Fluorescent boronate-based polymer nanoparticles with reactive oxygen species (ROS)-triggered cargo release for drug-delivery applications

Reactive oxygen species driven prodrug-based nanoscale carriers for transformative therapies

Reactive oxygen species (ROS) drive processes in various pathological conditions serving as an attractive target for therapeutic strategies. This review highlights the development and use of ROS-dependent prodrug-based nanoscale carriers that has transformed many biomedical applications. Incorporating prodrugs into nanoscale carriers not only improves their stability and solubility but also enables site-specific drug delivery ultimately enhancing the therapeutic effectiveness of the nanoscale carriers. We critically examine recent advances in ROS-responsive nanoparticulate platforms, encompassing liposomes, polymeric nanoparticles, and inorganic nanocarriers. These platforms facilitate precise control over drug release upon encountering elevated ROS levels at disease sites, thereby minimizing off-target effects and maximizing therapeutic efficiency. Furthermore, we investigate the potential of combination therapies in which ROS-activated prodrugs are combined with other therapeutic agents and underscore their synergistic potential for treating multifaceted diseases. This comprehensive review highlights the immense potential of ROS-dependent prodrug-based nanoparticulate systems in revolutionizing biomedical applications; such nanoparticulate systems can facilitate selective and controlled drug delivery, reduce toxicity, and improve therapeutic outcomes for ROS-associated diseases.

Codelivery of CPT and siPHB1 with GSH/ROS Dual-Responsive Hybrid Nanoparticles Based on a [12]aneN3-Derived Lipid for Synergistic Lung Cancer Therapy

The combination of small-interfering RNA (siRNA)-mediated gene silencing and chemotherapeutic agents for lung cancer treatment has attracted widespread attention in terms of a greater therapeutic effect, minimization of systemic toxicity, and inhibition of multiple drug resistance (MDR). In this work, three amphiphiles, CBN1-CBN3, were first designed and synthesized as a camptothecin (CPT) conjugate and gene condensation agents by the combination of CPT prodrugs and di(triazole-[12]aneN3) through the ROS-responsive phenylborate ester and different lengths of alkyl chains (with 6, 9, 12 carbon chains for CBN1-CBN3, respectively). CBN1-CBN3 were able to be self-assembled into liposomes with an average diameter in the range of 320-240 nm, showing the ability to effectively condense siRNA. Among them, CBN2, with a nine-carbon alkyl chain, displayed the best anticancer efficiency in A549 cells. In order to give nanomedicines a stealth property and PEGylation/dePEGylation transition, a GSH-responsive PEGylated TPE derivative containing a disulfide linkage (TSP) was further designed and prepared. A combination of CBN2/siRNA complexes and DOPE with TSP resulted in GSH/ROS dual-responsive lipid-polymer hybrid nanoparticles (CBN2-DP/siRNA NPs). In present GSH and H2O2, CBN2-DP/siRNA NPs were decomposed, resulting in the controlled release of CPT drug and siRNA. In vitro, CBN2-DP/siPHB1 NPs showed the best anticancer activity for suppression of about 75% of A549 cell proliferation in a serum medium. The stability of CBN2-DP/siRNA NPs was significantly prolonged in blood circulation, and they showed effective accumulation in the A549 tumor site through an enhanced permeability and retention (EPR) effect. In vivo, CBN2-DP/siPHB1 NPs demonstrated enhanced synergistic cancer therapy efficacy and tumor inhibition as high as 71.2%. This work provided a strategy for preparing lipid-polymer hybrid NPs with GSH/ROS dual-responsive properties and an intriguing method for lung cancer therapy.

ortho-Boronic Acid Carbonyl Compounds and Their Applications in Chemical Biology

Iminoboronates and diazaborines are related classes of compounds that feature an imine ortho to an arylboronic acid (iminoboronate) or a hydrazone that cyclizes with an ortho arylboronic acid (diazaborine). Rather than acting as independent chemical motifs, the arylboronic acid impacts the rate of imine/hydrazone formation, hydrolysis, and exchange with competing nucleophiles. Increasing evidence has shown that the imine/hydrazone functionality also impacts arylboronic acid reactivity toward diols and reactive oxygen and nitrogen species (ROS/RNS). Untangling the communication between C=N linked functionalities and arylboronic acids has revealed a powerful and tunable motif for bioconjugation chemistries and other applications in chemical biology. Here, we survey the applications of iminoboronates and diazaborines in these fields with an eye toward understanding their utility as a function of neighboring group effects.

Reactive oxygen species-responsive polymer drug delivery systems

Applying reactive polymer materials sensitive to biological stimuli has recently attracted extensive research interest. The special physiological effects of reactive oxygen species (ROS) on tumors or inflammation and the application of ROS-responsive polymers as drug-delivery systems in organisms have attracted much attention. ROS is a vital disease signal molecule, and the unique accumulation of ROS-responsive polymers in pathological sites may enable ROS-responsive polymers to deliver payload (such as drugs, ROS-responsive prodrugs, and gene therapy fragments) in a targeted fashion. In this paper, the research progress of ROS-responsive polymers and their application in recent years were summarized and analyzed. The research progress of ROS-responsive polymers was reviewed from the perspective of nanoparticle drug delivery systems, multi-responsive delivery systems, and ROS-responsive hydrogels. It is expected that our work will help understand the future development trends in this field.

