HDACs and HDAC Inhibitors in Urothelial Carcinoma - Perspectives for an Antineoplastic Treatment

Transcriptome-Based Network Analysis Related to Histone Deacetylase Genes and Identified EMP1 as a Potential Biomarker for Prognosis in Bladder Cancer

BACKGROUND

Abnormal expression and function of histone deacetylases (HDACs) are closely associated with the development of bladder cancer (BCa). Systematic elucidation of the role of HDACs in BCa is expected to improve BCa prognosis and treatment strategies.

METHODS

We explored the correlation and expression patterns of HDAC family genes in BCa. Consensus clustering was employed to categorize BCa into subtypes based on HDAC expression profiles. Differential analysis, pathway enrichment analysis, and drug responsiveness evaluation were conducted to characterize HDAC subtypes. Then, a prognostic model based on HDAC cluster related genes was constructed and validated across multiple cohorts.

RESULTS

We identified distinct HDAC expression patterns and correlations with immune cell infiltration and enrichment of pathways in cancer, highlighting their role in BCa. Consensus clustering revealed 2 HDAC gene subtypes. Gene cluster 1 showed worse survival, higher clinical stage, and lower immune cell infiltration compared to gene cluster 2. Additionally, pathway enrichment analysis revealed differences in tumor-promoting pathways between the clusters. Moreover, gene cluster 1 exhibited higher resistance to Rho kinase inhibitor drugs. Multi-omic analysis unveiled unique mutation and CNV profiles between the clusters, indicating distinct molecular features. Furthermore, a HDAC gene-related prognostic model demonstrated robust predictive accuracy and identified EMP1 as a key prognostic gene associated with poor survival and enriched metastatic pathways.

CONCLUSION

Our study provides comprehensive insights into the landscape of HDACs in BCa, elucidating their roles in tumor heterogeneity, immune modulation, drug responsiveness, and molecular features. EMP1 is a potential therapeutic target and prognostic marker for BCa.

Targeting histone modifiers in bladder cancer therapy - preclinical and clinical evidence

Bladder cancer in the most advanced, muscle-invasive stage is lethal, and very limited therapeutic advances have been reported for decades. To date, cisplatin-based chemotherapy remains the first-line therapy for advanced bladder cancer. Late-line options have historically been limited. In the past few years, next-generation sequencing technology has enabled chromatin remodelling gene mutations to be characterized, showing that these alterations are more frequent in urothelial bladder carcinoma than in other cancer types. Histone modifiers have functional roles in tumour progression by modulating the expression of tumour suppressors and oncogenes and, therefore, have been considered as novel drug targets for cancer therapy. The roles of epigenetic reprogramming through histone modifications have been increasingly studied in bladder cancer, and the therapeutic efficacy of targeting those histone modifiers genetically or chemically is being assessed in preclinical studies. Results from preclinical studies in bladder cancer encouraged the investigation of some of these drugs in clinical trials, which yield mixed results. Further understanding of how alterations of histone modification mechanistically contribute to bladder cancer progression, drug resistance and tumour microenvironment remodelling will be required to facilitate clinical application of epigenetic drugs in bladder cancer.

Ginsenoside Rh4 inhibits breast cancer growth through targeting histone deacetylase 2 to regulate immune microenvironment and apoptosis

