The combination of hypomethylating agents and histone deacetylase inhibitors produce marked synergy in preclinical models of T-cell lymphoma

Peripheral T-cell lymphoma: From biology to practice to the future

Recent advancements in comprehending peripheral T-cell lymphomas (PTCLs) validate and broaden our perspective, highlighting their diverse nature and the varying molecular mechanisms underlying the entities. Based on a comprehensive accumulated understanding, the PTCLs currently overcome the most challenging features of any disease: rarity, incredible heterogeneity, and a lack of any established standard of care. The treatments deployed in the front-line are extrapolated from regimens developed for other diseases. The recent approval of the three drugs brentuximab vedotin (BV), pralatrexate, and belinostat for patients with relapsed or refractory disease has provided clues about pathophysiology and future directions, though challenges satisfying post-marketing requirements (PMR) for those accelerated approvals have led to one of those drugs being withdrawn and put the other two in jeopardy. Edits of the front-line regimens, often called CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone)-plus approaches, look more like CHOP-minus strategies, as the toxicity of five-drug regimens often reduces the dose intensity of the added 'novel' drug, nullifying any hope of an advance. The turmoil in the field produced by the aforementioned, coupled with an ever-changing classification, has left the field uncertain about the path forward. Despite these challenges, empiric findings from studies of novel drug approaches, coupled with a logic emerging from studies of PTCL lymphomagenesis, have begun to illuminate, albeit faintly for some, a potential direction. The empiric finding that drugs targeting the discrete components of the PTCL epigenome, coupled with the description of multiple mutations in genes that govern epigenetic biology, offers, at the very least, an opportunity to finally be hypothesis-driven. The most recent recognition that the only combination of drugs shown to markedly improve progression-free survival (PFS) in patients with relapsed disease is one based on dual targeting of different and discrete components of that epigenetic biology has established a possibility that circumnavigating chemotherapy addition studies is both plausible, feasible, and likely the best prospect for a quantum advance in this disease. Herein, we analyze PTCL through a 2025 lens, highlighting and underscoring walls that have impeded progress. We will critically explore all the clues and the panoramic view of PTCL research.

A prospective phase 2 study of combination epigenetic therapy against relapsed/refractory peripheral T cell lymphoma

BACKGROUND

Peripheral T cell lymphomas (PTCLs) are prototypical epigenetic malignancies with invariably poor prognoses. Novel and effective therapeutic strategies are needed to improve clinical outcomes, particularly in relapsed/refractory patients.

METHODS

We conducted a multicenter phase 2 study to evaluate the therapeutic efficacy of azacitidine and chidamide, alone or in combination with gemcitabine and oxaliplatin (GemOx), in patients with relapsed/refractory PTCLs (registration number: ChiCTR2000037232). The primary endpoint was the best overall response rate.

FINDINGS

As of May 1st, 2024, thirty patients were evaluable for efficacy and toxicity. The best overall response rate was 53.3%, meeting its primary endpoint. Among the patients with angioimmunoblastic T cell lymphoma (AITL; N = 19), a numerically higher response rate was observed, regardless of whether chemotherapy was combined, compared to patients with non-AITL. After a median follow-up of 36.6 months, median progression-free survival and overall survival were 7.1 and 8.7 months, respectively. Patients with AITL who received combination chemotherapy (N = 12) achieved the most promising response rates (overall response rate, 91.7%; complete remission rate, 66.7%) and survival outcomes (median progression-free survival, 17.2 months; median overall survival, 38.8 months). The most common grade 3-4 toxicities were neutropenia (40.0%) and thrombocytopenia (30.0%).

CONCLUSIONS

The combination of epigenetic therapy with GemOx was well tolerated and highly effective in patients with relapsed/refractory PTCLs. Patients with AITL, in particular, may benefit more from this combination treatment and should be the focus of future studies.

FUNDING

This work was funded by the Natural Science Foundation of Jiangsu Province (BK20232039).

Novel clinical risk stratification and treatment strategies in relapsed/refractory peripheral T-cell lymphoma

Peripheral T cell lymphoma (PTCL) represents a group of heterogeneous hematological malignancies, which are notoriously challenging to treat and outcomes are typically poor. Over the past two decades, clinical prognostic indices for patient risk stratification have evolved, while several targeted agents are now available to complement combination chemotherapy in the frontline setting or as a salvage strategy. With further understanding of the molecular pathobiology of PTCL, several innovative approaches incorporating immunomodulatory agents, epigenetic therapies, oncogenic kinase inhibitors and immunotherapeutics have come to the forefront. In this review, we provide a comprehensive overview of the progress in developing clinical prognostic indices for PTCL and describe the broad therapeutic landscape, emphasizing novel targetable pathways that have entered early phase clinical studies.