Prevent Drug Leakage via the Boronic Acid Glucose-Insensitive Micelle for Alzheimer's Disease Combination Treatment

Boronic acid (BA) materials have been widely applied to glucose and oxidative stress-sensitive drug delivery for the treatment of cancer, diabetes, and Alzheimer's disease (AD). There are completely various BA-sensitive delivery conditions in different diseases. BA materials in the treatment of diabetes show better performance at a high-glucose environment than normal. In contrast, the concentration of glucose in the brain is much lower than that in the blood of AD patients. Hence, the typical glucose and oxidative stress dual-sensitive BA materials inevitably encounter drug leakage in circulation in AD. Attempts to decrease the glucose-sensitive capacity of BA materials are extremely essential for AD drug delivery. In this study, the epoxy group (electron-donating group) was introduced to increase the pKa values of BA materials by increasing the electron cloud density, and thus, the glucose-insensitive micelle (GIM) was obtained. The treatment effect and the synergism mechanism of the drug-loaded GIM micelle were studied on senescence-accelerated mouse prone 8 mice. This work provided excellent antioxidant drugs (vitamin E succinate, melatonin, and quercetin) and a glucose metabolism drug (insulin) loaded in GIM micelle for AD treatment. The discovery of the combination mechanism is enormously valuable for AD clinical research.

Reactive Oxygen Species─Responsive Lipid Nanoparticles for Effective RNAi and Corneal Neovascularization Therapy

Corneal neovascularization (CNV) is a common disease that affects the vision ability of more than 1 million people annually. Small interfering RNA (siRNA) delivery nanoparticle platforms are a promising therapeutic modality for CNV treatment. However, the efficient delivery of siRNA into cells and the effective release of siRNA from delivery vehicles in a particular cell type challenge effective RNAi clinical application for CNV suppression. This study reports the design of a novel reactive oxygen species (ROS)-responsive lipid nanoparticle for siRNA delivery into corneal lesions for enhanced RNAi as a potential CNV treatment. We demonstrated that lipid nanoparticles could efficiently deliver siRNA into human umbilical vein endothelial cells and release siRNA for enhanced gene silencing by using the upregulated ROS of CNV to promote lipid nanoparticle degradation. Moreover, the subconjunctival injection of siRNA nanocomplexes into corneal lesions effectively knocked down vascular endothelial growth factor expression and suppressed CNV formation in an alkali burn model. Thus, we believe that the strategy of using ROS-responsive lipid nanoparticles for enhanced RNAi in CNV could be further extended to a promising clinical therapeutic approach to attenuate CNV formation.

Nanocrystalline chloroxine possesses broad-spectrum antimicrobial activities and excellent skin tolerability in mice

Background: Antimicrobial submicrometer particles are being studied as promising interventions against a wide range of skin conditions, such as fungal or bacterial infections. Aims: To submicronize chloroxine, the crystalline compound 5,7-dichloro-8-hydroxyquinoline, by nanoprecipitation and characterize the resulting assemblies. Methods: The chloroxine particles were stabilized by a nonionic surfactant and were studied by a broth microdilution assay against 20 medically important bacteria and fungi. The intervention was studied using a murine model of skin irritation. Results & conclusions: Chloroxine nanoparticles with a diameter of 600-800 nm exhibit good tolerability in terms of skin irritation in vivo and good antimicrobial activity. Thus, the fabricated formulation shows great promise for interventions for both cutaneous infection control and prophylaxis.

Connecting the Dynamics and Reactivity of Arylboronic Acids to Emergent and Stimuli-Responsive Material Properties

Over the past two decades, arylboronic acid-functionalized biomaterials have been used in a variety of sensing and stimuli-responsive scaffolds. Their diverse applications result from the diverse reactivity of arylboronic acids,...

H2O2-Responsive amphiphilic polymer with aggregation-induced emission (AIE) for DOX delivery and tumor therapy

Stimuli-responsive drug delivery systems (DDSs) based on amphiphilic polymers have attracted much attention. In this study, we reported an innovative H₂O₂-responsive amphiphilic polymer (TBP), bearing a H₂O₂-sensitive phenylboronic ester, AIE fluorophore tetraphenylethene (TPE) hydrophobic, and polyethylene glycol hydrophilic (PEG) moieties. TBP could self-assemble into micelles with an encapsulation efficiency as high as 74.9% for doxorubicin (DOX) in aqueous solution. In the presence of H₂O₂, TBP micelles was decomposed by oxidation, hydrolysis and rearrangement, leading to almost 80% DOX release from TBP@DOX micelles. TBP and the corresponding degradation products were biocompatible, while TBP@DOX micelles only displayed obvious toxicity toward cancer cells. Drug delivery process was clearly monitored by confocal laser scanning microscopic (CLSM) and flow cytometry (FCM) analysis. Moreover, in vivo anticancer study showed that TBP@DOX micelles were accumulated in tumor region of nude mice and effectively inhibited tumor growth. The results suggested that the reported H₂O₂-responsive amphiphilic polymer displayed great potential in drug delivery and tumor therapy.