High expression of histone deacetylase 2 (HDAC2) is recognized as a marker of invasive breast cancer (BC). HDAC2 is not only responsible for enhancing tumor cell growth, development, and anti-apoptosis, but also plays a significant role in regulating PD-L1 on the surface of tumor cells. Continuous expression of PD-L1 allows tumor cells to escape immune surveillance. There is not much research on how HDAC2 affects the immune system in breast cancer. Ginsenoside Rh4 (Rh4) is a major rare saponin in heat-treated ginseng, which is widely applied in treating and preventing various diseases because of its potent medicinal value and stable safety. However, it is unclear how Rh4 affects the tumor immune microenvironment in breast cancer. Therefore, this paper aims to investigate the effect of Rh4 on HDAC2 in breast cancer, specifically the effect of HDAC2 on apoptosis and the immune microenvironment to inhibit breast cancer growth. According to our study, ginsenoside Rh4 has been shown to significantly suppress breast cancer cell proliferation without any adverse effects. The molecular docking results of Rh4 and HDAC2 indicate a binding energy of -6.06 kcal/mol, suggesting the potential of Rh4 as a targeting modulator of HDAC2. Mechanistically, Rh4 induces apoptosis of breast cancer cells by the HDAC2-mediated caspase pathway and inhibits the HDAC2-mediated JAK/STAT pathway to regulate the immune microenvironment, which inhibits breast cancer growth. Specifically, Rh4 was shown for the first time to blockade immune checkpoints (PD-1/PD-L1) and increase levels of T-lymphocytes in the tumor. In a word, our study establishes a theoretical framework for applying Rh4 as an immune checkpoint inhibitor as part of breast cancer treatment.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Epigenetic Priming and Development of New Combination Therapy Approaches

Muscle-invasive urothelial carcinoma of the bladder (MIBC) has been treated with cisplatin-based chemotherapy for over 30 years. With the advent of immune checkpoint inhibitors, antibody drug conjugates and FGFR3 inhibitors new therapeutic options have been approved for patients with urothelial carcinoma (UC) and are still under investigation regarding association between patients' response and recently defined molecular subtypes. Unfortunately, similar to chemotherapy, only a fraction of UC patients responds to these new treatment approaches. Thus, either further new efficacious therapeutic options for treatment of individual subtypes or new approaches to overcome treatment resistance and to increase patients' response to standard of care treatment are needed.Epigenetic modifications of DNA and chromatin are known to mediate cellular plasticity or treatment resistance, and the responsible epigenetic regulators are frequently mutated or aberrantly expressed in UC. Thus, these enzymes provide targets for novel drug combination therapies to "episensitize" toward approved standard therapies by epigenetic priming. In general, these epigenetic regulators comprise writers and erasers like DNA methyltransferases and DNA demethylases (for DNA methylation), histone methyltransferases and histone demethylases (for histone methylation), as well as acetyl transferases and histone deacetylases (for histone and nonhistone acetylation). Such modifications, e.g., acetyl groups, are recognized by further epigenetic reader proteins, e.g., like the bromodomain and extra-terminal domain (BET) family proteins that often interact in multi-protein complexes and finally regulate chromatin conformation and transcriptional activity.Concurringly, epigenetic regulators target a plethora of cellular functions. Their pharmaceutical inhibitors often inhibit enzymatic activity of more than one isoenzyme or may have further noncanonical cytotoxic effects. Thus, analysis of their functions in UC pathogenesis as well as of the antineoplastic capacity of corresponding inhibitors alone or in combination with other approved drugs should follow a multidimensional approach. Here, we present our standard approach to analyze cellular effects of new epigenetic inhibitors on UC cells alone to define their potency and to conclude on putative reasonable combination therapy partners. We further describe our approach to identify efficacious synergistic combination therapies (e.g., with cisplatin or PARP inhibitors) that may have reduced normal toxicity through dose reduction, which can then be further analyzed in animal experiments. This approach may also serve as prototype for the preclinical evaluation of other epigenetic treatment approaches.

The Potential Role of Mitochondrial Acetaldehyde Dehydrogenase 2 in Urological Cancers From the Perspective of Ferroptosis and Cellular Senescence

Overproduction of reactive oxygen species (ROS) and superlative lipid peroxidation promote tumorigenesis, and mitochondrial aldehyde dehydrogenase 2 (ALDH2) is associated with the detoxification of ROS-mediated lipid peroxidation-generated reactive aldehydes such as 4-hydroxy-2-nonenal (4-HNE), malondialdehyde, and acrolein due to tobacco smoking. ALDH2 has been demonstrated to be highly associated with the prognosis and chemoradiotherapy sensitivity of many types of cancer, including leukemia, lung cancer, head and neck cancer, esophageal cancer, hepatocellular cancer, pancreatic cancer, and ovarian cancer. In this study, we explored the possible relationship between ALDH2 and urological cancers from the aspects of ferroptosis, epigenetic alterations, proteostasis, mitochondrial dysfunction, and cellular senescence.

