A H2S-Nampt dependent energetic circuit is critical to survival and cytoprotection from damage in cancer cells

A mitochondria-targeted chemiluminescent probe for detection of hydrogen sulfide in cancer cells, human serum and in vivo

Hydrogen sulfide (H2S) as a critical messenger molecule plays vital roles in regular cell function. However, abnormal levels of H2S, especially mitochondrial H2S, are directly correlated with the formation of pathological states including neurodegenerative diseases, cardiovascular disorders, and cancer. Thus, monitoring fluxes of mitochondrial H2S concentrations both in vitro and in vivo with high selectivity and sensitivity is crucial. In this direction, herein we developed the first ever example of a mitochondria-targeted and H2S-responsive new generation 1,2-dioxetane-based chemiluminescent probe (MCH). Chemiluminescent probes offer unique advantages compared to conventional fluorophores as they do not require external light irradiation to emit light. MCH exhibited a dramatic turn-on response in its luminescence signal upon reacting with H2S with high selectivity. It was used to detect H2S activity in different biological systems ranging from cancerous cells to human serum and tumor-bearing mice. We anticipate that MCH will pave the way for development of new organelle-targeted chemiluminescence agents towards imaging of different analytes in various biological models.

Sol-Gel Dipping Devices for H2S Visualization

In this contribution we report the synthesis and full characterization, via a combination of different spectroscopies (e.g., ¹H NMR, UV-vis, fluorescence, MALDI), of a new family of fluorescent zinc complexes with extended π-conjugated systems, with the final aim of setting up higher performance H₂S sensing devices. Immobilization of the systems into a polymeric matrix for use in a solid-state portable device was also explored. The results provided proof-of-principle that the title complexes could be successfully implemented in a fast, simple and cost-effective H₂S sensing device.

The Role of Hydrogen Sulfide in the Development and Progression of Lung Cancer

Lung cancer is one of the 10 most common cancers in the world, which seriously affects the normal life and health of patients. According to the investigation report, the 3-year survival rate of patients with lung cancer is less than 20%. Heredity, the environment, and long-term smoking or secondhand smoke greatly promote the development and progress of the disease. The mechanisms of action of the occurrence and development of lung cancer have not been fully clarified. As a new type of gas signal molecule, hydrogen sulfide (H₂S) has received great attention for its physiological and pathological roles in mammalian cells. It has been found that H₂S is widely involved in the regulation of the respiratory system and digestive system, and plays an important role in the occurrence and development of lung cancer. H₂S has the characteristics of dissolving in water and passing through the cell membrane, and is widely expressed in body tissues, which determines the possibility of its participation in the occurrence of lung cancer. Both endogenous and exogenous H₂S may be involved in the inhibition of lung cancer cells by regulating mitochondrial energy metabolism, mitochondrial DNA integrity, and phosphoinositide 3-kinase/protein kinase B co-pathway hypoxia-inducible factor-1α (HIF-1α). This article reviews and discusses the molecular mechanism of H₂S in the development of lung cancer, and provides novel insights for the prevention and targeted therapy of lung cancer.

Emerging roles of cystathionine β-synthase in various forms of cancer

The expression of the reverse transsulfuration enzyme cystathionine-β-synthase (CBS) is markedly increased in many forms of cancer, including colorectal, ovarian, lung, breast and kidney, while in other cancers (liver cancer and glioma) it becomes downregulated. According to the clinical database data in high-CBS-expressor cancers (e.g. colon or ovarian cancer), high CBS expression typically predicts lower survival, while in the low-CBS-expressor cancers (e.g. liver cancer), low CBS expression is associated with lower survival. In the high-CBS expressing tumor cells, CBS, and its product hydrogen sulfide (H₂S) serves as a bioenergetic, proliferative, cytoprotective and stemness factor; it also supports angiogenesis and epithelial-to-mesenchymal transition in the cancer microenvironment. The current article reviews the various tumor-cell-supporting roles of the CBS/H₂S axis in high-CBS expressor cancers and overviews the anticancer effects of CBS silencing and pharmacological CBS inhibition in various cancer models in vitro and in vivo; it also outlines potential approaches for biomarker identification, to support future targeted cancer therapies based on pharmacological CBS inhibition.

Paper-Strip-Based Sensors for H2S Detection: A Proof-of-Principle Study

In this work, the authors explored the interaction of a suite of fluorescent zinc complexes with H₂S. The authors provide evidence that HS⁻ binds the zinc center of all the complexes under investigation, allowing them to possibly function as sensors by a ‘coordinative-based’ approach. Naked-eye color changes occur when treating the systems with HS⁻, so the fluorescence responses are modulated by the presence of HS⁻, which has been related to a change in the energy level and coupling of excited states through a computational study. The results show the potential of the systems to function as HS⁻/H₂S colorimetric and fluorescent sensors. Paper-strip-based sensing experiments foresee the potential of using this family of complexes as chemosensors of HS⁻ in more complex biological fluids.