Hydrogen Sulfide-Responsive Bicontinuous Nanospheres

Block copolymers (BCPs) that can self-assemble into particles and be triggered by disease-specific molecules such as hydrogen sulfide (H₂S) have the potential to impact on drug delivery, decreasing off-target toxicities while increasing drug efficacy. However, the incorporation of H₂S-responsive aryl azides into BCPs for self-assembly has been limited by heat, light, and radical sensitivities. In this study, a robust activator regenerated by the electron-transfer atom-transfer radical polymerization reaction was used to synthesize aryl-azide-containing BCPs under ambient conditions. Conditions controlling self-assembly of the BCPs into 150-200 nm particles and the physicochemical properties of the particles were investigated. The use of nanoprecipitation with tetrahydrofuran to promote self-assembly of the BCPs resulted in vesicle structures, while dimethylformamide or dimethylsulfoxide resulted in polymeric bicontinuous nanospheres (BCNs). Triggering of the BCPs and particles (vesicles or BCNs) via exposure to H₂S revealed that unsubstituted aryl azides were readily reduced (by HS^-), resulting in particle disruption or cross-linking. The relative polar nature of the particle bilayers containing unsubstituted aryl azides and the open structure of the BCNs did however limit encapsulation of small hydrophilic and hydrophobic payloads. Incorporation of a benzylamide substituent onto the aryl azide group increased the hydrophobicity of the particles and encapsulation of hydrophilic cargo but reduced sensitivity to H₂S, likely due to the reduced penetration of HS^- into the bilayer.

Intramitochondrial Disulfide Polymerization Controls Cancer Cell Fate

Recent advances in supramolecular chemistry research have led to the development of artificial chemical systems that can form self-assembled structures that imitate proteins involved in the regulation of cellular function. However, intracellular polymerization systems that operate inside living cells have been seldom reported. In this study, we developed an intramitochondrial polymerization-induced self-assembly system for regulating the cellular fate of cancer cells. It showed that polymeric disulfide formation inside cells occurred due to the high reactive oxygen species (ROS) concentration of cancer mitochondria. This polymerization barely occurs elsewhere in the cell owing to the reductive intracellular environment. The polymerization of the thiol-containing monomers further increases the ROS level inside the mitochondria, thereby autocatalyzing the polymerization process and creating fibrous polymeric structures. This process induces dysfunction of the mitochondria, which in turn activates cell necroptosis. Thus, this in situ polymerization system shows great potential for cancer treatment, including that of drug-resistant cancers.

Enhanced Antitumor Efficacy through an "AND gate" Reactive Oxygen-Species-Dependent pH-Responsive Nanomedicine Approach

Anticancer drug delivery strategies are designed to take advantage of the differential chemical environment in solid tumors independently, or to high levels of reactive oxygen species (ROS) or to low pH, compared to healthy tissue. Here, the design and thorough characterization of two functionalizable "AND gate" multiresponsive (MR) block amphiphilic copolymers are reported, aimed to take full advantage of the coexistence of two chemical cues-ROS and low pH-present in the tumor microenvironment. The hydrophobic blocks contain masked pH-responsive side chains, which are exposed exclusively in response to ROS. Hence, the hydrophobic polymer side chains will undergo a charge shift in a very relevant pH window present in the extracellular milieu in most solid tumors (pH 5.6-7.2) after demasking by ROS. Doxorubicin (DOX)-loaded nanosized "AND gate" MR polymersomes (MRPs) are fabricated via microfluidic self-assembly. Chemical characterization reveals ROS-dependent pH sensitivity and accelerated DOX release under influence of both ROS and low pH. Treatment of tumor-bearing mice with DOX-loaded nonresponsive and "AND gate" MRPs dramatically decreases cardiac toxicity. The most optimal "AND gate" MRPs outperform free DOX in terms of tumor growth inhibition and survival, shedding light on chemical requirements for successful cancer nanomedicine.

Inflammatory microenvironment-targeted nanotherapies

Inflammatory microenvironments (IMEs) are common pathological characteristics and drive the development of multiple chronic diseases. Thus, IME-targeted therapies exhibit potential for the treatment of inflammatory diseases. Nanoplatforms have significant advantages in improving the efficiency of anti-inflammatory treatments. Owing to their improved therapeutic effects and reduced side effects, IME-targeted nanotherapies have recently drawn interest from the research community. This review introduces IMEs and discusses the application of IME-targeted nanotherapies for inflammatory diseases. The development of rational targeting strategies tailored to IMEs in damaged tissues can help promote therapies for chronic diseases.

Thermo- and ROS-Responsive Self-Assembled Polymer Nanoparticle Tracers for 19F MRI Theranostics

Fluorine-19 magnetic resonance imaging (¹⁹F MRI) enables detailed in vivo tracking of fluorine-containing tracers and is therefore becoming a particularly useful tool in noninvasive medical imaging. In previous studies, we introduced biocompatible polymers based on the hydrophilic monomer N-(2-hydroxypropyl)methacrylamide (HPMA) and the thermoresponsive monomer N-(2,2-difluoroethyl)acrylamide (DFEA). These polymers have abundant magnetically equivalent fluorine atoms and advantageous properties as ¹⁹F MRI tracers. Furthermore, in this pilot study, we modified these polymers by introducing a redox-responsive monomer. As a result, our polymers changed their physicochemical properties once exposed to an oxidative environment. Reactive oxygen species (ROS)-responsive polymers were prepared by incorporating small amounts (0.9-4.5 mol %) of the N-[2-(ferrocenylcarboxamido)ethyl]acrylamide (FcCEA) monomer, which is hydrophobic and diamagnetic in the reduced electroneutral (Fe(II), ferrocene) state but hydrophilic and paramagnetic in the oxidized (Fe(III), ferrocenium cation) state. This property can be useful for theranostic purposes (therapy and diagnostic purposes), especially, in terms of ROS-responsive drug-delivery systems. In the reduced state, these nanoparticles remain self-assembled with the encapsulated drug but release the drug upon oxidation in ROS-rich tumors or inflamed tissues.

