Bromodomain inhibitor OTX015 in patients with lymphoma or multiple myeloma: a dose-escalation, open-label, pharmacokinetic, phase 1 study

BET inhibitors synergize with venetoclax to induce apoptosis in MYC-driven lymphomas with high BCL-2 expression

Although the MYC oncogenic network represents an attractive therapeutic target for lymphoma, MYC inhibitors have been difficult to develop. Alternatively, inhibitors of epigenetic/ transcriptional regulators, particularly the bromodomain and extraterminal (BET) family, have been used to modulate MYC. However, current benzodiazepine-derivative BET inhibitors (BETi) elicit disappointing responses and dose-limiting toxicity in relapsed/refractory lymphoma, potentially because of enrichment of high-risk molecular features and chemical backbone-associated toxicities. Consequently, novel nonbenzodiazepine BETi and improved mechanistic understanding are required. Here we characterize the responses of aggressive MYC-driven lymphomas to 2 nonbenzodiazepine BETi: PLX51107 and PLX2853. Both invoked BIM-dependent apoptosis and in vivo therapy, associated with miR-17∼92 repression, in murine Eµ-myc lymphomas, with PLX2853 exhibiting enhanced potency. Accordingly, exogenous BCL-2 expression abrogated these effects. Because high BCL-2 expression is common in diffuse large B-cell lymphoma (DLBCL), BETi were ineffective in driving apoptosis and in vivo therapy of DLBCL cell lines, mirroring clinical results. However, BETi-mediated BIM upregulation and miR-17∼92 repression remained intact. Consequently, coadministration of BETi and ABT199/venetoclax restored cell death and in vivo therapy. Collectively, these data identify BIM-dependent apoptosis as a critical mechanism of action for this class of BETi that, via coadministration of BH3 mimetics, can deliver effective tumor control in DLBCL.

Brd4-p300 inhibition downregulates Nox4 and accelerates lung fibrosis resolution in aged mice

Tissue regeneration capacity declines with aging in association with heightened oxidative stress. Expression of the oxidant-generating enzyme, NADPH oxidase 4 (Nox4), is elevated in aged mice with diminished capacity for fibrosis resolution. Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal (BET) family of proteins that function as epigenetic "readers" of acetylated lysine groups on histones. In this study, we explored the role of Brd4 and its interaction with the p300 acetyltransferase in the regulation of Nox4 and the in vivo efficacy of a BET inhibitor to reverse established age-associated lung fibrosis. BET inhibition interferes with the association of Brd4, p300, and acetylated histone H4K16 with the Nox4 promoter in lung fibroblasts stimulated with the profibrotic cytokine, TGF-β1. A number of BET inhibitors, including I-BET-762, JQ1, and OTX015, downregulate Nox4 gene expression and activity. Aged mice with established and persistent lung fibrosis recover capacity for fibrosis resolution with OTX015 treatment. This study implicates epigenetic regulation of Nox4 by Brd4 and p300 and supports BET/Brd4 inhibition as an effective strategy for the treatment of age-related fibrotic lung disease.

Targeting BET bromodomain proteins in cancer: The example of lymphomas

The Bromo- and Extra-Terminal domain (BET) family proteins act as "readers" of acetylated histones and they are important transcription regulators. BRD2, BRD3, BRD4 and BRDT, part of the BET family, are important in different tumors, where upregulation or translocation often occurs. The potential of targeting BET proteins as anti-cancer treatment originated with data obtained with a first series of compounds, and there are now several data supporting BET inhibition in both solid tumors and hematological malignancies. Despite very positive preclinical data in different tumor types, the clinical results have been so far moderate. Using lymphoma as an example to review the data produced in the laboratory and in the context of the early clinical trials, we discuss the modalities to make BET targeting more efficient both generating novel generation of compounds and by exploring the combination with small molecules affecting various signaling pathways, BCL2, or DNA damage response signaling, but also with additional epigenetic agents and with immunotherapy. We also discuss the mechanisms of resistance and the toxicity profiles so far reported.

Epigenetic Mechanisms of Resistance to Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) have demonstrated to be highly efficient in treating solid tumors; however, many patients have limited benefits in terms of response and survival. This rapidly led to the investigation of combination therapies to enhance response rates. Moreover, predictive biomarkers were assessed to better select patients. Although PD-L1 expression remains the only validated marker in clinics, molecular profiling has brought valuable information, showing that the tumor mutation load and microsatellite instability (MSI) status were associated to higher response rates in nearly all cancer types. Moreover, in lung cancer, EGFR and MET mutations, oncogene fusions or STK11 inactivating mutations were associated with low response rates. Cancer progression towards invasive phenotypes that impede immune surveillance relies on complex regulatory networks and cell interactions within the tumor microenvironment. Epigenetic modifications, such as the alteration of histone patterns, chromatin structure, DNA methylation status at specific promoters and changes in microRNA levels, may alter the cell phenotype and reshape the tumor microenvironment, allowing cells to grow and escape from immune surveillance. The objective of this review is to make an update on the identified epigenetic changes that target immune surveillance and, ultimately, ICI responses, such as histone marks, DNA methylation and miR signatures. Translational studies or clinical trials, when available, and potential epigenetic biomarkers will be discussed as perspectives in the context of combination treatment strategies to enhance ICI responses in patients with solid tumors.

Targeting complexes of super-enhancers is a promising strategy for cancer therapy

The hyperactivation and overexpression of critical oncogenes is a common occurrence in multiple types of malignant tumors. Recently, the abnormal activation mechanism of an oncogene by a super-enhancer (SE) has attracted significant attention. A series of changes (insertion, deletion, translocation and rearrangement) in the genome occurring in cancer cells may generate new SEs, leading to the overexpression of SE-driven oncogenes. SEs are composed of typical enhancers densely loaded with mediator complexes, transcription factors, and chromatin regulators, and drive the overexpression of oncogenes associated with cellular identity and disease. Cyclin-dependent kinase 7 (CDK7) and bromodomain protein 4 (BRD4) are critical mediator complexes associated with SE-mediated transcription. Clinical trials have shown that emerging small-molecule inhibitors (CDK7 and BRD4 inhibitor), targeting the SE exert a notable effect on cancer treatment. Increasing evidences has illustrated that the SE and its associated complexes play a critical role in the development of various types of cancer. The present review discusses the composition, function and regulation of SEs and their contribution to oncogenic transcription. In addition, creative therapeutic approaches that target SE, their advantages and disadvantages, as well as the problems with their clinical application are discussed. It was found that targeting SE may be used in conventional treatment and establish more access for patients with cancer.

Epigenetic targeting in lymphoma

Despite considerable progress in the treatment of patients with lymphoid malignancies in recent decades, the prognosis of patients with relapsed or refractory lymphomas often remains disappointing. Increasing evidence has established the relevance of epigenetic alterations in the pathogenesis of lymphoid malignancies, and a succession of agents has been evaluated in clinical studies with varying efficacy. In the present review, we outline the importance of epigenetic modifications in lymphoma biology and discuss the published experience with epigenetic modifying agents by lymphoma subtype before considering ongoing clinical studies in this area.

