SIRT1-mediated FoxO1 deacetylation is essential for multidrug resistance-associated protein 2 expression in tamoxifen-resistant breast cancer cells

Identification of phytoestrogens as sirtuin inhibitor against breast cancer: Multitargeted approach

Despite progress in diagnosis and treatment strategies, breast cancer remains a primary risk to female health as indicated by second most cancer-deaths globally caused by this cancer. High risk mutation is linked to prognosis of breast cancer. Due to high resistance of breast cancer against current therapies, there is necessity of novel treatment strategies. Sirtuins are signaling proteins belonging to histone deacetylase class III family, known to control several cellular processes. Therefore, targeting sirtuins could be one of the approaches to treat breast cancer. Several plants synthesize phytoestrogens which exhibit structural and physiological similarities to estrogens and have been recognized to possess anticancer activity. In our study, we investigated several phytoestrogens for sirtuin inhibition by conducting molecular docking studies, and in-vitro studies against breast cancer cell lines. In molecular docking studies, we identified coumestrol possessing high binding energy with sirtuin proteins 1-3 as compared to other phytoestrogens. The molecular dynamic studies showed stable interaction of ligand and protein with higher affinity at sirtuin proteins 1-3 binding sites. In cell proliferation assay and colony formation assay using breast cancer cell lines (MCF-7 and MDAMB-231) coumestrol caused significant reduction in cell proliferation and number of colonies formed. Further, the flow cytometric analysis showed that coumestrol induces intracellular reactive oxygen species and the western blot analysis revealed reduction in the level of SIRT-1 expression in breast cancer cell lines. In conclusion, in-silico data and in-vitro studies suggest that the phytoestrogen coumestrol has sirtuin inhibitory activity against breast cancer.

The dual role of sirtuins in cancer: biological functions and implications

Sirtuins are pivotal in orchestrating numerous cellular pathways, critically influencing cell metabolism, DNA repair, aging processes, and oxidative stress. In recent years, the involvement of sirtuins in tumor biology has garnered substantial attention, with a growing body of evidence underscoring their regulatory roles in various aberrant cellular processes within tumor environments. This article delves into the sirtuin family and its biological functions, shedding light on their dual roles-either as promoters or inhibitors-in various cancers including oral, breast, hepatocellular, lung, and gastric cancers. It further explores potential anti-tumor agents targeting sirtuins, unraveling the complex interplay between sirtuins, miRNAs, and chemotherapeutic drugs. The dual roles of sirtuins in cancer biology reflect the complexity of targeting these enzymes but also highlight the immense therapeutic potential. These advancements hold significant promise for enhancing clinical outcomes, marking a pivotal step forward in the ongoing battle against cancer.

The Role of Sirtuin 6 in the Deacetylation of Histone Proteins as a Factor in the Progression of Neoplastic Disease

SIRT6 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase, predominantly located in the nucleus, that is involved in the processes of histone modification, DNA repair, cell cycle regulation, and apoptosis. Disturbances in SIRT6 expression levels have been observed in the development and progression of various types of cancer. Therefore, it is important to better understand the role of SIRT6 in biochemical pathways and assign it specific biological functions. This review aims to summarize the role of SIRT6 in carcinogenesis and tumor development. A better understanding of the factors influencing SIRT6 expression and its biological role in carcinogenesis may help to develop novel anti-cancer therapeutic strategies. Moreover, we discuss the anti-cancer effects and mechanism of action of small molecule SIRT6 modulators (both activators and inhibitors) in different types of cancer.

Non-Coding RNAs Modulating Estrogen Signaling and Response to Endocrine Therapy in Breast Cancer

The largest part of human DNA is transcribed into RNA that does not code for proteins. These non-coding RNAs (ncRNAs) are key regulators of protein-coding gene expression and have been shown to play important roles in health, disease and therapy response. Today, endocrine therapy of ERα-positive breast cancer (BC) is a successful treatment approach, but resistance to this therapy is a major clinical problem. Therefore, a deeper understanding of resistance mechanisms is important to overcome this resistance. An increasing amount of evidence demonstrate that ncRNAs affect the response to endocrine therapy. Thus, ncRNAs are considered versatile biomarkers to predict or monitor therapy response. In this review article, we intend to give a summary and update on the effects of microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) on estrogen signaling in BC cells, this pathway being the target of endocrine therapy, and their role in therapy resistance. For this purpose, we reviewed articles on these topics listed in the PubMed database. Finally, we provide an assessment regarding the clinical use of these ncRNA types, particularly their circulating forms, as predictive BC biomarkers and their potential role as therapy targets to overcome endocrine resistance.

The sirtuin family in health and disease

Sirtuins (SIRTs) are nicotine adenine dinucleotide(+)-dependent histone deacetylases regulating critical signaling pathways in prokaryotes and eukaryotes, and are involved in numerous biological processes. Currently, seven mammalian homologs of yeast Sir2 named SIRT1 to SIRT7 have been identified. Increasing evidence has suggested the vital roles of seven members of the SIRT family in health and disease conditions. Notably, this protein family plays a variety of important roles in cellular biology such as inflammation, metabolism, oxidative stress, and apoptosis, etc., thus, it is considered a potential therapeutic target for different kinds of pathologies including cancer, cardiovascular disease, respiratory disease, and other conditions. Moreover, identification of SIRT modulators and exploring the functions of these different modulators have prompted increased efforts to discover new small molecules, which can modify SIRT activity. Furthermore, several randomized controlled trials have indicated that different interventions might affect the expression of SIRT protein in human samples, and supplementation of SIRT modulators might have diverse impact on physiological function in different participants. In this review, we introduce the history and structure of the SIRT protein family, discuss the molecular mechanisms and biological functions of seven members of the SIRT protein family, elaborate on the regulatory roles of SIRTs in human disease, summarize SIRT inhibitors and activators, and review related clinical studies.

SIRT1/FOXO1 Axis-Mediated Hippocampal Angiogenesis is Involved in the Antidepressant Effect of Chaihu Shugan San

Objective

Methods

Results

Conclusion

The Relationship of Redox With Hallmarks of Cancer: The Importance of Homeostasis and Context

Redox homeostasis is a lifelong pursuit of cancer cells. Depending on the context, reactive oxygen species (ROS) exert paradoxical effects on cancers; an appropriate concentration stimulates tumorigenesis and supports the progression of cancer cells, while an excessive concentration leads to cell death. The upregulated antioxidant system in cancer cells limits ROS to a tumor-promoting level. In cancers, redox regulation interacts with tumor initiation, proliferation, metastasis, programmed cell death, autophagy, metabolic reprogramming, the tumor microenvironment, therapies, and therapeutic resistance to facilitate cancer development. This review discusses redox control and the major hallmarks of cancer.

Panax notoginseng saponins reverse P-gp-mediated steroid resistance in lupus: involvement in the suppression of the SIRT1/FoxO1/MDR1 signalling pathway in lymphocytes

Background

P-glycoprotein (P-gp)-mediated steroid resistance (SR) has been suggested to play a significant role in lupus nephritis (LN) treatment failure. Panax notoginseng saponins (PNS), the main effective components of the traditional Chinese medicine notoginseng, exhibited potent reversal capability of P-gp-mediated SR, but its mechanism remains unknown. This study aimed to investigate the effect of PNS on reversing SR in lupus and its underlying mechanism in vivo and in vitro.