Molecularly Targeted Therapy towards Genetic Alterations in Advanced Bladder Cancer

Despite the introduction of immune checkpoint inhibitors and antibody-drug conjugates to the management of advanced urothelial carcinoma, the disease is generally incurable. The increasing incorporation of next-generation sequencing of tumor tissue into the characterization of bladder cancer has led to a better understanding of the somatic genetic aberrations potentially involved in its pathogenesis. Genetic alterations have been observed in kinases, such as FGFRs, ErbBs, PI3K/Akt/mTOR, and Ras-MAPK, and genetic alterations in critical cellular processes, such as chromatin remodeling, cell cycle regulation, and DNA damage repair. However, activating mutations or fusions of FGFR2 and FGFR3 remains the only validated therapeutically actionable alteration, with erdafitinib as the only targeted agent currently approved for this group. Bladder cancer is characterized by genomic heterogeneity and a high tumor mutation burden. This review highlights the potential relevance of aberrations and discusses the current status of targeted therapies directed at them.

Reduction of Metastasis via Epigenetic Modulation in a Murine Model of Metastatic Triple Negative Breast Cancer (TNBC)

This study investigates the effects of a dual selective Class I histone deacetylase (HDAC)/lysine-specific histone demethylase 1A (LSD1) inhibitor known as 4SC-202 (Domatinostat) on tumor growth and metastasis in a highly metastatic murine model of Triple Negative Breast Cancer (TNBC). 4SC-202 is cytotoxic and cytostatic to the TNBC murine cell line 4T1 and the human TNBC cell line MDA-MB-231; the drug does not kill the normal breast epithelial cell line MCF10A. Furthermore, 4SC-202 reduces cancer cell migration. In vivo studies conducted in the syngeneic 4T1 model, which closely mimics human TNBC in terms of sites of metastasis, reveal reduced tumor burden and lung metastasis. The mechanism of action of 4SC-202 may involve effects on cancer stem cells (CSC) which can self-renew and form metastatic lesions. Approximately 5% of the total 4T1 cell population grown in three-dimensional scaffolds had a distinct CD44high/CD24low CSC profile which decreased after treatment. Bulk transcriptome (RNA) sequencing analyses of 4T1 tumors reveal changes in metastasis-related pathways in 4SC-202-treated tumors, including changes to expression levels of genes implicated in cell migration and cell motility. In summary, 4SC-202 treatment of tumors from a highly metastatic murine model of TNBC reduces metastasis and warrants further preclinical studies.

Alterations of Chromatin Regulators in the Pathogenesis of Urinary Bladder Urothelial Carcinoma

Simple Summary

Urinary bladder cancer is one of the ten major cancers worldwide, with higher incidences in males, in smokers, and in highly industrialized countries. New therapies beyond cytotoxic chemotherapy are urgently needed to improve treatment of these tumors. A better understanding of the mechanisms underlying their development may help in this regard. Recently, it was discovered that a group of proteins regulating the state of chromatin and thus gene expression is exceptionally and frequently affected by gene mutations in bladder cancers. Altered function of these mutated chromatin regulators must therefore be fundamental in their development, but how and why is poorly understood. Here we review the current knowledge on changes in chromatin regulators and discuss their possible consequences for bladder cancer development and options for new therapies.