BET bromodomain inhibitor HMBA synergizes with MEK inhibition in treatment of malignant glioma

(1) Background: BET bromodomain proteins regulate transcription by binding acetylated histones and attracting key factors for, e.g., transcriptional elongation. BET inhibitors have been developed to block pathogenic processes such as cancer and inflammation. Despite having potent biological activities, BET inhibitors have still not made a breakthrough in clinical use for treating cancer. Multiple resistance mechanisms have been proposed but thus far no attempts to block this in glioma has been made. (2) Methods: Here, we have conducted a pharmacological synergy screen in glioma cells to search for possible combination treatments augmenting the apoptotic response to BET inhibitors. We first used HMBA, a compound that was developed as a differentiation therapy four decades ago but more recently was shown to primarily inhibit BET bromodomain proteins. Data was also generated using other BET inhibitors. (3) Results: In the synergy screen, we discovered that several MEK inhibitors can enhance apoptosis in response to HMBA in rat and human glioma cells in vitro as well as in vivo xenografts. The combination is not unique to HMBA but also other BET inhibitors such as JQ1 and I-BET-762 can synergize with MEK inhibitors. (4) Conclusions: Our findings validate a combination therapy previously demonstrated to exhibit anti-cancer activities in multiple other tumour types but which appears to have been lost in translation to the clinic.

Brd2 haploinsufficiency extends lifespan and healthspan in C57B6/J mice

Aging in mammals is the gradual decline of an organism's physical, mental, and physiological capacity. Aging leads to increased risk for disease and eventually to death. Here, we show that Brd2 haploinsufficiency (Brd2+/-) extends lifespan and increases healthspan in C57B6/J mice. In Brd2+/- mice, longevity is increased by 23% (p<0.0001), and, relative to wildtype animals (Brd2+/+), cancer incidence is reduced by 43% (p<0.001). In addition, relative to age-matched wildtype mice, Brd2 heterozygotes show healthier aging including: improved grooming, extended period of fertility, and lack of age-related decline in kidney function and morphology. Our data support a role for haploinsufficiency of Brd2 in promoting healthy aging. We hypothesize that Brd2 affects aging by protecting against the accumulation of molecular and cellular damage. Given the recent advances in the development of BET inhibitors, our research provides impetus to test drugs that target BRD2 as a way to understand and treat/prevent age-related diseases.

Understanding the mechanism of action of pyrrolo[3,2-b]quinoxaline-derivatives as kinase inhibitors

Two novel quinoxaline-based EphA3 tyrosine kinase inhibitors have been designed and characterized in vivo in a relevant lymphoma model, showing high efficacy in the control of tumor size.

The X-ray structure of the catalytic domain of the EphA3 tyrosine kinase in complex with a previously reported type II inhibitor was used to design two novel quinoxaline derivatives, inspired by kinase inhibitors that have reached clinical development. These two new compounds were characterized by an array of cell-based assays and gene expression profiling experiments. A global chemical proteomics approach was used to generate the drug-protein interaction profile, which suggested suitable therapeutic indications. Both inhibitors, studied in the context of angiogenesis and in vivo in a relevant lymphoma model, showed high efficacy in the control of tumor size.

BRD2 induces drug resistance through activation of the RasGRP1/Ras/ERK signaling pathway in adult T-cell lymphoblastic lymphoma

BACKGROUND

Adult patients with T-cell lymphoblastic lymphoma (T-LBL) are treated with high-intensity chemotherapy regimens, but the response rate is still unsatisfactory because of frequent drug resistance. We aimed to investigate the potential mechanisms of drug resistance in adults with T-LBL.

METHODS

Gene expression microarray was used to identify differential mRNA expression profiles between chemotherapy-resistant and chemotherapy-sensitive adult T-LBL tissues. Real-time PCR and immunohistochemistry were performed to detect the expression of bromodomain-containing protein 2 (BRD2) and c-Myc in fresh-frozen T-LBL tissues from 85 adult patients. The Ras pull-down assay was performed to monitor Ras activation. Chromatin immunoprecipitation assays were used to analyze the binding of E2F transcription factor 1 (E2F1)/BRD2 to the RAS guanyl releasing protein 1 (RasGRP1) promoter region. The drug resistance effect and mechanism of BRD2 were determined by both in vivo and in vitro studies.

RESULTS

A total of 86 chemotherapy resistance-related genes in adult T-LBL were identified by gene expression microarray. Among them, BRD2 was upregulated in chemotherapy-resistant adult T-LBL tissues and associated with worse progression-free survival and overall survival of 85 adult T-LBL patients. Furthermore, BRD2 suppressed doxorubicin (Dox)-induced cell apoptosis both in vitro and in vivo. The activation of RasGRP1/Ras/ERK signaling might contribute to the Dox resistance effect of BRD2. Besides, OTX015, a bromodomain and extra-terminal (BET) inhibitor, reversed the Dox resistance effect of BRD2. Patient-derived tumor xenograft demonstrated that the sequential use of OTX015 after Dox showed superior therapeutic effects.

CONCLUSIONS

Our data showed that BRD2 promotes drug resistance in adult T-LBL through the RasGRP1/Ras/ERK signaling pathway. Targeting BRD2 may be a novel strategy to improve the therapeutic efficacy and prolong survival of adults with T-LBL.

A Deregulated HOX Gene Axis Confers an Epigenetic Vulnerability in KRAS-Mutant Lung Cancers

While KRAS mutations are common in non-small cell lung cancer (NSCLC), effective treatments are lacking. Here, we report that half of KRAS-mutant NSCLCs aberrantly express the homeobox protein HOXC10, largely due to unappreciated defects in PRC2, which confers sensitivity to combined BET/MEK inhibitors in xenograft and PDX models. Efficacy of the combination is dependent on suppression of HOXC10 by BET inhibitors. We further show that HOXC10 regulates the expression of pre-replication complex (pre-RC) proteins in sensitive tumors. Accordingly, BET/MEK inhibitors suppress pre-RC proteins in cycling cells, triggering stalled replication, DNA damage, and death. These studies reveal a promising therapeutic strategy for KRAS-mutant NSCLCs, identify a predictive biomarker of response, and define a subset of NSCLCs with a targetable epigenetic vulnerability.

Selective targeting of BD1 and BD2 of the BET proteins in cancer and immunoinflammation

The two tandem bromodomains of the BET (bromodomain and extraterminal domain) proteins enable chromatin binding to facilitate transcription. Drugs that inhibit both bromodomains equally have shown efficacy in certain malignant and inflammatory conditions. To explore the individual functional contributions of the first (BD1) and second (BD2) bromodomains in biology and therapy, we developed selective BD1 and BD2 inhibitors. We found that steady-state gene expression primarily requires BD1, whereas the rapid increase of gene expression induced by inflammatory stimuli requires both BD1 and BD2 of all BET proteins. BD1 inhibitors phenocopied the effects of pan-BET inhibitors in cancer models, whereas BD2 inhibitors were predominantly effective in models of inflammatory and autoimmune disease. These insights into the differential requirement of BD1 and BD2 for the maintenance and induction of gene expression may guide future BET-targeted therapies.