SOHO State-of-the-Art Updates and Next Questions: Treatment for Newly Diagnosed Peripheral T-Cell Lymphomas

Although a rare subset of non-Hodgkin lymphomas, peripheral T-cell lymphomas (PTCL) account for a disproportionate proportion of patient mortality. Conventional therapies are derived from experience treating aggressive B-cell lymphomas and center around CHOP-based chemotherapy. However, due to the unique biology and diverse subtypes of PTCL, most patients fail to durably respond to this approach and 5-year survival is only 20% to 30%. There have been multiple attempts to improve outcomes for patients with PTCL. Among the more successful strategies are the use of consolidative autologous stem cell transplant, the augmentation of CHOP with etoposide (CHOEP), and the use of brentuximab vedotin in CD30-positive PTCL. Advances in the understanding of histology-specific biology has cultivated enthusiasm to evaluate hypomethylating agents, histone deacetylate inhibitors, and phosphoinositol-3-kinase inhibitors in the frontline setting. Improvements in monitoring disease response and prognostication including the use of cell-free DNA, mutational profiling, and interim PET/CT imaging are also on the horizon. For patients with acute T-cell leukemia/lymphoma, the use of mogamulizumab-based therapy in the frontline setting may lead to advances in care. The true impact of these new-era therapies will only be elucidated as clinical practices incorporate the rapidly changing evidence.

Mesenchymal stem cells under epigenetic control - the role of epigenetic machinery in fate decision and functional properties

Mesenchymal stem cells (mesenchymal stromal cells, MSC) are multipotent stem cells that can differentiate into cells of at least three mesodermal lineages, namely adipocytes, osteoblasts, and chondrocytes, and have potent immunomodulatory properties. Epigenetic modifications are critical regulators of gene expression and cellular differentiation of mesenchymal stem cells (MSCs). Epigenetic machinery controls MSC differentiation through direct modifications to DNA and histones. Understanding the role of epigenetic machinery in MSC is crucial for the development of effective cell-based therapies for degenerative and inflammatory diseases. In this review, we summarize the current understanding of the role of epigenetic control of MSC differentiation and immunomodulatory properties.

Biological insights into the role of TET2 in T cell lymphomas

Peripheral T cell lymphomas (PTCL) are a heterogenous group of mature T cell lymphomas with an overall poor prognosis. Understanding the molecular heterogeneity in PTCL subtypes may lead to improved understanding of the underlying biological mechanisms driving these diseases. Mutations in the epigenetic regulator TET2 are among the most frequent mutations identified in PTCL, with the highest frequency in angioimmunoblastic T cell lymphomas and other nodal T follicular helper (TFH) lymphomas. This review dissects the role of TET2 in nodal TFH cell lymphomas with a focus on emerging biological insights into the molecular mechanism promoting lymphomagenesis and the potential for epigenetic therapies to improve clinical outcomes.

Update on histone deacetylase inhibitors in peripheral T-cell lymphoma (PTCL)

Peripheral T-cell lymphomas (PTCLs) are a group of highly aggressive malignancies with generally poor prognoses, and the first-line chemotherapy of PTCL has limited efficacy. Currently, several novel targeted agents, including histone deacetylase inhibitors (HDACis), have been investigated to improve the therapeutic outcome of PTCLs. Several HDACis, such as romidepsin, belinostat, and chidamide, have demonstrated favorable clinical efficacy and safety in PTCLs. More novel HDACis and new combination therapies are undergoing preclinical or clinical trials. Mutation analysis based on next-generation sequencing may advance our understanding of the correlation between epigenetic mutation profiles and relevant targeted therapies. Multitargeted HDACis and HDACi-based prodrugs hold promising futures and offer further directions for drug design.

