Regulation of STAT3 by histone deacetylase-3 in diffuse large B-cell lymphoma: implications for therapy

Chemical interplay between gut microbiota and epigenetics: Implications in circadian biology

Circadian rhythms are intrinsic molecular mechanisms that synchronize biological functions with the day/night cycle. The mammalian gut is colonized by a myriad of microbes, collectively named the gut microbiota. The microbiota impacts host physiology via metabolites and structural components. A key mechanism is the modulation of host epigenetic pathways, especially histone modifications. An increasing number of studies indicate the role of the microbiota in regulating host circadian rhythms. However, the mechanisms remain largely unknown. Here, we summarize studies on microbial regulation of host circadian rhythms and epigenetic pathways, highlight recent findings on how the microbiota employs host epigenetic machinery to regulate circadian rhythms, and discuss its impacts on host physiology, particularly immune and metabolic functions. We further describe current challenges and resources that could facilitate research on microbiota-epigenetic-circadian rhythm interactions to advance our knowledge of circadian disorders and possible therapeutic avenues.

Deacetylase Sirtuin 1 mitigates type I IFN- and type II IFN-induced signaling and antiviral immunity

Type I and type II IFNs are important immune modulators in both innate and adaptive immunity. They transmit signaling by activating JAK-STAT pathways. Sirtuin 1 (SIRT1), a class III NAD+-dependent deacetylase, has multiple functions in a variety of physiological processes. Here, we characterized the novel functions of SIRT1 in the regulation of type I and type II IFN-induced signaling. Overexpression of SIRT1 inhibited type I and type II IFN-induced interferon-stimulated response element activation. In contrast, knockout of SIRT1 promoted type I and type II IFN-induced expression of ISGs and inhibited viral replication. Treatment with SIRT1 inhibitor EX527 had similar positive effects. SIRT1 physically associated with STAT1 or STAT3, and this interaction was enhanced by IFN stimulation or viral infection. By deacetylating STAT1 at K673 and STAT3 at K679/K685/K707/K709, SIRT1 downregulated the phosphorylation of STAT1 (Y701) and STAT3 (Y705). Sirt1+/- primary peritoneal macrophages and Sirt1+/- mice exhibited enhanced IFN-induced signaling and antiviral activity. Thus, SIRT1 is a novel negative regulator of type I and type II IFN-induced signaling through its deacetylase activity.IMPORTANCESIRT1 has been reported in the precise regulation of antiviral (RNA and DNA) immunity. However, its functions in type I and type II IFN-induced signaling are still unclear. In this study, we deciphered the important functions of SIRT1 in both type I and type II IFN-induced JAK-STAT signaling and explored the potential acting mechanisms. It is helpful for understanding the regulatory roles of SIRT1 at different levels of IFN signaling. It also consolidates the notion that SIRT1 is an important target for intervention in viral infection, inflammatory diseases, or even interferon-related therapies.

Current treatment strategies targeting histone deacetylase inhibitors in acute lymphocytic leukemia: a systematic review

Acute lymphocytic leukemia is a hematological malignancy that primarily affects children. Long-term chemotherapy is effective, but always causes different toxic side effects. With the application of a chemotherapy-free treatment strategy, we intend to demonstrate the most recent results of using one type of epigenetic drug, histone deacetylase inhibitors, in ALL and to provide preclinical evidence for further clinical trials. In this review, we found that panobinostat (LBH589) showed positive outcomes as a monotherapy, whereas vorinostat (SAHA) was a better choice for combinatorial use. Preclinical research has identified chidamide as a potential agent for investigation in more clinical trials in the future. In conclusion, histone deacetylase inhibitors play a significant role in the chemotherapy-free landscape in cancer treatment, particularly in acute lymphocytic leukemia.

The acetylation of STAT3 at K685 attenuates NPM-ALK-induced tumorigenesis

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), a fusion protein generated by a chromosomal translocation, is a causative gene product of anaplastic large cell lymphoma (ALCL). It induces cell proliferation and tumorigenesis by activating the transcription factor, signal transducer and activator of transcription factor 3 (STAT3). We herein demonstrated that STAT3 underwent acetylation at K685 in a manner that was dependent on the kinase activity of NPM-ALK. To investigate the role of STAT3 acetylation in NPM-ALK-induced oncogenesis, we generated Ba/F3 cells expressing NPM-ALK in which STAT3 was silenced by shRNA, named STAT3-KD cells, and then reconstituted wild-type STAT3 or the STAT3 K685R mutant into these cells. The phosphorylation level of the K685R mutant at Y705 and S727 was significantly higher than that of wild-type STAT3 in STAT3-KD cells. The expression of STAT3 target genes, such as IL-6, Pim1, Pim2, and Socs3, was more strongly induced by the reconstitution of the K685R mutant than wild-type STAT3. In addition, the proliferative ability of STAT3-KD cells reconstituted with the K685R mutant was slightly higher than that of STAT3-KD cells reconstituted with wild-type STAT3. In comparisons with the inoculation of STAT3-KD cells reconstituted with wild-type STAT3, the inoculation of STAT3-KD cells reconstituted with the K685R mutant significantly enhanced tumorigenesis and hepatosplenomegaly in nude mice. Collectively, these results revealed for the first time that the acetylation of STAT3 at K685 attenuated NPM-ALK-induced oncogenesis.

Romidepsin and Afatinib Abrogate Jak-Signal Transducer and Activator of Transcription Signaling and Elicit Synergistic Antitumor Effects in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphomas are mature lymphoid neoplasias resulting from the malignant transformation of skin-resident T-cells. A distinctive clinical feature of cutaneous T-cell lymphomas is their sensitivity to treatment with histone deacetylase inhibitors. However, responses to histone deacetylase inhibitor therapy are universally transient and noncurative, highlighting the need for effective and durable drug combinations. In this study, we demonstrate that the combination of romidepsin, a selective class I histone deacetylase inhibitor, with afatinib, an EGFR family inhibitor, induces strongly synergistic antitumor effects in cutaneous T-cell lymphoma models in vitro and in vivo through abrogation of Jak-signal transducer and activator of transcription signaling. These results support a previously unrecognized potential role for histone deacetylase inhibitor plus afatinib combination in the treatment of cutaneous T-cell lymphomas.

Integrative function of histone deacetylase 3 in inflammation

Inflammation is a complex biological response triggered when an organism encounters internal or external stimuli. These triggers activate various signaling pathways, leading to the release of numerous inflammatory mediators aimed at the affected tissue. Ensuring precision and avoiding the excessive activation, the inflammatory process is subject to tight regulation. Histone deacetylase 3 (HDAC3), a member of class I HDACs family, stands out for its significant role in modulating various inflammatory signaling, including Nuclear Factor kappa B (NF-κB) signaling, Mitogen-activated protein kinase (MAPK) signaling and Janus kinase/signal transduction and activator of transcription (JAK-STAT) signaling. In this review, we illuminate the intricate molecular mechanisms of HDAC3 across these inflammatory pathways. We emphasize its importance in orchestrating a balanced inflammatory response and highlight its promising potential as a therapeutic target.

Discovery of 4-((3,4-dichlorophenyl)amino)-2-methylquinolin-6-ol derivatives as EGFR and HDAC dual inhibitors

In patients with non-small cell lung cancer (NSCLC), the standard therapy consists of selective tyrosine kinase inhibitors that target epidermal growth factor receptors (EGFR). Nonetheless, their clinical utility is primarily limited by the development of resistance to drugs. HDAC inhibitors have been shown in studies to reduce the level of EGFR that is expressed and downregulate the EGFR-induced phosphorylation of AKT and ERK. Therefore, dual inhibitors of EGFR and HDAC provide a potential approach as combination treatment synergistically inhibited the growth of NSCLC. Herein, we examined the EGFR inhibition effect of twenty compounds which designed and synthesized by us previously. Among them, compounds 12c and 12d exhibited powerful antiproliferative activity against the NCI-H1975 cell line with IC50 values of 0.48 ± 0.07 and 0.35 ± 0.02 μM, correspondingly. In cell-free kinase assays, both 12c and 12d demonstrated target-specific EGFR inhibition against wild type (EGFRwt). Furthermore, the expression of EGFR and phosphorylation of the EGF-induced pathways were significantly suppressed under the treatment of 12c and 12d. Besides, both histones H3 and H4 exhibited increased levels of acetylation following 12c and 12d treatment. The animal experiments shown that 12d could prevent the growth of tumor, inhibited the expression of EGFR and the phosphorylation levels of p70 S6K, AKT and p38 MAPK in vivo, and did not cause organ damage to the mice during the experiment. Overall, the results illustrated that compound 12c and 12d could serve as effective EGFR and HDAC dual inhibitors in NSCLC cells. Our work offers an alternative strategy for NSCLC therapy.

