DT-diaphorase: a target for new anticancer drugs

Exploration of novel isoxazole-fused quinone derivatives as anti-colorectal cancer agents through inhibiting STAT3 and elevating ROS level

Colorectal cancer (CRC) is trending to be a major health problem throughout the world. Therapeutics with dual modes of action have shown latent capacity to create ideal anti-tumor activity. Signal transducer and activator of transcription 3 (STAT3) has been proved to be a potential target for the development of anti-colon cancer drug. In addition, modulation of tumor redox homeostasis through deploying exogenous reactive oxygen species (ROS)-enhancing agents has been widely applied as anti-tumor strategy. Thus, simultaneously targeting STAT3 and modulation ROS balance would offer a fresh avenue to combat CRC. In this work, we designed and synthesized a novel series of isoxazole-fused quinones, which were evaluated for their preliminary anti-proliferative activity against HCT116 cells. Among these quinones, compound 41 exerted excellent in vitro anti-tumor effect against HCT116 cell line with an IC50 value of 10.18 ± 0.4 nM. Compound 41 was proved to bind to STAT3 by using Bio-Layer Interferometry (BLI) assay, and can significantly inhibit phosphorylation of STAT3. It also elevated ROS of HCT116 cells by acting as a substrate of NQO1. Mitochondrial dysfunction, apoptosis, and cell cycle arrest, which was caused by compound 41, might be partially due to the inhibition of STAT3 phosphorylation and ROS production induced by 41. Moreover, it exhibited ideal anti-tumor activity in human colorectal cancer xenograft model and good safety profiles in vivo. Overall, this study provided a novel quinone derivative 41 with excellent anti-tumor activity by inhibiting STAT3 and elevating ROS level, and gave insights into designing novel anti-tumor therapeutics by simultaneously modulation of STAT3 and ROS.

Liver Antioxidant Capacity and Steatosis in Laying Hens Exposed to Various Quantities of Lupin (Lupinus angustifolius) Seeds in the Diet

Despite the many beneficial properties of legume plants, their use in diets for poultry is limited by the presence of antinutritional factors. The aim of the study was to determine the activity of DT-diaphorase, ethoxycoumarin O-deethylase, and catalase, and the concentration of malondialdehyde in liver tissue, as well as the activity of SOD and CAT in the serum of Hy-line Brown hens fed a diet supplemented with various doses of Lupinus angustifolius seeds. The results indicate that the use of large amounts of lupin in the diet resulted in an increase in MDA concentration in the liver and the lipid vacuolization of hepatocytes. A significant increase in DTD activity was observed in chickens receiving 15% lupin. Regardless of lupin dose, no increase in SOD activity was observed in chicken serum after 33 days of the experiment. From the 66th day of the experiment, an increase in catalase activity in the serum of laying hens was observed, while low activity of this enzyme was found in the liver. It can be concluded that the short-term use of lupin in the diet of laying hens does not affect the activity of antioxidant enzymes and, therefore, does not affect the oxidative-antioxidant balance of their body.

Distinct oligomerization and NADPH binding modes observed between L. donovani and human quinone oxidoreductases

Electron-driven process helps the living organism in the generations of energy, biomass production and detoxification of synthetic compounds. Soluble quinone oxidoreductases (QORs) mediate the transfer of an electron from NADPH to various quinone and other compounds, helping in the detoxification of quinones. QORs play a crucial role in cellular metabolism and are thus potential targets for drug development. Here we report the crystal structure of the NADPH-dependent QOR from Leishmania donovani (LdQOR) at 2.05 Å. The enzyme exists as a homo-dimer, with each protomer consisting of two domains, responsible for binding NADPH cofactor and the substrate. Interestingly, the human QOR exists as a tetramer. Comparative analysis of the oligomeric interfaces of LdQOR with HsQOR shows no significant differences in the protomer/dimer assembly. The tetrameric interface of HsQOR is stabilized by salt bridges formed between Arg 169 and Glu 271 which is non-existent in LdQOR, with an Alanine replacing the glutamate. This distinct feature is conserved across other dimeric QORs, indicating the importance of this interaction for tetramer association. Among the homologs, the sequences of the loop region involved in the stabilization and binding of the adenine ring of the NADPH shows significant differences except for an Arginine & glycine residues. In dimer QORs, this Arginine acts as a gate to the co-factor, while the NADPH binding mode in the human homolog is distinct, stabilized by His 200 and Asn 229, which are not conserved in LdQOR. These distinct features have the potential to be utilized for therapeutic interventions.