Methods

In this study, an SR animal and splenic lymphocyte model were established using low-dose methylprednisolone (MP). Flow cytometry was used to detect the effect of PNS on reversing P-gp-mediated SR and the expression of P-gp in different T-cells phenotypes. Serum levels of ANA and dsDNA in lupus mice were measured by ELISA. Apoptosis was identified by Annexin V-FITC/PI staining. RT–PCR and Western blotting were used to detect the protein and mRNA expression levels of SIRT1, FoxO1, and MDR1 in SR splenic lymphocytes from lupus mice (SLCs/MPs).

Results

PNS could reverse the SR in lupus mice. Simultaneously, PNS increased the apoptotic effect of MP on SLCs/MP cells. The increased accumulation of rhodamine-123 (Rh-123) indicated that intracellular steroid accumulation could be increased by the action of PNS. Moreover, PNS decreased the expression of P-gp levels. Further experiments elucidated that the SIRT1/FoxO1/MDR1 signalling pathway existed in SLCs/MP cells, and PNS suppressed its expression level to reverse SR. The expression of P-gp in Th17 from SLCs/MP cells was increased, while PNS could reduce its level in a more obvious trend.

Conclusion

The present study suggested that PNS reversed P-gp-mediated SR via the SIRT1/FoxO1/MDR1 signalling pathway, which might become a valuable drug for the treatment of SR in lupus. Th17 might be the main effector cell of PNS reversing SR.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03499-5.

Design and synthesis of amino acid derivatives of substituted benzimidazoles and pyrazoles as Sirt1 inhibitors

Owing to its presence in several biological processes, Sirt1 acts as a potential therapeutic target for many diseases. Here, we report the structure-based designing and synthesis of two distinct series of novel Sirt1 inhibitors, benzimidazole mono-peptides and amino-acid derived 5-pyrazolyl methylidene rhodanine carboxylic acid. The compounds were evaluated for in vitro enzyme-based and cell-based Sirt1 inhibition assay, and cytotoxic-activity in both liver and breast cancer cells. The tryptophan conjugates i.e.13h (IC₅₀ = 0.66 μM, ΔG_bind = −1.1 kcal mol⁻¹) and 7d (IC₅₀ = 0.77 μM, ΔG_bind = −4.4 kcal mol⁻¹) demonstrated the maximum efficacy to inhibit Sirt1. The MD simulation unveiled that electrostatic complementarity at the substrate-binding-site through a novel motif “SLxVxP(V/F)A” could be a cause of increased Sirt1 inhibition by 13h and 13l over Sirt2 in cell-based assay, as compared to the control Ex527 and 7d. Finally, this study highlights novel molecules 7d and 13h, along with a new key hot-spot in Sirt1, which could be used as a starting lead to design more potent and selective sirtuin inhibitors as a potential anticancer molecule.

Owing to its presence in several biological processes, Sirt1 acts as a potential therapeutic target for many diseases.

Deacetylation of Transcription Factors in Carcinogenesis

Reversible Nε-lysine acetylation/deacetylation is one of the most common post-translational modifications (PTM) of histones and non-histone proteins that is regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs). This epigenetic process is highly involved in carcinogenesis, affecting histone and non-histone proteins' properties and their biological functions. Some of the transcription factors, including tumor suppressors and oncoproteins, undergo this modification altering different cell signaling pathways. HDACs deacetylate their targets, which leads to either the upregulation or downregulation of proteins involved in the regulation of cell cycle and apoptosis, ultimately influencing tumor growth, invasion, and drug resistance. Therefore, epigenetic modifications are of great clinical importance and may constitute a new therapeutic target in cancer treatment. This review is aimed to present the significance of HDACs in carcinogenesis through their influence on functions of transcription factors, and therefore regulation of different signaling pathways, cancer progression, and metastasis.

PROTACs: Promising Approaches for Epigenetic Strategies to Overcome Drug Resistance

Epigenetic modulation of gene expression is essential for tissue-specific development and maintenance in mammalian cells. Disruption of epigenetic processes, and the subsequent alteration of gene functions, can result in inappropriate activation or inhibition of various cellular signaling pathways, leading to cancer. Recent advancements in the understanding of the role of epigenetics in cancer initiation and progression have uncovered functions for DNA methylation, histone modifications, nucleosome positioning, and non-coding RNAs. Epigenetic therapies have shown some promise for hematological malignancies, and a wide range of epigenetic-based drugs are undergoing clinical trials. However, in a dynamic survival strategy, cancer cells exploit their heterogeneous population which frequently results in the rapid acquisition of therapy resistance. Here, we describe novel approaches in drug discovery targeting the epigenome, highlighting recent advances the selective degradation of target proteins using Proteolysis Targeting Chimera (PROTAC) to address drug resistance.

Role of Forkhead Box O Proteins in Hepatocellular Carcinoma Biology and Progression (Review)

Hepatocellular carcinoma (HCC), the most common type of malignant tumor of the digestive system, is associated with high morbidity and mortality. The main treatment for HCC is surgical resection. Advanced disease, recurrence, and metastasis are the main factors affecting prognosis. Chemotherapy and radiotherapy are not sufficiently efficacious for the treatment of primary and metastatic HCC; therefore, optimizing targeted therapy is essential for improving outcomes. Forkhead box O (FOXO) proteins are widely expressed in cells and function to integrate a variety of growth factors, oxidative stress signals, and other stimulatory signals, thereby inducing the specific expression of downstream signal factors and regulation of the cell cycle, senescence, apoptosis, oxidative stress, HCC development, and chemotherapy sensitivity. Accordingly, FOXO proteins are considered multifunctional targets of cancer treatment. The current review discusses the roles of FOXO proteins, particularly FOXO1, FOXO3, FOXO4, and FOXO6, in HCC and establishes a theoretical basis for the potential targeted therapy of HCC.

Hsa-miR-34a-5p reverses multidrug resistance in gastric cancer cells by targeting the 3'-UTR of SIRT1 and inhibiting its expression

Multidrug resistance (MDR) is a major obstacle to chemotherapy, which leads to ineffective chemotherapy, an important treatment strategy for gastric cancer (GC). The abnormality of microRNAs (miRNAs) is critical to the occurrence and progression of MDR in various tumors. In this study, hsa-miR-34a-5p was found to be decreased in multidrug resistant GC cells SGC-7901/5-Fluorouracil (SGC-7901/5-Fu) compared to the parental SGC-7901 cells. Overexpression of hsa-miR-34a-5p in SGC-7901/5-Fu cells promoted apoptosis and decreased migration and invasiveness after chemotherapy. In addition, overexpression of hsa-miR-34a-5p suppressed the growth of drug-resistant tumor in vivo. The mechanism of the effects of hsa-miR-34a-5p could include the regulation of the expression of Sirtuin 1 (SIRT1), P-glycoprotein (P-gp) or Multidrug resistance-related protein 1 (MRP1) through direct binding to the 3'-untranslated region (UTR) of SIRT1. Functional gain-and-loss experiments indicated that hsa-miR-34a-5p enhances the chemotherapy sensitivity of MDR GC cells by inhibiting SIRT1, P-gp and MRP1. In conclusion, hsa-miR-34a-5p can reverse the MDR of GC cells by inhibiting the expression of SIRT1, P-gp or MRP1.