Smart Responsive Quercetin-Conjugated Glycol Chitosan Prodrug Micelles for Treatment of Inflammatory Bowel Diseases

The incidence and progression of inflammatory bowel disease are closely related to oxidative stress caused by excessive production of reactive oxygen species (ROS). To develop an efficacious and safe nanotherapy against inflammatory bowel diseases (IBD), we designed a novel pH/ROS dual-responsive prodrug micelle GC-B-Que as an inflammatory-targeted drug, which was comprised by active quercetin (Que) covalently linked to biocompatible glycol chitosan (GC) by aryl boronic ester as a responsive linker. The optimized micelles exhibited well-controlled physiochemical properties and stability in a physiological environment. Time-dependent NMR spectra traced the changes in the polymer structure in the presence of H₂O₂, confirming the release of the drug. The in vitro drug release studies indicated a low release rate (<20 wt %) in physiological conditions, but nearly complete release (>95 wt % after 72 h incubation) in a pH 5.8 medium containing 10 μM H₂O₂, exhibiting a pH/ROS dual-responsive property and sustained release behavior. Importantly, the negligible drug release in a simulated gastric environment in 1 h allowed us to perform intragastric administration, which has potential to achieve the oral delivery by mature enteric-coating modification in future. Further in vivo activities and biodistribution experiments found that the GC-B-Que micelles tended to accumulate in intestinal inflammation sites and showed better therapeutic efficacy than the free drugs (quercetin and mesalazine) in a colitis mice model. Typical inflammatory cytokines including TNF-α, IL-6, and iNOS were significantly suppressed by GC-B-Que micelle treatment. Our work promoted inflammatory-targeted delivery and intestinal drug accumulation for active single drug quercetin and improved the therapeutic effect of IBD. The current study also provided an alternative strategy for designing a smart responsive nanocarrier for a catechol-based drug to better achieve the target drug delivery.

Amine-containing diblock terpolymers via AROP: a versatile method for the generation of multifunctional micelles

We herein report the synthesis and block copolymerization via AROP of three glycidyl amine species (PiGA; OPGA, and MPGA) with different hydrophobicity. Micelles formed from these block copolymers respond to changes in pH and H₂O₂ concentration.

Highly colloidally stable trimodal 125I-radiolabeled PEG-neridronate-coated upconversion/magnetic bioimaging nanoprobes

"All-in-one" multifunctional nanomaterials, which can be visualized simultaneously by several imaging techniques, are required for the efficient diagnosis and treatment of many serious diseases. This report addresses the design and synthesis of upconversion magnetic NaGdF4:Yb3+/Er3+(Tm3+) nanoparticles by an oleic acid-stabilized high-temperature coprecipitation of lanthanide precursors in octadec-1-ene. The nanoparticles, which emit visible or UV light under near-infrared (NIR) irradiation, were modified by in-house synthesized PEG-neridronate to facilitate their dispersibility and colloidal stability in water and bioanalytically relevant phosphate buffered saline (PBS). The cytotoxicity of the nanoparticles was determined using HeLa cells and human fibroblasts (HF). Subsequently, the particles were modified by Bolton-Hunter-neridronate and radiolabeled by 125I to monitor their biodistribution in mice using single-photon emission computed tomography (SPECT). The upconversion and the paramagnetic properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles were evaluated by photoluminescence, magnetic resonance (MR) relaxometry, and magnetic resonance imaging (MRI) with 1 T and 4.7 T preclinical scanners. MRI data were obtained on phantoms with different particle concentrations and during pilot long-time in vivo observations of a mouse model. The biological and physicochemical properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles make them promising as a trimodal optical/MRI/SPECT bioimaging and theranostic nanoprobe for experimental medicine.

Design Strategies and Applications of ROS-Responsive Phenylborate Ester-Based Nanomedicine

Reactive oxygen species (ROS)-responsive nanomedicine has been extensively developed to improve the therapeutic effects while reducing the systemic toxicity. ROS, as important biological metabolites and signaling molecules, are known to overexpress in most of tumors and inflammations. Among various ROS-sensitive moieties, phenylborate ester (PBAE) with easy modifiable structure and excellent biocompatibility, represents one of the most ROS-sensitive structures. To harness it as a switch, the past several years had witnessed a booming of ROS-sensitive PBAE-based nanomedicine for various medical purposes. Much of the efforts were devoted to exploiting the potential in the management of antitumor and anti-inflammation. This review first summarizes the design strategies of PBAE in the construction of nanomedicine, with PBAE acting as not only the ROS-responsive unit, but also the roles of hydrophobic backbone or bridging segment in the macromolecular structures. The ROS-responsive mechanisms are then briefly discussed. Afterward, we focus on the introduction of the state-of-the-art research on ROS-responsive PBAE-based nanomedicine for antitumor and anti-inflammation applications. The conclusion and future perspectives of ROS-responsive nanomedicine are also provided.

