The role of mammalian sirtuins in cancer metabolism

O-GlcNAcylation and stablization of SIRT7 promote pancreatic cancer progression by blocking the SIRT7-REGγ interaction

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers and its dismal prognosis indicates the urgent need to elucidate the potential oncogenic mechanisms. SIRT7 is a classic NAD+-dependent deacetylase that stabilizes the transformed state of cancer cells. However, its functional roles in PDAC are still unclear. Here, we found that SIRT7 expression is upregulated and predicts poor prognosis in PDAC. Then we screened the new interacting proteins of SIRT7 by mass spectrometry and the results showed that SIRT7 can interact with O-GlcNAc transferase (OGT). O-GlcNAcylation stabilizes the SIRT7 protein by inhibiting its interaction with REGγ to prevent degradation, and hyper-O-GlcNAcylation in pancreatic cancer cells leads to hypoacetylation of H3K18 via SIRT7, which promotes transcriptional repression of several tumour suppressor genes. In addition, SIRT7 O-GlcNAcylation at the serine 136 residue (S136) is required to maintain its protein stability and deacetylation ability. In vivo and in vitro experiments showed that blocking SIRT7 O-GlcNAcylation at S136 attenuates tumour progression. Collectively, we demonstrate that O-GlcNAcylation is an important post-translational modification of SIRT7 in pancreatic cancer cells, and elucidating this mechanism of SIRT7 is expected to pave the way for the development of novel therapeutic methods in the future.

Sirtuins are crucial regulators of T cell metabolism and functions

It is well known that metabolism underlies T cell differentiation and functions. The pathways regulating T cell metabolism and function are interconnected, and changes in T cell metabolic activity directly impact the effector functions and fate of T cells. Thus, understanding how metabolic pathways influence immune responses and ultimately affect disease progression is paramount. Epigenetic and posttranslational modification mechanisms have been found to control immune responses and metabolic reprogramming. Sirtuins are NAD⁺-dependent histone deacetylases that play key roles during cellular responses to a variety of stresses and have recently been reported to have potential roles in immune responses. Therefore, sirtuins are of significant interest as therapeutic targets to treat immune-related diseases and enhance antitumor immunity. This review aims to illustrate the potential roles of sirtuins in different subtypes of T cells during the adaptive immune response.

Sirtuins, enzymes that regulate how cells respond to stress, regulate T cell metabolism and functions, and therefore blocking or boosting sirtuins influences immune responses. As part of the immune system, some types of T cells attack specific targets; others keep the immune response in check. Imene Hamaidi and Sungjune Kim at H. Lee Moffitt Cancer Center, Tampa, USA, have reviewed how sirtuins affect different subsets of T cells to either promote or suppress immune responses. Boosting sirtuins that increase the function of inflammation-suppressing T cells can improve outcomes for transplant recipients or help treat autoimmune diseases. Conversely, stimulating immune-activating sirtuins can help re-energize exhausted antitumor T cells. Understanding the complex web of sirtuin–T cell interactions may help in developing therapeutic strategies for improving transplant outcomes, and for treating autoimmune diseases and cancer.

Sirt3, 6, and 7 Genes Expression in Gastric Antral Epithelial Cells of Patients with Helicobacter pylori Infection

Sirtuins, known as the intracellular acylation enzymes, play a major role in regulating the cell's physiological activities. The relevant studies have shown diversely sirtuin genes expression in various cancers in humans. This study has surveyed the transcription of sirt3, 6, and 7 genes in gastric antral epithelial cells (GAECs) of gastritis and gastric adenocarcinoma patients with and without Helicobacter pylori infection. First of all, a case-control study was conducted, including 50 and 53 gastric antral biopsy samples collected from gastritis and gastric adenocarcinoma patients with and without H. pylori infection referred to hospitals of Sanandaj City during 2018-2019. Total RNAs were extracted from biopsy samples, then cDNAs were synthesized by using TaKaRa kits. Quality essay of H. pylori virulence genes expression and relative quantitative essay of sirt3, 6, and 7 genes expressions in gastric antral biopsy samples were performed using the real-time RT-PCR method. The statistical analysis showed the significant correlations between H. pylori vacA s1m2 and sabA cDNAs with sirt3 geneś expression in GAECs (P < 0.05, 0.05 respectively). In addition, sirt6 gene's expression decreased along increasing age in gastric adenocarcinoma patients (P < 0.05). The samples of gastritis patients with gastric antral epithelial biopsy containing H. pylori hopQII, oipA, and sabB cDNA showed an increased amount of sirt7 genes expression (P < 0.05, 0.05, and 0.05 respectively). In conclusion, the H. pylori virulence genes expression and increasing age of patients showed the significant correlations with sirt3, 6, and 7 genes expressions in GAECs of gastric and gastric cancer patients.

