Histone deacetylases 1 and 2 cooperate in regulating BRCA1, CHK1, and RAD51 expression in acute myeloid leukemia cells

A high-throughput approach to identify BRCA1-downregulating compounds to enhance PARP inhibitor sensitivity

PARP inhibitors (PARPi) are efficacious in BRCA1-null tumors; however, their utility is limited in tumors with functional BRCA1. We hypothesized that pharmacologically reducing BRCA1 protein levels could enhance PARPi effectiveness in BRCA1 wild-type tumors. To identify BRCA1 downregulating agents, we generated reporter cell lines using CRISPR-mediated editing to tag endogenous BRCA1 protein with HiBiT. These reporter lines enable the sensitive measurement of BRCA1 protein levels by luminescence. Validated reporter cells were used in a pilot screen of epigenetic-modifying probes and a larger screen of more than 6,000 compounds. We identified 7 compounds that could downregulate BRCA1-HiBiT expression and synergize with olaparib. Three compounds, N-acetyl-N-acetoxy chlorobenzenesulfonamide (NANAC), A-443654, and CHIR-124, were validated to reduce BRCA1 protein levels and sensitize breast cancer cells to the toxic effects of olaparib. These results suggest that BRCA1-HiBiT reporter cells hold promise in developing agents to improve the clinical utility of PARPi.

Epigenetic Dysregulation and Its Correlation with the Steroidogenic Machinery Impacting Breast Pathogenesis: Data Mining and Molecular Insights into Therapeutics

Breast cancer (BC) is a heterogeneous condition and comprises molecularly distinct subtypes. An imbalance in the levels of epigenetic histone deacetylases (HDACs), modulating estrogen accumulation, especially 17β-estradiol (E2), promotes breast tumorigenesis. In the present study, analyses of The Cancer Genome Atlas (TCGA) pan-cancer normalized RNA-Seq datasets revealed the dysregulation of 16 epigenetic enzymes (among a total of 18 members) in luminal BC subtypes, in comparison to their non-cancerous counterparts. Explicitly, genomic profiling of these epigenetic enzymes displayed increases in HDAC1, 2, 8, 10, 11, and Sirtuins (SIRTs) 6 and 7, and decreases in HDAC4-7, -9, and SIRT1-4 levels, respectively, in TCGA breast tumors. Kaplan-Meier plot analyses showed that these HDACs, with the exception of HDAC2 and SIRT2, were not correlated with the overall survival of BC patients. Additionally, disruption of the epigenetic signaling in TCGA BC subtypes, as assessed using both heatmaps and boxplots, was associated with the genomic expression of factors that are instrumental for cholesterol trafficking/utilization for accelerating estrogen/E2 levels, in which steroidogenic acute regulatory protein (STAR) mediates the rate-limiting step in steroid biosynthesis. TCGA breast samples showed diverse expression patterns of a variety of key steroidogenic markers and hormone receptors, including LIPE, CYP27A1, STAR, STARD3, CYP11A1, CYP19A1, ER, PGR, and ERBB2. Moreover, regulation of STAR-governed steroidogenic machinery was found to be influenced by various transcription factors, i.e., CREB1, CREM, SF1, NR4A1, CEBPB, SREBF1, SREBF2, SP1, FOS, JUN, NR0B1, and YY1. Along these lines, ingenuity pathway analysis (IPA) recognized a number of new targets and downstream effectors influencing BCs. Of note, genomic, epigenomic, transcriptional, and hormonal anomalies observed in human primary breast tumors were qualitatively similar in pertinent BC cell lines. These findings identify the functional correlation between dysregulated epigenetic enzymes and estrogen/E2 accumulation in human breast tumors, providing the molecular insights into more targeted therapeutic approaches involving the inhibition of HDACs for combating this life-threatening disease.