Abstract

Urothelial carcinoma (UC) is the most frequent histological type of cancer in the urinary bladder. Genomic changes in UC activate MAPK and PI3K/AKT signal transduction pathways, which increase cell proliferation and survival, interfere with cell cycle and checkpoint control, and prevent senescence. A more recently discovered additional category of genetic changes in UC affects chromatin regulators, including histone-modifying enzymes (KMT2C, KMT2D, KDM6A, EZH2), transcription cofactors (CREBBP, EP300), and components of the chromatin remodeling complex SWI/SNF (ARID1A, SMARCA4). It is not yet well understood how these changes contribute to the development and progression of UC. Therefore, we review here the emerging knowledge on genomic and gene expression alterations of chromatin regulators and their consequences for cell differentiation, cellular plasticity, and clonal expansion during UC pathogenesis. Our analysis identifies additional relevant chromatin regulators and suggests a model for urothelial carcinogenesis as a basis for further mechanistic studies and targeted therapy development.

Molecular Characterization and Clinical Relevance of Lysine Acetylation Regulators in Urological Cancers

Background

Lysine acetylation and deacetylation are posttranslational modifications that are able to link extracellular signals to intracellular responses. However, knowledge regarding the status of lysine regulators in urological cancers is still unknown.

Methods

We first systematically analyzed the genetic and expression alterations of 31 lysine acetylation regulators in urological cancers. The correlation between lysine acetylation regulators and activation of cancer pathways was explored. The clinical relevance of lysine acetylation regulators was further analyzed.

Results

We identified that there are widespread genetic alterations of lysine acetylation regulators, and that their expression levels are significantly associated with the activity of cancer hallmark-related pathways. Moreover, lysine acetylation regulators were found to be potentially useful for prognostic stratification. HDAC11 may act as a potential oncogene in cell cycle and oxidative phosphorylation of urological cancers.

Conclusion

Lysine acetylation regulators are involved in tumorigenesis and progression. Our results provide a valuable resource that will guide both mechanistic and therapeutic analyses of the role of lysine acetylation regulators in urological cancers.

Epigenetic Treatment of Urothelial Carcinoma Cells Sensitizes to Cisplatin Chemotherapy and PARP Inhibitor Treatment

Simple Summary

Muscle-invasive urothelial carcinoma of the bladder (UC) is treated with chemotherapies based on the DNA-damaging drug cisplatin, which only works temporarily due to the development of drug resistance. In this study, we show that it may be possible to overcome such resistances by treating the cancer cells with specific epigenetic drugs. We investigated the “epidrug” PLX51107 that inhibits the chromatin regulator BRD4 (Bromodomain Containing 4). PLX51107 inhibited cell growth, caused DNA damage, and blocked DNA repair response in UC cells. Concomitant application of PLX51107 with cisplatin or the drug talazoparib, interfering with DNA repair, caused cell death very efficiently. PLX51107 thus sensitizes UC cells to other drugs and may allow therapy with novel effective anti-tumor drugs like talazoparib that normally only work in a small proportion of patients with specific gene mutations. These results may help to improve current standard therapy and to develop new treatment options urgently required for UC patients.

Abstract

Muscle-invasive urothelial carcinoma (UC) is treated with cisplatin-based chemotherapy, which is only moderately efficient, mostly due to development of resistance. New therapy approaches are therefore urgently needed. Epigenetic alterations due to frequent mutations in epigenetic regulators contribute to development of the disease and to treatment resistance, and provide targets for novel drug combination therapies. Here, we determined the cytotoxic impact of the second-generation bromodomain protein inhibitor (BETi) PLX51107 on UC cell lines (UCC) and normal HBLAK control cells. PLX51107 inhibited proliferation, induced apoptosis, and acted synergistically with the histone deacetylase inhibitor romidepsin. While PLX51107 caused significant DNA damage, DNA damage signaling and DNA repair were impeded, a state defined as BRCAness. Accordingly, the drug strongly synergized with cisplatin more efficiently than romidepsin, and with the PARP inhibitor talazoparib to inhibit proliferation and induce cell death in UCC. Thus, a BETi can be used to “episensitize” UC cells to cytotoxic chemotherapy and inhibitors of DNA repair by inducing BRCAness in non BRCA1/2 mutated cancers. In clinical applications, the synergy between PLX51107 and other drugs should permit significant dosage reductions to minimize effects on normal tissues.