Updated Functional Roles of NAMPT in Carcinogenesis and Therapeutic Niches

Simple Summary

The advantages and applications of using the non-invasive way to detect serum biomarkers for assessing cancer diagnosis and prognosis have been explored. Nicotinamide phosphoribosyltransferase (NAMPT), also designated as pre-B-cell colony-enhancing factor (PBEF) or visfatin, is a secreted adipokine known to modulate tumor malignancies. Its significance in predicting cancer patient’s survival outcome further renders the implementation of NAMPT in clinical practice. In this review, recent discoveries of NAMPT in cancer studies were focused and integrated. We aim to provide updates for researchers who are proposing relevant objectives.

Abstract

Nicotinamide phosphoribosyltransferase (NAMPT) is notable for its regulatory roles in tumor development and progression. Emerging evidence regarding NAMPT somatic mutations in cancer patients, NAMPT expressional signatures in normal tissues and cancers, and the prognostic significance of NAMPT in many cancer types has attracted attention, and NAMPT is considered a potential biomarker of cancer. Recent discoveries have demonstrated the indirect association and direct biological functions of NAMPT in modulating cancer metastasis, proliferation, angiogenesis, cancer stemness, and chemoresistance to anticancer drugs. These findings warrant further investigation of the underlying mechanisms to provide knowledge for developing novel cancer therapeutics. In this review article, we explore recent research developments involving the oncogenic activities of NAMPT by summarizing current knowledge regarding NAMPT somatic mutations, clinical trials, transcriptome data, and clinical information and discoveries related to the NAMPT-induced signaling pathway in modulating hallmarks of cancer. Furthermore, the comprehensive representation of NAMPT RNA expression in a pancancer panel as well as in specific normal cell types at single-cell level are demonstrated. The results suggest potential sites and cell types that could facilitate NAMPT-related tumorigenesis. With this review, we aim to shed light on the regulatory roles of NAMPT in tumor development and progression, and provide information to guide future research directions in this field.

The nicotinamide phosphoribosyltransferase antagonist FK866 inhibits growth of prostate tumour spheroids and increases doxorubicin retention without changes in drug transporter and cancer stem cell protein expression

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme for nicotinamide adenine dinucleotide (NAD) synthesis and is involved in cancer cell proliferation through regulation of energy production pathways. Therefore, NAMPT inhibitors are promising drugs for cancer therapy by limiting energy supply of tumours. Herein, we demonstrated that the NAMPT inhibitor FK866 ((E)-N-(4-(1-Benzoylpiperidin-4-yl)butyl)-3-(pyridin-3-yl)acrylamide) dose-dependently inhibited growth and cell motility of DU-145 prostate tumour spheroids and decreased the intracellular ATP concentration. The apoptosis marker cleaved caspase-3 remained unchanged, but the autophagy marker microtubule-associated protein 1A/1B-light chain 3 (LC3) was upregulated. Growth inhibition was reversed upon co-administration of NAD to the cell culture medium. FK866 decreased calcein as well as pheophorbide A efflux from tumour spheroids and increased doxorubicin toxicity, indicating interference with function of drug efflux transporters. DU-145 multicellular tumour spheroids expressed the stem cell associated markers CD133, CD44, Oct4, Nanog, Sox2, and drug transporters ABCB1, ABCG2, and ABCC1 which are associated with stem cell properties in cancer cells. The ABCB1 inhibitor zosuquidar, the ABCG2 inhibitor Ko143, and the ABCC1 inhibitor MK571 increased calcein retention. Neither protein expression of stem cell markers, nor drug transporters was significantly changed upon FK866 treatment. In conclusion, our data suggest that FK866 inhibits prostate cancer cell proliferation by interference with the energy metabolism, and function of drug efflux transporters.

Pharmacological induction of mesenchymal-epithelial transition via inhibition of H2S biosynthesis and consequent suppression of ACLY activity in colon cancer cells