Therapeutic efficacy of an injectable formulation of purinostat mesylate in SU-DHL-6 tumour model

Background: Previous studies have proven that Purinostat Mesylate (PM) is a new HDAC inhibitor and exhibits significant antitumor efficacy. However, the clinical application of PM was greatly limited by its poor solubility in water and low bioavailability.Objective:To increase the solubility of PM through pharmaceutical research, and prepare it into an injection that meets the needs of intravenous use to promote its clinical application.MethodsThe prepared PM/HP-β-CD inclusion complex was studied by computer simulation, fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H-NMR spectroscopy), and scanning electron microscopy (SEM). Then, the antitumor effects of PM/HP-β-CD inclusion complex were studied by in vitro cytotoxicity assay, apoptosis assay, pharmacokinetic study and in vivo antitumor assay.Results:Phase Solubility Analysis revealed that PM and HP-β-CD were compatible and the solubility of PM increased almost 220 times, to 2.02 mg/mL. The interaction mechanism studies revealed that PM could be embedded into the cavity of HP-β-CD through the side of the aminobenzene ring. Cell viability and apoptosis assays showed that PM/HP-β-CD complex maintained the good anti-cancer activity of PM, and PM/HP-β-CD complex has a better anti-tumor effect and lower toxicity than LBH589 and Hyper-CVAD/RTX in vivo. All the results suggest that HP-β-CD can solve the problem of PM administration and provide a way for clinical application of PM.Conclusions: In this study, an injectable formulation of PM in HP-β-CD (10% w/v) was prepared to improve its water solubility. Our research provides a way for clinical administration of PM, which has been under phase I clinical trial for the treatment of relapsed or refractory B-cell-related hematologic malignancies in China and the USA.KEY MESSAGESWe developed a preparation of Purinostat Mesylate that can be administered intravenously, reducing the toxicity associated with oral administration.This preparation has an outstanding therapeutic effect on SU-DHL-6 xenograft tumour, indicating its clinical value, which has been under phase I clinical trial for the treatment of relapsed or refractory B-cell-related haematologic malignancies in China and the USA.

Prevention of anticancer therapy-induced neurotoxicity: putting DNA damage in perspective

Chemotherapy-induced peripheral neuropathy (CIPN) is a severe side effect of conventional cancer therapeutics (cAT) that significantly impacts the quality of life of tumor patients. The molecular mechanisms of CIPN are incompletely understood and there are no effective preventive or therapeutic measures available to date. Here, we present a brief overview of the current knowledge about mechanisms underlying CIPN and discuss DNA damage-related stress responses as feasible targets for the prevention of CIPN. In addition, we discuss that the nematode Caenorhabditis elegans is a useful 3R-conform model organism to further elucidate molecular mechanisms of CIPN and to identify novel lead compounds protecting from cAT-triggered neuropathy.

VPA and TSA Interrupt the Interplay between mutp53 and HSP70, Leading to CHK1 and RAD51 Down-Regulation and Sensitizing Pancreatic Cancer Cells to AZD2461 PARP Inhibitor

HDAC inhibitors (HDACi) represent promising anti-cancer treatments, as the acetylation of histone and non-histone proteins is often dysregulated in cancer and contributes to cancer onset and progression. HDACi have been also reported to increase the cytotoxicity of DNA-damaging agents, such as radiation or cisplatin. In this study, we found that TSA and, even more effectively, VPA synergized with AZD2461, PARP1, 2 and 3 inhibitor (PARPi) to induce DNA damage and reduce pancreatic cancer cell survival. At a molecular level, VPA and TSA down-regulated CHK1 and RAD51, which is correlated with the interruption of the cross-talk between mutp53 and HSP70. Moreover, VPA and to a lesser extent TSA reactivated wtp53 in these cells, which contributed to CHK1 and RAD51 reduction. These findings suggest that the combination of HDACi and PARPi might improve the treatment of pancreatic cancer, which remains one of the most aggressive and therapy-resistant cancers.

Inhibitors of class I HDACs and of FLT3 combine synergistically against leukemia cells with mutant FLT3