Role of Reductive versus Oxidative Stress in Tumor Progression and Anticancer Drug Resistance

Redox homeostasis is not only essential for the maintenance of normal physiological functions, but also plays an important role in the growth, survival, and therapy resistance of cancer cells. Altered redox balance and consequent disruption of redox signaling are implicated in the proliferation and progression of cancer cells and their resistance to chemo- and radiotherapy. The nuclear factor erythroid 2 p45-related factor (Nrf2) is the principal stress-responsive transcription factor that plays a pivotal role in maintaining cellular redox homeostasis. Aberrant Nrf2 overactivation has been observed in many cancerous and transformed cells. Uncontrolled amplification of Nrf2-mediated antioxidant signaling results in reductive stress. Some metabolic pathways altered due to reductive stress have been identified as major contributors to tumorigenesis. This review highlights the multifaceted role of reductive stress in cancer development and progression.

Sirtuin 1 and 2 inhibitors enhance the inhibitory effect of sorafenib in hepatocellular carcinoma cells

Multidrug resistance (MDR) counteracts the efficiency of sorafenib, an important first-line therapy for hepatocellular carcinoma (HCC). Sirtuins (SIRTs) 1 and 2 are associated with tumor progression and MDR. We treated 2D and 3D cultures (which mimic the features of in vivo tumors) from HCC cells with sorafenib alone or in the presence of SIRTs 1 and 2 inhibitors (cambinol or EX-527; combined treatments). Cultures subjected to combined treatments showed a greater fall in cellular viability, proliferation (PCNA, cyclin D1 and Ki-67 expression and cell cycle analysis), migration and invasion when compared with cultures treated only with sorafenib. Similarly, combined treatments produced more apoptosis (annexin V/PI, caspase-3/7 activity) than sorafenib alone. Since cell cycle dysregulation and apoptotic blockage are reported mechanisms of MDR, the modulation found in PCNA, cyclin D1, Ki-67 and caspase-3/7 proteins by cambinol and EX-527 are probably playing a role in enhancing the sensitivity of HCC cell lines to sorafenib. EX-527 reduced MRP3 and BCRP expression in sorafenib-treated HCC cells. Since ABC transporters contribute to MDR, MRP3 and BCRP could be also influencing in the response of HCC cells to sorafenib. Overall, 2D and 3D cultures behave similarly except that 3D cultures were less sensitive to treatments, reinforcing the clinical relevance of the current study. Findings presented in this manuscript support a potential application for SIRTs 1 and 2 inhibitors since we demonstrated that these compounds enhance the inhibitory effect of sorafenib upon treatment of hepatocellular carcinoma cells lines.

SRC Promotes Tamoxifen Resistance in Breast Cancer via Up-Regulating SIRT1

Background

Endocrine therapy plays a key role in estrogen receptor-positive breast cancer patients; but, tamoxifen resistance could be a real difficulty for these patients. Several attempts have been made to explore the mechanism and new therapies for these patients. We intend to clarify the expression change of SRC and SIRT1 in tamoxifen-resistant breast cancer cells and explore their functions on tamoxifen resistance.

Methods

SRC and SIRT1 expressions were analyzed by RNA sequencing, qPCR and Western blotting. Loss and gain of function of SRC and SIRT1 were utilized to indicate their oncogenic roles in tamoxifen resistance in vitro and in vivo. Kaplan–Meier analysis and receiver operating characteristic curve were used to evaluate the survival and the predicted effects of SRC and SIRT1 on patients’ prognosis.

Results

High expressions of SRC and/or SIRT1 were found in tamoxifen-resistant cells and related to poor overall survival (p<0.05 for SRC, p<0.001 for SIRT1, p<0.001 for SRC and SIRT1) and cancer-specific survival (p<0.05 for SRC, p<0.01 for SIRT1, p<0.01 for SRC and SIRT1) of tamoxifen-treated breast cancer patients. Down-regulation of SRC (p<0.01) or SIRT1 (p<0.05) separately reversed the resistance to tamoxifen and the minimal concentration of SRC inhibitor KX-01 (p<0.05) or SIRT1 inhibitor EX527 (p<0.001) could also suppress cell proliferation. The expression level of SIRT1 was positively correlated with that of SRC. Overexpression of SRC significantly promotes the cell resistance to tamoxifen inhibited by SIRT1 (p<0.01). In vivo experiments confirmed the effects of SRC on tumor growth by over- or down-regulating SRC expression (p<0.001 and p<0.001, respectively).

Conclusion

SRC and SIRT1 are both up-regulated in tamoxifen-resistant breast cancer cells and related to a poor prognosis in tamoxifen-treated breast cancer. Moreover, SRC could promote tamoxifen resistance by up-regulating SIRT1. SRC and SIRT1 might be novel therapeutic targets in tamoxifen-resistant breast cancer and the interaction between SRC and SIRT1 needs to be further explored.

Emerging role of sirtuins in breast cancer metastasis and multidrug resistance: Implication for novel therapeutic strategies targeting sirtuins

Sirtuins (SIRTs), a class III histone deacetylases (HDACs) that require NAD⁺ as a cofactor and include SIRT1-7 proteins in mammals. Accumulative evidence has established that every sirtuin possesses exclusive and poised biology, implicating their role in the regulation of multifaceted biological functions leading to breast cancer initiation, progression, and metastasis. This article provides an outline of recent developments in the role of sirtuins in breast cancer metastasis and development of multidrug resistance (MDR). In addition, we have also highlighted the impending prospects of targeting SIRTs to overcome MDR to bring advancement in breast cancer management. Further, this review will focus on strategies for improving the activity and efficacy of existing cancer therapeutics by combining (adjuvant treatment/therapy) them with sirtuin inhibitors/modulators. All available as well as newly discovered synthetic and dietary sirtuin inhibitors, activators/modulators have been extensively reviewed and compiled to provide a rationale for targeting sirtuins. Further, we discuss their potential in developing future therapeutics against sirtuins proposing their use along with conventional chemotherapeutics to overcome the problem of breast cancer metastasis and MDR.

High Expression of SIRT1 Associates with the Doxorubicin Resistance of Breast Cancer through the Activation of Akt

Background and Purpose:

Although limited by side effects and development of resistance, doxorubicin still represent the most common chemotherapy for breast cancer. Thus, the identification of critical molecules to alleviate doxorubicin resistance is crucial. Here, we provide a molecular rationale for the breast cancer patients potentially benefitting from doxorubicin based on the expression levels of SIRT1, a identified member of longevity genes.

Methods:

SIRT1-overexpressed and SIRT1-knockdown breast cancer cells were established to investigate the functions of SIRT1 in regulating doxorubicin resistance both in vitro and in vivo. Cell proliferation was analyzed via CCK8 assay, cell apoptosis was studied by TUNEL anslysis. Molecule interaction was analyzed through co-immunoprecipitation and immunofluorescence techniques. Sensibility to doxorubicin was assessed in vivo through nude mice tumorigenicity experiment.

Results::

First, SIRT1 was found higher-expressed in breast cancer doxorubicin-resistant cells MCF-7/ADR than that in doxorubicin- sensitive cells MCF-7. Moreover, SIRT1-knockdown MCF-7/ADR cells showed higher susceptible to doxorubicin both in vitro and in vivo models, whereas overexpressing of SIRT1 obviously inhibited this phenotype. Accordingly, SIRT1 was found interacted with Akt, consequently promoted the activity of Akt in MCF-7/ADR cells in vitro and positively correlated with the expression of P-Akt in vivo. Reversion the activity of Akt partially downturned the doxorubicin-resistant effects mediated by SIRT1.