Exploring the role of epigenetic alterations and non-coding RNAs in melanoma pathogenesis and therapeutic strategies

Melanoma is a rare but highly lethal type of skin cancer whose incidence is increasing globally. Melanoma is characterized by high resistance to therapy and relapse. Despite significant advances in the treatment of metastatic melanoma, many patients experience progression due to resistance mechanisms. Epigenetic changes, including alterations in chromatin remodeling, DNA methylation, histone modifications, and non-coding RNA rearrangements, contribute to neoplastic transformation, metastasis, and drug resistance in melanoma. This review summarizes current research on epigenetic mechanisms in melanoma and their therapeutic potential. Specifically, we discuss the role of histone acetylation and methylation in gene expression regulation and melanoma pathobiology, as well as the promising results of HDAC inhibitors and DNMT inhibitors in clinical trials. We also examine the dysregulation of non-coding RNA, particularly miRNAs, and their potential as targets for melanoma therapy. Finally, we highlight the challenges of epigenetic therapies, such as the complexity of epigenetic mechanisms combined with immunotherapies and the need for combination therapies to overcome drug resistance. In conclusion, epigenetic changes may be reversible, and the use of combination therapy between traditional therapies and epigenetically targeted drugs could be a viable solution to reverse the increasing number of patients who develop treatment resistance or even prevent it. While several clinical trials are underway, the complexity of these mechanisms presents a significant challenge to the development of effective therapies. Further research is needed to fully understand the role of epigenetic mechanisms in melanoma and to develop more effective and targeted therapies.

Development of Lysine Crotonyl-Mimic Probe to Covalently Identify H3K27Cr Interacting Proteins

Histone lysine crotonylation (Kcr) is one newly discovered acylation modification and regulates numerous pathophysiological processes. The binding affinity between Kcr and its interacting proteins is generally weak, which makes it difficult to effectively identify Kcr-interacting partners. Changing the amide of crotonyl to an ester increased reactivity with proximal cysteines and retained specificity for Kcr antibody. The probe "H3g27Cr" was designed by incorporating the ester functionality into a H3K27 peptide. Using this probe, multiple Kcr-interacting partners including STAT3 were successfully identified, and this has not been reported previously. Further experiments suggested that STAT3 possibly could form complexes with Histone deacetylase HDACs to downregulate the acetylation and crotonylation of Histone H3K27. Our unique design provided intriguing tools to further explore Kcr-interacting proteins and elucidate their working mechanisms.

PROTAC chemical probes for histone deacetylase enzymes

Over the past three decades, we have witnessed the progression of small molecule chemical probes designed to inhibit the catalytic active site of histone deacetylase (HDAC) enzymes into FDA approved drugs. However, it is only in the past five years we have witnessed the emergence of proteolysis targeting chimeras (PROTACs) capable of promoting the proteasome mediated degradation of HDACs. This is a field still in its infancy, however given the current progress of PROTACs in clinical trials and the fact that FDA approved HDAC drugs are already in the clinic, there is significant potential in developing PROTACs to target HDACs as therapeutics. Beyond therapeutics, PROTACs also serve important applications as chemical probes to interrogate fundamental biology related to HDACs via their unique degradation mode of action. In this review, we highlight some of the key findings to date in the discovery of PROTACs targeting HDACs by HDAC class and HDAC isoenzyme, current gaps in PROTACs to target HDACs and future outlooks.

Histone modifications in drug-resistant cancers: From a cancer stem cell and immune evasion perspective

The development and immune evasion of cancer stem cells (CSCs) limit the efficacy of currently available anticancer therapies. Recent studies have shown that epigenetic reprogramming regulates the expression of characteristic marker proteins and tumor plasticity associated with cancer cell survival and metastasis in CSCs. CSCs also possess unique mechanisms to evade external attacks by immune cells. Hence, the development of new strategies to restore dysregulated histone modifications to overcome cancer resistance to chemotherapy and immunotherapy has recently attracted attention. Restoring abnormal histone modifications can be an effective anticancer strategy to increase the therapeutic effect of conventional chemotherapeutic and immunotherapeutic drugs by weakening CSCs or by rendering them in a naïve state with increased sensitivity to immune responses. In this review, we summarize recent findings regarding the role of histone modifiers in the development of drug-resistant cancer cells from the perspectives of CSCs and immune evasion. In addition, we discuss attempts to combine currently available histone modification inhibitors with conventional chemotherapy or immunotherapy.

Research progress of STAT3-based dual inhibitors for cancer therapy

Signal transducer and activator of transcription 3 (STAT3), a transcription factor, regulates gene levels that are associated with cell survival, cell cycle, and immune reaction. It is correlated with the grade of malignancy and the development of various cancers and targeting STAT3 protein is a potentially promising therapeutic strategy for tumors. Over the past 20 years, various compounds have been found to directly inhibit STAT3 activity via different strategies. However, numerous difficulties exist in the development of STAT3 inhibitors, such as serious toxic effects, poor therapeutic effects, and intrinsic and acquired drug resistance. STAT3 inhibitors synergistically suppress cancer development with additional anti-tumor drugs, such as indoleamine 2,3-dioxygenase 1 inhibitors (IDO1i), histone deacetylase inhibitors (HDACi), DNA inhibitors, pro-tumorigenic cytokine inhibitors (PTCi), NF-κB inhibitors, and tubulin inhibitors. Therefore, individual molecule- based dual-target inhibitors can be the candidate alternative or complementary treatment to overcome the disadvantages of just STAT3 or other targets as a monotherapy. In this review, we discuss the theoretical basis for formulating STAT3-based dual-target inhibitors and also summarize their structure-activity relationships (SARs).

The MEF2A transcription factor interactome in cardiomyocytes

Transcriptional regulators encoded by the Myocyte Enhancer Factor 2 (MEF2) gene family play a fundamental role in cardiac development, homeostasis and pathology. Previous studies indicate that MEF2A protein-protein interactions serve as a network hub in several cardiomyocyte cellular processes. Based on the idea that interactions with regulatory protein partners underly the diverse roles of MEF2A in cardiomyocyte gene expression, we undertook a systematic unbiased screen of the MEF2A protein interactome in primary cardiomyocytes using an affinity purification-based quantitative mass spectrometry approach. Bioinformatic processing of the MEF2A interactome revealed protein networks involved in the regulation of programmed cell death, inflammatory responses, actin dynamics and stress signaling in primary cardiomyocytes. Further biochemical and functional confirmation of specific protein-protein interactions documented a dynamic interaction between MEF2A and STAT3 proteins. Integration of transcriptome level data from MEF2A and STAT3-depleted cardiomyocytes reveals that the balance between MEF2A and STAT3 activity exerts a level of executive control over the inflammatory response and cardiomyocyte cell survival and experimentally ameliorates Phenylephrine induced cardiomyocyte hypertrophy. Lastly, we identified several MEF2A/STAT3 co-regulated genes, including the MMP9 gene. Herein, we document the cardiomyocyte MEF2A interactome, which furthers our understanding of protein networks involved in the hierarchical control of normal and pathophysiological cardiomyocyte gene expression in the mammalian heart.