NAD(P)H:Quinone Acceptor Oxidoreductase 1 (NQO1) Activatable Salicylamide H+ /Cl- Transporters

NAD(P)H:quinone acceptor oxidoreductase 1 (NQO1), a detoxifying enzyme overexpressed in tumors, plays a key role in protecting cancer cells against oxidative stress and thus has been considered an attractive candidate for activating prodrug(s). Herein, we report the first use of NQO1 for the selective activation of 'protransporter' systems in cancer cells leading to the induction of apoptosis. Salicylamides, easily synthesizable small molecules, have been effectively used for efficient H+ /Cl- symport across lipid membranes. The ion transport activity of salicylamides was efficiently abated by caging the OH group with NQO1 activatable quinones via either ether or ester linkage. The release of active transporters, following the reduction of quinone caged 'protransporters' by NQO1, was verified. Both the transporters and protransporters exhibited significant toxicity towards the MCF-7 breast cancer line, mediated via the induction of oxidative stress, mitochondrial membrane depolarization, and lysosomal deacidification. Induction of cell death via intrinsic apoptotic pathway was verified by monitoring PARP1 cleavage.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Skullcapflavone II, a novel NQO1 inhibitor, alleviates aristolochic acid I-induced liver and kidney injury in mice

Aristolochic acid I (AAI) is a well established nephrotoxin and human carcinogen. Cytosolic NAD(P)H quinone oxidoreductase 1 (NQO1) plays an important role in the nitro reduction of aristolochic acids, leading to production of aristoloactam and AA-DNA adduct. Application of a potent NQO1 inhibitor dicoumarol is limited by its life-threatening side effect as an anticoagulant and the subsequent hemorrhagic complications. As traditional medicines containing AAI remain available in the market, novel NQO1 inhibitors are urgently needed to attenuate the toxicity of AAI exposure. In this study, we employed comprehensive 2D NQO1 biochromatography to screen candidate compounds that could bind with NQO1 protein. Four compounds, i.e., skullcapflavone II (SFII), oroxylin A, wogonin and tectochrysin were screened out from Scutellaria baicalensis. Among them, SFII was the most promising NQO1 inhibitor with a binding affinity (K_D = 4.198 μmol/L) and inhibitory activity (IC₅₀ = 2.87 μmol/L). In human normal liver cell line (L02) and human renal proximal tubular epithelial cell line (HK-2), SFII significantly alleviated AAI-induced DNA damage and apoptosis. In adult mice, oral administration of SFII dose-dependently ameliorated AAI-induced renal fibrosis and dysfunction. In infant mice, oral administration of SFII suppressed AAI-induced hepatocellular carcinoma initiation. Moreover, administration of SFII did not affect the coagulation function in short term in adult mice. In conclusion, SFII has been identified as a novel NQO1 inhibitor that might impede the risk of AAI to kidney and liver without obvious side effect.

Rational Design of a Dual-Channel Fluorescent Probe for the Simultaneous Imaging of Hypochlorous Acid and Peroxynitrite in Living Organisms

Hypochlorous acid (HOCl) and peroxynitrite (ONOO^-) are two important highly reactive oxygen/nitrogen species, which commonly coexist in biosystems and play pivotal roles in many physiological and pathological processes. To investigate their function and correlations, it is urgently needed to construct chemical tools that can track the production of HOCl and ONOO^- in biological systems with distinct fluorescence signals. Here, we found that the coumarin fluorescence of coumarin-benzopyrylium (CB) hydrazides (spirocyclic form) is dim, and their fluorescence properties are controlled by their benzopyran moiety via an intramolecular photo-induced electron transfer (PET) process. Based on this mechanism, we report the development of a fluorescent probe CB2-H for the simultaneous detection of HOCl and ONOO^-. ONOO^- can selectively oxidize the hydrazide group of CB2-H to afford the parent dye CB2 (Abs_max/Em_max = 631/669 nm). In the case of HOCl, it undergoes an electrophilic attack on the benzopyran moiety of CB2-H to give a chlorinated product CB2-H-Cl, which inhibits the PET process within the probe and thus affords a turn-on fluorescence response at the coumarin channel (Abs_max/Em_max = 407/468 nm). Due to the marked differences in absorption/emission wavelengths between the HOCl and ONOO^- products, CB2-H enables the concurrent detection of HOCl and ONOO^- at two independent channels without spectral cross-interference. CB2-H has been applied for dual-channel fluorescence imaging of endogenously produced HOCl and ONOO^- in living cells and zebrafish under different stimulants. The present probe provides a useful tool for further exploring the distribution and correlation of HOCl and ONOO^- in more biosystems.

Enzyme-activated Prodrugs and Their Release Mechanisms for Treatment of Cancer

Enzyme-activated prodrugs have received a lot of attention in recent years. These prodrugs have low toxicity to cells before they are activated, and when they interact with specific enzymes, they...