Conclusion:

This investigation suggested the value of SIRT1 as biomarker of response to doxorubicin, leading to the development of new tools for the management of breast cancer patients.

The role of noncoding RNAs and sirtuins in cancer drug resistance

Cancer is a rising and major health issue around the world. The acquisition of resistance to chemotherapeutic drugs is a great obstacle for the effective treatment of nearly all cancers. Drug resistance is regulated by multiple factors and mechanisms including genetic mutations, abnormal expression of some cellular transporters such as multidrug resistance (MDR) transporters, changes in apoptotic pathways, cancer stem cells, tumor microenvironment, and noncoding RNAs (ncRNAs). Evidence clearly indicates a key role for sirtuins in several characteristics of cancer drug resistance. Recent studies demonstrated the crucial impact of some ncRNAs on sirtuins expression leading to modulation of chemotherapy resistance in cancers. In this review, we will focus on the current findings about the impacts of ncRNAs on the sirtuins pathway and their role in drug resistance of cancer.

The role of transporters in cancer redox homeostasis and cross-talk with nanomedicines

Tumor cell usually exhibits high levels of reactive oxygen species and adaptive antioxidant system due to the metabolic, genetic, and microenvironment-associated alterations. The altered redox homeostasis can promote tumor progression, development, and treatment resistance. Several membrane transporters are involved in the resetting redox homeostasis and play important roles in tumor progression. Therefore, targeting the involved transporters to disrupt the altered redox balance emerges as a viable strategy for cancer therapy. In addition, nanomedicines have drawn much attention in the past decades. Using nanomedicines to target or reset the redox homeostasis alone or combined with other therapies has brought convincing data in cancer treatment. In this review, we will introduce the altered redox balance in cancer metabolism and involved transporters, and highlight the recent advancements of redox-modulating nanomedicines for cancer treatment.

Catalpol alleviates adriamycin-induced nephropathy by activating the SIRT1 signalling pathway in vivo and in vitro

BACKGROUND AND PURPOSE

Catalpol, a water-soluble active ingredient isolated from Rehmannia glutinosa, exhibits multiple pharmacological activities. However, the mechanism(s) underlying protection against renal injury by catalpol remains unknown.

EXPERIMENTAL APPROACH

Adriamycin-induced kidney injury models associated with podocyte damage were employed to investigate the nephroprotective effects of catalpol. In vivo, TUNEL and haematoxylin-eosin staining was used to evaluate the effect of catalpol on kidney injury in mice. In vitro, effects of catalpol on podocyte damage induced by adriamycin was determined by elisa kit, flow cytometry, Hoechst 33342, and TUNEL staining. The mechanism was investigated by siRNA, EX527, and docking simulations.

KEY RESULTS

In vivo, catalpol treatment significantly improved adriamycin-induced kidney pathological changes and decreased the number of apoptotic cells. In vitro, catalpol markedly decreased the intracellular accumulation of adriamycin and reduced the calcium ion level in podocytes and then attenuated apoptosis. Importantly, the regulatory effects of catalpol on sirtuin 1 (SIRT1), multidrug resistance-associated protein 2 (MRP2), and the TRPC6 channel were mostly abolished after incubation with SIRT1 siRNA or the SIRT1-specific inhibitor EX527. Furthermore, docking simulations showed that catalpol efficiently oriented itself in the active site of SIRT1, indicating a higher total binding affinity score than that of other SIRT1 activators, such as resveratrol, SRT2104, and quercetin.

CONCLUSION AND IMPLICATIONS

Taken together, our results suggest that catalpol exhibits strong protective effects against adriamycin-induced nephropathy by inducing SIRT1-mediated inhibition of TRPC6 expression and enhancing MRP2 expression.

Novel and Alternative Targets Against Breast Cancer Stemness to Combat Chemoresistance

Breast cancer stem cells (BCSCs) play a vital role in tumor progression and metastasis. They are heterogeneous and inherently radio- and chemoresistant. They have the ability to self-renew and differentiate into non-BCSCs. These determinants of BCSCs including the plasticity between the mesenchymal and epithelial phenotypes often leads to minimal residual disease (MRD), tumor relapse, and therapy failure. By studying the resistance mechanisms in BCSCs, a combinatorial therapy can be formulated to co-target BCSCs and bulk tumor cells. This review addresses breast cancer stemness and molecular underpinnings of how the cancer stemness can lead to pharmacological resistance. This might occur through rewiring of signaling pathways and modulated expression of various targets that support survival and self-renewal, clonogenicity, and multi-lineage differentiation into heterogeneous bulk tumor cells following chemotherapy. We explore emerging novel and alternative molecular targets against BC stemness and chemoresistance involving survival, drug efflux, metabolism, proliferation, cell migration, invasion, and metastasis. Strategic targeting of such vulnerabilities in BCSCs may overcome the chemoresistance and increase the longevity of the metastatic breast cancer patients.

Resveratrol Promotes Diabetic Wound Healing via SIRT1-FOXO1-c-Myc Signaling Pathway-Mediated Angiogenesis

Background/Aims: Diabetic non-healing skin ulcers represent a serious challenge in clinical practice, in which the hyperglycemia-induced disturbance of angiogenesis, and endothelial dysfunction play a crucial role. Resveratrol (RES), a silent information regulator 1 (SIRT1) agonist, can improve endothelial function and has strong pro-angiogenic properties, and has thus become a research focus for the treatment of diabetic non-healing skin ulcers; however, the underlying mechanism by which RES regulates these processes remains unclear. Therefore, the present study was intended to determine if RES exerts its observed protective role in diabetic wound healing by alleviating hyperglycemia-induced endothelial dysfunction and the disturbance of angiogenesis.

Methods: We investigated the effects of RES on cell migration, cell proliferation, apoptosis, tube formation, and the underlying molecular mechanisms in 33 mM high glucose-stimulated human umbilical vein endothelial cells (HUVECs) by semi-quantitative RT-PCR, western blot analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and immunofluorescence in vitro. We further explored the role of RES on endothelial dysfunction and wound healing disturbance in db/db mice by TUNEL staining, immunofluorescence, and photography in vivo.

Results: We observed an obvious inhibition of hyperglycemia-triggered endothelial dysfunction and a disturbance of angiogenesis, followed by the promotion of diabetic wound healing via RES, along with restoration of the activity of the hyperglycemia-impaired SIRT1 signaling pathway. Pretreatment with EX-527, a SIRT1 inhibitor, abolished the RES-mediated endothelial protection and pro-angiogenesis action, and then delayed diabetic wound healing. Furthermore, examination of the overexpression of forkhead box O1 (FOXO1), a transcription factor substrate of SIRT1, in HUVECs and db/db mice revealed that RES activated SIRT1 to restore hyperglycemia-triggered endothelial dysfunction and disturbance of angiogenesis, followed by the promotion of diabetic wound healing in a c-Myc-dependent manner. Pretreatment with 10058-F4, a c-Myc inhibitor, repressed RES-mediated endothelial protection, angiogenesis, and diabetic wound healing.

Conclusion: Our findings indicate that the positive role of RES in diabetic wound healing via its SIRT1-dependent endothelial protection and pro-angiogenic effects involves the inhibition of FOXO1 and the de-repression of c-Myc expression.