α-Hederin inhibits the growth of lung cancer A549 cells in vitro and in vivo by decreasing SIRT6 dependent glycolysis

CONTEXT

α-Hederin, a potent bioactive compound of Pulsatilla chinensis (Bunge) Regel (Ranunculaceae), has many pharmacological uses, but its effect on cancer cell metabolism is still unclear.

OBJECTIVE

To elucidate the role of α-hederin in the glucose metabolism of lung cancer cells.

MATERIALS AND METHODS

Cell Counting Kit 8 and colony formation assays were employed to assess the antiproliferative effects of α-hederin. Glucose uptake, ATP generation, and lactate production were measured. Glycolysis-related proteins were detected using western blotting, and a sirtuin 6 (SIRT6) inhibitor was used to verify A549 cell proliferation. Sixty male BALB/c nude mice were divided into normal control, 5-FU (25 mg/kg), and α-hederin (5 and 10 mg/kg) groups to assess the antitumor effect for 32 days. Glycolysis-related protein expression was evaluated using immunohistochemical analysis.

RESULTS

α-Hederin inhibited A549 (IC₅₀ = 13.75 μM), NCI-H460 (IC₅₀ = 17.57 μM), and NCI-H292 (IC₅₀ = 18.04 μM) proliferation; inhibited glucose uptake and ATP generation; and reduced lactate production. Furthermore, α-hederin (10 and 15 μM) markedly inhibited hexokinase 2, glucose transporter 1, pyruvate kinase M2, lactate dehydrogenase A, monocarboxylate transporter, c-Myc, hypoxia-inducible factor-1α, and activated SIRT6 protein expression. Using a SIRT6 inhibitor, we demonstrated that α-hederin inhibits glycolysis by activating SIRT6. A tumour xenograft mouse model of lung cancer confirmed that α-hederin (5 and 10 mg/kg) inhibits lung cancer growth by inhibiting glycolysis in vivo.

DISCUSSION AND CONCLUSIONS

α-Hederin inhibits A549 cell growth by inhibiting SIRT6-dependent glycolysis. α-Hederin might serve as a potential agent to suppress cancer.

Sirtuins as Metabolic Regulators of Immune Cells Phenotype and Function

Beyond its role on the conversion of nutrients into energy and biomass, cellular metabolism is actively involved in the control of many physiological processes. Among these, it is becoming increasingly evident that specific metabolic pathways are associated with the phenotype of several immune cell types and, importantly, are crucial in controlling their differentiation, proliferation, and effector functions, thus shaping the immune response against pathogens and tumors. In this context, data generated over the last decade have uncovered mammalian sirtuins as important regulators of cellular metabolism, immune cell function, and cancer. Here, we summarize our current knowledge on the roles of this family of protein deacylases on the metabolic control of immune cells and their implications on immune-related diseases and cancer.

Molecular imaging of NAD+ -dependent deacetylase SIRT1 in the brain

INTRODUCTION

Aging is an inevitable physiological process and the biggest risk factor of Alzheimer's disease (AD). Developing an imaging tracer to visualize aging-related changes in the brain may provide a useful biomarker in elucidating neuroanatomical mechanisms of AD.

METHODS

We developed and characterized a new tracer that can be used to visualize SIRT1 in brains related to aging and AD by positron emission tomography imaging.

RESULTS

The SIRT1 tracer displayed desirable brain uptake and selectivity, as well as stable metabolism and proper kinetics and distribution in rodent and nonhuman primate brains. This new tracer was further validated by visualizing SIRT1 in brains of AD transgenic mice, compared to nontransgenic animals.