Epigenetic targets in B- and T-cell lymphomas: latest developments

Non-Hodgkin's lymphomas (NHLs) comprise a diverse group of diseases, either of mature B-cell or of T-cell derivation, characterized by heterogeneous molecular features and clinical manifestations. While most of the patients are responsive to standard chemotherapy, immunotherapy, radiation and/or stem cell transplantation, relapsed and/or refractory cases still have a dismal outcome. Deep sequencing analysis have pointed out that epigenetic dysregulations, including mutations in epigenetic enzymes, such as chromatin modifiers and DNA methyltransferases (DNMTs), are prevalent in both B- cell and T-cell lymphomas. Accordingly, over the past decade, a large number of epigenetic-modifying agents have been developed and introduced into the clinical management of these entities, and a few specific inhibitors have already been approved for clinical use. Here we summarize the main epigenetic alterations described in B- and T-NHL, that further supported the clinical development of a selected set of epidrugs in determined diseases, including inhibitors of DNMTs, histone deacetylases (HDACs), and extra-terminal domain proteins (bromodomain and extra-terminal motif; BETs). Finally, we highlight the most promising future directions of research in this area, explaining how bioinformatics approaches can help to identify new epigenetic targets in B- and T-cell lymphoid neoplasms.

Potential of Synthetic and Natural Compounds as Novel Histone Deacetylase Inhibitors for the Treatment of Hematological Malignancies

Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are enzymes that remove or add acetyl groups to lysine residues of histones, respectively. Histone deacetylation causes DNA to more snugly encircle histones and decreases gene expression, whereas acetylation has the opposite effect. Through these small alterations in chemical structure, HATs and HDACs regulate DNA expression. Recent research indicates histone deacetylase inhibitors (HDACis) may be used to treat malignancies, including leukemia, B-cell lymphoma, virus-associated tumors, and multiple myeloma. These data suggest that HDACis may boost the production of immune-related molecules, resulting in the growth of CD8-positive T-cells and the recognition of nonreactive tumor cells by the immune system, thereby diminishing tumor immunity. The argument for employing epigenetic drugs in the treatment of acute myeloid leukemia (AML) patients is supported by evidence that both epigenetic changes and mutations in the epigenetic machinery contribute to AML etiology. Although hypomethylating drugs have been licensed for use in AML, additional epigenetic inhibitors, such as HDACis, are now being tested in humans. Preclinical studies evaluating the efficacy of HDACis against AML have shown the ability of specific agents, such as anobinostat, vorinostat, and tricostatin A, to induce growth arrest, apoptosis, autophagy and cell death. However, these inhibitors do not seem to be successful as monotherapies, but instead achieve results when used in conjunction with other medications. In this article, we discuss the mounting evidence that HDACis promote extensive histone acetylation, as well as substantial increases in reactive oxygen species and DNA damage in hematological malignant cells. We also evaluate the potential of various natural product-based HDACis as therapeutic agents to combat hematological malignancies.

Mechanisms of myeloid leukemogenesis: Current perspectives and therapeutic objectives

Acute myeloid leukemia (AML) is a heterogeneous hematopoietic neoplasm which results in clonal proliferation of abnormally differentiated hematopoietic cells. In this review, mechanisms contributing to myeloid leukemogenesis are summarized, highlighting aberrations of epigenetics, transcription factors, signal transduction, cell cycling, and the bone marrow microenvironment. The mechanisms contributing to AML are detailed to spotlight recent findings that convey clinical impact. The applications of current and prospective therapeutic targets are accentuated in addition to reviews of treatment paradigms stratified for each characteristic molecular lesion - with a focus on exploring novel treatment approaches and combinations to improve outcomes in AML.

Epigenetic Aberrations and Targets in Peripheral T-Cell Lymphoma

Peripheral T cell lymphomas (PTCL) comprise a diverse group of aggressive T-cell and NK-cell lymphomas with many subtypes sharing same treatment algorithms despite having different pathobiology and responses to treatment. The molecular advances made in discovery of genetic mutations that disrupt epigenetic modulation in some subtypes of PTCL such as angioimmunoblastic T cell lymphoma and PTCL-not otherwise specified (NOS) may explain the poor outcomes and unsatisfactory responses to frontline line CHOP and CHOP-like therapy seen in this group of lymphomas. In this article, we address the main genetic mutations such as IDH2, TET2 and DNMT3A seen in PTCL and that disrupt the epigenetic modulation pathways, focusing on acetylation, deacetylation and methylation. Since therapeutic agents that target the disrupted epigenetic modulation pathways in PTCL may change treatment landscape in the near future, we will highlight the ones approved for treatment of refractory and/or relapsed PTCL and also the pivotal regimens being evaluated in clinical trials for treatment of frontline and refractory relapsed disease. We stress the importance of determining whether there is an association between the discussed genetic mutations and responses to the highlighted therapeutic agents such that treatments could be better tailored in patients with this kind of lymphoma with unmet needs.