Histone deacetylase 5-induced deficiency of signal transducer and activator of transcription-3 acetylation contributes to spinal astrocytes degeneration in painful diabetic neuropathy

Diabetes patients with painful diabetic neuropathy (PDN) show severe spinal atrophy, suggesting pathological changes of the spinal cord contributes to central sensitization. However, the cellular changes and underlying molecular mechanisms within the diabetic spinal cord are less clear. By using a rat model of type 1 diabetes (T1D), we noted an extensive and irreversible spinal astrocyte degeneration at an early stage of T1D, which is highly associated with the chronification of PDN. Molecularly, acetylation of astrocytic signal transducer and activator of transcription-3 (STAT3) that is essential for maintaining the homeostatic astrocytes population was significantly impaired in the T1D model, resulting in a dramatic loss of spinal astrocytes and consequently promoting pain hypersensitivity. Mechanistically, class IIa histone deacetylase, HDAC5 were aberrantly activated in spinal astrocytes of diabetic rats, which promoted STAT3 deacetylation by direct protein-protein interactions, leading to the PDN phenotypes. Restoration of STAT3 signaling or inhibition of HDAC5 rescued astrocyte deficiency and attenuated PDN in the T1D model. Our work identifies the inhibitory axis of HDAC5-STAT3 induced astrocyte deficiency as a key mechanism underlying the pathogenesis of the diabetic spinal cord that paves the way for potential therapy development for PDN.

Pharmacological Modulation of the Crosstalk between Aberrant Janus Kinase Signaling and Epigenetic Modifiers of the Histone Deacetylase Family to Treat Cancer

Hyperactivated Janus kinase (JAK) signaling is an appreciated drug target in human cancers. Numerous mutant JAK molecules as well as inherent and acquired drug resistance mechanisms limit the efficacy of JAK inhibitors (JAKi). There is accumulating evidence that epigenetic mechanisms control JAK-dependent signaling cascades. Like JAKs, epigenetic modifiers of the histone deacetylase (HDAC) family regulate the growth and development of cells and are often dysregulated in cancer cells. The notion that inhibitors of histone deacetylases (HDACi) abrogate oncogenic JAK-dependent signaling cascades illustrates an intricate crosstalk between JAKs and HDACs. Here, we summarize how structurally divergent, broad-acting as well as isoenzyme-specific HDACi, hybrid fusion pharmacophores containing JAKi and HDACi, and proteolysis targeting chimeras for JAKs inactivate the four JAK proteins JAK1, JAK2, JAK3, and tyrosine kinase-2. These agents suppress aberrant JAK activity through specific transcription-dependent processes and mechanisms that alter the phosphorylation and stability of JAKs. Pharmacological inhibition of HDACs abrogates allosteric activation of JAKs, overcomes limitations of ATP-competitive type 1 and type 2 JAKi, and interacts favorably with JAKi. Since such findings were collected in cultured cells, experimental animals, and cancer patients, we condense preclinical and translational relevance. We also discuss how future research on acetylation-dependent mechanisms that regulate JAKs might allow the rational design of improved treatments for cancer patients. SIGNIFICANCE STATEMENT: Reversible lysine-ɛ-N acetylation and deacetylation cycles control phosphorylation-dependent Janus kinase-signal transducer and activator of transcription signaling. The intricate crosstalk between these fundamental molecular mechanisms provides opportunities for pharmacological intervention strategies with modern small molecule inhibitors. This could help patients suffering from cancer.

Targeting Histone Deacetylases in Idiopathic Pulmonary Fibrosis: A Future Therapeutic Option

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited therapeutic options, and there is a huge unmet need for new therapies. A growing body of evidence suggests that the histone deacetylase (HDAC) family of transcriptional corepressors has emerged as crucial mediators of IPF pathogenesis. HDACs deacetylate histones and result in chromatin condensation and epigenetic repression of gene transcription. HDACs also catalyse the deacetylation of many non-histone proteins, including transcription factors, thus also leading to changes in the transcriptome and cellular signalling. Increased HDAC expression is associated with cell proliferation, cell growth and anti-apoptosis and is, thus, a salient feature of many cancers. In IPF, induction and abnormal upregulation of Class I and Class II HDAC enzymes in myofibroblast foci, as well as aberrant bronchiolar epithelium, is an eminent observation, whereas type-II alveolar epithelial cells (AECII) of IPF lungs indicate a significant depletion of many HDACs. We thus suggest that the significant imbalance of HDAC activity in IPF lungs, with a “cancer-like” increase in fibroblastic and bronchial cells versus a lack in AECII, promotes and perpetuates fibrosis. This review focuses on the mechanisms by which Class I and Class II HDACs mediate fibrogenesis and on the mechanisms by which various HDAC inhibitors reverse the deregulated epigenetic responses in IPF, supporting HDAC inhibition as promising IPF therapy.

Tumor Immune Microenvironment in Lymphoma: Focus on Epigenetics

Lymphoma is a neoplasm arising from B or T lymphocytes or natural killer cells characterized by clonal lymphoproliferation. This tumor comprises a diverse and heterogeneous group of malignancies with distinct clinical, histopathological, and molecular characteristics. Despite advances in lymphoma treatment, clinical outcomes of patients with relapsed or refractory disease remain poor. Thus, a deeper understanding of molecular pathogenesis and tumor progression of lymphoma is required. Epigenetic alterations contribute to cancer initiation, progression, and drug resistance. In fact, over the past decade, dysregulation of epigenetic mechanisms has been identified in lymphomas, and the knowledge of the epigenetic aberrations has led to the emergence of the promising epigenetic therapy field in lymphoma tumors. However, epigenetic aberrations in lymphoma not only have been found in tumor cells, but also in cells from the tumor microenvironment, such as immune cells. Whereas the epigenetic dysregulation in lymphoma cells is being intensively investigated, there are limited studies regarding the epigenetic mechanisms that affect the functions of immune cells from the tumor microenvironment in lymphoma. Therefore, this review tries to provide a general overview of epigenetic alterations that affect both lymphoma cells and infiltrating immune cells within the tumor, as well as the epigenetic cross-talk between them.

Exploring the oncogenic and therapeutic target potential of the MYB-TYK2 fusion gene in B-cell acute lymphoblastic leukemia

TYK2-rearrangements have recently been identified in high-risk acute lymphoblastic leukemia (HR-ALL) cases and are associated with poor outcome. Current understanding of the leukemogenic potential and therapeutic targetability of activating TYK2 alterations in the ALL setting is unclear, thus further investigations are warranted. Consequently, we developed in vitro, and for the first time, in vivo models of B-cell ALL from a patient harboring the MYB-TYK2 fusion gene. These models revealed JAK/STAT signaling activation and the oncogenic potential of the MYB-TYK2 fusion gene in isolation. High throughput screening identified the HDAC inhibitor, vorinostat and the HSP90 inhibitor, tanespimycin plus the JAK inhibitor, cerdulatinib as the most effective agents against cells expressing the MYB-TYK2 alteration. Evaluation of vorinostat and cerdulatinib in pre-clinical models of MYB-TYK2-rearranged ALL demonstrated that both drugs exhibited anti-leukemic effects and reduced the disease burden in treated mice. Importantly, these findings indicate that activating TYK2 alterations can function as driver oncogenes rather than passenger or secondary events in disease development. In addition, our data provide evidence for use of vorinostat and cerdulatinib in the treatment regimens of patients with this rare yet aggressive type of high-risk ALL that warrants further investigation in the clinical setting.

Dietary phytate primes epithelial antibacterial immunity in the intestine

Although diet has long been associated with susceptibility to infection, the dietary components that regulate host defense remain poorly understood. Here, we demonstrate that consuming rice bran decreases susceptibility to intestinal infection with Citrobacter rodentium, a murine pathogen that is similar to enteropathogenic E. coli infection in humans. Rice bran naturally contains high levels of the substance phytate. Interestingly, phytate supplementation also protected against intestinal infection, and enzymatic metabolism of phytate by commensal bacteria was necessary for phytate-induced host defense. Mechanistically, phytate consumption induced mammalian intestinal epithelial expression of STAT3-regulated antimicrobial pathways and increased phosphorylated STAT3, suggesting that dietary phytate promotes innate defense through epithelial STAT3 activation. Further, phytate regulation of epithelial STAT3 was mediated by the microbiota-sensitive enzyme histone deacetylase 3 (HDAC3). Collectively, these data demonstrate that metabolism of dietary phytate by microbiota decreases intestinal infection and suggests that consuming bran and other phytate-enriched foods may represent an effective dietary strategy for priming host immunity.

