Potential use of histone deacetylase inhibitors in cancer therapy

Romidepsin (FK228), A Histone Deacetylase Inhibitor and its Analogues in Cancer Chemotherapy

BACKGROUND

Human HDACs represent a group of enzymes able to modify histone and non-histone proteins, which interact with DNA to generate chromatin. The correlation between irregular covalent modification of histones and tumor development has been proved over the last decades. Therefore, HDAC inhibitors are considered as potential drugs in cancer treatment. Romidepsin (FK228), Belinostat (PXD-101), Vorinostat (SAHA), Panobinostat (LBH-589) and Chidamide were approved by FDA as novel antitumor agents.

OBJECTIVE

The aim of this review article is to highlight the structure-activity relationships of several FK228 analogues as HDAC inhibitors. In addition, the synergistic effects of a dual HDAC/PI3K inhibition by some derivatives have been investigated.

MATERIALS AND METHODS

PubMed, MEDLINE, CAPLUS, SciFinder Scholar database were considered by selecting articles which fulfilled the objectives of this review, dating from 2015 till present time.

RESULTS

HDAC inhibitors have a significant role in cancer pathogenesis and evolution. Class I HDAC isoforms are expressed in many tumor types, therefore, potent and selective Class I HDAC inhibitors are of great interest as candidate therapeutic agents with limited side effects. By structurebased optimization, several FK228 analogues [15 (FK-A5), 22, 23 and 26 (FK-A11)] were identified, provided with significant activity against Class I HDAC enzymes and dose dependent antitumor activity. Compound 26 was recognized as an interesting HDAC/PI3K dual inhibitor (IC₅₀ against p110α of 6.7 μM while for HDAC1 inhibitory activity IC₅₀ was 0.64 nM).

CONCLUSION

Romidepsin analogues HDAC inhibitors have been confirmed as useful anticancer agents. In addition, dual HDAC/PI3K inhibition showed by some of them exhibited synergistic effects in inducing apoptosis in human cancer cells. Further studies on FK228 analogues may positively contribute to the availability of potent agents in tumor treatment.

Natural Products Impacting DNA Methyltransferases and Histone Deacetylases

Epigenetics refers to heritable changes in gene expression and chromatin structure without change in a DNA sequence. Several epigenetic modifications and respective regulators have been reported. These include DNA methylation, chromatin remodeling, histone post-translational modifications, and non-coding RNAs. Emerging evidence has revealed that epigenetic dysregulations are involved in a wide range of diseases including cancers. Therefore, the reversible nature of epigenetic modifications concerning activation or inhibition of enzymes involved could be promising targets and useful tools for the elucidation of cellular and biological phenomena. In this review, emphasis is laid on natural products that inhibit DNA methyltransferases (DNMTs) and histone deacetylases (HDACs) making them promising candidates for the development of lead structures for anticancer-drugs targeting epigenetic modifications. However, most of the natural products targeting HDAC and/or DNMT lack isoform selectivity, which is important for determining their potential use as therapeutic agents. Nevertheless, the structures presented in this review offer the well-founded basis that screening and chemical modifications of natural products will in future provide not only leads to the identification of more specific inhibitors with fewer side effects, but also important features for the elucidation of HDAC and DNMT function with respect to cancer treatment.

Current status of histone deacetylase inhibitors in cutaneous T-cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a non-Hodgkin's lymphoma with a heterogenous presentation and highly variable disease course. The most common subtypes of CTCL are mycosis fungoides (MF) and Sézary Syndrome (SS). Treatment varies based on the stage of the disease with skin directed therapies typically utilized for early stage disease, and systemic therapies employed for more advanced disease. There are few highly effective treatments available, and systemic therapies have limited response rates. Histone deacetylase inhibitors have emerged as mainstream treatments for MF/SS over the past several years. Here, we discuss the mechanism of action of histone deacetylase inhibitors in relation to the pathogenesis of MF/SS, evaluate the clinical trials that led to Food and Drug Administration approval of two of the histone deacetylase inhibitors for MF/SS and describe the results for those still under investigation. Additionally, we discuss the potential for combination therapies in order to optimize outcomes of treatment with histone deacetylase inhibitors.

