BET inhibition in advanced cutaneous T cell lymphoma is synergistically potentiated by BCL2 inhibition or HDAC inhibition

Targeting anti-apoptotic mechanisms in tumour cells: Strategies for enhancing Cancer therapy

Anti-cancer drug's cytotoxicity is determined by their ability to induce predetermined cell demise, commonly called apoptosis. The cancer-causing cells are able to evade cell death, which has been affiliated with both malignancy as well as resistance to cancer treatments. In order to avoid cell death, cancerous tumour cells often produce an abundance of anti-apoptotic proteins, becoming "dependent" on them. Consequently, protein inhibitors of cell death may prove to be beneficial as pharmacological targets for the future creation of cancer therapies. This article examines the molecular routes of apoptosis, its clinical manifestations, anti-cancer therapy options that target the intrinsic mechanism of apoptosis, proteins that prevent cell death, and members of the B-lymphoma-2 subset. In addition, novel approaches to cell death are highlighted, including how curcumin mitigates chemotherapy-induced apoptosis in healthy tissues and the various ways melatonin modifies apoptosis to improve cancer treatment efficacy, particularly through the TNF superfamily. Cancer treatment-induced increases in anti-apoptotic proteins lead to drug resistance; yet, ligands that trigger cell death by inhibiting these proteins are expected to improve chemotherapy's efficacy. The potential of frequency-modulated dietary phytochemicals as a cancer therapeutic pathway, including autophagy and apoptosis, is also explored. This approach may be more efficient than inhibition alone in overcoming drug resistance. Consequently, this method has the potential to allow for lower medication concentrations, reducing cytotoxicity and unwanted side effects.

A Yale Dermatology perspective on cutaneous T cell lymphoma: Historic reflection to emerging therapies

Cutaneous T cell lymphoma (CTCL) is a form of non-Hodgkin lymphoma that can involve the skin, along with lymph nodes and blood. The two most common subtypes of CTCL are mycosis fungoides and Sézary syndrome. Since the initial description of mycosis fungoides by Dr Jean-Louis Alibert in 1806, there have been significant advances in our understanding of the pathogenesis of CTCL, its diverse clinical and histologic variants, and the evolving treatment landscape. One major contributor to this story has been Dr Irwin M. Braverman, former vice chair of Dermatology at the Yale School of Medicine. Herein, we provide tribute to his discoveries, teaching, mentorship, and clinical care that have influenced our insights into CTCL and emerging treatments for this challenging malignancy.

HDAC10 and its implications in Sézary syndrome pathogenesis

Cutaneous T-cell lymphomas (CTCL) are a group of rare hematological malignancies characterized by infiltration of malignant T-cells into the skin. Two main types of CTCL constitute of Mycosis Fungoides (MF), a more indolent form of the disease, and Sézary syndrome (SS), the aggressive and leukemic variant with blood involvement. Sézary syndrome presents a significant clinical challenge due to its very aggressive nature, poor prognosis, and treatment resistance, and to date, the disease remains incurable. Histone deacetylase inhibitors have gained attention in CTCL treatment with promising results, but they expose limited specificity and strong side effects. Recent genomic studies underscore the role of epigenetic modifiers in CTCL pathogenesis, prompting an investigation into HDAC10, a member of class IIb HDACs, in SS. HDAC10 was investigated in different cancers, revealing its involvement in cell cycle regulation, apoptosis, and autophagy, but its role in CTCL is unknown. In this study we aimed to determine the role of HDAC10 in SS, focusing on its cellular localization, role in cell growth, and therapeutic potential. We indicated that HDAC10 is overexpressed in SS patients and located mainly in the cytoplasm. Its overexpression leads to an inhibitory effect on apoptosis progression when exposed to the pro-apoptotic compound Camptothecin (CPT). Knockdown of HDAC10 resulted in reduced cell growth and induction of apoptosis and autophagy, highlighting its potential importance in CTCL pathogenesis. Whole transcriptome analysis indicated that HDAC10 is associated with crucial cancer-related pathways, for example, hematopoietic cell lineage, PI3K-Akt signaling pathway, Ras signaling pathway, MAPK signaling pathway or JAK-STAT signaling pathway, which are critical for the survival and proliferation of malignant T cells. Inhibition of HDAC10 with selective HDAC10i increased the sensitivity of Sézary cells to the pro-apoptotic CPT. Our findings demonstrate that HDAC10 plays a key role in the molecular background of Sézary syndrome, highlighting its importance in the cellular mechanisms of the disease.

RUNX1 expression is regulated by a super-enhancer and is a therapeutic target in adult T-cell leukemia/lymphoma

Super-enhancers (SEs) play an important role in regulating tumor-specific gene expression. JQ1, a Bromodomain-containing protein 4 (BRD4) inhibitor, exerts antitumor effects by disrupting SE-mediated regulation of gene expression. We investigated the anti-adult T-cell leukemia/lymphoma (ATL) effects of JQ1. JQ1 induced apoptosis and inhibited ATL cell proliferation. JQ1 suppressed RUNX1expression through the disruption of SE-mediated gene regulation. In the previous reports, it was shown that IC50s of AI-10-104 and Ro5-3335, RUNX1 inhibitors were 1-10 µM for lymphoblastic leukemia cell lines carrying RUNX1 mutations. In the present study, we demonstrated that IC50s of AI-10-104 and Ro5-3335 were also 1-10 µM or lower for ATL cell lines. Simultaneously, AI-10-104 suppressed MYC proto-oncogene (c-MYC) expression. RUNX1 is a potential therapeutic target for ATL that promotes c-MYC expression. We showed that RUNX1 expression is regulated via SEs in ATL and that RUNX1 may be a novel therapeutic target for ATL.

