Selective inhibition of histone deacetylase 6 (HDAC6) induces DNA damage and sensitizes transformed cells to anticancer agents

Unlocking the potential of novel tetrahydro-β-carboline-based HDAC6 inhibitors for colorectal cancer therapy: Design, synthesis and biological evaluation

Altered histone deacetylase 6 (HDAC6) expression and function have been linked to cancer progression, positioning it as a promising therapeutic target for cancer treatment. Herein, we introduce HDAC6 inhibitors based on the tetrahydro-β-carboline scaffold, with compound 18d exhibiting the strongest HDAC6 inhibitory potency, achieving an IC50 of 1.3 nM. Compound 18d exhibited significant growth inhibitory activity against an NCI panel of 60 human cancer cell lines with a minimal cytotoxic effect on non-tumor cells. In vitro mechanistic investigations were conducted in HCT-116 colorectal cancer cells where the capability of 18d to enhance the acetylation of α-tubulin (HDAC6 substrate) rather than nuclear H3 histone (HDAC1 substrate) confirmed selective inhibition of HDAC6 subtype. Additionally, compound 18d was observed to suppress the S phase and promote accumulation in the apoptotic sub-G1 phase, potentially through increasing cleaved caspase 3 and reducing Bcl-2 levels in HCT-116 cells. A wound healing assay also elicited the ability of 18d to hinder cell migration. Notably, 18d could suppress the phosphorylation of extracellular signal-regulated kinase (ERK)1/2, a crucial signaling pathway implicated in cancer cell proliferation, migration and apoptosis. Moreover, downregulation of the critical immune checkpoint protein programmed death-ligand 1 (PD-L1) revealed a potential role of 18d in augmenting immune response towards tumor cells. In summary, these findings highlight 18d's dual role in direct tumor growth suppression and immune system sensitization, highlighting a broader cancer therapeutic potential beyond conventional HDAC inhibition.

Design and synthesis of novel Hydroxamate and non-Hydroxamate HDAC inhibitors based on Chromone and Quinazolone scaffolds

The development of selective histone deacetylase (HDAC) inhibitors represents an encouraging approach for cancer therapy. In this study, we report design, synthesis, and biological evaluation of hydroxamate, amidoxime, and carboxylic acid-based derivatives as novel HDAC inhibitors. The synthesized compounds were assessed for their inhibitory activity against multiple HDAC isoforms, particularly HDAC6, 7, and 8. Compounds 13, 16, 20, and 26 exhibited potent and selective inhibition of HDAC6. Compound 26 exhibited the most potent inhibitory activity against HDAC6, with an IC50 value of 70 nM. Additionally, compounds 17 and 23 demonstrated significant broad-spectrum antiproliferative activity across various cancer cell lines compared to other tested derivatives. Furthermore, compounds 17 and 23 showed promising total pan-HDAC inhibitory activity. Subsequent biological studies revealed that compounds 13, 16, 17, 20, 23, and 26 induced a combination of early and late apoptosis along with necrosis. In silico studies, including molecular docking and ADME predictions, were also conducted. Collectively, these findings highlight the potential of these compounds as promising candidates for the development of a novel class of selective HDAC6 inhibitors in the future.

Mutant p53 upregulates HDAC6 to resist ER stress and facilitates Ku70 deacetylation, which prevents its degradation and mitigates DNA damage in colon cancer cells

Cancer cells employ interconnected mechanisms to withstand intrinsic and extrinsic stress, with mutant p53 (mutp53) playing a key role in bolstering resistance to endoplasmic reticulum (ER) stress. In this study, we further investigated this phenomenon, focusing on the DNA damage triggered by ER stress. Our findings indicate that mutp53 mitigates ER stress-induced DNA damage by sustaining high levels of Ku70, a critical protein in DNA repair via the non-homologous end joining (NHEJ) pathway, which functions alongside Ku80. HDAC6 upregulation emerged as a crucial driver of this response. HDAC6 deacetylates Ku70, promoting its nuclear localization and protecting it from degradation. This mechanism ensures continuous activity of the NHEJ repair pathway, allowing mutp53-expressing cells to better manage DNA damage from ER stress, thus contributing to the genomic instability characteristic of cancer progression. Furthermore, HDAC6 maintains the activation of the ATF6 branch of the unfolded protein response (UPR), enhancing the ability of mutp53 cells to resist ER stress, as ATF6 supports cellular adaptation to misfolded proteins and stressful conditions. Since HDAC6 is central to this enhanced stress resistance and DNA repair, targeting it could disrupt these protective mechanisms, increasing the vulnerability of mutp53 cancer cells to ER stress and inhibiting cancer progression.

HDAC6 deficiency aggravates ductular reactions through aggresome-mediated hepatocyte apoptosis

Ductular reactions (DRs) contribute significantly to the occurrence and development of liver disease. While histone deacetylase 6 (HDAC6) is known to regulate injury repair in multiple tissues, its exact role in DRs remains unclear. This study examined the role and underlying mechanism of HDAC6 in DRs using an HDAC6 knockout (HDAC6-/y) male mouse model. Wild type and HDAC6-deficient male mice were administered 3,5 diethoxicarbonyl-1,4 dihydrocollidine (DDC) to induce DRs. The impact of HDAC6 inhibition on aggresome formation was assessed in vitro using AML-12 hepatocytes exposed to H2O2 and treated with tubastatin A (TSA), a selective HDAC6 inhibitor. Fluorescence immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to quantify protein and gene expression levels, respectively. Immunohistochemical and qRT-PCR analyses revealed that HDAC6 deficiency exacerbated DRs and fibrosis, accompanied by increased expression of transforming growth factor β (TGF-β) and activation of the Notch signaling pathway. Additionally, genetic knockout or pharmacological inhibition of HDAC6 promoted hepatocyte apoptosis in vivo and in vitro, as evidenced by elevated caspase3, caspase9, and p53 expression. Furthermore, TSA treatment induced the formation of aggresomes in H2O2-exposed AML-12 hepatocytes, which were encased by vimentin filaments. These findings demonstrate that HDAC6 deficiency promotes DRs and liver fibrosis through the formation of intracellular aggregates, ultimately leading to hepatocyte apoptosis.

HDAC6 Facilitates PRV and VSV Infection by Inhibiting Type I Interferon Production

HDAC6 modulates viral infection through diverse mechanisms. Here, we investigated the role of HDAC6 in influencing viral infection in pig cells with the aim of exploiting the potential antiviral gene targets in pigs. Using gene knockout and overexpression strategies, we found that HDAC6 knockout greatly reduced PRV and VSV infectivity, whereas HDAC6 overexpression increased their infectivity in PK15 cells. Mechanistic studies identified HDAC6 as a DNA damage inhibitor in PK15 cells. HDAC6 overexpression attenuated DNA damage levels, which can further reduce type I IFN production to promote viral infection. Conversely, HDAC6 deficiency can limit viral infection by increasing DNA damage-mediated type I IFN production. This work demonstrates that HDAC6 affects the infection process of multiple viruses by modulating type I IFN production, highlighting a regulatory role of HDAC6 linking host immune response and viral infection levels in pig cells.

Network pharmacology and transcriptomics explore the therapeutic effects of Ermiao Wan categorized formulas for diabetes in mice

Ermiao wan (EMW) is a classical traditional Chinese medicine formula, with two modified versions including Sanmiao wan (SMW) and Simiao wan (FMW). These Ermiao wan categorized formulas (ECFs) are traditionally used to treat gouty arthritis and hyperuricemia. However, their potential benefits and mechanisms on diabetes remain to be explored. This study aims to investigate the overall effects and biological differences of ECFs in high fat diet (HFD)-fed mice based on network pharmacology and transcriptomics. ECFs significantly reduced body weight, improved oral glucose tolerance, decreased fat accumulation, and lowered serum insulin and inflammatory cytokine levels in HFD-fed mice. FMW had better efficacy than EMW and SMW. Network pharmacology analysis revealed that ECFs targeted functional modules associated with chronic inflammation, lipid metabolism, and glucose metabolism. Transcriptome results also showed ECFs could inhibit genes associated with inflammation and upregulated some genes in lipid metabolism. Comprehensive analysis and QPCR verification indicated the beneficial effects of ECFs on diabetes might be attributed to the regulation of Ddit3, Ccl2, Esr1, and Cyp7a1. This study provides a theoretical basis for the clinical use of ECFs.

