Cytotoxicity mediated by histone deacetylase inhibitors in cancer cells: mechanisms and potential clinical implications

Tissue-Engineered Disease Modeling of Lymphangioleiomyomatosis Exposes a Therapeutic Vulnerability to HDAC Inhibition

Lymphangioleiomyomatosis (LAM) is a rare disease involving cystic lung destruction by invasive LAM cells. These cells harbor loss-of-function mutations in TSC2, conferring hyperactive mTORC1 signaling. Here, tissue engineering tools are employed to model LAM and identify new therapeutic candidates. Biomimetic hydrogel culture of LAM cells is found to recapitulate the molecular and phenotypic characteristics of human disease more faithfully than culture on plastic. A 3D drug screen is conducted, identifying histone deacetylase (HDAC) inhibitors as anti-invasive agents that are also selectively cytotoxic toward TSC2-/- cells. The anti-invasive effects of HDAC inhibitors are independent of genotype, while selective cell death is mTORC1-dependent and mediated by apoptosis. Genotype-selective cytotoxicity is seen exclusively in hydrogel culture due to potentiated differential mTORC1 signaling, a feature that is abrogated in cell culture on plastic. Importantly, HDAC inhibitors block invasion and selectively eradicate LAM cells in vivo in zebrafish xenografts. These findings demonstrate that tissue-engineered disease modeling exposes a physiologically relevant therapeutic vulnerability that would be otherwise missed by conventional culture on plastic. This work substantiates HDAC inhibitors as possible therapeutic candidates for the treatment of patients with LAM and requires further study.

Identification of m7G-Related miRNA Signatures Associated with Prognosis, Oxidative Stress, and Immune Landscape in Lung Adenocarcinoma

The role of N7-methylguanosine(m7G)-related miRNAs in lung adenocarcinoma (LUAD) remains unclear. We used LUAD data from The Cancer Genome Atlas (TCGA) to establish a risk model based on the m7G-related miRNAs, and divided patients into high-risk or low-risk subgroups. A nomogram for predicting overall survival (OS) was then constructed based on the independent risk factors. In addition, we performed a functional enrichment analysis and defined the oxidative stress-related genes, immune landscape as well as a drug response profile in the high-risk and low-risk subgroups. This study incorporated 28 m7G-related miRNAs into the risk model. The data showed a significant difference in the OS between the high-risk and low-risk subgroups. The receiver operating characteristic curve (ROC) predicted that the area under the curve (AUC) of one-year, three-year and five-year OS was 0.781, 0.804 and 0.853, respectively. The C-index of the prognostic nomogram for predicting OS was 0.739. We then analyzed the oxidative stress-related genes and immune landscape in the high-risk and low-risk subgroups. The data demonstrated significant differences in the expression of albumin (ALB), estimated score, immune score, stromal score, immune cell infiltration and functions between the high-risk and low-risk subgroups. In addition, the drug response analysis showed that low-risk subgroups may be more sensitive to tyrosine kinase inhibitor (TKI) and histone deacetylase (HDAC) inhibitors. We successfully developed a novel risk model based on m7G-related miRNAs in this study. The model can predict clinical prognosis and guide therapeutic regimens in patients with LUAD. Our data also provided new insights into the molecular mechanisms of m7G in LUAD.

Selectivity of Hydroxamate- and Difluoromethyloxadiazole-Based Inhibitors of Histone Deacetylase 6 In Vitro and in Cells

Histone deacetylase 6 (HDAC6) is a unique member of the HDAC family of enzymes due to its complex domain organization and cytosolic localization. Experimental data point toward the therapeutic use of HDAC6-selective inhibitors (HDAC6is) for use in both neurological and psychiatric disorders. In this article, we provide side-by-side comparisons of hydroxamate-based HDAC6is frequently used in the field and a novel HDAC6 inhibitor containing the difluoromethyl-1,3,4-oxadiazole function as an alternative zinc-binding group (compound 7). In vitro isotype selectivity screening uncovered HDAC10 as a primary off-target for the hydroxamate-based HDAC6is, while compound 7 features exquisite 10,000-fold selectivity over all other HDAC isoforms. Complementary cell-based assays using tubulin acetylation as a surrogate readout revealed approximately 100-fold lower apparent potency for all compounds. Finally, the limited selectivity of a number of these HDAC6is is shown to be linked to cytotoxicity in RPMI-8226 cells. Our results clearly show that off-target effects of HDAC6is must be considered before attributing observed physiological readouts solely to HDAC6 inhibition. Moreover, given their unparalleled specificity, the oxadiazole-based inhibitors would best be employed either as research tools in further probing HDAC6 biology or as leads in the development of truly HDAC6-specific compounds in the treatment of human disease states.

Cutaneous T-cell lymphomas: 2023 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Cutaneous T-cell lymphomas are a heterogenous group of T-cell neoplasms involving the skin, the majority of which may be classified as Mycosis Fungoides (MF) or Sézary Syndrome (SS).

DIAGNOSIS

The diagnosis of MF or SS requires the integration of clinical and histopathologic data.

RISK-ADAPTED THERAPY

TNMB (tumor, node, metastasis, blood) staging remains the most important prognostic factor in MF/SS and forms the basis for a "risk-adapted," multidisciplinary approach to treatment. For patients with disease limited to the skin, expectant management or skin-directed therapies is preferred, as both disease-specific and overall survival for these patients is favorable. In contrast, patients with advanced-stage disease with significant nodal, visceral or the blood involvement are generally approached with systemic therapies, including biologic-response modifiers, histone deacetylase inhibitors, or antibody-based strategies, in an escalating fashion. In highly-selected patients, allogeneic stem-cell transplantation may be considered, as this may be curative in some patients.

[In vitro pharmacodynamic studies of novel class Ⅰ and Ⅱb selective histone deacetylase inhibitor purinostat mesylate in the treatment of diffuse large B-cell lymphoma and its mechanism]

Objective: To investigate the in vitro inhibitory activity of a novel class Ⅰ and Ⅱb selective histone deacetylase (HDAC) inhibitor, purinostat mesylate (PM) , in diffuse large B-cell lymphoma and its mechanism. Methods: The 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyl tetrazolium bromide method was used to detect the effect of PM on cell proliferation. The effects of PM on cell cycle and apoptosis were detected by flow cytometry. The acetylation levels of HDAC substrate, cell cycle protein, apoptosis-related protein, and oncogene protein expression were detected by Western blot. Results: PM significantly inhibited the proliferation of lymphoma SUDHL-4 and SUDHL-6 cells and increased the acetylation levels of HDAC substrates H3, H4, and α-tubulin. In cell cycle experiments, PM induced G(0)/G(1) phase arrest in SUDHL-4 and SUDHL-6 cells. Western blot experiment showed that PM could significantly downregulate the expression of cyclin-dependent kinases Cdk2, Cdk4, Cdk6, cyclin D1, and cyclin E and upregulate the expression of CDK inhibitor protein p21. In the apoptosis experiment, PM could induce the apoptosis of SUDHL-4 and SUDHL-6 cells. Western blot experiment demonstrated that PM promoted endogenous apoptosis by activating caspase-3 kinase and affecting antiapoptotic protein Bcl-2. In addition, PM could downregulate the expression of oncogene marker proteins MYC, IKZF1, and IKZF3. Conclusion: PM has an efficient biological activity in vitro for diffuse large B-cell lymphoma, including double-hit lymphoma, and provides valuable experimental evidence for PM in clinical treatment.

