A hydrogen peroxide responsive prodrug of Keap1-Nrf2 inhibitor for improving oral absorption and selective activation in inflammatory conditions

Transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) and its negative regulator, the E3 ligase adaptor Kelch-like ECH-associated protein 1 (Keap1), control the redox and metabolic homeostasis and oxidative stress. Inhibitors of Keap1-Nrf2 interaction are promising in oxidative stress related inflammatory diseases but now hit hurdles. By utilizing thiazolidinone moiety to shield the key carboxyl pharmacophore in Keap1-Nrf2 inhibitor, a hydrogen peroxide (H₂O₂)-responsive prodrug pro2 was developed. The prodrug modification improved the physicochemical properties and cell membrane permeability of the parent drug. Pro2 was stable and stayed inactive under various physiological conditions, while became active by stimulation of H₂O₂ or inflammation derived reactive oxygen species. Moreover, pro2 exhibited proper pharmacokinetic profile suitable for oral administration and enhanced anti-inflammatory efficiency in vivo. Thus, this novel prodrug approach may not only provide an important advance in the therapy of chronic inflammatory diseases with high level of H₂O₂, but also offer a fresh solution to improve the drug-like and selectivity issues of Keap1-Nrf2 inhibitors.

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Pro2 was developed by utilizing H₂O₂-responsive thiazolidinone moiety to shield carboxyl group in Keap1-Nrf2 inhibitor.

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Pro2 was stable and inactive under various physiological conditions, while became active under inflammatory conditions.

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Pro2 exhibited proper pharmacokinetic profile for oral administration and enhanced anti-inflammatory efficiency in vivo.

Metal-free carbon monoxide-releasing micelles undergo tandem photochemical reactions for cutaneous wound healing

Carbon monoxide (CO) has shown broad biomedical applications. The site-specific delivery and controlled release of CO is of crucial importance to achieve maximum therapeutic benefits. The development of carbon monoxide (CO)-releasing polymers (CORPs) can increase the stability, optimize pharmacokinetic behavior, and reduce the side effects of small molecule precursors. However, almost all established CORPs were synthesized through a post functional approach, although the direct polymerization strategy is more powerful in controlling the chain compositions and architectures. Herein, a direct polymerization strategy is proposed toward metal-free CO-releasing polymers (CORPs) based on photoresponsive 3-hydroxyflavone (3-HF) derivatives. Such CO-releasing amphiphiles self-assemble into micelles, having excellent water-dispersity. Intriguingly, photo-triggered tandem photochemical reactions confer successive fluorescence transitions from blue-to-red-to-colorless, enabling self-reporting CO release in vitro and in vivo as a result of the incorporation of 3-HF derivatives. More importantly, the localized CO delivery of CORPs by taking advantage of the spatiotemporal control of light stimulus outperformed conventional metal carbonyls such as CORMs in terms of anti-inflammation and cutaneous wound healing. This work opens a novel avenue toward metal-free CORPs for potential biomedical applications.

Imaging of hydrogen peroxide (H2O2) during the ferroptosis process in living cancer cells with a practical fluorescence probe

Hydrogen peroxide (H₂O₂) plays an important role in intracellular signal transduction pathway. It has been closely associated with the occurrence and development of tumors as well as the recent studied ferroptosis. In this work, monitoring the H₂O₂ level during the ferroptosis process in living cancer cells was achieved by using a new practical fluorescence probe, HP, accompanying with a series of property evaluation and model construction. As a practical tool, HP indicated high sensitivity (LOD 0.77 μM), high selectivity and low toxicity. Most satisfactorily, it could realize the applications of mapping the variation of intracellular H₂O₂ level regulated by the inducer or activator and visualizing the H₂O₂ release event as a significant feature during the ferroptosis process. This work was a challenging trial to monitor dynamic parameters of ferroptosis, and offered crucial information about the role of H₂O₂ for investigating further physiological or pathological processes.

Extracellular vs Intracellular Delivery of CO: Does It Matter for a Stable, Diffusible Gasotransmitter?

Carbon monoxide (CO) is a gasotransmitter produced in humans. An essential unanswered question in the design of carbon monoxide releasing molecules (CORMs) is whether the delivery molecule should be localized extra- or intracellularly to produce desired biological effects. Herein we show that extracellular CO release is less toxic and is sufficient to produce an anti-inflammatory effect similar to that of intracellular CO release at nanomolar concentrations. This information is valuable for the design of CORMs.

CO release with ratiometric fluorescence changes: a promising visible-light-triggered metal-free CO-releasing molecule

The first visible-light-triggered metal-free and ratiometric fluorescent CORM is reported. This CORM can be used to release CO with distinct ratiometric fluorescence changes in aqueous solution, living cells, zebrafish, and mice, which provided an excellent controllable and trackable CORM for living systems.