Acute myeloid leukemia (AML) with mutations in the FMS-like tyrosine kinase (FLT3) is a clinically unresolved problem. AML cells frequently have a dysregulated expression and activity of epigenetic modulators of the histone deacetylase (HDAC) family. Therefore, we tested whether a combined inhibition of mutant FLT3 and class I HDACs is effective against AML cells. Low nanomolar doses of the FLT3 inhibitor (FLT3i) AC220 and an inhibition of class I HDACs with nanomolar concentrations of FK228 or micromolar doses of the HDAC3 specific agent RGFP966 synergistically induce apoptosis of AML cells that carry hyperactive FLT3 with an internal tandem duplication (FLT3-ITD). This does not occur in leukemic cells with wild-type FLT3 and without FLT3, suggesting a preferential toxicity of this combination against cells with mutant FLT3. Moreover, nanomolar doses of the new FLT3i marbotinib combine favorably with FK228 against leukemic cells with FLT3-ITD. The combinatorial treatments potentiated their suppressive effects on the tyrosine phosphorylation and stability of FLT3-ITD and its downstream signaling to the kinases ERK1/ERK2 and the inducible transcription factor STAT5. The beneficial pro-apoptotic effects of FLT3i and HDACi against leukemic cells with mutant FLT3 are associated with dose- and drug-dependent alterations of cell cycle distribution and DNA damage. This is linked to a modulation of the tumor-suppressive transcription factor p53 and its target cyclin-dependent kinase inhibitor p21. While HDACi induce p21, AC220 suppresses the expression of p53 and p21. Furthermore, we show that both FLT3-ITD and class I HDAC activity promote the expression of the checkpoint kinases CHK1 and WEE1, thymidylate synthase, and the DNA repair protein RAD51 in leukemic cells. A genetic depletion of HDAC3 attenuates the expression of such proteins. Thus, class I HDACs and hyperactive FLT3 appear to be valid targets in AML cells with mutant FLT3.

Inhibition of the DSB repair protein RAD51 potentiates the cytotoxic efficacy of doxorubicin via promoting apoptosis-related death pathways

The anthracycline derivative doxorubicin (Doxo) induces DNA double-strand breaks (DSBs) by inhibition of DNA topoisomerase type II. Defective mismatch repair (MMR) contributes to Doxo resistance and has been reported for colon and mammary carcinomas. Here, we investigated the outcome of pharmacological inhibition of various DNA repair-related mechanisms on Doxo-induced cytotoxicity employing MMR-deficient HCT-116 colon carcinoma cells. Out of different inhibitors tested (i.e. HDACi, PARPi, MRE11i, RAD52i, RAD51i), we identified the RAD51-inhibitor B02 as the most powerful compound to synergistically increase Doxo-induced cytotoxicity. B02-mediated synergism rests on pleiotropic mechanisms, including pronounced G2/M arrest, damage to mitochondria and caspase-driven apoptosis. Of note, B02 also promotes the cytotoxicity of oxaliplatin and 5-fluoruracil (5-FU) in HCT-116 cells and, furthermore, also increases Doxo-induced cytotoxicity in MMR-proficient colon and mammary carcinoma cells. Summarizing, pharmacological inhibition of RAD51 is suggested to synergistically increase the cytotoxic efficacy of various types of conventional anticancer drugs in different tumor entities. Hence, pre-clinical in vivo studies are preferable to determine the therapeutic window of B02 in a clinically oriented therapeutic regimen.

Epigenetic Mechanisms in DNA Double Strand Break Repair: A Clinical Review

Upon the induction of DNA damage, the chromatin structure unwinds to allow access to enzymes to catalyse the repair. The regulation of the winding and unwinding of chromatin occurs via epigenetic modifications, which can alter gene expression without changing the DNA sequence. Epigenetic mechanisms such as histone acetylation and DNA methylation are known to be reversible and have been indicated to play different roles in the repair of DNA. More importantly, the inhibition of such mechanisms has been reported to play a role in the repair of double strand breaks, the most detrimental type of DNA damage. This occurs by manipulating the chromatin structure and the expression of essential proteins that are critical for homologous recombination and non-homologous end joining repair pathways. Inhibitors of histone deacetylases and DNA methyltransferases have demonstrated efficacy in the clinic and represent a promising approach for cancer therapy. The aims of this review are to summarise the role of histone deacetylase and DNA methyltransferase inhibitors involved in DNA double strand break repair and explore their current and future independent use in combination with other DNA repair inhibitors or pre-existing therapies in the clinic.