Advances of Epigenetic Biomarkers and Epigenome Editing for Early Diagnosis in Breast Cancer

Epigenetic modifications are known to regulate cell phenotype during cancer progression, including breast cancer. Unlike genetic alterations, changes in the epigenome are reversible, thus potentially reversed by epi-drugs. Breast cancer, the most common cause of cancer death worldwide in women, encompasses multiple histopathological and molecular subtypes. Several lines of evidence demonstrated distortion of the epigenetic landscape in breast cancer. Interestingly, mammary cells isolated from breast cancer patients and cultured ex vivo maintained the tumorigenic phenotype and exhibited aberrant epigenetic modifications. Recent studies indicated that the therapeutic efficiency for breast cancer regimens has increased over time, resulting in reduced mortality. Future medical treatment for breast cancer patients, however, will likely depend upon a better understanding of epigenetic modifications. The present review aims to outline different epigenetic mechanisms including DNA methylation, histone modifications, and ncRNAs with their impact on breast cancer, as well as to discuss studies highlighting the central role of epigenetic mechanisms in breast cancer pathogenesis. We propose new research areas that may facilitate locus-specific epigenome editing as breast cancer therapeutics.

Temporal perturbation of histone deacetylase activity reveals a requirement for HDAC1-3 in mesendoderm cell differentiation

Histone deacetylases (HDACs) are a class of enzymes that control chromatin state and influence cell fate. We evaluated the chromatin accessibility and transcriptome dynamics of zinc-containing HDACs during cell differentiation in vitro coupled with chemical perturbation to identify the role of HDACs in mesendoderm cell fate specification. Single-cell RNA sequencing analyses of HDAC expression during human pluripotent stem cell (hPSC) differentiation in vitro and mouse gastrulation in vivo reveal a unique association of HDAC1 and -3 with mesendoderm gene programs during exit from pluripotency. Functional perturbation with small molecules reveals that inhibition of HDAC1 and -3, but not HDAC2, induces mesoderm while impeding endoderm and early cardiac progenitor specification. These data identify unique biological functions of the structurally homologous enzymes HDAC1-3 in influencing hPSC differentiation from pluripotency toward mesendodermal and cardiac progenitor populations.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Cutaneous T-cell lymphomas: 2021 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Cutaneous T-cell lymphomas are a heterogenous group of T-cell neoplasms involving the skin, the majority of which may be classified as Mycosis Fungoides (MF) or Sézary Syndrome (SS).

DIAGNOSIS

The diagnosis of MF or SS requires the integration of clinical and histopathologic data.

RISK-ADAPTED THERAPY

TNMB (tumor, node, metastasis, blood) staging remains the most important prognostic factor in MF/SS and forms the basis for a "risk-adapted," multi-disciplinary approach to treatment. For patients with disease limited to the skin, expectant management or skin-directed therapies is preferred, as both disease-specific and overall survival for these patients is favorable. In contrast, patients with advanced-stage disease with significant nodal, visceral or blood involvement are generally approached with systemic therapies, including biologic-response modifiers, histone deacetylase inhibitors, or antibody-based strategies, in an escalating fashion. In highly-selected patients, allogeneic stem-cell transplantation may be considered, as this may be curative in some patients.

Novel Suberoylanilide Hydroxamic Acid Analogs Inhibit Angiogenesis and Induce Apoptosis in Breast Cancer Cells

BACKGROUND

Histone deacetylases (HDACs) are the enzymes that catalyze the removal of the acetyl group from lysine residues and regulate several biological processes. Suberoylanilide hydroxamic acid (SAHA) is a notable HDAC inhibitor that exhibited remarkable anti-proliferative efficiency by alleviating gene regulation against solid and hematologic cancers.

AIM

The aim of this study was to develop new chemotherapeutic agents for breast cancer treatment, therefore, a novel series of Suberoylanilide hydroxamic acid (SAHA) analogs were investigated as anticancer agents.

METHODS

We designed and synthesized a novel series of analogs derived from SAHA by substituting alkyl, alkoxy, halo, and benzyl groups at different positions of the phenyl ring. The newly synthesized analogs were assessed for their cytotoxic potential against four human cancer cell lines in comparison with healthy cell lines, using several biological assays.

RESULTS

SAHA analogs displayed significant cytotoxic potential with IC50 values ranging from 1.6 to 19.2 µM in various tumor cell lines. Among these analogs, 2d (containing 3-chloro, 4-floro substitutions on phenyl moiety), 2h (containing 3,4-di chloro substitutions on phenyl moiety), and 2j (containing 4-chloro, 3-methyl substitutions on phenyl moiety) showed significant cytotoxic potential with IC50 values ranging from 1.6 to 1.8 µM in MCF-7 (breast carcinoma) cell line. More importantly, these analogs were found to be non-toxic towards healthy primary human hepatocytes (PHH) and mouse fibroblast cells (NIH3T3), which represent their tumor selectivity. These analogs were further analyzed for their effect on cell migration, BrdU incorporation, Annexin V-FITC and cell cycle arrest (Sub-G1 phase). Remarkably, analogs 2d, 2h, and 2j displayed significant HDAC inhibition than the parent SAHA molecule. Further studies also confirmed that these SAHA analogs are efficient in inducing apoptosis, as they regulated the expression of several proteins involved in mitochondrial or intrinsic apoptosis pathways. Findings in the Chick Chorioallantoic Membrane (CAM) assay studies revealed anti-angiogenic properties of the currently described SAHA analogs.

CONCLUSION

From anti-proliferative study results, it is clearly evident that 3,4-substitution at the SAHA phenyl ring improves the anti-proliferative activity of SAHA. Based on these findings, we presume that the synthesized novel SAHA analogs could be potential therapeutic agents in treating breast cancer.

Combination of Chidamide-Mediated Epigenetic Modulation with Immunotherapy: Boosting Tumor Immunogenicity and Response to PD-1/PD-L1 Blockade

Improving tumor immunogenicity is critical for increasing the responsiveness of triple-negative breast cancer (TNBC) to anti-PD-(L)1 treatment. Here, we verified that chidamide (CHI), an epigenetic modulator, could elicit immunogenic cell death within TNBC to enhance cancer immunogenicity and elicit an antitumor immune response. Additionally, CHI increased the expression level of PD-L1, MHC I, and MHC II on cancer cells, which contributed to T-cell recognition and PD-1/PD-L1 blockade therapy response. The synergistic antitumor efficacy of CHI and PD-L1 blockade therapy was further explored through liposomes co-delivering CHI and BMS-202 (a small-molecule PD-L1 inhibitor). The liposomes possessed good biocompatibility, security, and controllable drug release and endowed therapeutics drugs with favorable tumor accumulation. Furthermore, the drug-loaded liposomes could obviously boost the antitumor immunity of TNBC through CHI-enhanced tumor immunogenicity and BMS-202-mediated PD-L1 blockade, thereby effectively inhibiting the growth of primary and metastatic tumors with an inhibitory rate of metastasis of up to 96%. In summary, this work provided a referable and optional approach for clinical antitumor therapy based on the combination of an epigenetic modulator and PD-1/PD-L1 blockade therapy.

