The biological significance of histone modifiers in multiple myeloma: clinical applications

JMJD1C forms condensate to facilitate a RUNX1-dependent gene expression program shared by multiple types of AML cells

JMJD1C (Jumonji Domain Containing 1C), a member of the lysine demethylase 3 (KDM3) family, is universally required for the survival of several types of acute myeloid leukemia (AML) cells with different genetic mutations, representing a therapeutic opportunity with broad application. Yet how JMJD1C regulates the leukemic programs of various AML cells is largely unexplored. Here we show that JMJD1C interacts with the master hematopoietic transcription factor RUNX1, which thereby recruits JMJD1C to the genome to facilitate a RUNX1-driven transcriptional program that supports leukemic cell survival. The underlying mechanism hinges on the long N-terminal disordered region of JMJD1C, which harbors two inseparable abilities: condensate formation and direct interaction with RUNX1. This dual capability of JMJD1C may influence enhancer-promoter contacts crucial for the expression of key leukemic genes regulated by RUNX1. Our findings demonstrate a previously unappreciated role for the non-catalytic function of JMJD1C in transcriptional regulation, underlying a mechanism shared by different types of leukemias.

Epigenetic Plasticity Drives Carcinogenesis and Multi-Therapy Resistance in Multiple Myeloma

We demonstrate that carcinogenesis and multi-therapy resistance in multiple myeloma (MM)-a treatable yet incurable plasma cell malignancy-are driven by epigenetic dysregulation. In this new paradigm, genomic and cytogenetic events unlock epigenetic plasticity, reshaping MM cell biology to evade tumor microenvironment constraints and therapeutic pressure. These conclusions are derived from a newly assembled cohort of nearly 1,000 patients, spanning premalignant to late-stage refractory MM, comprehensively characterized at molecular and clinical levels. Our findings provide a unifying framework to explain inter-patient genomic heterogeneity and the emergence of therapy resistance in sequential samples without new genomic alterations. In conclusion, we propose targeting epigenetic plasticity-mediated plasma cell evasion as a promising therapeutic strategy in MM.

The Genetic and Molecular Drivers of Multiple Myeloma: Current Insights, Clinical Implications, and the Path Forward

Background

Multiple myeloma (MM) is a hematological malignancy characterized by the clonal proliferation of malignant plasma cells within the bone marrow. The disease's complexity is underpinned by a variety of genetic and molecular abnormalities that drive its progression.

Methods

This review was conducted through a state-of-The-art literature search, primarily utilizing PubMed to gather peer-reviewed articles. We focused on the most comprehensive and cited studies to ensure a thorough understanding of the genetic and molecular landscapes of MM.

Results

We detail primary and secondary alterations such as translocations, hyperdiploidy, single nucleotide variants (SNVs), copy number alterations (CNAs), gene fusions, epigenetic modifications, non-coding RNAs, germline predisposing variants, and the influence of the tumor microenvironment (TME). Our analysis highlights the heterogeneity of MM and the challenges it poses in treatment and prognosis, emphasizing the distinction between driver mutations, which actively contribute to oncogenesis, and passenger mutations, which arise due to genomic instability and do not contribute to disease progression.

Conclusion & Future Perspectives

We report key controversies and challenges in defining the genetic drivers of MM, and examine their implications for future therapeutic strategies. We discuss the importance of systems biology approaches in understanding the dependencies and interactions among these alterations, particularly highlighting the impact of double and triple-hit scenarios on disease outcomes. By advancing our understanding of the molecular drivers and their interactions, this review sets the stage for novel therapeutic targets and strategies, ultimately aiming to improve clinical outcomes in MM patients.

Comprehensive analysis of microRNAs modulated by histone deacetylase inhibitors identifies microRNA-7-5p with anti-myeloma effect