Ubiquitin specific peptidase 5 promotes ovarian cancer cell proliferation through deubiquitinating HDAC2

Globally, epithelial ovarian cancer (EOC) is the most common gynecological malignancy with poor prognosis. The expression and oncogenic roles of ubiquitin specific peptidase 5 (USP5) have been reported in several cancers except EOC. In the current study, USP5 amplification was highly prevalent in patients with EOC and associated with higher mRNA expression of USP5. USP5 amplification and overexpression was positively correlated with poor prognosis of patients of ovarian serous carcinomas. Disruption of USP5 profoundly repressed cell proliferation by inducing cell cycle G0/G1 phase arrest in ovarian cancer cells. Additionally, USP5 knockdown inhibited xenograft growth in nude mice. Knockdown of USP5 decreased histone deacetylase 2 (HDAC2) expression and increased p27 (an important cell cycle inhibitor) expression in vitro and in vivo. The promoting effects of USP5 overexpression on cell proliferation and cell cycle transition, as well as the inhibitory effects of USP5 overexpression on p27 expression were mediated by HDAC2. Moreover, USP5 interacted with HDAC2, and disruption of USP5 enhanced the ubiquitination of HDAC2. HDAC2 protein was positively correlated USP5 protein, and negatively correlated with p27 protein in ovarian serous carcinomas tissues. Collectively, our data suggest the oncogenic function of USP5 and the potential regulatory mechanisms in ovarian carcinogenesis.

DNA methylome and transcriptome alterations and cancer prevention by triterpenoid ursolic acid in UVB-induced skin tumor in mice

Nonmelanoma skin cancers (NMSCs) are the most common type of skin cancers. Major risk factors for NMSCs include exposure to ultraviolet (UV) irradiation. Ursolic acid (UA) is a natural triterpenoid enriched in blueberries and herbal medicinal products, and possess anticancer activities. This study focuses on the impact of UA on epigenomic, genomic mechanisms and prevention of UVB-mediated NMSC. CpG methylome and RNA transcriptome alterations of early, promotion and late stages of UA treated on UVB-induced NMSC in SKH-1 hairless mice were conducted using CpG methyl-seq and RNA-seq. Samples were collected at weeks 2, 15, and 25, and integrated bioinformatic analyses were performed to identify key pathways and genes modified by UA against UVB-induced NMSC. Morphologically, UA significantly reduced NMSC tumor volume and tumor number. DNA methylome showed inflammatory pathways IL-8, NF-κB, and Nrf2 pathways were highly involved. Antioxidative stress master regulator Nrf2, cyclin D1, DNA damage, and anti-inflammatory pathways were induced by UA. Nrf2, cyclin D1, TNFrsf1b, and Mybl1 at early (2 weeks) and late (25 weeks) stages were identified and validated by quantitative polymerase chain reaction. In summary, integration of CpG methylome and RNA transcriptome studies show UA alters antioxidative, anti-inflammatory, and anticancer pathways in UVB-induced NMSC carcinogenesis. Particularly, UA appears to drive Nrf2 and its upstream/downstream genes, anti-inflammatory (at early stages) and cell cycle regulatory (both early and late stages) genes, of which might contribute to the overall chemopreventive effects of UVB-induced MNSC. This study may provide potential biomarkers/targets for chemoprevention of early stage of UVB-induced NMSC in human.

Trichostatin A promotes GLI1 degradation and P21 expression in multiple myeloma cells

Background

Histone deacetylase inhibitors are promising drugs for the future application in cancer therapy. Trichostatin A (TSA), a histone deacetylase inhibitor, exhibits effective antitumor effects in various cancers. However, the effects and underlying mechanisms of TSA on multiple myeloma (MM) are not fully investigated.

Methods

In the present study, RPMI8226 and MM.1S cells treated with TSA were used for cell proliferation, cell cycle, and survival examinations, then the localization and post transcriptional modification of GLI1 protein as well as the target gene P21 were analyzed using immunofluorescence, immunoprecipitation, western blots and qPCR, respectively.

Results

TSA exerted a time and dose-dependent cytotoxicity on MM cell lines, and suppressed the proliferation of MM cells and induced an upregulation of p21 protein accompanied by a decreased expression of cyclin D1. TSA treatment led to a downregulation of GLI1, and the nuclear accumulation of GLI1 was also inhibited. As a result of hedgehog inhibition, the expression of MYC and SURVIVIN was greatly weakened after TSA treatment. Furthermore, TSA accelerated GLI1 degradation in a proteasome-dependent manner. Additionally, p21 induction also contributed to GLI1 downregulation via reducing the transcription of GLI in mRNA level. Rescue experiments verified that exogenous expression of GLI1 alleviated MM cell apoptosis induced by TSA.