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

An Edaravone-Guided Design of a Rhodamine-Based Turn-on Fluorescent Probe for Detecting Hydroxyl Radicals in Living Systems

The hydroxyl radical (·OH), one of the reactive oxygen species (ROS) in biosystems, is found to be involved in many physiological and pathological processes. However, specifically detecting endogenous ·OH remains an outstanding challenge owing to the high reactivity and short lifetime of this radical. Herein, inspired by the scavenging mechanism of a neuroprotective drug edaravone toward ·OH, we developed a new ·OH-specific fluorescent probe RH-EDA. RH-EDA is a hybrid of rhodamine and edaravone and exploits a ·OH-specific 3-methyl-pyrazolone moiety to control its fluorescence behavior. RH-EDA itself is almost nonfluorescent in physiological conditions, which was attributed to the formation of a twisted intramolecular charge transfer (TICT) state upon photoexcitation and the acylation of its rhodamine nitrogen at the 3' position. However, upon a treatment with ·OH, its edaravone subunit was converted to the corresponding 2-oxo-3-(phenylhydrazono)-butanoic acid (OPB) derivative (to afford RH-OPB), thus leading to a significant fluorescence increase (ca. 195-fold). RH-EDA shows a high sensitivity and selectivity to ·OH without interference from other ROS. RH-EDA has been utilized for imaging endogenous ·OH production in living cells and zebrafishes under different stimuli. Moreover, RH-EDA allows a high-contrast discrimination of cancer cells from normal ones by monitoring their different ·OH levels upon stimulation with β-Lapachone (β-Lap), an effective ROS-generating anticancer therapeutic agent. The present study provides a promising methodology for the construction of probes through a drug-guided approach.

Murdannia loriformis: A Review of Ethnomedicinal Uses, Phytochemistry, Pharmacology, Contemporary Application, and Toxicology

This review provides an updated and comprehensive overview on the ethnomedicinal use, phytochemistry, pharmacology, and toxicology of M. loriformis. Phytochemical analysis of M. loriformis revealed that it is composed of phenolics, flavonoids, condensed tannins, chlorophylls, alkaloids, and steroids. Numerous compounds including syringic acid, ß-O-D-glucopyranosyl-2-(2′-hydroxy-Z-6′-enecosamide) sphingosine, isovitexin, and 3β-O-D-glucopyranosyl-24ξ-ethylcholest-5-ene have been identified and isolated from this plant species. The present review attempts to bridge the gap between traditional use and pharmacological studies of M. loriformis while improving their existing therapeutic agents and product applications based on this plant.

High-Contrast Fluorescence Diagnosis of Cancer Cells/Tissues Based on β-Lapachone-Triggered ROS Amplification Specific in Cancer Cells

Discrimination of cancer cells/tissues from normal ones is of critical importance for early diagnosis and treatment of cancers. Herein, we present a new strategy for high-contrast fluorescence diagnosis of cancer cells/tissues based on β-Lapachone (β-Lap, an anticancer agent) triggered ROS (reactive oxygen species) amplification specific in cancer cells/tissues. With the strategy, a wide range of cancer cells/tissues, including surgical tissue specimens harvested from patients, were distinguished from normal ones by using a combination of β-Lap and a Si-rhodamine-based NIR fluorescent ROS probe PSiR3 developed in this work with average tumor-to-normal (T/N) ratios up to 15 in cell level and 24 in tissue level, far exceeding the clinically acceptable threshold of 2.0. What's more, the strategy allowed the fluorescence discrimination of tumor tissues from inflammatory ones based on whether a marked fluorescence enhancement could be induced when treated with PSiR3 and β-Lap/PSiR3 combination, respectively.

Design, synthesis, and biological evaluation of 3-(1-benzotriazole)-nor-β-lapachones as NQO1-directed antitumor agents

A series of novel 3-(1-benzotriazole)-nor-β-lapachones 5a-5l were synthesized as the NQO1-targeted anticancer agents. Most of these compounds displayed good antiproliferative activity against the breast cancer MCF-7, lung cancer A549 and hepatocellular carcinoma HepG2 cells in agreements with their NQO1 activity. Among them, compound 5k was identified as a favorable NQO1 substrate. It could activate the ROS production in a NQO1-dependent manner, arrest tumor cell cycle at G0/G1 phase, promote tumor cell apoptosis, and decrease the mitochondrial membrane potential. In HepG2 xenograft models, 5k significantly suppressed the tumor growth with no influences on animal body weights. Therefore, 5k could be a good lead for further anticancer drug developments.

Effects of Shengmai San on key enzymes involved in hepatic and intestinal drug metabolism in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Shengmai San (SMS) has been commonly used as a traditional Chinese medicine for the treatment of cardiovascular disorders, of which drug interactions need to be assessed for the safety concern. There is little evidence for the alterations of hepatic and intestinal drug-metabolizing enzymes after repeated SMS treatments to assess drug interactions.

AIM OF THE STUDY

The studies aim to illustrate the effects of repeated treatments with SMS on cytochrome P450s (CYPs), reduced nicotinamide adenine dinucleotide (phosphate)-quinone oxidoreductase (NQO), uridine diphosphate-glucuronosyltransferase (UGT), and glutathione S-transferase (GST) using in vivo rat model.