Basic research to expand treatment options for multiple myeloma is greatly needed due to the refractory nature of the disease. Histone deacetylase (HDAC) inhibitors, which are epigenetic regulators, are attractive but have limited applications. MicroRNAs (miRNAs), which are also epigenetic regulators, are important molecules that may lead to future therapeutic breakthroughs. In this study, we comprehensively searched for miRNAs that are altered by HDAC inhibitors in myeloma cells. We identified miR-7-5p (miR-7) as a miRNA downregulated by HDAC inhibitors. Transfection of myeloma cell lines with miR-7 suppressed cell proliferation, induced apoptosis, and enhanced the effects of the HDAC inhibitor panobinostat. Expression of miR-7 was downregulated by c-Myc inhibition, but upregulated by bortezomib. Comprehensive examination of miR-7 targets revealed four candidates: SLC6A9, LRRC59, EXOSC2, and PSME3. Among these, we focused on PSME3, an oncogene involved in proteasome capacity in myeloma cells. PSME3 knockdown increases myeloma cell death and panobinostat sensitivity. In conclusion, miR-7, which is downregulated by HDAC inhibitors, is a tumor suppressor that targets PSME3. This miR-7 downregulation may be involved in HDAC inhibitor resistance. In addition, combinations of anti-myeloma drugs that complement changes in miRNA expression should be considered.

PRMT5 as a Potential Therapeutic Target in MYC-Amplified Medulloblastoma

MYC amplification or overexpression is most common in Group 3 medulloblastomas and is positively associated with poor clinical outcomes. Recently, protein arginine methyltransferase 5 (PRMT5) overexpression has been shown to be associated with tumorigenic MYC functions in cancers, particularly in brain cancers such as glioblastoma and medulloblastoma. PRMT5 regulates oncogenes, including MYC, that are often deregulated in medulloblastomas. However, the role of PRMT5-mediated post-translational modification in the stabilization of these oncoproteins remains poorly understood. The potential impact of PRMT5 inhibition on MYC makes it an attractive target in various cancers. PRMT5 inhibitors are a promising class of anti-cancer drugs demonstrating preclinical and preliminary clinical efficacies. Here, we review the publicly available preclinical and clinical studies on PRMT5 targeting using small molecule inhibitors and discuss the prospects of using them in medulloblastoma therapy.

Histone deacetylase-based dual targeted inhibition in multiple myeloma

Despite enormous advances in terms of therapeutic strategies, multiple myeloma (MM) still remains an incurable disease with MM patients often becoming resistant to standard treatments. To date, multiple combined and targeted therapies have proven to be more beneficial compared to monotherapy approaches, leading to a decrease in drug resistance and an improvement in median overall survival in patients. Moreover, recent breakthroughs highlighted the relevant role of histone deacetylases (HDACs) in cancer treatment, including MM. Thus, the simultaneous use of HDAC inhibitors with other conventional regimens, such as proteasome inhibitors, is of interest in the field. In this review, we provide a general overview of HDAC-based combination treatments in MM, through a critical presentation of publications from the past few decades related to in vitro and in vivo studies, as well as clinical trials. Furthermore, we discuss the recent introduction of dual-inhibitor entities that could have the same beneficial effects as drug combinations with the advantage of having two or more pharmacophores in one molecular structure. These findings could represent a starting-point for both reducing therapeutic doses and lowering the risk of developing drug resistance.

Decoding the role of miRNAs in multiple myeloma pathogenesis: A focus on signaling pathways

Multiple myeloma (MM) is a cancer of plasma cells that has been extensively studied in recent years, with researchers increasingly focusing on the role of microRNAs (miRNAs) in regulating gene expression in MM. Several non-coding RNAs have been demonstrated to regulate MM pathogenesis signaling pathways. These pathways might regulate MM development, apoptosis, progression, and therapeutic outcomes. They are Wnt/β-catenin, PI3K/Akt/mTOR, P53 and KRAS. This review highlights the impending role of miRNAs in MM signaling and their relationship with MM therapeutic interventions.

The roles of histone modifications in tumorigenesis and associated inhibitors in cancer therapy

Histone modifications are key factors in chromatin packaging, and are responsible for gene regulation during cell fate determination and development. Abnormal alterations in histone modifications potentially affect the stability of the genome and disrupt gene expression patterns, leading to many diseases, including cancer. In recent years, mounting evidence has shown that various histone modifications altered by aberrantly expressed modifier enzymes contribute to tumor development and metastasis through the induction of epigenetic, transcriptional, and phenotypic changes. In this review, we will discuss the existing histone modifications, both well-studied and rare ones, and their roles in solid tumors and hematopoietic cancers, to identify the molecular pathways involved and investigate targeted therapeutic drugs to reorganize the chromatin and enhance cancer treatment efficiency. Finally, clinical inhibitors of histone modifications are summarized to better understand the developmental stage of cancer therapy in using these drugs to inhibit the histone modification enzymes.

