SIRT1 Modulation as a Novel Approach to the Treatment of Diseases of Aging

Pharmacological modulation of circadian rhythms by synthetic activators of the deacetylase SIRT1

Circadian rhythms govern a wide variety of physiological and metabolic functions in many organisms, from prokaryotes to humans. We previously reported that silent information regulator 1 (SIRT1), a NAD(+)-dependent deacetylase, contributes to circadian control. In addition, SIRT1 activity is regulated in a cyclic manner in virtue of the circadian oscillation of the coenzyme NAD(+). Here we used specific SIRT1 activator compounds both in vitro and in vivo. We tested a variety of compounds to show that the activation of SIRT1 alters CLOCK:BMAL1-driven transcription in different systems. Activation of SIRT1 induces repression of circadian gene expression and decreases H3 K9/K14 acetylation at corresponding promoters in a time-specific manner. Specific activation of SIRT1 was demonstrated in vivo using liver-specific SIRT1-deficient mice, where the effect of SIRT1 activator compounds was shown to be dependent on SIRT1. Our findings demonstrate that SIRT1 can fine-tune circadian rhythm and pave the way to the development of pharmacological strategies to address a broad range of therapeutic indications.

Fragmentation studies of SIRT1-activating drugs and their detection in human plasma for doping control purposes

RATIONALE

The efficiency of Sirtuin1, a major target for the treatment of various metabolic disorders such as inflammation and type 2 diabetes mellitus, can be modulated via low molecular mass SIRT1 activators (e.g. resveratrol, SRT1720, and SRT2104).The administration of such compounds results in increased deacetylation of substrates including p53, FOXO1, and PGC1alpha, potentially leading to an improved physical performance. Consequently, proactive and preventive anti-doping measures are required and an assay dedicated to serum and plasma was desirable.

METHODS

Model substances of emerging SIRT1 drug candidates were obtained and synthesized and their mass spectrometric behavior following positive or negative electrospray ionization and collision-induced dissociation was elucidated using low and high resolution/high accuracy (tandem) mass spectrometry. Subsequently, a screening and confirmation procedure necessitating 100 μL of plasma was established employing liquid chromatography/tandem mass spectrometry (LC/MS/MS) based on diagnostic ion transitions recorded in multiple reaction monitoring mode. Sample preparation consisted of the addition of two deuterated internal standards (D(8)-SRT1720 and D(4)-resveratrol) to the plasma specimen and subsequent protein precipitation.

RESULTS

Characteristic product ions indicative of the core structures of the model analytes were characterized and utilized for the development of a multi-analyte LC/MS/MS detection method applicable to sports drug testing programs. The doping control assay was validated with regard to specificity, limits of detection (0.1-1 ng/mL), recoveries (90-98%), intraday and interday precisions (2-18%), and ion suppression/enhancement effects.

CONCLUSIONS

The fragmentation pathways of SRT1720 and 4 SIRT1 activator models based on a common thiazole-imidazole nucleus as well as two different complementary activators (SIRT1 activator 3 and CAY10602), comprising a quinoxaline core, were studied. The resulting information was used to establish and validate a sports drug testing methodology relevant for an efficient and timely anti-doping procedure, targeting a new class of emerging therapeutics possessing significant potential for misuse in elite and amateur sport.

Role of epigenetic mechanisms in the vascular complications of diabetes

Diabetes and metabolic disorders are leading causes of micro- and macrovascular complications. Furthermore, efforts to treat these complications are hampered by metabolic memory, a phenomenon in which prior exposure to hyperglycemia predisposes diabetic patients to the continued development of vascular diseases despite subsequent glycemic control. Persistently increased levels of oxidant stress and inflammatory genes are key features of these pathologies. Biochemical and molecular studies showed that hyperglycemia induced activation of NF-κB, signaling and actions of advanced glycation end products and other inflammatory mediators play key roles in the expression of pathological genes. In addition, epigenetic mechanisms such as posttranslational modification of histones and DNA methylation also play central roles in gene regulation by affecting chromatin structure and function. Recent studies have suggested that dysregulation of such epigenetic mechanisms may be involved in metabolic memory leading to persistent changes in the expression of genes associated with diabetic vascular complications. Further exploration of these mechanisms by also taking advantages of recent advances in high throughput epigenomics technologies will greatly increase our understanding of epigenetic variations in diabetes and its complications. This in turn can lead to the development of novel new therapies.

