The histone deacetylase inhibitor vorinostat prevents TNFα-induced necroptosis by regulating multiple signaling pathways

Histone deacetylase-mediated silencing of PSTPIP2 expression contributes to aristolochic acid nephropathy-induced PANoptosis

BACKGROUND AND PURPOSE

Aristolochic acid nephropathy (AAN) is a progressive kidney disease caused by using herbal medicines. Currently, no therapies are available to treat or prevent aristolochic acid nephropathy. Histone deacetylase (HDAC) plays a crucial role in the development and progression of renal disease. We tested whether HDAC inhibitors could prevent aristolochic acid nephropathy and determined the underlying mechanism.

EXPERIMENTAL APPROACH

HDACs expression in the aristolochic acid nephropathy model was examined. The activation of PANoptosis of mouse kidney and renal tubular epithelial cell were assessed after exposure to HDAC1 and HDAC2 blockade. Kidney-specific knock-in of proline-serine-threonine-phosphatase-interacting protein 2 (PSTPIP2) mice were used to investigate whether PSTPIP2 affected the production of PANoptosome.

KEY RESULTS

Aristolochic acid upregulated the expression of HDAC1 and HDAC2 in the kidneys. Notably, the HDAC1 and HDAC2 specific inhibitor, romidepsin (FK228, depsipeptide), suppressed aristolochic acid-induced kidney injury, epithelial cell pyroptosis, apoptosis and necroptosis (PANoptosis). Moreover, romidepsin upregulated PSTPIP2 in renal tubular epithelial cells, which was enhanced by aristolochic acid treatment. Conditional knock-in of PSTPIP2 in the kidney protected against aristolochic acid nephropathy. In contrast, the knockdown of PSTPIP2 expression in PSTPIP2-knock-in mice restored kidney damage and PANoptosis. PSTPIP2 function was determined in vitro using PSTPIP2 knockdown or overexpression in mouse renal tubular epithelial cells (mTECs). Additionally, PSTPIP2 was found to regulate caspase 8 in aristolochic acid nephropathy.

CONCLUSION AND IMPLICATIONS

HDAC-mediated silencing of PSTPIP2 may contribute to aristolochic acid nephropathy. Hence, HDAC1 and HDAC2 specific inhibitors or PSTPIP2 could be valuable therapeutic agents for preventing aristolochic acid nephropathy.

Unwinding the modalities of necrosome activation and necroptosis machinery in neurological diseases

Necroptosis, a regulated form of cell death, is involved in the genesis and development of various life-threatening diseases, including cancer, neurological disorders, cardiac myopathy, and diabetes. Necroptosis initiates with the formation and activation of a necrosome complex, which consists of RIPK1, RIPK2, RIPK3, and MLKL. Emerging studies has demonstrated the regulation of the necroptosis cell death pathway through the implication of numerous post-translational modifications, namely ubiquitination, acetylation, methylation, SUMOylation, hydroxylation, and others. In addition, the negative regulation of the necroptosis pathway has been shown to interfere with brain homeostasis through the regulation of axonal degeneration, mitochondrial dynamics, lysosomal defects, and inflammatory response. Necroptosis is controlled by the activity and expression of signaling molecules, namely VEGF/VEGFR, PI3K/Akt/GSK-3β, c-Jun N-terminal kinases (JNK), ERK/MAPK, and Wnt/β-catenin. Herein, we briefly discussed the implication and potential of necrosome activation in the pathogenesis and progression of neurological manifestations, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, traumatic brain injury, and others. Further, we present a detailed picture of natural compounds, micro-RNAs, and chemical compounds as therapeutic agents for treating neurological manifestations.