Novel estrogen receptor β/histone deacetylase dual-targeted near-infrared fluorescent probes as theranostic agents for imaging and treatment of prostate cancer

Estrogen receptor (ER) β and histone deacetylases (HDACs), when overexpressed, are associated closely with the occurrence and development of prostate cancer and are, therefore, considered important targets and biomarkers used in the clinical treatment of prostate cancer. The present study involved the design and synthesis of the first ERβ and HDAC dual-target near-infrared fluorescent probe with both imaging capacity and antitumor activity for prostate cancer. Both P1 and P2 probes exhibited excellent ERβ selectivity, with P1 being almost exclusively selective for ERβ compared to ERα. In addition, P1 exhibited good optical properties, such as strong near-infrared emission, large Stokes shift, and better anti-interference ability, along with excellent imaging ability for living cells. P1 also exhibited potent inhibitory activity against HDAC6 and DU-145 cells, with IC50 values of 52 nM and 0.96 μM, respectively. Further, P1 was applied successfully for the in vivo imaging of prostate cancer in a mouse model, and significant in vivo antitumor efficacy was achieved. The developed dual-target NIR fluorescent probe is expected to serve as an effective tool in the research on prostate cancer, leading to novel insights for the theranostic study of diseases related to ERβ and HDACs.

Radiotherapy-induced Immune Response Enhanced by Selective HDAC6 Inhibition

Radiotherapy is a curative cancer treatment modality that imparts damage to cellular DNA, induces immunogenic cell death, and activates antitumor immunity. Despite the radiotherapy-induced direct antitumor effect seen within the treated volume, accumulating evidence indicates activation of innate antitumor immunity. Acute proinflammatory responses mediated by anticancer M1 macrophages are observed in the immediate aftermath following radiotherapy. However, after a few days, these M1 macrophages are converted to anti-inflammatory and pro-cancer M2 phenotype, leading to cancer resistance and underlying potential tumor relapse. Histone deacetylase 6 (HDAC6) plays a crucial role in regulating macrophage polarization and innate immune responses. Here, we report targeting HDAC6 function with a novel selective inhibitor (SP-2-225) as a potential therapeutic candidate for combination therapy with radiotherapy. This resulted in decreased tumor growth and enhanced M1/M2 ratio of infiltrating macrophages within tumors. These observations support the use of selective HDAC6 inhibitors to improve antitumor immune responses and prevent tumor relapse after radiotherapy.

Epigenetic drugs as new emerging therapeutics: What is the scale's orientation of application and challenges?

Epigenetics is the study of heritable changes in gene expression or function without altering the DNA sequence. Important factors are part of epigenetic events, such as methylation, DNA histone rearrangements, nucleosome transposition, and non-coding RNAs. Dysregulated epigenetic mechanics are associated with various cancers' initiation, development, and metastasis. It is known that the occurrence and development of cancer can be controlled by regulating unexpected epigenetic events. Epi-drugs are used singly or in combination with chemotherapy and enhance antitumor activity, reduce drug resistance, and stimulate the host immune response. Despite these benefits, epigenetic therapy as a single therapy or in combination with other drugs leads to adverse effects. This review article introduces and compares the advantages, disadvantages, and side effects of using these drugs for the first time since their introduction. Also, this article describes the mechanism of action of various epigenetic drugs. Recommendations for future use of epigenetic drugs as cancer therapeutics are suggested as an overall conclusion.

Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development

Pulmonary arterial hypertension (PAH) is a multifactorial disease associated with the remodeling of pulmonary blood vessels. If left unaddressed, PAH can lead to right heart failure and even death. Multiple biological processes, such as smooth muscle proliferation, endothelial dysfunction, inflammation, and resistance to apoptosis, are associated with PAH. Increasing evidence suggests that epigenetic factors play an important role in PAH by regulating the chromatin structure and altering the expression of critical genes. For example, aberrant DNA methylation and histone modifications such as histone acetylation and methylation have been observed in patients with PAH and are linked to vascular remodeling and pulmonary vascular dysfunction. In this review article, we provide a comprehensive overview of the role of key epigenetic targets in PAH pathogenesis, including DNA methyltransferase (DNMT), ten-eleven translocation enzymes (TET), switch-independent 3A (SIN3A), enhancer of zeste homolog 2 (EZH2), histone deacetylase (HDAC), and bromodomain-containing protein 4 (BRD4). Finally, we discuss the potential of multi-omics integration to better understand the molecular signature and profile of PAH patients and how this approach can help identify personalized treatment approaches.

HDAC6 Deficiency Has Moderate Effects on Behaviors and Parkinson's Disease Pathology in Mice

Histone deacetylase 6 (HDAC6) is involved in the regulation of protein aggregation and neuroinflammation, but its role in Parkinson's disease (PD) remains controversial. In this study, Hdac6^-/- mice were generated by CRISPR-Cas9 technology for exploring the effect of HDAC6 on the pathological progression of PD. We found that male Hdac6^-/- mice exhibit hyperactivity and certain anxiety. In the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice, though motor injury was slightly alleviated by HDAC6 deficiency, dopamine (DA) depletion in the striatum, the decrease in the number of DA neurons in the substantia nigra (SN) and the reduction in DA neuronal terminals were not affected. In addition, activation of glial cells and the expression of α-synuclein, as well as the levels of apoptosis-related proteins in the nigrostriatal pathway, were not changed in MPTP-injected wild-type and Hdac6^-/- mice. Therefore, HDAC6 deficiency leads to moderate alterations of behaviors and Parkinson's disease pathology in mice.

HDAC6 Triggers the ATM-Dependent DNA Damage Response To Promote PRV Replication

Pseudorabies virus (PRV) infection is modulated by various cellular host factors. In this study, we investigated the role of histone deacetylase 6 (HDAC6) in this process. We determined HDAC6 expression in vitro and performed gene knockout, pharmacological inhibition analyses, immunofluorescence assays, and statistical analyses. We found that the pharmacological and genetic inhibition of HDAC6 significantly decreased PRV replication, whereas its overexpression promoted PRV replication. Additionally, we demonstrated that PRV infection can induce the phosphorylation of histone H2AX and lead to DNA damage response (DDR), and the ataxia telangiectasia mutated (ATM) inhibitor KU55933 inhibits DDR and PRV infection. Mechanistically, the HDAC6 inhibitor tubacin and HDAC6 knockout can decrease DDR. The results of this study suggested that HDAC6 may be a crucial factor in PRV-induced ATM-dependent DDR to promote PRV replication. IMPORTANCE Pseudorabies virus (PRV) is a member of the subfamily Alphaherpesvirinae of the family Herpesviridae. PRV infection in swine can lead to high morbidity and mortality of swine, causing huge economic losses. In particular, PRV variants can cause severe damage to the nervous and respiratory systems of humans, revealing that PRV may be a potential zoonotic pathogen. Vaccines for PRV have been developed that can delay or reduce the epidemic, but they currently cannot eliminate this disease completely. Therefore, studies should investigate new targets for the prevention and control of PRV infection. In this study, we demonstrated that HDAC6 can induce ataxia telangiectasia mutated-dependent DNA damage response to foster PRV replication, indicating that HDAC6 is a therapeutic target for PRV infection.

Selective inhibition of HDAC6 promotes bladder cancer radiosensitization and mitigates the radiation-induced CXCL1 signalling

BACKGROUND

Although trimodality therapy resecting tumours followed by chemoradiotherapy is emerged for muscle-invasive bladder cancer (MIBC), chemotherapy produces toxicities. Histone deacetylase inhibitors have been identified as an effective strategy to enhance cancer radiotherapy (RT).

METHODS

We examined the role of HDAC6 and specific inhibition of HDAC6 on BC radiosensitivity by performing transcriptomic analysis and mechanism study.