DISCUSSION

Our SIRT1 tracer not only enables, for the first time, the demonstration of SIRT1 in animal brains, but also allows visualization and recapitulation of AD-related SIRT1 neuropathological changes in animal brains.

Cyclic Tripeptide-based Potent and Selective Human SIRT5 Inhibitors

BACKGROUND

SIRT5 is one of the seven members (SIRT1-7) of the mammalian sirtuin family of protein acyl-lysine deacylase enzymes. In recent years, important regulatory roles of SIRT5 in (patho)physiological conditions (e.g. metabolism and cancer) have been increasingly demonstrated. For a better biological understanding and therapeutic exploitation of the SIRT5- catalyzed deacylation reaction, more effort on identifying potent and selective SIRT5 inhibitors beyond those currently known would be rewarding.

OBJECTIVE

In the current study, we would like to see if it would be possible to develop potent and selective SIRT5 inhibitory lead compounds with a novel structural scaffold than those of the currently known potent and selective SIRT5 inhibitors.

METHODS

In the current study, six N-terminus-to-side chain cyclic tripeptides (i.e. 8-13) each harboring the thiourea-type catalytic mechanism-based SIRT5 inhibitory warhead Nε-carboxyethylthiocarbamoyl- lysine as the central residue were designed, synthesized by the Nα-9- fluorenylmethoxycarbonyl (Fmoc) chemistry-based solid phase peptide synthesis (SPPS) on the Rink amide 4-methylbenzhydrylamine (MBHA) resin, purified by the semi-preparative reversedphase high performance liquid chromatography (RP-HPLC), characterized by the high-resolution mass spectrometry (HRMS); and were evaluated by the in vitro sirtuin inhibition assay and the in vitro proteolysis assay.

RESULTS

Among the cyclic tripeptides 8-13, we found that 10 exhibited a potent (IC50 ~2.2 μM) and selective (≥60-fold over the SIRT1/2/3/6-catalyzed deacylation reactions) inhibition against the SIRT5-catalyzed desuccinylation reaction. Moreover, 10 was found to exhibit a ~42.3-fold stronger SIRT5 inhibition and a greater proteolytic stability than its linear counterpart 14.

CONCLUSION

With a novel and modular structural scaffold as compared with those of all the currently reported potent and selective SIRT5 inhibitors, 10 could be also a useful and feasible lead compound for the quest for superior SIRT5 inhibitors as potential chemical/pharmacological probes of SIRT5 and therapeutics for human diseases in which SIRT5 desuccinylase activity is upregulated.

Sirtuins' Deregulation in Bladder Cancer: SIRT7 Is Implicated in Tumor Progression through Epithelial to Mesenchymal Transition Promotion

Sirtuins are emerging players in cancer biology and other age-related disorders, and their putative role in bladder cancer (BlCa) remains elusive. Further understanding of disease biology may allow for generation of more effective pathway-based biomarkers and targeted therapies. Herein, we aimed to illuminate the role of sirtuins’ family in BlCa and evaluate their potential as disease biomarkers and therapeutic targets. SIRT1-7 transcripts and protein levels were evaluated in a series of primary BlCa and normal bladder mucosa tissues. SIRT7 knockdown was performed through lentiviral transduction in MGHU3, 5637 and J82 cells and its functional role was assessed. SIRT1, 2, 4 and 5 expression levels were significantly lower in BlCa, whereas SIRT6 and 7 were overexpressed, and these results were corroborated by TCGA cohort analysis. SIRT7 transcript levels were significantly decreased in muscle-invasive vs. papillary BlCa. In vitro studies showed that SIRT7 downregulation promoted cells migration and invasion. Accordingly, increased EMT markers expression and decreased E-Cadherin (CDH1) was observed in those BlCa cells. Moreover, increased EZH2 expression and H3K27^me3 deposition in E-Cadherin promoter was found in sh-SIRT7 cells. We demonstrated that sirtuins are globally deregulated in BlCa, and specifically SIRT7 downregulation is implicated in EMT, fostering BlCa invasiveness through EZH2-CDH1 axis.