Bromodomain and extraterminal (BET) proteins: biological functions, diseases, and targeted therapy

BET proteins, which influence gene expression and contribute to the development of cancer, are epigenetic interpreters. Thus, BET inhibitors represent a novel form of epigenetic anticancer treatment. Although preliminary clinical trials have shown the anticancer potential of BET inhibitors, it appears that these drugs have limited effectiveness when used alone. Therefore, given the limited monotherapeutic activity of BET inhibitors, their use in combination with other drugs warrants attention, including the meaningful variations in pharmacodynamic activity among chosen drug combinations. In this paper, we review the function of BET proteins, the preclinical justification for BET protein targeting in cancer, recent advances in small-molecule BET inhibitors, and preliminary clinical trial findings. We elucidate BET inhibitor resistance mechanisms, shed light on the associated adverse events, investigate the potential of combining these inhibitors with diverse therapeutic agents, present a comprehensive compilation of synergistic treatments involving BET inhibitors, and provide an outlook on their future prospects as potent antitumor agents. We conclude by suggesting that combining BET inhibitors with other anticancer drugs and innovative next-generation agents holds great potential for advancing the effective targeting of BET proteins as a promising anticancer strategy.

FISH Panel for Leukemic Cutaneous T-Cell Lymphoma: Extended Patient Cohort Correlation with Blood Involvement and Clinical Outcomes

The genomic basis of cutaneous T-cell lymphoma has been characterized by gene copy number alterations and genomic sequencing, but there are few clinical tests that are being widely used to inform the diagnosis and prognosis of leukemic cutaneous T-cell lymphoma that may arise as a progression from mycosis fungoides or de novo as Sézary syndrome. An 11-gene FISH panel of TP53, RB1, DNMT3A, FAS, ZEB1, ARID1A, ATM, and CDKN2A deletions and MYC, signal transducer and activator of transcription gene (STAT)3/5B, and CARD11 amplifications was previously found to encapsulate >95% of gene copy number variations in leukemic cutaneous T-cell lymphoma. Through a retrospective analysis of patients with leukemic cutaneous T-cell lymphoma seen at the Yale Cancer Center from 2014 to 2020, we gathered the relevant genes as they became available and correlated them to factors with prognostic relevance as a proof of concept to show the potential utility in further developing a limited gene panel for prognosis. In this study, we show that the abnormal FISH results show an association with clinically relevant factors (blood stage, CD4:8 ratio, and percentage blood involvement) and have a nonsignificant statistical trend (>90%) toward correlation with overall survival. In addition, the previous cost-effective panels were signal transducer and activator of transcription (STAT)3/5B, MYC, TP53, and ARID1A. We now suggest adding RB1 and ZEB1 on the basis of our findings.

The Robust Tumoricidal Effects of Combined BET/HDAC Inhibition in Cutaneous T-Cell Lymphoma Can Be Reproduced by ΔNp73 Depletion

Combined BET inhibitor/histone deacetylase inhibitor treatment induces marked apoptosis of cutaneous T-cell lymphoma (CTCL) with minimal normal T-cell toxicity. At 96 hours when apoptosis was extensive, a majority of CTCL lines showed ≥2-fold suppression of T-cell survival factors (e.g., AKT1, BCL2 antiapoptotic factors, BIRC5, CD40, CD70, GADD45A, PRKCA, TNFRSF1B, ΔNp73) and ≥2-fold upregulation of proapoptotic factors and tumor suppressors (e.g., ATM, BAK, BIM, multiple caspases, FHIT, HIC1, MGMT, NOD1) (P < 0.05). The largest alterations were in TP73 isoform expression, resulting in increased TAp73/ΔNp73 ratios in CTCL lines and leukemic Sézary cells. Targeted ΔNp73 inhibition by small interfering RNA knockdown resulted in robust CTCL apoptosis comparable with that induced by BET inhibitor/histone deacetylase inhibitor with minimal normal T-cell toxicity. Chromatin immunoprecipitation analysis showed that BET inhibitor/histone deacetylase inhibitor treatment reduced RNA polymerase II binding to ΔNp73, MYC, and AKT1 while increasing its binding to TAp73. CTCL skin lesions expressed both TAp73 and ΔNp73 isoforms in situ. In aggregate, these findings implicate TAp73/ΔNp73 balance as a major factor governing CTCL survival, show that the expression of p73 isoforms can be altered by molecular biological and pharmaceutical means, show that p73 isoforms are expressed across the entire CTCL clinical spectrum, and identify the p73 pathway as a potential target for therapeutics.

DOT1L inhibition does not modify the sensitivity of cutaneous T cell lymphoma to pan-HDAC inhibitors in vitro

Cutaneous T-cell lymphomas (CTCLs) are a subset of T-cell malignancies presenting in the skin. The treatment options for CTCL, in particular in advanced stages, are limited. One of the emerging therapies for CTCL is treatment with histone deacetylase (HDAC) inhibitors. We recently discovered an evolutionarily conserved crosstalk between HDAC1, one of the targets of HDAC inhibitors, and the histone methyltransferase DOT1L. HDAC1 negatively regulates DOT1L activity in yeast, mouse thymocytes, and mouse thymic lymphoma. Here we studied the functional relationship between HDAC inhibitors and DOT1L in two human CTCL cell lines, specifically addressing the question whether the crosstalk between DOT1L and HDAC1 observed in mouse T cells plays a role in the therapeutic effect of clinically relevant broad-acting HDAC inhibitors in the treatment of human CTCL. We confirmed that human CTCL cell lines were sensitive to treatment with pan-HDAC inhibitors. In contrast, the cell lines were not sensitive to DOT1L inhibitors. Combining both types of inhibitors did neither enhance nor suppress the inhibitory effect of HDAC inhibitors on CTCL cells. Thus our in vitro studies suggest that the effect of commonly used pan-HDAC inhibitors in CTCL cells relies on downstream effects other than DOT1L misregulation.