Epigenomics-Guided Drug Development: Recent Advances in Solving the Cancer Treatment "jigsaw puzzle"

The human epigenome plays a key role in determining cellular identity and eventually function. Drug discovery undertakings have focused mainly on the role of genomics in carcinogenesis, with the focus turning to the epigenome recently. Drugs targeting DNA and histone modifications are under development with some such as 5-azacytidine, decitabine, vorinostat, and panobinostat already approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA). This expert review offers a critical analysis of the epigenomics-guided drug discovery and development and the opportunities and challenges for the next decade. Importantly, the coupling of epigenetic editing techniques, such as clustered regularly interspersed short palindromic repeat (CRISPR)-CRISPR-associated protein-9 (Cas9) and APOBEC-coupled epigenetic sequencing (ACE-seq) with epigenetic drug screens, will allow the identification of small-molecule inhibitors or drugs able to reverse epigenetic changes responsible for many diseases. In addition, concrete and sustainable innovation in cancer treatment ought to integrate epigenome targeting drugs with classic therapies such as chemotherapy and immunotherapy.

Phase 1 Study of Molibresib (GSK525762), a Bromodomain and Extra-Terminal Domain Protein Inhibitor, in NUT Carcinoma and Other Solid Tumors

BACKGROUND

Bromodomain and extra-terminal domain proteins are promising epigenetic anticancer drug targets. This first-in-human study evaluated the safety, recommended phase II dose, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of the bromodomain and extra-terminal domain inhibitor molibresib (GSK525762) in patients with nuclear protein in testis (NUT) carcinoma (NC) and other solid tumors.

METHODS

This was a phase I and II, open-label, dose-escalation study. Molibresib was administered orally once daily. Single-patient dose escalation (from 2 mg/d) was conducted until the first instance of grade 2 or higher drug-related toxicity, followed by a 3 + 3 design. Pharmacokinetic parameters were obtained during weeks 1 and 3. Circulating monocyte chemoattractant protein-1 levels were measured as a pharmacodynamic biomarker.

RESULTS

Sixty-five patients received molibresib. During dose escalation, 11% experienced dose-limiting toxicities, including six instances of grade 4 thrombocytopenia, all with molibresib 60-100 mg. The most frequent treatment-related adverse events of any grade were thrombocytopenia (51%) and gastrointestinal events, including nausea, vomiting, diarrhea, decreased appetite, and dysgeusia (22%-42%), anemia (22%), and fatigue (20%). Molibresib demonstrated an acceptable safety profile up to 100 mg; 80 mg once daily was selected as the recommended phase II dose. Following single and repeat dosing, molibresib showed rapid absorption and elimination (maximum plasma concentration: 2 hours; t1/2: 3-7 hours). Dose-dependent reductions in circulating monocyte chemoattractant protein-1 levels were observed. Among 19 patients with NC, four achieved either confirmed or unconfirmed partial response, eight had stable disease as best response, and four were progression-free for more than 6 months.

CONCLUSIONS

Once-daily molibresib was tolerated at doses demonstrating target engagement. Preliminary data indicate proof-of-concept in NC.

Phase I study of CC-90010, a reversible, oral BET inhibitor in patients with advanced solid tumors and relapsed/refractory non-Hodgkin's lymphoma

BACKGROUND

Bromodomain and extra-terminal (BET) proteins are epigenetic readers that regulate expression of genes involved in oncogenesis. CC-90010 is a novel, oral, reversible, small-molecule BET inhibitor.

PATIENTS AND METHODS

CC-90010-ST-001 (NCT03220347; 2015-004371-79) is a phase I dose-escalation and expansion study of CC-90010 in patients with advanced or unresectable solid tumors and relapsed/refractory (R/R) non-Hodgkin's lymphoma (NHL). We report results from the dose escalation phase, which explored 11 dose levels and four dosing schedules, two weekly (2 days on/5 days off; 3 days on/4 days off), one biweekly (3 days on/11 days off), and one monthly (4 days on/24 days off). The primary objectives were to determine the safety, maximum tolerated dose (MTD) and/or recommended phase II dose (RP2D) and schedule. Secondary objectives were to evaluate signals of early antitumor activity, pharmacokinetics, and pharmacodynamics.

RESULTS

This study enrolled 69 patients, 67 with solid tumors and two with diffuse large B-cell lymphoma (DLBCL). The median age was 57 years (range, 21-80) and the median number of prior regimens was four (range, 1-9). Treatment-related adverse events (TRAEs) were mostly mild and manageable; grade 3/4 TRAEs reported in more than two patients were thrombocytopenia (13%), anemia, and fatigue (4% each). Six patients had dose-limiting toxicities. MTDs were 15 mg (2 days on/5 days off), 30 mg (3 days on/11 days off), and 45 mg (4 days on/24 days off). The RP2D and schedule selected for expansion was 45 mg (4 days on/24 days off). As of 8 October 2019, one patient with grade 2 astrocytoma achieved a complete response, one patient with endometrial carcinoma had a partial response, and six patients had prolonged stable disease ≥11 months.

CONCLUSIONS

CC-90010 is well tolerated, with single-agent activity in patients with heavily pretreated, advanced solid tumors.

Role of BET Inhibitors in Triple Negative Breast Cancers

Bromodomain and extraterminal domain (BET) proteins have evolved as key multifunctional super-regulators that control gene expression. These proteins have been shown to upregulate transcriptional machinery leading to over expression of genes involved in cell proliferation and carcinogenesis. Based on favorable preclinical evidence of BET inhibitors in various cancer models; currently, 26 clinical trials are underway in various stages of study on various hematological and solid organ cancers. Unfortunately, preliminary evidence for these clinical studies does not support the application of BET inhibitors as monotherapy in cancer treatment. Furthermore, the combinatorial efficiency of BET inhibitors with other chemo-and immunotherapeutic agents remain elusive. In this review, we will provide a concise summary of the molecular basis and preliminary clinical outcomes of BET inhibitors in cancer therapy, with special focus on triple negative breast cancer.