Review: The plant sirtuins

The sirtuin family of intracellular enzymes are able to catalyze a unique β-nicotinamide adenine dinucleotide (β-NAD⁺)-dependent N^ε-acyl-lysine deacylation reaction on histone and non-histone protein substrates. Since 2000, the sirtuin family members have been identified in both prokaryotes and eukaryotes; tremendous accomplishments have also been achieved on the mechanistic and functional (pharmacological) understanding of the sirtuin-catalyzed deacylation reaction. Among the eukaryotic organisms, past research has been focused more on the yeast and mammalian sirtuins than on the plant sirtuins, however, the very presence of sirtuins in various plant species and the functional studies on plant sirtuins published thus far attest to the importance of this particular subfamily of eukaryotic sirtuins in regulating the growth and development of plants and their responses to biotic and abiotic stresses. In this review, an integrated and updated account will be presented on the biochemical, cellular, and functional profiles of all the plant sirtuins identified thus far. It is hoped that this article will also set a stage for expanded efforts in the identification, characterization, and functional interrogation of plant sirtuins; and the development and exploration of their chemical modulators (activators and inhibitors) in plant research and agriculture.

Sirtuins and SIRT6 in Carcinogenesis and in Diet

Sirtuins are a highly conserved family of nicotinamide adenine dinucleotide (NAD)-dependent protein lysine modifying enzymes. They are key regulators for a wide variety of cellular and physiological processes such as cell proliferation, differentiation, DNA damage and stress response, genome stability, cell survival, metabolism, energy homeostasis, organ development and aging. Aging is one of the major risk factors of cancer, as many of the physiological mechanisms and pathologies associated with the aging process also contribute to tumor initiation, growth and/or metastasis. This review focuses on one the mammalian sirtuins, SIRT6, which has emerged as an important regulator of longevity and appears to have multiple biochemical functions that interfere with tumor development and may be useful in cancer prevention and for site-specific treatment. The recent evidence of the role of SIRT6 in carcinogenesis is also discussed, focusing on the potential use of SIRT6 modulators in cancer nanomedicine.

SIRT5 Promotes Hepatocellular Carcinoma Progression by Regulating Mitochondrial Apoptosis

SIRT5 belongs to a family of NAD⁺-dependent lysine deacetylases called sirtuins. Although accumulating evidence indicates SIRT5 upregulation in cancers, including liver cancer, the detailed roles and mechanisms remain to be revealed. Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths among men worldwide, and finding effective targets for HCC treatment and prevention is urgently needed. In the present study, we confirmed that mitochondrial sirtuins, particularly SIRT5, are more highly expressed in HCC cell lines than in normal liver cell lines. Moreover, SIRT5 knockdown suppresses HCC cell proliferation and SIRT5 overexpression promotes HCC cell proliferation. Furthermore, we verified that SIRT5 knockdown increases HCC cell apoptosis via the mitochondrial pathway. By co-IP and western blotting, we illustrated that SIRT5 deacetylates cytochrome c thus regulating HCC cell apoptosis. Taken together, our findings suggest that SIRT5 may function as a prognostic factor and drug target for HCC treatment.

Dual Tumor Suppressor and Tumor Promoter Action of Sirtuins in Determining Malignant Phenotype

Sirtuins (SIRTs), class III histone deacetylases, are differentially expressed in several human cancers, where they display both oncogenic and tumor-suppressive properties depending on cellular context and experimental conditions. SIRTs are involved in many important biological processes and play a critical role in cancer initiation, promotion, and progression. A growing body of evidence indicates the involvement of SIRTs in regulating three important tumor processes: epithelial-to-mesenchymal transition (EMT), invasion, and metastasis. Many SIRTs are responsible for cellular metabolic reprogramming and drug resistance by inactivating cell death pathways and promoting uncontrolled proliferation. In this review, we summarize current knowledge on the role of SIRTs in cancer and discuss their puzzling dual function as tumor suppressors and tumor promoters, important for the future development of novel tailored SIRT-based cancer therapies.

