Histone Deacetylase Inhibitor RGFP109 Overcomes Temozolomide Resistance by Blocking NF-κB-Dependent Transcription in Glioblastoma Cell Lines

Overview of class I HDAC modulators: Inhibitors and degraders

Class I histone deacetylases (HDACs) are closely associated with the development of a diverse array of diseases, including cancer, neurodegenerative disorders, HIV, and inflammatory diseases. Considering the essential roles in tumorigenesis, class I HDACs have emerged as highly desirable targets for therapeutic strategies, particularly in the field of anticancer drug development. However, the conventional class I HDAC inhibitors faced several challenges such as acquired resistance, inherent toxicities, and limited efficacy in inhibiting non-enzymatic functions of HDAC. To address these problems, novel strategies have emerged, including the development of class I HDAC dual-acting inhibitors, targeted protein degradation (TPD) technologies such as PROTACs, molecular glues, and HyT degraders, as well as covalent inhibitors. This review provides a comprehensive overview of class I HDAC enzymes and inhibitors, by initially introducing their structure and biological roles. Subsequently, we focus on the recent advancements of class I HDAC modulators, including isoform-selective class I inhibitors, dual-target inhibitors, TPDs, and covalent inhibitors, from the perspectives of rational design principles, pharmacodynamics, pharmacokinetics, and clinical progress. Finally, we also provide the challenges and outlines future prospects in the realm of class I HDAC-targeted drug discovery for cancer therapeutics.

Divergent Processing of Cell Stress Signals as the Basis of Cancer Progression: Licensing NFκB on Chromatin

Inflammation is activated by diverse triggers that induce the expression of cytokines and adhesion molecules, which permit a succession of molecules and cells to deliver stimuli and functions that help the immune system clear the primary cause of tissue damage, whether this is an infection, a tumor, or a trauma. During inflammation, short-term changes in the expression and secretion of strong mediators of inflammation occur, while long-term changes occur to specific groups of cells. Long-term changes include cellular transdifferentiation for some types of cells that need to regenerate damaged tissue, as well as death for specific immune cells that can be detrimental to tissue integrity if they remain active beyond the boundaries of essential function. The transcriptional regulator NFκB enables some of the fundamental gene expression changes during inflammation, as well as during tissue development. During recurrence of malignant disease, cell stress-induced alterations enable the growth of cancer cell clones that are substantially resistant to therapeutic intervention and to the immune system. A number of those alterations occur due to significant defects in feedback signal cascades that control the activity of NFκB. Specifically, cell stress contributes to feedback defects as it overrides modules that otherwise control inflammation to protect host tissue. NFκB is involved in both the suppression and promotion of cancer, and the key distinctive feature that determines its net effect remains unclear. This paper aims to provide a clear answer to at least one aspect of this question, namely the mechanism that enables a divergent response of cancer cells to critical inflammatory stimuli and to cell stress in general.

Histone acetylation risk model predicts prognosis and guides therapy selection in glioblastoma: implications for chemotherapy and anti-CTLA-4 immunotherapy

BACKGROUND

Glioblastoma is characterized by high aggressiveness, frequent recurrence, and poor prognosis. Histone acetylation-associated genes have been implicated in its occurrence and development, yet their predictive ability in glioblastoma prognosis remains unclear.

RESULTS

This study constructs a histone acetylation risk model using Cox and LASSO regression analyses to evaluate glioblastoma prognosis. We assessed the model's prognostic ability with univariate and multivariate Cox regression analyses. Additionally, immune infiltration was evaluated using ESTIMATE and TIMER algorithms, and the SubMAP algorithm was utilized to predict responses to CTLA4 inhibitor. Multiple drug databases were applied to assess drug sensitivity in high- and low-risk groups. Our results indicate that the histone acetylation risk model is independent and reliable in predicting prognosis.

CONCLUSIONS

Low-risk patients showed higher immune activity and longer overall survival, suggesting anti-CTLA4 immunotherapy suitability, while high-risk patients might benefit more from chemotherapy. This model could guide personalized therapy selection for glioblastoma patients.

Integrative function of histone deacetylase 3 in inflammation

Inflammation is a complex biological response triggered when an organism encounters internal or external stimuli. These triggers activate various signaling pathways, leading to the release of numerous inflammatory mediators aimed at the affected tissue. Ensuring precision and avoiding the excessive activation, the inflammatory process is subject to tight regulation. Histone deacetylase 3 (HDAC3), a member of class I HDACs family, stands out for its significant role in modulating various inflammatory signaling, including Nuclear Factor kappa B (NF-κB) signaling, Mitogen-activated protein kinase (MAPK) signaling and Janus kinase/signal transduction and activator of transcription (JAK-STAT) signaling. In this review, we illuminate the intricate molecular mechanisms of HDAC3 across these inflammatory pathways. We emphasize its importance in orchestrating a balanced inflammatory response and highlight its promising potential as a therapeutic target.

Multi-Omics Analyses Reveal Mitochondrial Dysfunction Contributing to Temozolomide Resistance in Glioblastoma Cells

Glioblastoma (GBM) is the most common and aggressive malignant brain tumor with poor prognosis. Temozolomide (TMZ) is the standard chemotherapy for glioblastoma treatment, but TMZ resistance significantly compromises its efficacy. In the present study, we generated a TMZ-resistant cell line and identified that mitochondrial dysfunction was a novel factor contributing to TMZ resistance though multi-omics analyses and energy metabolism analysis. Furthermore, we found that rotenone treatment induced TMZ resistance to a certain level in glioblastoma cells. Notably, we further demonstrated that elevated Ca2+ levels and JNK-STAT3 pathway activation contributed to TMZ resistance and that inhibiting JNK or STAT3 increases susceptibility to TMZ. Taken together, our results indicate that co-administering TMZ with a JNK or STAT3 inhibitor holds promise as a potentially effective treatment for glioblastoma.

Magnolol and Temozolomide exhibit a synergistic anti-glioma activity through MGMT inhibition

Temozolomide (TMZ) is the leading chemotherapeutic agent used for glioma therapy due to its good oral absorption and blood-brain barrier permeability. However, its anti-glioma efficacy may be limited due to its adverse effects and resistance development. O6-Methylguanine-DNA-methyltransferase (MGMT), an enzyme associated with TMZ resistance, is activated via the NF-κB pathway, which is found to be upregulated in glioma. TMZ also upregulates NF-κB signaling like many other alkylating agents. Magnolol (MGN), a natural anti-cancer agent, has been reported to inhibit NF-κB signaling in multiple myeloma, cholangiocarcinoma, and hepatocellular carcinoma. MGN has already shown promising results in anti-glioma therapy. However, the synergistic action of TMZ and MGN has not been explored. Therefore, we investigated the effect of TMZ and MGN treatment in glioma and observed their synergistic pro-apoptotic action in both in vitro and in vivo glioma models. To explore the mechanism of this synergistic action, we found that MGN inhibits MGMT enzyme both in vitro and in vivo glioma. Next, we established the link between NF-κB signaling and MGN-induced MGMT inhibition in glioma. MGN inhibits the phosphorylation of p65, a subunit of NF-κB, and its nuclear translocation to block NF-κB pathway activation in glioma. MGN-induced NF-κB inhibition results in the transcriptional inhibition of MGMT in glioma. TMZ and MGN combinatorial treatment also impedes p65 nuclear translocation to inhibit MGMT in glioma. We observed a similar effect of TMZ and MGN treatment in the rodent glioma model. Thus, we concluded that MGN potentiates TMZ-induced apoptosis in glioma by inhibiting NF-κB pathway-mediated MGMT activation.