Phase I Study of Entinostat in Combination with Enzalutamide for Treatment of Patients with Metastatic Castration-Resistant Prostate Cancer

LESSONS LEARNED

Entinostat at the selected dose levels in combination with a standard dose of enzalutamide showed a promising safety profile in this small phase I study BACKGROUND: Entinostat inhibits prostate cancer (PCa) growth and suppresses Treg cell function in vitro and in vivo.

METHODS

This was a phase I study to explore the safety and preliminary efficacy of entinostat (3 and 5 mg orally per week) in combination with enzalutamide in castration resistant PCa (CRPC). The study was carried out in an open-label two-cohort design. Patients who had developed disease progression on or were eligible for enzalutamide were enrolled in the study. The safety profile of the combination therapy, Prostate specific antigen (PSA) levels, the pharmacokinetics of enzalutamide after entinostat administration, peripheral T-cell subtype (including Treg quantitation), and mononuclear cell (PBMC) histone H3 acetylation were analyzed.

RESULTS

Six patients with metastatic CRPC were enrolled. There was no noticeable increment of fatigue related to entinostat. Toxicities possibly or probably related to entinostat or the combination therapy included grade 3 anemia 1/6 (17%), grade 2 white blood cell (WBC) decrease 1/6 (17%), and other self-limiting grade 1 adverse events (AEs). Median duration of treatment with entinostat was 18 weeks. Entinostat did not affect the steady plasma concentration of enzalutamide. Increased PBMC histone H3 acetylation was observed in blood samples. No evident T-cell subtype changes were detected, including in Treg quantitation.

CONCLUSION

Entinostat 5 mg weekly in combination with enzalutamide showed an acceptable safety profile in this small phase I study. A planned phase II part of the trial was terminated because of sponsor withdrawal.

MicroRNA-192-5p inhibits migration of triple negative breast cancer cells and directly regulates Rho GTPase activating protein 19

Among the different breast cancer subtypes, triple-negative breast cancer (TNBC) is associated with a poor prognosis, low survival rates, and high expression of histone deacetylases. Treatment with histone deacetylase inhibitor trichostatin A (TSA) leads to an increased expression of potential tumor-suppressive miRNAs. Characterization of these miRNAs can help to find new molecular targets for treatment of TNBC. We identified differentially expressed miRNAs by microarray analyses after treatment with TSA in the TNBC cell lines HCC38, HCC1395, and HCC1935. The gene locus of hsa-miRNA-192-5p (miR-192) and hsa-miR-194-2 (miR-194-2) with its host gene, long noncoding RNA miR-194-2HG, has been linked to inhibition of migration in different tumor types. Therefore, we examined tumor-relevant functional effects using WST-1-based proliferation, capsase-3/7-based apoptosis, and trans-well migration assays after transfection with miRNA mimics or specific siRNAs. We demonstrated the tumor-suppressive capacity of miR-192 in TNBC cells, which was exerted through inhibition of proliferation, induction of apoptosis, and reduction of migration. Gene expression and bioinformatics analyses of TNBC cell lines transfected with miR-192 mimics, identified a number of genes involved in migration including the Rho GTPase Activating Protein ARHGAP19. Through RNA immunoprecipitation we demonstrated the direct binding of miR-192 and ARHGAP19. Downregulation of ARHGAP19 expression by either miR-192 or siRNA inhibited migration of TNBC cells significantly. Our findings demonstrate that overexpression of epigenetically deregulated miR-192 decreases proliferation, promotes apoptosis, and inhibits migration of TNBC cell lines.

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

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

Protein Acetylation at the Interface of Genetics, Epigenetics and Environment in Cancer

Metabolic reprogramming is an emerging hallmark of cancer and is driven by abnormalities of oncogenes and tumor suppressors. Accelerated metabolism causes cancer cell aggression through the dysregulation of rate-limiting metabolic enzymes as well as by facilitating the production of intermediary metabolites. However, the mechanisms by which a shift in the metabolic landscape reshapes the intracellular signaling to promote the survival of cancer cells remain to be clarified. Recent high-resolution mass spectrometry-based proteomic analyses have spotlighted that, unexpectedly, lysine residues of numerous cytosolic as well as nuclear proteins are acetylated and that this modification modulates protein activity, sublocalization and stability, with profound impact on cellular function. More importantly, cancer cells exploit acetylation as a post-translational protein for microenvironmental adaptation, nominating it as a means for dynamic modulation of the phenotypes of cancer cells at the interface between genetics and environments. The objectives of this review were to describe the functional implications of protein lysine acetylation in cancer biology by examining recent evidence that implicates oncogenic signaling as a strong driver of protein acetylation, which might be exploitable for novel therapeutic strategies against cancer.

Inhibition of phospholipase D2 augments histone deacetylase inhibitor-induced cell death in breast cancer cells

BACKGROUND

Histone deacetylase (HDAC) inhibitors are promising anticancer drugs but their effect on tumor treatment has been disappointing mainly due to the acquisition of HDAC inhibitor resistance. However, the mechanisms underlying such resistance remain unclear.

METHODS

In this study, we performed Western blot, q-PCR, and promoter assay to examine the expression of HDAC inhibitor-induced phospholipase D2 (PLD2) in MDA-MB231and MDA-MB435 breast cancer cells. Apoptosis and proliferation were analyzed by flow cytometry. In addition to invasion and migration assay, angiogenesis was further measured using in vitro tube formation and chick embryo chorioallantoic membrane model.

RESULTS

HDAC inhibitors including suberoylanilide hydroxamic acid (SAHA), trichostatin, and apicidin, induce expression of PLD2 in a transcriptional level. SAHA upregulates expression of PLD2 via protein kinase C-ζ in breast cancer cells and increases the enzymatic activity of PLD. The combination treatment of SAHA with PLD2 inhibitor significantly enhances cell death in breast cancer cells. Phosphatidic acid, a product of PLD activity, prevented apoptosis promoted by cotreatment with SAHA and PLD2 inhibitor, suggesting that SAHA-induced PLD2 expression and subsequent activation of PLD2 might confers resistance of breast cancer cells to HDAC inhibitor. The combinational treatment of the drugs significantly suppressed invasion, migration, and angiogenesis, compared with that of either treatment.

CONCLUSION

These findings provide further insight into elucidating the advantages of combination therapy with HDAC and PLD2 inhibitors over single-agent strategies for the treatment of cancer.

[Research Progress of Epigenetics in Pathogenesis and Treatment of Malignant Tumors]

表观遗传学修饰与肿瘤的发生发展密切相关，其主要通过DNA甲基化、组蛋白修饰、非编码RNA调控和染色质结构重构等方式对基因功能和表达水平进行调控，从而影响肿瘤的进展。目前针对表观遗传学的药物已经逐渐应用于恶性肿瘤的治疗，常见的药物类型包括DNA甲基转移酶抑制剂和组蛋白去乙酰化酶抑制剂，但此类药物仍存在诸多不足之处广泛的临床应用仍需要进一步的研究，令人鼓舞的是表观遗传药物与多种抗肿瘤药物联合应用已表现出巨大的应用潜力。本文就表观遗传学在恶性肿瘤的发生发展机制和相关药物的新进展进行了综述。

Targeted therapy for mTORC1-driven tumours through HDAC inhibition by exploiting innate vulnerability of mTORC1 hyper-activation

BACKGOUND

The mechanistic target of rapamycin complex 1 (mTORC1) is important in the development and progression of many cancers. Targeted cancer therapy using mTORC1 inhibitors is used for treatment of cancers; however, their clinical efficacies are still limited.