Cyclic Peptide-Based Sirtuin Substrates

In the current study, four side chain-to-side chain cyclic peptides (three 5-mers and one 4-mer) harboring Nε-acetyl-lysine or Nε-myristoyl-lysine were found to be in vitro substrates of the human SIRT1/2/3-catalyzed deacylation with good substrate activities, as judged by the kcat/KM ratios.

Functional genetic variants within the SIRT2 gene promoter in type 2 diabetes mellitus

AIMS

Type 2 diabetes mellitus (T2D) is a common and complex metabolic diseases caused by interactions between environmental and genetic factors. Genome-wide association studies have identified more than 80 common genetic variants for T2D, which account for only ∼10% of the heritability of T2D cases. SIRT2, a member of NAD(+)-dependent class III deacetylases, is involved in genomic stability, metabolism, inflammation, oxidative stress and autophagy. In maintaining metabolic homeostasis, SIRT2 regulates adipocyte differentiation, fatty acid oxidation, gluconeogenesis, and insulin sensitivity. Thus, we hypothesized that DNA sequence variants (DSVs) in SIRT2 gene promoter may change SIRT2 levels, contributing to T2D.

METHODS

SIRT2 gene promoter was genetically and functionally analyzed in large cohorts of T2D patients (n = 365) and ethnic-matched controls (n = 358).

RESULTS

A total of 18 DSVs, including 5 SNPs, were identified in this study. Four novel heterozygous DSVs (g.38900912G > T, g.38900561C > T, g.38900359C > T and g.38900237G > A) were identified in four T2D patients, three of which (g.38900912G > T, g.38900359C > T and g.38900237G > A) significantly increased the transcriptional activity of the SIRT2 gene promoter in cultured pancreatic beta cells (P < .01). Seven novel heterozygous DSVs were only found in controls, and one heterozygous deletion DSV and five SNPs were found in both T2D patients and controls, which did not significantly affect SIRT2 gene promoter activity (P > .05).

CONCLUSIONS

Our findings suggested that the DSVs may increase SIRT2 gene promoter activity and SIRT2 levels, contributing to T2D development as a risk factor.

Mammalian Sirtuins SIRT4 and SIRT7

Sirtuins are a family of intracellular enzymes whose enzymatic activities include catalyzing the β-nicotinamide adenine dinucleotide (β-NAD⁺)-dependent N^ɛ-acyl-lysine deacylation and the β-NAD⁺-dependent mono-ADP-ribosylation. Among the seven sirtuin family members (i.e., SIRT1-7) thus far identified in mammals including humans, we know SIRT1/2/3/5/6 better than SIRT4/7 as for their enzymatic activities and the cellular roles of the reactions they catalyze. This chapter will provide an updated account on the enzymology and biology of SIRT4 and SIRT7, the two less well-understood mammalian sirtuins. It is hoped that this article will also be able to set a stage for the medicinal chemistry work on SIRT4 and SIRT7, potentially developing novel therapeutic agents for human diseases.

Epidermal SIRT1 regulates inflammation, cell migration, and wound healing

Sirtuins (SIRT1-7) are NAD-dependent proteins with the enzymatic activity of deacetylases and ADP ribosyltransferases. SIRT1 is the proto member of the proteins in the mammalian sirtuin family and plays multiple roles in aging and disease. Using mice with epidermis-specific SIRT1 deletion, we show that SIRT1 is required for efficient wound healing. SIRT1 deficiency in the epidermis inhibited the regeneration of both the epidermis and the dermal stroma. SIRT1 loss altered the production of many cytokines, inhibited the recruitment of macrophages, neutrophils, and mast cells, the recruitment and activation of fibroblasts, and angiogenesis in the granulation tissue. In keratinocytes, SIRT1 knockdown inhibited EMT, cell migration, and TGF-β signaling. For the first time, using skin-specific mouse model, we demonstrate that epidermal SIRT1 plays a crucial role in wound repair. These findings are novel in understanding how wound healing is regulated. Our findings provide in vivo and in vitro evidence that SIRT1 in the epidermis regulates cell migration, redox response, inflammation, epidermis re-epithelialization, granulation formation, and proper wound healing in mice.