The function of histone methylation and acetylation regulators in GBM pathophysiology

Glioblastoma (GBM) is the most common and lethal primary brain malignancy and is characterized by a high degree of intra and intertumor cellular heterogeneity, a starkly immunosuppressive tumor microenvironment, and nearly universal recurrence. The application of various genomic approaches has allowed us to understand the core molecular signatures, transcriptional states, and DNA methylation patterns that define GBM. Histone posttranslational modifications (PTMs) have been shown to influence oncogenesis in a variety of malignancies, including other forms of glioma, yet comparatively less effort has been placed on understanding the transcriptional impact and regulation of histone PTMs in the context of GBM. In this review we discuss work that investigates the role of histone acetylating and methylating enzymes in GBM pathogenesis, as well as the effects of targeted inhibition of these enzymes. We then synthesize broader genomic and epigenomic approaches to understand the influence of histone PTMs on chromatin architecture and transcription within GBM and finally, explore the limitations of current research in this field before proposing future directions for this area of research.

Introducing HDAC-Targeting Radiopharmaceuticals for Glioblastoma Imaging and Therapy

Despite recent advances in multimodality therapy for glioblastoma (GB) incorporating surgery, radiotherapy, chemotherapy and targeted therapy, the overall prognosis remains poor. One of the interesting targets for GB therapy is the histone deacetylase family (HDAC). Due to their pleiotropic effects on, e.g., DNA repair, cell proliferation, differentiation, apoptosis and cell cycle, HDAC inhibitors have gained a lot of attention in the last decade as anti-cancer agents. Despite their known underlying mechanism, their therapeutic activity is not well-defined. In this review, an extensive overview is given of the current status of HDAC inhibitors for GB therapy, followed by an overview of current HDAC-targeting radiopharmaceuticals. Imaging HDAC expression or activity could provide key insights regarding the role of HDAC enzymes in gliomagenesis, thus identifying patients likely to benefit from HDACi-targeted therapy.

Potentiation of temozolomide activity against glioblastoma cells by aromatase inhibitor letrozole

PURPOSE

The DNA alkylating agent temozolomide (TMZ), is the first-line therapeutic for the treatment of glioblastoma (GBM). However, its use is confounded by the occurrence of drug resistance and debilitating adverse effects. Previously, we observed that letrozole (LTZ), an aromatase inhibitor, has potent activity against GBM in pre-clinical models. Here, we evaluated the effect of LTZ on TMZ activity against patient-derived GBM cells.

METHODS

Employing patient-derived G76 (TMZ-sensitive), BT142 (TMZ-intermediately sensitive) and G43 and G75 (TMZ-resistant) GBM lines we assessed the influence of LTZ and TMZ on cell viability and neurosphere growth. Combination Index (CI) analysis was performed to gain quantitative insights of this interaction. We then assessed DNA damaging effects by conducting flow-cytometric analysis of ˠH2A.X formation and induction of apoptotic signaling pathways (caspase3/7 activity). The effects of adding estradiol on LTZ-induced cytotoxicity and DNA damage were also evaluated.

RESULTS

Co-treatment with LTZ at a non-cytotoxic concentration (40 nM) reduced TMZ IC50 by 8, 37, 240 and 640 folds in G76, BT-142, G43 and G75 cells, respectively. The interaction was deemed to be synergistic based on CI analysis. LTZ co-treatment also significantly increased DNA damaging effects of TMZ. Addition of estradiol abrogated these LTZ effects.

CONCLUSIONS

LTZ increases DNA damage and synergistically enhances TMZ activity in TMZ sensitive and TMZ-resistant GBM lines. These effects are abrogated by the addition of exogenous estradiol underscoring that the observed effects of LTZ may be mediated by estrogen deprivation. Our study provides a strong rationale for investigating the clinical potential of combining LTZ and TMZ for GBM therapy.

Histone deacetylase 1 and 3 inhibitors alleviate colon inflammation by inhibiting Th17 cell differentiation

Background

The etiology of inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), is not completely clear, but its pathogenesis is closely related to T helper 17 (Th17) cells. Several histone deacetylase (HDAC) inhibitors have been shown to exert potent anti‐inflammatory effects and modulate Th17 cell polarization. Owing to the large variety and broad expression of HDACs, finding specific therapeutic targets for IBD is of clinical importance.

Methods

The proportions of Th17 cells and interleukin (IL)‐17A produced between patients with UC and healthy volunteers were compared. The differentiation of human peripheral blood mononuclear cells (PBMCs) into Th17 cells was induced in vitro. Differentiated Th17 cells were treated with RGFP109 (RG), a selective inhibitor of HDAC1 and 3, to observe its effects on these cells. Subsequently, colitis was induced in mice and treated with RG. The proportion of Th17 cells, the severity of colitis in mice, and colon histopathology and immunohistochemistry were evaluated respectively.

Results

The proportion of Th17 cells and IL‐17A production was significantly increased in patients with UC than in healthy individuals. RG inhibited the differentiation of human PBMCs into Th17 cells and reduced IL‐17A secretion in vitro. RG‐treated colitis mice had a lower Th17 ratio, mild colon inflammation, and decreased expression of HDAC1 and 3 in the colon.

Conclusions

HDAC1 and 3 inhibitors can modulate the differentiation of inflammatory Th17 cells, downregulate IL‐17A levels, and exert anti‐inflammatory effects in experimental colitis mice, indicating that HDAC1 and 3 may be potential therapeutic targets for patients with IBD.