Downregulation of Cell Cycle and Checkpoint Genes by Class I HDAC Inhibitors Limits Synergism with G2/M Checkpoint Inhibitor MK-1775 in Bladder Cancer Cells

Since genes encoding epigenetic regulators are often mutated or deregulated in urothelial carcinoma (UC), they represent promising therapeutic targets. Specifically, inhibition of Class-I histone deacetylase (HDAC) isoenzymes induces cell death in UC cell lines (UCC) and, in contrast to other cancer types, cell cycle arrest in G2/M. Here, we investigated whether mutations in cell cycle genes contribute to G2/M rather than G1 arrest, identified the precise point of arrest and clarified the function of individual HDAC Class-I isoenzymes. Database analyses of UC tissues and cell lines revealed mutations in G1/S, but not G2/M checkpoint regulators. Using class I-specific HDAC inhibitors (HDACi) with different isoenzyme specificity (Romidepsin, Entinostat, RGFP966), cell cycle arrest was shown to occur at the G2/M transition and to depend on inhibition of HDAC1/2 rather than HDAC3. Since HDAC1/2 inhibition caused cell-type-specific downregulation of genes encoding G2/M regulators, the WEE1 inhibitor MK-1775 could not overcome G2/M checkpoint arrest and therefore did not synergize with Romidepsin inhibiting HDAC1/2. Instead, since DNA damage was induced by inhibition of HDAC1/2, but not of HDAC3, combinations between inhibitors of HDAC1/2 and of DNA repair should be attempted.

Histone deacetylase 6 inhibition in urothelial cancer as a potential new strategy for cancer treatment

Histone deacetylases (HDACs) are enzymes that remove acetyl groups from histones and have attracted attention as potential targets for cancer therapy. Several small molecule inhibitors have been developed to target HDACs; however, clinical trials of pan-HDAC inhibitors have found these types of inhibitors to be inefficient and to be relatively highly toxic. In the present study, the role of one HDAC isozyme, HDAC6, in urothelial cancer was investigated. Protein expression levels and subcellular localization of HDAC6 was identified in surgically resected bladder tumors using immunohistochemistry. The antitumor effects of 12 small molecule HDAC6 inhibitors were also examined in vitro using cultured urothelial cancer cells. The HDAC6 inhibitors decreased cell viability, with IC₅₀ values in the low µM range, as low as 2.20 µM. HDACi D, E and F had the lowest IC₅₀ values. HDAC6 has been previously reported to regulate programmed death-ligand 1 (PD-L1) and PD-L1 expression was found to be a predictor of decreased overall survival time. There was no association between the protein expression level of HDAC6 and PD-L1 in tumor tissues; however, HDAC6 inhibition by specific small molecule inhibitors resulted in decreased expression levels of membranous PD-L1 in cultured urothelial cancer cell lines. The results suggested that inhibition of HDAC6 could be a promising novel approach for the treatment of urothelial cancer.

HDAC5 Expression in Urothelial Carcinoma Cell Lines Inhibits Long-Term Proliferation but Can Promote Epithelial-to-Mesenchymal Transition

Class I histone deacetylases (HDACs) generally promote cell proliferation and tumorigenesis, whereas class IIA HDACs like HDAC4 and HDAC5 may promote or impede cancer development in a tissue-dependent manner. In urothelial carcinoma (UC), HDAC5 is often downregulated. Accordingly, HDAC5 was weakly expressed in UC cell lines suggesting a possible tumor-suppressive function. We therefore characterized the effects of stable HDAC5 expression in four UC cell lines (RT112, VM-Cub-1, SW1710 and UM-UC-3) with different phenotypes reflecting the heterogeneity of UC, by assessing proliferation, clonogenicity and migration ability. Further, we detailed changes in the proteome and transcriptome by immunoblotting, mass spectrometry and RNA sequencing analysis. We observed that HDAC5 overexpression in general decreased cell proliferation, but in one cell line (VM-Cub-1) induced a dramatic change from an epitheloid to a mesenchymal phenotype, i.e., epithelial-mesenchymal transition (EMT). These phenotypical changes were confirmed by comprehensive proteomics and transcriptomics analyses. In contrast to HDAC5, overexpression of HDAC4 exerted only weak effects on cell proliferation and phenotypes. We conclude that overexpression of HDAC5 may generally decrease proliferation in UC, but, intriguingly, may induce EMT on its own in certain circumstances.