Discovery of salermide-related sirtuin inhibitors: binding mode studies and antiproliferative effects in cancer cells including cancer stem cells

Chemical changes performed on 1a (sirtinol) led to a series of SIRT1/2 inhibitors, in some cases more potent than 1a mainly against SIRT1. Tested in human leukemia U937 cells, the benzamide and anilide derivatives 1b, 1c, 2b, and 2c as well as the 4-(2-phenylpropyl)thioanalogue 4c showed huge apoptosis induction, while some sulfinyl and sulfonyl derivatives (5b, 5c, and 6a-c) were highly efficient in granulocytic differentiation. When assayed in human leukemia MOLT4 as well as in human breast MDA-MB-231 and colon RKO cancer cell lines, the anilide 2b (salermide) and the phenylpropylthio analogue 4b emerged as the most potent antiproliferative agents. Tested on colorectal carcinoma and glioblastoma multiforme cancer stem cells (CSCs) from patients, 2b was particularly potent against colorectal carcinoma CSCs, while 4b, 6a, and the SIRT2-selective inhibitor AGK-2 showed the highest effect against glioblastoma multiforme CSCs. Such compounds will be further explored for their broad-spectrum anticancer properties.

Sirtuin catalysis and regulation

Sirtuins are a family of NAD(+)-dependent protein deacetylases/deacylases that dynamically regulate transcription, metabolism, and cellular stress response. Their general positive link with improved health span in mammals, potential regulation of pathways mediated by caloric restriction, and growing links to human disease have spurred interest in therapeutics that target their functions. Here, we review the current understanding of the chemistry of catalysis, biological targets, and endogenous regulation of sirtuin activity. We discuss recent efforts to generate small-molecule regulators of sirtuin activity.

Can targeting SIRT-1 to treat type 2 diabetes be a good strategy? A review

INTRODUCTION

Dysregulation of metabolic pathways, caused by imbalances in energy homeostasis, leads to type 2 diabetes characterized by high glucose concentration in the blood due to insulin resistance which is a major disorder in developed countries.

AREAS COVERED

One of the recent treatment strategies is using activators of SIRT1, which has been in clinical trials. Many of the cellular processes including insulin secretion, cell cycle, and apoptosis are imperatively regulated by a family of mediators called sirtuins. First known mammalian sirtuin, SIRT1 is a positive regulator of insulin secretion, which triggers glucose uptake and utilization. Since the past decade, a major outstanding question is whether SIRT1 activation is a safe therapy for human diseases such as type 2 diabetes? This review summarizes and discusses the advances of the past decade and the challenges that will brazen out perplexity about homeostasis and metabolic pathways linked to SIRT1 and type 2 diabetes. Furthermore, we described the interlink between SIRT1 metabolic pathways of various tissues such as pancreas, skeletal muscle, adipose tissue and liver.

EXPERT OPINION

However be the complexity of the pathways involved, T2DM regulated by SIRT1 affected metabolism is dropping down progressively due to profound research. In the context of interlinking all the SIRT1 pathways in T2DM we found various crucial intermediaries in metabolic tissues, which can also be targeted for future prospects.

Design, synthesis, and biological activity of a novel series of human sirtuin-2-selective inhibitors

Selective inhibitors of human sirtuin 2 (SIRT2), a deacetylase, are candidate therapeutic agents for neurodegenerative diseases such as Parkinson's disease and Huntington's disease as well as potential tools for elucidating the biological functions of SIRT2. On the basis of homology models of SIRT1 and SIRT2, we designed and prepared a series of 2-anilinobenzamide analogues. Enzyme assays using recombinant SIRT1 and SIRT2 revealed that 3'-phenethyloxy-2-anilinobenzamide analogues such as 33a and 33i are potent and selective SIRT2 inhibitors, showing more than 3.5-fold greater SIRT2-inhibitory activity and more than 35-fold greater SIRT2-selectivity compared with AGK2 (3), a previously reported SIRT2-selective inhibitor. Compound 33a also induced a dose-dependent selective increase of α-tubulin acetylation in human colon cancer HCT116 cells, indicating selective inhibition of SIRT2 in the cells. These 3'-phenethyloxy-2-anilinobenzamide derivatives represent an entry into a new class of SIRT2-selective inhibitors.

Substrates for efficient fluorometric screening employing the NAD-dependent sirtuin 5 lysine deacylase (KDAC) enzyme

The class III lysine deacylases (KDACs), also known as the sirtuins, have emerged as interesting drug targets for therapeutic intervention in a variety of diseases. To gain a deeper understanding of the processes affected by sirtuins, the development of selective small molecule modulators of individual isozymes has been a longstanding goal. Essential for the discovery of novel modulators, however, are good screening protocols and mechanistic insights with regard to the targets in question. We therefore evaluated the activities of the seven human sirtuin hydrolases against a panel of fluorogenic substrates. Both commonly used, commercially available substrates and novel chemotypes designed to address recent developments in the field of lysine post-translational modification were evaluated. Our investigations led to the discovery of two new fluorogenic ε-N-succinyllysine-containing substrates that enable highly efficient and enzyme-economical screening employing sirtuin 5 (SIRT5). Furthermore, optimized protocols for facile kinetic investigations were developed, which should be valuable for enzyme kinetic investigations. Finally, these protocols were applied to a kinetic analysis of the inhibition of SIRT5 by suramin, a potent sirtuin inhibitor previously shown by X-ray crystallography to bind the substrate pocket of the human SIRT5 KDAC enzyme.

Chondrocyte hypertrophy and osteoarthritis: role in initiation and progression of cartilage degeneration?