BET inhibition therapy counteracts cancer cell survival, clonogenic potential and radioresistance mechanisms in rhabdomyosarcoma cells

The antitumour effects of OTX015, a first-in-class BET inhibitor (BETi), were investigated as a single agent or in combination with ionizing radiation (IR) in preclinical in vitro models of rhabdomyosarcoma (RMS), the most common childhood soft tissue sarcoma. Herein, we demonstrated the upregulation of BET Bromodomain gene expression in RMS tumour biopsies and cell lines compared to normal skeletal muscle. In vitro experiments showed that OTX015 significantly reduced RMS cell proliferation by altering cell cycle modulators and apoptotic related proteins due to the accumulation of DNA breaks that cells are unable to repair. Interestingly, OTX015 also impaired migration capacity and tumour-sphere architecture by downregulating pro-stemness genes and was able to potentiate ionizing radiation effects by reducing the expression of different drivers of tumour dissemination and resistance mechanisms, including the GNL3 gene, that we correlated for the first time with the RMS phenotype. In conclusion, our research sheds further light on the molecular events of OTX015 action against RMS cells and indicates this novel BETi as an effective option to improve therapeutic strategies and overcome the development of resistant cancer cells in patients with RMS.

Preclinical Safety Assessment of a Highly Selective and Potent Dual Small-Molecule Inhibitor of CBP/P300 in Rats and Dogs

Cyclic adenosine monophosphate-response element (CREB)-binding protein (CBP) and EP300E1A-binding protein (p300) are members of the bromodomain and extraterminal motif (BET) family. These highly homologous proteins have a key role in modulating transcription, including altering the status of chromatin or through interactions with or posttranslational modifications of transcription factors. As CBP and p300 have known roles for stimulating c-Myc oncogenic activity, a small-molecule inhibitor, GNE-781, was developed to selectively and potently inhibit the CBP/p300 bromodomains (BRDs). Genetic models have been challenging to develop due to embryonic lethality arising from germline homozygous mutations in either CBP or P300. Hence, the purpose of this study was to characterize the role of dual inhibition of these proteins in adult rats and dogs. Repeat dose toxicity studies were conducted, and toxicologic and pathologic end points were assessed. GNE-781 was generally tolerated; however, marked effects on thrombopoiesis occurred in both species. Evidence of inhibition of erythroid, granulocytic, and lymphoid cell differentiation was also present, as well as deleterious changes in gastrointestinal and reproductive tissues. These findings are consistent with many preclinical (and clinical) effects reported with BET inhibitors targeting BRD proteins; thus, the current study findings indicate a likely important role for CBP/p300 in stem cell differentiation.

Comparative structure-function analysis of bromodomain and extraterminal motif (BET) proteins in a gene-complementation system

The widely expressed bromodomain and extraterminal motif (BET) proteins bromodomain-containing protein 2 (BRD2), BRD3, and BRD4 are multifunctional transcriptional regulators that bind acetylated chromatin via their conserved tandem bromodomains. Small molecules that target BET bromodomains are being tested for various diseases but typically do not discern between BET family members. Genomic distributions and protein partners of BET proteins have been described, but the basis for differences in BET protein function within a given lineage remains unclear. By establishing a gene knockout-rescue system in a Brd2-null erythroblast cell line, here we compared a series of mutant and chimeric BET proteins for their ability to modulate cell growth, differentiation, and gene expression. We found that the BET N-terminal halves bearing the bromodomains convey marked differences in protein stability but do not account for specificity in BET protein function. Instead, when BET proteins were expressed at comparable levels, their specificity was largely determined by the C-terminal half. Remarkably, a chimeric BET protein comprising the N-terminal half of the structurally similar short BRD4 isoform (BRD4S) and the C-terminal half of BRD2 functioned similarly to intact BRD2. We traced part of the BRD2-specific activity to a previously uncharacterized short segment predicted to harbor a coiled-coil (CC) domain. Deleting the CC segment impaired BRD2's ability to restore growth and differentiation, and the CC region functioned in conjunction with the adjacent ET domain to impart BRD2-like activity onto BRD4S. In summary, our results identify distinct BET protein domains that regulate protein turnover and biological activities.

Bromodomain and Extra-Terminal (BET) Domain Protein Inhibitors for Solid Tumor Cancers

The bromodomain and extraterminal (BET) domain protein family is involved in the process of transcription of genetic information. The BET protein family includes BRD2, BRD3, BRD4, and bromodomain testis-specific protein. BET protein alterations are associated with some solid tumor cancers, including nuclear protein in testis midline carcinoma. BET protein has a role in carcinogenesis and in the regulation of the cell cycle. A number of BET inhibitors have entered clinical trials. This review discusses the results of BET inhibitor clinical trials in solid tumor cancers.

Selective inhibition of the BD2 bromodomain of BET proteins in prostate cancer

Proteins of the bromodomain and extra-terminal (BET) domain family are epigenetic readers that bind acetylated histones through their bromodomains to regulate gene transcription. Dual-bromodomain BET inhibitors (DbBi) that bind with similar affinities to the first (BD1) and second (BD2) bromodomains of BRD2, BRD3, BRD4 and BRDt have displayed modest clinical activity in monotherapy cancer trials. A reduced number of thrombocytes in the blood (thrombocytopenia) as well as symptoms of gastrointestinal toxicity are dose-limiting adverse events for some types of DbBi^1-5. Given that similar haematological and gastrointestinal defects were observed after genetic silencing of Brd4 in mice⁶, the platelet and gastrointestinal toxicities may represent on-target activities associated with BET inhibition. The two individual bromodomains in BET family proteins may have distinct functions^7-9 and different cellular phenotypes after pharmacological inhibition of one or both bromodomains have been reported^10,11, suggesting that selectively targeting one of the bromodomains may result in a different efficacy and tolerability profile compared with DbBi. Available compounds that are selective to individual domains lack sufficient potency and the pharmacokinetics properties that are required for in vivo efficacy and tolerability assessment^10-13. Here we carried out a medicinal chemistry campaign that led to the discovery of ABBV-744, a highly potent and selective inhibitor of the BD2 domain of BET family proteins with drug-like properties. In contrast to the broad range of cell growth inhibition induced by DbBi, the antiproliferative activity of ABBV-744 was largely, but not exclusively, restricted to cell lines of acute myeloid leukaemia and prostate cancer that expressed the full-length androgen receptor (AR). ABBV-744 retained robust activity in prostate cancer xenografts, and showed fewer platelet and gastrointestinal toxicities than the DbBi ABBV-075¹⁴. Analyses of RNA expression and chromatin immunoprecipitation followed by sequencing revealed that ABBV-744 displaced BRD4 from AR-containing super-enhancers and inhibited AR-dependent transcription, with less impact on global transcription compared with ABBV-075. These results underscore the potential value of selectively targeting the BD2 domain of BET family proteins for cancer therapy.

IGF2BP3 From Physiology to Cancer: Novel Discoveries, Unsolved Issues, and Future Perspectives

RNA network control is a key aspect of proper cellular homeostasis. In this context, RNA-binding proteins (RBPs) play a major role as regulators of the RNA life cycle due to their capability to bind to RNA sequences and precisely direct nuclear export, translation/degradation rates, and the intracellular localization of their target transcripts. Alterations in RBP expression or functions result in aberrant RNA translation and may drive the emergence and progression of several pathological conditions, including cancer. Among the RBPs, insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) is of particular interest in tumorigenesis and tumor progression. This review highlights the molecular mechanisms underlying the oncogenic functions of IGF2BP3, summarizes the therapeutic potential related to its inhibition and notes the fundamental issues that remain unanswered. To fully exploit IGF2BP3 for tumor diagnosis and therapy, it is crucial to dissect the mechanisms governing IGF2BP3 re-expression and to elucidate the complex interactions between IGF2BP3 and its target mRNAs as normal cells become tumor cells.

