Redox integration of signaling and metabolism in a head and neck cancer model of radiation resistance using COSMRO.

Redox metabolism is increasingly investigated in cancer as driving regulator of tumor progression, response to therapies and long-term patients' quality of life. Well-established cancer therapies, such as radiotherapy, either directly impact redox metabolism or have redox-dependent mechanisms of action defining their clinical efficacy. However, the ability to integrate redox information across signaling and metabolic networks to facilitate discovery and broader investigation of redox-regulated pathways in cancer remains a key unmet need limiting the advancement of new cancer therapies. To overcome this challenge, we developed a new constraint-based computational method (COSMro) and applied it to a Head and Neck Squamous Cell Cancer (HNSCC) model of radiation resistance. This novel integrative approach identified enhanced capacity for H2S production in radiation resistant cells and extracted a key relationship between intracellular redox state and cholesterol metabolism; experimental validation of this relationship highlights the importance of redox state in cellular metabolism and response to radiation.

S-Persulfidation: Chemistry, Chemical Biology, and Significance in Health and Disease.

Significance: S-Persulfidation generates persulfide adducts (RSSH) on both small molecules and proteins. This process is believed to be critical in the regulation of biological functions of reactive sulfur species such as H2S, as well as in signal transduction. S-Persulfidation also plays regulatory roles in human health and diseases. Recent Advances: Some mechanisms underlying the generation of low-molecular-weight persulfides and protein S-persulfidation in living organisms have been uncovered. Some methods for the specific delivery of persulfides and the detection of persulfides in biological systems have been developed. These advances help to pave the road to better understand the functions of S-persulfidation. Critical Issues: Persulfides are highly reactive and unstable. Currently, their identification relies on trapping them by S-alkylation, but this is not always reliable due to rapid sulfur exchange reactions. Therefore, the presence, identity, and fates of persulfides in biological environments are sometimes difficult to track. Future Directions: Further understanding the fundamental chemistry/biochemistry of persulfides and development of more reliable detection methods are needed. S-Persulfidation in specific protein targets is essential in organismal physiological health and human disease states. Besides cardiovascular and neuronal systems, the roles of persulfidation in other systems need to be further explored. Contradictory results of persulfidation in biology, especially in cancer, need to be clarified.

S-Nitrosothiols: chemistry and reactions.

The formation of S-nitrosothiols (SNO) in protein cysteine residues is an important post-translational modification elicited by nitric oxide (NO). This process is involved in virtually every class of cell signaling and has attracted considerable attention in redox biology. On the other hand, their unique structural characters make SNO potentially useful synthons. In this review, we summarized the fundamental chemical/physical properties of SNO. We also highlighted the reported chemical reactions of SNO, including the reactions with phosphine reagents, sulfinic acids, various nucleophiles, SNO-mediated radical additions, and the reactions of acyl SNO species.

Discovery of Heteroaromatic Sulfones As a New Class of Biologically Compatible Thiol-Selective Reagents.

The selective reaction of chemical reagents with reduced protein thiols is critical to biological research. This reaction is utilized to prevent cross-linking of cysteine-containing peptides in common proteomics workflows and is applied widely in discovery and targeted redox investigations of the mechanisms underlying physiological and pathological processes. However, known and commonly used thiol blocking reagents like iodoacetamide, N-ethylmaleimide, and others were found to cross-react with oxidized protein sulfenic acids (-SOH) introducing significant errors in studies employing these reagents. We have investigated and are reporting here a new heteroaromatic alkylsulfone, 4-(5-methanesulfonyl-[1,2,3,4]tetrazol-1-yl)-phenol (MSTP), as a selective and highly reactive -SH blocking reagent compatible with biological applications.

The SAMHD1 dNTP Triphosphohydrolase Is Controlled by a Redox Switch.

AIMS: Proliferative signaling involves reversible posttranslational oxidation of proteins. However, relatively few molecular targets of these modifications have been identified. We investigate the role of protein oxidation in regulation of SAMHD1 catalysis. RESULTS: Here we report that SAMHD1 is a major target for redox regulation of nucleotide metabolism and cell cycle control. SAMHD1 is a triphosphate hydrolase, whose function involves regulation of deoxynucleotide triphosphate pools. We demonstrate that the redox state of SAMHD1 regulates its catalytic activity. We have identified three cysteine residues that constitute an intrachain disulfide bond "redox switch" that reversibly inhibits protein tetramerization and catalysis. We show that proliferative signals lead to SAMHD1 oxidation in cells and oxidized SAMHD1 is localized outside of the nucleus. Innovation and Conclusions: SAMHD1 catalytic activity is reversibly regulated by protein oxidation. These data identify a previously unknown mechanism for regulation of nucleotide metabolism by SAMHD1. Antioxid. Redox Signal. 27, 1317-1331.

