Context-dependent role of SIRT3 in cancer

Function of intramitochondrial melatonin and its association with Warburg metabolism

Warburg metabolism (aerobic glycolysis) is accompanied by high mitochondrial reactive oxygen species (ROS) generation from the electron transport chain; this is a "Hallmark of Cancer". The elevated ROS sustain the growth and proliferation of the cancer cells. Melatonin is a potent and functionally diverse free radical scavenger and antioxidant that is synthesized in the mitochondria of non-pathological cells and normally aids in keeping mitochondrial ROS levels low and in maintaining redox homeostasis. Because the glucose metabolite, pyruvate, does not enter mitochondria of Warburg metabolizing cells due to the inhibition of pyruvate dehydrogenase complex (PDH), acetyl coenzyme A production is diminished. Acetyl coenzyme A is a necessary co-substrate with serotonin for melatonin synthesis; thus, intramitochondrial melatonin levels become reduced in cancer cells. The hypothesis is that the depressed melatonin levels initiate aerobic glycolysis and allow the exaggerated ROS concentrations to go uncontested; the authors speculate that the elevated mtROS upregulates hypoxia inducible factor 1α (HIF-1α)/pyruvate dehydrogenase kinase (PDK) axis which inhibits PDH, thereby supporting cancer cell proliferation and stimulating cancer biomass. Exposing Warburg metabolizing cancer cells to melatonin elevates intramitochondrial melatonin, thereby reducing mtROS and concurrently interrupting aerobic glycolysis and inhibiting tumor cell proliferation. Mechanistically, higher mitochondrial melatonin levels by supplementation directly upregulates the sirtuin 3 (SIRT3)/FOXO/PDH axis, allowing pyruvate entry into mitochondria and enhancing intrinsic mitochondrial melatonin production as in non-pathological cells. Additionally, melatonin inhibits HIF1α, thereby decreasing PDK activity and disinhibiting PDH, so pyruvate enters mitochondria and is metabolized to acetyl coenzyme A, resulting in reversal of Warburg metabolism.

Functions and mechanisms of non-histone post-translational modifications in cancer progression

Protein post-translational modifications (PTMs) refer to covalent and enzymatic alterations to folded or nascent proteins during or after protein biosynthesis to alter the properties and functions of proteins. PTMs are modified in a variety of types and affect almost all aspects of cell biology. PTMs have been reported to be involved in cancer progression by influencing multiple signaling pathways. The mechanism of action of histone PTMs in cancer has been extensively studied. Notably, evidence is mounting that PTMs of non-histone proteins also play a vital role in cancer progression. In this review, we provide a systematic description of main non-histone PTMs associated with cancer progression, including acetylation, lactylation, methylation, ubiquitination, phosphorylation, and SUMOylation, based on recent studies.

Roles of SIRT3 in cardiovascular and neurodegenerative diseases

Sirtuin-3 (SIRT3) in mitochondria has nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase activity. As such, SIRT3 is crucial in cardiovascular and neurodegenerative diseases. Advanced proteomics and transcriptomics studies have revealed that SIRT3 expression becomes altered when the heart or brain is affected by external stimuli or disease, such as diabetic cardiomyopathy, atherosclerosis, myocardial infarction, Alzheimer's disease, Huntington's disease, and Parkinson's disease. More specifically, SIRT3 participates in the development of these disorders through its deacetylase activity and in combination with downstream signaling pathways. The paper reviews SIRT3's expression changes, roles, and mechanisms associated with the development of cardiovascular and neurodegenerative diseases. Additionally, strategies targeting SIRT3 to treat or regulate cardiovascular and neurodegenerative disease development are discussed.

Design, synthesis and biological evaluation of new SIRT3 activators for the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) represents a highly malignant subtype of breast cancer with limited therapeutic options. In this study, we designed and synthesized a series of 1,4-DHP derivatives by structure-based strategy, 43 was documented to be a potent SIRT3 activator and exhibited profound anti-proliferative activity in BT-549 and MDA-MB-231 cells with low toxicity over normal cells. Additionally, 43 displayed the ability of direct binding to SIRT3 with a Kd value of 51.51 μM in BLI assay, and the potential bonding mode was elucidated through molecular docking. 43 could inhibit the proliferation, migration, and glycolysis, induced mitochondrial membrane potential decreased and apoptosis in BT-549 and MDA-MB-231 cells. Collectively, these results demonstrate that 43 is a potent SIRT3 activator with the potential to anti-TNBC through signaling pathways regulated by SIRT3.

