with three immunostimulatory agonists for Toll-like receptors 7/8/9 (TLR7/8/9) and stimulator of interferon genes (STING). Upon in situ tumor vaccination, NvIH undergoes rapid sol-to-gel transformation, prolongs tumor retention, sustains the release of immunotherapeutics, and reduces acute systemic inflammation. In multiple poorly immunogenic tumor models, single-dose NvIH reduces multitier TME immunosuppression, elicits potent TME and systemic innate and adaptive antitumor immunity with memory, and regresses both local (vaccinated) and distant large tumors with abscopal effect, including distant orthotopic glioblastoma. Overall, NvIH holds great potential for tumor immunotherapy.

Thioanisole ester based logic gate cascade to control ROS-triggered micellar degradation

Thioanisole ester polymer side chains hydrolyze exclusively upon thioether oxidation, showing logic gate response. ROS-induced ester hydrolysis on the hydrophobic domain leads to nanocarrier disassembly with potential for targeted drug release.

Thioether-Based Polymeric Micelles with Fine-Tuned Oxidation Sensitivities for Chemotherapeutic Drug Delivery

Oxidation-sensitive drug delivery systems (DDSs) have attracted attention due to the potential to improve efficacy and safety of chemotherapeutics. These systems are designed to release the payload in response to oxidative stress conditions, which are associated with many types of cancer. Despite extensive research on the development of oxidation-sensitive DDS, the lack of selectivity toward cancer cells over healthy cells remains a challenge. Here, we report the design and characterization of polymeric micelles containing thioether groups with varying oxidation sensitivities within the micellar core, which become hydrophilic upon thioether oxidation, leading to destabilization of the micellar structure. We first used the thioether model compounds, 3-methylthiopropylamide (TPAM), thiomorpholine amide (TMAM), and 4-(methylthio)benzylamide (TPhAM) to investigate the effect of the chemical structures of the thioethers on the oxidation by hydrogen peroxide (H₂O₂). TPAM shows the fastest oxidation, followed by TMAM and TPhAM, showing that the oxidation reaction of thioethers can be modulated by changing the substituent groups bound to the sulfur atom. We next prepared micelles containing these different thioether groups within the core (TP, TM, and TPh micelles). The micelles containing the thioether groups with a higher oxidation sensitivity were destabilized by H₂O₂ at a lower concentration. Micelle destabilization was also tested in human liver cancer (HepG2) cells and human umbilical vein endothelial cells (HUVECs). The TP micelles having the highest oxidation sensitivity were destabilized in both HepG2 cells and HUVECs, while the TPh micelles, which showed the lowest reactivity toward H₂O₂, were stable in these cell lines. The TM micelles possessing a moderate oxidation sensitivity were destabilized in HepG2 cells but were stable in HUVECs. Furthermore, the micelles were loaded with doxorubicin (Dox) to evaluate their potential in drug delivery applications. Among the micelles, the TM micelles loaded with Dox showed the enhanced relative toxicity in HepG2 cells over HUVECs. Therefore, our approach to fine-tune the oxidation sensitivity of the micelles has potential for improving therapeutic efficacy and safety of drugs in cancer treatment.

Reversing Chemotherapy Resistance by a Synergy between Lysosomal pH-Activated Mitochondrial Drug Delivery and Erlotinib-Mediated Drug Efflux Inhibition

Mitochondrial drug delivery has attracted increasing attention in various mitochondrial dysfunction-associated disorders such as cancer owing to the important role of energy production. Herein, we report a lysosomal pH-activated mitochondrial-targeting polymer nanoparticle to overcome drug resistance by a synergy between mitochondrial delivery of doxorubicin (DOX, an anticancer drug) and erlotinib-mediated inhibition of drug efflux. The obtained nanoparticles, DE-NPs could maintain negative charge and have long blood circulation while undergoing charge reversal at lysosomal pH after internalization by cancer cells. Thereafter, the acidity-activated polycationic and hydrophobic polypeptide domains boost lysosomal escape and mitochondrial-targeting drug delivery, leading to mitochondrial dysfunction, ATP suppression, and cell apoptosis. Moreover, the suppressed ATP supply and erlotinib enabled dual inhibition of drug efflux by DOX-resistant MCF-7/ADR cells, leading to significantly augmented intracellular DOX accumulation and a synergistic anticancer effect with a 17-fold decrease of IC50 relative to DOX. In vivo antitumor study demonstrates that DE-NPs efficiently suppressed the tumor burden in MCF-7/ADR tumor-bearing mice and led to negligible toxicity. This work establishes that a combination of mitochondrial drug delivery and drug efflux inhibition could be a promising strategy for combating multidrug resistance.