Design, synthesis and binding mode of interaction of novel small molecule o-hydroxy benzamides as HDAC3-selective inhibitors with promising antitumor effects in 4T1-Luc breast cancer xenograft model

Histone deacetylase 3 (HDAC3) is one of the most promising targets to develop anticancer therapeutics. In continuation of our quest for selective HDAC3 inhibitors, a series of small molecules having o-hydroxy benzamide as the novel zinc binding group (ZBG) has been introduced for the first time that can be able to produce good HDAC3-selectivity over other HDACs. The most promising HDAC3 inhibitors, 11a and 12b, displayed promising in vitro anticancer activities with less toxicity to normal kidney cells. These compounds significantly upregulate histone acetylation and induce apoptosis with a G2/M phase arrest in B16F10 cells. Compound 11a exhibited potent antitumor efficacy in 4T1-Luc breast cancer xenograft mouse model in female Balb/c mice. It also showed significant tumor growth suppression with no general toxicity and extended survival rates post-tumor resection. It significantly induced higher ROS generation, leading to apoptosis. No considerable toxicity was noticed in major organs isolated from the compound 11a-treated mice. Compound 11a also induced the upregulation of acH3K9, acH4K12, caspase-3 and caspase-7 as analyzed by immunoblotting with treated tumor tissue. Overall, HDAC3 selective inhibitor 11a might be a potential lead for the clinical translation as an emerging drug candidate.

The contributory roles of histone deacetylases (HDACs) in hematopoiesis regulation and possibilities for pharmacologic interventions in hematologic malignancies

Although the definitive role of epigenetic modulations in a wide range of hematologic malignancies, spanning from leukemia to lymphoma and multiple myeloma, has been evidenced, few articles reviewed the task. Given the high accessibility of histone deacetylase (HDACs) to necessary transcription factors involved in hematopoiesis, this review aims to outline physiologic impacts of these enzymes in normal hematopoiesis, and also to outline the original data obtained from international research laboratories on their regulatory role in the differentiation and maturation of different hematopoietic lineages. Questions on how aberrant expression of HDACs contributes to the formation of hematologic malignancies are also responded, because these classes of enzymes have a respectable share in the development, progression, and recurrence of leukemia, lymphoma, and multiple myeloma. The last section provides a special focus on the therapeutic perspectiveof HDACs inhibitors, either as single agents or in a combined-modal strategy, in these neoplasms. In conclusion, optimizing the dose and the design of more patient-tailored inhibitors, while maintaining low toxicity against normal cells, will help improve clinical outcomes of HDAC inhibitors in hematologic malignancies.

The Roles of Post-Translational Modifications in STAT3 Biological Activities and Functions

STAT3 is an important transcription factor that regulates cell growth and proliferation by regulating gene transcription of a plethora of genes. This protein also has many roles in cancer progression and several tumors such as prostate, lung, breast, and intestine cancers that are characterized by strong STAT3-dependent transcriptional activity. This protein is post-translationally modified in different ways according to cellular context and stimulus, and the same post-translational modification can have opposite effects in different cellular models. In this review, we describe the studies performed on the main modifications affecting the activity of STAT3: phosphorylation of tyrosine 705 and serine 727; acetylation of lysine 49, 87, 601, 615, 631, 685, 707, and 709; and methylation of lysine 49, 140, and 180. The extensive results obtained by different studies demonstrate that post-translational modifications drastically change STAT3 activities and that we need further analysis to properly elucidate all the functions of this multifaceted transcription factor.

Secondary resistance to anti-EGFR therapy by transcriptional reprogramming in patient-derived colorectal cancer models

BACKGROUND

The development of secondary resistance (SR) in metastatic colorectal cancer (mCRC) treated with anti-epidermal growth factor receptor (anti-EGFR) antibodies is not fully understood at the molecular level. Here we tested in vivo selection of anti-EGFR SR tumors in CRC patient-derived xenograft (PDX) models as a strategy for a molecular dissection of SR mechanisms.

METHODS

We analyzed 21 KRAS, NRAS, BRAF, and PI3K wildtype CRC patient-derived xenograft (PDX) models for their anti-EGFR sensitivity. Furthermore, 31 anti-EGFR SR tumors were generated via chronic in vivo treatment with cetuximab. A multi-omics approach was employed to address molecular primary and secondary resistance mechanisms. Gene set enrichment analyses were used to uncover SR pathways. Targeted therapy of SR PDX models was applied to validate selected SR pathways.

RESULTS

In vivo anti-EGFR SR could be established with high efficiency. Chronic anti-EGFR treatment of CRC PDX tumors induced parallel evolution of multiple resistant lesions with independent molecular SR mechanisms. Mutations in driver genes explained SR development in a subgroup of CRC PDX models, only. Transcriptional reprogramming inducing anti-EGFR SR was discovered as a common mechanism in CRC PDX models frequently leading to RAS signaling pathway activation. We identified cAMP and STAT3 signaling activation, as well as paracrine and autocrine signaling via growth factors as novel anti-EGFR secondary resistance mechanisms. Secondary resistant xenograft tumors could successfully be treated by addressing identified transcriptional changes by tailored targeted therapies.

CONCLUSIONS

Our study demonstrates that SR PDX tumors provide a unique platform to study molecular SR mechanisms and allow testing of multiple treatments for efficient targeting of SR mechanisms, not possible in the patient. Importantly, it suggests that the development of anti-EGFR tolerant cells via transcriptional reprogramming as a cause of anti-EGFR SR in CRC is likely more prevalent than previously anticipated. It emphasizes the need for analyses of SR tumor tissues at a multi-omics level for a comprehensive molecular understanding of anti-EGFR SR in CRC.

The role of understudied post-translational modifications for the behavior and function of Signal Transducer and Activator of Transcription 3

The Signal Transducer and Activator of Transcription (STAT) family of transcription factors is involved in inflammation, immunity, development, cancer, and response to injury, among other biological phenomena. Canonical STAT signaling is often represented as a 3-step pathway involving the sequential activation of a membrane receptor, an intermediate kinase, and a STAT transcription factor. The rate-limiting phosphorylation at a highly conserved C-terminal tyrosine residue determines the nuclear translocation and transcriptional activity of STATs. This apparent simplicity is actually misleading and can hardly explain the pleiotropic nature of STATs, the existence of various noncanonical STAT pathways, or the key role of the N-terminal domain in STAT functions. More than 80 post-translational modifications (PTMs) have been identified for STAT3, but their functions remain barely understood. Here, we provide a brief but comprehensive overview of these underexplored PTMs and their role on STAT3 canonical and noncanonical functions. A less tyrosine-centric point of view may be required to advance our understanding of STAT signaling.

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.

Inactivation of the Akt/FOXM1 Signaling Pathway by Panobinostat Suppresses the Proliferation and Metastasis of Gastric Cancer Cells

Gastric cancer is the fifth most common cancer and the third leading cause of cancer-related deaths worldwide. Histone deacetylase (HDAC) inhibitors are a new class of cytostatic agents available for the treatment of various cancers and diseases. Although numerous clinical and pre-clinical trials on the anticancer effects of panobinostat have been conducted, only a few reports have investigated its efficacy in gastric cancer. The present study aimed to investigate the effects of panobinostat in gastric cancer cells. Panobinostat significantly inhibited the cell viability and proliferation of the gastric cancer cell lines SNU484 and SNU638 in a dose-dependent manner; it reduced the colony-forming ability of these cells. Moreover, it induced apoptosis as indicated by increased protein levels of cleaved poly ADP-ribose polymerase and cleaved caspase-3. Panobinostat induced the G2/M cell cycle arrest in SNU484 and SNU638 cells and subsequently decreased the G2/M phase regulatory-associated protein expression of p-Wee1, Myt1, and Cdc2. Furthermore, panobinostat significantly inhibited the metastasis of SNU484 and SNU638 cells by regulating the expression of MMP-9 and E-cadherin. Further, it decreased the protein levels of p-Akt and forkhead box protein M1 (FOXM1). These effects were reversed by the Akt agonist SC79 and were accelerated by the Akt inhibitor LY2940002. Moreover, tumor growth in xenograft animal experiments was suppressed by panobinostat. These results indicated that panobinostat inhibits the proliferation, metastasis, and cell cycle progression of gastric cancer cells by promoting apoptosis and inactivating Akt/FOXM1 signaling. Cumulatively, our present study suggests that panobinostat is a potential drug for the treatment of gastric cancer.