OBJECTIVE

To review the literature on the role and regulation of chondrocyte terminal differentiation (hypertrophy-like changes) in osteoarthritis (OA) and to integrate this in a conceptual model of primary OA development.

METHODS

Papers investigating chondrocyte terminal differentiation in human OA cartilage and experimental models of OA were recapitulated and discussed. Focus has been on the occurrence of hypertrophy-like changes in chondrocytes and the factors described to play a role in regulation of chondrocyte hypertrophy-like changes in OA.

RESULTS

Chondrocyte hypertrophy-like changes are reported in both human OA and experimental OA models by most investigators. These changes play a crucial part in the OA disease process by protease-mediated cartilage degradation. We propose that altered chondrocyte behavior and concomitant cartilage degradation result in a disease-amplifying loop, leading to a mixture of disease stages and cellular responses within an OA joint.

CONCLUSION

Chondrocyte hypertrophy-like changes play a role in early and late stage OA. Since not all cells in an OA joint are synchronized, inhibition of hypertrophy-like changes might be a therapeutic target to slow down further OA progression.

New synthetic approach to paullones and characterization of their SIRT1 inhibitory activity

A series of 7,12-dihydroindolo[3,2-d][1]benzazepine-6(5H)-ones (paullones) substituted at C9/C10 (Br) and C2 (Me, CF(3), CO(2)Me) have been synthesized by a one-pot Suzuki-Miyaura cross-coupling of an o-aminoarylboronic acid and methyl 2-iodoindoleacetate followed by intramolecular amide formation. Other approaches to the paullone scaffold based on Pd-catalyzed C-H activation were unsuccessful. In vitro enzymatic assay with recombinant human SIRT-1 indicated a strong inhibitory profile for the series, in particular the analogue with a methoxycarbonyl group at C2 and a bromine at C9. These compounds are, in general, inducers of granulocyte differentiation of the U937 acute leukemia cell line and cause a marked increase in pre-G1 of the cell cycle.

Synthesis and biological characterisation of sirtuin inhibitors based on the tenovins

The tenovins are small molecule inhibitors of the NAD(+)-dependent family of protein deacetylases known as the sirtuins. There remains considerable interest in inhibitors of this enzyme family due to possible applications in both cancer and neurodegenerative disease therapy. Through the synthesis of novel tenovin analogues, further insights into the structural requirements for activity against the sirtuins in vitro are provided. In addition, the activity of one of the analogues in cells led to an improved understanding of the function of SirT1 in cells.

Development of second generation epigenetic agents

This review focuses on the progress in the development of the second generation of epigenetic modifiers able to modulate histone marks, and restore normal gene transcription.

Sirtuins in neurodegenerative diseases: a biological-chemical perspective

Sirtuins, commonly known as NAD(+)-dependent class III histone deacetylase enzymes, have been extensively studied to evaluate their potential role in different disease states. Based on the published literature, sirtuins have been implicated in providing a myriad of intrinsic and extrinsic biological effects, which in turn may play an important role in the treatment of various disorders such as type II diabetes, obesity, cancer, aging and different neurodegenerative diseases. In particular, a number of studies have unequivocally supported the idea of sirtuins having therapeutic potential in neurodegenerative diseases such as stroke, ischemic brain injury, Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. To exploit the therapeutic potential of sirtuins, their manipulation in terms of development of small-molecule modulators, inhibitors and analogs has increased dramatically since their inception, in both scientific and industrial worlds. Studies on the structure and catalytic core of sirtuins along with chemical mechanisms and substrate specificity have provided important input into the design and synthesis of sirtuin modulators. To study the role of sirtuins in the biological system, it has become extremely important to understand the molecular and chemical structure of sirtuins. In this review, we have discussed the biological role of sirtuins in various neurodegenerative diseases, and also provided an insight into their chemical structure.

A mechanism-based potent sirtuin inhibitor containing Nε-thiocarbamoyl-lysine (TuAcK)

In the current study, we have identified N(ε)-thiocarbamoyl-lysine (TuAcK) as a general sirtuin inhibitory warhead which was shown to be able to confer potent sirtuin inhibition. This inhibition was also shown to be mechanism-based in that the TuAck residue was able to be processed by a sirtuin enzyme with the formation of a stalled S-alkylamidate intermediate.

Flavonoids as inhibitors of human CD38

CD38 is a multifunctional enzyme which is ubiquitously distributed in mammalian tissues. It is involved in the conversion of NAD(P)(+) into cyclic ADP-ribose, NAADP(+) and ADP-ribose and the role of these metabolites in multiple Ca(2+) signaling pathways makes CD38 a novel potential pharmacological target. The dire paucity of CD38 inhibitors, however, renders the search for new molecular tools highly desirable. We report that human CD38 is inhibited at low micromolar concentrations by flavonoids such as luteolinidin, kuromanin and luteolin (IC(50) <10 μM). Docking studies provide some clues on the mode of interaction of these molecules with the active site of CD38.