Make your best BET: The emerging role of BET inhibitor treatment in malignant tumors

Bromodomains are protein-protein interaction modules with a great diversity in terms of number of proteins and their function. The bromodomain and extraterminal protein (BET) represents a distinct subclass of bromodomain proteins mainly involved in transcriptional regulation via their interaction with acetylated chromatin. In cancer cells BET proteins are found to be altered in many ways such as overexpression, mutations and fusions of BET proteins or their interference with cancer relevant signaling pathways and transcriptional programs in order to sustain cancer growth and viability. Blocking BET protein function with small molecules is associated with therapeutic activity. Consequently, a variety of small molecules have been developed and a number of phase I clinical trials have explored their tolerability and efficacy in patients with solid tumors and hematological malignancies. We will review the rational for applying BET inhibitors in the clinic and we will discuss the toxicity profile as well as efficacy of this new class of protein inhibitors. We will also highlight the emerging problem of treatment resistance and the potential these drugs might have when combined with other anti-cancer therapies.

Cellular Target Engagement Approaches to Monitor Epigenetic Reader Domain Interactions

Malfunctions in the basic epigenetic mechanisms such as histone modifications, DNA methylation, and chromatin remodeling are implicated in a number of cancers and immunological and neurodegenerative conditions. Within GlaxoSmithKline (GSK) we have utilized a number of variations of the NanoBRET technology for the direct measurement of compound-target engagement within native cellular environments to drive high-throughput, routine structure-activity relationship (SAR) profiling across differing epigenetic targets. NanoBRET is a variation of the bioluminescence resonance energy transfer (BRET) methodology utilizing proteins of interest fused to either NanoLuc, a small, high-emission-intensity luciferase, or HaloTag, a modified dehalogenase enzyme that can be selectively labeled with a fluorophore. The combination of these two technologies has enabled the application of NanoBRET to biological systems such as epigenetic protein-protein interactions, which have previously been challenging. By synergizing target engagement assays with more complex primary cell phenotypic assays, we have been able to demonstrate compound-target selectivity profiles to enhance cellular potency and offset potential liability risks. Additionally, we have shown that in the absence of a robust, cell phenotypic assay, it is possible to utilize NanoBRET target engagement assays to aid chemistry in progressing at a higher scale than would have otherwise been achievable. The NanoBRET target engagement assays utilized have further shown an excellent correlation with more reductionist biochemical and biophysical assay systems, clearly demonstrating the possibility of using such assay systems at scale, in tandem with, or in preference to, lower-throughput cell phenotypic approaches.

The BET inhibitor GS-5829 targets chronic lymphocytic leukemia cells and their supportive microenvironment

Despite major improvements in treatment outcome with novel targeted therapies, such as the Bruton tyrosine kinase (BTK) inhibitor ibrutinib, chronic lymphocytic leukemia (CLL) remains incurable in the majority of patients. Activation of PI3K, NF-κB, and/or MYC has been linked to residual disease and/or resistance in ibrutinib-treated patients. These pathways can be targeted by inhibitors of bromodomain and extra-terminal (BET) proteins. Here we report about the preclinical activity of GS-5829, a novel BET inhibitor, in CLL. GS-5829 inhibited CLL cell proliferation and induced leukemia cell apoptosis through deregulation of key signaling pathways, such as BLK, AKT, ERK1/2, and MYC. IκBα modulation indicates that GS-5829 also inhibited NF-κB signaling. GS-5829-induced apoptosis resulted from an imbalance between positive (BIM) and negative regulators (BCL-X_L) of the intrinsic apoptosis pathway. The antileukemia activity of GS-5829 increased synergistically in combinations with B-cell receptor signaling inhibitors, the BTK inhibitor ibrutinib, the PI3Kδ inhibitor idelalisib, and the SYK inhibitor entospletinib. In cocultures that mimic the lymph node microenvironment, GS-5829 inhibited signaling pathways within nurselike cells and their growth, indicating that BET inhibitors also can target the supportive CLL microenvironment. Collectively, these data provide a rationale for the clinical evaluation of BET inhibitors in CLL.

Challenges and Opportunities for High-grade B-Cell Lymphoma With MYC and BCL2 and/or BCL6 Rearrangement (Double-hit Lymphoma)

The most common subtype of non-Hodgkin lymphoma, diffuse large B-cell lymphoma, is cured in approximately two thirds of patients after initial therapy. The remaining one-third of patients who suffer relapse or become refractory have very poor survival outcomes despite salvage chemotherapy with or without stem cell transplantation. A considerable proportion of relapsed or refractory large B cells belong to the WHO subtype known as high-grade B-cell lymphoma with rearrangement of MYC and BCL2 and/or BCL6, also known as double-hit lymphoma (DHL). Most DHL patients present with Ann Arbor's stage III/IV, a comparatively higher rate of extranodal involvement including bone marrow and central nervous system infiltration, high levels of lactate dehydrogenase, and an elevated Ki67 expression in the tumor cells. Newer therapeutic approaches, including targeted therapy against BCL2, MYC, or other associated pathways, are needed. In addition, recent therapies that harness the immune system, such as checkpoint inhibitors and chimeric antigen receptor T-cell therapy, are changing the paradigm of treatment for non-Hodgkin lymphoma and could impact the outcome of DHL.

Hippo Pathway and YAP Signaling Alterations in Squamous Cancer of the Head and Neck

Head and neck cancer affects the upper aerodigestive tract and is the sixth leading cancer worldwide by incidence and the seventh by cause of death. Despite significant advances in surgery and chemotherapy, molecularly targeted therapeutic options for this type of cancer are scarce and long term survival rates remain low. Recently, comprehensive genomic studies have highlighted the most commonly altered genes and signaling pathways in this cancer. The Hippo-YAP pathway has been identified as a key oncogenic pathway in multiple tumors. Expression of genes controlled by the Hippo downstream transcriptional coactivators YAP (Yes-associated protein 1) and TAZ (WWTR1, WW domain containing transcription regulator 1) is widely deregulated in human cancer including head and neck squamous cell carcinoma (HNSCC). Interestingly, YAP/TAZ signaling might not be as essential for the normal homeostasis of adult tissues as for oncogenic growth, altogether making the pathway an amenable therapeutic target in cancer. Recent advances in the role of Hippo-YAP pathway in HNSCC have provided evidence that genetic alterations frequent in this type of cancer such as PIK3CA (phosphatidylinositide 3-kinase catalytic subunit alpha) overexpression or FAT1 (FAT atypical cadherin 1) functional loss can result in YAP activation. We discuss current therapeutic options targeting this pathway which are currently in use for other tumor types.

