ER stress promotes mitochondrial calcium overload and activates the ROS/NLRP3 axis to mediate fatty liver ischemic injury.

BACKGROUND: Fatty livers are widely accepted as marginal donors for liver transplantation but are more susceptible to liver ischemia and reperfusion (IR) injury. Increased macrophage-related inflammation plays an important role in the aggravation of fatty liver IR injury. Here, we investigate the precise mechanism by which endoplasmic reticulum (ER) stress activates macrophage NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) signaling by regulating mitochondrial calcium overload in fatty liver IR. METHODS: Control- and high-fat diet-fed mice were subjected to a partial liver IR model. The ER stress, mitochondrial calcium levels, and NLRP3 signaling pathway in macrophages were analyzed. RESULTS: Liver steatosis exacerbated liver inflammation and IR injury and enhanced NLRP3 activation in macrophages. Myeloid NLRP3 deficiency attenuated intrahepatic inflammation and fatty liver injury following IR. Mechanistically, increased ER stress and mitochondrial calcium overload were observed in macrophages obtained from mouse fatty livers after IR. Suppression of ER stress by tauroursodeoxycholic acid effectively downregulated mitochondrial calcium accumulation and suppressed NLRP3 activation in macrophages, leading to decreased inflammatory IR injury in fatty livers. Moreover, Xestospongin-C-mediated inhibition of mitochondrial calcium influx decreased reactive oxygen species (ROS) expression in macrophages after IR. Scavenging of mitochondrial ROS by mito-TEMPO suppressed macrophage NLRP3 activation and IR injury in fatty livers, indicating that excessive mitochondrial ROS production was responsible for macrophage NLRP3 activation induced by mitochondrial calcium overload. Patients with fatty liver also exhibited upregulated activation of NLRP3 and the ER stress signaling pathway after IR. CONCLUSIONS: Our findings suggest that ER stress promotes mitochondrial calcium overload to activate ROS/NLRP3 signaling pathways within macrophages during IR-stimulated inflammatory responses associated with fatty livers.

Chemical Strategies Toward Prodrugs and Fluorescent Probes for Gasotransmitters.

Three gaseous molecules are widely accepted as important gasotransmitters in mammalian cells, namely NO, CO and H2S. Due to the pharmacological effects observed in preclinical studies, these three gasotransmitters represent promising drug candidates for clinical translation. Fluorescent probes of the gasotransmitters are also in high demand; however, the mechanisms of actions or the roles played by gasotransmitters under both physiological and pathological conditions remain to be answered. In order to bring these challenges to the attention of both chemists and biologists working in this field, we herein summarize the chemical strategies used for the design of both probes and prodrugs of these three gasotransmitters.

Bioorthogonal Bond Cleavage Chemistry for On-demand Prodrug Activation: Opportunities and Challenges.

Time- and space-resolved drug delivery is highly demanded for cancer treatment, which, however, can barely be achieved with a traditional prodrug strategy. In recent years, the prodrug strategy based on a bioorthogonal bond cleavage chemistry has emerged with the advantages of high temporospatial resolution over drug activation and homogeneous activation irrespective of individual heterogeneity. In the past five years, tremendous progress has been witnessed in this field with one such bioorthogonal prodrug entering Phase II clinical trials. This Perspective aims to highlight these new advances (2019-2023) and critically discuss their pros and cons. In addition, the remaining challenges and potential strategic directions for future progress will also be included.

Indole-pyridine carbonitriles: multicomponent reaction synthesis and bio-evaluation as potential hits against diabetes mellitus.

Background: Diabetes mellitus is a significant health disorder; therefore, researchers should focus on discovering new drug candidates. Methods: A series of indole-pyridine carbonitrile derivatives, 1-34, were synthesized through a one-pot multicomponent reaction and evaluated for antidiabetic and antioxidant potential. Results: In this library, 12 derivatives - 1, 2, 4, 5, 7, 8, 10-12, 14, 15 and 31 - exhibited potent inhibitory activities against α-glucosidase and α-amylase enzymes, in comparison to acarbose (IC50 = 14.50 ± 0.11 µM). Furthermore, kinetics, absorption, distribution, metabolism, excretion and toxicity and molecular docking studies were used to interpret the type of inhibition, binding energies and interactions of ligands with target enzymes. Conclusion: These results indicate that the compounds may be promising hits for controlling diabetes mellitus and its related complications.

A Bioorthogonal Decaging Chemistry of N-Oxide and Silylborane for Prodrug Activation both In Vitro and In Vivo.