Polymeric micelles amplify tumor oxidative stresses through combining PDT and glutathione depletion for synergistic cancer chemotherapy

Cancer has been one of the major healthcare burdens, which demands innovative therapeutic strategies to improve the treatment outcomes. Combination therapy hold great potential to leverage multiple synergistic pathways to improve cancer treatment. Cancer cells often exhibit an increased generation of reactive oxygen species (ROS) and antioxidant species compared with normal cells, and the levels of these species can be further elevated by common therapeutic modalities such as photodynamic therapy (PDT) or chemotherapy. Taking advantage that cancer cells are vulnerable to further oxidative stress, we aim to design a drug delivery system by simultaneously increasing the cellular ROS level, reducing antioxidative capacity, and inducing anticancer chemotherapy in cancer cells. Here, we designed a star-shape polymer, PEG(-b-PCL-Ce6)-b-PBEMA, based on the Passerini three-component reaction, which can both enhance ROS generation during PDT and decrease the GSH level in cancer cells. The polycaprolactone conjugated with photosensitizer Ce6 served as hydrophobic segments to promote micelle formation, and Ce6 was used for PDT. The H₂O₂-labile group of arylboronic esters pendent on the third segment was designed for H₂O₂-induced quinone methide (QM) release for GSH depletion. We thoroughly investigated the spectral properties of blank micelle during its assembling process, ROS generation, and H₂O₂-induced QM release in vitro. Moreover, this polymeric micelle could successfully load hydrophobic anticancer drug Doxorubicin (DOX) and efficiently deliver DOX into cancer cells. The triple combination of ROS generation, GSH elimination, and chemotherapy dramatically improved antitumor efficiency relative to each of them alone in vitro and in vivo.

Selective Oxidation of Polysulfide Latexes to Produce Polysulfoxide and Polysulfone in a Waterborne Environment

Polymers containing sulfur centers with high oxidation states in the main chain, polysulfoxide and polysulfone, display desirable properties such as thermomechanical and chemical stability. To circumvent their challenging direct synthesis, methods based on the oxidation of a parent polysulfide have been developed but are plagued by uncontrolled reactions, leading either to ill-defined mixtures of polysulfoxides and polysulfones or to polysulfones with reduced degrees of polymerization due to overoxidation of the polymer. We developed an alternative method to produce well-defined polysulfoxide and polysulfone in a waterborne colloidal emulsion using different oxidants to control the oxidation state of sulfur in the final materials. The direct oxidation of water-based polysulfide latexes avoided the use of volatile organic solvents and allowed for the control of the oxidation state of the sulfur atoms. Oxidation of parent polysulfides by tert-butyl hydroperoxide led to the production of pure polysulfoxides, even after 70 days of reaction time. Additionally, hydrogen peroxide produced both species through the course of the reaction but yielded fully converted polysulfones after 24 h. By employing mild oxidants, our approach controlled the oxidation state of the sulfur atoms in the final sulfur-containing polymer and prevented any overoxidation, thus ensuring the integrity of the polymer chains and colloidal stability of the system. We also verified the selectivity, versatility, and robustness of the method by applying it to polysulfides of different chemical compositions and structures. The universality demonstrated by this method makes it a powerful yet simple platform for the design of sulfur-containing polymers and nanoparticles.

Poly(ester-thioether) microspheres co-loaded with erlotinib and α-tocopheryl succinate for combinational therapy of non-small cell lung cancer

Polymer microspheres are attracting wide attention in localized cancer therapy owing to the excellent biocompatibility and drug loading capacity, controllable biodegradation speeds, and minimized systemic toxicity. Herein, we presented poly(ester-thioether) microspheres, porous and nonporous, as drug depots for localized therapy of non-small cell lung cancer (NSCLC). Specifically, erlotinib and α-tocopheryl succinate (α-TOS), which are respectively an epidermal growth factor receptor (EGFR) inhibitor and mitochondria destabilizer, were efficiently loaded into porous and nonporous poly(ester-thioether) microspheres for the treatment of EGFR-overexpressing NSCLC (A549 cells). The poly(ester-thioether) microspheres significantly improved the bioavailability of both erlotinib and α-TOS in comparison to the free drug combination, realizing synergistic inhibition of A549 cells both in vitro and in vivo. The porous microspheres displayed faster degradation and drug release than the nonporous counterpart, thereby showing better anticancer efficacy. Overall, our study reported a new anticancer strategy of erlotinib and α-TOS combination for therapy of NSCLC, and established that poly(ester-thioether) microspheres could be a robust and biodegradable reservoir for drug delivery and localized cancer therapy.