Conclusion

These results indicated that TSA represses MM cell growth and induces cell apoptosis. The inhibition of hedgehog signaling is an important mechanism accounting for the cytotoxic effects of TSA.

Histone modifications in fatty acid synthase modulated by carbohydrate responsive element binding protein are associated with non‑alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a manifestation of metabolic syndrome in the liver and is closely associated with diabetes; however, its pathogenesis remains to be elucidated. Carbohydrate responsive element binding protein (ChREBP), the hub of glucolipid metabolism, regulates the induction of fatty acid synthase (FASN), the key enzyme of de novo lipogenesis, by directly binding to carbohydrate response element (ChoRE) in its promoter. Investigations of histone modifications on NAFLD remain in their infancy. In the present study, by using ChIP, the association between histone modifications and FASN transcription was investigated and histone modifications in FASN modulated by ChREBP were measured. It was demonstrated that ChREBP induced FASN ChREBP-ChoRE binding to accelerate the expression of FASN, leading to hepatocellular steatosis by facilitating H3 and H4 acetylation, H3K4 trimethylation and the phosphorylation of H3S10, but inhibiting the trimethylation of H3K9 and H4K20 in FASN promoter regions of HepG2 and L02 cells. It was also found that ChREBP-ChoRE binding of FASN relied on histone acetylation and that the transcriptional activity of ChREBP on FASN is required, based on the premise that histone acetylation causes conformational changes in FASN chromatin. This indicated histone acetylation as a crucial mechanism involved in the transcription of FASN modulated by ChREBP. Consequently, the present study provides further insight into the pathophysiology and a novel therapeutic potential of NAFLD based on epigenetic mechanisms.

An epigenetic regulator-related score (EpiScore) predicts survival in patients with diffuse large B cell lymphoma and identifies patients who may benefit from epigenetic therapy

Diffuse large B-cell lymphoma (DLBCL) is the most common form of lymphoma and shows considerable clinical and biological heterogeneity. Much research is currently focused on the identification of prognostic markers for more specific patients’ risk stratification and on the development of therapeutic approaches to improve the long-term outcome. Epigenetic alterations are involved in various cancers, including lymphoma. Interestingly, epigenetic alterations are reversible and drugs to target some of them have been developed. In this study, we demonstrated that the gene expression profile of epigenetic regulators has a prognostic value in DLBCL and identified pathways that could be involved in DLBCL poor outcome. We then designed a new risk score (EpiScore) based on the gene expression level of the epigenetic regulators DNMT3A, DOT1L, SETD8. EpiScore was predictive of overall survival in DLBCL and allowed splitting patients with DLBCL from two independent cohorts (n = 414 and n = 69) in three groups (high, intermediate and low risk). EpiScore was an independent predictor of survival when compared with previously described prognostic factors, such as the International Prognostic Index (IPI), germinal center B cell and activated B cell molecular subgroups, gene expression-based risk score (GERS) and DNA repair score. Immunohistochemistry analysis of DNMT3A in 31 DLBCL samples showed that DNMT3A overexpression (>42% of positive tumor cells) correlated with reduced overall and event-free survival. Finally, an HDAC gene signature was significantly enriched in the DLBCL samples included in the EpiScore high-risk group. We conclude that EpiScore identifies high-risk patients with DLBCL who could benefit from epigenetic therapy.