Bioorthogonal decaging chemistry with both fast kinetics and high efficiency is highly demanded for in vivo applications but remains very sporadic. Herein, we describe a new bioorthogonal decaging chemistry between N-oxide and silylborane. A simple replacement of "C" in boronic acid with "Si" was able to substantially accelerate the N-oxide decaging kinetics by 106 fold (k2: up to 103 M-1 s-1). Moreover, a new N-oxide-masked self-immolative spacer was developed for the traceless release of various payloads upon clicking with silylborane with fast kinetics and high efficiency (>90%). Impressively, one such N-oxide-based self-assembled bioorthogonal nano-prodrug in combination with silylborane led to significantly enhanced tumor suppression effects as compared to the parent drug in a 4T1 mouse breast tumor model. In aggregate, this new bioorthogonal click-and-release chemistry is featured with fast kinetics and high efficiency and is perceived to find widespread applications in chemical biology and drug delivery.

Reactive Oxygen Species-Activated Metal-Free Carbon Monoxide Prodrugs for Targeted Cancer Treatment.

Carbon monoxide has shown promise as a therapeutic agent against cancers. Reactive oxygen species (ROS)-activated CO prodrugs are highly demanded for targeted cancer treatment but remain sporadic. In addition, little attention is on how the release rate affects CO's biological effects. Herein, we describe a new type of ROS-activated metal-free CO prodrug, which releases CO with tunable release rates in response to multiple ROS and exhibits very pronounced tumor suppression effects in a mouse 4t1 breast tumor model. Importantly, for the first time, we observe both in vitro and in vivo that CO release rate has a direct impact on its antiproliferative potency and a correlation between release rate and antiproliferative activity is observed. In aggregates, our results not only deliver ROS-sensitive CO prodrugs for cancer treatment but also represent a promising starting point for further in-depth studies of how CO release kinetics affect anticancer activity.

Design, synthesis, and structure-activity relationships of a novel class of quinazoline derivatives as coronavirus inhibitors.

There remain great unmet needs to treat coronavirus infections in clinic, and the development of novel antiviral agents is highly demanded. In this work, a phenotypic screening against our in-house compound library identified several cajanine derivatives with moderate antiviral activity against HCoV-OC43. Based on the scaffold of cajanine, a series of quinazoline derivatives were designed employing a scaffold-hopping strategy. After an iterative structural optimization campaign, several quinazoline derivatives with potent antiviral efficacy (EC50: ∼0.1 µM) and high selectivity (SI > 1000) were successfully identified. The preliminary mechanism of action study indicated that such quinazoline derivatives functioned at the early stage of infection. In aggregate, this work delivered a new chemical type of coronavirus inhibitors, which could be employed not only for further development of antiviral drugs but also as important chemical tools to delineate the target of action.

Dichloromethanol but not difluoromethanol as a viable surrogate of carbon monoxide for prodrug design.

Herein, we demonstrate that dichloromethanol but not difluoromethanol is a viable surrogate of carbon monoxide for prodrug design. A proof of concept was established by the successful development of a ROS-responsive carbon monoxide prodrug, presenting specific CO release in response to endogenous ROS in cells.

Recent applications of phase-change materials in tumor therapy and theranostics.

Phase-change materials (PCMs) are a type of special material which can store and release a large amount of thermal energy without any significant temperature change. They are emerging in recent years as a promising functional material in tumor therapy and theranostics due to their accurate responses to the temperature variations, biocompatibility and low toxicity. In this review, we will introduce the main types of PCMs and their desirable physiochemical properties for biomedical applications, and highlight the recent progress of PCM's applications in the modulated release of antitumor drugs, with special attentions paid to various ways to initiate temperature-dependent phase change, the concomitant thermal therapy and its combination with or activation of other therapies, particularly unconventional therapies. We will also summarize PCM's recent applications in tumor theranostics, where both drugs and imaging probes are delivered by PCMs for controlled drug release and imaging-guided therapy. Finally, the future perspectives and potential limitations of harnessing PCMs in tumor therapy will be discussed.

Synthetic benzofuran-linked chalcones with dual actions: a potential therapeutic approach to manage diabetes mellitus.

Background: Identification of molecules having dual capabilities to reduce postprandial hyperglycemia and oxidative stress is one of the therapeutic approaches to treat diabetes mellitus. In this connection, a library of benzofuran-linked chalcone derivatives were evaluated for their dual action. Methods: A series of substituted benzofuran-linked chalcones (2-33) were synthesized and tested for α-amylase inhibitory as well as 2,2-diphenylpicrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activities. Results: All compounds showed α-amylase inhibitory activity ranging from IC50 = 12.81 ± 0.03 to 87.17 ± 0.15 µM, compared with the standard acarbose (IC50 = 13.98 ± 0.03 µM). Compounds also demonstrated radical scavenging potential against DPPH and ABTS radicals. Conclusion: The identified compounds may serve as potential leads for further advanced research.

Surface-tethered electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions.