Small Molecule Inhibitors in Adult High-Grade Glioma: From the Past to the Future

Glioblastoma is the most common primary malignant tumor in the brain and has a dismal prognosis despite patients accepting standard therapies. Alternation of genes and deregulation of proteins, such as receptor tyrosine kinase, PI3K/Akt, PKC, Ras/Raf/MEK, histone deacetylases, poly (ADP-ribose) polymerase (PARP), CDK4/6, branched-chain amino acid transaminase 1 (BCAT1), and Isocitrate dehydrogenase (IDH), play pivotal roles in the pathogenesis and progression of glioma. Simultaneously, the abnormalities change the cellular biological behavior and microenvironment of tumor cells. The differences between tumor cells and normal tissue become the vulnerability of tumor, which can be taken advantage of using targeted therapies. Small molecule inhibitors, as an important part of modern treatment for cancers, have shown significant efficacy in hematologic cancers and some solid tumors. To date, in glioblastoma, there have been more than 200 clinical trials completed or ongoing in which trial designers used small molecules as monotherapy or combination regimens to correct the abnormalities. In this review, we summarize the dysfunctional molecular mechanisms and highlight the outcomes of relevant clinical trials associated with small-molecule targeted therapies. Based on the outcomes, the main findings were that small-molecule inhibitors did not bring more benefit to newly diagnosed glioblastoma, but the clinical studies involving progressive glioblastoma usually claimed “noninferiority” compared with historical results. However, as to the clinical inferiority trial, similar dosing regimens should be avoided in future clinical trials.

N-acetyl l-aspartate and Triacetin modulate tumor suppressor MicroRNA and class I and II HDAC gene expression induce apoptosis in Glioblastoma cancer cells in vitro

Glioblastoma multiforme (GBM), grade IV glioma and is aggressive, malignant primary brain cancer. Altered expression and activity of epigenetic proteins such as histone deacetylases (HDACs) are involved in GBM metastasis. Also, acetates are important to brain metabolites that regulate cell proliferation and apoptosis. Here, we have examined the effect of the acetates on the cell-cycle. U87MG cancer cells treated with N-acetyl l-aspartate (NAA) and sodium acetate have exhibited G1 phase cell-cycle arrest whereas U87MG cells treated with Triacetin (TA), and potassium acetate has induced G2/M cell cycle arrest. We have observed inhibition of histone deacetylase (HDAC) mRNA levels in acetate treated U87MG cells. Interestingly, acetates-treated U87MG cells have shown a significant reduction in the mRNA level of class II HDACs than class I HDACs. Acetate treated cells have exhibited an enhanced expression of various microRNAs such as miR-15b, miR-92, miR-101, miR-155, miR-199, miR-200, miR-223, miR-16, and miR-17 that are involved in the inhibition of cancer cell proliferation, invasion, migration, and angiogenesis. Further, these acetate molecules regulate genes involved in mammalian target of rapamycin complex 2 (mTORC2) such as mammalian stress-activated protein kinase-interacting protein (mSIN1), protein observed with Rictor 2 (Protor 2), and protein kinase C α (PKCα). The present study reveals the possible involvement of the mTORC2 complex during acetate-mediated HDAC inhibition, as well as microRNA modulation. Furthermore, molecular modeling studies were employed to understand the binding mode of these acetate molecules to mTOR, Rapamycin-insensitive companion of mammalian target of rapamycin (Rictor), and HDAC-8 proteins. Thus in this study, we have identified the pivotal role of acetates in the modulation of mTOR complex, epigenetic genes and provide structural as well as functional insights that will help in future drug discovery against GBM cancer therapy.

Differential gene expression-based connectivity mapping identified novel drug candidate and improved Temozolomide efficacy for Glioblastoma

BACKGROUND

Glioblastoma (GBM) has a devastating median survival of only one year. Treatment includes resection, radiation therapy, and temozolomide (TMZ); however, the latter increased median survival by only 2.5 months in the pivotal study. A desperate need remains to find an effective treatment.

METHODS

We used the Connectivity Map (CMap) bioinformatic tool to identify candidates for repurposing based on GBM's specific genetic profile. CMap identified histone deacetylase (HDAC) inhibitors as top candidates. In addition, Gene Expression Profiling Interactive Analysis (GEPIA) identified HDAC1 and HDAC2 as the most upregulated and HDAC11 as the most downregulated HDACs. We selected PCI-24781/abexinostat due to its specificity against HDAC1 and HDAC2, but not HDAC11, and blood-brain barrier permeability.

RESULTS

We tested PCI-24781 using in vitro human and mouse GBM syngeneic cell lines, an in vivo murine orthograft, and a genetically engineered mouse model for GBM (PEPG - PTENflox/+; EGFRvIII+; p16Flox/- & GFAP Cre +). PCI-24781 significantly inhibited tumor growth and downregulated DNA repair machinery (BRCA1, CHK1, RAD51, and O6-methylguanine-DNA- methyltransferase (MGMT)), increasing DNA double-strand breaks and causing apoptosis in the GBM cell lines, including an MGMT expressing cell line in vitro. Further, PCI-24781 decreased tumor burden in a PEPG GBM mouse model. Notably, TMZ + PCI increased survival in orthotopic murine models compared to TMZ + vorinostat, a pan-HDAC inhibitor that proved unsuccessful in clinical trials.

CONCLUSION

PCI-24781 is a novel GBM-signature specific HDAC inhibitor that works synergistically with TMZ to enhance TMZ efficacy and improve GBM survival. These promising MGMT-agnostic results warrant clinical evaluation.

Nonredundant, isoform-specific roles of HDAC1 in glioma stem cells

Glioblastoma (GBM) is characterized by an aberrant yet druggable epigenetic landscape. One major family of epigenetic regulators, the histone deacetylases (HDACs), are considered promising therapeutic targets for GBM due to their repressive influences on transcription. Although HDACs share redundant functions and common substrates, the unique isoform-specific roles of different HDACs in GBM remain unclear. In neural stem cells, HDAC2 is the indispensable deacetylase to ensure normal brain development and survival in the absence of HDAC1. Surprisingly, we find that HDAC1 is the essential class I deacetylase in glioma stem cells, and its loss is not compensated for by HDAC2. Using cell-based and biochemical assays, transcriptomic analyses, and patient-derived xenograft models, we find that knockdown of HDAC1 alone has profound effects on the glioma stem cell phenotype in a p53-dependent manner. We demonstrate marked suppression in tumor growth upon targeting of HDAC1 and identify compensatory pathways that provide insights into combination therapies for GBM. Our study highlights the importance of HDAC1 in GBM and the need to develop isoform-specific drugs.

The IL13α 2R paves the way for anti-glioma nanotherapy

Glioblastoma (GBM) is one of the most aggressive (grade IV) gliomas characterized by a high rate of recurrence, resistance to therapy and a grim survival prognosis. The long-awaited improvement in GBM patients' survival rates essentially depends on advances in the development of new therapeutic approaches. Recent preclinical studies show that nanoscale materials could greatly contribute to the improvement of diagnosis and management of brain cancers. In the current review, we will discuss how specific features of glioma pathobiology can be employed for designing efficient targeting approaches. Moreover, we will summarize the main evidence for the potential of the IL-13R alpha 2 receptor (IL13α2R) targeting in GBM early diagnosis and experimental therapy.