Tumor microenvironment responsive drug delivery systems

Conventional tumor-targeted drug delivery systems (DDSs) face challenges, such as unsatisfied systemic circulation, low targeting efficiency, poor tumoral penetration, and uncontrolled drug release. Recently, tumor cellular molecules-triggered DDSs have aroused great interests in addressing such dilemmas. With the introduction of several additional functionalities, the properties of these smart DDSs including size, surface charge and ligand exposure can response to different tumor microenvironments for a more efficient tumor targeting, and eventually achieve desired drug release for an optimized therapeutic efficiency. This review highlights the recent research progresses on smart tumor environment responsive drug delivery systems for targeted drug delivery. Dynamic targeting strategies and functional moieties sensitive to a variety of tumor cellular stimuli, including pH, glutathione, adenosine-triphosphate, reactive oxygen species, enzyme and inflammatory factors are summarized. Special emphasis of this review is placed on their responsive mechanisms, drug loading models, drawbacks and merits. Several typical multi-stimuli responsive DDSs are listed. And the main challenges and potential future development are discussed.

Faster, sharper, more precise: Automated Cluster-FLIM in preclinical testing directly identifies the intracellular fate of theranostics in live cells and tissue

Fluorescence microscopy is widely used for high content screening in 2D cell cultures and 3D models. In particular, 3D tissue models are gaining major relevance in modern drug development. Enabling direct multiparametric evaluation of complex samples, fluorescence lifetime imaging (FLIM) adds a further level to intensity imaging by the sensitivity of the fluorescence lifetime to the microenvironment. However, the use of FLIM is limited amongst others by the acquisition of sufficient photon numbers without phototoxic effects in live cells. Herein, we developed a new cluster-based analysis method to enhance insight, and significantly speed up analysis and measurement time for the accurate translation of fluorescence lifetime information into pharmacological pathways. Methods: We applied a fluorescently-labeled dendritic core-multishell nanocarrier and its cargo Bodipy as molecules of interest (MOI) to human cells and reconstructed human tissue. Following the sensitivity and specificity assessment of the fitting-free Cluster-FLIM analysis of data in silico and in vitro, we evaluated the dynamics of cellular molecule uptake and intracellular interactions. For 3D live tissue investigations, we applied multiphoton (mp) FLIM. Owing to Cluster-FLIM's statistics-based fitting-free analysis, we utilized this approach for automatization. Results: To discriminate the fluorescence lifetime signatures of 5 different fluorescence species in a single color channel, the Cluster-FLIM method requires only 170, respectively, 90 counts per pixel to obtain 95% sensitivity (hit rate) and 95% specificity (correct rejection rate). Cluster-FLIM revealed cellular interactions of MOIs, representing their spatiotemporal intracellular fate. In a setting of an automated workflow, the assessment of lysosomal trapping of the MOI revealed relevant differences between normal and tumor cells, as well as between 2D and 3D models. Conclusion: The automated Cluster-FLIM tool is fitting-free, providing images with enhanced information, contrast, and spatial resolution at short exposure times and low fluorophore concentrations. Thereby, Cluster-FLIM increases the applicability of FLIM in high content analysis of target molecules in drug development and beyond.

Oxidative instability of boronic acid-installed polycarbonate nanoparticles

Oxidative stress, caused by the overproduction of reactive oxygen species (ROS), is often observed in degenerative and/or metabolic diseases, tumors, and inflamed tissues. Boronic acids are emerging as a unique class of responsive biomaterials targeting ROS because of their reactivity toward H2O2. Herein, we examine the oxidative reactivity of nanoparticles from a boronic acid-installed polycarbonate. The extent of oxidation under different concentrations of H2O2 was tracked by the change in fluorescence intensity of an encapsulated solvatochromic reporter dye, demonstrating their sensitivity to biologically-relevant concentrations of hydrogen peroxide. Oxidation-triggered particle destabilization, however, was shown to be highly dependent on the concentration of the final oxidized polymer product, and was only achieved if it fell below polymer critical micelle concentration. Our results indicate that these nanocarriers serve as an excellent dual pH/H2O2 responsive vehicle for drug delivery.

Reactive Oxygen Species (ROS)-Responsive Polymersomes with Site-Specific Chemotherapeutic Delivery into Tumors via Spacer Design Chemistry