Regulation of radiation-induced liver damage by modulation of SIRT-1 activity: In vivo rat model

Silent information regulator 1 (SIRT-1), a nicotinamide adenine dinucleotide-dependent deacetylase, was found to regulate cell apoptosis, inflammation, and oxidative stress response in living organisms. Therefore, the role of SIRT-1 in regulating forkhead box O/poly ADP-ribose polymerase-1 (FOXO-1/PARP-1) signaling could provide the necessary validation for developing new pharmacological targets for the promotion or inhibition of SIRT-1 activity toward radiation sensitivity. In the present study, the SIRT-1 signaling pathway is being investigated to study the possible modulatory effect of resveratrol (RSV, SIRT-1 activator) versus nicotinamide (NAM, SIRT-1 inhibitor) in case of liver damage induced by whole-body gamma irradiation. Rats were exposed to 6 Gy gamma radiation after being pretreated with either RSV (10 mg/kg/day) or NAM (100 mg/kg/day) for 5 days, and subsequent examining hepatic morphological changes and apoptotic markers were assessed. The expression of SIRT-1, FOXO-1, and cleaved PARP-1 in the liver was analyzed. RSV improved radiation-induced apoptosis, mitochondrial dysfunction, and inflammation signified by low expression of caspase-3, lactate dehydrogenase, complex-I activity, myeloperoxidase, and total nitric oxide content. RSV increased the expression of SIRT-1, whereas cleaved PARP-1 and FOXO-1 were suppressed. These protective effects were suppressed by inhibition of SIRT-1 activity using NAM. These findings suggest that RSV can attenuate radiation-induced hepatic injury by reducing apoptosis and inflammation via SIRT-1 activity modulation.

Social isolation reinforces aging-related behavioral inflexibility by promoting neuronal necroptosis in basolateral amygdala

Aging is characterized with a progressive decline in many cognitive functions, including behavioral flexibility, an important ability to respond appropriately to changing environmental contingencies. However, the underlying mechanisms of impaired behavioral flexibility in aging are not clear. In this study, we reported that necroptosis-induced reduction of neuronal activity in the basolateral amygdala (BLA) plays an important role in behavioral inflexibility in 5-month-old mice of the senescence-accelerated mice prone-8 (SAMP8) line, a well-established model with age-related phenotypes. Application of Nec-1s, a specific inhibitor of necroptosis, reversed the impairment of behavioral flexibility in SAMP8 mice. We further observed that the loss of glycogen synthase kinase 3α (GSK-3α) was strongly correlated with necroptosis in the BLA of aged mice and the amygdala of aged cynomolgus monkeys (Macaca fascicularis). Moreover, genetic deletion or knockdown of GSK-3α led to the activation of necroptosis and impaired behavioral flexibility in wild-type mice, while the restoration of GSK-3α expression in the BLA arrested necroptosis and behavioral inflexibility in aged mice. We further observed that GSK-3α loss resulted in the activation of mTORC1 signaling to promote RIPK3-dependent necroptosis. Importantly, we discovered that social isolation, a prevalent phenomenon in aged people, facilitated necroptosis and behavioral inflexibility in 4-month-old SAMP8 mice. Overall, our study not only revealed the molecular mechanisms of the dysfunction of behavioral flexibility in aged people but also identified a critical lifestyle risk factor and a possible intervention strategy.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Exogenous sodium hydrosulfide protects against high glucose‑induced injury and inflammation in human umbilical vein endothelial cells by inhibiting necroptosis via the p38 MAPK signaling pathway

In recent years hydrogen sulfide (H2S) has demonstrated vasculoprotective effects against cell death, which suggests its promising therapeutic potential for numerous types of disease. Additionally, a protective effect of exogenous H2S in HG‑induced injuries in HUVECs was demonstrated, suggesting a potential protective effect for diabetic vascular complications. The present study aimed to investigate the mechanism accounting for the cytoprotective role of exogenous H2S against high glucose [HG (40 mM glucose)]‑induced injury and inflammation in human umbilical vein endothelial cells (HUVECs). HUVECs were exposed to HG for 24 h to establish an in vitro model of HG‑induced cytotoxicity. The cells were pretreated with sodium hydrosulfide (NaHS), a donor of H2S, or inhibitors of necroptosis and p38 MAPK prior to the exposure to HG. Cell viability, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), IL‑1β, IL‑6, IL‑8, TNF‑α, phosphorylated‑(p)38 and receptor‑interacting protein 3 (RIP3) expression levels were detected using the indicated methods, including Cell Counting Kit 8, fluorescence detection, western blotting, immunofluorescence assay and ELISAs. The results demonstrated that necroptosis and the p38 MAPK signaling pathway mediated HG‑induced injury and inflammation. Notably, NaHS was discovered to significantly ameliorate p38 MAPK/necroptosis‑mediated injury and inflammation in response to HG, as evidenced by an increase in cell viability, a decrease in ROS generation and loss of MMP, as well as the reduction in the secretion of proinflammatory cytokines. In addition, the upregulated expression of RIP3 induced by HG was repressed by treatment with SB203580, while the HG‑induced upregulation of p‑p38 expression levels were significantly downregulated following the treatment of Nec‑1 and RIP3‑siRNA. In conclusion, the findings of the present study indicated that NaHS may protect HUVECs against HG‑induced injury and inflammation by inhibiting necroptosis via the p38 MAPK signaling pathway, which may represent a promising drug for the therapy of diabetic vascular complications.