RESULTS

HDAC6 knockdown or HDAC6 inhibitor (HDAC6i) tubacin exerted a radiosensitizing effect, including decreased clonogenic survival, increased H3K9ac and α-tubulin acetylation, and accumulated γH2AX, which are similar to the effect of panobinostat, a pan-HDACi, on irradiated BC cells. Transcriptomics of shHDAC6-transduced T24 under irradiation showed that shHDAC6 counteracted RT-induced mRNA expression of CXCL1, SERPINE1, SDC1 and SDC2, which are linked to cell migration, angiogenesis and metastasis. Moreover, tubacin significantly suppressed RT-induced CXCL1 and radiation-enhanced invasion/migration, whereas panobinostat elevated RT-induced CXCL1 expression and invasion/migration abilities. This phenotype was significantly abrogated by anti-CXCL1 antibody, indicating the key regulator of CXCL1 contributing to BC malignancy. Immunohistochemical evaluation of tumours from urothelial carcinoma patients supported the correlation between high CXCL1 expression and reduced survival.

CONCLUSION

Unlike pan-HDACi, the selective HDAC6i can enhance BC radiosensitization and effectively inhibit RT-induced oncogenic CXCL1-Snail-signalling, thus further advancing its therapeutic potential with RT.

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.

Universal Strategy to Develop Fluorogenic Probes for Lysine Deacylase/Demethylase Activity and Application in Discriminating Demethylation States

Dynamically controlling the post-translational modification of the ε-amino groups of lysine residues is critical for regulating many cellular events. Increasing studies have revealed that many important diseases, including cancer and neurological disorders, are associated with the malfunction of lysine deacylases and demethylases. Developing fluorescent probes that are capable of detecting lysine deacylase and demethylase activity is highly useful for interrogating their roles in epigenetic regulation and diseases. Due to the distinct substrate recognition of these epigenetic eraser enzymes, designing a universal strategy for detecting their activity poses substantial difficulty. Moreover, designing activity-based probes for differentiating their demethylation states is even more challenging and still remains largely unexplored. Herein, we report a universal strategy to construct probes that can detect the enzymatic activity of epigenetic "erasers" through NBD-based long-distance intramolecular reactions. The probes can be easily prepared by installing the O-NBD group at the C-terminal residue of specific peptide substrates by click chemistry. Based on this strategy, detecting the activity of lysine deacetylase, desuccinylase, or demethylase with superior sensitivity and selectivity has been successfully achieved through single-step probe development. Furthermore, the demethylase probe based on this strategy is capable of distinguishing different demethylation states by both absorption and fluorescence lifetime readout. We envision that these newly developed probes will provide powerful tools to facilitate drug discovery in epigenetics in the future.

Novel dual LSD1/HDAC6 inhibitor for the treatment of cancer

Dually targeting the epigenetic proteins lysine specific demethylase 1 (LSD1) and histone deacetylases (HDACs) that play a key role in cancer cells by modulating gene repressor complexes including CoREST will have a profound effect in inhibiting tumour growth. Here, we evaluated JBI-097 a dual LSD1/HDAC6 inhibitor, for its in vitro and in vivo activities in various tumor models. In vitro, JBI-097 showed a strong potency in inhibiting LSD1 and HDAC6 enzymatic activities with the isoform selectivity over other HDACs. Cell-based experiments demonstrated a superior anti-proliferative profile against haematological and solid tumor cell lines. JBI-097 also showed strong modulation of HDAC6 and LSD1 specific biomarkers, alpha-tubulin, CD86, CD11b, and GFi1b. In vivo, JBI-097 showed a stronger effect in erythroleukemia, multiple myeloma xenograft models, and in CT-26 syngeneic model. JBI-097 also showed efficacy as monotherapy and additive or synergistic efficacy in combination with the standard of care or with immune checkpoint inhibitors. These and other findings suggest that JBI-097 could be a promising molecule for targeting the LSD1 and HDAC6. Further studies are warranted to elucidate the mechanism of action.

Hydroxypyrone derivatives in drug discovery: from chelation therapy to rational design of metalloenzyme inhibitors

The versatile structural motif of hydroxypyrone is found in natural products and can be easily converted into hydroxypyridone and hydroxythiopyridone analogues. The favourable toxicity profile and ease of functionalization to access a vast library of compounds make them an ideal structural scaffold for drug design and discovery. This versatile scaffold possesses excellent metal chelating properties that can be exploited for chelation therapy in clinics. Deferiprone [1,2-dimethyl-3-hydroxy-4(1H)-one] was the first orally active chelator to treat iron overload in thalassemia major. Metal complexes of hydroxy-(thio)pyr(id)ones have been investigated as magnetic resonance imaging contrast agents, and anticancer and antidiabetic agents. In recent years, this compound class has demonstrated potential in discovering and developing metalloenzyme inhibitors. This review article summarizes recent literature on hydroxy-(thio)pyr(id)ones as inhibitors for metalloenzymes such as histone deacetylases, tyrosinase and metallo-β-lactamase. Different approaches to the design of hydroxy-(thio)pyr(id)ones and their biological properties against selected metalloenzymes are discussed.

HDAC6: A unique HDAC family member as a cancer target

BACKGROUND

HDAC6, a structurally and functionally distinct member of the HDAC family, is an integral part of multiple cellular functions such as cell proliferation, apoptosis, senescence, DNA damage and genomic stability, all of which when deregulated contribute to carcinogenesis. Among several HDAC family members known so far, HDAC6 holds a unique position. It differs from the other HDAC family members not only in terms of its subcellular localization, but also in terms of its substrate repertoire and hence cellular functions. Recent findings have considerably expanded the research related to the substrate pool, biological functions and regulation of HDAC6. Studies in HDAC6 knockout mice highlighted the importance of HDAC6 as a cell survival player in stressful situations, making it an important anticancer target. There is ample evidence stressing the importance of HDAC6 as an anti-cancer synergistic partner of many chemotherapeutic drugs. HDAC6 inhibitors have been found to enhance the effectiveness of conventional chemotherapeutic drugs such as DNA damaging agents, proteasome inhibitors and microtubule inhibitors, thereby highlighting the importance of combination therapies involving HDAC6 inhibitors and other anti-cancer agents.

CONCLUSIONS

Here, we present a review on HDAC6 with emphasis on its role as a critical regulator of specific physiological cellular pathways which when deregulated contribute to tumorigenesis, thereby highlighting the importance of HDAC6 inhibitors as important anticancer agents alone and in combination with other chemotherapeutic drugs. We also discuss the synergistic anticancer effect of combination therapies of HDAC6 inhibitors with conventional chemotherapeutic drugs.

Discovery of Histone Deacetylase Inhibitor Using Molecular Modeling and Free Energy Calculations

The histone acetylation-deacetylation at lysine regulates the functions of many cellular proteins. An increased expression of HDAC6 can cause an increased amount of deacetylated histones, which leads to an inhibition of gene expression and has been associated with cancer cell proliferation. The present study screened the ZINC database to find novel HDAC6 inhibitors using virtual high-throughput screening techniques. The docking score, free energy, and binding pattern of the complexes were used to select a best ligand for further study. Molecular dynamic simulations, binding interactions, and the stability of docked conformations were investigated. Several parameters that determine protein-ligand interactions, such as root-mean-square deviation (RMSD), root-mean-square fluctuation (RMSF), radius of gyration (Rg), and binding pattern, were observed. Hydrogen bonds were observed at His 573 and Gly 582 after a 150 ns simulation with identified compound ZINC000002845205, and they were similar to known inhibitor Panobinostat. The molecular mechanics with generalised Born and surface area solvation (MM/GBSA) free energy was comparable to known inhibitor Panobinostat. ZINC000002845205 qualifies drug-likeness according to Lipinski's rule-of-five, rule-of-three, and the World Drug Index (WDI)-like rule, but there is one violation in the lead-like rule.

Therapeutic Potential of CKD-504, a Novel Selective Histone Deacetylase 6 Inhibitor, in a Zebrafish Model of Neuromuscular Junction Disorders

The neuromuscular junction (NMJ), which is a synapse for signal transmission from motor neurons to muscle cells, has emerged as an important region because of its association with several peripheral neuropathies. In particular, mutations in GARS that affect the formation of NMJ result in Charcot-Marie-Tooth disease and distal hereditary motor neuropathy. These disorders are mainly considered to be caused by neuronal axon abnormalities; however, no treatment is currently available. Therefore, in order to determine whether the NMJ could be targeted to treat neurodegenerative disorders, we investigated the NMJ recovery effect of HDAC6 inhibitors, which have been used in the treatment of several peripheral neuropathies. In the present study, we demonstrated that HDAC6 inhibition was sufficient to enhance movement by restoring NMJ impairments observed in a zebrafish disease model. We found that CKD-504, a novel HDAC6 inhibitor, was effective in repairing NMJ defects, suggesting that treatment of neurodegenerative diseases via NMJ targeting is possible.