The Impact of Epigenetic Modifications on Adaptive Resistance Evolution in Glioblastoma

Glioblastoma (GBM) is a highly lethal cancer that is universally refractory to the standard multimodal therapies of surgical resection, radiation, and chemotherapy treatment. Temozolomide (TMZ) is currently the best chemotherapy agent for GBM, but the durability of response is epigenetically dependent and often short-lived secondary to tumor resistance. Therapies that can provide synergy to chemoradiation are desperately needed in GBM. There is accumulating evidence that adaptive resistance evolution in GBM is facilitated through treatment-induced epigenetic modifications. Epigenetic alterations of DNA methylation, histone modifications, and chromatin remodeling have all been implicated as mechanisms that enhance accessibility for transcriptional activation of genes that play critical roles in GBM resistance and lethality. Hence, understanding and targeting epigenetic modifications associated with GBM resistance is of utmost priority. In this review, we summarize the latest updates on the impact of epigenetic modifications on adaptive resistance evolution in GBM to therapy.

Dissecting Histone Deacetylase 3 in Multiple Disease Conditions: Selective Inhibition as a Promising Therapeutic Strategy

The acetylation of histone and non-histone proteins has been implicated in several disease states. Modulation of such epigenetic modifications has therefore made histone deacetylases (HDACs) important drug targets. HDAC3, among various class I HDACs, has been signified as a potentially validated target in multiple diseases, namely, cancer, neurodegenerative diseases, diabetes, obesity, cardiovascular disorders, autoimmune diseases, inflammatory diseases, parasitic infections, and HIV. However, only a handful of HDAC3-selective inhibitors have been reported in spite of continuous efforts in design and development of HDAC3-selective inhibitors. In this Perspective, the roles of HDAC3 in various diseases as well as numerous potent and HDAC3-selective inhibitors have been discussed in detail. It will surely open up a new vista in the discovery of newer, more effective, and more selective HDAC3 inhibitors.

Synthesis, biological evaluation, and molecular docking analysis of novel linker-less benzamide based potent and selective HDAC3 inhibitors

A series of novel linker-less benzamides with different aryl and heteroaryl cap groups have been designed, synthesized, and screened as potent histone deacetylase (HDAC) inhibitors with promising anticancer activity. Two lead compounds 5e and 5f were found as potent and highly selective HDAC3 inhibitors over other Class-I HDACs and HDAC6. Compound 5e bearing a 6-quinolinyl moiety as the cap group was found to be a highly potent HDAC3 inhibitor (IC₅₀ = 560 nM) and displayed 46-fold selectivity for HDAC3 over HDAC2, and 33-fold selectivity for HDAC3 over HDAC1. The synthesized compounds possess antiproliferative activities against different cancer cell lines and significantly less cytotoxic to normal cells. Molecular Docking studies of compounds 5e and 5f reveal a similar binding mode of interactions as CI994 at the HDAC3 active site. These observations agreed with the in vitro HDAC3 inhibitory activities. Significant enhancement of the endogenous acetylation level on H3K9 and H4K12 was found when B16F10 cells were treated with compounds 5e and 5f in a dose-dependent manner. The compounds induced apoptotic cell death in Annexin-V/FITC-PI assay and caused cell cycle arrest at G2/M phase of cell cycle in B16F10 cells. These compounds may serve as potential HDAC3 inhibitory anticancer therapeutics.

Mechanisms of temozolomide resistance in glioblastoma - a comprehensive review

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and has an exceedingly low median overall survival of only 15 months. Current standard-of-care for GBM consists of gross total surgical resection followed by radiation with concurrent and adjuvant chemotherapy. Temozolomide (TMZ) is the first-choice chemotherapeutic agent in GBM; however, the development of resistance to TMZ often becomes the limiting factor in effective treatment. While O6-methylguanine-DNA methyltransferase repair activity and uniquely resistant populations of glioma stem cells are the most well-known contributors to TMZ resistance, many other molecular mechanisms have come to light in recent years. Key emerging mechanisms include the involvement of other DNA repair systems, aberrant signaling pathways, autophagy, epigenetic modifications, microRNAs, and extracellular vesicle production. This review aims to provide a comprehensive overview of the clinically relevant molecular mechanisms and their extensive interconnections to better inform efforts to combat TMZ resistance.

NFAT2-HDAC1 signaling contributes to the malignant phenotype of glioblastoma

BACKGROUND

Deregulation of the nuclear factor of activated T cell (NFAT) pathway has been reported in several human cancers. Particularly, NFAT2 is involved in the malignant transformation of tumor cells and is identified as an oncogene. However, the role of NFAT2 in glioblastoma (GBM) is largely unknown.

METHODS

The expression and prognostic value of NFAT2 were examined in the databases of the Repository of Molecular Brain Neoplasia Data and The Cancer Genome Atlas (TCGA) and clinical samples. The functional effects of silencing or overexpression of NFAT2 were evaluated in glioma stem cell (GSC) viability, invasion, and self-renewal in vitro and in tumorigenicity in vivo. The downstream target of NFAT2 was investigated.

RESULTS

High NFAT2 expression was significantly associated with mesenchymal (MES) subtype and recurrent GBM and predicted poor survival. NFAT2 silencing inhibited the invasion and clonogenicity of MES GSC-enriched spheres in vitro and in vivo. NFAT2 overexpression promoted tumor growth and MES differentiation of GSCs. A TCGA database search showed that histone deacetylase 1 (HDAC1) expression was significantly correlated with that of NFAT2. NFAT2 regulates the transcriptional activity of HDAC1. Rescue of HDAC1 in NFAT2-knockdown GSCs partially restored tumor growth and MES phenotype. Loss of NFAT2 and HDAC1 expression resulted in hyperacetylation of nuclear factor-kappaB (NF-κB), which inhibits NF-κB-dependent transcriptional activity.

CONCLUSION

Our findings suggest that the NFAT2-HDAC1 pathway might play an important role in the maintenance of the malignant phenotype and promote MES transition in GSCs, which provide potential molecular targets for the treatment of GBMs.

Reduction of Neuroinflammation by δ-Opioids Via STAT3-Dependent Pathway in Chronic Glaucoma Model

The main objective of this study was to determine the inhibition of pro-inflammatory cytokines and their associated signaling molecules by δ-opioid receptor activation by a selective ligand, SNC-121 in chronic rat glaucoma model. Intraocular pressure was raised in rat eyes by injecting 2 M hypertonic saline into the limbal veins. SNC-121 (1 mg/kg; i. p) or Stattic (5 mg/kg; i. p) was administered in Brown Norway rats daily for 7 days. The mRNA expression of IL-1β, TNF-α, Fas, IL-6, leukemia inhibitory factor, and IFN-γ was increased significantly in the retina of ocular hypertensive animals at day 7, post injury. Administration of SNC-121 (1 mg/kg; i. p. injection) for 7 days (once a day) completely inhibited the increase in the mRNA and protein expression of pro-inflammatory cytokines. Mechanistically, we provide data showing a significant increase in the phosphorylation of STAT3 at tyrosine 705 whereas a moderate but significant increase in the total STAT3 protein expression was also seen in the retina of ocular hypertensive animals. Data illustrated that SNC-121 administration completely abrogated ocular hypertension-induced increase in STAT3^Y705 phosphorylation. Interestingly, acetylation of STAT3 at lysine 685 (AcK685) was reduced in ocular hypertensive animals and subsequently increased significantly by SNC-121 treatment. Stattic, a selective STAT3 inhibitor, administration resulted in a complete attenuation in the production of IL-1β and IL-6 in ocular hypertensive animals. In conclusion, δ-opioid receptor activation suppressed the phosphorylation of STAT3 at tyrosine 705 and increased acetylation at lysine 686 and these posttranslational modifications can regulate the production of some but not all pro-inflammatory cytokines in response to glaucomatous injury.