The Expression of SIRT3 in Endometrial Carcinoma and Its Effect on Promoting Apoptosis of Ishikawa Cells

Endometrial cancer (EC) is one of the three most common malignancies of the female reproductive system. SIRT3 is an NAD+-dependent protein deacetylase that maintains the stability of the intracellular environment. This study aims to investigate the mechanism of SIRT3 in regulating apoptosis in endometrial cancer and further reveal the role of SIRT3 in endometrial cancer. Differential expression of SIRT3 in tumors was analyzed by GEPIA using TCGA database data. Meanwhile, mRNA and protein expression levels of SIRT3 in tissues and cells were examined using RT-qPCR, Western Blot, and immunohistochemistry. The expression of SIRT3 after estradiol (E2) stimulation of Ishikawa cells was detected using RT-qPCR and Western Blot techniques. The effect of transfection after SIRT3 knockdown and overexpression was verified using RT-qPCR and Western Blot. Flow cytometry and TUNEL assay were used to detect the effect of SIRT3 on apoptosis. Reactive oxygen species (ROS) was used to detect the effect of SIRT3 on the level of oxidative stress in cells. The expression of apoptotic protein (BAX, cleaved-Caspase 3) and autophagy protein (cyto C and LC3A) were detected in transfected Ishikawa cell. Differences analysis of TCGA database data showed that the expression of SIRT3 in EC was significantly lower than that in normal endometrial tissue. The mRNA and protein levels of SIRT3 were significantly lower in EC tissues or cells than normal controls. E2 stimulation in Ishikawa cells resulted in the down-regulation of SIRT3 expression. After transfection, SIRT3 promoted the apoptosis of Ishikawa cells and attenuated the levels of ROS. Overexpression of SIRT3 promoted apoptosis and autophagy-related proteins. Thus, high expression of SIRT3 inhibits the development of EC whereas low expression of SIRT3 may promote the progression of EC, which provides a new direction for studying the treatment of EC.

Design, synthesis and biological evaluation of novel SIRT3 inhibitors targeting both NAD+ and substrate binding sites for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) represents a highly malignant subtype of leukemia with limited therapeutic options. In this study, we propose a novel therapeutic strategy for treating AML by inhibiting SIRT3 to regulate mitochondrial metabolism network involved in energy metabolism and epigenetic modifications essential for AML survival. A series of thieno [3,2-d]pyrimidine-6-carboxamide derivatives were designed and synthesized by structure-based strategy, 17f was documented to be a potent and acceptable selective SIRT3 inhibitor with IC50 value of 0.043 μM and exhibited profound anti-proliferative activity in MOLM13, MV4-11, and HL-60 cells. Through CETSA assay and the degree of deacetylation of intracellular SIRT3 substrates, we confirmed that 17f could effectively bind and inhibit SIRT3 activity in AML cells. Mechanistically, 17f suppressed mitochondrial function, triggered the accumulation of ROS, and significantly inhibited the production of ATP in AML cells. With the breakdown of mitochondrial function, 17f eventually induced apoptosis of AML cells. In addition, 17f also showed excellent anti-AML potential in nude mouse tumor models of HL-60-Luc. Collectively, these results demonstrate that 17f is a potent and acceptable selective SIRT3 inhibitor with promising potential to treat AML.

Sirt1: An Increasingly Interesting Molecule with a Potential Role in Bone Metabolism and Osteoporosis

Osteoporosis (OP) is a common metabolic bone disease characterized by low bone mass, decreased bone mineral density, and degradation of bone tissue microarchitecture. However, our understanding of the mechanisms of bone remodeling and factors affecting bone mass remains incomplete. Sirtuin1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent deacetylase that regulates a variety of cellular metabolisms, including inflammation, tumorigenesis, and bone metabolism. Recent studies have emphasized the important role of SIRT1 in bone homeostasis. This article reviews the role of SIRT1 in bone metabolism and OP and also discusses therapeutic strategies and future research directions for targeting SIRT1.

Therapeutic strategies of targeting non-apoptotic regulated cell death (RCD) with small-molecule compounds in cancer