Ricolinostat enhances adavosertib‑induced mitotic catastrophe in TP53‑mutated head and neck squamous cell carcinoma cells

TP53 mutation is one of the most frequent gene mutations in head and neck squamous cell carcinoma (HNSCC) and could be a potential therapeutic target. Recently, the WEE1 G2 checkpoint kinase (WEE1) inhibitor adavosertib (Adv) has attracted attention because of its selective cytotoxicity against TP53-mutated cells and has shown promising activity in early phase clinical trials. In the present study, it was demonstrated that combined treatment with Adv and a selective histone deacetylase 6 (HDAC6) inhibitor, ricolinostat (RCS), synergistically enhanced cell death induction in four out of five HNSCC cell lines with TP53 mutation (CAL27, SAS, HSC-3, and OSC-19), one HNSCC cell line with impaired TP53 function by HPV-infection (UPCI-SCC154), and TP53-knockout human lung cancer cell line (A549 TP53-KO), but not in TP53 wild-type A549 cells. Time-lapse imaging showed that RCS enhanced the Adv-induced mitotic catastrophe. Consistent with this, RCS treatment suppressed checkpoint kinase 1 (Chk1) (Ser345) phosphorylation and co-administration of RCS with Adv suppressed cyclin-dependent kinase 1 (Tyr15) phosphorylation along with increased expression of γ-H2A.X, a marker of DNA double-strand breaks in CAL27 cells. These data showed that RCS enhanced Adv-induced premature mitotic entry and cell death induction in the mitotic phase. However, although HDAC6 knockdown enhanced Adv-induced cell death with γ-H2A.X elevation, HDAC6 knockdown did not repress Chk1 phosphorylation in CAL27 cells. Our data demonstrated that the co-administration of RCS with Adv in HNSCC cells resulted in the suppression of Chk1 activity, leading to synergistically enhanced apoptosis via mitotic catastrophe in a p53-dependent manner. This enhanced cell death appeared to be partially mediated by the inhibition of HDAC6 activity by RCS.

HDAC Inhibitor Sodium Butyrate Attenuates the DNA Repair in Transformed but Not in Normal Fibroblasts

Many cancer therapy strategies cause DNA damage leading to the death of tumor cells. The DNA damage response (DDR) modulators are considered as promising candidates for use in combination therapy to enhance the efficacy of DNA-damage-mediated cancer treatment. The inhibitors of histone deacetylases (HDACis) exhibit selective antiproliferative effects against transformed and tumor cells and could enhance tumor cell sensitivity to genotoxic agents, which is partly attributed to their ability to interfere with DDR. Using the comet assay and host-cell reactivation of transcription, as well as γH2AX staining, we have shown that sodium butyrate inhibited DNA double-strand break (DSB) repair of both endo- and exogenous DNA in transformed but not in normal cells. According to our data, the dysregulation of the key repair proteins, especially the phosphorylated Mre11 pool decrease, is the cause of DNA repair impairment in transformed cells. The inability of HDACis to obstruct DSB repair in normal cells shown in this work demonstrates the advantages of HDACis in combination therapy with genotoxic agents to selectively enhance their cytotoxic activity in cancer cells.

N-Methylpropargylamine-Conjugated Hydroxamic Acids as Dual Inhibitors of Monoamine Oxidase A and Histone Deacetylase for Glioma Treatment

Glioma treatment remains a challenge with a low survival rate due to the lack of effective therapeutics. Monoamine oxidase A (MAO A) plays a role in glioma development, and MAO A inhibitors reduce glioma growth. Histone deacetylase (HDAC) inhibition has emerged as a promising therapy for various malignancies including gliomas. We have synthesized and evaluated N-methylpropargylamine-conjugated hydroxamic acids as dual inhibitors of MAO A and HDAC. Compounds display potent MAO A inhibition with IC₅₀ from 0.03 to <0.0001 μM and inhibit HDAC isoforms and cell growth in the micromolar to nanomolar IC₅₀ range. These selective MAO A inhibitors increase histone H3 and α-tubulin acetylation and induce cell death via nonapoptotic mechanisms. Treatment with 15 reduced tumor size, reduced MAO A activity in brain and tumor tissues, and prolonged the survival. This first report on dual inhibitors of MAO A and HDAC establishes the basis of translational research for an improved treatment of glioma.

Histone deacetylases: A novel class of therapeutic targets for pancreatic cancer

Pancreatic cancer is the seventh leading cause of cancer death worldwide, with a low 5-year survival rate. Novel agents are urgently necessary to treat the main pathological type, known as pancreatic ductal carcinoma (PDAC). The dysregulation of histone deacetylases (HDACs) has been identified in association with PDAC, which can be more easily targeted by small molecular inhibitors than gene mutations and may represent a therapeutic breakthrough for PDAC. However, the contributions of HDACs to PDAC remain controversial, and pharmacokinetic challenges have limited the application of HDAC inhibitors (HDACis) in PDAC. This review summarizes the mechanisms associated with success and failure of HDACis in PDAC and discusses the recent progress made in HDACi development and application, such as combination therapies designed to enhance efficacy. More precise strategies involving HDACis might eventually improve the outcomes of PDAC treatment.

Improved Anticancer Activities of a New Pentafluorothio-Substituted Vorinostat-Type Histone Deacetylase Inhibitor

The development of new anticancer drugs is necessary in order deal with the disease and with the drawbacks of currently applied drugs. Epigenetic dysregulations are a central hallmark of cancerogenesis and histone deacetylases (HDACs) emerged as promising anticancer targets. HDAC inhibitors are promising epigenetic anticancer drugs and new HDAC inhibitors are sought for in order to obtain potent drug candidates. The new HDAC inhibitor SF5-SAHA was synthesized and analyzed for its anticancer properties. The new compound SF5-SAHA showed strong inhibition of tumor cell growth with IC₅₀ values similar to or lower than that of the clinically applied reference compound vorinostat/SAHA (suberoylanilide hydroxamic acid). Target specific HDAC inhibition was demonstrated by Western blot analyses. Unspecific cytotoxic effects were not observed in LDH-release measurements. Pro-apoptotic formation of reactive oxygen species (ROS) and caspase-3 activity induction in prostate carcinoma and hepatocellular carcinoma cell lines DU145 and Hep-G2 seem to be further aspects of the mode of action. Antiangiogenic activity of SF5-SAHA was observed on chorioallantoic membranes of fertilized chicken eggs (CAM assay). The presence of the pentafluorothio-substituent of SF5-SAHA increased the antiproliferative effects in both solid tumor and leukemia/lymphoma cell models when compared with its parent compound vorinostat. Based on this preliminary study, SF5-SAHA has the prerequisites to be further developed as a new HDAC inhibitory anticancer drug candidate.

Impact of Chromatin Dynamics and DNA Repair on Genomic Stability and Treatment Resistance in Pediatric High-Grade Gliomas

Simple Summary

Pediatric high-grade gliomas (pHGGs) are the leading cause of mortality in pediatric neuro-oncology, due in great part to treatment resistance driven by complex DNA repair mechanisms. pHGGs have recently been divided into molecular subtypes based on mutations affecting the N-terminal tail of the histone variant H3.3 and the ATRX/DAXX histone chaperone that deposits H3.3 at repetitive heterochromatin loci that are of paramount importance to the stability of our genome. This review addresses the functions of H3.3 and ATRX/DAXX in chromatin dynamics and DNA repair, as well as the impact of mutations affecting H3.3/ATRX/DAXX on treatment resistance and how the vulnerabilities they expose could foster novel therapeutic strategies.