Hypermethylation-Mediated Silencing of CIDEA, MAL and PCDH17 Tumour Suppressor Genes in Canine DLBCL: From Multi-Omics Analyses to Mechanistic Studies

Gene expression is controlled by epigenetic deregulation, a hallmark of cancer. The DNA methylome of canine diffuse large B-cell lymphoma (cDLBCL), the most frequent malignancy of B-lymphocytes in dog, has recently been investigated, suggesting that aberrant hypermethylation of CpG loci is associated with gene silencing. Here, we used a multi-omics approach (DNA methylome, transcriptome and copy number variations) combined with functional in vitro assays, to identify putative tumour suppressor genes subjected to DNA methylation in cDLBCL. Using four cDLBCL primary cell cultures and CLBL-1 cells, we found that CiDEA, MAL and PCDH17, which were significantly suppressed in DLBCL samples, were hypermethylated and also responsive (at the DNA, mRNA and protein level) to pharmacological unmasking with hypomethylating drugs and histone deacetylase inhibitors. The regulatory mechanism underneath the methylation-dependent inhibition of those target genes expression was then investigated through luciferase and in vitro methylation assays. In the most responsive CpG-rich regions, an in silico analysis allowed the prediction of putative transcription factor binding sites influenced by DNA methylation. Interestingly, regulatory elements for AP2, MZF1, NF-kB, PAX5 and SP1 were commonly identified in all three genes. This study provides a foundation for characterisation and experimental validation of novel epigenetically-dysregulated pathways in cDLBCL.

The Synergistic Anti-Tumor Activity of EZH2 Inhibitor SHR2554 and HDAC Inhibitor Chidamide through ORC1 Reduction of DNA Replication Process in Diffuse Large B Cell Lymphoma

Simple Summary

The EZH2-targeted drugs have demonstrated notable therapeutic effects in EZH2 mutant B-cell lymphoma patients. In this study, we demonstrated that the combination of EZH2 inhibitor SHR2554 and HDAC inhibitor HBI8000 exert synergistic anti-proliferative activity in both EZH2 wide-type and mutation B-cell lymphoma. More importantly, gene expression profile analysis revealed simultaneous treatment with these agents led to dramatic inhibition of DNA replication initiator protein ORC1, which might contribute to great efficacy of combination strategy. The combination of EZH2 inhibitor and HDAC inhibitor could provide a potential therapeutic treatment for both EZH2 wide-type and mutation B-cell lymphoma patients.

Abstract

Background: Upregulation of H3K27me3 induced by EZH2 overexpression or somatic heterozygous mutations were implicated in lymphomagenesis. It has been demonstrated that several EZH2-target agents have notable therapeutic effects in EZH2-mutant B-cell lymphoma patients. Here we present a novel highly selective EZH2 inhibitor SHR2554 and possible combination strategy in diffuse large B-cell lymphoma (DLBCL). Methods: Cell proliferation, cell cycle and apoptosis were analyzed by CellTiter-Glo Luminescent Cell Viability Assay and flow cytometry. Western Blot was used to detect the expression of related proteins. The gene expression profiling post combination treatment was analyzed by RNA-Seq. Finally, CDX and PDX models were used to evaluate the synergistic anti-tumor effects of the combination treatment in vivo. Results: The novel EZH2 inhibitor SHR2554 inhibited proliferation and induced G1 phase arrest in EZH2-mutant DLBCL cell lines. The combination of EZH2 inhibitor SHR2554 with histone deacetylase (HDAC) inhibitor chidamide (hereafter referred to as HBI8000) exerted synergistic anti-proliferative activity in vitro and in vivo. Gene expression profile analysis revealed dramatic inhibition of the DNA replication process in combined treatment. Conclusions: SHR2554, a potent, highly selective small molecule inhibitor of EZH2, inhibited EZH2-mutant DLBCL more significantly in vitro and in vivo. The combination of HDAC inhibitor HBI8000 with EZH2 inhibitor SHR2554 exhibited dramatic anti-tumor activity in both mutant and wild-type DLBCL, which may become a potential therapeutic modality for the treatment of DLBCL patients.