Regulated cell death (RCD) is a controlled form of cell death orchestrated by one or more cascading signaling pathways, making it amenable to pharmacological intervention. RCD subroutines can be categorized as apoptotic or non-apoptotic and play essential roles in maintaining homeostasis, facilitating development, and modulating immunity. Accumulating evidence has recently revealed that RCD evasion is frequently the primary cause of tumor survival. Several non-apoptotic RCD subroutines have garnered attention as promising cancer therapies due to their ability to induce tumor regression and prevent relapse, comparable to apoptosis. Moreover, they offer potential solutions for overcoming the acquired resistance of tumors toward apoptotic drugs. With an increasing understanding of the underlying mechanisms governing these non-apoptotic RCD subroutines, a growing number of small-molecule compounds targeting single or multiple pathways have been discovered, providing novel strategies for current cancer therapy. In this review, we comprehensively summarized the current regulatory mechanisms of the emerging non-apoptotic RCD subroutines, mainly including autophagy-dependent cell death, ferroptosis, cuproptosis, disulfidptosis, necroptosis, pyroptosis, alkaliptosis, oxeiptosis, parthanatos, mitochondrial permeability transition (MPT)-driven necrosis, entotic cell death, NETotic cell death, lysosome-dependent cell death, and immunogenic cell death (ICD). Furthermore, we focused on discussing the pharmacological regulatory mechanisms of related small-molecule compounds. In brief, these insightful findings may provide valuable guidance for investigating individual or collaborative targeting approaches towards different RCD subroutines, ultimately driving the discovery of novel small-molecule compounds that target RCD and significantly enhance future cancer therapeutics.

2-APQC, a small-molecule activator of Sirtuin-3 (SIRT3), alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis

Sirtuin 3 (SIRT3) is well known as a conserved nicotinamide adenine dinucleotide+ (NAD+)-dependent deacetylase located in the mitochondria that may regulate oxidative stress, catabolism and ATP production. Accumulating evidence has recently revealed that SIRT3 plays its critical roles in cardiac fibrosis, myocardial fibrosis and even heart failure (HF), through its deacetylation modifications. Accordingly, discovery of SIRT3 activators and elucidating their underlying mechanisms of HF should be urgently needed. Herein, we identified a new small-molecule activator of SIRT3 (named 2-APQC) by the structure-based drug designing strategy. 2-APQC was shown to alleviate isoproterenol (ISO)-induced cardiac hypertrophy and myocardial fibrosis in vitro and in vivo rat models. Importantly, in SIRT3 knockout mice, 2-APQC could not relieve HF, suggesting that 2-APQC is dependent on SIRT3 for its protective role. Mechanically, 2-APQC was found to inhibit the mammalian target of rapamycin (mTOR)-p70 ribosomal protein S6 kinase (p70S6K), c-jun N-terminal kinase (JNK) and transforming growth factor-β (TGF-β)/ small mother against decapentaplegic 3 (Smad3) pathways to improve ISO-induced cardiac hypertrophy and myocardial fibrosis. Based upon RNA-seq analyses, we demonstrated that SIRT3-pyrroline-5-carboxylate reductase 1 (PYCR1) axis was closely assoiated with HF. By activating PYCR1, 2-APQC was shown to enhance mitochondrial proline metabolism, inhibited reactive oxygen species (ROS)-p38 mitogen activated protein kinase (p38MAPK) pathway and thereby protecting against ISO-induced mitochondrialoxidative damage. Moreover, activation of SIRT3 by 2-APQC could facilitate AMP-activated protein kinase (AMPK)-Parkin axis to inhibit ISO-induced necrosis. Together, our results demonstrate that 2-APQC is a targeted SIRT3 activator that alleviates myocardial hypertrophy and fibrosis by regulating mitochondrial homeostasis, which may provide a new clue on exploiting a promising drug candidate for the future HF therapeutics.

Discovery of a novel small-molecule activator of SIRT3 that inhibits cell proliferation and migration by apoptosis and autophagy-dependent cell death pathways in colorectal cancer

Colorectal cancer (CRC) is well known as a prevalent malignancy affecting the digestive tract, yet its precise etiological determinants remain to be elusive. Accordingly, identifying specific molecular targets for colorectal cancer and predicting potential malignant tumor behavior are potential strategies for therapeutic interventions. Of note, apoptosis (type I programmed cell death) has been widely reported to play a pivotal role in tumorigenesis by exerting a suppressive effect on cancer development. Moreover, autophagy-dependent cell death (type II programmed cell death) has been implicated in different types of human cancers. Thus, investigating the molecular mechanisms underlying apoptosis and autophagy-dependent cell death is paramount in treatment modalities of colorectal cancer. In this study, we uncovered that a new small-molecule activator of SIRT3, named MY-13, triggered both autophagy-dependent cell death and apoptosis by modulating the SIRT3/Hsp90/AKT signaling pathway. Consequently, this compound inhibited tumor cell proliferation and migration in RKO and HCT-116 cell lines. Moreover, we further demonstrated that the small-molecule activator significantly suppressed tumor growth in vivo. In conclusion, these findings demonstrate that the novel small-molecule activator of SIRT3 may hold a therapeutic potential as a drug candidate in colorectal cancer.