Fucoxanthin Elicits Epigenetic Modifications, Nrf2 Activation and Blocking Transformation in Mouse Skin JB6 P+ Cells

Nuclear factor erythroid-2-related factor-2 (Nrf2 or NFE2L2) is a master regulator of the anti-oxidative stress response, which is involved in the defense against many oxidative stress/inflammation-mediated diseases, including anticancer effects elicited by an increasing number of natural products. Our previous studies showed that the epigenetic modification of the Nrf2 gene plays a key role in restoring the expression of Nrf2. In this study, we aimed to investigate the epigenetic regulation of Nrf2 by astaxanthin (AST) and fucoxanthin (FX), carotenoids which are abundant in microalgae and seaweeds, in mouse skin epidermal JB6 P+ cells. FX induced the anti-oxidant response element (ARE)-luciferase and upregulated the mRNA and protein levels of Nrf2 and Nrf2 downstream genes in HepG2-C8 cells overexpressing the ARE-luciferase reporter. Both FX and AST decreased colony formation in 12-Otetradecanoylphorbol-13-acetate (TPA)-induced transformation of JB6 P+ cells. FX decreased the methylation of the Nrf2 promoter region in the JB6 P+ cells by the bisulfite conversion and pyrosequencing. Both FX and AST significantly reduced DNA methyltransferase (DNMT) activity but did not affect histone deacetylase (HDAC) activity in JB6 P+ cells. In summary, our results show that FX activates the Nrf2 signaling pathway, induces the epigenetic demethylation of CpG sites in Nrf2 and blocks the TPA-induced transformation of JB6 P+ cells, indicating the potential health-promoting effects of FX in skin cancer prevention.

HDAC inhibitor PAC-320 induces G2/M cell cycle arrest and apoptosis in human prostate cancer

HDAC inhibitors (HDACis) have been demonstrated with profound antiproliferative activities in various tumor types. Previously, we screened several polyoxometalate HDACis based on our p21 luciferase promoter system and demonstrated that such HDACis have antitumor activity. Here, we further investigate the antitumor mechanism of PAC-320, a compound among the polyoxometalates, in human prostate cancer. We demonstrate that PAC-320 is a broad-spectrum HDACi and could inhibit growth of prostate cancer cells in vitro and in vivo. Furthermore, we find that PAC-320 induces cell cycle arrest at G2/M phase and apoptosis. Mechanically, PAC-320 induced cell cycle arrest is associated with an increase of p21 and decrease of cyclin A and cyclin B1, while PAC-320 induced apoptosis is mediated through mitochondria apoptotic pathway and is closely associated with increase of BH3-only proteins Noxa and Hrk. Meanwhile, we demonstrate that p38 MAPK pathway is involved in PAC-320 induced antiproliferative activities in prostate cancer. Taken together, our data indicates that PAC-320 has potent prostate cancer inhibitory activity in vitro and in vivo, which is mediated by G2/M cell cycle arrest and apoptosis.

High Expression of Retinoblastoma-Binding Protein 2 (RBP2) in Patients with Hepatocellular Carcinoma and Its Prognostic Significance

Background

Recently, some studies have found that retinoblastoma-binding protein 2 (RBP2) is involved in the development and progression of many kinds of malignant tumors. This study aimed to explore the expression level of RBP2 in hepatocellular carcinoma (HCC) and its prognostic significance.

Material/Methods

Immunohistochemical analysis was used to evaluate the RBP2 expression level in 130 HCC patients and adjacent normal tissues. Tumor angiogenesis was marked by CD31 and vascular endothelial growth factor (VEGF) staining. Kaplan-Meier and Cox regression analyses were performed to examine the relationship between RBP2 expression and prognosis of HCC patients.

Results

RBP2 expression was significantly higher in HCC tissues (positive expression rate: 72.3%, 94/130). Increased RBP2 expression was dramatically associated with AFP level (P=0.016), degree of differentiation (P=0.000), and TNM stage (P=0.035). Moreover, tumors with RBP2-positive expression showed significantly higher intratumoral MVD than those with RBP2-negative expression (P=0.000). Kaplan-Meier analysis revealed RBP2-positive expression was related to decreased disease-free survival (DFS) (P=0.000) and overall survival (OS) (P=0.000). Furthermore, RBP2 was an independent poor prognostic factor of DFS and OS (P=0.029 and 0.010, respectively) as demonstrated by multivariate analysis.

Conclusions

Increased RBP2 expression, as an independent poor prognostic factor for DFS and OS of HCC patients, is closely related to tumor angiogenesis. RBP2 is expected to become a new potential therapeutic target for HCC.