Abstract

Despite their low incidence, pediatric high-grade gliomas (pHGGs), including diffuse intrinsic pontine gliomas (DIPGs), are the leading cause of mortality in pediatric neuro-oncology. Recurrent, mutually exclusive mutations affecting K27 (K27M) and G34 (G34R/V) in the N-terminal tail of histones H3.3 and H3.1 act as key biological drivers of pHGGs. Notably, mutations in H3.3 are frequently associated with mutations affecting ATRX and DAXX, which encode a chaperone complex that deposits H3.3 into heterochromatic regions, including telomeres. The K27M and G34R/V mutations lead to distinct epigenetic reprogramming, telomere maintenance mechanisms, and oncogenesis scenarios, resulting in distinct subgroups of patients characterized by differences in tumor localization, clinical outcome, as well as concurrent epigenetic and genetic alterations. Contrasting with our understanding of the molecular biology of pHGGs, there has been little improvement in the treatment of pHGGs, with the current mainstays of therapy—genotoxic chemotherapy and ionizing radiation (IR)—facing the development of tumor resistance driven by complex DNA repair pathways. Chromatin and nucleosome dynamics constitute important modulators of the DNA damage response (DDR). Here, we summarize the major DNA repair pathways that contribute to resistance to current DNA damaging agent-based therapeutic strategies and describe the telomere maintenance mechanisms encountered in pHGGs. We then review the functions of H3.3 and its chaperones in chromatin dynamics and DNA repair, as well as examining the impact of their mutation/alteration on these processes. Finally, we discuss potential strategies targeting DNA repair and epigenetic mechanisms as well as telomere maintenance mechanisms, to improve the treatment of pHGGs.

Xbp1s-Ddit3 promotes MCT-induced pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening disease characterized by vascular remodeling. Exploring new therapy target is urgent. The purpose of the present study is to investigate whether and how spliced x-box binding protein 1 (xbp1s), a key component of endoplasmic reticulum stress (ERS), contributes to the pathogenesis of PH. Forty male SD rats were randomly assigned to four groups: Control, Monocrotaline (MCT), MCT+AAV-CTL (control), and MCT+AAV-xbp1s. The xbp1s protein levels were found to be elevated in lung tissues of the MCT group. Intratracheal injection of adeno-associated virus serotype 1 carrying xbp1s shRNA (AAV-xbp1s) to knock down the expression of xbp1s effectively ameliorated the MCT-induced elevation of right ventricular systolic pressure (RVSP), total pulmonary resistance (TPR), right ventricular hypertrophy and medial wall thickness of muscularized distal pulmonary arterioles. The abnormally increased positive staining rates of proliferating cell nuclear antigen (PCNA) and Ki67 and decreased positive staining rates of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) in pulmonary arterioles were also reversed in the MCT+AAV-xbp1s group. For mechanistic exploration, bioinformatics prediction of the protein network was performed on the STRING database, and further verification was performed by qRT-PCR, Western blots and co-immunoprecipitation (Co-IP). DNA damage-inducible transcript 3 (Ddit3) was identified as a downstream protein that interacted with xbp1s. Overexpression of Ddit3 restored the decreased proliferation, migration and cell viability caused by silencing of xbp1s. The protein level of Ddit3 was also highly consistent with xbp1s in the animal model. Taken together, our study demonstrated that xbp1s-Ddit3 may be a potential target to interfere with vascular remodeling in PH.

Regulation of valproic acid induced EMT by AKT/GSK3β/β-catenin signaling pathway in triple negative breast cancer

Valproic acid (VPA) is a selective histone deacetylation (HDAC) inhibitor and exerts anti-cancer properties in different types of cancer. The epithelial-to-mesenchymal transition (EMT) mediating by different signaling cascade can be a potential target in aggressive human cancers. Therefore, we aimed to clarified the unravel relationship between AKT/GSK3β/β-catenin signalling pathway and VPA-induced EMT in triple negative breast cancer (TNBC). The cytotoxicity of VPA in MDA-MB-231 TNBC and MCF-10A control cells was evaluated. Alterations in the expression levels of Snail, E-cadherin, AKT, GSK3β, β-catenin were analyzed by RT-PCR. Additionally, Annexin V, cell cycle and wound healing assays were performed. Our results showed that VPA remarkably inhibited the growth of TNBC cell and triggered apoptotic cell death through G0/G1 arrest. Furthermore, VPA increased cell migration and activated the EMT process through significantly increasing Snail expression and in turn downregulation of E-cadherin and GKS3β levels. However, the level of AKT and β-catenin was reduced after treatment of VPA. Our data showed that VPA induced EMT process and cell migration in TNBC cells. However, AKT/GSK3β/β-catenin signaling pathway did not mediate EMT activation.

Implantable HDAC-inhibiting chemotherapeutics derived from hydrophobic amino acids for localized anticancer therapy

Epigenetic targeting of different cancers by inhibiting particular histone deacetylase (HDAC) isozymes is a promising treatment approach against cancer. Development of locally-implantable molecular inhibitors of HDAC (henceforth called HDACi) promises high tumour site concentration and reduced systemic degradation of the HDACi. Herein, we report the design of such implantable HDACi based on amphiphilic derivatives of hydrophobic amino acids endowed with a hydroxamic acid (hxa)-based zinc-binding residue. The amino acids present in HDACi influenced the HDAC isozyme that could be inhibited most effectively; the l-phenylalanine derivative 4e inhibited the HDAC6 isozyme most potently (IC50 ∼ 88 nM), while the l-isoleucine derivative 4h was most effective against the isozyme HDAC2 (IC50 ∼ 94 nM). We also noticed that the l-Phe derivative 4e was up to 5× more potent towards inhibiting HDAC6 than its optical antipode 4f derived from d-Phe. This was rationalized in terms of the varying extent of penetration of the enantiomeric inhibitors inside the catalytic tunnel of the enzyme. Since the isozymes HDAC6 and HDAC2 are overexpressed in different cancer cells, 4e and 4h elicited selective anticancer activity in different cancer cell lines. Additive therapeutic action of the combination therapy of 4e and 4h was observed on lung cancer cells that overexpress both these isozymes. Further, 4e formed implantable self-assembled hydrogels that achieved sustained and selective killing of cancer cells in the vicinity of implantation.

Real-Time and Sensitive Immunosensor for Label-Free Detection of Specific Antigen with a Comb of Microchannel Long-Period Fiber Grating

This study aimed to develop a comb of microchannel and immunosensor based on long-period fiber grating using the process of Lithographie Galvanoformung Abformung-like micro-electromechanical systems (LIGA-like MEMS) for real-time and label-free detection of specific antigen. The coupling between propagating core and cladding modes was conducted from the comb of microchannel long-period fiber grating (CM-LPFG). The CM-LPFG-based immunosensor consisted of a microchannel structure through photoresist stacking processes and was sandwiched with an optical fiber to obtain a long-period structure. Specific immunoglobulin against protein antigen was immobilized onto an optical fiber surface and produced a real-time resonance effect on sensing specific protein antigen from the extracted protein mixtures of the cancer cell lines. The variable transmission loss was -14.07 dB, and the resonant wavelength shift was 11.239 nm. The low limit of detection for total protein concentration was 1.363 ng/μL. Our results revealed that the CM-LPFG-based immnosensor for real-time detection of label-free protein antigen is feasible and sensitive based on the diversification of a transmission loss and achieves specific immunosensing purposes for lab-on-fiber technology.

UNG2 deacetylation confers cancer cell resistance to hydrogen peroxide-induced cytotoxicity

Cancer therapeutics produce reactive oxygen species (ROS) that damage the cancer genome and lead to cell death. However, cancer cells can resist ROS-induced cytotoxicity and survive. We show that nuclear-localized uracil-DNA N-glycosylase isoform 2 (UNG2) has a critical role in preventing ROS-induced DNA damage and enabling cancer-cell resistance. Under physiological conditions, UNG2 is targeted for rapid degradation via an interaction with the E3 ligase UHRF1. In response to ROS, however, UNG2 protein in cancer cells exhibits a remarkably extended half-life. Upon ROS exposure, UNG2 is deacetylated at lysine 78 by histone deacetylases, which prevents the UNG2-UHRF1 interaction. Accumulated UNG2 protein can thus excise the base damaged by ROS and enable the cell to survive these otherwise toxic conditions. Consequently, combining HDAC inhibitors (to permit UNG2 degradation) with genotoxic agents (to produce cytotoxic cellular levels of ROS) leads to a robust synergistic killing effect in cancer cells in vitro. Altogether, these data support the application of a novel approach to cancer treatment based on promoting UNG2 degradation by altering its acetylation status using an HDAC inhibitor.