Mechanisms of venetoclax resistance and solutions

The BCL-2 inhibitor venetoclax is currently approved for treatment of hematologic diseases and is widely used either as monotherapy or in combination strategies. It has produced promising results in the treatment of refractory or relapsed (R/R) and aged malignant hematologic diseases. However, with clinical use, resistance to venetoclax has emerged. We review the mechanism of reduced dependence on BCL-2 mediated by the upregulation of antiapoptotic proteins other than BCL-2, such as MCL-1 and BCL-XL, which is the primary mechanism of venetoclax resistance, and find that this mechanism is achieved through different pathways in different hematologic diseases. Additionally, this paper also summarizes the current investigations of the mechanisms of venetoclax resistance in terms of altered cellular metabolism, changes in the mitochondrial structure, altered or modified BCL-2 binding domains, and some other aspects; this article also reviews relevant strategies to address these resistance mechanisms.

Co-Binding of JQ1 and Venetoclax Exhibited Synergetic Inhibitory Effect for Cancer Therapy; Potential Line of Treatment for the Waldenström Macroglobulinemia Lymphoma

In recent times, the development of combination therapy has been a focal point in drug discovery. This article explores the potential synergistic effect of co-administration of Bcl2 inhibitor Venetoclax and BET inhibitor JQ1. We envisioned that the 'dual-site'-binding of Bcl2 has significant prospects and paves the way for the next round of rational design of potent Waldenström macroglobulinemia (WM) therapy. The preferential binding mechanisms of the multi-catalytic sites of the Bcl2 enzyme have been a subject of debate in the literature. This study conducted a systematic procedure to explore the preferred binding modes and the structural effects of co-binding at each catalytic active site. Interestingly, a mutual enhanced binding effect was observed - Venetoclax increased the binding affinity of JQ1 by 11.5 %, while JQ1 boosted the binding affinity of Venetoclax by 16.3 % when compared with individual inhibition of each drug. This synergistic binding effect has significantly increased protein stability, with substantial correlated movements and multiple van der Waals interactions. The structural and thermodynamic insights unveiled in this report would assist the future design of improved combined therapy against WM.

Apoptosis and Pharmacological Therapies for Targeting Thereof for Cancer Therapeutics

Apoptosis is an evolutionarily conserved sequential process of cell death to maintain a homeostatic balance between cell formation and cell death. It is a vital process for normal eukaryotic development as it contributes to the renewal of cells and tissues. Further, it plays a crucial role in the elimination of unnecessary cells through phagocytosis and prevents undesirable immune responses. Apoptosis is regulated by a complex signaling mechanism, which is driven by interactions among several protein families such as caspases, inhibitors of apoptosis proteins, B-cell lymphoma 2 (BCL-2) family proteins, and several other proteases such as perforins and granzyme. The signaling pathway consists of both pro-apoptotic and pro-survival members, which stabilize the selection of cellular survival or death. However, any aberration in this pathway can lead to abnormal cell proliferation, ultimately leading to the development of cancer, autoimmune disorders, etc. This review aims to elaborate on apoptotic signaling pathways and mechanisms, interacting members involved in signaling, and how apoptosis is associated with carcinogenesis, along with insights into targeting apoptosis for disease resolution.

Combination of Resminostat with Ruxolitinib Exerts Antitumor Effects in the Chick Embryo Chorioallantoic Membrane Model for Cutaneous T Cell Lymphoma

Simple Summary

The combination of Resminostat (HDACi) and Ruxolitinib (JAKi) exerted cytotoxic effects and inhibited proliferation of CTCL cell lines (MyLa, SeAx) in vitro. The aim of the present study was to validate their antitumor effects in vivo using the chick embryo chorioallantoic membrane (CAM) model, which allows quick and efficient monitoring of tumor growth, migration, invasion, and metastatic potential. The drug combination exhibited a significant inhibition of primary tumor size, and inhibited intravasation and extravasation of tumor cells to the liver and lung. It also exerted an inhibitory effect in the migration and invasion of tumor cells and significantly reduced key signaling pathway activation. Our data demonstrate that the CAM assay could be employed as a preclinical in vivo model in CTCL for pharmacological testing, and that the combination of Resminostat and Ruxolitinib exerts significant antitumor effects in CTCL progression that need to be further evaluated in a clinical setting.

Abstract

The combination of Resminostat (HDACi) and Ruxolitinib (JAKi) exerted cytotoxic effects and inhibited proliferation of CTCL cell lines (MyLa, SeAx) in previously published work. A xenograft tumor formation was produced by implanting the MyLa or SeAx cells on top of the chick embryo chorioallantoic membrane (CAM). The CAM assay protocol was developed to monitor the metastatic properties of CTCL cells and the effects of Resminostat and/or Ruxolitinib in vivo. In the spontaneous CAM assays, Resminostat and Ruxolitinib treatment inhibited the cell proliferation (p < 0.001) of MyLa and SeAx, and induced cell apoptosis (p < 0.005, p < 0.001, respectively). Although monotherapies reduced the size of primary tumors in the metastasis CAM assay, the drug combination exhibited a significant inhibition of primary tumor size (p < 0.0001). Furthermore, the combined treatment inhibited the intravasation of MyLa (p < 0.005) and SeAx cells (p < 0.0001) in the organs, as well as their extravasation to the liver (p < 0.0001) and lung (p < 0.0001). The drug combination also exerted a stronger inhibitory effect in migration (p < 0.0001) rather in invasion (p < 0.005) of both MyLa and SeAx cells. It further reduced p-p38, p-ERK, p-AKT, and p-STAT in MyLa cells, while it decreased p-ERK and p-STAT in SeAx cells in CAM tumors. Our data demonstrated that the CAM assay could be employed as a preclinical in vivo model in CTCL for pharmacological testing. In agreement with previous in vitro data, the combination of Resminostat and Ruxolitinib was shown to exert antitumor effects in CTCL in vivo.