The effect of adipocyte-macrophage crosstalk in obesity-related breast cancer

Adipose tissue is the primary source of many pro-inflammatory cytokines in obesity. Macrophage numbers and pro-inflammatory gene expression are positively associated with adipocyte size. Free fatty acid and tumor necrosis factor-α involve in a vicious cycle between adipocytes and macrophages aggravating inflammatory changes. Thereby, M1 macrophages form a characteristic 'crown-like structure (CLS)' around necrotic adipocytes in obese adipose tissue. In obese women, CLSs of breast adipose tissue are responsible for both increase in local aromatase activity and aggressive behavior of breast cancer cells. Interlinked molecular mechanisms between adipocyte-macrophage-breast cancer cells in obesity involve seven consecutive processes: Excessive release of adipocyte- and macrophage-derived inflammatory cytokines, TSC1-TSC2 complex-mTOR crosstalk, insulin resistance, endoplasmic reticulum (ER) stress and excessive oxidative stress generation, uncoupled respiration and hypoxia, SIRT1 controversy, the increased levels of aromatase activity and estrogen production. Considering elevated risks of estrogen receptor (E2R)-positive postmenopausal breast cancer growth in obesity, adipocyte-macrophage crosstalk is important in the aforementioned issues. Increased mTORC1 signaling in obesity ensures the strong activation of oncogenic signaling in E2Rα-positive breast cancer cells. Since insulin and insulin-like growth factors have been identified as tumor promoters, hyperinsulinemia is an independent risk factor for poor prognosis in breast cancer despite peripheral insulin resistance. The unpredictable effects of adipocyte-derived leptin-estrogen-macrophage axis, and sirtuin 1 (SIRT1)-adipose-resident macrophage axis in obese postmenopausal patients with breast cancer are unresolved mechanistic gaps in the molecular links between the tumor growth and adipocytokines.

Endoplasmic reticulum stress: major player in size-dependent inhibition of P-glycoprotein by silver nanoparticles in multidrug-resistant breast cancer cells

Background

Development of multidrug resistance (MDR) is a major burden of successful chemotherapy, therefore, novel approaches to defeat MDR are imperative. Although the remarkable anti-cancer propensity of silver nanoparticles (AgNP) has been demonstrated and their potential application in MDR cancer has been proposed, the nanoparticle size-dependent cellular events directing P-glycoprotein (Pgp) expression and activity in MDR cancer have never been addressed. Hence, in the present study we examined AgNP size-dependent cellular features in multidrug resistant breast cancer cells.

Results

In this study we report that 75 nm AgNPs inhibited significantly Pgp efflux activity in drug-resistant breast cancer cells and potentiated the apoptotic effect of doxorubicin, which features were not observed upon 5 nm AgNP treatment. Although both sized AgNPs induced significant ROS production and mitochondrial damage, 5 nm AgNPs were more potent than 75 nm AgNPs in this respect, therefore, these effects can not to be accounted for the reduced transport activity of ATP-driven pumps observed after 75 nm AgNP treatments. Instead we found that 75 nm AgNPs depleted endoplasmic reticulum (ER) calcium stores, caused notable ER stress and decreased plasma membrane positioning of Pgp.

Conclusion

Our study suggests that AgNPs are potent inhibitors of Pgp function and are promising agents for sensitizing multidrug resistant breast cancers to anticancer drugs. This potency is determined by their size, since 75 nm AgNPs are more efficient than smaller counterparts. This is a highly relevant finding as it renders AgNPs attractive candidates in rational design of therapeutically useful agents for tumor targeting. In the present study we provide evidence that exploitation of ER stress can be a propitious target in defeating multidrug resistance in cancers.

Electronic supplementary material

The online version of this article (10.1186/s12951-019-0448-4) contains supplementary material, which is available to authorized users.

Role of FoxO Proteins in Cellular Response to Antitumor Agents

FoxO proteins (FoxOs) are transcription factors with a common DNA binding domain that confers selectivity for DNA interaction. In human cells, four proteins (FoxO1, FoxO3, FoxO4 and FoxO6), with redundant activity, exhibit mainly a positive effect on genes involved in cell cycle, apoptosis regulation and drug resistance. Thus, FoxOs can affect cell response to antitumor agent treatment. Their transcriptional activity depends on post-translational modifications, including phosphorylation, acetylation, and mono/poly-ubiquitination. Additionally, alterations in microRNA network impact on FoxO transcripts and in turn on FoxO levels. Reduced expression of FoxO1 has been associated with resistance to conventional agents (e.g., cisplatin) and with reduced efficacy of drug combinations in ovarian carcinoma cells. FoxO3 has been shown as a mediator of cisplatin toxicity in colorectal cancer. A requirement for FoxO3-induced apoptosis has been reported in cells exposed to targeted agents (e.g., gefitinib). Recently, the possibility to interfere with FoxO1 localization has been proposed as a valuable approach to improve cell sensitivity to cisplatin, because nuclear retention of FoxO1 may favor the induction of pro-apoptotic genes. This review focuses on the role of FoxOs in drug treatment response in tumor cells and discusses the impact of the expression of these transcription factors on drug resistance/sensitivity.

Novel and Alternative Targets Against Breast Cancer Stemness to Combat Chemoresistance

Breast cancer stem cells (BCSCs) play a vital role in tumor progression and metastasis. They are heterogeneous and inherently radio- and chemoresistant. They have the ability to self-renew and differentiate into non-BCSCs. These determinants of BCSCs including the plasticity between the mesenchymal and epithelial phenotypes often leads to minimal residual disease (MRD), tumor relapse, and therapy failure. By studying the resistance mechanisms in BCSCs, a combinatorial therapy can be formulated to co-target BCSCs and bulk tumor cells. This review addresses breast cancer stemness and molecular underpinnings of how the cancer stemness can lead to pharmacological resistance. This might occur through rewiring of signaling pathways and modulated expression of various targets that support survival and self-renewal, clonogenicity, and multi-lineage differentiation into heterogeneous bulk tumor cells following chemotherapy. We explore emerging novel and alternative molecular targets against BC stemness and chemoresistance involving survival, drug efflux, metabolism, proliferation, cell migration, invasion, and metastasis. Strategic targeting of such vulnerabilities in BCSCs may overcome the chemoresistance and increase the longevity of the metastatic breast cancer patients.

Breaking down the Contradictory Roles of Histone Deacetylase SIRT1 in Human Breast Cancer

Breast cancer (BC) is the most common type of cancer in women worldwide; it is a multifactorial genetic disease. Acetylation and deacetylation are major post-translational protein modifications that regulate gene expression and the activity of a myriad of oncoproteins. Aberrant deacetylase activity can promote or suppress tumorigenesis and cancer metastasis in different types of human cancers, including breast cancer. Sirtuin-1 (SIRT1) is a class-III histone deacetylase (HDAC) that deacetylates both histone and non-histone targets. The often-described ‘regulator of regulators’ is deeply implicated in apoptosis, gene regulation, genome maintenance, DNA repair, aging, and cancer development. However, despite the accumulated studies over the past decade, the role of SIRT1 in human breast cancer remains a subject of debate and controversy. The ambiguity surrounding the implications of SIRT1 in breast tumorigenesis stems from the discrepancy between studies, which have shown both tumor-suppressive and promoting functions of SIRT1. Furthermore, studies have shown that SIRT1 deficiency promotes or suppresses tumors in breast cancer, making it an attractive therapeutic target in cancer treatment. This review provides a comprehensive examination of the various implications of SIRT1 in breast cancer development and metastasis. We will also discuss the mechanisms underlying the conflicting roles of SIRT1, as well as its selective modulators, in breast carcinogenesis.