Characterization of newly established Pralatrexate-resistant cell lines and the mechanisms of resistance

Background

Pralatrexate (PDX) is a novel antifolate approved for the treatment of patients with relapsed/refractory peripheral T-cell lymphoma, but some patients exhibit intrinsic resistance or develop acquired resistance. Here, we evaluated the mechanisms underlying acquired resistance to PDX and explored potential therapeutic strategies to overcome PDX resistance.

Methods

To investigate PDX resistance, we established two PDX-resistant T-lymphoblastic leukemia cell lines (CEM and MOLT4) through continuous exposure to increasing doses of PDX. The resistance mechanisms were evaluated by measuring PDX uptake, apoptosis induction and folate metabolism-related protein expression. We also applied gene expression analysis and methylation profiling to identify the mechanisms of resistance. We then explored rational drug combinations using a spheroid (3D)-culture assay.

Results

Compared with their parental cells, PDX-resistant cells exhibited a 30-fold increase in half-maximal inhibitory concentration values. Induction of apoptosis by PDX was significantly decreased in both PDX-resistant cell lines. Intracellular uptake of [¹⁴C]-PDX decreased in PDX-resistant CEM cells but not in PDX-resistant MOLT4 cells. There was no significant change in expression of dihydrofolate reductase (DHFR) or folylpolyglutamate synthetase (FPGS). Gene expression array analysis revealed that DNA-methyltransferase 3β (DNMT3B) expression was significantly elevated in both cell lines. Gene set enrichment analysis revealed that adipogenesis and mTORC1 signaling pathways were commonly upregulated in both resistant cell lines. Moreover, CpG island hypermethylation was observed in both PDX resistant cells lines. In the 3D-culture assay, decitabine (DAC) plus PDX showed synergistic effects in PDX-resistant cell lines compared with parental lines.

Conclusions

The resistance mechanisms of PDX were associated with reduced cellular uptake of PDX and/or overexpression of DNMT3B. Epigenetic alterations were also considered to play a role in the resistance mechanism. The combination of DAC and PDX exhibited synergistic activity, and thus, this approach might improve the clinical efficacy of PDX.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08607-9.

Procainamide-SAHA Fused Inhibitors of hHDAC6 Tackle Multidrug-Resistant Malaria Parasites

Epigenetic post-translational modifications are essential for human malaria parasite survival and progression through its life cycle. Here, we present new functionalized suberoylanilide hydroxamic acid (SAHA) derivatives that chemically combine the pan-histone deacetylase inhibitor SAHA with the DNA methyltransferase inhibitor procainamide. A three- or four-step chemical synthesis was designed starting from cheap raw materials. Compared to the single drugs, the combined molecules showed a superior activity in Plasmodium and a potent inhibition against human HDAC6, exerting no cytotoxicity in human cell lines. These new compounds are fully active in multidrug-resistant Plasmodium falciparum Cambodian isolates. They target transmission of the parasite by inducing irreversible morphological changes in gametocytes and inhibiting exflagellation. The compounds are slow-acting and have an additive antimalarial effect in combination with fast-acting epidrugs and dihydroartemisinin. The lead compound decreases parasitemia in mice in a severe malaria model. Taken together, this novel fused molecule offers an affordable alternative to current failing antimalarial therapy.

Updates in the Treatment of Peripheral T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCLs) represent a heterogeneous group of rare hematologic malignancies accounting for less than 10% of non-Hodgkin lymphomas. The 2016 classification of World Health Organization recognized 29 different entities of PTCLs. These subgroups are characterized by different molecular and genetic patterns. For nearly 30 years, little improvement in the treatment of PTCLs has been noticed due to the paucity of randomized trials and anthracycline-based chemotherapy remains the mainstay of first-line treatment. In front-line setting, ECHELON-2, the first randomized controlled Phase III clinical trial, recently met its primary endpoint of PFS demonstrating the superiority of BV containing regimen when compared to standard CHOP in patients with CD30 positive PTCLs. The role of therapeutic intensifications such as autologous or allogenic stem cell transplantations remains controversial in first-line setting and in relapsed/refractory disease due to the lack of studies clearly addressing this question and the recently published negative studies. PTCLs are often refractory to first-line chemotherapy and tend to relapse after an initial response. New agents have been approved for relapsed/refractory disease such as Histone deacetylase inhibitors, folate analogue metabolic inhibitor or CD30 antibody drug conjugated. Despite an acceptable response to these agents, progression-free survival remains very poor. New strategies such as combinations of different agents have been evaluated in order to improve outcomes. Innovative drugs in the fields of epigenetics, immunomodulation within the tumor microenvironment, and direct targeting of tumor cells to CD30 and T-cell receptor abnormalities open new perspectives to improve the treatment of PTCLs.