HDAC5-Mediated Acetylation of p100 Suppresses Its Processing

INTRODUCTION

Periodontitis is a condition involving chronic inflammation in the gums, periodontal ligaments, cementum, and alveolar bone. Nuclear factor-κB (NF-κB) activation is the prominent mediator of inflammation and osteoclast differentiation. The role of histone deacetylase 5 (HDAC5) in periodontitis development and NF-κB regulation is not fully understood.

METHODS

We used primary mouse bone marrow-derived osteoclast cultures in vitro and a mouse model of chronic periodontists (CPD) treated with the HDAC4/5 inhibitor LMK-235. Real-time polymerase chain reaction, micro computed tomography, flow cytometry, western blot, and immunoprecipitation were used to study proinflammatory cytokines, NF-κB activation, HDAC5 activity, and the interaction of HDAC5 with NF-κB p100.

RESULTS

LMK-235, a selective inhibitor of HDAC4 and HDAC5, reduced osteoclast marker gene expression (Cstk, Acp5, and Calcr) and tartrate-resistant acid phosphatase activity in primary osteoclast cultures. LMK-235 reduced the increase in cementoenamel junction-alveolar bone crest distance, inflammatory cell infiltration of gingival tissues, and expression levels of interleukin (IL)-1β, tumor necrosis factor alpha, IL-6, and IL-23a, indicating an ameliorative effect on CPD. Immunoprecipitation experiments have further confirmed p100-HDAC5 interaction, acetylation levels of p100, and NF-κB activation.

CONCLUSIONS

These results indicate that HDAC5 binds and deacetylates p100, leading to its activation, increased proinflammatory cytokine production, gingival infiltration, and osteoclast differentiation, thus promoting alveolar bone resorption. HDAC5 inhibition is therefore a potentially promising therapeutic strategy for the treatment of periodontitis.

The epigenetic regulation of the germinal center response

In response to T-cell-dependent antigens, antigen-experienced B cells migrate to the center of the B-cell follicle to seed the germinal center (GC) response after cognate interactions with CD4⁺ T cells. These GC B cells eventually mature into memory and long-lived antibody-secreting plasma cells, thus generating long-lived humoral immunity. Within GC, B cells undergo somatic hypermutation of their B cell receptors (BCR) and positive selection for the emergence of high-affinity antigen-specific B-cell clones. However, this process may be dangerous, as the accumulation of aberrant mutations could result in malignant transformation of GC B cells or give rise to autoreactive B cell clones that can cause autoimmunity. Because of this, better understanding of GC development provides diagnostic and therapeutic clues to the underlying pathologic process. A productive GC response is orchestrated by multiple mechanisms. An emerging important regulator of GC reaction is epigenetic modulation, which has key transcriptional regulatory properties. In this review, we summarize the current knowledge on the biology of epigenetic mechanisms in the regulation of GC reaction and outline its importance in identification of immunotherapy decision making.

Diverse Functions of KDM5 in Cancer: Transcriptional Repressor or Activator?

Epigenetic modifications are crucial for chromatin remodeling and transcriptional regulation. Post-translational modifications of histones are epigenetic processes that are fine-tuned by writer and eraser enzymes, and the disorganization of these enzymes alters the cellular state, resulting in human diseases. The KDM5 family is an enzymatic family that removes di- and tri-methyl groups (me2 and me3) from lysine 4 of histone H3 (H3K4), and its dysregulation has been implicated in cancer. Although H3K4me3 is an active chromatin marker, KDM5 proteins serve as not only transcriptional repressors but also transcriptional activators in a demethylase-dependent or -independent manner in different contexts. Notably, KDM5 proteins regulate the H3K4 methylation cycle required for active transcription. Here, we review the recent findings regarding the mechanisms of transcriptional regulation mediated by KDM5 in various contexts, with a focus on cancer, and further shed light on the potential of targeting KDM5 for cancer therapy.