A novel dual HDAC and HSP90 inhibitor, MPT0G449, downregulates oncogenic pathways in human acute leukemia in vitro and in vivo

Acute leukemia is a highly heterogeneous disease; therefore, combination therapy is commonly used for patient treatment. Drug–drug interaction is a major concern of combined therapy; hence, dual/multi-target inhibitors have become a dominant approach for cancer drug development. HDACs and HSP90 are involved in the activation of various oncogenic signaling pathways, including PI3K/AKT/mTOR, JAK/STAT, and RAF/MEK/ERK, which are also highly enriched in acute leukemia gene expression profiles. Therefore, we suggest that dual HDAC and HSP90 inhibitors could represent a novel therapeutic approach for acute leukemia. MPT0G449 is a dual effect inhibitor, and it showed cytotoxic effectiveness in acute leukemia cells. Molecular docking analysis indicated that MPT0G449 possessed dual HDAC and HSP90 inhibitory abilities. Furthermore, MPT0G449 induced G₂ arrest and caspase-mediated cell apoptosis in acute leukemia cells. The oncogenic signaling molecules AKT, mTOR, STAT3, STAT5, MEK, and ERK were significantly downregulated after MPT0G449 treatment in HL-60 and MOLT-4 cells. In vivo xenograft models confirmed the antitumor activity and showed the upregulation of acetyl-histone H3 and HSP70, biomarkers of pan-HDAC and HSP90 inhibition, with MPT0G449 treatment. These findings suggest that the dual inhibition of HDAC and HSP90 can suppress the expression of oncogenic pathways in acute leukemia, and MPT0G449 represents a novel therapeutic for anticancer treatment.

From Anti-infective Agents to Cancer Therapy: a Drug Repositioning Study Revealed a New Use for Nitrofuran Derivatives

BACKGROUND

The progression of ovarian cancer seems to be related to HDAC1, HDAC3 and HDAC6 activity. A possible strategy for improving therapies for treating ovarian carcinoma, minimizing the preclinical screenings, is the repurposing of already approved pharmaceutical products as inhibitors of these enzymes.

OBJECTIVE

This work was aimed to implement a computational strategy for identifying new HDAC inhibitors for ovarian carcinoma treatment among approved drugs.

METHOD

The CHEMBL database was used to construct training, test and decoys sets for performing and validating HDAC1, HDAC3 and HDAC6 3D-QSAR models obtained by using FLAP program. Docking and MD simulations were used in combination with the generated models to identify novel potential HDAC inhibitors. Cell viability assays and Western blot analyses were performed on normal and cancer cells for a direct evaluation of the anti-proliferative activity and an in vitro estimation of HDAC inhibition of the compounds selected through in silico screening.

RESULT

The best quantitative prediction was obtained for the HDAC6 3D-QSAR model. The screening of approved drugs highlighted a new potential use as HDAC inhibitors for some compounds, in particular nitrofuran derivatives, usually known for their antibacterial activity, and frequently used as antimicrobial adjuvant therapy in cancer treatment. Experimental evaluation of these derivatives highlighted a significant antiproliferative activity against cancer cell lines overexpressing HDAC6, and an increase in acetylated alpha-tubulin levels.

CONCLUSION

Experimental results support the hypothesis of a potential direct interaction of nitrofuran derivatives with HDACs. In addition to the possible repurposing of already approved drugs, this work suggests the nitro group as a new zinc binding group, able to interact with the catalytic zinc ion of HDACs.

Single-Cell Atlas Reveals Fatty Acid Metabolites Regulate the Functional Heterogeneity of Mesenchymal Stem Cells

Bone marrow mesenchymal stem cells (MSCs) are widely used clinically due to their versatile roles in multipotency, immunomodulation, and hematopoietic stem cell (HSC) niche function. However, cellular heterogeneity limits MSCs in the consistency and efficacy of their clinical applications. Metabolism regulates stem cell function and fate decision; however, how metabolites regulate the functional heterogeneity of MSCs remains elusive. Here, using single-cell RNA sequencing, we discovered that fatty acid pathways are involved in the regulation of lineage commitment and functional heterogeneity of MSCs. Functional assays showed that a fatty acid metabolite, butyrate, suppressed the self-renewal, adipogenesis, and osteogenesis differentiation potential of MSCs with increased apoptosis. Conversely, butyrate supplement significantly promoted HSC niche factor expression in MSCs, which suggests that butyrate supplement may provide a therapeutic approach to enhance their HSC niche function. Overall, our work demonstrates that metabolites are essential to regulate the functional heterogeneity of MSCs.

R-CHOP resistance in diffuse large B-cell lymphoma: biological and molecular mechanisms

Although the first-line rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone regimen (R-CHOP) substantially improved outcomes for patients with diffuse large B-cell lymphoma (DLBCL), 40% of the patients suffered from relapsed/refractory disease and had poor survival outcomes. The detailed mechanism underlying R-CHOP resistance has not been well defined. For this review, we conducted a thorough search for literature and clinical trials involving DLBCL resistance. We discussed DLBCL biology, epigenetics, and aberrant signaling of the B-cell receptor (BCR), phosphatidylinositol 3-kinase (PI3K)/Akt, nuclear factor kappa light chain enhancer of activated B-cells (NF-κB), and the Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) pathways as defining mechanisms of DLBCL heterogeneity and R-CHOP resistance. The cell of origin, double- or triple-hit lymphoma and double-protein-expression, clonal evolution, tumor microenvironment, and multi-drug resistance help to contextualize DLBCL resistance in an (epi)genetically and biologically comparative manner. With better understanding of the biological and molecular landscape of DLBCL, a more detailed classification system and tailored treatments will ideally become available to further improve the prognosis of DLBCL patients.

Structure-Based Inhibitor Discovery of Class I Histone Deacetylases (HDACs)

Class I histone deacetylases (HDACs) are promising targets for epigenetic therapies for a range of diseases such as cancers, inflammations, infections and neurological diseases. Although six HDAC inhibitors are now licensed for clinical treatments, they are all pan-inhibitors with little or no HDAC isoform selectivity, exhibiting undesirable side effects. A major issue with the currently available HDAC inhibitors is that they have limited specificity and target multiple deacetylases. Except for HDAC8, Class I HDACs (1, 2 and 3) are recruited to large multiprotein complexes to function. Therefore, there are rising needs to develop new, hopefully, therapeutically efficacious HDAC inhibitors with isoform or complex selectivity. Here, upon the introduction of the structures of Class I HDACs and their complexes, we provide an up-to-date overview of the structure-based discovery of Class I HDAC inhibitors, including pan-, isoform-selective and complex-specific inhibitors, aiming to provide an insight into the discovery of additional HDAC inhibitors with greater selectivity, specificity and therapeutic utility.

Diagnosis and treatment of lymphomas in the era of epigenetics

Lymphomas represent a heterogeneous group of cancers characterized by clonal lymphoproliferation. Over the past decades, frequent epigenetic dysregulations have been identified in hematologic malignancies including lymphomas. Many of these impairments occur in genes with established roles and well-known functions in the regulation and maintenance of the epigenome. In hematopoietic cells, these dysfunctions can result in abnormal DNA methylation, erroneous chromatin state and/or altered miRNA expression, affecting many different cellular functions. Nowadays, it is evident that epigenetic dysregulations in lymphoid neoplasms are mainly caused by genetic alterations in genes encoding for enzymes responsible for histone or chromatin modifications. We summarize herein the recent epigenetic modifiers findings in lymphomas. We focus also on the most commonly mutated epigenetic regulators and emphasize on actual epigenetic therapies.