Combination of Decitabine and a Modified Regimen of Cisplatin, Cytarabine and Dexamethasone: A Potential Salvage Regimen for Relapsed or Refractory Diffuse Large B-Cell Lymphoma After Second-Line Treatment Failure

Objective

The prognosis for patients with relapsed or refractory diffuse large B-cell lymphoma (R/R-DLBCL) after second-line treatment failure is extremely poor. This study prospectively observed the efficacy and safety of decitabine with a modified cisplatin, cytarabine, and dexamethasone (DHAP) regimen in R/R-DLBCL patients who failed second-line treatment.

Methods

Twenty-one R/R-DLBCL patients were enrolled and treated with decitabine and a modified DHAP regimen. The primary endpoints were overall response rate (ORR) and safety. The secondary endpoints were progression-free survival (PFS) and overall survival (OS).

Results

ORR reached 50% (complete response rate, 35%), five patients (25%) had stable disease (SD) with disease control rate (DCR) of 75%. Subgroup analysis revealed patients over fifty years old had a higher complete response rate compared to younger patients (P = 0.005), and relapsed patients had a better complete response rate than refractory patients (P = 0.031). Median PFS was 7 months (95% confidence interval, 5.1-8.9 months). Median OS was not achieved. One-year OS was 59.0% (95% CI, 35.5%-82.5%), and two-year OS was 51.6% (95% confidence interval, 26.9%-76.3%). The main adverse events (AEs) were grade 3/4 hematologic toxicities such as neutropenia (90%), anemia (50%), and thrombocytopenia (70%). Other main non-hematologic AEs were grade 1/2 nausea/vomiting (40%) and infection (50%). No renal toxicity or treatment-related death occurred.

Conclusion

Decitabine with a modified DHAP regimen can improve the treatment response and prognosis of R/R-DLBCL patients with good tolerance to AEs, suggesting this regimen has potential as a possible new treatment option for R/R-DLBCL patients after second-line treatment failure.

Clinical Trial Registration

ClinicalTrials.gov, identifier: NCT03579082.

Targeting the T-Cell Lymphoma Epigenome Induces Cell Death, Cancer Testes Antigens, Immune-Modulatory Signaling Pathways

The peripheral T-cell lymphomas (PTCL) could be considered the prototypical epigenetic disease. As a disease, they are uniquely sensitive to histone deacetylase (HDAC) and DNA methyltransferase (DNMT) inhibitors, both alone and in combination, are characterized by a host of mutations in epigenetic genes, and can develop spontaneously in genetically engineered murine models predicated on established recurring mutations in (RHOAG17V) and TET2, an epigenetic gene governing DNA methylation. Given the clinical benefit of HDAC inhibitors (HDACi) and hypomethlyation agents alone and in combination in PTCL, we sought to explore a mechanistic basis for these agents in PTCL. Herein, we reveal profound class synergy between HDAC and DNMT inhibitors in PTCL, and that the combination induces degrees of gene expression that are substantially different and more extensive than that observed for the single agents. A prominent signature of the combination relates to the transcriptional induction of cancer testis antigens and genes involved in the immune response. Interestingly, TBX21 and STAT4, master regulators of TH1 differentiation, were among the genes upregulated by the combination, suggesting the induction of a TH1-like phenotype. Moreover, suppression of genes involved in cholesterol metabolism and the matrisome were also identified. We believe that these data provide a strong rationale for clinical studies, and future combinations leveraging an immunoepigenetic platform.