Revisiting Histone Deacetylases in Human Tumorigenesis: The Paradigm of Urothelial Bladder Cancer

Urinary bladder cancer is a common malignancy, being characterized by substantial patient mortality and management cost. Its high somatic-mutation frequency and molecular heterogeneity usually renders tumors refractory to the applied regimens. Hitherto, methotrexate-vinblastine-adriamycin-cisplatin and gemcitabine-cisplatin represent the backbone of systemic chemotherapy. However, despite the initial chemosensitivity, the majority of treated patients will eventually develop chemoresistance, which severely reduces their survival expectancy. Since chromatin regulation genes are more frequently mutated in muscle-invasive bladder cancer, as compared to other epithelial tumors, targeted therapies against chromatin aberrations in chemoresistant clones may prove beneficial for the disease. “Acetyl-chromatin” homeostasis is regulated by the opposing functions of histone acetyltransferases (HATs) and histone deacetylases (HDACs). The HDAC/SIRT (super-)family contains 18 members, which are divided in five classes, with each family member being differentially expressed in normal urinary bladder tissues. Since a strong association between irregular HDAC expression/activity and tumorigenesis has been previously demonstrated, we herein attempt to review the accumulated published evidences that implicate HDACs/SIRTs as critical regulators in urothelial bladder cancer. Moreover, the most extensively investigated HDAC inhibitors (HDACis) are also analyzed, and the respective clinical trials are also described. Interestingly, it seems that HDACis should be preferably used in drug-combination therapeutic schemes, including radiation.

Effects of novel HDAC inhibitors on urothelial carcinoma cells

Background

Histone deacetylase inhibitors (HDACi) are promising anti-cancer drugs that could also be employed for urothelial carcinoma (UC) therapy. It is unclear, however, whether inhibition of all 11 zinc-dependent HDACs or of individual enzymes is more efficacious and specific. Here, we investigated the novel HDACi 19i (LMK235) with presumed preferential activity against class IIA HDAC4/5 in comparison to the pan-HDACi vorinostat (SAHA) and the HDAC4-specific HDACi TMP269 in UC cell lines with basal expression of HDAC4 and characterized two HDAC4-overexpressing UC cell lines.

Methods

Cytotoxic concentrations 50% (CC₅₀s) for HDACi were determined by MTT assay and high-content analysis-based fluorescent live/dead assay in UC cell lines with different expression of HDAC4 and as well as in normal urothelial cell cultures, HBLAK and HEK-293 cell lines. Effects of HDACis were analyzed by flow cytometry; molecular changes were followed by qRT-PCR and Western blots. UC lines overexpressing HDAC4 were established by lentiviral transduction. Inhibitor activity profiles of HDACi were obtained by current state in vitro assays, and docking analysis was performed using an updated crystal structure of HDAC4.

Results

In UC cell lines, 19i CC₅₀s ranged around 1 μM; control lines were similarly or less sensitive. Like SAHA, 19i increased the G2/M-fraction, disturbed mitosis, and elicited apoptosis or in some cells senescence. Thymidylate synthase expression was diminished, and p21^CIP1 was induced; global histone acetylation and α-tubulin acetylation also increased. In most cell lines, 19i as well as SAHA induced HDAC5 and HDAC4 mRNAs while rather repressing HDAC7. UC cell lines overexpressing HDAC4 were not significantly less sensitive to 19i. Reevaluation of the in vitro HDAC isoenzyme activity inhibition profile of 19i and its docking to HDAC4 using current assays suggested rather low activity against class IIA HDACs. The specific class IIA HDAC inhibitor TMP269 impeded proliferation of UC cell lines only at concentrations > 10 μM.