NADPH levels affect cellular epigenetic state by inhibiting HDAC3-Ncor complex

NADPH has long been recognized as a key cofactor for antioxidant defence and reductive biosynthesis. Here we report a metabolism-independent function of NADPH in modulating epigenetic status and transcription. We find that the reduction of cellular NADPH levels, achieved by silencing malic enzyme or glucose-6-phosphate dehydrogenase, impairs global histone acetylation and transcription in both adipocytes and tumour cells. These effects can be reversed by supplementation with exogenous NADPH or by inhibition of histone deacetylase 3 (HDAC3). Mechanistically, NADPH directly interacts with HDAC3 and interrupts the association between HDAC3 and its co-activator nuclear receptor corepressor 2 (Ncor2; SMRT) or Ncor1, thereby impairing HDAC3 activation. Interestingly, NADPH and the inositol tetraphosphate molecule Ins(1,4,5,6)P₄ appear to bind to the same domains on HDAC3, with NADPH having a higher affinity towards HDAC3 than Ins(1,4,5,6)P₄. Thus, while Ins(1,4,5,6)P₄ promotes formation of the HDAC3-Ncor complex, NADPH inhibits it. Collectively, our findings uncover a previously unidentified and metabolism-independent role of NADPH in controlling epigenetic change and gene expression by acting as an endogenous inhibitor of HDAC3.

The application of histone deacetylases inhibitors in glioblastoma

The epigenetic abnormality is generally accepted as the key to cancer initiation. Epigenetics that ensure the somatic inheritance of differentiated state is defined as a crucial factor influencing malignant phenotype without altering genotype. Histone modification is one such alteration playing an essential role in tumor formation, progression, and resistance to treatment. Notably, changes in histone acetylation have been strongly linked to gene expression, cell cycle, and carcinogenesis. The balance of two types of enzyme, histone acetyltransferases (HATs) and histone deacetylases (HDACs), determines the stage of histone acetylation and then the architecture of chromatin. Changes in chromatin structure result in transcriptional dysregulation of genes that are involved in cell-cycle progression, differentiation, apoptosis, and so on. Recently, HDAC inhibitors (HDACis) are identified as novel agents to keep this balance, leading to numerous researches on it for more effective strategies against cancers, including glioblastoma (GBM). This review elaborated influences on gene expression and tumorigenesis by acetylation and the antitumor mechanism of HDACis. Besdes, we outlined the preclinical and clinical advancement of HDACis in GBM as monotherapies and combination therapies.

Selective Inhibition of HDAC1 by Macrocyclic Polypeptide for the Treatment of Glioblastoma: A Binding Mechanistic Analysis Based on Molecular Dynamics

Glioblastoma (GBM) is the most common and aggressive intracranial malignant brain tumor, and the abnormal expression of HDAC1 is closely correlated to the progression, recurrence and metastasis of GBM cells, making selective inhibition of HDAC1 a promising strategy for GBM treatments. Among all available selective HDAC1 inhibitors, the macrocyclic peptides have gained great attention due to their remarkable inhibitory selectivity on HDAC1. However, the binding mechanism underlying this selectivity is still elusive, which increases the difficulty of designing and synthesizing the macrocyclic peptide-based anti-GBM drug. Herein, multiple computational approaches were employed to explore the binding behaviors of a typical macrocyclic peptide FK228 in both HDAC1 and HDAC6. Starting from the docking conformations of FK228 in the binding pockets of HDAC1&6, relatively long MD simulation (500 ns) shown that the hydrophobic interaction and hydrogen bonding of E91 and D92 in the Loop2 of HDAC1 with the Cap had a certain traction effect on FK228, and the sub-pocket formed by Loop1 and Loop2 in HDAC1 could better accommodate the Cap group, which had a positive effect on maintaining the active conformation of FK228. While the weakening of the interactions between FK228 and the residues in the Loop2 of HDAC6 during the MD simulation led to the large deflection of FK228 in the binding site, which also resulted in the decrease in the interactions between the Linker region of FK228 and the previously identified key amino acids (H134, F143, H174, and F203). Therefore, the residues located in Loop1 and Loop2 contributed in maintaining the active conformation of FK228, which would provide valuable hints for the discovery and design of novel macrocyclic polypeptide HDAC inhibitors.

ING4 alleviated lipopolysaccharide-induced inflammation by regulating the NF-κB pathway via a direct interaction with SIRT1

Sepsis is a complex inflammatory disorder in which high mortality is associated with an excessive inflammatory response. Inhibitor of growth 4 (ING4), which is a cofactor of histone acetyltransferase and histone deacetylase complexes, could negatively regulate this inflammation. However, the exact molecular signaling pathway regulated by ING4 remains uncertain. As a pivotal histone deacetylase, Sirtuin1 (SIRT1), which is widely accepted to be an anti‐inflammatory molecule, has not been found to be linked to ING4. This study investigated how ING4 is involved in the regulation of inflammation by constructing lipopolysaccharide (LPS)‐induced macrophage and mouse sepsis models. Our results revealed that ING4 expression decreased, whereas the levels of proinflammatory cytokines increased in LPS‐stimulated cultured primary macrophages and RAW 264.7 cells. ING4 transfection was confirmed to alleviate the LPS‐induced upregulation of proinflammatory cytokine expression both in vitro and in vivo. In addition, ING4‐overexpressing mice were hyposensitive to an LPS challenge and displayed reduced organ injury. Furthermore, immunoprecipitation indicated a direct interaction between ING4 and the SIRT1 protein. Moreover, ING4 could block nuclear factor‐kappa B (NF‐κB) P65 nuclear translocation and restrict P65 acetylation at lysine 310 induced by LPS treatment. These results are the first to clarify that the anti‐inflammatory role of ING4 is associated with SIRT1, through which ING4 inhibits NF‐κB signaling activation. Our studies provide a novel signaling axis involving ING4/SIRT1/NF‐κB in LPS‐induced sepsis.

Design, synthesis, and biological evaluation of novel nicotinamide derivatives as potential histone deacetylase-3 inhibitors

The selected nicotinamide-based HDACi displayed selectivity towards HDAC3 over pan HDAC and exhibited potent cytotoxicity against the used cell lines.