CPEB1 mediates hepatocellular carcinoma cancer stemness and chemoresistance

Cancer stem cells (CSCs) are a subpopulation of cells within tumors that are believed to possess pluripotent properties and thought to be responsible for tumor initiation, progression, relapse and metastasis. Cytoplasmic polyadenylation element-binding protein 1 (CPEB1), a sequence-specific RNA-binding protein that regulates mRNA polyadenylation and translation, has been linked to cancer progression and metastasis. However, the involvement of CPEB1 in hepatocellular carcinoma (HCC) remains unclear. In this study, we have demonstrated that CPEB1 directly regulates sirtuin 1 (SIRT1) mRNA to mediate cancer stemness in HCC. Cancer stemness was analyzed by self-renewal ability, chemoresistance, metastasis, expression of stemness-related genes and CSC marker-positive cell populations. The results indicate that CPEB1 is downregulated in HCC. Overexpression of CPEB1 dramatically reduced HCC cell stemness, whereas silencing CPEB1 enhances it. Using site-directed mutagenesis, a luciferase reporter assay, and immunoprecipitation, we found that CPEB1 could directly target the 3′-UTR of SIRT1, control poly(A) tail length and suppress its translation to mediate cancer stemness in vitro and in vivo. Overall, our findings suggest that the negative regulation between CPEB1 and SIRT1 contributes to the suppression of cancer stemness in HCC. CPEB1 may have potential as a therapeutic target in HCC.

Combination of SIRT1 and Src overexpression suggests poor prognosis in luminal breast cancer

Objectives

1) Analyze the correlation of SIRT1 and Src with human breast cancer (BC) prognosis; 2) explore the roles of SIRT1 and Src in BC cell proliferation, tumor invasion, and metastasis; and 3) analyze the correlation and interaction between SIRT1 and Src.

Materials and methods

1) Tissue microarray was used to analyze the expression of SIRT1 and Src in human BC tissues and the correlation between protein expression and cancer prognosis; 2) CCK8 assay was used to determine the influence of SIRT1 and Src inhibitors on BC cell proliferation; 3) Transwell migration assay and wound healing assay were used to determine the effect of SIRT1 and Src inhibitors on BC cell migration and invasion; and 4) Western blotting was used to analyze the correlation and interaction between SIRT1 and Src.

Results

1) Combination of SIRT1 and/or Src positivity is a prognosis factor in BC, especially in luminal type; 2) MCF-7 cell proliferation is suppressed by SIRT1 inhibitor Ex527, and cell migration and invasion were inhibited by Src inhibitor bosutinib; 3) combined with Ex527, bosutinib has a significantly increased effect on MCF-7 cell migration suppression; and 4) there is a positive association between SIRT1 and Src both in BC tissues and in MCF-7 cells.

Conclusion

1) SIRT1 and Src overexpression are both correlated with poor prognosis in human BC; 2) SIRT1 + Src (SIRT1 and/or Src positivity) is a fine prognosis model for luminal-type BC; 3) SIRT1 is a copromotor of Src in BC migration and invasion, but not in cell proliferation; and 4) our results suggest a potential interaction or a common regulation pathway between SIRT1 and Src expression and activity.

FOXOs Maintaining the Equilibrium for Better or for Worse

A paradigm shift is emerging within the FOXO field and accumulating evidence indicates that we need to reappreciate the role of FOXOs, at least in cancer development. Here, we discuss the possibility that FOXOs are both tumor suppressors as well as promoters of tumor progression. This is mostly dependent on the biological context. Critical to this dichotomous role is the notion that FOXOs are central in preserving cellular homeostasis in redox control, genomic stability, and protein turnover. From this perspective, a paradoxical role in both suppressing and enhancing tumor progression can be reconciled. As many small molecules targeting the PI3K pathway are developed by big pharmaceutical companies and/or are in clinical trial, we will discuss what the consequences may be for the context-dependent role of FOXOs in tumor development in treatment options based on active PI3K signaling in tumors.

SIRT1 and Estrogen Signaling Cooperation for Breast Cancer Onset and Progression

Breast cancer remains a significant female mortality cause. It constitutes a multifactorial disease for which research on environmental factors offers little help in predicting onset or progression. The pursuit for its foundations by analyzing hormonal changes as a motive for disease development, indicates that increased exposure to estrogens associates with increased risk. A prevalent number of breast cancer cases show dependence on the increased activity of the classic nuclear estrogen receptor (ER) for cell proliferation and survival. SIRT1 is a Type III histone deacetylase which is receiving increasing attention due to its ability to perform activities over relevant non-histone proteins and transcription factors. Interestingly, concomitant SIRT1 overexpression is commonly found in ER-positive breast cancer cases. Both proteins had been shown to directly interact, in a process related to altered intracellular signaling and aberrant transcription, then promoting tumor progression. Moreover, SIRT1 activities had been also linked to estrogenic effects through interaction with the G-protein coupled membrane bound estrogen receptor (GPER). This work aims to summarize present knowledge on the interplay between SIRT1 and ER/GPER for breast cancer onset and progression. Lastly, evidences on the ability of SIRT1 to interact with TGFß signaling, a concurrent pathway significantly involved in breast cancer progression, are reported. The potential of this research field for the development of innovative strategies in the assessment of orphan breast cancer subtypes, such as triple negative breast cancer (TNBC), is discussed.

SIRT1 inhibition impairs non-homologous end joining DNA damage repair by increasing Ku70 acetylation in chronic myeloid leukemia cells

Most chemotherapeutic agents for leukemia are DNA damaging agents. However, DNA lesions can be repaired by activities of DNA repair systems. Increasing evidence have shown that enhanced DNA damage repair capacity contributes to chemotherapy resistance in leukemia cells. Thus, targeting DNA repair mechanisms is a promising strategy for novel leukemia treatment. SIRT1 expressions were downregulated by lentivirus-delivered SIRT1 shRNA in myeloid leukemia cells. SIRT1 mRNA and protein levels were analyzed by real-time PCR and Western blot, respectively. Flow cytometry was carried out to analyze cell cycle progression, apoptosis and DNA damage repair efficiency. DNA damage levels were assessed by alkaline comet assay, and H2AX phosphorylation was analyzed by immunoblotting and immunofluorescence. A mouse leukemia model was established by transplanting lentivirus-infected K562 cells containing SIRT1 shRNA into sublethally irradiated NOD/SCID mice, and tumorigenesis was evaluated by detecting tumor weights and mice survival. SIRT1 expressions were upregulated in myeloid leukemic patients. Downregulation of SIRT1 by RNAi promoted etoposide-induced DNA damage in myeloid leukemia cells accompanied by reduced NHEJ activity, and increased Ku70 acetylation. Furthermore, SIRT1 knockdown resulted in cell cycle arrest, induction of apoptosis and reduction of K562 cell proliferation accompanied by enhanced p53 and FOXO1 acetylation in K562 cells after etoposide treatment. Importantly, SIRT1 downregulation reduced the tumorigenesis ability of K562 cells in mouse xenografts following chemotherapy treatment. These results revealed that SIRT1 promotes the NHEJ repair pathway by deacetylating Ku70 in K562 cells, suggesting that SIRT1 is a novel therapeutic target for treating myeloid leukemia.