Beta-Hydroxybutyrate, Friend or Foe for Stressed Hearts

One of the characteristics of the failing human heart is a significant alteration in its energy metabolism. Recently, a ketone body, β-hydroxybutyrate (β-OHB) has been implicated in the failing heart’s energy metabolism as an alternative “fuel source.” Utilization of β-OHB in the failing heart increases, and this serves as a “fuel switch” that has been demonstrated to become an adaptive response to stress during the heart failure progression in both diabetic and non-diabetic patients. In addition to serving as an alternative “fuel,” β-OHB represents a signaling molecule that acts as an endogenous histone deacetylase (HDAC) inhibitor. It can increase histone acetylation or lysine acetylation of other signaling molecules. β-OHB has been shown to decrease the production of reactive oxygen species and activate autophagy. Moreover, β-OHB works as an NLR family pyrin domain-containing protein 3 (Nlrp3) inflammasome inhibitor and reduces Nlrp3-mediated inflammatory responses. It has also been reported that β-OHB plays a role in transcriptional or post-translational regulations of various genes’ expression. Increasing β-OHB levels prior to ischemia/reperfusion injury results in a reduced infarct size in rodents, likely due to the signaling function of β-OHB in addition to its role in providing energy. Sodium-glucose co-transporter-2 (SGLT2) inhibitors have been shown to exert strong beneficial effects on the cardiovascular system. They are also capable of increasing the production of β-OHB, which may partially explain their clinical efficacy. Despite all of the beneficial effects of β-OHB, some studies have shown detrimental effects of long-term exposure to β-OHB. Furthermore, not all means of increasing β-OHB levels in the heart are equally effective in treating heart failure. The best timing and therapeutic strategies for the delivery of β-OHB to treat heart disease are unknown and yet to be determined. In this review, we focus on the crucial role of ketone bodies, particularly β-OHB, as both an energy source and a signaling molecule in the stressed heart and the overall therapeutic potential of this compound for cardiovascular diseases.

Heat stress induces RIP1/RIP3-dependent necroptosis through the MAPK, NF-κB, and c-Jun signaling pathways in pulmonary vascular endothelial cells

Necroptosis represents a newly defined form of regulated necrosis and participates in various human inflammatory diseases. It remains unclear whether necroptosis is presented in heatstroke-induced lung injury. We show that heat stress(HS) triggered an significant upregulation of receptor-interacting protein 1 (RIP1) and mixed lineage kinase domain-like protein (MLKL) expression in a time-dependent manner, without a significant change of receptor-interacting protein 3 (RIP3). Furthermore, co-immunoprecipitation assays showed that RIP1 binds to RIP3 to form the necrosome in heat stress-induced PMVECs. In vitro, necrostatin-1 (Nec-1) pre-treatment reduced heat stress-induced PMVECs necroptosis, which also inhibited HMGB1 translocation from the nucleus into the cytoplasm. Similarly, inhibition for ERK (PD98059), NF-κB (BAY11-7082) and c-Jun (c-Jun peptide), respectively, also suppressed the HMGB1 cytoplasm translocation. Furthermore, siRNA-mediated RIP1/RIP3 knockdown negatively regulated the release of HMGB1 in HS-induced necroptosis through the ERK, NF-κB, and c-Jun signaling pathways. Our study reveals that HS induces RIP1/RIP3-dependent necroptosis through the MAPK, NF-κB, and c-Jun signaling pathways in PMVECs.