Rapid In Vivo Validation of HDAC Inhibitor-Based Treatments in Neuroblastoma Zebrafish Xenografts

The survival rate among children with relapsed neuroblastomas continues to be poor, and thus new therapeutic approaches identified by reliable preclinical drug testing models are urgently needed. Zebrafish are a powerful vertebrate model in preclinical cancer research. Here, we describe a zebrafish neuroblastoma yolk sac model to evaluate efficacy and toxicity of histone deacetylase (HDAC) inhibitor treatments. Larvae were engrafted with fluorescently labeled, genetically diverse, established cell lines and short-term cultures of patient-derived primary cells. Engrafted tumors progressed locally and disseminated remotely in an intact environment. Combination treatments involving the standard chemotherapy doxorubicin and HDAC inhibitors substantially reduced tumor volume, induced tumor cell death, and inhibited tumor cell dissemination to the tail region. Hence, this model allows for fast, cost-efficient, and reliable in vivo evaluation of toxicity and response of the primary and metastatic tumor sites to drug combinations.

HDAC6 Regulates Radiosensitivity of Non-Small Cell Lung Cancer by Promoting Degradation of Chk1

We have previously discovered that HDAC6 regulates the DNA damage response (DDR) via modulating the homeostasis of a DNA mismatch repair protein, MSH2, through HDAC6’s ubiquitin E3 ligase activity. Here, we have reported HDAC6’s second potential E3 ligase substrate, a critical cell cycle checkpoint protein, Chk1. We have found that HDAC6 and Chk1 directly interact, and that HDAC6 ubiquitinates Chk1 in vivo and in vitro. Specifically, HDAC6 interacts with Chk1 via the DAC1 domain, which contains its ubiquitin E3 ligase activity. During the cell cycle, Chk1 protein levels fluctuate, peaking at the G2 phase, subsequently resolving via the ubiquitin-proteasome pathway, and thereby allowing cells to progress to the M phase. However, in HDAC6 knockdown non-small cell lung cancer (NSCLC) cells, Chk1 is constitutively active and fails to resolve post-ionizing radiation (IR), and this enhanced Chk1 activity leads to preferential G2 arrest in HDAC6 knockdown cells accompanied by a reduction in colony formation capacity and viability. Depletion or pharmacological inhibition of Chk1 in HDAC6 knockdown cells reverses this radiosensitive phenotype, suggesting that the radiosensitivity of HDAC6 knockdown cells is dependent on increased Chk1 kinase activity. Overall, our results highlight a novel mechanism of Chk1 regulation at the post-translational level, and a possible strategy for sensitizing NSCLC to radiation via inhibiting HDAC6’s E3 ligase activity.

BCAS2, a protein enriched in advanced prostate cancer, interacts with NBS1 to enhance DNA double-strand break repair

Background

Breast cancer amplified sequence 2 (BCAS2) plays crucial roles in pre-mRNA splicing and androgen receptor transcription. Previous studies suggested that BCAS2 is involved in double-strand breaks (DSB); therefore, we aimed to characterise its mechanism and role in prostate cancer (PCa).

Methods

Western blotting and immunofluorescence microscopy were used to assay the roles of BCAS2 in the DSBs of PCa cells and apoptosis in Drosophila, respectively. The effect of BCAS2 dosage on non-homologous end joining (NHEJ) and homologous recombination (HR) were assayed by precise end-joining assay and flow cytometry, respectively. Glutathione-S-transferase pulldown and co-immunoprecipitation assays were used to determine whether and how BCAS2 interacts with NBS1. The expression of BCAS2 and other proteins in human PCa was determined by immunohistochemistry.

Results

BCAS2 helped repair radiation-induced DSBs efficiently in both human PCa cells and Drosophila. BCAS2 enhanced both NHEJ and HR, possibly by interacting with NBS1, which involved the BCAS2 N-terminus as well as both the NBS1 N- and C-termini. The overexpression of BCAS2 was significantly associated with higher Gleason and pathology grades and shorter survival in patients with PCa.

Conclusion

BCAS2 promotes two DSB repair pathways by interacting with NBS1, and it may affect PCa progression.

Histone lysine specific demethylase 1 inhibitors

LSD1 plays a pivotal role in numerous biological functions. The overexpression of LSD1 is reported to be associated with different malignancies. Over the last decade, LSD1 has emerged as an interesting target for the treatment of acute myeloid leukaemia (AML). Numerous researchers have designed, synthesized, and evaluated various LSD1 inhibitors with diverse chemical architectures. Some of these inhibitors have entered clinical trials and are currently at different phases of clinical evaluation. This comprehensive review enlists recent research developments in LSD1 targeting pharmacophores reported over the last few years.

Harnessing DNA Replication Stress for Novel Cancer Therapy

DNA replication is the fundamental process for accurate duplication and transfer of genetic information. Its fidelity is under constant stress from endogenous and exogenous factors which can cause perturbations that lead to DNA damage and defective replication. This can compromise genomic stability and integrity. Genomic instability is considered as one of the hallmarks of cancer. In normal cells, various checkpoints could either activate DNA repair or induce cell death/senescence. Cancer cells on the other hand potentiate DNA replicative stress, due to defective DNA damage repair mechanism and unchecked growth signaling. Though replicative stress can lead to mutagenesis and tumorigenesis, it can be harnessed paradoxically for cancer treatment. Herein, we review the mechanism and rationale to exploit replication stress for cancer therapy. We discuss both established and new approaches targeting DNA replication stress including chemotherapy, radiation, and small molecule inhibitors targeting pathways including ATR, Chk1, PARP, WEE1, MELK, NAE, TLK etc. Finally, we review combination treatments, biomarkers, and we suggest potential novel methods to target DNA replication stress to treat cancer.

Recent Progress in Histone Deacetylase Inhibitors as Anticancer Agents

Histone Deacetylase (HDAC) inhibitors are a relatively new class of anti-cancer agents that play important roles in epigenetic or non-epigenetic regulation, inducing death, apoptosis, and cell cycle arrest in cancer cells. Recently, their use has been clinically validated in cancer patients resulting in the approval by the FDA of four HDAC inhibitors, vorinostat, romidepsin, belinostat and panobinostat, used for the treatment of cutaneous/peripheral T-cell lymphoma and multiple myeloma. Many more HDAC inhibitors are at different stages of clinical development for the treatment of hematological malignancies as well as solid tumors. Also, clinical trials of several HDAC inhibitors for use as anti-cancer drugs (alone or in combination with other anti-cancer therapeutics) are ongoing. In the intensifying efforts to discover new, hopefully, more therapeutically efficacious HDAC inhibitors, molecular modelingbased rational drug design has played an important role. In this review, we summarize four major structural classes of HDAC inhibitors (hydroxamic acid derivatives, aminobenzamide, cyclic peptide and short-chain fatty acids) that are in clinical trials and different computer modeling tools available for their structural modifications as a guide to discover additional HDAC inhibitors with greater therapeutic utility.