BDA-410 Treatment Reduces Body Weight and Fat Content by Enhancing Lipolysis in Sedentary Senescent Mice.

Loss of muscle mass and force with age leads to fall risk, mobility impairment, and reduced quality of life. This article shows that BDA-410, a calpain inhibitor, induced loss of body weight and fat but not lean mass or skeletal muscle proteins in a cohort of sedentary 23-month-old mice. Food and water intake and locomotor activity were not modified, whereas BDA-410 treatment decreased intramyocellular lipid and perigonadal fat, increased serum nonesterified fatty acids, and upregulated the genes mediating lipolysis and oxidation, lean phenotype, muscle contraction, muscle transcription regulation, and oxidative stress response. This finding is consistent with our recent report that lipid accumulation in skeletal myofibers is significantly correlated with slower fiber-contraction kinetics and diminished power in obese older adult mice. A proteomic analysis and immunoblot showed downregulation of the phosphatase PPP1R12B, which increases phosphorylated myosin half-life and modulates the calcium sensitivity of the contractile apparatus. This study demonstrates that BDA-410 exerts a beneficial effect on skeletal muscle contractility through new, alternative mechanisms, including enhanced lipolysis, upregulation of "lean phenotype-related genes," downregulation of the PP1R12B phosphatase, and enhanced excitation-contraction coupling. This single compound holds promise for treating age-dependent decline in muscle composition and strength.

Biological chemistry and functionality of protein sulfenic acids and related thiol modifications.

Selective modification of proteins at cysteine residues by reactive oxygen, nitrogen or sulfur species formed under physiological and pathological states is emerging as a critical regulator of protein activity impacting cellular function. This review focuses primarily on protein sulfenylation (-SOH), a metastable reversible modification connecting reduced cysteine thiols to many products of cysteine oxidation. An overview is first provided on the chemistry principles underlining synthesis, stability and reactivity of sulfenic acids in model compounds and proteins, followed by a brief description of analytical methods currently employed to characterize these oxidative species. The following chapters present a selection of redox-regulated proteins for which the -SOH formation was experimentally confirmed and linked to protein function. These chapters are organized based on the participation of these proteins in the regulation of signaling, metabolism and epigenetics. The last chapter discusses the therapeutic implications of altered redox microenvironment and protein oxidation in disease.

Reactive cysteine persulfides and S-polythiolation regulate oxidative stress and redox signaling.

Using methodology developed herein, it is found that reactive persulfides and polysulfides are formed endogenously from both small molecule species and proteins in high amounts in mammalian cells and tissues. These reactive sulfur species were biosynthesized by two major sulfurtransferases: cystathionine ß-synthase and cystathionine γ-lyase. Quantitation of these species indicates that high concentrations of glutathione persulfide (perhydropersulfide >100 µM) and other cysteine persulfide and polysulfide derivatives in peptides/proteins were endogenously produced and maintained in the plasma, cells, and tissues of mammals (rodent and human). It is expected that persulfides are especially nucleophilic and reducing. This view was found to be the case, because they quickly react with H2O2 and a recently described biologically generated electrophile 8-nitroguanosine 3',5'-cyclic monophosphate. These results indicate that persulfides are potentially important signaling/effector species, and because H2S can be generated from persulfide degradation, much of the reported biological activity associated with H2S may actually be that of persulfides. That is, H2S may act primarily as a marker for the biologically active of persulfide species.

Detection of protein S-sulfhydration by a tag-switch technique.

Protein S-sulfhydration (forming -S-SH adducts from cysteine residues) is a newly defined oxidative posttranslational modification and plays an important role in H2 S-mediated signaling pathways. In this study we report the first selective, "tag-switch" method which can directly label protein S-sulfhydrated residues by forming stable thioether conjugates. Furthermore we demonstrate that H2 S alone cannot lead to S-sulfhydration and that the two possible physiological mechanisms include reaction with protein sulfenic acids (P-SOH) or the involvement of metal centers which would facilitate the oxidation of H2 S to HS(.) .

Synthesis and evaluation of phosphorodithioate-based hydrogen sulfide donors.