Functional genetic variants within the SIRT2 gene promoter in acute myocardial infarction

Coronary artery disease (CAD), including acute myocardial infarction (AMI) is the complication of atherosclerosis. Recently, genome-wide association studies have identified a large number of CAD-related genetic variants. However, only 10% of CAD cases could be explained. Low frequent and rare genetic variants have been recently proposed to be main causes for CAD. SIRT2 is a member of sirtuin family, NAD(+)-dependent class III deacetylases. SIRT2 is involved in genomic stability, metabolism, inflammation, oxidative stress and autophagy, as well as in platelet function. Thus, we hypothesized that genetic variants in SIRT2 gene may contribute to AMI. In this study, SIRT2 gene promoter was analyzed in large cohorts of AMI patients (n = 375) and ethnic-matched controls (n = 377). Three novel heterozygous DSVs (g.38900888_91delTAAA, g.38900270A>G and g.38899853C>T) were identified in three AMI patients, but in none of controls. These DSVs significantly altered the transcriptional activity of the SIRT2 gene promoter (P<0.05) in both HEK-293 and H9c2 cells. Five novel heterozygous DSVS (g.38900562C>T, g.38900413A>C, g.38900030G>A, g.38899925A>C and g.38899852C>T) were only found in controls, which did not significantly affected SIRT2 gene promoter activity (P>0.05). In addition, four novel heterozygous DSVs and five SNPs were found in both AMI patients and control with similar frequencies (P>0.05), two SNPs of which were examined and did not affect SIRT2 gene promoter activity (P>0.05). Taken together, the DSVs identified in AMI patients may change SIRT2 level by affecting the transcriptional activity of SIRT2 gene promoter, contributing to the AMI development as a rare risk factor.

Sirtuin Inhibition: Strategies, Inhibitors, and Therapeutic Potential

The β-NAD⁺-dependent N^ε-acyl-lysine deacylation reaction catalyzed by sirtuin family members has been increasingly demonstrated to be important in regulating multiple crucial cellular processes and has also been proposed to be a therapeutic target for multiple human diseases. Accordingly, its inhibitors have been actively pursued over the past few years. In addition, we have also seen the pharmacological assessment of sirtuin inhibitory compounds, although to a lesser extent. In this review, we first discuss how sirtuin inhibitors were discovered with the use of various approaches. We then follow with a discussion of pharmacological studies using sirtuin inhibitors. Our aim here is to set a stage for developing future superior sirtuin inhibitors and for an expanded effort in exploiting inhibitors to explore and/or validate the therapeutic potential stemming from the inhibition of the sirtuin-catalyzed deacylation reaction.

Thienopyrimidinone Based Sirtuin-2 (SIRT2)-Selective Inhibitors Bind in the Ligand Induced Selectivity Pocket

Sirtuins (SIRTs) are NAD-dependent deacylases, known to be involved in a variety of pathophysiological processes and thus remain promising therapeutic targets for further validation. Previously, we reported a novel thienopyrimidinone SIRT2 inhibitor with good potency and excellent selectivity for SIRT2. Herein, we report an extensive SAR study of this chemical series and identify the key pharmacophoric elements and physiochemical properties that underpin the excellent activity observed. New analogues have been identified with submicromolar SIRT2 inhibtory activity and good to excellent SIRT2 subtype-selectivity. Importantly, we report a cocrystal structure of one of our compounds (29c) bound to SIRT2. This reveals our series to induce the formation of a previously reported selectivity pocket but to bind in an inverted fashion to what might be intuitively expected. We believe these findings will contribute significantly to an understanding of the mechanism of action of SIRT2 inhibitors and to the identification of refined, second generation inhibitors.

Bivalent SIRT1 inhibitors

In the current study, bivalent compounds 1-17 constructed by covalently linking the ɛ-amino group of lysine in a tripeptidic scaffold to a functionality via a linker were prepared and examined for their inhibitory potencies against SIRT1, a prototypical member of the β-nicotinamide adenine dinucleotide (β-NAD⁺)-dependent sirtuin family of protein N^ε-acyl-lysine deacylases. A few of them were found to be stronger SIRT1 inhibitors than the N^ɛ-acetyl-lysine-containing monovalent counterparts 18 and 19. As exemplified with compounds 6 and 18, a bivalent SIRT1 inhibitor could exhibit a greater degree of inhibitory selectivity among SIRT1/2/3 than the corresponding monovalent counterpart. This study has laid a foundation for the future development of superior bivalent inhibitors against the (patho)physiologically and therapeutically important sirtuin family of deacylase enzymes.