MATERIALS AND METHODS

The SMS was prepared using Schisandrae Fructus, Ginseng Radix, and Ophiopogonis Radix (OR) (1:2:2). Chromatographic analyses of decoctions were performed using ultra-performance liquid chromatography (UPLC) and LC-mass spectrometry. Sprague-Dawley rats were orally treated with the SMS and its component herbal decoctions for 2 or 3 weeks. Hepatic and intestinal enzyme activities were determined. CYP3A expression and the kinetics of intestinal nifedipine oxidation (NFO, a CYP3A marker reaction) were determined.

RESULTS

Schisandrol A, schisandrin B, ginsenoside Rb1 and ophiopogonin D were identified in SMS. SMS selectively suppressed intestinal, but not hepatic, NFO activity in a dose- and time-dependent manner. Hepatic and intestinal UGT, NQO and GST activities were not affected. A 3-week SMS treatment decreased the maximal velocity of intestinal NFO by 50%, while the CYP3A protein level remained unchanged. Among SMS component herbs, the decoction of OR decreased intestinal NFO activity.

CONCLUSIONS

These findings demonstrate that 3-week treatment with SMS and OR suppress intestinal, but not hepatic CYP3A function. It suggested that the potential interactions of SMS with CYP 3A drug substrates should be noticed, especially the drugs whose bioavailability depends heavily on intestinal CYP3A.

Enzyme-Triggered Disassembly of Polymeric Micelles by Controlled Depolymerization via Cascade Cyclization for Anticancer Drug Delivery

The high activity of specific enzymes in cancer has been utilized in cancer diagnosis, as well as tumor-targeted drug delivery. NAD(P)H:quinone oxidoreductase-1 (NQO1), an overexpressed enzyme in certain tumor types, maintains homeostasis and inhibits oxidative stress caused by elevated reactive oxygen species (ROS) in tumor cells. The activity of NQO1 in lung and liver cancer cells is increased compared to that in normal cells. Interestingly, NQO1 reacts with trimethyl-locked quinone propionic acid (QPA) and produces a lactone-based group via intramolecular cyclization. Toward this objective, we synthesized an amphiphilic block copolymer (QPA-P) composed of NQO1 enzyme-triggered depolymerizable QPA-locked polycaprolactone (PCL) and poly(ethylene glycol) (PEG) as hydrophobic and hydrophilic constituents, respectively. This QPA-P formed self-assembled micelles in aqueous conditions. It was observed that NQO1 catalyzed the depolymerization of QPA-locked PCL via a cascade two-step cyclization process, which eventually induced the dissociation of micellar structure and triggered the release of loaded drugs at the target cancer cells. Compared to the control group, the NQO1-responsive micelle showed NQO1-triggered intracellular drug release and enhanced anticancer effects. These results indicate that the NQO1-responsive polymeric micelles present a promising potential for improving therapeutic efficacy of an anticancer drug delivery system.

Ubiquinone-BODIPY nanoparticles for tumor redox-responsive fluorescence imaging and photodynamic activity

Successful applications of photodynamic therapy (PDT) in cancer treatment require the development of effective photosensitizers with controllable singlet oxygen generation. Here we report a ubiquinone-BODIPY photosensitizer that self-assembles into nanoparticles (PS-Q-NPs) and undergoes selective activation and deaggregation within the highly reductive intracellular environment of tumor cells. PS-Q-NPs are highly stable in aqueous buffer solution, and exhibit minimal fluorescence and photosensitization due to a rapid non-radiative relaxation process. Upon endocytosis by cancer cells, reduction of the ubiquinone moiety by intracellular glutathione (GSH) triggers the conversion of the aggregated hydrophobic precursor into the active hydrophilic carboxylate derivative PS-A. The conversion results in enhanced fluorescence and therapeutic singlet oxygen generation, portending to its application as an activatable photosensitizer for fluorescence imaging-guided photodynamic cancer therapy.

Synthesis and biological evaluation of NQO1-activated prodrugs of podophyllotoxin as antitumor agents

Podophyllotoxin (PPT), a toxic polyphenol derived from the roots of genus Podophyllum, had been reported with strong inhibition on both normal human cells and tumor cells, which hindered the development of PPT as the candidate antitumor agent. In the present work, multiple NQO1-activatable PPT prodrugs were synthesized for reducing normal cell toxicity and keeping tumor cell toxicity. The antiproliferative activities in vitro showed prodrug 3 was greatly selectively toxic to tumor cells over-expressing NQO1, taxol-resistant A549, hypoxia A549 and HepG2, and lower damage to normal cells in comparison with podophyllotoxin, prodrug 1 and 2. As elucidated by further mechanistic research, prodrug 3 was activated via NQO1 to efficiently while gently produce cytotoxic PPT units and kill tumor cells. In additions, in vivo study revealed that 3 significantly suppressed cancer growth in HepG2 xenograft models without obvious toxicity. Therefore, this NQO1-activatable prodrug delivery system exhibits good biosafety and provides a novel strategy for the development of drug delivery systems.