Hydrogen sulfide (H₂S) is an important endogenous gaseous transmitter mediator, which regulates a variety of cellular functions in autocrine and paracrine manner. The enzymes responsible for the biological generation of H₂S include cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST). Increased expression of these enzymes and overproduction of H₂S has been implicated in essential processes of various cancer cells, including the stimulation of metabolism, maintenance of cell proliferation and cytoprotection. Cancer cell identity is characterized by so-called "transition states". The progression from normal (epithelial) to transformed (mesenchymal) state is termed epithelial-to-mesenchymal transition (EMT) whereby epithelial cells lose their cell-to-cell adhesion capacity and gain mesenchymal characteristics. The transition process can also proceed in the opposite direction, and this process is termed mesenchymal-to-epithelial transition (MET). The current project was designed to determine whether inhibition of endogenous H₂S production in colon cancer cells affects the EMT/MET balance in vitro. Inhibition of H₂S biosynthesis in HCT116 human colon cancer cells was achieved either with aminooxyacetic acid (AOAA) or 2-[(4-hydroxy-6-methylpyrimidin-2-yl)sulfanyl]-1-(naphthalen-1-yl)ethan-1-one (HMPSNE). These inhibitors induced an upregulation of E-cadherin and Zonula occludens-1 (ZO-1) expression and downregulation of fibronectin expression, demonstrating that H₂S biosynthesis inhibitors can produce a pharmacological induction of MET in colon cancer cells. These actions were functionally reflected in an inhibition of cell migration, as demonstrated in an in vitro "scratch wound" assay. The mechanisms involved in the action of endogenously produced H₂S in cancer cells in promoting (or maintaining) EMT (or tonically inhibiting MET) relate, at least in part, in the induction of ATP citrate lyase (ACLY) protein expression, which occurs via upregulation of ACLY mRNA (via activation of the ACLY promoter). ACLY in turn, regulates the Wnt-β-catenin pathway, an essential regulator of the EMT/MET balance. Taken together, pharmacological inhibition of endogenous H₂S biosynthesis in cancer cells induces MET. We hypothesize that this may contribute to anti-cancer / anti-metastatic effects of H₂S biosynthesis inhibitors.

NAD+ metabolism, stemness, the immune response, and cancer

NAD⁺ was discovered during yeast fermentation, and since its discovery, its important roles in redox metabolism, aging, and longevity, the immune system and DNA repair have been highlighted. A deregulation of the NAD⁺ levels has been associated with metabolic diseases and aging-related diseases, including neurodegeneration, defective immune responses, and cancer. NAD⁺ acts as a cofactor through its interplay with NADH, playing an essential role in many enzymatic reactions of energy metabolism, such as glycolysis, oxidative phosphorylation, fatty acid oxidation, and the TCA cycle. NAD⁺ also plays a role in deacetylation by sirtuins and ADP ribosylation during DNA damage/repair by PARP proteins. Finally, different NAD hydrolase proteins also consume NAD⁺ while converting it into ADP-ribose or its cyclic counterpart. Some of these proteins, such as CD38, seem to be extensively involved in the immune response. Since NAD cannot be taken directly from food, NAD metabolism is essential, and NAMPT is the key enzyme recovering NAD from nicotinamide and generating most of the NAD cellular pools. Because of the complex network of pathways in which NAD⁺ is essential, the important role of NAD⁺ and its key generating enzyme, NAMPT, in cancer is understandable. In the present work, we review the role of NAD⁺ and NAMPT in the ways that they may influence cancer metabolism, the immune system, stemness, aging, and cancer. Finally, we review some ongoing research on therapeutic approaches.

Implications of hydrogen sulfide in liver pathophysiology: Mechanistic insights and therapeutic potential

Background

Over the last several decades, hydrogen sulfide (H₂S) has been found to exert multiple physiological functions in mammal systems. The endogenous production of H₂S is primarily mediated by cystathione β-synthase (CBS), cystathione γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are widely expressed in the liver tissues and regulate hepatic functions by acting on various molecular targets.

Aim of Review

In the present review, we will highlight the recent advancements in the cellular events triggered by H₂S under liver diseases. The therapeutic effects of H₂S donors on hepatic diseases will also be discussed.

Key Scientific Concepts of Review

As a critical regulator of liver functions, H₂S is critically involved in the etiology of various liver disorders, such as nonalcoholic steatohepatitis (NASH), hepatic fibrosis, hepatic ischemia/reperfusion (IR) injury, and liver cancer. Targeting H₂S-producing enzymes may be a promising strategy for managing hepatic disorders.

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

Hydrogen Sulfide: Emerging Role in Bladder, Kidney, and Prostate Malignancies

Hydrogen sulfide (H₂S) is the latest member of the gasotransmitter family and known to play essential roles in cancer pathophysiology. H₂S is produced endogenously and can be administered exogenously. Recent studies showed that H₂S in cancers has both pro- and antitumor roles. Understanding the difference in the expression and localization of tissue-specific H₂S-producing enzymes in healthy and cancer tissues allows us to develop tools for cancer diagnosis and treatment. Urological malignancies are some of the most common cancers in both men and women, and their early detection is vital since advanced cancers are recurrent, metastatic, and often resistant to treatment. This review summarizes the roles of H₂S in cancer and looks at current studies investigating H₂S activity and expression of H₂S-producing enzymes in urinary cancers. We specifically focused on urothelial carcinoma, renal cell carcinoma, and prostate cancer, as they form the majority of newly diagnosed urinary cancers. Recent studies show that besides the physiological activity of H₂S in cancer cells, there are patterns between the development and prognosis of urinary cancers and the expression of H₂S-producing enzymes and indirectly the H₂S levels. Though controversial and not completely understood, studying the expression of H₂S-producing enzymes in cancer tissue may represent an avenue for novel diagnostic and therapeutic strategies for addressing urological malignancies.