Inhibition of cell migration and induction of apoptosis by a novel class II histone deacetylase inhibitor, MCC2344

Epigenetic modifiers provide a new target for the development of anti-cancer drugs. The eraser histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase that targets various non-histone proteins such as transcription factors, nuclear receptors, cytoskeletal proteins, DNA repair proteins, and molecular chaperones. Therefore, it became an attractive target for cancer treatment. In this study, virtual screening was applied to the MicroCombiChem database with 1162 drug-like compounds to identify new HDAC6 inhibitors. Five compounds were tested in silico and in vitro as HDAC6 inhibitors. Both analyses revealed 1-cyclohexene-1-carboxamide, 2-hydroxy-4,4-dimethyl-N-1-naphthalenyl-6-oxo- (MCC2344) as the best HDAC6 inhibitor among the five ligands. The binding affinity of MCC2344 to HDAC6 was further confirmed by microscale thermophoresis. Additionally, the anti-cancer activity of MCC2344 was tested in several tumor cell lines. Leukemia cells were the most sensitive cells towards MCC2344, particularly the P-glycoprotein-overexpressing multidrug-resistant cell line CEM/ADR5000 exhibited remarkable collateral sensitivity towards MCC2344. Transcriptome analysis using microarray hybridization was performed for investigating downstream mechanisms of action of MCC2344 in leukemia cells. MCC2344 affected microtubule dynamics and suppressed cell migration in the wound healing assay as well as in a spheroid model by hyper-acetylation of tubulin and HSP-90. MCC2344 induced cell death in CEM/ADR5000 cells by activation of PARP, caspase-3, and p21 in addition to the downregulation of p62. MCC2344 significantly inhibited tumor growth in vivo in zebrafish larvae without mortality until 20 pM. We propose MCC2344 as a novel HDAC6 inhibitor for cancer treatment.

Molecular docking-based virtual drug screening revealing an oxofluorenyl benzamide and a bromonaphthalene sulfonamido hydroxybenzoic acid as HDAC6 inhibitors with cytotoxicity against leukemia cells

HDAC6 is a crucial epigenetic modifier that plays a vital role in tumor progression and carcinogenesis due to its multiple biological functions. It is a unique member of class-II HDAC enzymes. It possesses two catalytic domains, which function independently of the overall enzyme activity. Up to date, there are only a few selective HDAC6 inhibitors with anti-cancer activity. In this study, 175,204 ligands obtained from the ZINC15 and OTAVAchemical databases were used for virtual drug screening against HDAC6. Molecular docking studies were performed for 100 selected compounds. Furthermore, the top 10 compounds obtained from docking were tested for their efficacy to inhibit the function of HDAC6. Five compounds (N-(9-oxo-9H-fluoren-3-yl)benzamide, 2-hydroxy-5-[(5-oxo-6-phenyl-4,5-dihydro-1,2,4-triazin-3-yl)amino]benzoic acid, 5-(4-bromonaphthalene-1-sulfonamido)-2-hydroxybenzoic acid, 2-(naphthalen-2-yl)-N-(1H-1,2,3,4-tetrazol-5-yl)cyclopropane-1-carboxamide, and 4-oxa-5,6 diazapentacyclo[10.7.1.0³,⁷.0⁸,²⁰.0¹⁴,¹⁹]icosa-1,3(7),5,8(20),9,11,14,16,18-nonaen-13-one) inhibited enzymatic activity by more than 50 % compared to DMSO as the control. Two candidates, (N-(9-oxo-9H-fluoren-3-yl)benzamide and 5-(4-bromonaphthalene-1-sulfonamido)-2-hydroxybenzoic acid), were identified with considerable cytotoxicity towards drug-sensitive CCRF-CEM and multidrug-resistant CEM/ADR5000 leukemia cells. Microscale thermophoresis revealed the binding of N-(9-oxo-9H-fluoren-3-yl)benzamide and 5-(4-bromonaphthalene-1-sulfonamido)-2-hydroxybenzoic acid to purified HDAC6 protein. Both compounds induced apoptosis in a dose-dependent manner as analyzed by flow cytometry. In conclusion, we demonstrate for the first time that these two compounds bind to HDAC6, inhibit its function, and exert cytotoxic activity by apoptosis induction.

Proteasome inhibitors trigger mutations via activation of caspases and CAD, but mutagenesis provoked by the HDAC inhibitors vorinostat and romidepsin is caspase/CAD-independent

Genotoxic anti-cancer therapies such as chemotherapy and radiotherapy can contribute to an increase in second malignancies in cancer survivors due to their oncogenic effects on non-cancerous cells. Inhibition of histone deacetylase (HDAC) proteins or the proteasome differ from chemotherapy in that they eliminate cancer cells by regulating gene expression or cellular protein equilibrium, respectively. As members of these drug classes have been approved for clinical use in recent times, we investigated whether these two drug classes exhibit similar mutagenic capabilities as chemotherapy. The HDAC inhibitors vorinostat/SAHA and romidepsin/FK288 were found to induce DNA damage, and mis-repair of this damage manifested into mutations in clonogenically viable surviving cells. DNA damage and mutations were also detected in cells treated with the proteasome inhibitor bortezomib. Exposure to both drug classes stimulated caspase activation consistent with apoptotic cell death. Inhibition of caspases protected cells from bortezomib-induced acute (but not clonogenic) death and mutagenesis, implying caspases were required for the mutagenic action of bortezomib. This was also observed for second generation proteasome inhibitors. Cells deficient in caspase-activated DNase (CAD) also failed to acquire DNA damage or mutations following treatment with bortezomib. Surprisingly, vorinostat and romidepsin maintained an equivalent level of killing and mutagenic ability regardless of caspase or CAD activity. Our findings indicate that both drug classes harbour mutagenic potential in vitro. If recapitulated in vivo, the mutagenicity of these agents may influence the treatment of cancer patients who are more susceptible to oncogenic mutations due to dysfunctional DNA repair pathways.

In Vitro and In Vivo Effects of the Polymyxin-Vorinostat Combination Therapy Against Multidrug-Resistant Gram-Negative Pathogens

With the stagnancy of antibiotics development, polymyxins have become the last defense for treatment of multidrug-resistant (MDR) Gram-negative bacteria, whereas the effect of polymyxin monotherapy is limited by resistance. The objective of this study was to evaluate the effects of polymyxin B (PMNB)-vorinostat (SAHA) combination therapy against Gram-negative pathogens in vitro and in vivo. The antibacterial activities of PMNB and SAHA were evaluated by susceptibility testing. The synergistic effect was assessed by checkerboard tests and time-killing kinetics experiments. Cellular morphology studies and reactive oxygen species (ROS) assay were conducted to explore potential mechanisms. Also, Galleria mellonella models were made to evaluate the antibacterial effects in vivo. PMNB-SAHA had the synergistic effect against all tested isolates, reducing >2 log₁₀ colony-forming units (CFU)/mL at 40 minutes, and showed more powerful antibacterial effects than PMNB alone in the 24-hour window. Cellular morphology study showed the change of membrane and disruption of integrity. ROS assay showed more oxidative stress in combination than PMNB or SAHA monotherapy. In animal models, PMNB-SAHA showed a higher survival rate than that of monotherapy. This study is the first to report the synergistic antibacterial effect of PMNB-SAHA therapy against MDR Gram-negative bacteria. Further clinical research is needed to confirm the results.

Indocyanine Green-Nexturastat A-PLGA Nanoparticles Combine Photothermal and Epigenetic Therapy for Melanoma

In this study, we describe poly (lactic-co-glycolic) acid (PLGA)-based nanoparticles that combine photothermal therapy (PTT) with epigenetic therapy for melanoma. Specifically, we co-encapsulated indocyanine green (ICG), a PTT agent, and Nexturastat A (NextA), an epigenetic drug within PLGA nanoparticles (ICG-NextA-PLGA; INAPs). We hypothesized that combining PTT with epigenetic therapy elicits favorable cytotoxic and immunomodulatory responses that result in improved survival in melanoma-bearing mice. We utilized a nanoemulsion synthesis scheme to co-encapsulate ICG and NextA within stable and monodispersed INAPs. The INAPs exhibited concentration-dependent and near-infrared (NIR) laser power-dependent photothermal heating characteristics, and functioned as effective single-use agents for PTT of melanoma cells in vitro. The INAPs functioned as effective epigenetic therapy agents by inhibiting the expression of pan-histone deacetylase (HDAC) and HDAC6-specific activity in melanoma cells in vitro. When used for both PTT and epigenetic therapy in vitro, the INAPs increased the expression of co-stimulatory molecules and major histocompatibility complex (MHC) Class I in melanoma cells relative to controls. These advantages persisted in vivo in a syngeneic murine model of melanoma, where the combination therapy slowed tumor progression and improved median survival. These findings demonstrate the potential of INAPs as agents of PTT and epigenetic therapy for melanoma.