Interrogating the Roles of Post-Translational Modifications of Non-Histone Proteins

Post-translational modifications (PTMs) allot versatility to the biological functions of highly conserved proteins. Recently, modifications to non-histone proteins such as methylation, acetylation, phosphorylation, glycosylation, ubiquitination, and many more have been linked to the regulation of pivotal pathways related to cellular response and stability. Due to the roles these dynamic modifications assume, their dysregulation has been associated with cancer and many other important diseases such as inflammatory disorders and neurodegenerative diseases. For this reason, we present a review and perspective on important post-translational modifications on non-histone proteins, with emphasis on their roles in diseases and small molecule inhibitors developed to target PTM writers. Certain PTMs' contribution to epigenetics has been extensively expounded; yet more efforts will be needed to systematically dissect their roles on non-histone proteins, especially for their relationships with nononcological diseases. Finally, current research approaches for PTM study will be discussed and compared, including limitations and possible improvements.

Panobinostat Enhances Growth Suppressive Effects of Progestin on Endometrial Carcinoma by Increasing Progesterone Receptor and Mitogen-Inducible Gene-6

Although progestin has been used to treat endometrial hyperplasia and endometrial carcinoma (EC), its therapeutic efficacy is limited. In order to improve this, the underlining mechanisms of the effects of progestin need to be elucidated in more detail. In the present study, we examined the involvement of mitogen-inducible gene-6 (MIG6), a negative regulator of the EGF receptor, in the progestin-mediated growth suppression of endometrial epithelia. The immunohistochemical expression of MIG6 was elevated in the early to mid-secretory phases of normal endometrium and also with endometrial hyperplasia after medroxyprogesterone acetate (MPA) therapy. The addition of progesterone (P4) to progesterone receptor (PR)-positive EC cells reduced the viability and induced MIG6 messenger RNA (mRNA) and protein expression. The silencing of MIG6 using siRNA eliminated the P4-mediated reduction of EC cell viability, indicating that MIG6 is an essential downstream component of PR-mediated growth suppression. In order to enhance PR-driven signals, we examined the effects of histone deacetylase (HDAC) inhibitors because histone acetylation has been shown to increase the expression of PR. The addition of three HDAC inhibitors (panobinostat, LBH589; trichostatin A, TSA; suberoylanilide hydroxamic acid, SAHA) decreased the viability of EC cells and up-regulated the expression of PR and MIG6, and these effects were the strongest with LBH589. The addition of LBH589 and MPA synergistically decreased the viability and increased apoptosis in EC cells. These results indicate that LBH589 has potential as an enhancer of progestin therapy via the up-regulation of PR and MIG6.

Strategies of targeting the extracellular domain of RON tyrosine kinase receptor for cancer therapy and drug delivery

PURPOSE

Cancer is one of the most important life-threatening diseases in the world. The current efforts to combat cancer are being focused on molecular-targeted therapies. The main purpose of such approaches is based on targeting cancer cell-specific molecules to minimize toxicity for the normal cells. RON (Recepteur d'Origine Nantais) tyrosine kinase receptor is one of the promising targets in cancer-targeted therapy and drug delivery.

METHODS

In this review, we will summarize the available agents against extracellular domain of RON with potential antitumor activities.

RESULTS

The presented antibodies and antibody drug conjugates against RON in this review showed wide spectrum of in vitro and in vivo antitumor activities promising the hope for them entering the clinical trials.

CONCLUSION

Due to critical role of extracellular domain of RON in receptor activation, the development of therapeutic agents against this region could lead to fruitful outcome in cancer therapy.

Exposure to the environmental endocrine disruptor TCDD and human reproductive dysfunction: Translating lessons from murine models

Humans and other animals are exposed to a wide array of man-made toxicants, many of which act as endocrine disruptors that exhibit differential effects across the lifespan. In humans, while the impact of adult exposure is known for some compounds, the potential consequences of developmental exposure to endocrine disrupting chemicals (EDCs) is more difficult to ascertain. Animal studies have revealed that exposure to EDCs prior to puberty can lead to adult reproductive disease and dysfunction. Specifically, in adult female mice with an early life exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we demonstrated a transgenerational occurrence of several reproductive diseases that have been linked to endometriosis in women. Herein, we review the evidence for TCDD-associated development of adult reproductive disease as well as known epigenetic alterations associated with TCDD and/or endometriosis. We will also introduce new "Organ-on-Chip" models which, combined with our established murine model, are expected to further enhance our ability to examine alterations in gene-environment interactions that lead to heritable disease.