Bone Marrow Stroma-Induced Transcriptome and Regulome Signatures of Multiple Myeloma

Multiple myeloma (MM) is a hematological cancer with inevitable drug resistance. MM cells interacting with bone marrow stromal cells (BMSCs) undergo substantial changes in the transcriptome and develop de novo multi-drug resistance. As a critical component in transcriptional regulation, how the chromatin landscape is transformed in MM cells exposed to BMSCs and contributes to the transcriptional response to BMSCs remains elusive. We profiled the transcriptome and regulome for MM cells using a transwell coculture system with BMSCs. The transcriptome and regulome of MM cells from the upper transwell resembled MM cells that coexisted with BMSCs from the lower chamber but were distinctive to monoculture. BMSC-induced genes were enriched in the JAK2/STAT3 signaling pathway, unfolded protein stress, signatures of early plasma cells, and response to proteasome inhibitors. Genes with increasing accessibility at multiple regulatory sites were preferentially induced by BMSCs; these genes were enriched in functions linked to responses to drugs and unfavorable clinic outcomes. We proposed JUNB and ATF4::CEBPβ as candidate transcription factors (TFs) that modulate the BMSC-induced transformation of the regulome linked to the transcriptional response. Together, we characterized the BMSC-induced transcriptome and regulome signatures of MM cells to facilitate research on epigenetic mechanisms of BMSC-induced multi-drug resistance in MM.

Potential effect of epigenetic drugs in the treatment of multiple-site extramedullary plasmacytoma involving the respiratory system: a case report and review of the literature

We report the case of a 23-year-old man with a medical history of idiopathic thrombocytopenic purpura (ITP) and newly diagnosed with the Epstein-Barr virus (EBV)-positive multiple-site extramedullary plasmacytoma (EMP), which involves the respiratory system. The patient was referred to our hospital because of progressive nasal congestion and nasal mass. Nasopharyngoscopy and bronchoscopy were performed. The biopsy pathological hematoxylin and eosin (HE) staining indicated plasma cell myeloma, and further immunohistochemistry CD99(+), CD79a(+), CD38(+), MUM-1(+), and Lambda(+) confirmed the diagnosis. The patient's bone marrow was normal, and hypercalcemia, renal insufficiency, anemia, evident bone lesions were not observed. Serum immunoglobulin quantification, serum protein electrophoresis, and blood and urine light chain quantification were all within the normal range. The serum immunofixation electrophoresis was negative, and the serum-free light chain was normal. These results could rule out multiple myeloma (MM) and prove to be EMP involving the nasal cavity, main bronchus, lung, and left hip. No desired effect was achieved after receiving PAD (bortezomib, adriamycin, and dexamethasone) and VRD (bortezomib, lenalidomide, and dexamethasone) treatments. Even if the tumor was remarkably relieved after receiving the 2-course CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) regimen, secondary resistance to CHOP unfortunately occurred in this case. We attempted to apply epigenetic therapy in the treatment of refractory multiple EMP. Although no complete remission (CR) was achieved, the maximum standard uptake value (SUVmax) in tumor lesions was significantly lower than before, and the patient's symptoms significantly improved. The patient tolerated decitabine and chidamide. We speculated that epigenetic drugs have potential effect in the treatment of multiple-site EMP.

Decoding DNA methylation in epigenetics of multiple myeloma

Dysregulation of DNA methylation in B cells has been observed during their neoplastic transformation and therefore closely associated with various B-cell malignancies including multiple myeloma (MM), a malignancy of terminally differentiated plasma cells. Emerging evidence has unveiled pronounced alterations in DNA methylation in MM, including both global and gene-specific changes that can affect genome stability and gene transcription. Moreover, dysregulated expression of DNA methylation-modifying enzymes has been related with myelomagenesis, disease progression, and poor prognosis. However, the functional roles of the epigenetic abnormalities involving DNA methylation in MM remain elusive. In this article, we review current understanding of the alterations in DNA methylome and DNA methylation modifiers in MM, particularly focusing on DNA methyltransferases (DNMTs) and tet methylcytosine dioxygenases (TETs). We also discuss how these DNA methylation modifiers may be regulated and function in MM cells, therefore providing a rationale for developing novel epigenetic therapies targeting DNA methylation in MM.

Epigenetic Modifications in Myeloma: Focused Review of Current Data and Potential Therapeutic Applications

Multiple myeloma is a common hematologic malignancy with an incidence of 1 per 100,000 population and is characterized by a nearly 100% risk of relapse, necessitating treatment with newer therapeutic agents at each instance of progression. However, use of newer agents is often precluded by cost and accessibility in a resource-constrained setting. Description of newer pathways of disease pathogenesis potentially provides opportunities for identification of therapeutic targets and a better understanding of disease biology. Identification of epigenetic changes in myeloma is an emerging premise, with several pathways contributing to pathogenesis and progression of disease. Greater understanding of epigenetic alterations provides opportunities to detect several targetable enzymes or pathways that can be of clinical use.