Temozolomide Treatment Induces lncRNA MALAT1 in an NF-κB and p53 Codependent Manner in Glioblastoma

Alkylating chemotherapy is a central component of the management of glioblastoma (GBM). Among the factors that regulate the response to alkylation damage, NF-κB acts to both promote and block cytotoxicity. In this study, we used genome-wide expression analysis in U87 GBM to identify NF-κB-dependent factors altered in response to temozolomide and found the long noncoding RNA (lncRNA) MALAT1 as one of the most significantly upregulated. In addition, we demonstrated that MALAT1 expression was coregulated by p50 (p105) and p53 via novel κB- and p53-binding sites in the proximal MALAT1 coding region. Temozolomide treatment inhibited p50 recruitment to its cognate element as a function of Ser329 phosphorylation while concomitantly increasing p53 recruitment. Moreover, luciferase reporter studies demonstrated that both κB and p53 cis-elements were required for efficient transactivation in response to temozolomide. Depletion of MALAT1 sensitized patient-derived GBM cells to temozolomide cytotoxicity, and in vivo delivery of nanoparticle-encapsulated anti-MALAT1 siRNA increased the efficacy of temozolomide in mice bearing intracranial GBM xenografts. Despite these observations, in situ hybridization of GBM specimens and analysis of publicly available datasets revealed that MALAT1 expression within GBM tissue was not prognostic of overall survival. Together, these findings support MALAT1 as a target for chemosensitization of GBM and identify p50 and p52 as primary regulators of this ncRNA. SIGNIFICANCE: These findings identify NF-κB and p53 as regulators of the lncRNA MALAT1 and suggest MALAT1 as a potential target for the chemosensitization of GBM.

Santacruzamate A Ameliorates AD-Like Pathology by Enhancing ER Stress Tolerance Through Regulating the Functions of KDELR and Mia40-ALR in vivo and in vitro

Aggregated amyloid-β protein (Aβ) and Aβ-induced neuronal apoptosis have been implicated as critical factors in the pathophysiology of Alzheimer's disease (AD). Certain preclinical results have indicated that the increased accumulation of protein aggregates in AD-affected neurons activates the unfolded protein response (UPR), a pathological phenomenon, which predominantly mediates the aberrant endoplasmic reticulum (ER) stress and apoptotic cascades in neuronal cells. In the present study, we confirmed that Santacruzamate A (STA, a natural product isolated from a Panamanian marine cyanobacterium) attenuates Aβ protein fragment 25-35 (Aβ25-35)-induced toxicity in PC12 cells and rescues cognitive deficits in APPswe/PS1dE9 mice by enhancing ER stress tolerance. We first demonstrated the anti-apoptotic effects of STA by evaluating caspase-3 activity, annexin V/propidium iodide (PI) staining, and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Behavioral testing of STA-treated APPswe/PS1dE9 mice showed that the pronounced memory impairments were ameliorated and that the consolidated memories were stably maintained over a 2-week period. The mechanistic studies provided evidence that STA inhibited Aβ25-35-induced UPR and ER stress by regulating the ER retention signal (KDEL) receptor, which reinforced the retention of resident chaperones in the ER lumen. Furthermore, STA regulated the expression of the mitochondrial intermembrane space assembly protein 40 (Mia40) and augmenter of liver regeneration (ALR), which ultimately attenuated the mitochondrial fission and apoptosis pathways. Together, our present findings suggest that the KDEL receptor and Mia40-ALR play a role in mitigating Aβ25-35-induced neurotoxicity, which might in turn positively regulate learning and memory. These observations support that STA may be a promising agent for reversing the progression of AD.

Role of HDAC3-miRNA-CAGE Network in Anti-Cancer Drug-Resistance

Histone modification is associated with resistance to anti-cancer drugs. Epigenetic modifications of histones can regulate resistance to anti-cancer drugs. It has been reported that histone deacetylase 3 (HDAC3) regulates responses to anti-cancer drugs, angiogenic potential, and tumorigenic potential of cancer cells in association with cancer-associated genes (CAGE), and in particular, a cancer/testis antigen gene. In this paper, we report the roles of microRNAs that regulate the expression of HDAC3 and CAGE involved in resistance to anti-cancer drugs and associated mechanisms. In this review, roles of HDAC3-miRNAs-CAGE molecular networks in resistance to anti-cancer drugs, and the relevance of HDAC3 as a target for developing anti-cancer drugs are discussed.

Design, synthesis and biological evaluation of β-peptoid-capped HDAC inhibitors with anti-neuroblastoma and anti-glioblastoma activity

Histone deacetylases (HDACs) have been identified as promising epigenetic drug targets for the treatment of neuroblastoma and glioblastoma. In this work, we have rationally designed a novel class of peptoid-based histone deacetylase inhibitors (HDACi). A mini library of β-peptoid-capped HDACi was synthesized using a four-step protocol. All compounds were screened in biochemical assays for their inhibition of HDAC1 and HDAC6 and docking studies were performed to rationalize the observed selectivity profile. The synthesized compounds were further examined for tumor cell-inhibitory activity against a panel of neuroblastoma and glioblastoma cell lines. In particular, non-selective compounds with potent activity against HDAC1 and HDAC6 showed strong antiproliferative effects. The most promising HDACi, compound 6i, displayed submicromolar tumor cell-inhibitory potential (IC₅₀: 0.21-0.67 μM) against all five cancer cell lines investigated and exceeded the activity of the FDA-approved HDACi vorinostat.

Nitazoxanide, an antiprotozoal drug, inhibits late-stage autophagy and promotes ING1-induced cell cycle arrest in glioblastoma

Glioblastoma is the most common and aggressive primary brain tumor in adults. New drug design and development is still a major challenge for glioma treatment. Increasing evidence has shown that nitazoxanide, an antiprotozoal drug, has a novel antitumor role in various tumors and exhibits multiple molecular functions, especially autophagic regulation. However, whether nitazoxanide-associated autophagy has an antineoplastic effect in glioma remains unclear. Here, we aimed to explore the underlying molecular mechanism of nitazoxanide in glioblastoma. Our results showed that nitazoxanide suppressed cell growth and induced cell cycle arrest in glioblastoma by upregulating ING1 expression with a favorable toxicity profile. Nitazoxanide inhibited autophagy through blockage of late-stage lysosome acidification, resulting in decreased cleavage of ING1. A combination with chloroquine or Torin1 enhanced or impaired the chemotherapeutic effect of nitazoxanide in glioblastoma cells. Taken together, these findings indicate that nitazoxanide as an autophagy inhibitor induces cell cycle arrest in glioblastoma via upregulated ING1 due to increased transcription and decreased post-translational degradation by late-stage autophagic inhibition.