Sirtuin 7: a new marker of aggressiveness in prostate cancer

Predictive biomarkers for advanced prostate cancer (PCa) are still missing. The sirtuin 7 (SIRT7) has been linked to tumorogenesis but its role in prostate cancer is poorly documented. To determine if SIRT7 can be a biomarker for aggressive prostate cancer and plays a role in PCa aggressiveness. We analyzed the expression of SIRT7 by immunohistochemistry in 57 patients comparing healthy with adjacent cancer tissue. SIRT7 levels were significantly elevated in tumors and its expression was positively associated with the grade. We also demonstrated that the knock down of SIRT7 decreased the migration of DU145 and PC3 cells (two androgen-independent prostate cancer cell lines) whereas the overexpression of the native protein but not the mutated form increased the cell migration and the invasion of the poorly aggressive prostate cancer cell line LNCaP. Finally, we also showed that SIRT7 overexpression induced the resistance to docetaxel. Our results demonstrate that SIRT7 promotes prostate cancer cell aggressiveness and chemoresistance and suggest that SIRT7 is a good predictive biomarker of PCa aggressiveness.

Members of FOX family could be drug targets of cancers

FOX families play important roles in biological processes, including metabolism, development, differentiation, proliferation, apoptosis, migration, invasion and longevity. Here we are focusing on roles of FOX members in cancers, FOX members and drug resistance, FOX members and stem cells. Finally, FOX members as drug targets of cancer treatment were discussed. Future perspectives of FOXC1 research were described in the end.

Low Rap1-interacting factor 1 and sirtuin 6 expression predict poor outcome in radiotherapy-treated Hodgkin lymphoma patients

Sirtuins (SIRTs) are a family of histone deacetylases, which widely regulate cellular metabolism and are also involved in DNA repair. Rap1-interacting factor 1 (Rif1) and O⁶-alkylguanine DNA alkyltransferase (MGMT) are DNA-repair enzymes, which may potentially be involved in resistance to treatment of classical Hodgkin lymphoma (HL). We assessed the expression levels of (previously unstudied) SIRT1, SIRT4, SIRT6, Rif1, and MGMT immunohistochemically in 85 patients with untreated classical HL. Aberrant distributions of SIRT1, SIRT4, and SIRT6 were detected in Hodgkin neoplastic Reed-Sternberg (RS) cells compared with reactive elements. Low-level expression of both Rif1 and SIRT6 predicted dismal relapse-free survival in radiotherapy-treated patients (multivariate analysis; HR 8.521; 95% CI 1.714-42.358; p = .0088). Expression levels of SIRT1, 4, and 6 were abnormally distributed in RS cells, suggesting a putative role of aberrant acetylation in classical HL carcinogenesis. Rif1 and SIRT6 may also have substantial prognostic and even predictive roles in classical HL.

The prognostic role of Sirt1 expression in solid malignancies: a meta-analysis

Although many studies have discussed the association of abnormally expressed silent information regulator 1 (Sirt1) with the prognosis of patients with a variety of solid carcinomas, they failed to agree on whether excessive Sirt1 indicates a good or poor overall survival for the patients. We conducted the current meta-analysis to illustrate the prognostic value of Sirt1 in solid malignancies. Articles published before December 2016 were searched using Pubmed and Web of Science. The studies were selected for the meta-analysis based on certain criteria. A total of 7,369 cases from 37 studies were included, in which 48.6% of the patients overexpressed Sirt1. The overall survival (OS) and clinical features, such as age and TNM stage, were analyzed using RevMan 5.3 software. Sirt1 overexpression was significantly correlated with the OS (HR: 1.52, 95% CI: [1.23, 1.88], P = 0.0001), especially in liver cancer (HR: 1.78, 95% CI: [1.46, 2.18], P < 0.00001) and lung cancer (HR: 1.80, 95% CI: [1.06, 3.05], P = 0.03), which suggested that the overexpression of Sirt1 indicates poor prognosis of patients with solid cancers.

Characterization of acquired paclitaxel resistance of breast cancer cells and involvement of ABC transporters

Development of taxane resistance has become clinically very important issue. The molecular mechanisms underlying the resistance are still unclear. To address this issue, we established paclitaxel-resistant sublines of the SK-BR-3 and MCF-7 breast cancer cell lines that are capable of long-term proliferation in 100nM and 300nM paclitaxel, respectively. Application of these concentrations leads to cell death in the original counterpart cells. Both sublines are cross-resistant to doxorubicin, indicating the presence of the MDR phenotype. Interestingly, resistance in both paclitaxel-resistant sublines is circumvented by the second-generation taxane SB-T-1216. Moreover, we demonstrated that it was not possible to establish sublines of SK-BR-3 and MCF-7 cells resistant to this taxane. It means that at least the tested breast cancer cells are unable to develop resistance to some taxanes. Employing mRNA expression profiling of all known human ABC transporters and subsequent Western blot analysis of the expression of selected transporters, we demonstrated that only the ABCB1/PgP and ABCC3/MRP3 proteins were up-regulated in both paclitaxel-resistant sublines. We found up-regulation of ABCG2/BCRP and ABCC4 proteins only in paclitaxel-resistant SK-BR-3 cells. In paclitaxel-resistant MCF-7 cells, ABCB4/MDR3 and ABCC2/MRP2 proteins were up-regulated. Silencing of ABCB1 expression using specific siRNA increased significantly, but did not completely restore full sensitivity to both paclitaxel and doxorubicin. Thus we showed a key, but not exclusive, role for ABCB1 in mechanisms of paclitaxel resistance. It suggests the involvement of multiple mechanisms in paclitaxel resistance in tested breast cancer cells.

SIRT1 in B[a]P-induced lung tumorigenesis

Benzo[a]pyrene (B[a]P) is a carcinogen in cigarette smoke. We found that B[a]P induced SIRT1 in human bronchial epithelial BEAS-2B cell. SIRT1 was overexpressed in the lung of B[a]P-exposed mice and in human lung cancer biopsies. SIRT1 up-regulated TNF-α and β-catenin and down-regulated the membrane fraction of E-cadherin. In addition, SIRT1 promoted invasion, migration and tumorigenesis of BEAS-2B cells in nude mice upon B[a]P exposure. Thus, SIRT1 is involved in B[a]P-induced transformation associated with activation of the TNF-α/β-catenin axis and is as a potential therapeutic target for lung cancer.

Minireview: The Link Between ERα Corepressors and Histone Deacetylases in Tamoxifen Resistance in Breast Cancer

Approximately 70% of breast cancers express the estrogen receptor (ER)α and are treated with the ERα antagonist, tamoxifen. However, resistance to tamoxifen frequently develops in advanced breast cancer, in part due to a down-regulation of ERα corepressors. Nuclear receptor corepressors function by attenuating hormone responses and have been shown to potentiate tamoxifen action in various biological systems. Recent genomic data on breast cancers has revealed that genetic and/or genomic events target ERα corepressors in the majority of breast tumors, suggesting that the loss of nuclear receptor corepressor activity may represent an important mechanism that contributes to intrinsic and acquired tamoxifen resistance. Here, the biological functions of ERα corepressors are critically reviewed to elucidate their role in modifying endocrine sensitivity in breast cancer. We highlight a mechanism of gene repression common to corepressors previously shown to enhance the antitumorigenic effects of tamoxifen, which involves the recruitment of histone deacetylases (HDACs) to DNA. As an indicator of epigenetic disequilibrium, the loss of ERα corepressors may predispose cancer cells to the cytotoxic effects of HDAC inhibitors, a class of drug that has been shown to effectively reverse tamoxifen resistance in numerous studies. HDAC inhibition thus appears as a promising therapeutic approach that deserves to be further explored as an avenue to restore drug sensitivity in corepressor-deficient and tamoxifen-resistant breast cancers.