METHODS

We recently created a new mouse model for human lymphangiosarcoma by deleting Tsc1 in endothelial cells and consequent hyper-activation of mTORC1. Using Tsc1iΔEC tumour cells from this mouse model, we assessed the efficacies of histone deacetylase (HDAC) inhibitors as anti-tumour agents for mTORC1-driven tumours.

RESULTS

Unlike the cytostatic effect of mTORC1 inhibitors, HDAC inhibitors induced Tsc1iΔEC tumour cell death in vitro and their growth in vivo. Analysis of several HDAC inhibitors suggested stronger anti-tumour activity of class I HDAC inhibitor than class IIa or class IIb inhibitors, but these or pan HDAC inhibitor SAHA did not affect mTORC1 activation in these cells. Moreover, HDAC inhibitor-induced cell death required elevated autophagy, but was not affected by disrupting caspase-dependent apoptosis pathways. We also observed increased reactive oxygen species and endoplasmic reticulum stress in SAHA-treated tumour cells, suggesting their contribution to autophagic cell death, which were dependent on mTORC1 hyper-activation.

CONCLUSION

These studies suggest a potential new treatment strategy for mTORC1-driven cancers like lymphangiosarcoma through an alternative mechanism.

Elevated HDAC activity and altered histone phospho-acetylation confer acquired radio-resistant phenotype to breast cancer cells

Background

Poor-responsiveness of tumors to radiotherapy is a major clinical problem. Owing to the dynamic nature of the epigenome, the identification and targeting of potential epigenetic modifiers may be helpful to curb radio-resistance. This requires a detailed exploration of the epigenetic changes that occur during the acquirement of radio-resistance. Such an understanding can be applied for effective utilization of treatment adjuncts to enhance the efficacy of radiotherapy and reduce the incidence of tumor recurrence.

Results

This study explored the epigenetic alterations that occur during the acquirement of radio-resistance. Sequential irradiation of MCF7 breast cancer cell line up to 20 Gy generated a radio-resistant model. Micrococcal nuclease digestion demonstrated the presence of compact chromatin architecture coupled with decreased levels of histone PTMs H3K9ac, H3K27 ac, and H3S10pK14ac in the G₀/G₁ and mitotic cell cycle phases of the radio-resistant cells. Further investigation revealed that the radio-resistant population possessed high HDAC and low HAT activity, thus making them suitable candidates for HDAC inhibitor–based radio-sensitization. Treatment of radio-resistant cells with HDAC inhibitor valproic acid led to the retention of γH2AX and decreased H3S10p after irradiation. Additionally, an analysis of 38 human patient samples obtained from 8 different tumor types showed variable tumor HDAC activity, thus demonstrating inter-tumoral epigenetic heterogeneity in a patient population.

Conclusion

The study revealed that an imbalance of HAT and HDAC activities led to the loss of site-specific histone acetylation and chromatin compaction as breast cancer cells acquired radio-resistance. Due to variation in the tumor HDAC activity among patients, our report suggests performing a prior assessment of the tumor epigenome to maximize the benefit of HDAC inhibitor–based radio-sensitization.

Graphical abstract

The "ART" of Epigenetics in Melanoma: From histone "Alterations, to Resistance and Therapies"

Malignant melanoma is the most deadly form of skin cancer. It originates from melanocytic cells and can also arise at other body sites. Early diagnosis and appropriate medical care offer excellent prognosis with up to 5-year survival rate in more than 95% of all patients. However, long-term survival rate for metastatic melanoma patients remains at only 5%. Indeed, malignant melanoma is known for its notorious resistance to most current therapies and is characterized by both genetic and epigenetic alterations. In cutaneous melanoma (CM), genetic alterations have been implicated in drug resistance, yet the main cause of this resistance seems to be non-genetic in nature with a change in transcription programs within cell subpopulations. This change can adapt and escape targeted therapy and immunotherapy cytotoxic effects favoring relapse. Because they are reversible in nature, epigenetic changes are a growing focus in cancer research aiming to prevent or revert the drug resistance with current therapies. As such, the field of epigenetic therapeutics is among the most active area of preclinical and clinical research with effects of many classes of epigenetic drugs being investigated. Here, we review the multiplicity of epigenetic alterations, mainly histone alterations and chromatin remodeling in both cutaneous and uveal melanomas, opening opportunities for further research in the field and providing clues to specifically control these modifications. We also discuss how epigenetic dysregulations may be exploited to achieve clinical benefits for the patients, the limitations of these therapies, and recent data exploring this potential through combinatorial epigenetic and traditional therapeutic approaches.

Chronic respiratory diseases: An introduction and need for novel drug delivery approaches

Globally, chronic respiratory diseases (CRDs), both communicable and noncommunicable, are among the leading causes of mortality, morbidity, economic and societal burden, and disability-adjusted life years (DALYs). CRDs affect multiple components of respiratory system, including the airways, parenchyma, and pulmonary vasculature. Although noncommunicable respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), cystic fibrosis (CF), and lung cancer (LC), account for enormous disease burden, the currently available therapies only focus on alleviating the symptoms of diseases rather than providing optimal treatment and/or prevention. Similarly a major respiratory communicable disease, that is, tuberculosis (TB), is associated with the challenge of increasingly developing antibiotic resistance in the bacterial pathogen Mycobacterium tuberculosis. In light of these challenges, we aim to summarize the underlying molecular and cellular mechanisms that lead to hallmark pathophysiology of CRDs. Moreover, we will also highlight the limitations of current therapeutic strategies and explore novel drug delivery options that may be potentially more effective in the management of CRDs.

Mycosis fungoides and Sézary syndrome: 2019 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Cutaneous T-cell lymphomas (CTCL) are a heterogenous group of T-cell neoplasms involving the skin, the majority of which may be classified as Mycosis fungoides (MF) or Sézary syndrome (SS).

DIAGNOSIS

The diagnosis of MF or SS requires the integration of clinical and histopathologic data.

RISK-ADAPTED THERAPY

TNMB (tumor, node, metastasis, blood) staging remains the most important prognostic factor in MF/SS and forms the basis for a "risk-adapted," multi-disciplinary approach to treatment. For patients with disease limited to the skin, skin-directed therapies are preferred, as both disease-specific and overall survival for these patients is favorable. In contrast, patients with advanced-stage disease with significant nodal, visceral or blood involvement are generally approached with systemic therapies. These include biologic-response modifiers, histone deacetylase (HDAC) inhibitors, or antibody-based strategies, in an escalating fashion. In highly-selected patients, allogeneic stem-cell transplantation may be considered, as this may be curative in some patients.