The translational repressor 4E-BP1 regulates RRM2 levels and functions as a tumor suppressor in Ewing sarcoma tumors

Ribonucleotide reductase (RNR), which is a heterodimeric tetramer composed of RRM1 and RRM2 subunits, is the rate-limiting enzyme in the synthesis of deoxyribonucleoside triphosphates (dNTPs) and essential for both DNA replication and the repair of DNA damage. The activity of RNR is coordinated with the cell cycle and regulated by fluctuations in the level of the RRM2 subunit. Multiple cancer types, including Ewing sarcoma tumors, are sensitive to inhibitors of RNR or a reduction in the levels of either the RRM1 or RRM2 subunits of RNR. Here, we show that the expression of the RRM2 protein is dependent on active protein synthesis and that 4E-BP1, a repressor of cap-dependent protein translation, specifically regulates the level of the RRM2 protein. Furthermore, inhibition of mTORC1/2, but not mTORC1, activates 4E-BP1, inhibits protein synthesis, and reduces the level of the RRM2 protein in multiple sarcoma cell lines. This effect of mTORC1/2 inhibitors on protein synthesis and RRM2 levels was rescued in cell lines with the CRISPR/Cas9-mediated knockout of 4E-BP1. In addition, the inducible expression of a mutant 4E-BP1 protein that cannot be phosphorylated by mTOR blocked protein synthesis and inhibited the growth of Ewing sarcoma cells in vitro and in vivo in a xenograft. Overall, these results provide insight into the multifaceted regulation of RRM2 protein levels and identify a regulatory link between protein translation and DNA replication.

Regulating the Regulators: The Role of Histone Deacetylase 1 (HDAC1) in Erythropoiesis

Histone deacetylases (HDACs) play important roles in transcriptional regulation in eukaryotic cells. Class I deacetylase HDAC1/2 often associates with repressor complexes, such as Sin3 (Switch Independent 3), NuRD (Nucleosome remodeling and deacetylase) and CoREST (Corepressor of RE1 silencing transcription factor) complexes. It has been shown that HDAC1 interacts with and modulates all essential transcription factors for erythropoiesis. During erythropoiesis, histone deacetylase activity is dramatically reduced. Consistently, inhibition of HDAC activity promotes erythroid differentiation. The reduction of HDAC activity not only results in the activation of transcription activators such as GATA-1 (GATA-binding factor 1), TAL1 (TAL BHLH Transcription Factor 1) and KLF1 (Krüpple-like factor 1), but also represses transcription repressors such as PU.1 (Putative oncogene Spi-1). The reduction of histone deacetylase activity is mainly through HDAC1 acetylation that attenuates HDAC1 activity and trans-repress HDAC2 activity through dimerization with HDAC1. Therefore, the acetylation of HDAC1 can convert the corepressor complex to an activator complex for gene activation. HDAC1 also can deacetylate non-histone proteins that play a role on erythropoiesis, therefore adds another layer of gene regulation through HDAC1. Clinically, it has been shown HDACi can reactivate fetal globin in adult erythroid cells. This review will cover the up to date research on the role of HDAC1 in modulating key transcription factors for erythropoiesis and its clinical relevance.

Small subset of Wnt-activated cells is an initiator of regrowth in colorectal cancer organoids after irradiation

Most colorectal cancers (CRCs) are differentiated adenocarcinomas, which maintain expression of both stemness and differentiation markers. This observation suggests that CRC cells could retain a regeneration system of normal cells upon injury. However, the role of stemness in cancer cell regeneration after irradiation is poorly understood. Here, we examined the effect of radiation on growth, stemness, and differentiation in organoids derived from differentiated adenocarcinomas. Following a sublethal dose of irradiation, proliferation and stemness markers, including Wnt target genes, were drastically reduced, but differentiation markers remained. After a static growth phase after high dose of radiation, regrowth foci appeared; these consisted of highly proliferating cells that expressed stem cell markers. Radiosensitivity and the ability to form foci differed among the cancer tissue‐originated spheroid (CTOS) lines examined and showed good correlation with in vivo radiation sensitivity. Pre‐treating organoids with histone deacetylase inhibitors increased radiation sensitivity; this increase was accompanied by the suppression of Wnt signal‐related gene expression. Accordingly, Wnt inhibitors increased organoid radiosensitivity. These results suggested that only a small subset of, but not all, cancer cells with high Wnt activity at the time of irradiation could give rise to foci formation. In conclusion, we established a radiation sensitivity assay using CRC organoids that could provide a novel platform for evaluating the effects of radiosensitizers on differentiated adenocarcinomas in CRC.