Review of cancer cell resistance mechanisms to apoptosis and actual targeted therapies

The apoptosis pathway is a programmed cell death mechanism that is crucial for cellular and tissue homeostasis and organ development. There are three major caspase-dependent pathways of apoptosis that ultimately lead to DNA fragmentation. Cancerous cells are known to highly regulate the apoptotic pathway and its role in cancer hallmark acquisition has been discussed over the past decades. Numerous mutations in cancer cell types have been reported to be implicated in chemoresistance and treatment outcome. In this review, we summarize the mutations of the caspase-dependant apoptotic pathways that are the source of cancer development and the targeted therapies currently available or in trial.

BET Proteins as Attractive Targets for Cancer Therapeutics

Transcriptional dysregulation is a hallmark of cancer and can be an essential driver of cancer initiation and progression. Loss of transcriptional control can cause cancer cells to become dependent on certain regulators of gene expression. Bromodomain and extraterminal domain (BET) proteins are epigenetic readers that regulate the expression of multiple genes involved in carcinogenesis. BET inhibitors (BETis) disrupt BET protein binding to acetylated lysine residues of chromatin and suppress the transcription of various genes, including oncogenic transcription factors. Phase I and II clinical trials demonstrated BETis’ potential as anticancer drugs against solid tumours and haematological malignancies; however, their clinical success was limited as monotherapies. Emerging treatment-associated toxicities, drug resistance and a lack of predictive biomarkers limited BETis’ clinical progress. The preclinical evaluation demonstrated that BETis synergised with different classes of compounds, including DNA repair inhibitors, thus supporting further clinical development of BETis. The combination of BET and PARP inhibitors triggered synthetic lethality in cells with proficient homologous recombination. Mechanistic studies revealed that BETis targeted multiple essential homologous recombination pathway proteins, including RAD51, BRCA1 and CtIP. The exact mechanism of BETis’ anticancer action remains poorly understood; nevertheless, these agents provide a novel approach to epigenome and transcriptome anticancer therapy.

Potent Anticancer Effects of Epidithiodiketopiperazine NT1721 in Cutaneous T Cell Lymphoma

Simple Summary

Cutaneous T cell lymphomas (CTCLs) are a group of blood cancers that cannot be cured with current chemotherapeutical or biological drugs. Patients with advanced disease are severely immunocompromised due to the unchecked expansion of malignant T cells and have low survival rates of less than four years. Hence, new treatment options for CTCLs are urgently needed. In this study the anti-CTCL activity of a new compound, NT1721, was determined in vitro and in two CTCL mouse models. We found that NT1721 increased apoptosis (programmed cell death) in the malignant T cells and reduced tumor growth better than two drugs that are currently clinically used for CTCL treatment (i.e., gemcitabine, romidepsin). These results suggest that NT1721 may represent a potent new agent for the treatment of advanced CTCL.

Abstract

Cutaneous T cell lymphomas (CTCLs) are a heterogeneous group of debilitating, incurable malignancies. Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common subtypes, accounting for ~65% of CTCL cases. Patients with advanced disease have a poor prognosis and low median survival rates of four years. CTCLs develop from malignant skin-homing CD4⁺ T cells that spread to lymph nodes, blood, bone marrow and viscera in advanced stages. Current treatments options for refractory or advanced CTCL, including chemotherapeutic and biological approaches, rarely lead to durable responses. The exact molecular mechanisms of CTCL pathology remain unclear despite numerous genomic and gene expression profile studies. However, apoptosis resistance is thought to play a major role in the accumulation of malignant T cells. Here we show that NT1721, a synthetic epidithiodiketopiperazine based on a natural product, reduced cell viability at nanomolar concentrations in CTCL cell lines, while largely sparing normal CD4⁺ cells. Treatment of CTCL cells with NT1721 reduced proliferation and potently induced apoptosis. NT1721 mediated the downregulation of GLI1 transcription factor, which was associated with decreased STAT3 activation and the reduced expression of downstream antiapoptotic proteins (BCL2 and BCL-xL). Importantly, NT1721, which is orally available, reduced tumor growth in two CTCL mouse models significantly better than two clinically used drugs (romidepsin, gemcitabine). Moreover, a combination of NT1721 with gemcitabine reduced the tumor growth significantly better than the single drugs. Taken together, these results suggest that NT1721 may be a promising new agent for the treatment of CTCLs.

JAK inhibition synergistically potentiates BCL2, BET, HDAC, and proteasome inhibition in advanced CTCL

Cutaneous T-cell lymphoma (CTCL) is a malignancy of skin-homing T lymphocytes that is more likely to involve the peripheral blood in advanced stages. For such patients with advanced disease, there are few available systemic treatment options, and prognosis remains poor. Exome sequencing studies of CTCL have suggested therapeutic targets, including within the JAK/STAT pathway, but JAK inhibition strategies may be limited by patient-specific mutational status. Because our recent research has highlighted the potential roles of single and combination approaches specifically using BCL2, bromodomain and extra-terminal domain (BET), and histone deacetylase (HDAC) inhibition, we aimed to investigate the effects of JAK inhibition on CTCL cells and established CTCL cell lines when paired with these and other targeting agents. Peripheral blood malignant CTCL isolates exhibited differential responses to JAK inhibition, with JAK2 expression levels negatively correlating to 50% inhibitory concentration (IC50) values. Regardless of single-agent sensitivity, JAK inhibition potentiated malignant cell cytotoxicity in combination with BCL2, BET, HDAC, or proteasome inhibition. Combination inhibition of JAK and BCL2 showed the strongest potentiation of CTCL cytotoxicity, driven by both intrinsic and extrinsic apoptosis pathways. JAK inhibition decreased expression of BCL2 in the high-responder samples, suggesting a putative mechanism for this combination activity. These results indicate that JAK inhibition may have major effects on CTCL cells, and that combination strategies using JAK inhibition may allow for more generalized cytotoxic effects against the malignant cells from patients with CTCL. Such preclinical assessments help inform prioritization for combination targeted drug approaches for clinical utilization in the treatment of CTCL.