Conclusions

Anti-neoplastic effects of 19i on UC cells appear to be exerted by targeting class I HDACs. In fact, HDAC4 may rather impede UC growth. Our results suggest that targeting of class IIA HDACs 4/5 may not be optimal for UC therapy. Moreover, our investigation provides further evidence for cross-regulation of class IIA HDACs by class I HDACs.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0531-y) contains supplementary material, which is available to authorized users.

Combined inhibition of BET proteins and class I HDACs synergistically induces apoptosis in urothelial carcinoma cell lines

Background

New efficient therapies for urothelial carcinoma (UC) are urgently required. Small-molecule drugs targeting chromatin regulators are reasonable candidates because these regulators are frequently mutated or deregulated in UC. Indeed, in previous work, Romidepsin, which targets class I histone deacetylases (HDAC), efficiently killed UC cells, but did not elicit canonical apoptosis and affected benign urothelial cells indiscriminately. Combinations of HDAC inhibitors with JQ1, an inhibitor of bromodomain-containing acetylation reader proteins like BRD4, which promote especially the transcription of pro-tumorigenic genes, have shown efficacy in several tumor types. We therefore investigated the effects of combined Romidepsin and JQ1 treatment on UC and benign urothelial control cells.

Results

JQ1 alone induced cell cycle arrest, but only limited apoptosis in eight UC cell lines with strongly varying IC₅₀ values between 0.18 and 10 μM. Comparable effects were achieved by siRNA-mediated knockdown of BRD4. Romidepsin and JQ1 acted in a synergistic manner across all UC cell lines, efficiently inhibiting cell cycle progression, suppressing clonogenic growth, and inducing caspase-dependent apoptosis. Benign control cells were growth-arrested without apoptosis induction, but retained long-term proliferation capacity. In UC cells, anti-apoptotic and oncogenic factors Survivin, BCL-2, BCL-XL, c-MYC, EZH2 and SKP2 were consistently downregulated by the drug combination and AKT phosphorylation was diminished. Around the transcriptional start sites of these genes, the drug combination enhanced H3K27 acetylation, but decreased H3K4 trimethylation. The cell cycle inhibitor CDKN1C/p57^KIP2 was dramatically induced at mRNA and protein levels. However, Cas9-mediated CDKN1C/p57^KIP2 knockout did not rescue UC cells from apoptosis.

Conclusion

Our results demonstrate significant synergistic effects on induction of apoptosis in UC cells by the combination treatment with JQ1 and Romidepsin, but only minor effects in benign cells. Thus, this study established a promising new small-molecule combination therapy approach for UC.

Electronic supplementary material

The online version of this article (10.1186/s13148-017-0434-3) contains supplementary material, which is available to authorized users.

Epigenetic Treatment Options in Urothelial Carcinoma

Mutations, dysregulation, and dysbalance of epigenetic regulators are especially frequent in urothelial carcinoma (UC) compared to other malignancies. Accordingly, targeting epigenetic regulators may provide a window of opportunity particularly in anticancer therapy of UC. In general, these epigenetic regulators comprise DNA methyltransferases and DNA demethylases (for DNA methylation), histone methyltransferases, and histone demethylases (for histone methylation) as well as acetyl transferases and histone deacetylases (for histone and non-histone acetylation).As epigenetic regulators target a plethora of cellular functions and available inhibitors often inhibit enzymatic activity of more than one isoenzyme or may have further off-target effects, analysis of their functions in UC pathogenesis as well as of the antineoplastic capacity of according inhibitors should follow a multidimensional approach.Here, we present our standard approach for the analysis of the cellular and molecular functions of individual HDAC enzymes, their suitability as treatment targets and for the evaluation of isoenzyme-specific HDAC inhibitors regarding their antineoplastic efficacy. This approach may also serve as prototype for the preclinical evaluation of other epigenetic treatment approaches.