Subcellular compartmentalization of NAD+ and its role in cancer: A sereNADe of metabolic melodies

Nicotinamide adenine dinucleotide (NAD+) is an essential biomolecule involved in many critical processes. Its role as both a driver of energy production and a signaling molecule underscores its importance in health and disease. NAD+ signaling impacts multiple processes that are dysregulated in cancer, including DNA repair, cell proliferation, differentiation, redox regulation, and oxidative stress. Distribution of NAD+ is highly compartmentalized, with each subcellular NAD+ pool differentially regulated and preferentially involved in distinct NAD+-dependent signaling or metabolic events. Emerging evidence suggests that targeting NAD+ metabolism is likely to repress many specific mechanisms underlying tumor development and progression, including proliferation, survival, metabolic adaptations, invasive capabilities, heterotypic interactions with the tumor microenvironment, and stress response including notably DNA maintenance and repair. Here we provide a comprehensive overview of how compartmentalized NAD+ metabolism in mitochondria, nucleus, cytosol, and extracellular space impacts cancer formation and progression, along with a discussion of the therapeutic potential of NAD+-targeting drugs in cancer.

Exogenous H2S reduces the acetylation levels of mitochondrial respiratory enzymes via regulating the NAD+-SIRT3 pathway in cardiac tissues of db/db mice

Hydrogen sulfide (H₂S), a gaseous molecule, is involved in modulating multiple physiological functions, such as antioxidant, antihypertension, and the production of polysulfide cysteine. H₂S may inhibit reactive oxygen species generation and ATP production through modulating respiratory chain enzyme activities; however, the mechanism of this effect remains unclear. In this study, db/db mice, neonatal rat cardiomyocytes, and H9c2 cells treated with high glucose, oleate, and palmitate were used as animal and cellular models of type 2 diabetes. The mitochondrial respiratory rate, respiratory chain complex activities, and ATP production were decreased in db/db mice compared with those in db/db mice treated with exogenous H₂S. Liquid chromatography with tandem mass spectrometry analysis showed that the acetylation level of proteins involved in the mitochondrial respiratory chain were increased in the db/db mice hearts compared with those with sodium hydrosulfide (NaHS) treatment. Exogenous H₂S restored the ratio of NAD⁺/NADH, enhanced the expression and activity of sirtuin 3 (SIRT3) and decreased mitochondrial acetylation level in cardiomyocytes under hyperglycemia and hyperlipidemia. As a result of SIRT3 activation, acetylation of the respiratory complexe enzymes NADH dehydrogenase 1 (ND1), ubiquinol cytochrome c reductase core protein 1, and ATP synthase mitochondrial F1 complex assembly factor 1 was reduced, which enhanced the activities of the mitochondrial respiratory chain activity and ATP production. We conclude that exogenous H₂S plays a critical role in improving cardiac mitochondrial function in diabetes by upregulating SIRT3.

Cystathione β-Synthase Is Increased in Thyroid Malignancies

BACKGROUND

Cystathione β-synthase (CBS) catalyzes the conversion of homocysteine and cysteine to hydrogen sulfide (H₂S) and cystathione, via the trans-sulfuration pathway. CBS protein expression levels are increased in several different human malignancies, with increased protein expression correlating with parameters such as tumor stage, anaplasia, metastases, and chemotherapy resistance.

MATERIALS AND METHODS

This study employed tissue microarrays to examine CBS expression in benign thyroid tissue, thyroid oncocytomas, thyroid follicular adenomas, and in follicular, papillary, anaplastic, and medullary thyroid carcinomas.

RESULTS

CBS expression was increased in all thyroid carcinomas types compared to benign thyroid tissue, but not in thyroid follicular adenomas or oncocytomas. A similar pattern was observed for nicotinamide phosphoribosyltransferase (NAMPT) tissue microarray analysis comparing thyroid adenomas and follicular carcinomas.

CONCLUSION

For the first time, we showed that an H₂S-syntheszing enzyme plays a role in thyroid malignancies. Additionally, our data suggest that CBS and NAMPT immunohistochemistry may be useful in differentiating follicular adenomas from follicular carcinomas.