Targeting epigenetic mechanisms to overcome venetoclax resistance

The BH-3 mimetic venetoclax overcomes apoptosis and therapy resistance caused by high expression of BCL2 or loss of BH3-only protein function. Although a promising therapy for hematologic malignancies, increased expression of anti-apoptotic MCL-1 or BCL-XL, as well as other resistance mechanisms prevent a durable response to venetoclax. Recent studies demonstrate that agents targeting epigenetic mechanisms such as DNA methyltransferase inhibitors, histone deacetylase (HDAC) inhibitors, histone methyltransferase EZH2 inhibitors, or bromodomain reader protein inhibitors may disable oncogenic gene expression signatures responsible for venetoclax resistance. Combination therapies including venetoclax and epigenetic therapies are effective in preclinical models and the subject of many current clinical trials. Here we review epigenetic strategies to overcome venetoclax resistance mechanisms in hematologic malignancies.

Current status in the discovery of dual BET/HDAC inhibitors

The development of desired multitarget agents may provide an attractive and cost-effective complement or alternative to drug combinations. Bromodomain and extraterminal domain (BET) and histone deacetylase (HDAC), as important epigenetic modulators, are attractive targets in drug discovery and development. Considering the fact that BET and HDAC inhibitors exert a synergistic effect on cellular processes in cancer cells, the design of dual BET/HDAC inhibitors may be a rational strategy to improve the efficacy of their single-target drugs for tumor treatment. In the current review, we depict the development of dual BET/HDAC inhibitors and particularly highlight their structure-activity relationships (SARs), binding modes, and biological functions with the aim to facilitate rational drug design and develop more dual BET/HDAC inhibitors.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Current status in the discovery of dual BET/HDAC inhibitors

The development of desired multitarget agents may provide an attractive and cost-effective complement or alternative to drug combinations. BET and HDAC, as important epigenetic modulators, are both attractive targets in drug discovery and development. Considering the fact that BET and HDAC inhibitors exert a synergistic effect on cellular processes in cancer cells, the design of dual BET/HDAC inhibitors may be a rational strategy to improve the efficacy of their single-target drugs for tumor treatment. In current review, we depict the development of dual BET/HDAC inhibitors and particularly highlight their SARs, binding modes and biological functions with the aim to facilitate rational design and develop more dual BET/HDAC inhibitors.

Novel targeted therapies of T cell lymphomas

T cell lymphomas (TCL) comprise a heterogeneous group of non-Hodgkin lymphomas (NHL) that often present at an advanced stage at the time of diagnosis and that most commonly have an aggressive clinical course. Treatment in the front-line setting is most often cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) or CHOP-like regimens, which are effective in B cell lymphomas, but in TCL are associated with a high failure rate and frequent relapses. Furthermore, in contrast to B cell NHL, in which substantial clinical progress has been made with the introduction of monoclonal antibodies, no comparable advances have been seen in TCL. To change this situation and improve the prognosis in TCL, new gene-targeted therapies must be developed. This is now possible due to enormous progress that has been made in the last years in the understanding of the biology and molecular pathogenesis of TCL, which enables the implementation of the research findings in clinical practice. In this review, we present new therapies and current clinical and preclinical trials on targeted treatments for TCL using histone deacetylase inhibitors (HDACi), antibodies, chimeric antigen receptor T cells (CARTs), phosphatidylinositol 3-kinase inhibitors (PI3Ki), anaplastic lymphoma kinase inhibitors (ALKi), and antibiotics, used alone or in combinations. The recent clinical success of ALKi and conjugated anti-CD30 antibody (brentuximab-vedotin) suggests that novel therapies for TCL can significantly improve outcomes when properly targeted.

Epigenetic targeting of Waldenström macroglobulinemia cells with BET inhibitors synergizes with BCL2 or histone deacetylase inhibition

Aim: Waldenström macroglobulinemia (WM) is a low-grade B-cell lymphoma characterized by overproduction of monoclonal IgM. To date, there are no therapies that provide a cure for WM patients, and therefore, it is important to explore new therapies. Little is known about the efficiency of epigenetic targeting in WM. Materials & methods: WM cells were treated with BET inhibitors (JQ1 and I-BET-762) and venetoclax, panobinostat or ibrutinib. Results: BET inhibition reduces growth of WM cells, with little effect on survival. This finding was enhanced by combination therapy, with panobinostat (LBH589) showing the highest synergy. Conclusion: Our studies identify BET inhibitors as effective therapy for WM, and these inhibitors can be enhanced in combination with BCL2 or histone deacetylase inhibition.