The HDAC Inhibitor, SAHA, Combined with Cisplatin Synergistically Induces Apoptosis in Alpha-fetoprotein-producing Hepatoid Adenocarcinoma Cells

Hepatoid adenocarcinoma (HAC) is a rare and aggressive gastrointestinal tract cancer that is characterized by hepatic differentiation and production of alpha-fetoprotein (AFP). Cisplatin is mainly used to treat HAC, but the efficacy is poor. Recently, the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), was approved as an anticancer agent. In this study, we investigated the anticancer effect of SAHA in combination with cisplatin in VAT-39 cells, a newly established HAC cell line. Cell viability and apoptosis were examined by MTT assay, flow cytometry and TUNEL assay. Expression of H3S10, cleaved caspase-3, Bax, and Bcl-2 were evaluated by immunohistochemistry and western blotting. AFP levels were examined in VAT-39 cells and culture medium. Combined treatment with cisplatin and SAHA efficiently inhibited cell proliferation and decreased cell viability. Apoptotic cells, but not necrotic cells, were significantly increased following the combined treatment, and an increase in the Bax/Bcl-2 ratio indicated that the combination of cisplatin and SAHA induced apoptosis through the mitochondrial pathway. VAT-39 cells treated with cisplatin and SAHA also partially lost their main characteristic of AFP production. We conclude that cisplatin and SAHA have a synergistic anticancer effect of inducing apoptosis, and that this combination treatment may be effective for HAC.

p21Waf1 deficiency does not decrease DNA repair in E1A+cHa-Ras transformed cells by HDI sodium butyrate

This study aimed to explore a role of p21Waf1 in γH2AX foci formation and DNA repair as assessed by a Host-Cell Reactivation Assay in wild-type (p21Waf+/+) and p21Waf1-deficient E1A+Ras-transformed cells. p21Waf1+/+ cells have low γH2AX background compared to p21Waf1-/- cells. The treatment with histone deacetylase inhibitor (HDI) sodium butyrate (NaBut) causes to accumulation of γH2AX in p21Waf+/+ cells with little effect in p21Waf-/- cells. Moreover, NaBut inhibits DNA repair in wt cells but not in p21Waf1-/- cells. This could be explained by the weakening of GADD45 and PCNA proteins binding in NaBut-treated p21Waf1-expressing cells but not in p21Waf1-/- cells. We suggest that in wt-ERas cells NaBut activates both p21Waf1 expression and a release of p21Waf1 from the complexes with E1A that leads to suppression of DNA repair and promotes γH2AX persistency. The absence of p21Waf1 is by itself considered by the cell as stressful factor with formation of γH2AX. But the lack of p21Waf1 interferes with an inhibitory effect of NaBut to inhibit DNA repair and thereby to stop concomitant accumulation of harmful mutations. We conclude that p21Waf1 is directly involved in control of genome integrity and DNA repair acting through modulation of the components of the DNA repair machinery.

Tackling Pseudomonas aeruginosa Virulence by a Hydroxamic Acid-Based LasB Inhibitor

In search of novel antibiotics to combat the challenging spread of resistant pathogens, bacterial proteases represent promising targets for pathoblocker development. A common motif for protease inhibitors is the hydroxamic acid function, yet this group has often been related to unspecific inhibition of various metalloproteases. In this work, the inhibition of LasB, a harmful zinc metalloprotease secreted by Pseudomonas aeruginosa, through a hydroxamate derivative is described. The present inhibitor was developed based on a recently reported, highly selective thiol scaffold. Using X-ray crystallography, the lack of inhibition of a range of human matrix metalloproteases could be attributed to a distinct binding mode sparing the S1' pocket. The inhibitor was shown to restore the effect of the antimicrobial peptide LL-37, decrease the formation of P. aeruginosa biofilm and, for the first time for a LasB inhibitor, reduce the release of extracellular DNA. Hence, it is capable of disrupting several important bacterial resistance mechanisms. These results highlight the potential of protease inhibitors to fight bacterial infections and point out the possibility to achieve selective inhibition even with a strong zinc anchor.

The Therapeutic Strategy of HDAC6 Inhibitors in Lymphoproliferative Disease

Histone deacetylases (HDACs) are master regulators of chromatin remodeling, acting as epigenetic regulators of gene expression. In the last decade, inhibition of HDACs has become a target for specific epigenetic modifications related to cancer development. Overexpression of HDAC has been observed in several hematologic malignancies. Therefore, the observation that HDACs might play a role in various hematologic malignancies has brought to the development of HDAC inhibitors as potential antitumor agents. Recently, the class IIb, HDAC6, has emerged as one potential selective HDACi. This isoenzyme represents an important pharmacological target for selective inhibition. Its selectivity may reduce the toxicity related to the off-target effects of pan-HDAC inhibitors. HDAC6 has also been studied in cancer especially for its ability to coordinate a variety of cellular processes that are important for cancer pathogenesis. HDAC6 has been reported to be overexpressed in lymphoid cells and its inhibition has demonstrated activity in preclinical and clinical study of lymphoproliferative disease. Various studies of HDAC6 inhibitors alone and in combination with other agents provide strong scientific rationale for the evaluation of these new agents in the clinical setting of hematological malignancies. In this review, we describe the HDACs, their inhibitors, and the recent advances of HDAC6 inhibitors, their mechanisms of action and role in lymphoproliferative disorders.

Inhibition of histone deacetylases induces formation of multipolar spindles and subsequent p53-dependent apoptosis in nasopharyngeal carcinoma cells

Histone deacetylases (HDACs) play crucial roles in the initiation and progression of cancer, offering a promising target for cancer therapy. HDACs inhibitor MGCD0103 (MGCD) exhibits effective anti-tumor activity by blocking proliferation and inducing cell death in malignant cells. However, the molecular mechanisms of HDACs inhibition induces cell death have not been well elucidated. In this study, we showed that MGCD effectively restored histone acetylation, suppressed cell growth and induced apoptosis in two-dimensional (2D) and three-dimensional (3D) cultured CNE1 and CNE2 nasopharyngeal carcinoma (NPC) cells. Importantly, MGCD arrested cell cycle at mitosis (M) phase with formation of multipolar spindles, which was associated with activated p53-mediated postmitotic checkpoint pathway to induce apoptotic cell death. Moreover, MGCD-induced apoptosis was decreased by inhibition of p53 using short interfering RNA (siRNA), suggesting that p53 was required for MGCD-induced cell apoptosis. Consistently, MGCD in combination with Nutlin-3, a MDM2 inhibitor showed synergistic effect on inducing apoptosis in 2D and 3D cultured CNE2 cells. Collectively, our data revealed that MGCD induced p53-dependent cell apoptosis following formation of multipolar spindles in NPC cells, suggesting the therapeutic potential of combinations of HDACs and MDM2 inhibitors for NPC treatment.