Cytosolic NQO1 Enzyme-Activated Near-Infrared Fluorescence Imaging and Photodynamic Therapy with Polymeric Vesicles

The utilization of enzymes as a triggering module could endow responsive polymeric nanostructures with selectivity in a site-specific manner. On the basis of the fact that endogenous NAD(P)H:quinone oxidoreductase isozyme 1 (NQO1) is overexpressed in many types of tumors, we report on the fabrication of photosensitizer-conjugated polymeric vesicles, exhibiting synergistic NQO1-triggered turn-on of both near-infrared (NIR) fluorescence emission and a photodynamic therapy (PDT) module. For vesicles self-assembled from amphiphilic block copolymers containing quinone trimethyl lock-capped self-immolative side linkages and quinone-bridged photosensitizers (coumarin and Nile blue) in the hydrophobic block, both fluorescence emission and PDT potency are initially in the "off" state due to "double quenching" effects, that is, dye-aggregation-caused quenching and quinone-rendered PET (photoinduced electron transfer) quenching. After internalization into NQO1-positive vesicles, the cytosolic NQO1 enzyme triggers self-immolative cleavage of quinone linkages and fluorogenic release of conjugated photosensitizers, leading to NIR fluorescence emission turn-on and activated PDT. This process is accompanied by the transformation of vesicles into cross-linked micelles with hydrophilic cores and smaller sizes and triggered dual drug release, which could be directly monitored by enhanced magnetic resonance (MR) imaging for vesicles conjugated with a DOTA(Gd) complex in the hydrophobic bilayer. We further demonstrate that the above strategy could be successfully applied for activated NIR fluorescence imaging and tissue-specific PDT under both cellular and in vivo conditions.

Cancer-Specific hNQO1-Responsive Biocompatible Naphthalimides Providing a Rapid Fluorescent Turn-On with an Enhanced Enzyme Affinity

Human NAD(P)H:quinone oxidoreductase 1 (hNQO1) is overexpressed in cancer cells and associated with the drug resistance factor of cancer. The objective of this work is the development of fluorescent probes for the efficient detection of hNQO1 activity in cancer cells, which can be employed for the cancer diagnosis and therapeutic agent development. Herein, we report naphthalimide-based fluorescent probes 1 and 2 that can detect hNQO1. For hNQO1 activity, the probes showed a significant fluorescence increase at 540 nm. In addition, probe 1, the naphthalimide containing a triphenylphosphonium salt, showed an enhanced enzyme efficiency and rapid detection under a physiological condition. The detection ability of probe 1 was superior to that of other previously reported probes. Moreover, probe 1 was less cytotoxic during the cancer cell imaging and readily provided a strong fluorescence in hNQO1-overexpressed cancer cells (A549). We proposed that probe 1 can be used to detect hNQO1 expression in live cells and it will be applied to develop the diagnosis and customized treatment of hNQO1-related disease.

From in vitro to in silico: Modeling and recombinant production of DT-Diaphorase enzyme

DT-Diaphorase (DTD) belonging to the oxidoreductase family, is among the most important enzymes and is of great significance in present-day biotechnology. Also, it has potential applications in glucose and pyruvate biosensors. Another important role of the DTD enzyme is in the detection of Phenylketonuria disease. According to the above demands, at first, we tried to study molecular cloning and production of recombinant DTD in E. coli BL21 strain. We have successfully cloned, expressed, and purified functionally active diaphorase. The amount of enzyme was increased in 10-h using IPTG induction, and the recombinant protein was purified by Ni-NTA agarose affinity chromatography. After that, the kinetic and thermodynamic parameters of the enzyme, optimum temperature and pH were also investigated to find more in-depth information. In the end, to represent the connections between the structures and function of this enzyme, the molecular dynamics simulations have been considered at two temperatures in which DTD had maximum and minimum activity (310 and 293 K, respectively). The results of MD simulations indicated that the interaction between NADH with phenylalanine 232 residue at 310 K is more severe than other residues. So, to investigate the interaction details of NADH/PHE 232 the DFT calculations were done.

pH- and enzyme-triggered drug release as an important process in the design of anti-tumor drug delivery systems

It is necessary to design a reasonable drug delivery system(DDS) for targeted release to overcome the potential toxicity and poor selectivity of anti-tumor drug. How a drug is released from a DDS is a critical issue that determines whether the DDS is designed successfully. We all know that the microenvironment of tumors is quite different from normal tissues, such as its acidic environment, different expression levels of some enzymes, etc. These features are widely used in the design of DDSs and play an important role in the drug release process in vivo. Numerous DDSs have been designed and synthesized. This article attention to how drugs are released from DDSs. We summarizes and classify the characteristic enzymes and chemical bonds used in the drug release process by browsing a large number of papers, and describes how they are applied in DDSs with specific examples. By understanding these acid-sensitive chemical bonds and over-expressed enzymes in tumors, different DDSs can be designed for different drug structures to solve specific problems of anti-tumor drugs.