Drug therapy for double-hit lymphoma

Double-hit lymphoma (DHL) is a rare type of aggressive B-cell lymphoma defined as a high-grade B-cell lymphoma (HGBCL) with the presence of MYC, BCL2 and/or BCL6 rearrangements. Patients usually present with rapidly progressive and advanced stage of disease and, commonly, with extranodal involvement. Typically, patients become refractory to standard R-CHOP, and more aggressive regimens such as DA-EPOCH-R, R-hyperCVAD or CODOX-R regimens are typically needed. MYC is considered an “undruggable” mutation. Recent evidence suggests that pathogenic mechanisms associated with MYC could be potential targets. In this review, we also discuss the role of hematopoietic stem cell transplantation (HCT) and chimeric antigen receptor (CAR) T-cell therapy in DHL. We also discuss the role of potential novel agents such as BCL2 inhibitors, checkpoint inhibitors, bromodomain and extraterminal (BET) family inhibitors, Pi3K inhibitors, and others.

GLTSCR1 Negatively Regulates BRD4-Dependent Transcription Elongation and Inhibits CRC Metastasis

Frameshift mutations frequently occur in colorectal cancer (CRC) with microsatellite instability (MSI), but the nature and biological function of many MSI-associated mutations remain elusive. Here, an MSI frameshift mutation is identified in glioma tumor suppressor candidate region gene 1 (GLTSCR1) that produces two C-terminal-truncated proteins. Additionally, GLTSCR1 is verified as a tumor suppressor that inhibits CRC metastasis. Through binding to bromodomains and the phosphorylation-dependent interaction domain of bromodomain protein 4 (BRD4) via the C-terminus, GLTSCR1 blocks oncogenic transcriptional elongation. However, truncated GLTSCR1 translocates into the cytoplasm and loses BRD4 binding domain, which induces the phosphorylation of RNA Pol II at Ser2 and dephosphorylation at Ser5, then increases oncogenic transcriptional elongation. Importantly, GLTSCR1 deficiency decreases sensitivity to bromodomain and extra terminal domain inhibitors. This study highlights the molecular mechanism of the GLTSCR1-BRD4 interaction, which is a potential therapeutic target for CRC.

Emerging epigenetic-modulating therapies in lymphoma

Despite considerable advances in the treatment of lymphoma, the prognosis of patients with relapsed and/or refractory disease continues to be poor; thus, a continued need exists for the development of novel approaches and therapies. Epigenetic dysregulation might drive and/or promote tumorigenesis in various types of malignancies and is prevalent in both B cell and T cell lymphomas. Over the past decade, a large number of epigenetic-modifying agents have been developed and introduced into the clinical management of patients with haematological malignancies. In this Review, we provide a concise overview of the most promising epigenetic therapies for the treatment of lymphomas, including inhibitors of histone deacetylases (HDACs), DNA methyltransferases (DNMTs), enhancer of zeste homologue 2 (EZH2), bromodomain and extra-terminal domain proteins (BETs), protein arginine N-methyltransferases (PRMTs) and isocitrate dehydrogenases (IDHs), and highlight the most promising future directions of research in this area.

Genetic alterations and their clinical implications in DLBCL

Diffuse large B cell lymphoma (DLBCL) is a highly heterogeneous lymphoid neoplasm with variations in gene expression profiles and genetic alterations, which lead to substantial variations in clinical course and response to therapy. The advent of high-throughput genome sequencing platforms, and especially whole-exome sequencing, has helped to define the genetic landscape of DLBCL. In the past 10 years, these studies have identified many genetic alterations in DLBCL, some of which are specific to B cell lymphomas, whereas others can also be observed in other types of cancer. These aberrations result in altered activation of a wide range of signalling pathways and other cellular processes, including those involved in B cell differentiation, B cell receptor signalling, activation of the NF-κB pathway, apoptosis and epigenetic regulation. Further elaboration of the genetics of DLBCL will not only improve our understanding of disease pathogenesis but also provide further insight into disease classification, prognostication and therapeutic targets. In this Review, we describe the current understanding of the prevalence and causes of specific genetic alterations in DLBCL and their role in disease development and progression. We also summarize the available clinical data on therapies designed to target the aberrant pathways driven by these alterations.

An Overview of Molecular Mechanism, Clinicopathological Factors, and Treatment in NUT Carcinoma

NUT carcinoma (NC) is a rare and poorly differentiated tumor, with highly aggressive and fatal neoplasm. NC is characterized by chromosomal rearrangement involving NUTM1 gene, but lack of specific clinical and histomorphological features. It is more common in midline anatomic sites, such as head and neck, mediastinum, and other midline organs. NC may occur at any age, but mainly in children and young adults. In addition, male and female are equally affected. Most clinicians lack a clear understanding of the disease, and NC diagnostic reagents are still not widely used; therefore, misdiagnosis often occurs in clinic. Due to the highly aggressive nature of the disease and the insensitivity to nonspecific chemotherapy or radiotherapy, many patients have died before the confirmation of NC. In fact, the true incidence of NC is much higher than the current statistics. In recent years, targeted therapy for NC has also made some progress. This article aims to summarize the molecular mechanisms, clinicopathological characteristics, and treatment of NC.

Bromodomain and Extraterminal Proteins as Novel Epigenetic Targets for Renal Diseases

Epigenetic mechanisms, especially DNA methylation and histone modifications, are dynamic processes that regulate the gene expression transcriptional program in normal and diseased states. The bromodomain and extraterminal (BET) protein family (BRD2, BRD3, BRD4, and BRDT) are epigenetic readers that, via bromodomains, regulate gene transcription by binding to acetylated lysine residues on histones and master transcriptional factors. Experimental data have demonstrated the involvement of some BET proteins in many pathological conditions, including tumor development, infections, autoimmunity, and inflammation. Selective bromodomain inhibitors are epigenetic drugs that block the interaction between BET proteins and acetylated proteins, thus exerting beneficial effects. Recent data have described the beneficial effect of BET inhibition on experimental renal diseases. Emerging evidence underscores the importance of environmental modifications in the origin of pathological features in chronic kidney diseases (CKD). Several cellular processes such as oxidation, metabolic disorders, cytokines, inflammation, or accumulated uremic toxins may induce epigenetic modifications that regulate key processes involved in renal damage and in other pathological conditions observed in CKD patients. Here, we review how targeting bromodomains in BET proteins may regulate essential processes involved in renal diseases and in associated complications found in CKD patients, such as cardiovascular damage, highlighting the potential of epigenetic therapeutic strategies against BET proteins for CKD treatment and associated risks.