Effect of the immobilized microcystin-LR-degrading enzyme MlrA on nodularin degradation and its immunotoxicity study

In freshwater ecosystems with frequent cyanobacterial blooms, the cyanobacteria toxin pollution is becoming increasingly serious. Nodularin (NOD), which has strong biological toxicity, has emerged as a new pollutant and affects the normal growth, development and reproduction of aquatic organisms. However, little information is available regarding this toxin. In this study, a graphene oxide material modified by L-cysteine was synthesized and used to immobilize microcystin-LR (MC-LR)-degrading enzyme (MlrA) to form an immobilized enzyme nanocomposite, CysGO-MlrA. Free-MlrA was used as a control. The efficiency of NOD removal by CysGO-MlrA was investigated. Additionally, the effects of CysGO-MlrA and the NOD degradation product on zebrafish lymphocytes were detected to determine the biological toxicity of these two substances. The results showed the following: (1) There was no significant difference in the degradation efficiency of NOD between CysGO-MlrA and free-MlrA; the degradation rate of both was greater than 80% at 1 h (2) The degradation efficiency of the enzyme could retain greater than 81% of the initial degradation efficiency after the CysGO-MlrA had been reused 7 times. (3) CysGO-MlrA retained greater than 50% of its activity on the 8th day when preserved at 0 °C, while free-MlrA lost 50% of its activity on the 4th day. (4) CysGO-MlrA and the degradation product of NOD showed no obvious cytotoxicity to zebrafish lymphocytes. Therefore, CysGO-MlrA might be used as an efficient and ecologically safe degradation material for NOD.

Current translational potential and underlying molecular mechanisms of necroptosis

Cell death has a fundamental impact on the evolution of degenerative disorders, autoimmune processes, inflammatory diseases, tumor formation and immune surveillance. Over the past couple of decades extensive studies have uncovered novel cell death pathways, which are independent of apoptosis. Among these is necroptosis, a tightly regulated, inflammatory form of cell death. Necroptosis contribute to the pathogenesis of many diseases and in this review, we will focus exclusively on necroptosis in humans. Necroptosis is considered a backup mechanism of apoptosis, but the in vivo appearance of necroptosis indicates that both caspase-mediated and caspase-independent mechanisms control necroptosis. Necroptosis is regulated on multiple levels, from the transcription, to the stability and posttranslational modifications of the necrosome components, to the availability of molecular interaction partners and the localization of receptor-interacting serine/threonine-protein kinase 1 (RIPK1), receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL). Accordingly, we classified the role of more than seventy molecules in necroptotic signaling based on consistent in vitro or in vivo evidence to understand the molecular background of necroptosis and to find opportunities where regulating the intensity and the modality of cell death could be exploited in clinical interventions. Necroptosis specific inhibitors are under development, but >20 drugs, already used in the treatment of various diseases, have the potential to regulate necroptosis. By listing necroptosis-modulated human diseases and cataloging the currently available drug-repertoire to modify necroptosis intensity, we hope to kick-start approaches with immediate translational potential. We also indicate where necroptosis regulating capacity should be considered in the current applications of these drugs.

Protective effects of Clematichinenoside AR against inflammation and cytotoxicity induced by human tumor necrosis factor-α