Three-dimensional tumor cell growth stimulates autophagic flux and recapitulates chemotherapy resistance

Current preclinical models in tumor biology are limited in their ability to recapitulate relevant (patho-) physiological processes, including autophagy. Three-dimensional (3D) growth cultures have frequently been proposed to overcome the lack of correlation between two-dimensional (2D) monolayer cell cultures and human tumors in preclinical drug testing. Besides 3D growth, it is also advantageous to simulate shear stress, compound flux and removal of metabolites, e.g., via bioreactor systems, through which culture medium is constantly pumped at a flow rate reflecting physiological conditions. Here we show that both static 3D growth and 3D growth within a bioreactor system modulate key hallmarks of cancer cells, including proliferation and cell death as well as macroautophagy, a recycling pathway often activated by highly proliferative tumors to cope with metabolic stress. The autophagy-related gene expression profiles of 2D-grown cells are substantially different from those of 3D-grown cells and tumor tissue. Autophagy-controlling transcription factors, such as TFEB and FOXO3, are upregulated in tumors, and 3D-grown cells have increased expression compared with cells grown in 2D conditions. Three-dimensional cultures depleted of the autophagy mediators BECN1, ATG5 or ATG7 or the transcription factor FOXO3, are more sensitive to cytotoxic treatment. Accordingly, combining cytotoxic treatment with compounds affecting late autophagic flux, such as chloroquine, renders the 3D-grown cells more susceptible to therapy. Altogether, 3D cultures are a valuable tool to study drug response of tumor cells, as these models more closely mimic tumor (patho-)physiology, including the upregulation of tumor relevant pathways, such as autophagy.

Ricolinostat, a selective HDAC6 inhibitor, shows anti-lymphoma cell activity alone and in combination with bendamustine

Histone deacetylase inhibitors (HDACis) have emerged as a new class of anticancer agents, targeting the biological process including cell cycle and apoptosis. We investigated and explained the anticancer effects of an HDAC6 inhibitor, ricolinostat alone and in combination with bendamustine in lymphoma cell lines. Cell viability was measured by MTT assay. Apoptosis, reactive oxygen species (ROS) generation, Bcl-2 protein expression, cell cycle progression and tubuline expression were determined by flow cytometry. The effects of ricolinostat alone and in combination on the caspases, PI3K/Akt, Bcl-2 pathways, ER stress and UPR were assessed by immunoblotting. Ricolinostat shows anti lymphoma activity when used as single agent and its capability to induce apoptosis is synergistically potentiated by the bendamustine in lymphoma cell lines. Drug combination reduced the proportion of cells in the G0/G1 and S phases and caused an increase of "sub-G0/G1" peak. The synergistic effect accompanied with the increased ROS, activation of caspase-8, -9, and -3, the cleavage of PARP and modulated by Bcl-2 proteins family. In addition, the exposure of ricolinostat induced the acetylation level of α-tubulin, the extend of which was not further modified by bendamustine. Finally, the apoptosis effect of ricolinostat/bendamustine may be mediated by a corresponding effect on microtubule stabilization. Our data suggest that ricolinostat in combination with bendamustine may be a novel combination with potential for use as an antitumor agent in lymphoma.

Induction of autophagy by valproic acid enhanced lymphoma cell chemosensitivity through HDAC-independent and IP3-mediated PRKAA activation

Autophagy is closely related to tumor cell sensitivity to anticancer drugs. The HDAC (histone deacetylase) inhibitor valproic acid (VPA) interacted synergistically with chemotherapeutic agents to trigger lymphoma cell autophagy, which resulted from activation of AMPK (AMP-activated protein kinase) and inhibition of downstream MTOR (mechanistic target of rapamycin [serine/threonine kinase]) signaling. In an HDAC-independent manner, VPA potentiated the effect of doxorubicin on lymphoma cell autophagy via reduction of cellular inositol 1,4,5 trisphosphate (IP3), blockade of calcium into mitochondria and modulation of PRKAA1/2-MTOR cascade. In murine xenograft models established with subcutaneous injection of lymphoma cells, dual treatment of VPA and doxorubicin initiated IP3-mediated calcium depletion and PRKAA1/2 activation, induced in situ autophagy and efficiently retarded tumor growth. Aberrant genes involving mitochondrial calcium transfer were frequently observed in primary tumors of lymphoma patients. Collectively, these findings suggested an HDAC-independent chemosensitizing activity of VPA and provided an insight into the clinical application of targeting autophagy in the treatment of lymphoma.

Belinostat and vincristine demonstrate mutually synergistic cytotoxicity associated with mitotic arrest and inhibition of polyploidy in a preclinical model of aggressive diffuse large B cell lymphoma

Diffuse Large B-cell lymphoma (DLBCL) is an aggressive malignancy that has a 60 percent 5-year survival rate, highlighting a need for new therapeutic approaches. Histone deacetylase inhibitors (HDACi) are novel therapeutics being clinically-evaluated in combination with a variety of other drugs. However, rational selection of companion therapeutics for HDACi is difficult due to their poorly-understood, cell-type specific mechanisms of action. To address this, we developed a pre-clinical model system of sensitivity and resistance to the HDACi belinostat using DLBCL cell lines. In the current study, we demonstrate that cell lines sensitive to the cytotoxic effects of HDACi undergo early mitotic arrest prior to apoptosis. In contrast, HDACi-resistant cell lines complete mitosis after a short delay and arrest in G1. To force mitotic arrest in HDACi-resistant cell lines, we used low dose vincristine or paclitaxel in combination with belinostat and observed synergistic cytotoxicity. Belinostat curtails vincristine-induced mitotic arrest and triggers a strong apoptotic response associated with downregulated MCL-1 expression and upregulated BIM expression. Resistance to microtubule targeting agents (MTAs) has been associated with their propensity to induce polyploidy and thereby increase the probability of genomic instability that enables cancer progression. Co-treatment with belinostat effectively eliminated a vincristine-induced, actively cycling polyploid cell population. Our study demonstrates that vincristine sensitizes DLBCL cells to the cytotoxic effects of belinostat and that belinostat prevents polyploidy that could cause vincristine resistance. Our findings provide a rationale for using low dose MTAs in conjunction with HDACi as a potential therapeutic strategy for treatment of aggressive DLBCL.

Cutaneous T-Cell Lymphoma: A Review with a Focus on Targeted Agents

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of extranodal lymphomas involving the skin. Diagnosis of the two main subtypes of CTCL-mycosis fungoides (MF) and Sézary syndrome (SS)-is based on the International Society for Cutaneous Lymphomas/European Organization for Research and Treatment of Cancer (ISCL/EORTC) classification system, which utilizes clinical, histopathological, molecular biologic, and immunopathologic features. Risk stratification, based on TNMB (tumor, node, metastasis, and blood) staging, provides prognostic information, with limited-stage disease conferring the longest median overall survival. Skin-directed therapies are preferred in the management of limited-stage disease, whereas advanced-stage disease requires systemic therapies. As the mechanisms of CTCL pathogenesis are increasingly understood, new monoclonal antibodies, checkpoint inhibitors, immunomodulatory agents, and small molecules are under investigation and may provide additional therapeutic options for those with advanced CTCL. This review examines the current landscape of targeted therapies in the treatment of CTCLs.