Metformin Combined with 4SC-202 Inhibited the Migration and Invasion of OSCC via STAT3/TWIST1

Background

Oral squamous cell carcinoma (OSCC), the most common epithelial malignant neoplasm in the head and neck, characterizes with local infiltration and metastasis of lymph nodes. The five-year survival rate of OSCC remains low despite the advances in clinical methods. Thus, it is necessary to develop a new effective therapeutic scheme for OSCC. Our previous results showed that metformin and 4SC-202 synergistically promoted the intrinsic apoptosis of OSCC in vitro and in vivo, but the effects on invasion and migration remained unclear.

Methods

Human OSCC cell lines HSC6 and CAL33 were cultured with metformin (16 mM) or/and 4SC-202 (0.4 μM) for 72 h. STAT3 inhibitor S31-201 was applied at concentration of 60 μM for 48 h. Wound-healing assays and transwell assays were used to determine the invasion and migration ability of OSCC. qRT-PCR and Western blot were performed to detect mRNA levels and protein levels.

Results

Metformin or/and 4SC-202 suppressed the migration and invasion of OSCC cells. Importantly, the expression of TWIST1 was suppressed by metformin and 4SC-202, while the invasion and migration inhibitory effects of metformin and 4SC-202 were countered by the overexpression of TWIST1. In addition, the phosphorylation level of STAT3 decreased after the administration of metformin or/and 4SC-202. Furthermore, inhibition of STAT3 by S31-201 suppressed the expression of TWIST1 and led to a decline in migration and invasion of OSCC, while overexpression of TWIST1 attenuated these effects.

Conclusion

Metformin and 4SC-202 suppressed the invasion and migration of OSCC through inhibition of STAT3/TWIST1, and this scheme can serve as a novel therapeutic strategy for OSCC.

Ketogenic Diet Elicits Antitumor Properties through Inducing Oxidative Stress, Inhibiting MMP-9 Expression, and Rebalancing M1/M2 Tumor-Associated Macrophage Phenotype in a Mouse Model of Colon Cancer

Many advanced cancers are characterized by metabolic disorders. A dietary therapeutic strategy was proposed to inhibit tumor growth through administration of low-carbohydrate, average-protein, and high-fat diet, which is also known as ketogenic diet (KD). In vivo antitumor efficacy of KD on transplanted CT26⁺ tumor cells in BALB/c mice was investigated. The results showed that the KD group had significantly higher blood β-hydroxybutyrate and lower blood glucose levels when compared with the normal diet group. Meanwhile, KD increased intratumor oxidative stress, and TUNEL staining showed KD-induced apoptosis against tumor cells. Interestingly, the distribution of CD16/32⁺ and iNOS⁺ M1 tumor-associated macrophages (TAMs) increased in the KD-treated group, with concomitantly less arginase-1⁺ M2 TAMs. Moreover, KD treatment downregulated the protein expression of matrix metalloproteinase-9 in CT26⁺ tumor-bearing mice. Western blot analysis demonstrated that the expression levels of HDAC3/PKM2/NF-κB 65/p-Stat3 proteins were reduced in the KD-treated group. Taken together, our results indicated that KD can prevent the progression of colon tumor via inducing intratumor oxidative stress, inhibiting the expression of the MMP-9, and enhancing M2 to M1 TAM polarization. A novel potential mechanism was identified that KD can prevent the progression of colon cancer by regulating the expression of HDAC3/PKM2/NF-κB65/p-Stat3 axis.

Parthenolide promotes the repair of spinal cord injury by modulating M1/M2 polarization via the NF-κB and STAT 1/3 signaling pathway

Spinal cord injury (SCI) is a severe neurological disease; however, there is no effective treatment for spinal cord injury. Neuroinflammation involves the activation of resident microglia and the infiltration of macrophages is the major pathogenesis of SCI secondary injury and considered to be the therapeutic target of SCI. Parthenolide (PN) has been reported to exert anti-inflammatory effects in fever, migraines, arthritis, and superficial inflammation; however, the role of PN in SCI therapeutics has not been clarified. In this study, we showed that PN could improve the functional recovery of spinal cord in mice as revealed by increased BMS scores and decreased cavity of spinal cord injury in vivo. Immunofluorescence staining experiments confirmed that PN could promote axonal regeneration, increase myelin reconstitution, reduce chondroitin sulfate formation, inhibit scar hyperplasia, suppress the activation of A1 neurotoxic reactive astrocytes and facilitate shift from M1 to M2 polarization of microglia/macrophages. To verify how PN exerts its effects on microglia/macrophages polarization, we performed the mechanism study in vitro in microglia cell line BV-2. PN could significantly reduce M1 polarization in BV2 cells and partially rescue the decrease in the expression of M2 phenotype markers of microglia/macrophage induced by LPS, but no significant effect on M2 polarization stimulated with IL-4 was observed. Further study demonstrated PN inhibited NF-κB signal pathway directly or indirectly, and suppressed activation of signal transducer and activator of transcription 1 or 3 (STAT1/3) via reducing the expression of HDAC1 and subsequently increasing the levels of STAT1/3 acetylation. Overall, our study illustrated that PN may be a promising strategy for traumatic SCI.

A Combination of BRD4 and HDAC3 Inhibitors Synergistically Suppresses Glioma Stem Cell Growth by Blocking GLI1/IL6/STAT3 Signaling Axis

Glioma stem cells (GSC) are essential for tumor maintenance, invasiveness, and recurrence. Using a global epigenetic screening with an shRNA library, we identified HDAC3 as an essential factor for GSC stemness. Here, we demonstrated that GSCs poorly respond to an HDAC3 inhibitor, RGFP966 (HDAC3i), owing to the production of IL6 and STAT3 activation. To enhance GSC sensitivity to HDAC3i, we explored whether cotreatment with a BRD4 inhibitor, JQ1 (BRD4i), in GSCs produced a better antitumor effect. BRD4i synergistically inhibits GSC growth in association with HDAC3i. HDAC3 inhibition upregulated the acetylation of H3K27, which allowed the recruitment of BRD4 to the GLI1 gene promoter and induced its expression. GLI1, a transcription factor, turned on the expression of IL6, which led to the activation of STAT3 signaling pathways. However, BRD4i inhibited transcription of the GLI1 gene, thereby blocking the GLI1/IL6/STAT3 pathway. In vivo, the HDAC3i/BRD4i combination caused stronger tumor growth suppression than either drug alone. Thus, HDAC3i/BRD4i might provide promising therapies for GBM.

Critical review of non-histone human substrates of metal-dependent lysine deacetylases

Lysine acetylation is a posttranslational modification that occurs on thousands of human proteins, most of which are cytoplasmic. Acetylated proteins are involved in numerous cellular processes and human diseases. Therefore, how the acetylation/deacetylation cycle is regulated is an important question. Eleven metal-dependent lysine deacetylases (KDACs) have been identified in human cells. These enzymes, along with the sirtuins, are collectively responsible for reversing lysine acetylation. Despite several large-scale studies which have characterized the acetylome, relatively few of the specific acetylated residues have been matched to a proposed KDAC for deacetylation. To understand the function of lysine acetylation, and its association with diseases, specific KDAC-substrate pairs must be identified. Identifying specific substrates of a KDAC is complicated both by the complexity of assaying relevant activity and by the non-catalytic interactions of KDACs with cellular proteins. Here, we discuss in vitro and cell-based experimental strategies used to identify KDAC-substrate pairs and evaluate each for the purpose of directly identifying non-histone substrates of metal-dependent KDACs. We propose criteria for a combination of reproducible experimental approaches that are necessary to establish a direct enzymatic relationship. This critical analysis of the literature identifies 108 proposed non-histone substrate-KDAC pairs for which direct experimental evidence has been reported. Of these, five pairs can be considered well-established, while another thirteen pairs have both cell-based and in vitro evidence but lack independent replication and/or sufficient cell-based evidence. We present a path forward for evaluating the remaining substrate leads and reliably identifying novel KDAC substrates.