The Ataxia telangiectasia-mutated and Rad3-related protein kinase regulates cellular hydrogen sulfide concentrations

The ataxia telangiectasia-mutated and Rad3-related (ATR) serine/threonine kinase plays a central role in the repair of replication-associated DNA damage, the maintenance of S and G2/M-phase genomic stability, and the promotion of faithful mitotic chromosomal segregation. A number of stimuli activate ATR, including persistent single-stranded DNA at stalled replication folks, R loop formation, hypoxia, ultraviolet light, and oxidative stress, leading to ATR-mediated protein phosphorylation. Recently, hydrogen sulfide (H₂S), an endogenous gasotransmitter, has been found to regulate multiple cellular processes through complex redox reactions under similar cell stress environments. Three enzymes synthesize H₂S: cystathionine-β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase. Since H₂S can under some conditions cause DNA damage, we hypothesized that ATR activity may regulate cellular H₂S concentrations and H₂S-syntheszing enzymes. Here we show that human colorectal cancer cells carrying biallelic knock-in hypomorphic ATR mutations have lower cellular H₂S concentrations than do syngeneic ATR wild-type cells, and all three H₂S-synthesizing enzymes show lower protein expression in the ATR hypomorphic mutant cells. Additionally, ATR serine 428 phosphorylation is altered by H₂S donor and H₂S synthesis enzyme inhibition, while the oxidative-stress induced phosphorylation of the ATR-regulated protein CHK1 on serine 345 is increased by H₂S synthesis enzyme inhibition. Lastly, inhibition of H₂S production potentiated oxidative stress-induced double-stranded DNA breaks in the ATR hypomorphic mutant compared to ATR wild-type cells. Our findings demonstrate that the ATR kinase regulates and is regulated by H₂S.

Hydrogen Sulfide-Synthesizing Enzymes Are Altered in a Case of Oral Cavity Mucoepidermoid Carcinoma

Mucoepidermoid carcinoma (MEC) is the most common malignant epithelial neoplasm of the salivary glands. MECs of the mouth floor are rare, with only a few cases reported. Here we report a MEC of the mouth floor in a 55-year-old woman. Since several studies have shown that hydrogen sulfide (H₂S)-synthesizing enzymes are often increased in malignant tumors compared to benign counterpart tissues, we used western blotting to compare the protein levels of cystathionine-β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST) in a mouth floor MEC to adjacent benign oral mucosae. We also used high-performance liquid chromatography to quantify possible differences in tissue sulfur fraction concentrations between the two biopsy types. Last, we used western blotting to examine nicotinamide phosphoribosyl transferase (Nampt), mitoNEET, and phospho-ser727-Stat3 levels in the biopsies. We found that all the proteins and phospho-ser727-Stat3 are increased in the MEC compared to benign mucosae. Interestingly, free H₂S levels, acid-labile, and the sulfane sulfur factions were essentially the same between the MEC and benign tissue. Although limited to a single and unusual tumor type, to our knowledge this is only the third time H₂S concentrations were directly quantified inside a human tumor. Last, our results replicate those of two previous studies where the H₂S-synthesizing enzymes are increased in a malignant tumor, while free H₂S is either not increased or only slightly increased, suggesting that malignant tumors rapidly metabolize H₂S as part of tumor maintenance and growth.

Hydrogen Sulfide and Hydrogen Sulfide-Synthesizing Enzymes Are Altered in a Case of Oral Adenoid Cystic Carcinoma

Adenoid cystic carcinomas (ACC) constitute 1% of all head and neck malignancies and are very rare in the oral cavity. With < 60 oral ACCs described, their pathobiology is incompletely understood. Here, we report a case of oral cavity ACC in a 54-year-old woman. Since recent studies have demonstrated that several human tumors overexpress the hydrogen sulfide (H₂S)-synthesizing enzymes cystathionine-β-synthase (CBS), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST), and also show dysregulated H₂S levels, we examined these biomarkers in the oral ACC and compared the results to those of adjacent benign oral epithelium. Western blotting was used to compare the protein expression of CBS, CSE, 3-MST, nicotinamide phosphoribosyl transferase, and mitoNEET in ACC and adjacent benign oral mucosae. High-performance liquid chromatography was used to quantify the differences in tissue H₂S concentrations between the two biopsy types. We found that all the proteins examined here were increased in the ACC compared to adjacent benign oral mucosae. Interestingly, H₂S concentrations were decreased approximately 30% in ACC compared to benign mucosae. Thus, in one example of this rare tumor type, the enzymes that synthesize H₂S are increased, while tissue H₂S levels are lower than those found in adjacent benign oral mucosae. Although limited to a single rare tumor type, to our knowledge this is the second time H₂S concentrations have been directly quantified inside a human tumor. Last, our results may indicate that alterations in H₂S synthesis and metabolism may be important in the pathobiology of ACC.

Hydrogen Sulfide Is Increased in Oral Squamous Cell Carcinoma Compared to Adjacent Benign Oral Mucosae

BACKGROUND/AIM

Hydrogen sulfide (H2S) and the enzymes that synthesize it, cystathionine-b-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate, are increased in different human malignancies. Due to its short half-life, H2S concentrations have not been directly measured in a human malignancy. Here we directly measured in vivo H2S levels within oral squamous cell carcinoma (OSCC).

PATIENTS AND METHODS

Punch biopsies of OSCC and benign mucosae from 15 patients were analyzed by HPLC, western blotting, and tissue microarray analyses.