The lack of cellular and tissue specificities in conventional chemotherapies along with the generation of a complex tumor microenvironment (TME) limits the dosage of active agents that reaches tumor sites, thereby resulting in ineffective responses and side effects. Therefore, the development of selective TME-responsive nanomedicines is of due relevance toward successful chemotherapies, albeit challenging. In this framework, we have synthesized novel, ready-to-use ROS-responsive amphiphilic block copolymers (BCs) with two different spacer chemistry designs to connect a hydrophobic boronic ester-based ROS sensor to the polymer backbone. Hydrodynamic flow focusing nanoprecipitation microfluidics (MF) was used in the preparation of well-defined ROS-responsive PSs; these were further characterized by a combination of techniques [¹H NMR, dynamic light scattering (DLS), static light scattering (SLS), transmission electron microscopy (TEM), and cryogenic TEM (cryo-TEM)]. The reaction with hydrogen peroxide releases an amphiphilic phenol or a hydrophilic carboxylic acid, which affects polymersome (PS) stability and cargo release. Therefore, the importance of the spacer chemistry in BC deprotection and PS stability and cargo release is herein highlighted. We have also evaluated the impact of spacer chemistry on the PS-specific release of the chemotherapeutic drug doxorubicin (DOX) into tumors in vitro and in vivo. We demonstrate that by spacer chemistry design one can enhance the efficacy of DOX treatments (decrease in tumor growth and prolonged animal survival) in mice bearing EL4 T cell lymphoma. Side effects (weight loss and cardiotoxicity) were also reduced compared to free DOX administration, highlighting the potential of the well-defined ROS-responsive PSs as TME-selective nanomedicines. The PSs could also find applications in other environments with high ROS levels, such as chronic inflammations, aging, diabetes, cardiovascular diseases, and obesity.

ROS-Sensitive Degradable PEG-PCL-PEG Micellar Thermogel

A reactive oxygen species (ROS)-sensitive degradable polymer would be a promising material in designing a disease-responsive system or accelerating degradation of polymers with slow hydrolysis kinetics. Here, a thermogelling poly(ethylene glycol)-polycaprolactone-poly(ethylene glycol) (PEG-PCL-PEG or EG₁₂ -CL₂₀ -EG₁₂ ) triblock copolymer with an oxalate group at the middle of the polymer is reported. The polymers form micelles with an average size of 100 nm in water. Thermogelation is observed in a concentration range of 8.0-37.0 wt%. In particular, the aqueous PEG-PCL-PEG triblock copolymer solutions are in a gel state at 37 °C in a concentration range of 25.0-37.0 wt%, whereas the aqueous PEG-PCL diblock copolymer solutions are in a sol state in the same concentration range at 37 °C. Thus, the gel depot could dissolve out once degradation of the triblock copolymers occurs at the oxalate group as confirmed by the in vitro experiment. In vivo gel formation is confirmed by injecting an aqueous PEG-PCL-PEG solution (36.0 wt%) into the subcutaneous layer of rats. The gel completely disappears in 21 d. A model polypeptide drug (cyclosporine A) is released over 21 d from the in situ formed gel. The micelle-based thermogel of PEG-PCL-PEG with ROS-triggering degradability is a promising injectable material for biomedical applications.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

The Chemistry of Boronic Acids in Nanomaterials for Drug Delivery

Interest in increasing drug delivery efficiency has risen over the past decade both as a means to improve efficacy of already clinically available drugs and due to the increased difficulties of approving new drugs. As a functional group for targeted drug delivery, boronic acids (BAs) have been incorporated in polymeric particles both as a stimuli-responsive functional group and as a targeting ligand. Here, BA chemistry presents a wealth of opportunities for biological applications. It not only reacts with several chemical markers of disease such as reactive oxygen species (ROS), adenosine triphosphate (ATP), glucose, and reduced pH, but it also acts as ligands for diols such as sialic acid. These stimuli-responsive drug delivery systems optimize delivery of therapeutics based on rational design and precise molecular engineering. When designing materials containing BA, the unique chemical properties are important to take into consideration such as its vacant p-orbital, its molecular geometry, and the designed acid's pK_a. Instead of behaving as most carboxylic acids that donate protons, BAs instead primarily act as Lewis acids that accept electrons. In aqueous solution, most polymers containing BA exist in an equilibrium between their triangular hydrophobic form and a tetrahedral hydrophilic form. The most common pK_a's are in the nonphysiological range of 8-10, and much ongoing research focuses on modifying BAs into materials sensitive to a more physiologically relevant pH range. So far, BA moieties have been incorporated into a stunning array of materials, ranging from small molecules that can self-assemble into higher order structures such as micelles and polymeric micelles, via larger polymeric assemblies, to large scale hydrogels. With the abundance of biological molecules containing diols and polyhydroxy motifs, BA-containing materials have proven valuable in several biomedical applications such as treatment of cancer, diabetes, obesity, and bacterial infections. Both materials functionalized with BA and boronic esters display good safety profiles in vitro and in vivo; thus, BA-containing materials represent promising carriers for responsive delivery systems with great potential for clinical translation. The intention of this Account is to showcase the versatility of BA for biomedical applications. We first discuss the chemistry of BA and what to consider when designing BA-containing materials. Further, we review how its chemistry recently has been applied to nanomaterials for enhanced delivery efficiency, both as a stimuli-responsive group and as a targeting ligand. Lastly, we discuss the current limitations and further perspectives of BA in biomaterials, based on the great benefits that can come from utilizing the unique BA chemistry to enhance drug delivery efficiency.

Paclitaxel-loaded biodegradable ROS-sensitive nanoparticles for cancer therapy

Background

Reactive oxygen species (ROS), such as hydrogen peroxide and superoxide, trigger biodegradation of polymer-based nanoparticles (NPs) bearing pinacol-type boronic ester groups. These NPs may selectively release their cargo, in this case paclitaxel (PTX), at the high levels of ROS present in the intracellular environment of inflamed tissues and most tumors.