PAICS contributes to gastric carcinogenesis and participates in DNA damage response by interacting with histone deacetylase 1/2

Phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase (PAICS), an essential enzyme involved in de novo purine biosynthesis, is connected with formation of various tumors. However, the specific biological roles and related mechanisms of PAICS in gastric cancer (GC) remain unclear. In the present study, we identified for the first time that PAICS was significantly upregulated in GC and high expression of PAICS was correlated with poor prognosis of patients with GC. In addition, knockdown of PAICS significantly induced cell apoptosis, and inhibited GC cell growth both in vitro and in vivo. Mechanistic studies first found that PAICS was engaged in DNA damage response, and knockdown of PAICS in GC cell lines induced DNA damage and impaired DNA damage repair efficiency. Further explorations revealed that PAICS interacted with histone deacetylase HDAC1 and HDAC2, and PAICS deficiency decreased the expression of DAD51 and inhibited its recruitment to DNA damage sites by impairing HDAC1/2 deacetylase activity, eventually preventing DNA damage repair. Consistently, PAICS deficiency enhanced the sensitivity of GC cells to DNA damage agent, cisplatin (CDDP), both in vitro and in vivo. Altogether, our findings demonstrate that PAICS plays an oncogenic role in GC, which act as a novel diagnosis and prognostic biomarker for patients with GC.

In Vitro Assessment of the Genotoxic Hazard of Novel Hydroxamic Acid- and Benzamide-Type Histone Deacetylase Inhibitors (HDACi)

Histone deacetylase inhibitors (HDACi) are already approved for the therapy of leukemias. Since they are also emerging candidate compounds for the treatment of non-malignant diseases, HDACi with a wide therapeutic window and low hazard potential are desirable. Here, we investigated a panel of 12 novel hydroxamic acid- and benzamide-type HDACi employing non-malignant V79 hamster cells as toxicology guideline-conform in vitro model. HDACi causing a ≥10-fold preferential cytotoxicity in malignant neuroblastoma over non-malignant V79 cells were selected for further genotoxic hazard analysis, including vorinostat and entinostat for control. All HDACi selected, (i.e., KSK64, TOK77, DDK137 and MPK77) were clastogenic and evoked DNA strand breaks in non-malignant V79 cells as demonstrated by micronucleus and comet assays, histone H2AX foci formation analyses (γH2AX), DNA damage response (DDR) assays as well as employing DNA double-strand break (DSB) repair-defective VC8 hamster cells. Genetic instability induced by hydroxamic acid-type HDACi seems to be independent of bulky DNA adduct formation as concluded from the analysis of nucleotide excision repair (NER) deficient mutants. Summarizing, KSK64 revealed the highest genotoxic hazard and DDR stimulating potential, while TOK77 and MPK77 showed the lowest DNA damaging capacity. Therefore, these compounds are suggested as the most promising novel candidate HDACi for subsequent pre-clinical in vivo studies.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Role of HDACs in normal and malignant hematopoiesis

Normal hematopoiesis requires the accurate orchestration of lineage-specific patterns of gene expression at each stage of development, and epigenetic regulators play a vital role. Disordered epigenetic regulation has emerged as a key mechanism contributing to hematological malignancies. Histone deacetylases (HDACs) are a series of key transcriptional cofactors that regulate gene expression by deacetylation of lysine residues on histone and nonhistone proteins. In normal hematopoiesis, HDACs are widely involved in the development of various lineages. Their functions involve stemness maintenance, lineage commitment determination, cell differentiation and proliferation, etc. Deregulation of HDACs by abnormal expression or activity and oncogenic HDAC-containing transcriptional complexes are involved in hematological malignancies. Currently, HDAC family members are attractive targets for drug design, and a variety of HDAC-based combination strategies have been developed for the treatment of hematological malignancies. Drug resistance and limited therapeutic efficacy are key issues that hinder the clinical applications of HDAC inhibitors (HDACis). In this review, we summarize the current knowledge of how HDACs and HDAC-containing complexes function in normal hematopoiesis and highlight the etiology of HDACs in hematological malignancies. Moreover, the implication and drug resistance of HDACis are also discussed. This review presents an overview of the physiology and pathology of HDACs in the blood system.