Targeting protein arginine methyltransferase 5 in cancers: Roles, inhibitors and mechanisms

The protein arginine methyltransferase 5 (PRMT5) as the major type II arginine methyltransferase catalyzes the mono- and symmetric dimethylation of arginine residues in both histone and non-histone proteins. Recently, increasing evidence has demonstrated that PRMT5 plays an indispensable role in the occurrence and development of various human cancers by promoting the cell proliferation, invasion, and migration. It has become a promising and valuable target in the cancer epigenetic therapy. This review is to summarize the clinical significance of PRMT5 in the cancers such as lung cancer, breast cancer and colorectal cancer, and the drug discovery targeting PRMT5. Importantly, the existing PRMT5 inhibitors representing different molecular mechanisms, and their pharmacological effect, mechanism of action and biological affinity are analyzed. Clinical status, current problems and future perspective of PRMT5 inhibitors for the treatment of cancers are also discussed, all of which provides crucial help for the future discovery of PRMT5 targeted drugs for cancer treatment.

Lysine Demethylase 5A is Required for MYC Driven Transcription in Multiple Myeloma

Lysine demethylase 5A (KDM5A) is a negative regulator of histone H3K4 trimethylation, a histone mark associated with activate gene transcription. We identify that KDM5A interacts with the P-TEFb complex and cooperates with MYC to control MYC targeted genes in multiple myeloma (MM) cells. We develop a cell-permeable and selective KDM5 inhibitor, JQKD82, that increases histone H3K4me3 but paradoxically inhibits downstream MYC-driven transcriptional output in vitro and in vivo. Using genetic ablation together with our inhibitor, we establish that KDM5A supports MYC target gene transcription independent of MYC itself, by supporting TFIIH (CDK7)- and P-TEFb (CDK9)-mediated phosphorylation of RNAPII. These data identify KDM5A as a unique vulnerability in MM functioning through regulation of MYC-target gene transcription, and establish JQKD82 as a tool compound to block KDM5A function as a potential therapeutic strategy for MM.

Panobinostat From Bench to Bedside: Rethinking the Treatment Paradigm for Multiple Myeloma

Relapsed and refractory multiple myeloma (RRMM) presents a therapeutic challenge due to the development of drug resistance. Panobinostat is an oral histone deacetylase inhibitor (HDACi) that affects multiple cellular pathways and has demonstrated the ability to resensitize refractory-multiple myeloma cells in preclinical studies, as well as in patients with RRMM in clinical trials. Synergy of panobinostat with a number of different classes of antimyeloma drugs (proteasome inhibitors, immunomodulatory drugs and monoclonal antibodies) has also been shown. Panobinostat is a promising HDACi for the treatment of multiple myeloma. Here, we present a comprehensive review of preclinical and clinical studies of panobinostat.

Role of microRNAs in Diagnosis, Prognosis and Management of Multiple Myeloma

Multiple myeloma (MM) is a cancerous bone disease characterized by malignant transformation of plasma cells in the bone marrow. MM is considered to be the second most common blood malignancy, with 20,000 new cases reported every year in the USA. Extensive research is currently enduring to validate diagnostic and therapeutic means to manage MM. microRNAs (miRNAs) were shown to be dysregulated in MM cases and to have a potential role in either progression or suppression of MM. Therefore, researchers investigated miRNAs levels in MM plasma cells and created tools to test their impact on tumor growth. In the present review, we discuss the most recently discovered miRNAs and their regulation in MM. Furthermore, we emphasized utilizing miRNAs as potential targets in the diagnosis, prognosis and treatment of MM, which can be useful for future clinical management.

Multiple myeloma: the (r)evolution of current therapy and a glance into future

Over the past 20 years, the regulatory approval of several novel agents to treat multiple myeloma (MM) has prolonged median patient survival from 3 to 8-10 years. Increased understanding of MM biology has translated to advances in diagnosis, prognosis, and response assessment, as well as informed the development of targeted and immune agents. Here we provide an overview of the recent progress in MM, and highlight research areas of greatest promise to further improve patient outcome in the future.