Synthesis of quinones with highlighted biological applications: A critical update on the strategies towards bioactive compounds with emphasis on lapachones

Naphthoquinones are of key importance in organic synthesis and medicinal chemistry. In the last few years, various synthetic routes have been developed to prepare bioactive compounds derived or based on lapachones. In this sense, this review is mainly focused on the synthetic aspects and strategies used for the design of these compounds on the basis of their biological activities for the development of drugs against the neglected diseases leishmaniases and Chagas disease and also cancer. Three strategies used to develop bioactive quinones are discussed and categorized: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Framed within these strategies for the development of naphthoquinoidal compounds against T. cruzi. Leishmania and cancer, reactions including copper-catalyzed azide-alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, C-H activation reactions, Ullmann couplings and heterocyclisations reported up to July 2019 will be discussed. The aim of derivatisation is the generation of novel molecules that can potentially inhibit cellular organelles/processes, generate reactive oxygen species and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against leishmaniases, Chagas disease and cancer.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Dual-biomarker-triggered fluorescence probes for differentiating cancer cells and revealing synergistic antioxidant effects under oxidative stress

Hydrogen sulfide (H2S) and human NAD(P)H:quinine oxidoreductase 1 (hNQO1) are potential cancer biomarkers and also vital participants in cellular redox homeostasis. Simultaneous detection of these two biomarkers would benefit the diagnostic precision of related cancers and could also help to investigate their crosstalk in response to oxidative stress. Despite this importance, fluorescent probes that can be activated by the dual action of H2S detection and hNQO1 activity have not been investigated. To this end, dual-biomarker-triggered fluorescent probes 1 and 2 were rationally constructed by installing two chemoselective triggering groups into one fluorophore. Probe 1 provides a small turn-on fluorescence response toward H2S but a much larger response to both H2S and hNQO1 in tandem. By contrast, fluorescence probe 2 is activated only in the presence of both H2S and hNQO1. Probe 2 exhibits a large fluorescence turn-on (>400 fold), high sensitivity, excellent selectivity as well as good biocompatibility, enabling the detection of both endogenous H2S and hNQO1 activity in living cells. Bioimaging results indicated that probe 2 could differentiate HT29 and HepG2 cancer cells from HCT116, FHC and HeLa cells owing to the existence of relatively high endogenous levels of both biomarkers. Expanded investigations using 2 revealed that cells could generate more endogenous H2S and hNQO1 upon exposure to exogenous hydrogen peroxide (H2O2), implying the synergistic antioxidant effects under conditions of cellular oxidative stress.

Hypoxia-targeted drug delivery

Hypoxia is a state of low oxygen tension found in numerous solid tumours. It is typically associated with abnormal vasculature, which results in a reduced supply of oxygen and nutrients, as well as impaired delivery of drugs. The hypoxic nature of tumours often leads to the development of localized heterogeneous environments characterized by variable oxygen concentrations, relatively low pH, and increased levels of reactive oxygen species (ROS). The hypoxic heterogeneity promotes tumour invasiveness, metastasis, angiogenesis, and an increase in multidrug-resistant proteins. These factors decrease the therapeutic efficacy of anticancer drugs and can provide a barrier to advancing drug leads beyond the early stages of preclinical development. This review highlights various hypoxia-targeted and activated design strategies for the formulation of drugs or prodrugs and their mechanism of action for tumour diagnosis and treatment.

Construction of Dual Stimuli-Responsive Platinum(IV) Hybrids with NQO1 Targeting Ability and Overcoming Cisplatin Resistance

Quinone oxidoreductase isozyme I (NQO1) is a cytoprotective two-electron-specific reductase that highly expresses in various cancer cells. Taking NQO1 as the target, we herein report three hybrid compounds from Pt(IV) complexes and a quinone propionic acid unit. The mechanism studies showed that the hybrids could be activated by both NQO1 and ascorbic acid to release the cytotoxic Pt(II) unit, exhibiting a dual stimuli-responsive character. In the pharmacological studies, complexes 2 and 3 presented higher antitumor activity than cisplatin. More importantly, the hybrid could also overcome cisplatin resistance due to the NQO1 targeting ability, improved cellular uptake, and/or different action mechanism. Significantly, complex 3 containing a coumarin moiety could be effectively activated in NQO1-overexpressed cancer cells to "turn on" fluorescence, showing a promising visual effect in cancer cells. In vivo study revealed that both 2 and 3 exhibited higher antitumor efficacy than cisplatin in the A549 xenograft mouse model at an equimolar dose to cisplatin. In all, the hybrids may serve as promising NQO1-targeting anticancer agents.

A highly selective fluorescent probe for human NAD(P)H:quinone oxidoreductase 1 (hNQO1) detection and imaging in living tumor cells

Human NAD(P)H:quinone oxidoreductase (hNQO1) can be used as a biomarker for the early diagnosis of cancer.