Cancer drug resistance: redox resetting renders a way

Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.

Synthesis and Characterization of 4,11-Diaminoanthra[2,3-b]furan-5,10-diones: Tumor Cell Apoptosis through tNOX-Modulated NAD(+)/NADH Ratio and SIRT1

A series of new 4,11-diaminoanthra[2,3-b]furan-5,10-dione derivatives with different side chains were synthesized. Selected 2-unsubstituted derivatives 11-14 showed high antiproliferative potency on a panel of mammalian tumor cell lines including multidrug resistance variants. Compounds 11-14 utilized multiple mechanisms of cytotoxicity including inhibition of Top1/Top2-mediated DNA relaxation, reduced NAD(+)/NADH ratio through tNOX inhibition, suppression of a NAD(+)-dependent sirtuin 1 (SIRT1) deacetylase activity, and activation of caspase-mediated apoptosis. Here, for the first time, we report that tumor-associated NADH oxidase (tNOX) and SIRT1 are important cellular targets of antitumor anthracene-9,10-diones.

Sirtuin 1 promotes the growth and cisplatin resistance of endometrial carcinoma cells: a novel therapeutic target

Sirtuin 1 (SIRT1), originally identified as a longevity gene, is induced by caloric restriction, and regulates various cellular functions including DNA repair, cell survival and metabolism via the deacetylation of target proteins such as histone and p53. These functions are considered to act dualistically as preventing or facilitating cancer. This study aimed to clarify the expression and role of SIRT1 in endometrial carcinoma. Because a high-calorie diet was a well-known risk factor for endometrial carcinoma, we first hypothesized that SIRT1 might be downregulated in normal endometrial glandular cells of obese women. However, no correlation was observed between the expression of SIRT1 and body mass index (BMI). In contrast, regardless of BMI, the immunohistochemical expression of SIRT1 was significantly higher in endometrial carcinoma (108 cases) than in normal endometria (60 cases) (P<0.05), and its overexpression was associated with a shorter survival (P<0.05). Our experiments in vivo revealed that SIRT1 accelerated the proliferation of endometrial carcinoma cell lines (HHUA, HEC151, and HEC1B). SIRT1 overexpression significantly enhanced the resistance for cisplatin and paclitaxel in HHUA cells. Although p53 is an important target protein for SIRT1, the selective SIRT1 inhibitor (EX527) significantly suppressed the proliferation and cisplatin resistance of three endometrial carcinoma cell lines regardless of the p53 mutation status. In addition, SIRT1 overexpression in HHUA cells accelerated tumor growth and cisplatin resistance in nude mice, and EX527 significantly suppressed the growth of tumors of HHUA and HEC1B cells. No adverse effect of EX527 was observed in these mice. In conclusion, SIRT1 is involved in the acquisition of the aggressive behavior associated with endometrial carcinoma, and the SIRT1 inhibitor, EX527, may be a useful agent for the treatment of this malignancy.

Distinctive role of SIRT1 expression on tumor invasion and metastasis in breast cancer by molecular subtype

The aim of this study was to evaluate silent mating type information regulation 2 homolog 1 (SIRT1) expression levels by subtype and evaluate its predictive power of axillary lymph node metastasis (LNM) and its association with clinical outcome. A total of 427 patients diagnosed with invasive ductal carcinoma were chosen, immunohistochemical staining for SIRT1 expression was performed on tissue microarrays, and in vitro experiments with each intrinsic subtype of human breast cancer cell line were carried out. Increased expression of SIRT1 in hormone receptor-positive breast cancer and HER2 breast cancer subtype significantly correlated with lower risks of LNM. On the contrary, in triple-negative breast cancer, increased SIRT1 expression was more frequently observed in LNM-positive subgroup than LNM-negative subgroup. Combination of statistically significant, independent parameters including SIRT1 revealed predictive performance for LNM with area under the curve of 0.602, 0.587, and 0.726 for hormone receptor-positive breast cancer, HER2 breast cancer, and triple-negative breast cancer subtype, respectively. Inhibition of SIRT1 expression with small interfering RNA suppressed tumor invasion in MDA-MB-231, specifically. This is the first study to examine SIRT1 expression in breast cancer by subtype, and we have observed the potentially different role of SIRT1 gene having tumor-suppressive or tumor-promoting influence depending on the subtype; thus, different associations between SIRT1 expression and prognosis by subtype should be considered in its target therapy.

Sirtuin inhibitors as anticancer agents

Sirtuins are a class of enzymes with nicotinamide adenine dinucleotide (NAD)-dependent protein lysine deacylase function. By deacylating various substrate proteins, including histones, transcription factors, and metabolic enzymes, sirtuins regulate various biological processes, such as transcription, cell survival, DNA damage and repair, and longevity. Small molecules that can inhibit sirtuins have been developed and many of them have shown anticancer activity. Here, we summarize the major biological findings that connect sirtuins to cancer and the different types of sirtuin inhibitors developed. Interestingly, biological data suggest that sirtuins have both tumor-suppressing and tumor-promoting roles. However, most pharmacological studies with small-molecule inhibitors suggest that inhibiting sirtuins has anticancer effects. We discuss possible explanations for this discrepancy and suggest possible future directions to further establish sirtuin inhibitors as anticancer agents.

Diverse roles of SIRT1 in cancer biology and lipid metabolism

SIRT1, an NAD⁺-dependent deacetylase, has been described in the literature as a major player in the regulation of cellular stress responses. Its expression has been shown to be altered in cancer cells, and it targets both histone and non-histone proteins for deacetylation and thereby alters metabolic programs in response to diverse physiological stress. Interestingly, many of the metabolic pathways that are influenced by SIRT1 are also altered in tumor development. Not only does SIRT1 have the potential to regulate oncogenic factors, it also orchestrates many aspects of metabolism and lipid regulation and recent reports are beginning to connect these areas. SIRT1 influences pathways that provide an alternative means of deriving energy (such as fatty acid oxidation and gluconeogenesis) when a cell encounters nutritive stress, and can therefore lead to altered lipid metabolism in various pathophysiological contexts. This review helps to show the various connections between SIRT1 and major pathways in cellular metabolism and the consequence of SIRT1 deregulation on carcinogenesis and lipid metabolism.

Multidrug-resistant breast cancer: current perspectives

Breast cancer is the most common cancer in women worldwide, and resistance to the current therapeutics, often concurrently, is an increasing clinical challenge. By understanding the molecular mechanisms behind multidrug-resistant breast cancer, new treatments may be developed. Here we review the recent advances in this understanding, emphasizing the common mechanisms underlying resistance to both targeted therapies, notably tamoxifen and trastuzumab, and traditional chemotherapies. We focus primarily on three molecular mechanisms, the phosphatidylinositide 3-kinase/Akt pathway, the role of microRNAs in gene silencing, and epigenetic alterations affecting gene expression, and discuss how these mechanisms can interact in multidrug resistance. The development of therapeutics targeting these mechanisms is also addressed.