The general electrochemical biosensors for telomerase detection require the immobilization of primers on the electrode surface for telomeric extension and hybridization reactions. However, immobilization of primers may suffer from the challenges of hindrance effect and configuration freedom, thus reducing the extension and hybridization efficiency. Herein, we developed a sensitive electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions and surface-tethered detection. In the presence of telomerase, the biotinylated primer (bio-primer) was efficiently elongated with telomeric repeats of (TTAGGG)n at the 3' end in solution. Then, the extension product (bio-DNA) was hybridized with the signal probe DNA modified on the surface of ferrocene (Fc)-capped gold nanoparticle (AuNP). The bio-DNA/DNA/Fc-AuNP hybrids were then tethered by streptavidin-modified electrodes through the specific avidin-biotin interactions, thus producing strong electrochemical signals from the oxidation of Fc tags. The biosensor was successfully used to determine telomerase in HeLa cells and monitor the inhibition efficiency of inhibitor. A wide linear range for the detection of telomerase extracted from HeLa cells was attained. This method has great potential in clinical diagnosis and anti-cancer drug development, and should be beneficial for the fabrication of novel biosensors by integration of homogeneous catalysis and hybridization reactions.

Strategies toward Metal-Free Carbon Monoxide Prodrugs: An Update.

Carbon monoxide is an important gasotransmitter in mammals, with pleiotropic therapeutic potential against a wide range of human diseases. However, clinical translation of CO is severely hampered by the lack of a reliable CO delivery form. The development of metal-free CO prodrugs is the key to resolving such delivery issues. Over the past three years, some new exciting progress has been made in this field. In this review, we highlight these advances and discuss related issues.

Photoclick and Release: Co-activation of Carbon Monoxide and a Fluorescent Self-reporter, COS or Sulfonamide with Fast Kinetics.

Bioorthogonal prodrugs with both fast reaction kinetics and multiple outputs are highly desirable but are only found sporadically. Herein, we report a novel photoclick-and-release strategy for the co-activation of carbon monoxide and a self-reporter, carbonyl sulfide, or sulfonamide with fast reaction kinetics (k: 1.4-22.6 M-1 s-1 ). Such a photoclick-and-release strategy was successfully applied in live cells to deliver carbon monoxide and a fluorescent self-reporter, both of which exhibited pronounced antiproliferative activity against 4T1 cancer cells. It is conceivable that this photoclick-and-release strategy could find applications in other fields, in which a controlled bond cleavage is preferred.

Mutual leveraging of proximity effects and click chemistry in chemical biology.

Nature has the remarkable ability to realize reactions under physiological conditions that normally would require high temperature and other forcing conditions. In doing so, often proximity effects such as simultaneous binding of two reactants in the same pocket and/or strategic positioning of catalytic functional groups are used as ways to achieve otherwise kinetically challenging reactions. Though true biomimicry is challenging, there have been many beautiful examples of how to leverage proximity effects in realizing reactions that otherwise would not readily happen under near-physiological conditions. Along this line, click chemistry is often used to endow proximity effects, and proximity effects are also used to further leverage the facile and bioorthogonal nature of click chemistry. This review brings otherwise seemingly unrelated topics in chemical biology and drug discovery under one unifying theme of mutual leveraging of proximity effects and click chemistry and aims to critically analyze the biomimicry use of such leveraging effects as powerful approaches in chemical biology and drug discovery. We hope that this review demonstrates the power of employing mutual leveraging proximity effects and click chemistry and inspires the development of new strategies that will address unmet needs in chemistry and biology.

A small molecule antagonist of SMN disrupts the interaction between SMN and RNAP II.

Survival of motor neuron (SMN) functions in diverse biological pathways via recognition of symmetric dimethylarginine (Rme2s) on proteins by its Tudor domain, and deficiency of SMN leads to spinal muscular atrophy. Here we report a potent and selective antagonist with a 4-iminopyridine scaffold targeting the Tudor domain of SMN. Our structural and mutagenesis studies indicate that both the aromatic ring and imino groups of compound 1 contribute to its selective binding to SMN. Various on-target engagement assays support that compound 1 specifically recognizes SMN in a cellular context and prevents the interaction of SMN with the R1810me2s of RNA polymerase II subunit POLR2A, resulting in transcription termination and R-loop accumulation mimicking SMN depletion. Thus, in addition to the antisense, RNAi and CRISPR/Cas9 techniques, potent SMN antagonists could be used as an efficient tool to understand the biological functions of SMN.

External stimuli-responsive gasotransmitter prodrugs: Chemistry and spatiotemporal release.