RESULTS

H2S concentrations were significantly higher in OSCC compared to adjacent benign oral mucosae. Western blot and tissue microarray studies revealed significantly increased cystathionine-b-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate, phopho-Stat3, mitoNEET, hTERT, and MAPK protein levels in OSCC.

CONCLUSION

H2S concentrations and the enzymes that synthesize it are significantly increased in OSCC. Here, for the first time H2S concentrations within a living human malignancy were measured and compared to adjacent counterpart benign tissue.

H2S Activated Drug Release from Protein Cages

We took advantage of gasotransmitter H₂S as a chemical reaction-based trigger for controlled release of doxorubicin which is precoordinated by copper ions and enclosed in horse spleen apoferritin. The nanocomposite is stable at physiological pH and temperature before H₂S activation. The drug release process avoids disassembly of protein shells and is controllable by the strong affinity of sulfide with copper ions. The in vitro cytotoxicity assay indicates the antitumor effect of doxorubicin toward tumor cells could be achievable by H₂S activation.

The NAMPT/E2F2/SIRT1 axis promotes proliferation and inhibits p53-dependent apoptosis in human melanoma cells

Melanoma is the most common primary malignant neoplasm in adults, causing more deaths than any other skin cancer, necessitating the development of new target-based approaches. Current evidence suggests SIRT1, the mammalian nicotinamide adenine dinucleotide (NAD⁺)-dependent protein deacetylase, and nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting NAD⁺ biosynthetic enzyme, together comprise a novel systemic regulatory network to play a pivotal role in cell proliferation and apoptosis. Nevertheless, how the regulation of this cofactor interfaces with signal transduction network remains poorly understood in melanoma. Here, we report NAMPT is highly expressed in melanomaassociated with poor overall survival in patients. Pharmacological and genetic inhibition of NAMPT decreased NAD⁺ levels and melanoma cell proliferation capacity, and NAMPT knockdown induced apoptosis through the activity of the tumor suppressor p53. Next, we demonstrate NAMPT regulates the transcription factor E2F family member 2 (E2F2) in the apoptosis process. Downstream, E2F2 control the mRNA and protein levels of SIRT1. Finally, we find NAMPT mediates the apoptosis resistance of melanoma cells through NAMPT-E2F2-SIRT1 axis, more than NAD⁺-driven transcriptional program. Accordingly, our results demonstrated that NAMPT is a prognostic marker in melanoma, and the identificationofNAMPT-E2F2-SIRT1 pathway establishes another link between NAMPT and apoptosis events in melanoma, with therapeutic implications for this deadly cancer.

Increased Nicotinamide Phosphoribosyltransferase and Cystathionine-β-Synthase in Renal Oncocytomas, Renal Urothelial Carcinoma, and Renal Clear Cell Carcinoma

BACKGROUND

Renal oncocytomas (ROs), and clear cell (RCC) and urothelial carcinomas (UC), are common renal neoplasms. Nicotinamide phosphoribosyltransferase (Nampt) catalyzes the rate-limiting step of NAD⁺ synthesis and its expression is increased in several tumors. Nampt concomitantly regulates hydrogen sulfide (H₂S)-synthesizing enzyme levels, including cystathionine-β-synthase (CBS).

MATERIALS AND METHODS

We used tissue microarrays to examine Nampt and the H₂S-synthesizing enzyme CBS protein levels in benign kidney, RCC, UC and ROs.

RESULTS

Compared to benign kidney, all three neoplasms showed increased Nampt and CBS protein levels, with the levels increasing in RCC at higher Fuhrman grades.

CONCLUSION

H₂S is known to ameliorate chronic renal failure but, as yet, no role for H₂S in renal neoplasia has been demonstrated. Here, we showed, for the first time, that Nampt, CBS and, likely, H₂S likely play a role in malignant and benign neoplastic renal disease.

Role of the cystathionine β-synthase/H2S system in liver cancer cells and the inhibitory effect of quinolone-indolone conjugate QIC2 on the system