Dual Release Model to Evaluate Dissolution Profiles from Swellable Drug Polyelectrolyte Matrices

Background:

Mathematical modeling in modified drug release is an important tool that allows predicting the release rate of drugs in their surrounding environment and elucidates the transport mechanisms involved in the process.

Objective:

The aim of this work was to develop a mathematical model that allows evaluating the release profile of drugs from polymeric carriers in which the swelling phenomenon is present.

Methods:

Swellable matrices based on ionic complexes of alginic acid or carboxymethylcellulose with ciprofloxacin were prepared and the effect of adding the polymer sodium salt on the swelling process and the drug release was evaluated. Experimental data from the ciprofloxacin release profiles were mathematically adjusted, considering the mechanisms involved in each stage of the release process.

Results:

A proposed model, named “Dual Release” model, was able to properly fit the experimental data of matrices presenting the swelling phenomenon, characterized by an inflection point in their release profile. This entails applying the extended model of Korsmeyer-Peppas to estimate the percentage of drug released from the first experimental point up to the inflection point and then a model called Lumped until the final time, allowing to adequately represent the complete range of the drug release profile. Different parameters of pharmaceutical relevance were calculated using the proposed model to compare the profiles of the studied matrices.

Conclusion:

The “Dual Release” model proposed in this article can be used to predict the behavior of complex systems in which different mechanisms are involved in the release process.

Novozym 435-Catalyzed Synthesis of Well-Defined Hyperbranched Aliphatic Poly(β-thioether ester)

A series of new hyperbranched aliphatic poly(β-thioether ester)s were prepared by the enzymatic ring-opening polycondensation of 1,4-oxathiepan-7-one (OTO) and AB2/ABB' comonomer with acid-labile β-thiopropionate groups. Two kinds of comonomers, methyl 3-((3-hydroxy-2-(hydroxymethyl)propyl)thio)propanoate (HHTP) and methyl 3-((2,3-dihydroxypropyl)thio)propanoate (DHTP), with different primary alcohols and secondary alcohols, were synthesized by thiol-ene click chemistry and thiol-ene Michael addition, respectively. Immobilized lipase B from Candida antarctica (CALB), Novozym 435, was used as the catalyst. The random copolymers were characterized by 1H-NMR, 13C-NMR, GPC, TGA, and DSC. All branched copolyesters had high molecular weights over 15,000 Da with narrow polydispersities in the range of 1.75-2.01 and were amorphous polymers. Their degradation properties under acidic conditions were also studied in vitro. The polymeric nanoparticles of hyperbranched poly(β-thioether ester)s were successfully obtained and showed good oxidation-responsive properties, indicating their potential for biomedical applications.

H2O2-responsive polymeric micelles with a benzil moiety for efficient DOX delivery and AIE imaging

Nano drug delivery is a promising domain in biomedical theranostics and has aroused more and more attention in recent years. We report here an amphiphilic polymer TPG1, bearing a H2O2-sensitive benzil and an AIE fluorophore tetraphenylethene (TPE) unit, which is able to self-assemble into spherical nanosized micelles in aqueous solution. Doxorubicin (DOX) can be encapsulated into TPG1 micelles efficiently with the loading capability of up to 59% by weight. The benzil moiety could be cleaved via the Baeyer-Villiger type reaction in the presence of H2O2, leading to the decomposition of TPG1 micelles and release of DOX. In vitro studies indicated that DOX-loaded TPG1 micelles can be internalized by cancer cells, followed by unloading encapsulated DOX under the stimulation of H2O2. The drug release process can be monitored by the AIE fluorescence from the degradation products containing a TPE moiety. MTT assays against HeLa and HepG2 cancer cells demonstrated that DOX-loaded micelles showed good anticancer efficacy. The polymer TPG1 and the corresponding decomposed products showed great biocompatibility. Our data suggest that TPG1 has the potential to be employed for the controlled drug delivery system.

Polyphosphazene-based nanocarriers for the release of agrochemicals and potential anticancer drugs

The synthesised polyphosphazene-based nanocarriers allowed sustained diosgenin and brassinosteroid release over 4 days, with strong to moderate MCF-7 cytotoxicity and good agrochemical activity at medium and low concentrations.

An amphiphilic, heterografted polythiophene copolymer containing biocompatible/biodegradable side chains for use as an (electro)active surface in biomedical applications

Design of an amphiphilic heterografted block copolymer composed of a hydrophobic core backbone and both hydrophilic side chains, able to detect the redox reaction of NADH.