Safety and efficacy of oral panobinostat plus chemotherapy in patients aged 65 years or younger with high-risk acute myeloid leukemia

The role of histone deacetylase inhibitors in the treatment of acute myeloid leukemia (AML) is not well characterized. The current study evaluated the safety and efficacy of panobinostat in combination with idarubicin and cytarabine in newly diagnosed patients aged ≤65 years with primary or secondary high-risk AML based on cytogenetic classification. Treatment included fixed dose idarubicin (12 mg/m²/d, IV; day 1-3) and cytarabine (100 mg/m²/d, continuous IV infusion; day 1-7) and escalating oral doses of panobinostat at 15 mg, 20 mg, and 25 mg, thrice weekly starting at week 2 of a 28-day cycle. Forty-six patients were enrolled (primary AML [n = 36], secondary AML [n = 10]). The median age was 55 years. The most common all-grade AEs were diarrhea (54.3%), nausea (39.1%), vomiting, and decreased appetite (each, 21.7%), stomatitis (19.6%), and fatigue (17.4%). The overall response rate was 60.9%, 43.5% achieved a complete remission (CR), and 17.4% achieved CR with incomplete count recovery. The event-free survival at 1-year was 78.3%. Panobinostat in combination with idarubicin and cytarabine demonstrated tolerable safety and efficacy in younger patients with high-risk AML. The recommended phase 2 dose of panobinostat in this combination was 20 mg. ClinicalTrials.gov registry no: NCT01242774, and European Trial Registry EudraCT no: 2009-016809-42.

Histone deacetylase 1 induced by neddylation inhibition contributes to drug resistance in acute myelogenous leukemia

Objective

This study aimed to investigate the function and mechanism of neddylation of HDAC1 underlying drug resistance of AML cells.

Methods

Evaluation experiments of effects of HDAC1 on drug resistance of AML cells were performed with AML cell transfected with constructs overexpressing HDAC1 or multi-drug resistance AML cells transfected with siRNA for HDAC1 through observing cell viability, percentage of apoptotic cell, doxorubicin-releasing index and multidrug resistance associated protein 1 (MRP1) expression. Neddylation or ubiquitination of HDAC1 was determined by immunoprecipitation or Ni2⁺ pull down assay followed by western blot. The role of HDAC1 was in vivo confirmed by xenograft in mice.

Results

HDAC1 was significantly upregulated in refractory AML patients, and in drug-resistant AML cells (HL-60/ADM and K562/A02). Intracellular HDAC1 expression promoted doxorubicin resistance of HL-60, K562, and primary bone marrow cells (BMCs) of remission AML patients as shown by increasing cell viability and doxorubicin-releasing index, inhibiting cell apoptosis. Moreover, HDAC1 protein level in AML cells was regulated by the Nedd8-mediated neddylation and ubiquitination, which further promoted HDAC1 degradation. In vivo, HDAC1 overexpression significantly increased doxorubicin resistance; while HDACs inhibitor Panobinostat markedly improved the inhibitory effect of doxorubicin on tumor growth. Furthermore, HDAC1 silencing by Panobinostat and/or lentivirus mediated RNA interference against HDAC1 effectively reduced doxorubicin resistance, resulting in the inhibition of tumor growth in AML bearing mice.

Conclusion

Our findings suggested that HDAC1 contributed to the multidrug resistance of AML and its function turnover was regulated, at least in part, by post-translational modifications, including neddylation and ubiquitination.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0393-8) contains supplementary material, which is available to authorized users.

HDAC2-dependent miRNA signature in acute myeloid leukemia

Acute myeloid leukemia (AML) arises from a complex sequence of biological and finely orchestrated events that are still poorly understood. Increasingly, epigenetic studies are providing exciting findings that may be exploited in promising and personalized cutting‐edge therapies. A more appropriate and broader screening of possible players in cancer could identify a master molecular mechanism in AML. Here, we build on our previously published study by evaluating a histone deacetylase (HDAC)2‐mediated miRNA regulatory network in U937 leukemic cells. Following a comparative miRNA profiling analysis in genetically and enzymatically HDAC2‐downregulated AML cells, we identified miR‐96‐5p and miR‐92a‐3p as potential regulators in AML etiopathology by targeting defined genes. Our findings support the potentially beneficial role of alternative physiopathological interventions.