Gasotransmitters like nitric oxide, carbon monoxide, and hydrogen sulfide with unique pleiotropic pharmacological effects in mammals are an emerging therapeutic modality for different human diseases including cancer, infection, ischemia-reperfusion injuries, and inflammation; however, their clinical translation is hampered by the lack of a reliable delivery form, which delivers such gasotransmitters to the action site with precisely controlled dosage. The external stimuli-responsive prodrug strategy has shown tremendous potential in developing gasotransmitter prodrugs, which affords precise temporospatial control and better dose control compared with endogenous stimuli-sensitive prodrugs. The promising external stimuli employed for gasotransmitter activation range from photo, ultrasound, and bioorthogonal click chemistry to exogenous enzymes. Herein, we highlight the recent development of external stimuli-mediated decaging chemistry for the temporospatial delivery of gasotransmitters including nitric oxide, carbon monoxide, hydrogen sulfide and sulfur dioxide, and discuss the pros and cons of different designs.

Chemiexcitation-Triggered Prodrug Activation for Targeted Carbon Monoxide Delivery.

Photolysis-based prodrug strategy can address some critical drug delivery issues, which otherwise are very challenging to tackle with traditional prodrug strategy. However, the need for external light irradiation significantly hampers its in vivo application due to the poor light accessibility of deep tissue. Herein, we propose a new strategy of chemiexcitation-triggered prodrug activation, wherein a photoresponsive prodrug is excited for drug payload release by chemiexcitation instead of photoirradiation. As such, the bond-cleavage power of photolysis can be employed to address some critical drug delivery issues while obviating the need for external light irradiation. We have established the proof of concept by the successful development of a chemiexcitation responsive carbon monoxide delivery platform, which exhibited specific CO release at the tumor site and pronounced tumor suppression effects. We anticipate that such a concept of chemiexcitation-triggered prodrug activation can be leveraged for the targeted delivery of other small molecule-based drug payloads.

On-Demand Activation of a Bioorthogonal Prodrug of SN-38 with Fast Reaction Kinetics and High Releasing Efficiency In Vivo.

Although a myriad of bioorthogonal prodrugs have been developed, very few of them present both fast reaction kinetics and complete cleavage. Herein, we report a new bioorthogonal prodrug strategy with both fast reaction kinetics (k2: ∼103 M-1 s-1) and complete cleavage (>90% within minutes) using the bioorthogonal reaction pair of N-oxide and boron reagent. Distinctively, an innovative 1,6-elimination-based self-immolative linker is masked by N-oxide, which can be bioorthogonally demasked by a boron reagent for the release of both amino and hydroxy-containing payload in live cells. Such a strategy was applied to prepare a bioorthogonal prodrug for a camptothecin derivative, SN-38, resulting in 10-fold weakened cytotoxicity against A549 cells, 300-fold enhanced water solubility, and "on-demand" activation upon a click reaction both in vitro and in vivo. This novel bioorthogonal prodrug strategy presents significant advances over the existing ones and may find wide applications in drug delivery in the future.

Prodrug Strategies for Critical Drug Developability Issues: Part I.

Drug development is a very time, capital, and labor-intensive process. It was anticipated that bringing a novel chemical entity to market would take over a billion dollars and around 14 years [1]. In addition, drug development is characterized by a very high attrition rate both in preclinical and clinical studies. It was reported that only 40% of drug candidates with the most drug-like properties could make their way into clinical trials, and only 10% of these can eventually reach FDA approval [2]. After analyzing the data from seven UK-based pharmaceutical companies from 1964 through 1985, Prentis et al. found that 39% of failure was attributed to poor pharmacokinetic (PK) profiles in humans, 29% was attributed to a lack of clinical efficacy, 21% was attributed to toxicity and adverse effects, and about 6% was attributed to commercial limitations [3]. When a drug candidate is identified with one of these issues (except the commercial limitations), normally, a new round of structureactivity or structure-property relationship (SAR/SPR) studies is carried out to generate a new chemical entity with improved profiles, and in most cases, such a process is time and labor-intensive. Alternatively, prodrug strategy can be leveraged to efficiently address associated drug developability issues without making enormous derivatives. Prodrug strategy has been demonstrated to be very successful and fruitful in drug development, with around 20% of approved drugs from 2008 through 2020 being clarified as prodrugs [4]. In recent years, prodrug strategy has also been leveraged to address the delivery issues associated with gasotransmitters, including NO, H2S, CO as well as SO2 [5-8]. In this thematic issue, six excellent reviews were included, focusing on varied prodrug strategies in addressing different drug developability issues associated with anticancer drugs, central nervous system (CNS) drugs, and gasotransmitters....

Medicinal Chemistry Strategies Towards SO2 Donors as Research Tools and Potential Therapeutics.

SO2 is emerging as a possible endogenous signaling molecule in mammals. In addition, SO2 has also shown pharmacological effects, presenting SO2 as a promising potential therapeutic agent. The past decade has witnessed steady advances in the development of small molecule-based SO2 prodrugs/donors with varied release mechanisms. Herein, we summarize various strategies employed for SO2 prodrug design. The remaining challenges and issues will also be discussed.