Molecular Determinants of Cancer Therapy Resistance to HDAC Inhibitor-Induced Autophagy

Histone deacetylation inhibitors (HDACi) offer high potential for future cancer therapy as they can re-establish the expression of epigenetically silenced cell death programs. HDACi-induced autophagy offers the possibility to counteract the frequently present apoptosis-resistance as well as stress conditions of cancer cells. Opposed to the function of apoptosis and necrosis however, autophagy activated in cancer cells can engage in a tumor-suppressive or tumor-promoting manner depending on mostly unclarified factors. As a physiological adaption to apoptosis resistance in early phases of tumorigenesis, autophagy seems to resume a tumorsuppressive role that confines tumor necrosis and inflammation or even induces cell death in malignant cells. During later stages of tumor development, chemotherapeutic drug-induced autophagy seems to be reprogrammed by the cancer cell to prevent its elimination and support tumor progression. Consistently, HDACi-mediated activation of autophagy seems to exert a protective function that prevents the induction of apoptotic or necrotic cell death in cancer cells. Thus, resistance to HDACi-induced cell death is often encountered in various types of cancer as well. The current review highlights the different mechanisms of HDACi-elicited autophagy and corresponding possible molecular determinants of therapeutic resistance in cancer.

The histone deacetylase inhibitor tubacin mitigates endothelial dysfunction by up-regulating the expression of endothelial nitric oxide synthase

Endothelial nitric oxide (NO) synthase (eNOS) plays a critical role in the maintenance of blood vessel homeostasis. Recent findings suggest that cytoskeletal dynamics play an essential role in regulating eNOS expression and activation. Here, we sought to test whether modulation of cytoskeletal dynamics through pharmacological regulation of histone deacetylase 6 (HDAC6)-mediated tubulin deacetylation affects eNOS expression and endothelial function in vitro and in vivo We found that tubulin acetylation inducer (tubacin), a compound that appears to selectively inhibit HDAC6 activity, dramatically increased eNOS expression in several different endothelial cell lines, as determined by both immunoblotting and NO production assays. Mechanistically, we found that these effects were not mediated by tubacin's inhibitory effect on HDAC6 activity, but rather were due to its ability to stabilize eNOS mRNA transcripts. Consistent with these findings, tubacin also inhibited proinflammatory cytokine-induced degradation of eNOS transcripts and impairment of endothelium-dependent relaxation in the mouse aorta. Furthermore, we found that tubacin-induced up-regulation in eNOS expression in vivo is associated with improved endothelial function in diabetic db/db mice and with a marked attenuation of ischemic brain injury in a murine stroke model. Our findings indicate that tubacin exhibits potent eNOS-inducing effects and suggest that this compound might be useful for the prevention or management of endothelial dysfunction-associated cardiovascular diseases.

A yeast phenomic model for the influence of Warburg metabolism on genetic buffering of doxorubicin

BACKGROUND

The influence of the Warburg phenomenon on chemotherapy response is unknown. Saccharomyces cerevisiae mimics the Warburg effect, repressing respiration in the presence of adequate glucose. Yeast phenomic experiments were conducted to assess potential influences of Warburg metabolism on gene-drug interaction underlying the cellular response to doxorubicin. Homologous genes from yeast phenomic and cancer pharmacogenomics data were analyzed to infer evolutionary conservation of gene-drug interaction and predict therapeutic relevance.

METHODS

Cell proliferation phenotypes (CPPs) of the yeast gene knockout/knockdown library were measured by quantitative high-throughput cell array phenotyping (Q-HTCP), treating with escalating doxorubicin concentrations under conditions of respiratory or glycolytic metabolism. Doxorubicin-gene interaction was quantified by departure of CPPs observed for the doxorubicin-treated mutant strain from that expected based on an interaction model. Recursive expectation-maximization clustering (REMc) and Gene Ontology (GO)-based analyses of interactions identified functional biological modules that differentially buffer or promote doxorubicin cytotoxicity with respect to Warburg metabolism. Yeast phenomic and cancer pharmacogenomics data were integrated to predict differential gene expression causally influencing doxorubicin anti-tumor efficacy.

RESULTS

Yeast compromised for genes functioning in chromatin organization, and several other cellular processes are more resistant to doxorubicin under glycolytic conditions. Thus, the Warburg transition appears to alleviate requirements for cellular functions that buffer doxorubicin cytotoxicity in a respiratory context. We analyzed human homologs of yeast genes exhibiting gene-doxorubicin interaction in cancer pharmacogenomics data to predict causality for differential gene expression associated with doxorubicin cytotoxicity in cancer cells. This analysis suggested conserved cellular responses to doxorubicin due to influences of homologous recombination, sphingolipid homeostasis, telomere tethering at nuclear periphery, actin cortical patch localization, and other gene functions.

CONCLUSIONS

Warburg status alters the genetic network required for yeast to buffer doxorubicin toxicity. Integration of yeast phenomic and cancer pharmacogenomics data suggests evolutionary conservation of gene-drug interaction networks and provides a new experimental approach to model their influence on chemotherapy response. Thus, yeast phenomic models could aid the development of precision oncology algorithms to predict efficacious cytotoxic drugs for cancer, based on genetic and metabolic profiles of individual tumors.

Comparison of Radiosensitization by HDAC Inhibitors CUDC-101 and SAHA in Pancreatic Cancer Cells

Pancreatic cancer has a poor prognosis. New treatment options are urgently required to improve patient outcomes. One promising new class of anticancer drugs are synthetic histone deacetylase inhibitors (HDACi) which modulate chromatin structure and gene expression by blocking histone deacetylation. In this study, we aimed at comparing the in vitro capacities of the HDACi SAHA and CUDC-101 to increase radiosensitivity of human pancreatic tumor cell lines. Therefore, three pancreatic cancer cell lines (Su.86.86, MIA Paca-2, T3M-4) were treated with SAHA (1.5–5 µM) or CUDC-101 (0.25–3 µM) and after 24 h irradiated. Cell proliferation, clonogenic survival and apoptosis was determined. Additionally, cell lysates were investigated for the expression of apoptosis-related proteins. CUDC-101 and SAHA increased the radiation sensitivity of pancreatic tumor cell lines in a dose-dependent manner. This was evidenced by cell proliferation and clonogenic survival. Furthermore, enhanced radiation sensitivity after CUDC-101 or SAHA treatment was confirmed for Su.86.86 and T3M-4 cells in a 3-D microtissue approach. Increased amounts of subG1 cells and diminished full length PARP-1 suggest increased radiation-induced apoptosis after SAHA or CUDC-101 treatment. The comparison of both inhibitors in these assays manifested CUDC-101 as more potent radiosensitizer than SAHA. In line, western blot quantification of the apoptosis-inhibitory proteins XIAP and survivin showed a stronger down-regulation in response to CUDC-101 treatment than after SAHA application. These proteins may contribute to the synergy between HDAC inhibition and radiation response. In conclusion, these preclinical results suggest that treatment with the HDAC inhibitors CUDC-101 or SAHA can enhance radiation-induced cytotoxicity in human pancreatic cells. However, comparison of both inhibitors identified the multi target inhibitor CUDC-101 as more potent radiosensitizer than the HDAC inhibitor SAHA.

Molecular Mechanisms of Epigenetic Regulators as Activatable Targets in Cancer Theranostics

Epigenetics is defined as somatically inheritable changes that are not accompanied by alterations in DNA sequence. Epigenetics encompasses DNA methylation, covalent histone modifications, non-coding RNA as well as nucleosome remodeling. Notably, abnormal epigenetic changes play a critical role in cancer development including malignant transformation, metastasis, prognosis, drug resistance and tumor recurrence, which can provide effective targets for cancer prognosis, diagnosis and therapy. Understanding these changes provide effective means for cancer diagnosis and druggable targets for better clinical applications. Histone modifications and related enzymes have been found to correlate well with cancer incidence and prognosis in recent years. Dysregulated expression or mutation of histone modification enzymes and histone modification status abnormalities have been considered to play essential roles in tumorigenesis and clinical outcomes of cancer treatment. Some of the histone modification inhibitors have been extensively employed in clinical practice and many others are still under laboratory research or pre-clinical assessment. Here we summarize the important roles of epigenetics, especially histone modifications in cancer diagnostics and therapeutics, and also discuss the developmental implications of activatable epigenetic targets in cancer theranostics.