Recent Advances in the Targeting of Epigenetic Regulators in B-Cell Non-Hodgkin Lymphoma

In the last 10 years, major advances have been made in the diagnosis and development of selective therapies for several blood cancers, including B-cell non-Hodgkin lymphoma (B-NHL), a heterogeneous group of malignancies arising from the mature B lymphocyte compartment. However, most of these entities remain incurable and current treatments are associated with variable efficacy, several adverse events, and frequent relapses. Thus, new diagnostic paradigms and novel therapeutic options are required to improve the prognosis of patients with B-NHL. With the recent deciphering of the mutational landscapes of B-cell disorders by high-throughput sequencing, it came out that different epigenetic deregulations might drive and/or promote B lymphomagenesis. Consistently, over the last decade, numerous epigenetic drugs (or epidrugs) have emerged in the clinical management of B-NHL patients. In this review, we will present an overview of the most relevant epidrugs tested and/or used so far for the treatment of different subtypes of B-NHL, from first-generation epigenetic therapies like histone acetyl transferases (HDACs) or DNA-methyl transferases (DNMTs) inhibitors to new agents showing selectivity for proteins that are mutated, translocated, and/or overexpressed in these diseases, including EZH2, BET, and PRMT. We will dissect the mechanisms of action of these epigenetic inhibitors, as well as the molecular processes underlying their lack of efficacy in refractory patients. This review will also provide a summary of the latest strategies being employed in preclinical and clinical settings, and will point out the most promising lines of investigation in the field.

Pharmacological Targeting of BET Bromodomain Proteins in Acute Myeloid Leukemia and Malignant Lymphomas: From Molecular Characterization to Clinical Applications

Alterations in protein-protein and DNA-protein interactions and abnormal chromatin remodeling are a major cause of uncontrolled gene transcription and constitutive activation of critical signaling pathways in cancer cells. Multiple epigenetic regulators are known to be deregulated in several hematologic neoplasms, by somatic mutation, amplification, or deletion, allowing the identification of specific epigenetic signatures, but at the same time providing new therapeutic opportunities. While these vulnerabilities have been traditionally addressed by hypomethylating agents or histone deacetylase inhibitors, pharmacological targeting of bromodomain-containing proteins has recently emerged as a promising approach in a number of lymphoid and myeloid malignancies. Indeed, preclinical and clinical studies highlight the relevance of targeting the bromodomain and extra-terminal (BET) family as an efficient strategy of target transcription irrespective of the presence of epigenetic mutations. Here we will summarize the main advances achieved in the last decade regarding the preclinical and clinical evaluation of BET bromodomain inhibitors in hematologic cancers, either as monotherapies or in combinations with standard and/or experimental agents. A mention will finally be given to the new concept of the protein degrader, and the perspective it holds for the design of bromodomain-based therapies.

Development of 2 Bromodomain and Extraterminal Inhibitors With Distinct Pharmacokinetic and Pharmacodynamic Profiles for the Treatment of Advanced Malignancies

PURPOSE

Bromodomain and extraterminal (BET) proteins are key epigenetic transcriptional regulators, inhibition of which may suppress oncogene expression. We report results from 2 independent first-in-human phase 1/2 dose-escalation and expansion, safety and tolerability studies of BET inhibitors INCB054329 (study INCB 54329-101; NCT02431260) and INCB057643 (study INCB 57643-101; NCT02711137).

PATIENTS AND METHODS

Patients (≥18 years) with advanced malignancies, ≥1 prior therapy, and adequate organ functions received oral INCB054329 (monotherapy) or INCB057643 (monotherapy or in combination with standard-of-care) in 21-day cycles (or 28-day cycles depending on standard-of-care combination). Primary endpoints were safety and tolerability.

RESULTS

Sixty-nine and 134 patients received INCB054329 and INCB057643, respectively. Study INCB 54329-101 has been completed; INCB 57643-101 is currently active, but not recruiting (no patients were receiving treatment as of January 8, 2019). Terminal elimination half-life was shorter for INCB054329 versus INCB057643 (mean [SD], 2.24 [2.03] vs. 11.1 [8.27] hours). INCB054329 demonstrated higher interpatient variability in oral clearance versus INCB057643 (CV%, 142% vs. 45.5%). Most common (>20%) any-grade treatment-related adverse events were similar for both drugs (INCB054329; INCB057643): nausea (35%; 30%), thrombocytopenia (33%; 32%), fatigue (29%; 30%), decreased appetite (26%; 22%). Two confirmed complete responses and 4 confirmed partial responses with INCB057643 were reported as best responses.

CONCLUSIONS

INCB057643 exhibited a more favorable PK profile versus INCB054329; exposure-dependent thrombocytopenia was observed with both drugs which limited the target inhibition that could be safely maintained. Further efforts are required to identify patient populations that can benefit most, and an optimal dosing scheme to maximize therapeutic index.

Emerging Epigenetic Therapeutic Targets in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a genetically heterogeneous malignancy for which treatment options have been largely limited to cytotoxic chemotherapy for the past four decades. Next-generation sequencing and other approaches have identified a spectrum of genomic and epigenomic alterations that contribute to AML initiation and maintenance. The key role of epigenetic modifiers and the reversibility of epigenetic changes have paved the way for evaluation of a new set of drug targets, and facilitated the design of novel candidate treatment strategies. More recently, seven new targeted therapies have been FDA-approved demonstrating successful implementation of the past decades' research. In this review, we will summarize the most recent advances in targeted therapeutics designed for a focused group of key epigenetic regulators in AML, outline their mechanism of action and their current status in clinical development. Furthermore, we will discuss promising new approaches for epigenetic targeted treatment in AML which are currently being tested in pre-clinical trials.

The next-generation BET inhibitor, PLX51107, delays melanoma growth in a CD8-mediated manner

Epigenetic agents such as bromodomain and extra-terminal region inhibitors (BETi) slow tumor growth via tumor intrinsic alterations; however, their effects on antitumor immunity remain unclear. A recent advance is the development of next-generation BETi that are potent and display a favorable half-life. Here, we tested the BETi, PLX51107, for immune-based effects on tumor growth in BRAF V600E melanoma syngeneic models. PLX51107 delayed melanoma tumor growth and increased activated, proliferating, and functional CD8+ T cells in tumors leading to CD8+ T-cell-mediated tumor growth delay. PLX51107 decreased Cox2 expression, increased dendritic cells, and lowered PD-L1, FasL, and IDO-1 expression in the tumor microenvironment. Importantly, PLX51107 delayed the growth of tumors that progressed on anti-PD-1 therapy; a response associated with decreased Cox2 levels, decreased PD-L1 expression on non-immune cells, and increased intratumoral CD8+ T cells. Thus, next-generation BETi represent a potential first-line and secondary treatment strategy for metastatic melanoma by eliciting effects, at least in part, on antitumor CD8+ T cells.