Discovery of selective HDAC/BRD4 dual inhibitors as epigenetic probes

According to the binding mode of ABBV-744 with bromodomains and the cape space of HDAC, the novel selective HDAC/BRD4 dual inhibitors were designed and synthesized by the pharmacophore fusion strategy. Evaluating the biomolecular activities through SARs exploration identified three kinds of selective dual inhibitors 41c (HDAC1/BRD4), 43a (pan-HDAC/BRD4) and 43d (HDAC6/BRD4(BD2)), whose target-related cellular activities in MV-4-11 cells were also confirmed. Significantly, the selective dual inhibitor 41c (HDAC1/BRD4) exhibited synergistic effects against MV-4-11 cells, which strongly induced G0/G1 cell cycle arrest and apoptosis, and the first HDAC6/BRD4(BD2) dual inhibitor was found. This study provides support for selective HDAC/BRD4 dual inhibitors as epigenetic probes based on pyrrolopyridone core for the future biological evaluation in different cancer cell lines.

Chromatin-Remodeled State in Lymphoma

PURPOSE OF REVIEW

Emerging evidence has shown that epigenetic derangements might drive and promote tumorigenesis in various types of malignancies and is prevalent in both B cell and T cell lymphomas. The purpose of this review is to explain how the epigenetic derangements result in a chromatin-remodeled state in lymphoma and contribute to the biology and clinical features of these tumors.

RECENT FINDINGS

Studies have explored on the functional role of epigenetic derangements in chromatin remodeling and lymphomagenesis. For example, the haploinsufficiency of CREBBP facilitates malignant transformation in mice and directly implicates the importance to re-establish the physiologic acetylation level. New findings identified 4 prominent DLBCL subtypes, including EZB-GC-DLBCL subtype that enriched in mutations of CREBBP, EP300, KMT2D, and SWI/SNF complex genes. EZB subtype has a worse prognosis than other GCB-tumors. Moreover, the action of the histone modifiers as well as chromatin-remodeling factors (e.g., SWI/SNF complex) cooperates to influence the chromatin state resulting in transcription repression. Drugs that alter the epigenetic landscape have been approved in T cell lymphoma. In line with this finding, epigenetic lesions in histone modifiers have recently been uncovered in this disease, further confirming the vulnerability to the therapies targeting epigenetic derangements. Modulating the chromatin state by epigenetic-modifying agents provides precision-medicine opportunities to patients with lymphomas that depend on this biology.

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.

Enhancing venetoclax activity in hematological malignancies

INTRODUCTION

Targeting anti-apoptotic pathways involving the BCL2 family proteins represents a novel treatment strategy in hematologic malignancies. Venetoclax, a selective BCL2 inhibitor, represents the first approved agent of this class, and is currently used in CLL and AML. However, monotherapy is rarely sufficient for sustained responses due to the development of drug resistance and loss of dependence upon the targeted protein. Numerous pre-clinical studies have shown that combining venetoclax with other agents may represent a more effective therapeutic strategy by circumventing resistance mechanisms. In this review, we summarize pre-clinical data providing a foundation for rational combination strategies involving venetoclax.

AREAS COVERED

Novel combination strategies in hematologic malignancies involving venetoclax, primarily at the pre-clinical level, will be reviewed. We emphasize novel agents that interrupt complementary or compensatory pro-survival pathways, and particularly mechanistic insights underlying synergism. PubMed, Cochrane, EMBASE, and Google scholar were searched from 2000.

EXPERT OPINION

Although venetoclax has proven to be an effective therapeutic in hematologic malignancies, monotherapy may be insufficient for maximal effectiveness due to the development of resistance and/or loss of BCL2 addiction. Further pre-clinical and clinical development of combination therapies may be necessary for optimal outcomes in patients with diverse blood cancers.

Targeting apoptosis in cancer therapy

For over three decades, a mainstay and goal of clinical oncology has been the development of therapies promoting the effective elimination of cancer cells by apoptosis. This programmed cell death process is mediated by several signalling pathways (referred to as intrinsic and extrinsic) triggered by multiple factors, including cellular stress, DNA damage and immune surveillance. The interaction of apoptosis pathways with other signalling mechanisms can also affect cell death. The clinical translation of effective pro-apoptotic agents involves drug discovery studies (addressing the bioavailability, stability, tumour penetration, toxicity profile in non-malignant tissues, drug interactions and off-target effects) as well as an understanding of tumour biology (including heterogeneity and evolution of resistant clones). While tumour cell death can result in response to therapy, the selection, growth and dissemination of resistant cells can ultimately be fatal. In this Review, we present the main apoptosis pathways and other signalling pathways that interact with them, and discuss actionable molecular targets, therapeutic agents in clinical translation and known mechanisms of resistance to these agents.

The novel dual BET/HDAC inhibitor TW09 mediates cell death by mitochondrial apoptosis in rhabdomyosarcoma cells

Targeting the epigenome of cancer cells with the combination of Bromodomain and Extra Terminal (BET) protein inhibitors and histone deacetylase (HDAC) inhibitors has shown synergistic antitumor effects in several cancer types. In this study, we investigate the antitumor potential of the novel dual BET/HDAC inhibitor TW09 in rhabdomyosarcoma (RMS) cells. TW09 reduces cell viability, suppresses long-term clonogenic survival and induces cell death in RMS cells in a dose-dependent manner. Compared to BET/HDAC co-inhibition using JQ1 and MS-275, TW09 induces similar cell death at equimolar concentrations and regulates BET and HDAC target proteins (e.g. c-MYC, H3 acetylation). Mechanistic studies revealed that TW09 upregulates BIM, NOXA, PUMA and BMF, while downregulating BCL-X_L, leading to proapoptotic rebalancing of BCL-2 proteins. This results in BAK and BAX activation and caspase-dependent apoptosis, since individual genetic silencing of BIM, NOXA, PUMA, BMF, BAK or BAX, overexpression of BCL-2 or the caspase inhibition with zVAD.fmk all rescue JQ1/BYL719-induced cell death. In conclusion, TW09 shows potent antitumor activity in RMS cells in vitro by inducing mitochondrial apoptosis and may represent a promising new therapeutic option for the treatment of RMS.