Hydrogen sulfide (H2S), the third gasotransmitter, plays important roles in cancer biological processes. As endogenous H2S exerts pro-cancer functions, inhibition of its production in cancer cells may provide a new cancer treatment strategy and be achieved via regulation of the function of cystathionine β-synthase (CBS), one of the main metabolic enzymes synthesizing H2S. This enzyme plays important roles in the development and progression of colon and ovarian cancer, primarily regulating mitochondrial bioenergetics and accelerating cell cycle progression. In the present study, we firstly investigated the role of the CBS/H2S system in human hepatoma cells, and then the inhibitory effect of a quinolone-indolone conjugate QIC2 on this system. When CBS was overexpressed in human hepatoma HepG2 and SMMC-7721 cells, inhibition of endogenous CBS/H2S significantly reduced their viability and growth rate, as well as the proliferation of SMMC-7721 cells. Meanwhile, CBS knockdown caused multiple effects, including apoptosis of SMMC-7721 cells, an increase in the Bcl-2-associated X protein (Bax)/B cell lymphoma/leukemia (Bcl-2) ratio, activation of caspase-3 and polyADP-ribose polymerase (PARP), when compared with the scramble siRNA (Sc siRNA)-transfected groups. Heme oxygenase-1 (HO-1; a microsomal enzyme) expression was significantly decreased while the reactive oxygen species (ROS) level was increased in the CBS siRNA-transfected SMMC-7721 cells. QIC2 significantly reduced SMMC-7721 cell viability in a dose-dependent manner and showed a lower toxicity in human normal liver HL-7702 cells relative to the positive controls sunitinib and doxorubicin (DOX). The compound also inhibited cell proliferation and induced cell apoptosis in SMMC-7721 cells. Further analysis indicated that QIC2 downregulated the CBS/H2S system, decreased both HO-1 protein and glutathione (GSH) levels while increased the ROS level and activated the caspase-3 cascade. Collectively, our results demonstrated that the CBS/H2S system plays important roles in human hepatoma cells and QIC2 significantly inhibited cell growth via downregulation of the system.

Replicative Senescence in Human Fibroblasts Is Delayed by Hydrogen Sulfide in a NAMPT/SIRT1 Dependent Manner

Recent evidence suggests that hydrogen sulfide (H2S) has cytoprotective and anti-aging effects. However, the mechanisms for such properties are not fully understood. Here, we show that the expression of the main H2S producing enzyme, CBS, and production of H2S are coordinately diminished in replicative senescent adult human dermal fibroblasts. The reduced production of H2S falls within the same time-frame that the hallmarks of replicative senescence appear including accumulation of SA-β-Gal, enhanced expression of p16, p21, and RRM2B while the expression of RRM2, hTERT, SIRT1, NAMPT, and NAD/NADH ratio all fall. Exogenous H2S increases the expression of hTERT, NAMPT, SIRT1 and NAD/NADH ratio in treated cells. Moreover, H2S safeguards the expression of hTERT in a NAMPT and SIRT1 dependent manner and delays the onset of replicative senescence as evidenced by reduced accumulation of age associated SA-β-Gal and cessation of proliferation. Postponement of loss of cell proliferative capacity without risk of mutagenesis shows implications for use of H2S in delaying the adverse effects of senescence in organisms.

Regulation and role of endogenously produced hydrogen sulfide in angiogenesis

Recent studies have implicated endogenously produced H₂S in the angiogenic process. On one hand, pharmacological inhibition and silencing of the enzymes involved in H₂S synthesis attenuate the angiogenic properties of endothelial cells, including proliferation, migration and tube-like structure network formation. On the other hand, enhanced production of H₂S by substrate supplementation or over-expression of H₂S-producing enzymes leads to enhanced angiogenic responses in cultured endothelial cells. Importantly, H₂S up-regulates expression of the key angiogenic factor vascular endothelial growth factor (VEGF) and contributes to the angiogenic signaling in response to VEGF. The signaling pathways mediating H₂S-induced angiogenesis include mitogen-activated protein kinases, phosphoinositide-3 kinase, nitric oxide/cGMP-regulated cascades and ATP-sensitive potassium channels. Endogenously produced H₂S has also been shown to facilitate neovascularization in prototypical model systems in vivo, and to contribute to wound healing, post-ischemic angiogenesis in the heart and other tissues, as well as in tumor angiogenesis. Targeting of H₂S synthesizing enzymes might offer novel therapeutic opportunities for angiogenesis-related diseases.

Nicotinamide phosphoribosyltransferase (Nampt) in carcinogenesis: new clinical opportunities

INTRODUCTION

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that catalyzes the first step in the mammalian nicotinamide adenine dinucleotide (NAD) salvage pathway. Aberrant NAD metabolism was associated with oncogenic signal transduction, suggesting the critical roles of Nampt in tumorigenesis and metastasis. Additionally, Nampt can be secreted out of the cell, and this extracellular form of Nampt (eNampt) was shown to induce inflammation and angiogenesis due to its cytokine activity, which may also be involved in carcinogenesis.

AREAS COVERED

This article reviews recent advances in the studies of Nampt in carcinogenesis, with a special highlight on Nampt inhibitors and future clinical application, including cancer diagnosis, prognosis and therapy. Expert commentary: Nampt not only maintains the balance of cellular metabolism, but also has a profound influence on multiple aspects of carcinogenesis. Therefore, elucidation of these mechanisms opens the door for future clinical applications targeting this protein. Additional studies are needed to address important questions including the relationship between extracellular Nampt and carcinogenesis.