Aberrant BUB1 Overexpression Promotes Mitotic Segregation Errors and Chromosomal Instability in Multiple Myeloma

Chromosome instability (CIN), the hallmarks of cancer, reflects ongoing chromosomal changes caused by chromosome segregation errors and results in whole chromosomal or segmental aneuploidy. In multiple myeloma (MM), CIN contributes to the acquisition of tumor heterogeneity, and thereby, to disease progression, drug resistance, and eventual treatment failure; however, the underlying mechanism of CIN in MM remains unclear. Faithful chromosomal segregation is tightly regulated by a series of mitotic checkpoint proteins, such as budding uninhibited by benzimidazoles 1 (BUB1). In this study, we found that BUB1 was overexpressed in patient-derived myeloma cells, and BUB1 expression was significantly higher in patients in an advanced stage compared to those in an early stage. This suggested the involvement of aberrant BUB1 overexpression in disease progression. In human myeloma-derived cell lines (HMCLs), BUB1 knockdown reduced the frequency of chromosome segregation errors in mitotic cells. In line with this, partial knockdown of BUB1 showed reduced variations in chromosome number compared to parent cells in HMCLs. Finally, BUB1 overexpression was found to promote the clonogenic potency of HMCLs. Collectively, these results suggested that enhanced BUB1 expression caused an increase in mitotic segregation errors and the resultant emergence of subclones with altered chromosome numbers and, thus, was involved in CIN in MM.

Synthesis, docking study and inhibitory activity of 2,6-diketopiperazines derived from α-amino acids on HDAC8

Diketopiperazines (DKPs) have been regarded as an important scaffold from the viewpoint of synthesis due to their biological properties for the treatment of several diseases, including cancer. In this work, two novel series of enantiomeric 2,6-DKPs derived from α-amino acids were synthesized through nucleophilic substitution and intramolecular cyclization reactions. All the compounds were docked against histone deacetylase 8 (HDAC8), which is a promising target for the development of anticancer drugs. These compounds bound into the active site of HDAC8 in a similar way to Trichostatin A (TSA), which is an HDAC8 inhibitor. This study showed that the conformation of the 2,6-DKP ring, stereochemistry, and the type of substituent on the chiral center had an important role in the binding modes. The Gibbs free energies and dissociation constants values of HDAC8-ligand complexes showed that compounds (S)-4hBn, (S)-4m, (R)-4h, and (R)-4m were more stable and affine towards HDAC8 than TSA. The inhibitory activities of 4a, (S)-4h, (S)- and (R)-4(g, l, m) were evaluated in vitro on HDAC8. It was found that compounds (R)-4g (IC₅₀ = 21.54 nM) and (R)-4m (IC₅₀ = 10.81 nM) exhibited better inhibitory activities than TSA (IC₅₀ = 28.32 nM). These results suggested that 2,6-DKPs derivatives may be promising anticancer agents for further biological studies.

Chidamide epigenetically represses autophagy and exerts cooperative antimyeloma activity with bortezomib

Autophagy and ubiquitin proteasome system are two distinct and cooperative proteolytic pathways. The dual-pathway suppression represents a promising therapeutic strategy for multiple myeloma. Chidamide is a novel benzamide inhibitor of histone deacetylase, and shows potent antimyeloma activity. Here, we revealed the autophagy-suppressive role of chidamide in myeloma cells. We then demonstrated that chidamide treatment markedly downregulated histone deacetylase SIRT1, and simultaneously resulted in dose-dependent upregulation of acetyltransferase hMOF and histone methyltransferase EZH2, which contributed to an increase in global levels of histone H4 lysine 16 acetylation (H4k16ac) and histone H3 lysine 27 trimethylation (H3k27me3). We next confirmed concomitant upregulation of H4k16ac and H3k27me3 in the same promoter regions of the autophagy-related gene LC3B, reinforcing the specific roles for H4k16ac and H3k27me3 in mediating chidamide-induced transcriptional repression of LC3B. Finally, we provided experimental evidence that co-treatment with chidamide and proteasome inhibitor bortezomib induced clear synergistic cytotoxicity against MM cells, which was associated with increased accumulation of ubiquitinated proteins and excessive endoplasmic reticulum stress or dysregulated unfolded protein response. Our results altogether suggest that chidamide cooperatively potentiates antimyeloma activity of bortezomib, at least in part, by epigenetically repressing autophagic degradation of ubiquitinated proteins.