Regulatory mechanisms of B cell responses and the implication in B cell-related diseases

Terminally differentiated B cell, the plasma cell, is the sole cell type capable of producing antibodies in our body. Over the past 30 years, the identification of many key molecules controlling B cell activation and differentiation has elucidated the molecular pathways for generating antibody-producing plasma cells. Several types of regulation modulating the functions of the important key molecules in B cell activation and differentiation add other layers of complexity in shaping B cell responses following antigen exposure in the absence or presence of T cell help. Further understanding of the mechanisms contributing to the proper activation and differentiation of B cells into antibody-secreting plasma cells may enable us to develop new strategies for managing antibody humoral responses during health and disease. Herein, we reviewed the effect of different types of regulation, including transcriptional regulation, post-transcriptional regulation and epigenetic regulation, on B cell activation, and on mounting memory B cell and antibody responses. We also discussed the link between the dysregulation of the abovementioned regulatory mechanisms and B cell-related disorders.

The Hippo pathway modulates resistance to BET proteins inhibitors in lung cancer cells

Inhibitors of BET proteins (BETi) are anti-cancer drugs that have shown efficacy in pre-clinical settings and are currently in clinical trials for different types of cancer, including non-small cell lung cancer (NSCLC). Currently, no predictive biomarker is available to identify patients that may benefit from this treatment. To uncover the mechanisms of resistance to BETi, we performed a genome-scale CRISPR/Cas9 screening in lung cancer cells. We identified three Hippo pathway genes, LATS2, TAOK1, and NF2, as key determinants for sensitivity to BETi. The knockout of these genes induces resistance to BETi, by promoting TAZ nuclear localization and transcriptional activity. Conversely, TAZ expression promotes resistance to these drugs. We also showed that TAZ, YAP, and their partner TEAD are direct targets of BRD4 and that treatment with BETi downregulates their expression. Noticeably, molecular alterations in one or more of these genes are present in a large fraction of NSCLC patients and TAZ amplification or overexpression correlates with a worse outcome in lung adenocarcinoma. Our data define the central role of Hippo pathway in mediating resistance to BETi and provide a rationale for using BETi to counter-act YAP/TAZ-mediated pro-oncogenic activity.

Insights into novel emerging epigenetic drugs in myeloid malignancies

Epigenetics has been defined as ‘a stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence’ and several epigenetic regulators are recurrently mutated in hematological malignancies. Epigenetic modifications include changes such as DNA methylation, histone modifications and RNA associated gene silencing. Transcriptional regulation, chromosome stability, DNA replication and DNA repair are all controlled by these modifications. Mutations in genes encoding epigenetic modifiers are a frequent occurrence in hematologic malignancies and important in both the initiation and progression of cancer. Epigenetic modifications are also frequently reversible, allowing excellent opportunities for therapeutic intervention. The goal of epigenetic therapies is to reverse epigenetic dysregulation, restore the epigenetic balance, and revert malignant cells to a more normal condition. The role of epigenetic therapies thus far is most established in hematologic malignancies, with several agents already approved by the US Food and Drug Administration. In this review, we discuss pharmacological agents targeting epigenetic regulators.

Epigenetic Control of Mitochondrial Fission Enables Self-Renewal of Stem-like Tumor Cells in Human Prostate Cancer

Cancer stem cells (CSCs) contribute to disease progression and treatment failure in human cancers. The balance among self-renewal, differentiation, and senescence determines the expansion or progressive exhaustion of CSCs. Targeting these processes might lead to novel anticancer therapies. Here, we uncover a novel link between BRD4, mitochondrial dynamics, and self-renewal of prostate CSCs. Targeting BRD4 by genetic knockdown or chemical inhibitors blocked mitochondrial fission and caused CSC exhaustion and loss of tumorigenic capability. Depletion of CSCs occurred in multiple prostate cancer models, indicating a common vulnerability and dependency on mitochondrial dynamics. These effects depended on rewiring of the BRD4-driven transcription and repression of mitochondrial fission factor (Mff). Knockdown of Mff reproduced the effects of BRD4 inhibition, whereas ectopic Mff expression rescued prostate CSCs from exhaustion. This novel concept of targeting mitochondrial plasticity in CSCs through BRD4 inhibition provides a new paradigm for developing more effective treatment strategies for prostate cancer.

Super-enhancers: critical roles and therapeutic targets in hematologic malignancies

Super-enhancers (SEs) in a broad range of human cell types are large clusters of enhancers with aberrant high levels of transcription factor binding, which are central to drive expression of genes in controlling cell identity and stimulating oncogenic transcription. Cancer cells acquire super-enhancers at oncogene and cancerous phenotype relies on these abnormal transcription propelled by SEs. Furthermore, specific inhibitors targeting SEs assembly and activation have offered potential targets for treating various tumors including hematological malignancies. Here, we first review the identification, functional significance of SEs. Next, we summarize recent findings of SEs and SE-driven gene regulation in normal hematopoiesis and hematologic malignancies. The importance and various modes of SE-mediated MYC oncogene amplification are illustrated. Finally, we highlight the progress of SEs as selective therapeutic targets in basic research and clinical trials. Some open questions regarding functional significance and future directions of targeting SEs in the clinic will be discussed too.

Bromodomains: a new target class for drug development

Less than a decade ago, it was shown that bromodomains, acetyl lysine 'reader' modules found in proteins with varied functions, were highly tractable small-molecule targets. This is an unusual property for protein-protein or protein-peptide interaction domains, and it prompted a wave of chemical probe discovery to understand the biological potential of new agents that targeted bromodomains. The original examples, inhibitors of the bromodomain and extra-terminal (BET) class of bromodomains, showed enticing anti-inflammatory and anticancer activities, and several compounds have since advanced to human clinical trials. Here, we review the current state of BET inhibitor biology in relation to clinical development, and we discuss the next wave of bromodomain inhibitors with clinical potential in oncology and non-oncology indications. The lessons learned from BET inhibitor programmes should affect efforts to develop drugs that target non-BET bromodomains and other epigenetic readers.

Future of Personalized Therapy Targeting Aberrant Signaling Pathways in Multiple Myeloma

Multiple myeloma (MM) is a genetically complex disease. Identification of mutations and aberrant signaling pathways that contribute to the progression of MM and drug resistance has potential to lead to specific targets and personalized treatment. Aberrant signal pathways include RAS pathway activation due to RAS or BRAF mutations (targeted by vemurafenib alone or combined with cobimetinib), BCL-2 overexpression in t(11:14) (targeted by venetoclax), JAK2 pathway activation (targeted by ruxolitinib), NF-κB pathway activation (treated with DANFIN combined with bortezomib), MDM2 overexpression, and PI3K/mTOR pathway activation (targeted by BEZ235). Cyclin D1 (CCND1) and MYC are also emerging as key potential targets. In addition, histone deacetylase inhibitors are already in use for the treatment of MM in combination therapy, and targeted inhibition of FGFR3 (AZD4547) is effective in myeloma cells with t(4;14) translocation. Bromodomain and extra terminal (BET) protein antagonists decrease the expression of MYC and have displayed promising antimyeloma activity. A better understanding of the alterations in signaling pathways that promote MM progression will further inform the development of precision therapy for patients.