The mTOR inhibitor everolimus overcomes CXCR4-mediated resistance to histone deacetylase inhibitor panobinostat through inhibition of p21 and mitotic regulators

Although having promising anti-myeloma properties, the pan-histone deacetylase inhibitor (HDACi) panobinostat lacks therapeutic activity as a single agent. The aim of the current study was to elucidate the mechanisms underlying multiple myeloma (MM) resistance to panobinostat monotherapy and to define strategies to overcome it. Sensitivity of MM cell lines and primary CD138+ cells from MM patients to panobinostat correlated with reduced expression of the chemokine receptor CXCR4, whereas overexpression of CXCR4 in MM cell lines increased their resistance to panobinostat. Decreased sensitivity to HDACi was associated with reversible G0/G1 cell growth arrest while response was characterized by apoptotic cell death. Analysis of intra-cellular signaling mediators revealed the pro-survival mTOR pathway to be regulated by CXCR4 overexpression. Combining panobinostat with mTOR inhibitor everolimus abrogated the resistance to HDACi and induced synergistic cell death. The combination of panobinostat/everolimus resulted in sustained DNA damage and irreversible suppression of proliferation accompanied by robust apoptosis. Gene expression analysis revealed distinct genetic profiles of single versus combined agent exposure. Whereas panobinostat increased the expression of the cell cycle inhibitor p21, co-treatment with everolimus abrogated the increase in p21 and synergistically downregulated the expression of DNA repair genes and mitotic checkpoint regulators. Importantly, the combination of panobinostat with everolimus effectively targeted CXCR4-expressing resistant MM cells in vivo in the BM niche. In summary, our results uncover the mechanism responsible for the strong synergistic anti-MM activity of dual HDAC and mTOR inhibition and provide the rationale for a novel potential therapeutic approach to treat MM.

Regulatory Roles of Histone Deacetylases 1 and 2 in Pb-induced Neurotoxicity

Lead (Pb) prevails among the environmental hazards against human health. Although increasing evidence highlights the epigenetic roles underlying the Pb-induced neurotoxicity, the exact mechanisms concerning histone acetylation and its causative agents are still at its infancy. In the present study, the roles of histone deacetylases 1 and 2 (HDAC1/2), as well as acetylation of Lys9 on histone H3 (Ac-H3K9), in Pb-induced neurotoxicity were investigated. Pb was administered to PC12 cells at 10 μM for 24 h. And Sprague Dawley rats were chronically exposed to Pb through drinking water containing 250 ppm Pb for 2 months. Owing to Pb exposure, it indicated that HDAC2 was up-regulated accompanied by Ac-H3K9 down-regulation. Meanwhile, chromatin immunoprecipitation assay revealed that the changes in HDAC2 were attributed to histone H3 Lys27 trimethylation occupancy on its promoter. Blockade of HDAC2 with either Trichostatin A or HDAC2-knocking down construct (shHDAC2) resulted in amelioration of neurite outgrowth deficits via increasing Ac-H3K9 levels. It implied that HDAC2 plays essential regulatory roles in Pb-induced neurotoxicity. And, coimmunoprecipitation trials revealed that HDAC2 colocalized with HDAC1, forming a so-called HDAC1/2 complex. Subsequently, it was shown that HDAC1/2 repression could markedly prevent neurite outgrowth impairment and rescue the spatial memory deficits caused by Pb exposure, unequivocally implicating this complex in the studied toxicological process. Furthermore, Notch2 maybe the functional target of the HDAC1/2 and Ac-H3K9 alterations. Our study provided insight into the precise roles of HDAC1/2 in Pb-induced neurotoxicity, and thereby provided a promising molecular target for medical intervention of neurological disorders with environmental etiology.