Starvation-amplified CO generation for enhanced cancer therapy via an erythrocyte membrane-biomimetic gas nanofactory

Carbon monoxide (CO)-based gas therapy has emerged as an attractive therapeutic strategy for cancer therapy. However, the main challenges are the in situ-triggered and efficient delivery of CO in tumors, which limit its further clinical application. Herein, we developed an erythrocyte membrane-biomimetic gas nanofactory (MGP@RBC) to amplify the in situ generation of CO for combined energy starvation of cancer cells and gas therapy. This nanofactory was constructed by encapsulating glucose oxidase (GOx) and Mn₂(CO)₁₀ (CO-donor) into the biocompatible polymer poly(lactic-co-glycolic acid), obtaining MGP nanoparticles, which are further covered by red blood cell (RBC) membrane. Because of the presence of proteins on RBC membranes, the nanoparticles could effectively avoid immune clearance in macrophages (Raw264.7) and significantly prolong their blood circulation time, thereby achieving higher accumulation at the tumor site. After that, the GOx in GMP@RBC could effectively catalyze the conversion of endogenous glucose to hydrogen peroxide (H₂O₂) in the presence of oxygen. The concomitant generation of H₂O₂ could efficiently trigger CO release to cause dysfunction of mitochondria and activate caspase, thereby resulting in apoptosis of the cancer cells. In addition, the depletion of intratumoral glucose could starve tumor cells by shutting down the energy supply. Altogether, the in vitro and in vivo studies of our synthesized biomimetic gas nanofactory exhibited an augmentative synergistic efficacy of CO gas therapy and energy starvation to inhibit tumor growth. It provides an attractive strategy to amplify CO generation for enhanced cancer therapy in an accurate and more efficient manner. STATEMENT OF SIGNIFICANCE: Carbon monoxide (CO) based gas therapy has emerged as an attractive therapeutic strategy for cancer therapy. In this study, we developed an erythrocyte membrane biomimetic gas nanofactory to amplify the in-situ generation of CO for combined cancer starvation and gas therapy. It is constructed by coating glucose oxidase (GOx) and CO donor-loaded nanoparticles with erythrocyte membrane. Due to the erythrocyte membrane, it can effectively prolong blood circulation time and achieve higher tumor accumulation. After accumulated in tumor, endogenous glucose can be effectively catalyzed to hydrogen peroxide, in-situ amplified CO release to induce the apoptosis of cancer cells. In addition, depleting glucose can also starve tumor cells by shutting down the energy supply. Overall, our biomimetic gas nanofactory exhibits an augmentative synergistic efficacy of CO gas therapy and starvation to increased tumor inhibition. It provide a novel strategy to deliver CO in an accurate and more efficient manner, promising for combined cancer therapy in future clinical application.

An H2S-activated ratiometric CO photoreleaser enabled by excimer/monomer conversion

Based on the excimer-monomer conversion of a pyrene-flavone hybrid, a ratiometric CO photoreleaser, PFN, was constructed for simultaneous H2S quantification and CO release in inflammatory cells.

Photocontrolled endogenous reactive oxygen species (ROS) generation

A cell-permeable small molecule for light-triggered generation of endogenous reactive oxygen species (ROS) is reported.

3-Hydroxyflavones and 3-Hydroxy-4-oxoquinolines as Carbon Monoxide-Releasing Molecules

Carbon monoxide-releasing molecules (CORMs) that enable the delivery of controlled amounts of CO are of strong current interest for applications in biological systems. In this review, we examine the various conditions under which CO is released from 3-hydroxyflavones and 3-hydroxy-4-oxoquinolines to advance the understanding of how these molecules, or derivatives thereof, may be developed as CORMs. Enzymatic pathways from quercetin dioxygenases and 3-hydroxy-4-oxoquinoline dioxygenases leading to CO release are examined, along with model systems for these enzymes. Base-catalyzed and non-redox-metal promoted CO release, as well as UV and visible light-driven CO release from 3-hydroxyflavones and 3-hydroxy-4-oxoquinolines, are summarized. The visible light-induced CO release reactivity of recently developed extended 3-hydroxyflavones and a 3-hydroxybenzo[g]quinolone, and their uses as intracellular CORMs, are discussed. Overall, this review provides insight into the chemical factors that affect the thermal and photochemical dioxygenase-type CO release reactions of these heterocyclic compounds.

Tracking CO release in cells via the luminescence of donor molecules and/or their by-products

Carbon monoxide (CO) is a bioactive signalling molecule that is produced endogenously via the breakdown of heme. Beneficial health effects associated with the delivery of CO gas have spurred the development of CO-releasing molecules (CORMs) that can be used to provide specific amounts of the gas. In addition to their potential use as therapeutics, CORMs are needed to provide insight into the biological targets of CO. In this regard, light-activated CO-releasing molecules (photoCORMs), are valuable for examining the effects of localized CO release. Herein we examine luminescent CORMs and photoCORMs that have been reported for tracking CO delivery in cells. A variety of motifs are available that exhibit differing luminescence properties and cover a wide range of wavelengths. Trackable CO donors have been successfully applied to targeting CO delivery to mitochondria, thus demonstrating the feasibility of using such molecules in detailed investigations of the biological roles of CO.