Emerging Applications of Fluorogenic and Non-fluorogenic Bifunctional Linkers

Homo- and hetero-bifunctional linkers play vital roles in constructing a variety of functional systems, ranging from protein bioconjugates with drugs and functional agents, to surface modification of nanoparticles and living cells, and to the cyclization/dimerization of synthetic polymers and biomolecules. Conventional approaches for assaying conjugation extents typically rely on ex situ techniques, such as mass spectrometry, gel electrophoresis, and size-exclusion chromatography. If the conjugation process involving bifunctional linkers was rendered fluorogenic, then in situ monitoring, quantification, and optical tracking/visualization of relevant processes would be achieved. In this review, conventional non-fluorogenic linkers are first discussed. Then the focus is on the evolution and emerging applications of fluorogenic bifunctional linkers, which are categorized into hetero-bifunctional single-caging fluorogenic linkers, homo-bifunctional double-caging fluorogenic linkers, and hetero-bifunctional double-caging fluorogenic linkers. In addition, stimuli-cleavable bifunctional linkers designed for both conjugation and subsequent site-specific triggered release are also summarized.

Development of novel amino-quinoline-5,8-dione derivatives as NAD(P)H:quinone oxidoreductase 1 (NQO1) inhibitors with potent antiproliferative activities

Fourteen novel amino-quinoline-5,8-dione derivatives (6a-h and 7a-h) were designed and synthesized by coupling different alkyl- or aryl-amino fragments at the C6- or C7-position of quinoline-5,8-dione. All target compounds showed antiproliferative potency in the low micromolar range in both drug sensitive HeLaS3 and multidrug resistant KB-vin cell lines. Compounds 6h, 6d, 7a, and 7d exhibited more potent antiproliferative effects than the other compounds. Especially, compounds 6d and 7d displayed NQO1-dependent cytotoxicity and competitive NQO1 inhibitory effects in both drug sensitive HeLaS3 and multidrug resistant KB-vin cell lines. Furthermore, compounds 6h, 6d, 7a, and 7d induced a dose-dependent lethal mitochondrial dysfunction in both drug sensitive HeLaS3 and multidrug resistant KB-vin cells by increasing intracellular reactive oxygen species (ROS) levels. Notably, compound 7d selectively inhibited cancer cells, but not non-tumor liver cell proliferation in vitro, and significantly triggered HeLaS3 cell apoptosis by regulating apoptotic proteins of Bcl-2, Bax, and cleaved caspase-3 in a dose-dependent manner. Our findings suggest that these novel C6- or C7-substituted amino-quinoline-5,8-dione derivatives, such as 7d, could be further developed in the future as potent and selective antitumor agents to potentially circumvent multi-drug resistance (MDR).

A sequential enzyme-activated and light-triggered pro-prodrug nanosystem for cancer detection and therapy

A sequential enzyme-activated and light-triggered pro-prodrug has been developed for cancer biomarker detection and on-demand therapy.

Recent progresses in small-molecule enzymatic fluorescent probes for cancer imaging

An overview of recent advances in small-molecule enzymatic fluorescent probes for cancer imaging, including design strategies and cancer imaging applications.

A Probe for the Detection of Hypoxic Cancer Cells

Hypoxia is a common feature of tumor cells. Nitroreductase (NTR), a common biomarker of hypoxia, has been widely used to evaluate the extent of tumor hypoxia. In this study, three fluorescent probes (FBN-1-3) were synthesized to monitor the extent of hypoxia in cancer cells in real time. FBN-1-3 were composed of a fluorescein analogue and one of three different aromatic nitro groups. Of these probes, FBN-1 showed excellent sensitivity and selectivity in detecting hypoxia via a reduction in O2 concentration. Confocal fluorescence imaging and flow cytometry demonstrated that HepG-2, A549, and SKOV-3 cells incubated with FBN-1 under reduced oxygen conditions showed significantly enhanced fluorescence. A mouse HepG-2 tumor model confirmed that FBN-1 responds rapidly to NTR and can be used to evaluate the degree of tumor hypoxia. The changes in intra- and extracellular NTR in tumor cells were also concurrently monitored, which did not reveal a link between NTR concentration and degree of hypoxia. Our work provides a functional probe for tumor hypoxia, and our results suggest the fluorescent response of our probe is due to a decrease in O2 concentration, and not NTR concentration.

Combined molecular modelling and 3D-QSAR study for understanding the inhibition of NQO1 by heterocyclic quinone derivatives

A combination of three-dimensional quantitative structure-activity relationship (3D-QSAR), and molecular modelling methods were used to understand the potent inhibitory NAD(P)H:quinone oxidoreductase 1 (NQO1) activity of a set of 52 heterocyclic quinones. Molecular docking results indicated that some favourable interactions of key amino acid residues at the binding site of NQO1 with these quinones would be responsible for an improvement of the NQO1 activity of these compounds. The main interactions involved are hydrogen bond of the amino group of residue Tyr128, π-stacking interactions with Phe106 and Phe178, and electrostatic interactions with flavin adenine dinucleotide (FADH) cofactor. Three models were prepared by 3D-QSAR analysis. The models derived from Model I and Model III, shown leave-one-out cross-validation correlation coefficients (q²_LOO ) of .75 and .73 as well as conventional correlation coefficients (R² ) of .93 and .95, respectively. In addition, the external predictive abilities of these models were evaluated using a test set, producing the predicted correlation coefficients (r²_pred ) of .76 and .74, respectively. The good concordance between the docking results and 3D-QSAR contour maps provides helpful information about a rational modification of new molecules based in quinone scaffold, in order to design more potent NQO1 inhibitors, which would exhibit highly potent antitumor activity.