DDX23-Linc00630-HDAC1 axis activates the Notch pathway to promote metastasis

Emerging studies demonstrated the roles of long non-coding RNAs (LncRNAs) are being implicated in the progression of many cancers. Here we report the discovery of a critical role for the linc00630 in the development of Non-Small-Cell Lung Cancers (NSCLCs). Screening from the microarray of six paired NSCLCs and adjacent non-tumor tissues, linc00630 showed a significantly higher RNA levels in NSCLCs. With the higher level confirmed in a separate cohort 90 NSCLCs patients, overexpressed of linc00630 also positive associated with tumor size, TNM tumor stage, lymph node status positive and overall patient outcomes. Linc00630 overexpression increased cell proliferation and metastasis in vitro and in vivo whereas linc00630 silencing had opposite effects. By RNA pull-down and mass spectrometry we identified Histone deacetylases 1 (HDAC1) and DEAD-box helicase 23 (DDX23) as the linc00630-binding protein that associated with mechanism of linc00630. DDX23 can specific bind with the promoter of Linc00630 to up-regulate the RNA level and high level of linc00630 strength the protein stability of HDAC1 to regulate the downstream pathway.

Our study demonstrates the effectiveness of Linc00630 oligonucleotide-based promotion of NSCLCs metastasis and proliferation, illuminating a new basis of DDX23-Linc00630-HDAC1 signal axis for understanding its pathogenicity, which could be further developed as a valuable therapeutic strategy.

Vorinostat enhances the anticancer effect of oxaliplatin on hepatocellular carcinoma cells

Oxaliplatin-based systemic chemotherapy has been proposed to have efficacy in hepatocellular carcinoma (HCC). We investigated the combination of vorinostat and oxaliplatin for possible synergism in HCC cells. SMMC7721, BEL7402, and HepG2 cells were treated with vorinostat and oxaliplatin. Cytotoxicity assay, tumorigenicity assay in vitro, cell cycle analysis, apoptosis analysis, western blot analysis, animal model study, immunohistochemistry, and quantitative PCR were performed. We found that vorinostat and oxaliplatin inhibited the proliferation of SMMC7721, BEL7402, and HepG2 cells. The combination index (CI) values were all <1, and the dose-reduction index values were all greater than 1 in the three cell lines, indicating a synergistic effect of combination of the two agents. Coadministration of vorinostat and oxaliplatin induced G2/M phase arrest, triggered caspase-dependent apoptosis, and decreased tumorigenicity both in vitro and in vivo. Vorinostat suppressed the expression of BRCA1 induced by oxaliplatin. In conclusion, cotreatment with vorinostat and oxaliplatin exhibited synergism in HCC cells. The combination inhibited cell proliferation and tumorigenicity both in vitro and in vivo through induction of cell cycle arrest and apoptosis. Our results predict that a combination of vorinostat and oxaliplatin may be useful in the treatment of advanced HCC.

Targeting PI3K, mTOR, ERK, and Bcl-2 signaling network shows superior antileukemic activity against AML ex vivo

Acute myeloid leukemia (AML) remains challenging to treat and needs more effective treatments. The PI3K/mTOR pathway is involved in cell survival and has been shown to be constitutively active in 50-80% of AML patients. However, targeting the PI3K/mTOR pathway results in activation of the ERK pathway, which also plays an important role in cell survival. In addition, AML cells often overexpress antiapoptotic Bcl-2 family proteins (e.g., Bcl-2), preventing cell death. Thus, our strategy here is to target the PI3K, mTOR (by VS-5584, a PI3K and mTOR dual inhibitor), ERK (by SCH772984, an ERK-selective inhibitor), and Bcl-2 (by ABT-199, a Bcl-2-selective inhibitor) signaling network to kill AML cells. In this study, we show that while inhibition of PI3K, mTOR, and ERK showed superior induction of cell death compared to inhibition of PI3K and mTOR, the levels of cell death were modest in some AML cell lines and primary patient samples tested. Although simultaneous inhibition of PI3K, mTOR, and ERK caused downregulation of Mcl-1 and upregulation of Bim, immunoprecipitation of Bcl-2 revealed increased binding of Bim to Bcl-2, which was abolished by the addition of ABT-199, suggesting that Bim was bound to Bcl-2 which prevented cell death. Treatment with combined VS-5584, SCH772984, and ABT-199 showed significant increase in cell death in AML cell lines and primary patient samples and significant reduction in AML colony formation in primary patient samples, while there was no significant effect on colony formation of normal human CD34+ hematopoietic progenitor cells. Taken together, our findings show that inhibition of PI3K, mTOR, and ERK synergistically induces cell death in AML cells, and addition of ABT-199 enhances cell death further. Thus, our data support targeting the PI3K, mTOR, ERK, and Bcl-2 signaling network for the treatment of AML.