Update on Biology of Cutaneous T-Cell Lymphoma

Cutaneous T cell lymphomas (CTCL) comprise of a heterogeneous group of non-Hodgkin lymphomas derived from skin-homing T cells. Variation in clinical presentation and lack of definitive molecular markers make diagnosis especially challenging. The biology of CTCL remains elusive and clear links between genetic aberrations and epigenetic modifications that would result in clonal T cell expansion have not yet been identified. Nevertheless, in recent years, next generation sequencing (NGS) has enabled a much deeper understanding of the genomic landscape of CTCL by uncovering aberrant genetic pathways and epigenetic dysregulations. Additionally, single cell profiling is rapidly advancing our understanding of patients-specific tumor landscape and its interaction with the surrounding microenvironment. These studies have paved the road for future investigations that will explore the functional relevance of genetic alterations in the progression of disease. The ultimate goal of elucidating the pathogenesis of CTCL is to establish effective therapeutic targets with more durable clinical response and treat relapsing and refractory CTCL.

Insights Into the Molecular and Cellular Underpinnings of Cutaneous T Cell Lymphoma

Cutaneous T cell lymphoma (CTCL) is a rare malignancy of skin-homing T lymphocytes. Advances in whole exome sequencing have identified a vast number of both single nucleotide variants (SNVs) and genomic copy number alterations (GCNAs) as driver mutations present in CTCL cells. These alterations cluster within several key pathways - T cell/NF-κB/JAK-STAT activation, cell cycle dysregulation/apoptosis, and DNA structural dysregulation affecting gene expression - allowing the maintenance of a population of proliferating, activated malignant T lymphocytes. While much of the clinical spectrum, genetic alterations, and oncogenic behavior of CTCL have been elucidated, little is known about the etiology that underlies CTCL malignant transformation and progression. Herein, we review the epidemiology, clinical presentation, and pathophysiology of CTCL to provide a perspective on CTCL pathogenesis. We outline a series of alterations by which mature, activated T lymphocytes are endowed with apoptosis resistance and cutaneous persistence. Subsequent genomic alterations including the loss of chromosomal structural controls further promote proliferation and constitutive T cell activation. CTCL cells are both malignant cells and highly functional T cells that can have major cutaneous and immunologic effects on the patient, including the suppression of cell-mediated immunity that facilitates malignant cell expansion. A deeper understanding of the molecular and cellular underpinnings of CTCL can help guide clinical management as well as inform prognosis and therapeutic discovery.

Integrative data modeling from lung and lymphatic cancer predicts functional roles for miR-34a and miR-16 in cell fate regulation

MiR-34a and miR-16 coordinately control cell cycle checkpoint in non-small cell lung cancer (NSCLC) cells. In cutaneous T-cell lymphoma (CTCL) cells miR-16 regulates a switch between apoptosis and senescence, however the role of miR-34a in this process is unclear. Both miRNAs share many common targets and experimental evidences suggest that they synergistically control the cell-fate regulation of NSCLC. In this work we investigate whether the coordinate action between miR-34a and miR-16 can explain experimental results in multiple cell lines of NSCLC and CTCL. For that we propose a Boolean model of the G1/S checkpoint regulation contemplating the regulatory influences of both miRNAs. Model validation was performed by comparisons with experimental information from the following cell lines: A549, H460, H1299, MyLa and MJ presenting excellent agreement. The model integrates in a single logical framework the mechanisms responsible for cell fate decision in NSCLC and CTCL cells. From the model analysis we suggest that miR-34a is the main controller of miR-16 activity in these cells. The model also allows to investigate perturbations of single or more molecules with the purpose to intervene in cell fate mechanisms of NSCLC and CTCL cells.

Targeting epigenetic regulators in the treatment of T-cell lymphoma

Introduction: T-cell lymphomas represent a broad group of malignant T-cell neoplasms with marked molecular, clinical, and biologic heterogeneity. Survival rates after conventional chemotherapy regimens are poor for most subtypes and new therapies are needed. Rapidly expanding knowledge in the field of epigenomics and the development of an increasing number of epigenetic-modifying agents have created new opportunities for epigenetic therapies for patients with this complex group of diseases.Areas covered: The present review summarizes current knowledge on epigenetic alterations in T-cell lymphomas, availability, and mechanisms of action of epigenetic-modifying agents, results of clinical trials of epigenetic therapies in T-cell lymphomas, status of FDA approval, and biomarker approaches to guide therapy. Promising future directions are discussed.Expert opinion: Mutations in epigenetic-modifying genes are among the most common genetic alterations in T-cell lymphomas, highlighting the potential for epigenetic therapies to improve management of this group of diseases. Single-agent efficacy is well documented, leading to FDA approval for several indications, but overall response rates and durability of responses remain modest. Critical next steps for the field include optimizing combination therapies that incorporate epigenetic-modifying agents and developing predictive biomarkers that help guide patient and drug selection.

Epigenetic polypharmacology: A new frontier for epi-drug discovery

Recently, despite the great success achieved by the so-called "magic bullets" in the treatment of different diseases through a marked and specific interaction with the target of interest, the pharmacological research is moving toward the development of "molecular network active compounds," embracing the related polypharmacology approach. This strategy was born to overcome the main limitations of the single target therapy leading to a superior therapeutic effect, a decrease of adverse reactions, and a reduction of potential mechanism(s) of drug resistance caused by robustness and redundancy of biological pathways. It has become clear that multifactorial diseases such as cancer, neurological, and inflammatory disorders, may require more complex therapeutic approaches hitting a certain biological system as a whole. Concerning epigenetics, the goal of the multi-epi-target approach consists in the development of small molecules able to simultaneously and (often) reversibly bind different specific epi-targets. To date, two dual histone deacetylase/kinase inhibitors (CUDC-101 and CUDC-907) are in an advanced stage of clinical trials. In the last years, the growing interest in polypharmacology encouraged the publication of high-quality reviews on combination therapy and hybrid molecules. Hence, to update the state-of-the-art of these therapeutic approaches avoiding redundancy, herein we focused only on multiple medication therapies and multitargeting compounds exploiting epigenetic plus nonepigenetic drugs reported in the literature in 2018. In addition, all the multi-epi-target inhibitors known in literature so far, hitting two or more epigenetic targets, have been included.