Histone deacetylase inhibitor-induced cell death in bladder cancer is associated with chromatin modification and modifying protein expression: A proteomic approach

The Cancer Genome Atlas (TCGA) project recently identified the importance of mutations in chromatin remodeling genes in human carcinomas. These findings imply that epigenetic modulators might have a therapeutic role in urothelial cancers. To exploit histone deacetylases (HDACs) as targets for cancer therapy, we investigated the HDAC inhibitors (HDACIs) romidepsin, trichostatin A, and vorinostat as potential chemotherapeutic agents for bladder cancer. We demonstrate that the three HDACIs suppressed cell growth and induced cell death in the bladder cancer cell line 5637. To identify potential mechanisms associated with the anti-proliferative and cytotoxic effects of the HDACIs, we used quantitative proteomics to determine the proteins potentially involved in these processes. Our proteome studies identified a total of 6003 unique proteins. Of these, 2472 proteins were upregulated and 2049 proteins were downregulated in response to HDACI exposure compared to the untreated controls (P<0.05). Bioinformatic analysis further revealed that those differentially expressed proteins were involved in multiple biological functions and enzyme-regulated pathways, including cell cycle progression, apoptosis, autophagy, free radical generation and DNA damage repair. HDACIs also altered the acetylation status of histones and non-histone proteins, as well as the levels of chromatin modification proteins, suggesting that HDACIs exert multiple cytotoxic actions in bladder cancer cells by inhibiting HDAC activity or altering the structure of chromatin. We conclude that HDACIs are effective in the inhibition of cell proliferation and the induction of apoptosis in the 5637 bladder cancer cells through multiple cell death-associated pathways. These observations support the notion that HDACIs provide new therapeutic options for bladder cancer treatment and thus warrant further preclinical exploration.

Novel HDAC inhibitors exhibit pre-clinical efficacy in lymphoma models and point to the importance of CDKN1A expression levels in mediating their anti-tumor response

We investigated the pre-clinical activities of two novel histone deacetylase inhibitors (HDACi), ITF-A and ITF-B, in a large panel of pre-clinical lymphoma models. The two compounds showed a dose-dependent anti-proliferative activity in the majority of cell lines. Gene expression profiling (GEP) of diffuse large B-cell lymphoma (DLBCL) cells treated with the compounds showed a modulation of genes involved in chromatin structure, cell cycle progression, apoptosis, B-cell signaling, and genes encoding metallothioneins. Cell lines showed differences between the concentrations of ITF-A and ITF-B needed to cause anti-proliferative or cytotoxic activity, and cell cycle and apoptosis genes appeared implicated in determining the type of response. In particular, CDKN1A expression was higher in DLBCL cells that, to undergo apoptosis, required a much higher amount of drug than that necessary to induce only an anti-proliferative effect.

In conclusion, the two novel HDACi ITF-A and ITF-B demonstrated anti-proliferative activity across different mature B-cell lymphoma cell lines. Basal CDKN1A levels appeared to be important in determining the gap between HDACi concentrations causing cell cycle arrest and those that lead to cell death.

Cutaneous T-cell lymphoma: 2016 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Cutaneous T-cell lymphomas are a heterogenous group of T-cell lymphoproliferative disorders involving the skin, the majority of which may be classified as Mycosis Fungoides (MF) or Sézary Syndrome (SS).

DIAGNOSIS

The diagnosis of MF or SS requires the integration of clinical and histopathologic data.

RISK-ADAPTED THERAPY

TNMB (tumor, node, metastasis, blood) staging remains the most important prognostic factor in MF/SS and forms the basis for a "risk-adapted," multidisciplinary approach to treatment. For patients with disease limited to the skin, expectant management or skin-directed therapies is preferred, as both disease-specific and overall survival for these patients is favorable. In contrast, patients with advanced-stage disease with significant nodal, visceral, or blood involvement are generally approached with biologic-response modifiers or histone deacetylase inhibitors before escalating therapy to include systemic, single-agent chemotherapy. In highly-selected patients, allogeneic stem-cell transplantation may be considered, as this may be curative in some patients.

Lung cancer: Biology and treatment options

Lung cancer remains the leading cause of cancer mortality in men and women in the U.S. and worldwide. About 90% of lung cancer cases are caused by smoking and the use of tobacco products. However, other factors such as radon gas, asbestos, air pollution exposures, and chronic infections can contribute to lung carcinogenesis. In addition, multiple inherited and acquired mechanisms of susceptibility to lung cancer have been proposed. Lung cancer is divided into two broad histologic classes, which grow and spread differently: small-cell lung carcinomas (SCLCs) and non-small cell lung carcinomas (NSCLCs). Treatment options for lung cancer include surgery, radiation therapy, chemotherapy, and targeted therapy. Therapeutic-modalities recommendations depend on several factors, including the type and stage of cancer. Despite the improvements in diagnosis and therapy made during the past 25 years, the prognosis for patients with lung cancer is still unsatisfactory. The responses to current standard therapies are poor except for the most localized cancers. However, a better understanding of the biology pertinent to these challenging malignancies, might lead to the development of more efficacious and perhaps more specific drugs. The purpose of this review is to summarize the recent developments in lung cancer biology and its therapeutic strategies, and discuss the latest treatment advances including therapies currently under clinical investigation.

Inhibition of class I histone deacetylases by romidepsin potently induces Epstein-Barr virus lytic cycle and mediates enhanced cell death with ganciclovir

Pan-histone deacetylase (HDAC) inhibitors, which inhibit 11 HDAC isoforms, are widely used to induce Epstein-Barr virus (EBV) lytic cycle in EBV-associated cancers in vitro and in clinical trials. Here, we hypothesized that inhibition of one or several specific HDAC isoforms by selective HDAC inhibitors could potently induce EBV lytic cycle in EBV-associated malignancies such as nasopharyngeal carcinoma (NPC) and gastric carcinoma (GC). We found that inhibition of class I HDACs, particularly HDAC-1, -2 and -3, was sufficient to induce EBV lytic cycle in NPC and GC cells in vitro and in vivo. Among a panel of selective HDAC inhibitors, the FDA-approved HDAC inhibitor romidepsin was found to be the most potent lytic inducer, which could activate EBV lytic cycle at ∼0.5 to 5 nM (versus ∼800 nM achievable concentration in patients' plasma) in more than 75% of cells. Upregulation of p21(WAF1) , which is negatively regulated by class I HDACs, was observed before the induction of EBV lytic cycle. The upregulation of p21(WAF1) and induction of lytic cycle were abrogated by a specific inhibitor of PKC-δ but not the inhibitors of PI3K, MEK, p38 MAPK, JNK or ATM pathways. Interestingly, inhibition of HDAC-1, -2 and -3 by romidepsin or shRNA knockdown could confer susceptibility of EBV-positive epithelial cells to the treatment with ganciclovir (GCV). In conclusion, we demonstrated that inhibition of class I HDACs by romidepsin could potently induce EBV lytic cycle and mediate enhanced cell death with GCV, suggesting potential application of romidepsin for the treatment of EBV-associated cancers.

Inhibition of breast cancer progression by a novel histone deacetylase inhibitor, LW479, by down-regulating EGFR expression

BACKGROUND AND PURPOSE

Compounds targeting epigenetic events of tumours are likely to be an important addition to anticancer therapy. Histone deacetylase inhibitors (HDACI) have emerged as a promising novel class for therapeutic interventions associated with cancer, and many of them are currently in clinical investigation. Here, we assessed a novel hydroxamate-based HDACI, LW479, in breast cancer progression and explored its underlying mechanism(s).

EXPERIMENTAL APPROACH

LW479 was identified using the HDACI screening kit. Western blot and flow cytometry were used to analyse the biological effects of LW479 as a novel HDACI. The effects of LW479 were assessed in mouse models of spontaneous and experimental breast cancer. Co-immunoprecipitation, immunofluorescent staining and chromatin immunoprecipitation assays along with immunohistochemical analysis, were used to elucidate the molecular basis of the actions of LW479.