Clematichinenoside AR (AR), a major active ingredient extracted from traditional Chinese herb Clematis chinensis Osbeck, has been demonstrated to possess anti-inflammatory and immune-modulatory activities in the treatment of experimental rheumatoid arthritis (RA). The therapeutic potential of AR was supposed to be closely correlated to its ability against tumor necrosis factor-α (TNF-α). Therefore, we aimed to explore the protective effects of Clematichinenoside AR against inflammation and cytotoxicity induced by human TNF-α. AR treatment significantly decreased IL-6 and IL-8 secretion, and attenuated MMP-1 production in human RA-derived fibroblast-like synoviocyte MH7A cells stimulated by recombinant human TNF-α (rhTNF-α). AR might antagonize rhTNF-α-induced responses in MH7A cells through inhibiting p38 and ERK MAPKs signal activation. In TNF-α-sensitive murine fibroblast L929 cells, AR treatment attenuated the proliferation inhibition ratio induced by rhTNF-α/ActD and antagonized rhTNF-α-induced cytotoxicity. The cellular and nuclear morphological alterations in apoptotic characteristics induced by rhTNF-α/ActD in L929 cells were observed to be attenuated by the pretreatment with AR under a phase-contrast and fluorescence microscopy, respectively. The Annexin V-FITC/PI double-staining assay was performed to confirm that AR pretreatment obviously decreased the cell death. The antagonistic effects of AR against rhTNF-α-induced cytotoxicity might be potentially attributed to the degeneration of reactive oxygen species and the increasing of mitochondrial membrane potential, along with the suppression of durative phosphorylation of c-Jun N-terminal kinase (JNK). Collectively, our results indicated that AR antagonizes the inflammatory and cytotoxic activities induced by human TNF-α effectively in vitro, which provided further evidence for a novel mechanism underlying AR for treating RA correlating with excessive TNF-α production.

A phase 1 trial of Vorinostat in combination with concurrent chemoradiation therapy in the treatment of advanced staged head and neck squamous cell carcinoma

Purpose Vorinostat is a potent HDAC inhibitor that sensitizes head and neck squamous cell carcinoma (HNSCC) to cytotoxic therapy while sparing normal epithelium. The primary objective of this Phase I study was to determine the maximally tolerated dose (MTD) and safety of Vorinostat in combination with standard chemoradiation therapy treatment in HNSCC. Patients and Methods Eligible patients had pathologically confirmed Stage III, IVa, IVb HNSCC, that was unresectable or borderline resectable involving the larynx, hypopharynx, nasopharynx, and oropharynx. Vorinostat was administered at the assigned dosage level (100-400 mg, three times weekly) in a standard 3 + 3 dose escalation design. Vorinostat therapy began 1 week prior to initiation of standard, concurrent chemoradiation therapy and continued during the entire course of therapy. Results Twenty six patients met eligibility criteria and completed the entire protocol. The primary tumor sites included tonsil (12), base of tongue (9), posterior pharyngeal wall (1), larynx (4) and hypopharynx (3). Of the 26 patients, 17 were HPV-positive and 9 were HPV-negative. The MTD of Vorinostat was 300 mg administered every other day. Anemia (n = 23/26) and leukopenia (n = 20/26) were the most commonly identified toxicities. The most common Grade3/4 events included leukopenia (n = 11) and lymphopenia (n = 17). No patient had Grade IV mucositis, dermatitis or xerostomia. The median follow time was 33.8 months (range 1.6-82.9 months). Twenty four of 26 (96.2%) patients had a complete response to therapy. Conclusion Vorinostat in combination with concurrent chemoradiation therapy is a safe and highly effective treatment regimen in HNSCC. There was a high rate of complete response to therapy with toxicity rates comparable, if not favorable to existing therapies. Further investigation in Phase II and III trials is strongly recommended.

Necroptosis: a regulated inflammatory mode of cell death

Programmed cell death has a vital role in embryonic development and tissue homeostasis. Necroptosis is an alternative mode of regulated cell death mimicking features of apoptosis and necrosis. Necroptosis requires protein RIPK3 (previously well recognized as regulator of inflammation, cell survival, and disease) and its substrate MLKL, the crucial players of this pathway. Necroptosis is induced by toll-like receptor, death receptor, interferon, and some other mediators. Shreds of evidence based on a mouse model reveals that deregulation of necroptosis has been found to be associated with pathological conditions like cancer, neurodegenerative diseases, and inflammatory diseases. In this timeline article, we are discussing the molecular mechanisms of necroptosis and its relevance to diseases.

Necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy

While the mechanisms underlying apoptosis and autophagy have been well characterized over recent decades, another regulated cell death event, necroptosis, remains poorly understood. Elucidating the signaling networks involved in the regulation of necroptosis may allow this form of regulated cell death to be exploited for diagnosis and treatment of cancer, and will contribute to the understanding of the complex tumor microenvironment. In this review, we have summarized the mechanisms and regulation of necroptosis, the converging and diverging features of necroptosis in tumorigenesis, activation of anti-tumor immunity, and cancer therapy, as well as attempts to exploit this newly gained knowledge to provide therapeutics for cancer.

The Contribution of Necroptosis in Neurodegenerative Diseases

Over the past decades, cell apoptosis has been significantly reputed as an accidental, redundant and alternative manner of cell demise which partakes in homeostasis in the development of extensive diseases. Nevertheless, necroptosis, another novel manner of cell death through a caspase-independent way, especially in neurodegenerative diseases remains ambiguous. The cognition of this form of cell demise is helpful to understand other forms of morphological resemblance of necrosis. Additionally, the concrete signal mechanism in the regulation of necroptosis is beneficial to the diagnosis and treatment of neurodegenerative diseases. Recent studies have demonstrated that necroptotic inhibitor, 24(S)-Hydroxycholesterol and partial specific histone deacetylase inhibitors could alleviate pathogenetic conditions of neurodegenerative diseases via necroptosis pathway. In this review, we summarize recent researches about mechanisms and modulation of necroptotic signaling pathways and probe into the role of programmed necroptotic cell demise in neurodegenerative diseases such as Parkinson's disease, Multiple sclerosis, Amyotrophic lateral sclerosis.

Necroptosis inhibitors as therapeutic targets in inflammation mediated disorders - a review of the current literature and patents

INTRODUCTION

Recent studies have shown substantial interplay between the apoptosis and necroptosis pathways. Necroptosis, a form of programmed cell death, has been found to stimulate the immune system contributing to the pathophysiology of several inflammation-mediated disorders. Determining the contribution of necroptotic signaling pathways to inflammation may lead to the development of selective and specific molecular target implicated necroptosis inhibitors. Areas covered: This review summarizes the recently published and patented necroptosis inhibitors as therapeutic targets in inflammation-mediated disorders. The role of several necroptosis inhibitors, focusing on specific signaling molecules, was discussed with particular attention to inflammation-mediated disorders. Data was obtained from Espacenet®, WIPO®, USPTO® patent websites, and other relevant sources (2006-2016). Expert opinion: Necroptosis inhibitors hold promise for treatment of inflammation-mediated clinical conditions in which necroptotic cell death plays a major role. Although necroptosis inhibitors reviewed in this survey showed inhibitory effects against several inflammation-mediated disorders, only a few have passed to the stage of clinical testing and need extensive research for therapeutic practice. Revisiting the existing drugs and developing novel necroptosis inhibiting agents as well as understanding their mechanism are essential. A detailed study of necroptosis function in animal models of inflammation may provide us an alternative strategy for the development of drug-like necroptosis inhibitors.

A structure-activity relationship of non-peptide macrocyclic histone deacetylase inhibitors and their anti-proliferative and anti-inflammatory activities

Inhibition of the enzymatic activity of histone deacetylase (HDAC) is a promising therapeutic strategy for cancer treatment and several distinct small molecule histone deacetylase inhibitors (HDACi) have been reported. We have previously identified a new class of non-peptide macrocyclic HDACi derived from 14- and 15-membered macrolide skeletons. In these HDACi, the macrocyclic ring is linked to the zinc chelating hydroxamate moiety through a para-substituted aryl-triazole cap group. To further delineate the depth of the SAR of this class of HDACi, we have synthesized series of analogous compounds and investigated the influence of various substitution patterns on their HDAC inhibitory, anti-proliferative and anti-inflammatory activities. We identified compounds 25b and 38f with robust anti-proliferative activities and compound 26f (IC50 47.2 nM) with superior anti-inflammatory (IC50 88 nM) activity relative to SAHA.