Histone Deacetylase Inhibitors to Overcome Resistance to Targeted and Immuno Therapy in Metastatic Melanoma

Therapies that target oncogenes and immune checkpoint molecules constitute a major group of treatments for metastatic melanoma. A mutation in BRAF (BRAF V600E) affects various signaling pathways, including mitogen activated protein kinase (MAPK) and PI3K/AKT/mammalian target of rapamycin (mTOR) in melanoma. Target-specific agents, such as MAPK inhibitors improve progression-free survival. However, BRAF^V600E mutant melanomas treated with BRAF kinase inhibitors develop resistance. Immune checkpoint molecules, such as programmed death-1 (PD-1) and programmed death ligand-1(PD-L1), induce immune evasion of cancer cells. MAPK inhibitor resistance results from the increased expression of PD-L1. Immune checkpoint inhibitors, such as anti-PD-L1 or anti-PD-1, are main players in immune therapies designed to target metastatic melanoma. However, melanoma patients show low response rate and resistance to these inhibitors develops within 6–8 months of treatment. Epigenetic reprogramming, such as DNA methylaion and histone modification, regulates the expression of genes involved in cellular proliferation, immune checkpoints and the response to anti-cancer drugs. Histone deacetylases (HDACs) remove acetyl groups from histone and non-histone proteins and act as transcriptional repressors. HDACs are often dysregulated in melanomas, and regulate MAPK signaling, cancer progression, and responses to various anti-cancer drugs. HDACs have been shown to regulate the expression of PD-1/PD-L1 and genes involved in immune evasion. These reports make HDACs ideal targets for the development of anti-melanoma therapeutics. We review the mechanisms of resistance to anti-melanoma therapies, including MAPK inhibitors and immune checkpoint inhibitors. We address the effects of HDAC inhibitors on the response to MAPK inhibitors and immune checkpoint inhibitors in melanoma. In addition, we discuss current progress in anti-melanoma therapies involving a combination of HDAC inhibitors, immune checkpoint inhibitors, and MAPK inhibitors.

Emerging role of histone deacetylase inhibitors in the treatment of diffuse large B-cell lymphoma

Although current immunochemotherapy has increased the therapeutic efficacy in diffuse large B-cell lymphoma (DLBCL), there are still some patients who present unfavorable outcomes. Novel effective treatment strategies are needed to improve the prognosis of DLBCL. In this review, we discussed the functional mechanisms and therapeutic applications of histone deacetylases inhibitors (HDIs) in DLBCL from preclinical and clinical studies. The mechanistic rationale of HDIs involved a wide range of effects including the regulation of transcription factors, tumor suppressors, and cell surface molecules. Histone deacetylases inhibitors as monotherapy performed limited activity in the treatment of DLBCL in present clinical trials, but its combination with other regimens has emerged as potential treatment candidates with generally acceptable and manageable adverse effects. Further investigation on the anti-tumor mechanisms of HDIs and ongoing clinical trials will hopefully facilitate the application of HDIs in patients with DLBCL.

Emerging roles of histone modifications and HDACs in RNA splicing

Histone modifications and RNA splicing, two seemingly unrelated gene regulatory processes, greatly increase proteome diversity and profoundly influence normal as well as pathological eukaryotic cellular functions. Like many histone modifying enzymes, histone deacetylases (HDACs) play critical roles in governing cellular behaviors and are indispensable in numerous biological processes. While the association between RNA splicing and histone modifications is beginning to be recognized, a lack of knowledge exists regarding the role of HDACs in splicing. Recent studies however, reveal that HDACs interact with spliceosomal and ribonucleoprotein complexes, actively control the acetylation states of splicing-associated histone marks and splicing factors, and thereby unexpectedly could modulate splicing. Here, we review the role of histone/protein modifications and HDACs in RNA splicing and discuss the convergence of two parallel fields, which supports the argument that HDACs, and perhaps most histone modifying enzymes, are much more versatile and far more complicated than their initially proposed functions. Analogously, an HDAC-RNA splicing connection suggests that splicing is regulated by additional upstream factors and pathways yet to be defined or not fully characterized. Some human diseases share common underlying causes of aberrant HDACs and dysregulated RNA splicing and, thus, further support the potential link between HDACs and RNA splicing.

Epstein-Barr virus (EBV) activates NKL homeobox gene HLX in DLBCL

NKL homeobox genes encode developmental transcription factors regulating basic processes in cell differentiation. According to their physiological expression pattern in early hematopoiesis and lymphopoiesis, particular members of this homeobox gene subclass constitute an NKL-code. B-cell specific NKL-code genes generate a regulatory network and their deregulation is implicated in B-cell lymphomagenesis. Epstein-Barr virus (EBV) infects B-cells and influences the activity of signalling pathways including JAK/STAT and several genes encoding developmental regulators. Therefore, EBV-infection impacts the pathogenesis and the outcome of B-cell malignancies including Hodgkin lymphoma and diffuse large B-cell lymphoma (DLBCL). Here, we isolated EBV-positive and EBV-negative subclones from the DLBCL derived cell line DOHH-2. These subclones served as models to investigate the role of EBV in deregulation of the B-cell specific NKL-code members HHEX, HLX, MSX1 and NKX6-3. We showed that the EBV-encoded factors LMP1 and LMP2A activated the expression of HLX via STAT3. HLX in turn repressed NKX6-3, SPIB and IL4R which normally mediate plasma cell differentiation. In addition, HLX repressed the pro-apoptotic factor BCL2L11/BIM and hence supported cell survival. Thus, EBV aberrantly activated HLX in DLBCL, thereby disturbing both B-cell differentiation and apoptosis. The results of our study appreciate the pathogenic role of EBV in NKL homeobox gene deregulation and B-cell malignancies.

Apoptosis Induction byHistone Deacetylase Inhibitors in Cancer Cells: Role of Ku70

Histone deacetylases (HDACs) are a group of enzymes that regulate gene transcription by controlling deacetylation of histones and non-histone proteins. Overexpression of HDACs is found in some types of tumors and predicts poor prognosis. Five HDAC inhibitors are approved for the treatment of cutaneous T-cell lymphoma, peripheral T-cell lymphoma, and multiple myeloma. Treatment with HDAC inhibitors regulates gene expression with increased acetylated histones with unconfirmed connection with therapy. Apoptosis is a key mechanism by which HDAC inhibitors selectively kill cancer cells, probably due to acetylation of non-histone proteins. Ku70 is a protein that repairs DNA breaks and stabilizes anti-apoptotic protein c-FLIP and proapoptotic protein Bax, which is regulated by acetylation. HDAC inhibitors induce Ku70 acetylation with repressed c-FLIP and activated Bax in cancer cells. Current studies indicate that Ku70 is a potential target of HDAC inhibitors and plays an important role during the induction of apoptosis.

Clinicopathologic implication of PD-L1 and phosphorylated STAT3 expression in diffuse large B cell lymphoma

BACKGROUND

Antitumor immune response of programmed cell death ligand (PD-L1) has shown clinical value not only in Hodgkin lymphoma and EBV-associated lymphomas but also in EBV-negative diffuse large B cell lymphoma (DLBCL) of non-germinal center B cell-like (non-GCB) subtype. Signal transducer and activator of transcription 3 (STAT3) is known to induce PD-L1 in immune cells and its activated form, phosphorylated STAT3 (pSTAT3), is also frequently expressed in non-GCB DLBCL. Herein, we investigated associations between PD-L1 expression/gene alteration, pSTAT3 expression and clinicopathologic variables in EBV-negative DLBCL.

METHODS

In 107 cases of DLBCLs with non-GCB subtype (67%; 72/107), GCB subtype (25%; 27/107) and unclassifiable cases (8%; 8/107), we performed PD-L1 and pSTAT3 immunohistochemistry and fluorescence in situ hybridization for PD-L1 gene translocation and copy number gain/amplification.

RESULTS

PD-L1 was expressed in tumor cells (PD-L1t) in 21% (23/107; 30% cutoff), immune cells (PD-L1i) in 36% (38/107; 20% cutoff), and pSTAT3 in tumor nuclei in 41% (44/107; 40% cutoff). PD-L1 gene alteration was observed in 10% (10/102) including translocation in 6% (6/102) and copy number gain/amplification in 4% (4/102). Non-GCB subtype was associated with PD-L1t and pSTAT3 (p = 0.006 and p = 0.042), and tended to have PD-L1 gene alteration (p = 0.058). Tumoral PD-L1 expression without gene alteration (PD-L1t+ GA-) correlated with pSTAT3-positive tumor cell proportions (%) (p = 0.033). In survival analysis, pSTAT3 expression independently predicted shorter PFS in total cohort (p = 0.017) and R-CHOP-treated group (p = 0.007), and in pSTAT3-negative R-CHOP-treated subset, PD-L1 expression in immune cells (PD-L1i) correlated with shorter PFS (p = 0.042).