Cytotoxic impact of a perillyl alcohol-temozolomide conjugate, NEO212, on cutaneous T-cell lymphoma in vitro

Background:

Mycosis fungoides (MF) and Sézary syndrome (SS) are subtypes of primary cutaneous lymphomas and represent complex diseases regarding their physiopathology and management. Depending on the stage of the disease, different treatment regimens are applied, but there is no consensus on an optimal approach. Prognosis for patients with early stage MF is favorable, but significantly worsens in advanced disease and in SS, where patients frequently relapse and require multiple therapies.

Methods:

We investigated the potential anticancer effects of NEO212, a novel compound generated by covalently conjugating perillyl alcohol (a natural monoterpene) to temozolomide (an alkylating agent), on MF and SS cell lines in vitro. HUT-78, HUT-102, and MyLa cells were treated with NEO212 under different conditions, and drug effects on proliferation, viability, and apoptosis were characterized.

Results:

NEO212 inhibited proliferation, diminished viability, and stimulated apoptosis in all cell lines, although with varying degrees of potency in the different cell lines. It down-regulated c-myc and cyclin D1 proteins, which are required for cell proliferation, but triggered endoplasmic reticulum stress and activation of caspases. Pretreatment of cells with antioxidants ascorbic acid and beta-mercaptoethanol prevented these NEO212-induced effects.

Conclusions:

NEO212 exerted promising anticancer effects on SS and MF cell lines. The generation of reactive oxygen species (ROS) appears to play a key role in the NEO212-induced cell death process, because the blockage of ROS with antioxidants prevented caspase activation. We propose that NEO212 should be investigated further toward clinical testing in these tumor types.

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.

Bromodomain and Extra-Terminal domain inhibitors for lymphoid malignancies

PURPOSE OF REVIEW

Pharmacological inhibition of Bromodomain and Extra-Terminal (BET) domain proteins is a very exciting epigenetic therapeutic modality. Due to the central role of BET proteins in transcription regulation, their inhibition heavily affects lymphoma cells and BET inhibitors show a clear preclinical antitumor activity as single agents and in combination, paired with early reports of clinical activity.

RECENT FINDINGS

Relevant data have been recently presented on the mechanism of action of the BET inhibitors, on modalities to improve their activity in lymphomas, and their clinical evaluation.

SUMMARY

There are now plenty of preclinical data sustaining BET proteins as therapeutic targets in lymphomas. Newer compounds and combinations with other agents may be pursued in the future aiming also to identify those patients that they most likely benefit from BET inhibition.

CD30-positive primary cutaneous lymphoproliferative disorders: molecular alterations and targeted therapies

Primary cutaneous CD30-positive T-cell lymphoproliferative disorders are the second most common subgroup of cutaneous T-cell lymphomas. They include two clinically different entities with some overlapping features and borderline cases: lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma. Molecular studies of primary cutaneous anaplastic large cell lymphoma reveal an increasing level of heterogeneity that is associated with histological and immunophenotypic features of the cases and their response to specific therapies. Here, we review the most significant genetic, epigenetic and molecular alterations described to date in primary cutaneous CD30-positive T-cell lymphoproliferative disorders, and their potential as therapeutic targets.

Preclinical Studies Support Combined Inhibition of BET Family Proteins and Histone Deacetylases as Epigenetic Therapy for Cutaneous T-Cell Lymphoma

Advanced-stage cutaneous T-cell lymphoma (CTCL) is usually a fatal malignancy despite optimal use of currently available treatments. In this preclinical study of novel CTCL therapy, we performed in vitro and ex vivo experiments to determine the efficacy of combination treatment with a panel of BET bromodomain inhibitors (BETi) (JQ1, OTX015, CPI-0610, I-BET762) and HDAC inhibitors (HDACi) (SAHA/Vorinostat, Romidepsin). BETi/HDACi combinations were synergistic (combination index <1) against cell viability and induced G0/G1 cell cycle arrest. Apoptosis was uniformly enhanced. From a mechanistic standpoint, proliferative drivers c-Myc, Cyclin D1, NFkB, and IL-15Rα were reduced. Inhibitory CDKN1A was increased. CDKN1B, IL-7R, IL-17Rα, STAT3, and STAT5 alterations varied. There were significant increases in extrinsic apoptotic pathway death receptors and ligands (FasL, DR4, DR5, TRAIL, and TNFR1). At clinically tolerable levels of single agents, Romidepsin (1 nM) + OTX015 (125 nM) induced the greatest apoptosis (60%_80%) at 96 hours. Ex vivo studies of leukemic CTCL cells obtained from patients with Sezary syndrome also showed higher levels of apoptosis (about 60%-90%) in response to combination treatments relative to single agents. In contrast, combination treatment of normal CD4+ T cells induced only minimal apoptosis (<10%). Our findings show that the mechanism of action of BETi/HDACi therapy in CTCL involves induction of both cell cycle arrest and apoptosis with reduced proliferative drivers and enhanced expression of apoptotic extrinsic pathway death receptors and ligands. Relative to single agents, the superior anti-CTCL effects of BETi/HDACi combinations in vitro and ex vivo provide a rationale for clinical trials exploring their efficacy as therapy for CTCL.