Organelle-Targeted H2S Probes Enable Visualization of the Subcellular Distribution of H2S Donors

Hydrogen sulfide (H2S) is an essential biological signaling molecule in diverse biological regulatory pathways. To provide new chemical tools for H2S imaging, we report here a fluorescent H2S detection platform (HSN2-BG) that is compatible with subcellular localization SNAP-tag fusion protein methodologies and use appropriate fusion protein constructs to demonstrate mitochondrial and lysosomal localization. We also demonstrate the efficacy of this detection platform to image endogenous H2S in Chinese hamster ovary (CHO) cells and use the developed constructs to report on the subcellular H2S distributions provided by common H2S donor molecules AP39, ADT-OH, GYY4137, and diallyltrisulfide (DATS). The developed constructs provide a platform poised to provide new insights into the subcellular distribution of common H2S donors and a useful tool for investigating H2S biochemistry.

Biological signaling by small inorganic molecules

Small redox active molecules such as reactive nitrogen and oxygen species and hydrogen sulfide have emerged as important biological mediators that are involved in various physiological and pathophysiological processes. Advancement in understanding of cellular mechanisms that tightly regulate both generation and reactivity of these molecules is central to improved management of various disease states including cancer and cardiovascular dysfunction. Imbalance in the production of redox active molecules can lead to damage of critical cellular components such as cell membranes, proteins and DNA and thus may trigger the onset of disease. These small inorganic molecules react independently as well as in a concerted manner to mediate physiological responses. This review provides a general overview of the redox biology of these key molecules, their diverse chemistry relevant to physiological processes and their interrelated nature in cellular signaling.

Gasotransmitters in cancer: from pathophysiology to experimental therapy

The three endogenous gaseous transmitters - nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) - regulate a number of key biological functions. Emerging data have revealed several new mechanisms for each of these three gasotransmitters in tumour biology. It is now appreciated that they show bimodal pharmacological character in cancer, in that not only the inhibition of their biosynthesis but also elevation of their concentration beyond a certain threshold can exert anticancer effects. This Review discusses the role of each gasotransmitter in cancer and the effects of pharmacological agents - some of which are in early-stage clinical studies - that modulate the levels of each gasotransmitter. A clearer understanding of the pharmacological character of these three gases and the mechanisms underlying their biological effects is expected to guide further clinical translation.

Endogenously produced hydrogen sulfide is involved in porcine oocyte maturation in vitro

Hydrogen sulfide, one of three known gasotransmitters, is involved in physiological processes, including reproductive functions. Oocyte maturation and surrounding cumulus cell expansion play an essential role in female reproduction and subsequent embryonic development. Although the positive effects of exogenous hydrogen sulfide on maturing oocytes are well known, the role of endogenous hydrogen sulfide, which is physiologically released by enzymes, has not yet been described in oocytes. In this study, we observed the presence of Cystathionine β-Synthase (CBS), Cystathionine γ-Lyase (CTH) and 3-Mercaptopyruvate Sulfurtransferase (3-MPST), hydrogen sulfide-releasing enzymes, in porcine oocytes. Endogenous hydrogen sulfide production was detected in immature and matured oocytes as well as its requirement for meiotic maturation. Individual hydrogen sulfide-releasing enzymes seem to be capable of substituting for each other in hydrogen sulfide production. However, meiosis suppression by inhibition of all hydrogen sulfide-releasing enzymes is not irreversible and this effect is a result of M-Phase/Maturation Promoting Factor (MPF) and Mitogen-Activated Protein Kinase (MAPK) activity inhibition. Futhermore, cumulus expansion expressed by hyaluronic acid (HA) production is affected by the inhibition of hydrogen sulfide production. Moreover, quality changes of the expanded cumuli are indicated. These results demonstrate hydrogen sulfide involvement in oocyte maturation as well as cumulus expansion. As such, hydrogen sulfide appears to be an important cell messenger during mammalian oocyte meiosis and adequate cumulus expansion.

Inhibition of endogenous hydrogen sulfide production in clear-cell renal cell carcinoma cell lines and xenografts restricts their growth, survival and angiogenic potential

Clear cell renal cell carcinoma (ccRCC) is characterized by Von Hippel-Lindau (VHL)-deficiency, resulting in pseudohypoxic, angiogenic and glycolytic tumours. Hydrogen sulfide (H2S) is an endogenously-produced gasotransmitter that accumulates under hypoxia and has been shown to be pro-angiogenic and cytoprotective in cancer. It was hypothesized that H2S levels are elevated in VHL-deficient ccRCC, contributing to survival, metabolism and angiogenesis. Using the H2S-specific probe MeRhoAz, it was found that H2S levels were higher in VHL-deficient ccRCC cell lines compared to cells with wild-type VHL. Inhibition of H2S-producing enzymes could reduce the proliferation, metabolism and survival of ccRCC cell lines, as determined by live-cell imaging, XTT/ATP assay, and flow cytometry respectively. Using the chorioallantoic membrane angiogenesis model, it was found that systemic inhibition of endogenous H2S production was able to decrease vascularization of VHL-deficient ccRCC xenografts. Endogenous H2S production is an attractive new target in ccRCC due to its involvement in multiple aspects of disease.