CONCLUSIONS

Gene alteration and protein expression of PD-L1 and pSTAT3 expression were closely related in DLBCL and constituted features of non-GCB subtype. In addition to known clinical significance of pSTAT3, immune cell expression of PD-L1 (PD-L1i) had also clinical value in pSTAT3-dependent manner. These findings may provide an insight into immunotherapeutic strategy and risk stratification in DLBCL patients.

Tyrosine phosphorylation of HDAC3 by Src kinase mediates proliferation of HER2-positive breast cancer cells

The role of histone deacetylase 3 (HDAC3) is to repress the expression of various genes by eliminating acetyl group from histone. Thus, the regulation of HDAC3 activity is essential to maintain cellular homeostasis. In this study, we found that HDAC3 interacts with c-Src kinase. However, the interaction between HDAC3 and c-Src was previously reported, it has still been ambiguous whether c-Src phosphorylates HDAC3 and affects the function of HDAC3. First, we confirmed that HDAC3 directly binds to c-Src, and c-Src identified to interact with C-terminal domain (277-428 a.a.) of HDAC3. c-Src also phosphorylated three tyrosine sites of HDAC3 at tyrosine 325, 328, and 331. Importantly, wild-type c-Src increases HDAC3 activity, but not mutant c-Src^K298M (kinase inactive form). When these tyrosine residues are all substituted for alanine residues, the deacetylase activity of mutant HDAC3 was abolished. In addition, a proliferation of HER2-positive breast cancer cells expressing phosphorylation deficient mutant HDAC3 is decreased in comparison with control cells. Thus, our findings suggested that phosphorylation of HDAC3 by c-Src kinase regulates the HDAC3 activity and the proliferation of breast cancer cells.

Therapeutic Opportunities of Targeting Histone Deacetylase Isoforms to Eradicate Cancer Stem Cells

Cancer stem cells (CSCs), or tumor-initiating cells, are a small subset of cancer cells with the capacity for self-renewal and differentiation, which have been shown to drive tumor initiation, progression, and metastasis in many types of cancer. Moreover, therapeutic regimens, such as cisplatin and radiation were reported to induce the enrichment of CSCs, thereby conferring chemoresistance on cancer cells. Therefore, therapeutic targeting of CSCs represents a clinical challenge that needs to be addressed to improve patient outcome. In this context, the effectiveness of pan or class-I histone deacetylase (HDAC) inhibitors in suppressing the CSC population is especially noteworthy in light of the new paradigm of combination therapy. Evidence suggests that this anti-CSC activity is associated with the ability of HDAC inhibitors to target multiple signaling pathways at different molecular levels. Beyond chromatin remodeling via histone acetylation, HDAC inhibitors can also block key signaling pathways pertinent to CSC maintenance. Especially noteworthy is the ability of different HDAC isoforms to regulate the protein stability and/or activity of a series of epithelial-mesenchymal transition (EMT)-inducing transcription factors, including HIF-1α, Stat3, Notch1, β-catenin, NF-κB, and c-Jun, each of which plays a critical role in regulating CSCs. From the translational perspective, these mechanistic links constitute a rationale to develop isoform-selective HDAC inhibitors as anti-CSC agents. Thus, this review aims to provide an overview on the roles of HDAC isoforms in maintaining CSC homeostasis via distinct signaling pathways independent of histone acetylation.

STAT3 Interactors as Potential Therapeutic Targets for Cancer Treatment

Signal transducers and activators of transcription (STATs) mediate essential signaling pathways in different biological processes, including immune responses, hematopoiesis, and neurogenesis. Among the STAT members, STAT3 plays crucial roles in cell proliferation, survival, and differentiation. While STAT3 activation is transient in physiological conditions, STAT3 becomes persistently activated in a high percentage of solid and hematopoietic malignancies (e.g., melanoma, multiple myeloma, breast, prostate, ovarian, and colon cancers), thus contributing to malignant transformation and progression. This makes STAT3 an attractive therapeutic target for cancers. Initial strategies aimed at inhibiting STAT3 functions have focused on blocking the action of its activating kinases or sequestering its DNA binding ability. More recently, the diffusion of proteomic-based techniques, which have allowed for the identification and characterization of novel STAT3-interacting proteins able to modulate STAT3 activity via its subcellular localization, interact with upstream kinases, and recruit transcriptional machinery, has raised the possibility to target such cofactors to specifically restrain STAT3 oncogenic functions. In this article, we summarize the available data about the function of STAT3 interactors in malignant cells and discuss their role as potential therapeutic targets for cancer treatment.

Histone deacetylase 3 promotes liver regeneration and liver cancer cells proliferation through signal transducer and activator of transcription 3 signaling pathway

Histone deacetylase 3 (HDAC3) plays pivotal roles in cell cycle regulation and is often aberrantly expressed in various cancers including hepatocellular carcinoma (HCC), but little is known about its role in liver regeneration and liver cancer cells proliferation. Using an inducible hepatocyte-selective HDAC3 knockout mouse, we find that lack of HDAC3 dramatically impaired liver regeneration and blocked hepatocyte proliferation in the G1 phase entry. HDAC3 inactivation robustly disrupted the signal transducer and activator of transcription 3 (STAT3) cascade. HDAC3 silencing impaired the ac-STAT3-to-p-STAT3 transition in the cytoplasm, leading to the subsequent breakdown of STAT3 signaling. Furthermore, overexpressed HDAC3 was further associated with increased tumor growth and a poor prognosis in HCC patients. Inhibition of HDAC3 expression reduced liver cancer cells growth and inhibited xenograft tumor growth. Our results suggest that HDAC3 is an important regulator of STAT3-dependent cell proliferation in liver regeneration and cancer. These findings provide novel insights into the HDAC3-STAT3 pathway in liver pathophysiological processes.

Broccoli Sprouts Delay Prostate Cancer Formation and Decrease Prostate Cancer Severity with a Concurrent Decrease in HDAC3 Protein Expression in Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) Mice

BACKGROUND

Cruciferous vegetables have been associated with the chemoprevention of cancer. Epigenetic regulators have been identified as important targets for prostate cancer chemoprevention. Treatment of human prostate cancer cells with sulforaphane (SFN), a chemical from broccoli and broccoli sprouts, inhibits epigenetic regulators such as histone deacetylase (HDAC) enzymes, but it is not known whether consumption of a diet high in broccoli sprouts impacts epigenetic mechanisms in an in vivo model of prostate cancer.

OBJECTIVE

In the transgenic adenocarcinoma of the mouse prostate (TRAMP) model, we tested the hypothesis that a broccoli sprout diet suppresses prostate cancer, inhibits HDAC expression, alters histone modifications, and changes the expression of genes regulated by HDACs.

METHODS

TRAMP mice were fed a 15% broccoli sprout or control AIN93G diet; tissue samples were collected at 12 and 28 wk of age.

RESULTS

Mice fed broccoli sprouts had detectable amounts of SFN metabolites in liver, kidney, colon, and prostate tissues. Broccoli sprouts reduced prostate cancer incidence and progression to invasive cancer by 11- and 2.4-fold at 12 and 28 wk of age, respectively. There was a significant decline in HDAC3 protein expression in the epithelial cells of prostate ventral and anterior lobes at age 12 wk. Broccoli sprout consumption also decreased histone H3 lysine 9 trimethylation in the ventral lobe (age 12 wk), and decreased histone H3 lysine 18 acetylation in all prostate lobes (age 28 wk). A decline in p16 mRNA levels, a gene regulated by HDAC3, was associated with broccoli sprout consumption, but no significant changes were noted at the protein level.

CONCLUSIONS

Broccoli sprout intake was associated with a decline in prostate cancer occurrence and HDAC3 protein expression in the prostate, extending prior work that implicated loss of HDAC3/ corepressor interactions as a key preventive mechanism by SFN in vivo.