KEY RESULTS

LW479 was identified as a novel HDACI and showed marked cytotoxicity and induced apoptosis, as well as cell cycle arrest, in a panel of breast cancer cell lines. Intraperitoneal injections of LW479 markedly suppressed breast tumour growth and pulmonary metastasis in nude mice. LW479 also decreased levels of EGF receptors (EGFR) by blocking the binding of the transcription factor Sp1 and HDAC1 to the EGFR promoter region.

CONCLUSIONS AND IMPLICATIONS

Our data have elucidated the mechanisms underlying the inhibition by LW479 of tumour growth and metastasis, in models of breast cancer with aberrant EGFR expression. LW479 could be a candidate drug for breast cancer prevention.

Epigenetic Regulation by Sulforaphane: Opportunities for Breast and Prostate Cancer Chemoprevention

Sulforaphane (SFN) is a phytochemical derived from cruciferous vegetables that has multiple molecular targets and anti-cancer properties. Researchers have demonstrated several chemopreventive benefits of SFN consumption, such as reductions in tumor growth, increases in cancer cell apoptosis, and disruption of signaling within tumor microenvironments both in vitro and in vivo. Emerging evidence indicates that SFN exerts several of its chemopreventive effects by altering epigenetic mechanisms. This review summarizes evidence of the impact of SFN on epigenetic events and how they relate to the chemopreventive effects of SFN observed in preclinical and clinical studies of breast and prostate cancers. Specific areas of focus include the role of SFN in the regulation of cell cycle, apoptosis, inflammation, antioxidant defense, and cancer cell signaling and their relationships to epigenetic mechanisms. Finally, remaining challenges and research needs for translating mechanistic work with SFN into human studies and clinical intervention trials are discussed.

The potential of histone deacetylase inhibitors in breast cancer therapy

SUMMARY 

Breast cancer is the second leading cause of cancer-related mortality in women. Despite improvements in prevention, detection and treatment, breast cancer will be responsible for nearly 40,000 deaths in 2014. The function of histone deacetylases (HDACs) and their potential as therapeutic targets has become an area of intense investigation and small molecule inhibitors of HDACs (HDACi) are now being investigated as potential chemotherapeutics for breast cancer. In addition to altering chromatin structure through stabilization of histone acetylation, HDACi treatment induces the accumulation of acetylated isoforms of many nonhistone proteins, altering their structure and function. These structural changes influence protein–protein interactions and cellular processes including cell cycle arrest, apoptosis, autophagy, induction of reactive oxygen species and mitotic catastrophe. While the usefulness of these compounds as single agents for treatment of breast cancer is still under investigation, cotreatment with other therapies is being evaluated in a number of clinical trials.

Mechanisms and clinical significance of histone deacetylase inhibitors: epigenetic glioblastoma therapy

Glioblastoma is the most common and deadliest of malignant primary brain tumors (Grade IV astrocytoma) in adults. Current standard treatments have been improving but patient prognosis still remains unacceptably devastating. Glioblastoma recurrence is linked to epigenetic mechanisms and cellular pathways. Thus, greater knowledge of the cellular, genetic and epigenetic origin of glioblastoma is the key for advancing glioblastoma treatment. One rapidly growing field of treatment, epigenetic modifiers; histone deacetylase inhibitors (HDACis), has now shown much promise for improving patient outcomes through regulation of the acetylation states of histone proteins (a form of epigenetic modulation) and other non-histone protein targets. HDAC inhibitors have been shown, in a pre-clinical setting, to be effective anticancer agents via multiple mechanisms, by up-regulating expression of tumor suppressor genes, inhibiting oncogenes, inhibiting tumor angiogenesis and up-regulating the immune system. There are many HDAC inhibitors that are currently in pre-clinical and clinical stages of investigation for various types of cancers. This review will explain the theory of epigenetic cancer therapy, identify HDAC inhibitors that are being investigated for glioblastoma therapy, explain the mechanisms of therapeutic effects as demonstrated by pre-clinical and clinical studies and describe the current status of development of these drugs as they pertain to glioblastoma therapy.

Determination of thailandepsin B in rat plasma with a LC–MS/MS method

Background: Thailandepsin B (TDP-B) is a potent histone deacetylase inhibitor under development. A reliable bioanalytical method for the quantification of TDP-B in plasma samples is required. Results: The stabilizer mixture containing hydrochloric acid, formic acid and dichlorvos was applied to stabilize TDP-B in matrix samples. The method validation was conducted over the curve range of 1.00 to 1000 ng/ml. The intrabatch and interbatch precision and accuracy of the quality control samples showed ≤10.9% relative standard deviation and -6.7% to 15.0% relative error. Moreover, a possible metabolite M of TDP-B was tentatively characterized. Conclusion: A reliable LC–MS/MS method was developed and validated for the quantification of TDP-B and was successfully applied to a rat pharmacokinetic study.

Epigenetic therapy of acute myeloid leukemia using 5-aza-2'-deoxycytidine (decitabine) in combination with inhibitors of histone methylation and deacetylation

BACKGROUND

The silencing of tumor suppressor genes (TSGs) by aberrant DNA methylation occurs frequently in acute myeloid leukemia (AML). This epigenetic alteration can be reversed by 5-aza-2'-deoxcytidine (decitabine, 5-AZA-CdR). Although 5-AZA-CdR can induce complete remissions in patients with AML, most patients relapse. The effectiveness of this therapy may be limited by the inability of 5-AZA-CdR to reactivate all TSGs due to their silencing by other epigenetic mechanisms such as histone methylation or chromatin compaction. EZH2, a subunit of the polycomb repressive complex 2, catalyzes the methylation of histone H3 lysine 27 (H3K27) to H3K27me3. 3-Deazaneplanocin-A (DZNep), an inhibitor of methionine metabolism, can reactivate genes silenced by H3K27me3 by its inhibition of EZH2. In a previous report, we observed that 5-AZA-CdR, in combination with DZNep, shows synergistic antineoplastic action against AML cells. Gene silencing due to chromatin compaction is attributable to the action of histone deacetylases (HDAC). This mechanism of epigenetic gene silencing can be reversed by HDAC inhibitors such as trichostatin-A (TSA). Silent TSGs that cannot be reactivated by 5-AZA-CdR or DZNep have the potential to be reactivated by TSA. This provides a rationale for the use of HDAC inhibitors in combination with 5-AZA-CdR and DZNep to treat AML.

RESULTS

The triple combination of 5-AZA-CdR, DZNep, and TSA induced a remarkable synergistic antineoplastic effect against human AML cells as demonstrated by an in vitro colony assay. This triple combination also showed a potent synergistic activation of several key TSGs as determined by real-time PCR. The triple combination was more effective than the combination of two agents or a single agent. Microarray analysis showed that the triple combination generated remarkable changes in global gene expression.

CONCLUSIONS

Our data suggest that it may be possible to design a very effective therapy for AML using agents that target the reversal of the following three epigenetic "lock" mechanisms that silence gene expression: DNA methylation, histone methylation, and histone deacetylation. This approach merits serious consideration for clinical investigation in patients with advanced AML.