Combined treatment of adenosine nucleoside inhibitor NITD008 and histone deacetylase inhibitor vorinostat represents an immunotherapy strategy to ameliorate West Nile virus infection

West Nile virus (WNV), a member of the Flaviviridae family, is the leading cause of viral encephalitis in the United States. Despite efforts to control the spread of WNV, there has been an increase in the number of outbreaks and clinical cases with neurological problems. There are no antiviral compounds currently in trials for WNV. NITD008 is an adenosine analogue inhibitor that interrupts the RNA-dependent RNA polymerase of flaviviruses. Previous studies demonstrated NITD008 as a potent antiviral for dengue virus, however this drug was associated with preclinical toxicity. The ability of NITD008 to block WNV replication is only shown in Vero cells. Neuroinflammation is also a major cause of the WNV-associated pathology, therefore we evaluated the effect of NITD008 and a newly characterized anti-inflammatory drug vorinostat (SAHA), a histone deacetylase inhibitor, on WNV replication and disease progression in a mouse model. When administered at 10 and 25mg/kg at days 1-6 after WNV infection in C57BL/6 mice, NITD008 conferred complete protection from clinical symptoms and death, which correlated with reduced viral load in the serum and restriction of virus-CNS entry. Delay of NITD008 treatment to days 3-6 and days 5-9 after infection, when WNV replication was high in the periphery and brain, resulted in the gradual loss of protection against WNV infection. However, co-treatment with SAHA and NITD008 during the CNS phase of disease improved disease outcome significantly by reducing inflammation and neuronal death. Our results support potential synergistic effect of combination therapy of NITD008 with SAHA for the treatment of WNV encephalitis.

Histone deacetylase inhibition protects hearing against acute ototoxicity by activating the Nf-κB pathway

Auditory hair cells have repeatedly been shown to be susceptible to ototoxicity from a multitude of drugs including aminoglycoside antibiotics. Here, we found that systemic HDAC inhibition using suberoylanilide hydroxamic acid (SAHA) on adult mice offers almost complete protection against hair cell loss and hearing threshold shifts from acute ototoxic insult from kanamycin potentiated with furosemide. We also found that the apparent lack of hair cell loss was completely independent of spontaneous or facilitated (ectopic Atoh1 induction) hair cell regeneration. Rather, SAHA treatment correlated with RelA acetylation (K310) and subsequent activation of the Nf-κB pro-survival pathway leading to expression of pro-survival genes such as Cflar (cFLIP) and Bcl2l1 (Bcl-xL). In addition, we also detected increased expression of pro-survival genes Cdkn1a (p21) and Hspa1a (Hsp70), and decreased expression of the pro-apoptosis gene Bcl2l11 (Bim). These data combined provide evidence that class I HDACs control the transcriptional activation of pro-survival pathways in response to ototoxic insult by regulating the acetylation status of transcription factors found at the crossroads of cell death and survival in the mammalian inner ear.

Histone deacetylase 4 selectively contributes to podocyte injury in diabetic nephropathy

Studies have highlighted the importance of histone deacetylase (HDAC)-mediated epigenetic processes in the development of diabetic complications. Inhibitors of HDAC are a novel class of therapeutic agents in diabetic nephropathy, but currently available inhibitors are mostly nonselective inhibit multiple HDACs, and different HDACs serve very distinct functions. Therefore, it is essential to determine the role of individual HDACs in diabetic nephropathy and develop HDAC inhibitors with improved specificity. First, we identified the expression patterns of HDACs and found that, among zinc-dependent HDACs, HDAC2/4/5 were upregulated in the kidney from streptozotocin-induced diabetic rats, diabetic db/db mice, and in kidney biopsies from diabetic patients. Podocytes treated with high glucose, advanced glycation end products, or transforming growth factor-β (common detrimental factors in diabetic nephropathy) selectively increased HDAC4 expression. The role of HDAC4 was evaluated by in vivo gene silencing by intrarenal lentiviral gene delivery and found to reduce renal injury in diabetic rats. Podocyte injury was associated with suppressing autophagy and exacerbating inflammation by HDAC4-STAT1 signaling in vitro. Thus, HDAC4 contributes to podocyte injury and is one of critical components of a signal transduction pathway that links renal injury to autophagy in diabetic nephropathy.