Purpose

The main objective was to determine anti-tumor efficacy of PTX-loaded ROS-sensitive NPs and to examine whether macrophage infiltration had any impact on treatment efficacy.

Methods

NPs were synthesized and their characteristics in the presence of H₂O₂ were demonstrated. Both confocal microscopy as well as flow cytometry approaches were used to determine degradation of ROS-sensitive NPs. HeLa cells were cultured in vitro and used to establish tumor xenografts in nude mice. In vivo experiments were performed to understand toxicity, biodistribution and anti-tumor efficacy of the NPs. Moreover, we performed immunohistochemistry on tumor sections to study infiltration of M1 and M2 subsets of macrophages.

Results

We demonstrated that PTX delivered in NPs containing a ROS-sensitive polymer exhibits a better anti-tumor efficacy than PTX in NPs containing ROS-non-sensitive polymer, free PTX or Abraxane^® (nab-PTX). The biodistribution revealed that ROS-sensitive NPs exhibit retention in liver, spleen and lungs, suggesting a potential to target cancer metastasizing to these organs. Finally, we demonstrated a correlation between infiltrated macrophage subsets and treatment efficacy, possibly contributing to the efficient anti-tumor effects.

Conclusion

Treatment with ROS-sensitive NPs containing PTX gave an improved therapeutic effect in HeLa xenografts than their counterpart, free PTX or nab-PTX. Our data revealed a correlation between macrophage infiltration and efficiency of the different antitumor treatments, as the most effective NPs resulted in the highest infiltration of the anti-tumorigenic M1 macrophages.

Selectively Biodegradable Polyesters: Nature-Inspired Construction Materials for Future Biomedical Applications

In the last half-century, the development of biodegradable polyesters for biomedical applications has advanced significantly. Biodegradable polyester materials containing external stimuli-sensitive linkages are favored in the development of therapeutic devices for pharmacological applications such as delivery vehicles for controlled/sustained drug release. These selectively biodegradable polyesters degrade after particular external stimulus (e.g., pH or redox potential change or the presence of certain enzymes). This review outlines the current development of biodegradable synthetic polyesters materials able to undergo hydrolytic or enzymatic degradation for various biomedical applications, including tissue engineering, temporary implants, wound healing and drug delivery.

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.

Enzymatic synthesis of selenium-containing amphiphilic aliphatic polycarbonate as an oxidation-responsive drug delivery vehicle

Although functional aliphatic polycarbonates (APCs) have attracted prominent research interest as stimuli-responsive biomaterials, the majority of functional APCs are fabricated by detrimental organometallic catalysts or organo-catalysts. Herein, a facile synthetic strategy based on enzymatic polymerization was developed to construct a selenium-containing amphiphilic aliphatic polycarbonate (mPEG-b-CMP₄₅). Specifically, the selenium in its backbone framework underwent a hydrophobic–hydrophilic transition upon exposure to the abnormal ROS level of the tumor, thus providing a promising platform for ROS-triggered drug release. This amphiphilic mPEG-b-CMP₄₅ efficiently encapsulated doxorubicin (DOX) via self-assembly in aqueous solution and showed an excellent ability to regulate the release of DOX in response to H₂O₂ at biologically relevant concentrations (100 μM). These DOX-loaded nanoparticles could easily be internalized into U87 cells and possess the inherent antitumor properties of DOX, while they exhibited much lower cytotoxicity in normal cells HL-7702. Moreover, in many cases, the introduction of selenium caused high cytotoxicity of the materials, but the cytotoxicity results in HL-7702 cells demonstrated the good biocompatibility of mPEG-b-CMP₄₅. These collective data suggested the potential use of mPEG-b-CMP₄₅ as a biocompatible and smart drug delivery vehicle.

A facile synthetic strategy based on enzymatic polymerization was developed to construct a ROS-responsive polycarbonate served as biocompatible drug vehicle.

Poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) Nanoparticles: Synthesis and Characterization, Enzymatic and Cellular Degradation, Micellar Solubilization of Paclitaxel, and in Vitro and in Vivo Evaluation

Polyester-based nanostructures are widely studied as drug-delivery systems due to their biocompatibility and biodegradability. They are already used in the clinic. In this work, we describe a new and simple biodegradable and biocompatible system as the Food and Drug Administration approved polyesters (poly-ε-caprolactone, polylactic acid, and poly(lactic- co-glycolic acid)) for the delivery of the anticancer drug paclitaxel (PTX) as a model drug. A hydrophobic polyester, poly(propylene succinate) (PPS), was prepared from a nontoxic alcohol (propylene glycol) and monomer from the Krebs's cycle (succinic acid) in two steps via esterification and melt polycondensation. Furthermore, their amphiphilic block copolyester, poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) (mPEO- b-PPS), was prepared by three steps via esterification followed by melt polycondensation and the addition of mPEO to the PPS macromolecules. Analysis of the in vitro cellular behavior of the prepared nanoparticle carriers (NPs) (enzymatic degradation, uptake, localization, and fluorescence resonance energy-transfer pair degradation studies) was performed by fluorescence studies. PTX was loaded to the NPs of variable sizes (30, 70, and 150 nm), and their in vitro release was evaluated in different cell models and compared with commercial PTX formulations. The mPEO- b-PPS copolymer analysis displays glass transition temperature < body temperature < melting temperature, lower toxicity (including the toxicity of their degradation products), drug solubilization efficacy, stability against spontaneous hydrolysis during transport in bloodstream, and simultaneous enzymatic degradability after uptake into the cells. The detailed cytotoxicity in vitro and in vivo tumor efficacy studies have shown the superior efficacy of the NPs compared with PTX and PTX commercial formulations.