H19 induced by oxidative stress confers temozolomide resistance in human glioma cells via activating NF-κB signaling

BACKGROUND

Recent findings around long noncoding RNAs (lncRNAs) have opened novel areas of research around their prospective use in overcoming chemoresistance. Herein, we aimed to investigate the role of lncRNA H19 in temozolomide (TMZ) resistance of human glioma cells and the possible mechanisms.

METHODS

Short-/long-term oxidative stress was induced, and TMZ-resistant glioma cells (U251TMZ and LN229TMZ) were established. Small interfering RNA (siRNA) and overexpression plasmids were used to modulate the expression of H19 and/or luciferase the reporters. The MTT assay and immunoblotting of cleaved caspase-3, cyclin D1, XIAP and Bcl-2 were conducted to evaluate TMZ sensitivity. Luciferase reporter and quantitative real-time PCR (qRT-PCR) assays were used to verify the activation of NF-κB pathways by H19.

RESULTS

Knockdown of H19 in U251TMZ and LN229TMZ cells decreased half maximal inhibitory concentration (IC50) values for TMZ and increased cell apoptosis, and H19 overexpression in U251 and LN229 cells led to the opposite effects, indicating that the H19 confers TMZ resistance to glioma cells. Furthermore, knockdown of H19 decreased the NF-κB signaling, which was revealed by repressed reporter activity and declined expression of its downstream targets in TMZ-resistant glioma cells. In contrast, H19 overexpression in U251 and LN229 cells resulted in an increase in NF-κB activation. Blockage of NF-κB activation by its inhibitor abolished TMZ resistance caused by H19 overexpression. Addition of H2O2 to induce oxidative stress largely reversed TMZ sensitivity caused by H19 knockdown.

CONCLUSION

H19 confers TMZ resistance through activating NF-κB signaling and may represent a novel therapeutic target for TMZ-resistant gliomas.

Sporadic DUX4 expression in FSHD myocytes is associated with incomplete repression by the PRC2 complex and gain of H3K9 acetylation on the contracted D4Z4 allele

BACKGROUND

Facioscapulohumeral muscular dystrophy 1 (FSHD1) has an autosomal dominant pattern of inheritance and primarily affects skeletal muscle. The genetic cause of FSHD1 is contraction of the D4Z4 macrosatellite array on chromosome 4 alleles associated with a permissive haplotype causing infrequent sporadic expression of the DUX4 gene. Epigenetically, the contracted D4Z4 array has decreased cytosine methylation and an open chromatin structure. Despite these genetic and epigenetic changes, the majority of FSHD myoblasts are able to repress DUX4 transcription. In this study we hypothesized that histone modifications distinguish DUX4 expressing and non-expressing cells from the same individuals.

RESULTS

FSHD myocytes containing the permissive 4qA haplotype with a long terminal D4Z4 unit were sorted into DUX4 expressing and non-expressing groups. We found similar CpG hypomethylation between the groups of FSHD-affected cells suggesting that CpG hypomethylation is not sufficient to trigger DUX4 expression. A survey of histone modifications present at the D4Z4 region during cell lineage commitment revealed that this region is bivalent in FSHD iPS cells with both H3K4me3 activating and H3K27me3 repressive marks present, making D4Z4 poised for DUX4 activation in pluripotent cells. After lineage commitment, the D4Z4 region becomes univalent with H3K27me3 in FSHD and non-FSHD control myoblasts and a concomitant increase in H3K4me3 in a small fraction of cells. Chromatin immunoprecipitation (ChIP) for histone modifications, chromatin modifier proteins and chromatin structural proteins on sorted FSHD myocytes revealed that activating H3K9Ac modifications were ~ fourfold higher in DUX4 expressing FSHD myocytes, while the repressive H3K27me3 modification was ~ fourfold higher at the permissive allele in DUX4 non-expressing FSHD myocytes from the same cultures. Similarly, we identified EZH2, a member of the polycomb repressive complex involved in H3K27 methylation, to be present more frequently on the permissive allele in DUX4 non-expressing FSHD myocytes.

CONCLUSIONS

These results implicate PRC2 as the complex primarily responsible for DUX4 repression in the setting of FSHD and H3K9 acetylation along with reciprocal loss of H3K27me3 as key epigenetic events that result in DUX4 expression. Future studies focused on events that trigger H3K9Ac or augment PRC2 complex activity in a small fraction of nuclei may expose additional drug targets worthy of study.

Under explored epigenetic modulators: role in glioma chemotherapy

Patients with somatic mutations of epigenetic regulators are characterized by aberrant chromatin modification patterns. Recent mechanistic studies pairing chemical tool compounds and deep-sequencing technology have greatly broadened our understanding of epigenetic regulation in glioma progression and underpinned alternative treatment of epigenetic inhibitors. However, the effect of most inhibitors is condition-dependent, and the overall results of clinical trials still have not been applied to patients. There is an intense need to develop more potent and specific compounds as well as identify the population who may achieve clinical benefits. Besides, combination therapy with conventional therapeutics is another alternative strategy. In this review, we summarize well-characterized chemical probes in glioma research and clinical translation. We also discuss the target population and combination of therapy regimens of various agents. In a holistic sense, we try to provide guidance for selecting targeted chemical probes and pave the way for personalized rational therapy.

Unconventional Approaches to Modulating the Immunogenicity of Tumor Cells

For several years, it has been known that histone deacetylase inhibitors have the potential to alter the immunogenicity of tumor cells exposed to checkpoint inhibitory immunotherapy antibodies. HDAC inhibitors can rapidly reduce expression of PD-L1 and increase expression of MHCA in various tumor types that subsequently facilitate the antitumor actions of checkpoint inhibitors. Recently, we have discovered that drug combinations which cause a rapid and intense autophagosome formation also can modulate the expression of HDAC proteins that control tumor cell immunogenicity via their regulation of PD-L1 and MHCA. These drug combinations, in particular those using the irreversible ERBB1/2/4 inhibitor neratinib, can result in parallel in the internalization of growth factor receptors as well as fellow-traveler proteins such as mutant K-RAS and mutant N-RAS into autophagosomes. The drug-induced autophagosomes contain HDAC proteins/signaling proteins whose expression is subsequently reduced by lysosomal degradation processes. These findings argue that cancer therapies which strongly promote autophagosome formation and autophagic flux may facilitate the subsequent use of additional antitumor modalities using checkpoint inhibitor antibodies.

HDAC inhibition as a treatment concept to combat temsirolimus-resistant bladder cancer cells

Introduction

Although the mechanistic target of rapamycin (mTOR) might be a promising molecular target to treat advanced bladder cancer, resistance develops under chronic exposure to an mTOR inhibitor (everolimus, temsirolimus). Based on earlier studies, we proposed that histone deacetylase (HDAC) blockade might circumvent resistance and investigated whether HDAC inhibition has an impact on growth of bladder cancer cells with acquired resistance towards temsirolimus.