A Selective Cyclic Peptidic Human SIRT5 Inhibitor

In the current study, we discovered that a side chain-to-side chain cyclic pentapeptide harboring a central N^ε-carboxyethyl-thiocarbamoyl-lysine residue behaved as a strong and selective (versus human SIRT1/2/3/6) inhibitor against human SIRT5-catalyzed deacylation reaction. This compound was also found to be proteolytically much more stable than its linear counterpart. This compound could be a valuable lead for developing stronger, selective, metabolically stable, and cell permeable human SIRT5 inhibitors.

Cyclic peptide-based potent human SIRT6 inhibitors

Six side chain-to-side chain cyclic pentapeptides (4–9) harboring a central N^ε-dodecyl (or tetradecyl)-thiocarbamoyl-lysine residue all behaved as highly potent (IC₅₀ ∼ 256–495 nM) inhibitors against human SIRT6-catalyzed deacylation reaction.

Identification of sirtuin 5 inhibitors by ultrafast microchip electrophoresis using nanoliter volume samples

Sirtuin 5 (SIRT5) is a member of the sirtuin family of protein deacylases that catalyzes removal of post-translational modifications, such as succinyl and malonyl moieties, on lysine residues. In light of SIRT5's roles in regulating metabolism, and its reported oncogenic functions, SIRT5 modulators would be valuable tools for basic biological research and perhaps clinically. Several fluorescence assays for sirtuin modulators have been developed; however, the use of fluorogenic substrates has the potential to cause false positive results due to interactions of engineered substrates with enzyme or test compounds. Therefore, development of high-throughput screening (HTS) assays based on other methods is valuable. In this study, we report the development of a SIRT5 assay using microchip electrophoresis (MCE) for identification of SIRT5 modulators. A novel SIRT5 substrate based on succinate dehydrogenase (SDH) was developed to allow rapid and efficient separation of substrate and product peptide. To achieve high throughput, samples were injected onto the microchip using a droplet-based scheme. By coupling this approach to existing HTS sample preparation workflows, 1408 samples were analyzed at 0.5 Hz in 46 min. Using a 250 ms separation time, eight MCE injections could be made from each sample generating >11,000 electropherograms during analysis. Of the 1280 chemicals tested, eight were identified as inhibiting SIRT5 activity by at least 70% and verified by dose-response analysis.

Novel sirtuin inhibitory warheads derived from the N(ε)-acetyl-lysine analog L-2-amino-7-carboxamidoheptanoic acid

Built upon the catalytic mechanism-based pan-SIRT1/2/3 inhibitory warhead L-2-amino-7-carboxamidoheptanoic acid (L-ACAH, a close structural analog of N(ε)-acetyl-lysine) that our laboratory discovered recently, in the current study, its carboxamide NH2-ethylated analog was found to be a ∼2.4-6.6-fold stronger SIRT1/2/3 inhibitory warhead than L-ACAH. Carboxamide NH2-dodecylated and carboxymethylated analogs of L-ACAH were also identified as potent SIRT6 and SIRT5 inhibitory warheads, respectively.

Different facets of sex anxiety

The involvement of sirtuins (SIRTs) in modulating metabolic and stress response pathways is attracting growing scientific interest. Some SIRT family members are located in mitochondria, dynamic organelles that perform several crucial functions essential for eukaryotic life. Mitochondrial dysfunction has emerged as having a key role in a number of human diseases, including cancer. Here, we investigated mitochondrial damage resulting from treatment with a recently characterized pan-SIRT inhibitor, MC2494. MC2494 was able to block mitochondrial biogenesis and function in terms of ATP synthesis and energy metabolism, suggesting that it might orchestrate cell response to metabolic stress and thereby interfere with cancer promotion and progression. Targeting mitochondrial function could thus be considered a potential anticancer strategy for use in clinical therapy.