Near infrared light triggered reactive oxygen species responsive nanoparticles for chemo-photodynamic combined therapy

Nanoparticles with ROS-responsive properties could realize spatial and temporal drug release under NIR irradiation and the excess ROS could be used for PDT.

Accelerated hydrolysis of boronic acid in a modified poly(amidoamine) dendrimer: identification of a factor leading to the production of an impurity in boronic acid containing poly(amidoamine) dendrimers

The preparation of boronic acid containing dendrimers is still a difficult task in dendrimer chemistry. In this investigation, an unanticipated hydrolysis product (4) was identified during the preparation of (G:2)-PAMAM-dendri-(4-phenyl boronic acid)14 (3) by acquiring its 1H NMR, 13C NMR, and UV–vis absorption spectra and IR spectra and comparing them with those of 4-hydroxylbenzoic acid (5). Furthermore, an Alizarin Red S staining analysis, ICP-MS, and 11B NMR spectrum indicated the lack of boronic acid in 4. Finally, treatment of 3 with hydrogen peroxide gave a product that was determined to be identical to dendrimer 4. By analyzing the formation of 4 under various conditions, the presence of numerous primary amines in a PAMAM dendrimer did accelerate the hydrolysis of peripheral boronic acid. This investigation revealed an apparent intrinsic problem that needs to be overcome during the preparation of boronic acid containing dendrimers and related boronic acid containing macromolecules.

Leveraging H2 O2 Levels for Biomedical Applications

Hydrogen peroxide (H₂ O₂ )-responsive materials have been employed as drug delivery or diagnostic systems to treat or detect diseases with abnormal oxidative stress. A number of H₂ O₂ -responsive systems have been developed, and they have achieved great progress in controlled drug delivery for disease treatment. However, pathological sites with elevated H₂ O₂ level, such as cancer and inflammation, have their own characteristics; therefore the material structures and the subsequent formulations should be reasonably designed to acquire maximized therapeutic effects. In this progress report, we overview the development of H₂ O₂ -responsive functional groups for constructing H₂ O₂ -responsive formulations, as well as the guidance for designing suitable formulations to treat each specific pathological condition. The challenges and perspectives in this field are also discussed.

Intracellular fate of polymer therapeutics investigated by fluorescence lifetime imaging and fluorescence pattern analysis

Nanocarriers bearing anticancer drugs are promising candidates to improve the efficacy of cancer therapy and minimize side effects. The most potent cytostatics used in the treatment of various cancers are anthracyclines, e.g. doxorubicin or pirarubicin. Recently, polymer therapeutics carrying anthracyclines have been intensively studied. The precise characterization of in vitro nanocarrier biological behavior brings a better understanding of the nanocarrier characteristics and enables prediction of the behavior of the nanocarrier during in vivo application. Advanced fluorescence detection methods, e.g. fluorescence lifetime imaging microscopy (FLIM), were successfully exploited to describe the properties of various polymeric nano-systems and contributed to a complex view of anthracyclines' intracellular transport and DNA intercalation. Here, we report the application of a specific technique for processing FLIM images, called fluorescence pattern decomposition, to evaluate early events after doxorubicin or pirarubicin treatment of cells. Moreover, we characterized changes in the intracellular localization and release of the anthracyclines during the incubation of cells with polymer nanotherapeutics based on poly[N-(2-hydroxypropyl)-methacrylamide] (pHPMA).

Synthesis of a phenylboronic ester-linked PEG-lipid conjugate for ROS-responsive drug delivery

A kind of phenylboronic ester-linked PEG-lipid conjugate was designed and synthesized for ROS-responsive drug delivery.

One-pot synthesis of reactive oxygen species (ROS)-self-immolative polyoxalate prodrug nanoparticles for hormone dependent cancer therapy with minimized side effects

One-pot synthesis of ROS-self-immolative polyoxalate prodrug NPs for cancer therapy.

ROS and Brain Gliomas: An Overview of Potential and Innovative Therapeutic Strategies

Reactive oxygen species (ROS) represent reactive products belonging to the partial reduction of oxygen. It has been reported that ROS are involved in different signaling pathways to control cellular stability. Under normal conditions, the correct function of redox systems leads to the prevention of cell oxidative damage. When ROS exceed the antioxidant defense system, cellular stress occurs. The cellular redox impairment is strictly related to tumorigenesis. Tumor cells, through the generation of hydrogen peroxide, tend to the alteration of cell cycle phases and, finally to cancer progression. In adults, the most common form of primary malignant brain tumors is represented by gliomas. The gliomagenesis is characterized by numerous molecular processes all characterized by an altered production of growth factor receptors. The difficulty to treat brain cancer depends on several biological mechanisms such as failure of drug delivery through the blood-brain barrier, tumor response to chemotherapy, and intrinsic resistance of tumor cells. Understanding the mechanisms of ROS action could allow the formulation of new therapeutic protocols to treat brain gliomas.