Results

The HDAC inhibitor valproic acid (VPA) significantly inhibited growth, proliferation and caused G0/G1 phase arrest in RT112^res and UMUC-3^res. cdk1, cyclin B, cdk2, cyclin A and Skp1 p19 were down-regulated, p27 was elevated. Akt-mTOR signaling was deactivated, whereas acetylation of histone H3 and H4 in RT112^res and UMUC-3^res increased in the presence of VPA. Knocking down cdk2 or cyclin A resulted in a significant growth blockade of RT112^res and UMUC-3^res.

Materials And Methods

Parental (par) and resistant (res) RT112 and UMUC-3 cells were exposed to the HDAC inhibitor VPA. Tumor cell growth, proliferation, cell cycling and expression of cell cycle regulating proteins were then evaluated. siRNA blockade was used to investigate the functional impact of the proteins.

Conclusions

HDAC inhibition induced a strong response of temsirolimus-resistant bladder cancer cells. Therefore, the temsirolimus-VPA-combination might be an innovative strategy for bladder cancer treatment.

HDAC6 regulates microRNA-27b that suppresses proliferation, promotes apoptosis and target MET in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. Histone deacetylase 6 (HDAC6) is frequently altered in DLBCL and inhibition of HDAC6 has potent anti-tumor effects in vitro and in vivo. We profiled miRNAs that altered in the HDAC6 knockdown DLBCL cells with NanoString nCounter assay and identified microRNA-27b (miR-27b) as the most significantly increased miRNA. We validated decreased expression of miR-27b in DLBCL tissues, and we found that low expression of miR-27b was associated with poor overall survival of patients with DLBCL. In addition, forced expression of miR-27b suppressed DLBCL cell viability and proliferation in vitro, and inhibited tumor growth in vivo. Mechanistically, Rel A/p65 is found to negatively regulate miR-27b expression, and its acetylation and block of nuclear translocalization caused by HDAC6 inhibition significantly elevates miR-27b expression. Furthermore, miR-27b targets MET and thus represses the MET/PI3K/AKT pathway. These findings highlight an important role of miR-27b in the development of DLBCL and uncover a HDAC6-Rel A/p65-miR-27b-MET signaling pathway. Elevating miR-27b through HDAC6 inhibition would be a promising strategy for DLBCL treatment.

Inhibition of HDAC enhances STAT acetylation, blocks NF-κB, and suppresses the renal inflammation and fibrosis in Npr1 haplotype male mice

Guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) plays a critical role in the regulation of blood pressure and fluid volume homeostasis. Mice lacking functional Npr1 (coding for GC-A/NPRA) exhibit hypertension and congestive heart failure. However, the underlying mechanisms remain largely less clear. The objective of the present study was to determine the physiological efficacy and impact of all-trans-retinoic acid (ATRA) and sodium butyrate (NaBu) in ameliorating the renal fibrosis, inflammation, and hypertension in Npr1 gene-disrupted haplotype (1-copy; +/-) mice (50% expression levels of NPRA). Both ATRA and NaBu, either alone or in combination, decreased the elevated levels of renal proinflammatory and profibrotic cytokines and lowered blood pressure in Npr1+/- mice compared with untreated controls. The treatment with ATRA-NaBu facilitated the dissociation of histone deacetylase (HDAC) 1 and 2 from signal transducer and activator of transcription 1 (STAT1) and enhanced its acetylation in the kidneys of Npr1+/- mice. The acetylated STAT1 formed a complex with nuclear factor-κB (NF-κB) p65, thereby inhibiting its DNA-binding activity and downstream proinflammatory and profibrotic signaling cascades. The present results demonstrate that the treatment of the haplotype Npr1+/- mice with ATRA-NaBu significantly lowered blood pressure and reduced the renal inflammation and fibrosis involving the interactive roles of HDAC, NF-κB (p65), and STAT1. The current findings will help in developing the molecular therapeutic targets and new treatment strategies for hypertension and renal dysfunction in humans.

Systematic Quantification of Population Cell Death Kinetics in Mammalian Cells

Cytotoxic compounds are important drugs and research tools. Here, we introduce a method, scalable time-lapse analysis of cell death kinetics (STACK), to quantify the kinetics of compound-induced cell death in mammalian cells at the population level. STACK uses live and dead cell markers, high-throughput time-lapse imaging, and mathematical modeling to determine the kinetics of population cell death over time. We used STACK to profile the effects of over 1,800 bioactive compounds on cell death in two human cancer cell lines, resulting in a large and freely available dataset. 79 potent lethal compounds common to both cell lines caused cell death with widely divergent kinetics. 13 compounds triggered cell death within hours, including the metallophore zinc pyrithione. Mechanistic studies demonstrated that this rapid onset lethal phenotype was caused in human cancer cells by metabolic disruption and ATP depletion. These results provide the first comprehensive survey of cell death kinetics and analysis of rapid-onset lethal compounds.

A novel HDAC6 inhibitor Tubastatin A: Controls HDAC6-p97/VCP-mediated ubiquitination-autophagy turnover and reverses Temozolomide-induced ER stress-tolerance in GBM cells

Temozolomide (TMZ) is the cornerstone of therapy for glioblastoma multiforme (GBM). However, its efficacy is limited due to the development of multidrug resistance (MDR). In this study, we first identified the occurrence of ER stress-tolerance (ERST) in glioma cells and confirmed that ERST was positively correlated with TMZ resistance. We further showed that the seesaw-effect of HDAC6-p97/VCP (increased HDAC6 and decreased p97/VCP) in glioma cells was crucial to ERST-associated TMZ resistance. Moreover, the combination treatment of Tubastatin A (TUB, a selective inhibitor of HDAC6) and TMZ synergistically overcame ERST, reduced cell viability and induced apoptosis in TMZ-resistant glioma cells. TUB and TMZ triggered pro-apoptotic signals of the unfolded protein response (UPR) and ER stress and reversed the ratio between HDAC6 and p97/VCP, which potentially attenuated the activation of heat shock proteins and mediated the reversal of ERST. The combination treatment also triggered the dissociation of Dynein-HDAC6 and attenuation of the Dynein-Dynactin motor complex. In addition, this treatment induced HDAC6-p97/VCP-mediated ubiquitination-autophagy turnover, which was involved in the degradation and clearance of ubiquitinated misfolded proteins. This effect could be partially reversed by HDAC6 KO and/or p97/VCP overexpression. Therefore, we proposed that glioma cells optimized the clearance of ubiquitinated misfolded proteins via the reinforcement of HDAC6-facilitated autophagy and attenuation of the p97/VCP-mediated ubiquitin-proteasome system (UPS). In conclusion, our findings showed that the balance of HDAC6-p97/VCP was crucial to ERST-associated TMZ resistance and that HDAC6 inhibition might be a synergistic target and strategy along with TMZ for the improvement of clinical glioma treatment.