Flavoenzyme-mediated reduction reactions and antitumor activity of nitrogen-containing tetracyclic ortho-quinone compounds and their nitrated derivatives

Nitrogen-based tetracyclic ortho-quinones (naphtho[1'2':4.5]imidazo[1,2-a]pyridine-5,6-diones, NPDOs) and their nitro-substituted derivatives (nitro-(P)NPDOs) were obtained by condensation of substituted 2,3-dichloro-1,4-naphthoquinones with 2-amino-pyridine and -pyrimidine and nitration at an elevated temperature. The structural features of the compounds as well as their global and regional electrophilic potency were characterized by means of DFT computation. The compounds were highly reactive substrates of single- and two-electron (hydride) - transferring P-450R (CPR; EC 1.6.2.4) and NQO-1 (DTD; EC 1.6.99.2), respectively, concomitantly producing reactive oxygen species. Their catalytic efficiency defined in terms of the apparent second-order rate constant (k_cat/K_{M (Q)}) values in P-450R- and NQO-1-mediated reactions varied in the range of 3-6 × 10⁷ M^-1 s^-1 and 1.6-7.4 × 10⁸ M^-1 s^-1, respectively. The cytotoxic activities of the compounds on tumor cell lines followed the concentration-dependent manner exhibiting relatively high cytotoxic potency against breast cancer MCF-7, with CL₅₀ values of 0.08-2.02 µM L^-1 and lower potency against lung cancer A-549 (CL₅₀ = 0.28-7.66 µM L^-1). 3-nitro-pyrimidino-NPDO quinone was the most active compound against MCF-7 with CL₅₀ of 0.08 ± 0.01 µM L^-1 (0.02 µg mL^-1)) which was followed by 3-nitro-NPDO with CL₅₀ of 0.12 ± 0.03 µM L^-1 (0.035 µg mL^-1)) and 0.28 ± 0.08 µM L^-1 (0.08 µg mL^-1) on A-549 and MCF-7 cells, respectively, while 1- and 4-nitro-quinoidals produced the least cytotoxic effects. Tumor cells quantified by AO/EB staining showed that the cell death induced by the compounds occurs primarily through apoptosis.

β-lapachone suppresses tumour progression by inhibiting epithelial-to-mesenchymal transition in NQO1-positive breast cancers

NQO1 is a FAD-binding protein that can form homodimers and reduce quinones to hydroquinones, and a growing body of evidence currently suggests that NQO1 is dramatically elevated in solid cancers. Here, we demonstrated that NQO1 was elevated in breast cancer and that its expression level was positively correlated with invasion and reduced disease free survival (DFS) and overall survival (OS) rates. Next, we found that β-lapachone exerted significant anti-proliferation and anti-metastasis effects in breast cancer cell lines due to its effects on NQO1 expression. Moreover, we revealed that the anti-cancer effects of β-lapachone were mediated by the inactivation of the Akt/mTOR pathway. In conclusion, these results demonstrated that NQO1 could be a useful prognostic biomarker for patients with breast cancer, and its bioactivatable drug, β-lapachone represented a promising new development and an effective strategy for indicating the progression of NQO1-positive breast cancers.

Cancer-Associated, Stimuli-Driven, Turn on Theranostics for Multimodality Imaging and Therapy

Advances in bioinformatics, genomics, proteomics, and metabolomics have facilitated the development of novel anticancer agents that have decreased side effects and increased safety. Theranostics, systems that have combined therapeutic effects and diagnostic capabilities, have garnered increasing attention recently because of their potential use in personalized medicine, including cancer-targeting treatments for patients. One interesting approach to achieving this potential involves the development of cancer-associated, stimuli-driven, turn on theranostics. Multicomponent constructs of this type would have the capability of selectively delivering therapeutic reagents into cancer cells or tumor tissues while simultaneously generating unique signals that can be readily monitored under both in vitro and in vivo conditions. Specifically, their combined anticancer activities and selective visual signal respond to cancer-associated stimuli, would make these theranostic agents more highly efficient and specific for cancer treatment and diagnosis. This article focuses on the progress of stimuli-responsive turn on theranostics that activate diagnostic signals and release therapeutic reagents in response to the cancer-associated stimuli. The present article not only provides the fundamental backgrounds of diagnostic and therapeutic tools that have been widely utilized for developing theranostic agents, but also discusses the current approaches for developing stimuli-responsive turn on theranostics.