A series of O-aryl- and alkyl-substituted phosphorodithioates were designed and synthesized as hydrogen sulfide (H2S) donors. H2S releasing capability of these compounds was evaluated using fluorescence methods. O-aryl substituted donors showed slow and sustained H2S release while O-alkylated compounds showed very weak H2S releasing capability. We also evaluated donors' protective effects against hydrogen peroxide (H2O2)-induced oxidative damage in myocytes and donors' toxicity toward B16BL6 mouse melanoma cells.

Light-induced hydrogen sulfide release from "caged" gem-dithiols.

"Caged" gem-dithiol derivatives that release H2S upon light stimulation have been developed. This new class of H2S donors was proven, by various spectroscopic methods, to generate H2S in an aqueous/organic medium as well as in cell culture.

Direct methods for detection of protein S-nitrosylation.

S-nitrosylation of protein cysteine residues is known to be an important mechanism for nitric oxide signaling. However, the detection of protein S-nitrosylation is still challenging due to technical limitations of current methods. This chapter provides a brief review on recent developments of methods, which directly target S-nitroso moieties for detection. We also describe in detail the protocol of an organophosphine-based biotin labeling of protein S-nitroso moieties.

Controllable hydrogen sulfide donors and their activity against myocardial ischemia-reperfusion injury.

Hydrogen sulfide (H2S), known as an important cellular signaling molecule, plays critical roles in many physiological and/or pathological processes. Modulation of H2S levels could have tremendous therapeutic value. However, the study on H2S has been hindered due to the lack of controllable H2S releasing agents that could mimic the slow and moderate H2S release in vivo. In this work we report the design, synthesis, and biological evaluation of a new class of controllable H2S donors. Twenty-five donors were prepared and tested. Their structures were based on a perthiol template, which was suggested to be involved in H2S biosynthesis. H2S release mechanism from these donors was studied and proved to be thiol-dependent. We also developed a series of cell-based assays to access their H2S-related activities. H9c2 cardiac myocytes were used in these experiments. We tested lead donors' cytotoxicity and confirmed their H2S production in cells. Finally we demonstrated that selected donors showed potent protective effects in an in vivo murine model of myocardial ischemia-reperfusion injury, through a H2S-related mechanism.

Methylsulfonyl benzothiazole (MSBT): a selective protein thiol blocking reagent.

A new thiol blocking reagent, methylsulfonyl benzothiazole, was discovered. This reagent showed good selectivity and high reactivity for protein thiols.

Facile amide formation via S-nitrosothioacids.

Here we report a novel amide bond formation strategy from simple thioacid and amine starting materials. The reaction is mediated by unstable but very reactive S-nitrosothioacid intermediates. This fast reaction under mild conditions should be useful in synthesis.

One-pot thioether formation from S-nitrosothiols.

Protein S-nitrosation is an important post-translational modification. However, the detection of S-nitrosation is still problematic because S-nitrosation products, that is, S-nitrosothiols, are unstable species. Here a new reaction which can selectively convert unstable S-nitrosothiols to stable thioethers in one-pot under very mild conditions is reported. This reaction has the potential to be applied in the detection of protein S-nitrosation.

Facile preparation of 3-substituted benzisothiazoles from o-mercaptoacylphenones.

A synthesis of 3-substituted benzisothiazoles starting from readily available o-mercaptoacylphenones is presented. The key cyclization step features a mild S-nitrosation and its succeeding intramolecular aza-Wittig reaction leading to the construction of the title compounds.

Multicomponent type II anion relay chemistry (ARC): one-pot syntheses of 2,3-disubstituted furans and thiophenes.

Effective, one-pot syntheses of 2,3-disubstituted furans and thiophenes, exploiting 2-tert-butyldimethylsilyl-3-formylfuran and -thiophene as the respective bifunctional linchpins, have been developed. The synthetic protocol involves multicomponent type II Anion Relay Chemistry (ARC) mediated by a solvent-controlled C(sp(2))-->O 1,4-Brook rearrangement. Simple organolithiums and alpha-disubstituted ester enolates prove effective as the initiating nucleophiles.

Solvent-controlled Csp2-->O silyl migration: the "one-pot" synthesis of 2,3-disubsituted thiophenes.

An effective "one-pot" synthesis of disubstituted thiophene derivatives employing 3-bromo-2-silyl thiophenes has been developed. A solvent-controlled [1,4] Csp2-->O silyl migration was involved as the key step in this process.