HDAC5 Inhibitors as a Potential Treatment in Breast Cancer Affecting Very Young Women

Background: Breast cancer in very young women (BCVY) defined as <35 years old, presents with different molecular biology than in older patients. High HDAC5 expression has been associated with poor prognosis in breast cancer (BC) tissue. We aimed to analyze HDAC5 expression in BCVY and older patients and their correlation with clinical features, also studying the potential of HDAC5 inhibition in BC cell lines. Methods: HDAC5 expression in 60 BCVY and 47 older cases were analyzed by qRT-PCR and correlated with clinical data. The effect of the HDAC5 inhibitor, LMK-235, was analyzed in BC cell lines from older and young patients. We performed time and dose dependence viability, migration, proliferation, and apoptosis assays. Results: Our results correlate higher HDAC5 expression with worse prognosis in BCVY. However, we observed no differences between HDAC5 expression and pathological features. Our results showed greatly reduced progression in BCVY cell lines and also in all triple negative subtypes when cell lines were treated with LMK-235. Conclusions: In BCVY, we found higher expression of HDAC5. Overexpression of HDAC5 in BCVY correlates with lower survival rates. LMK-235 could be a potential treatment in BCVY.

New generation drugs for treatment of multiple myeloma

Multiple myeloma (MM), a plasma cell malignancy, is characterised by lesions in multiple bones involving transformed, matured post-follicular B cells. The course of the disease involves an initial development of monoclonal gammopathy of undetermined significance (MGUS), followed by smouldering MM, before the full MM disease emerges. Despite novel therapies, MM remains incurable, managed by combination therapies, including proteasome inhibitors (PIs), immunomodulators (IMiDs) and anti-human CD38 (daratumumab). MM patients have an increased risk of thromboembolic events due to combination treatments with IMiDs, PIs and anti-human CD38 antibody, and steroids. This review will examine the efficacy and pro-thrombotic effects of MM therapies.

Proteasome inhibitor induced SIRT1 deacetylates GLI2 to enhance hedgehog signaling activity and drug resistance in multiple myeloma

Multiple myeloma (MM) is still incurable despite the successful application of proteasome inhibitors in clinic. Bortezomib represents the most common chemotherapy for MM, whereas acquired drug resistance and eventually developed relapse remain the major obstruction. In the current study, we established bortezomib-resistant myeloma cell lines and screened gene expression profiles using single cell RNA-sequencing. Resistant MM cells exhibited increased clonogenic potential, specific metabolic, and epigenetic signatures, along with the self-renewal signaling characteristic of MM stem-like cells. Aberrant activation of hedgehog (Hh) signaling was correlated with drug resistance and stem cell-like transcriptional program. The key transcriptional factor GLI2 of the Hh pathway was restricted in the high acetylation and low ubiquitination states in bortezomib-resistant myeloma cells. Further investigation revealed that SIRT1 deacetylates and stabilizes GLI2 protein at lysine 757 and consequentially activates the Hh signaling, and itself serves as a direct target of Hh signaling to format a positive regulating loop. Using combination screening with an epigenetic compound library, we identified the SIRT1 specific inhibitor S1541 and S2804 had very obvious synergetic antimyeloma effect. Sirt1 inhibition could partially impeded the Hh pathway and conferred bortezomib sensitivity in vitro and in vivo. Notably, elevated SIRT1 level was also a prominent hallmark for the resistant myeloma cells, and this expression pattern was confirmed in myeloma patients, but independent of RAS/RAF mutations. Clinically, SIRT1 expression in patients with complete response was suppressed but elevated in relapsed patients, and retrospective analysis showed patients with higher SIRT1 expression had poorer outcomes. In conclusion, the cooperation of SIRT1 and Hh is an important mechanism of drug resistance in myeloma, and therapeutics combining SIRT1 inhibitors will sensitize myeloma cells to proteasome inhibitors.

MEF-2 isoforms' (A-D) roles in development and tumorigenesis

Myocyte enhancer factor (MEF)-2 plays a critical role in proliferation, differentiation, and development of various cell types in a tissue specific manner. Four isoforms of MEF-2 (A-D) differentially participate in controlling the cell fate during the developmental phases of cardiac, muscle, vascular, immune and skeletal systems. Through their associations with various cellular factors MEF-2 isoforms can trigger alterations in complex protein networks and modulate various stages of cellular differentiation, proliferation, survival and apoptosis. The role of the MEF-2 family of transcription factors in the development has been investigated in various cell types, and the evolving alterations in this family of transcription factors have resulted in a diverse and wide spectrum of disease phenotypes, ranging from cancer to infection. This review provides a comprehensive account on MEF-2 isoforms (A-D) from their respective localization, signaling, role in development and tumorigenesis as well as their association with histone deacetylases (HDACs), which can be exploited for therapeutic intervention.