Combined oral 5-azacytidine and romidepsin are highly effective in patients with PTCL: a multicenter phase 2 study

Peripheral T-cell lymphomas (PTCLs) are uniquely vulnerable to epigenetic modifiers. We demonstrated in vitro synergism between histone deacetylase inhibitors and DNA methyltransferase inhibitors in preclinical models of T-cell lymphoma. In a phase 1 trial, we found oral 5-azacytidine and romidepsin to be safe and effective, with lineage-selective activity among patients with relapsed/refractory (R/R) PTCL. Patients who were treatment naïve or who had R/R PTCL received azacytidine 300 mg once per day on days 1 to 14, and romidepsin 14 mg/m2 on days 8, 15, and 22 every 35 days. The primary objective was overall response rate (ORR). Targeted next-generation sequencing was performed on tumor samples to correlate mutational profiles and response. Among 25 enrolled patients, the ORR and complete response rates were 61% and 48%, respectively. However, patients with T-follicular helper cell (tTFH) phenotype exhibited higher ORR (80%) and complete remission rate (67%). The most frequent grade 3 to 4 adverse events were thrombocytopenia (48%), neutropenia (40%), lymphopenia (32%), and anemia (16%). At a median follow-up of 13.5 months, the median progression-free survival, duration of response, and overall survival were 8.0 months, 20.3 months, and not reached, respectively. The median progression-free survival and overall survival were 8.0 months and 20.6 months, respectively, in patients with R/R disease. Patients with tTFH enjoyed a particularly long median survival (median not reached). Responders harbored a higher average number of mutations in genes involved in DNA methylation and histone deacetylation. Combined azacytidine and romidepsin are highly active in PTCL patients and could serve as a platform for novel regimens in this disease. This trial was registered at www.clinicaltrials.gov as #NCT01998035.

Targeted based therapy in nodal T-cell lymphomas

T-cell lymphomas (TCL) are a group of biologically and clinically heterogenous neoplasms derived from mature T lymphocytes. Recent findings in biology have advanced the classification of these neoplasms; however, clinical investigations based on biologic features have yet to be designed. Two biomarker-driven treatments for TCL are promising: brentuximab vedotin (BV) in combination with chemotherapy or as monotherapy is the standard treatment for newly diagnosed CD30-positive TCL and relapsed/refractory anaplastic large cell lymphoma (ALCL), while ALK inhibitors have induced responses in ALK+ ALCLs. Common genetic alterations in TCL, such as aberrations in PI3K/mTOR, JAK/STAT, and epigenetic regulators are also targetable by pathway inhibitors and HDAC/DNMT inhibitors; however, responses to these treatments as monotherapy are neither satisfactory nor durable, even in patients pre-stratified by several biomarkers. Additional work is needed to extend biology/biomarker-driven treatment in these neoplasms. As T-cell lymphomagenesis is multistep and multifactorial, trials are ongoing to evaluate combination treatments. The focus of this article is to summarize the status and the current role of targeted-based therapy in nodal TCL.

Management of Angioimmunoblastic T-Cell Lymphoma (AITL) and other T Follicular Helper Cell lymphomas (TFH PTCL)

Despite the remarkable improvements in the treatment and outcome of patients with aggressive B-cell lymphoma, the peripheral T-cell lymphomas (PTCL) continue to carry a poor prognosis with the presently available treatment options. The PTCL are very rare diseases that account for only 10,000 to 15,000 new cases per year in the United States. The World Health Organization's 2016 classification describes 29 distinct subtypes of PTCL, thus making these both rate and incredibly heterogenous. The 2 most common forms of PTCL, for example, peripheral T-cell lymphoma-not otherwise specified and angioimmunoblastic T-cell lymphoma , have an incidence of only 2500 and 1800 cases per year respectively, in the United States.

Novel therapies targeting cutaneous T cell lymphomas and their microenvironment

Cutaneous T-cell lymphomas (CTCL) are rare non-Hodgkin lymphomas with a generally indolent course managed with topical, skin-directed therapies. A small subset, however, will progress to advanced stage disease necessitating systemic therapy for disease control. Currently approved therapies have low response rates and generally short durations of response. Novel therapies, therefore, are urgently needed to address this unmet need. In this review, the mechanisms of CTCL pathogenesis and progression, including the role of the tumor microenvironment and molecular alterations, are summarized. Based on these biologic insights, novel therapies currently under investigation and those with a strong preclinical biologic rationale including T cell and macrophage checkpoint inhibitors, epigenetic regulators, targeted antibodies, tyrosine kinase inhibitors, and apoptosis modulating therapies are discussed.

Epigenetic alterations and advancement of treatment in peripheral T-cell lymphoma

Peripheral T-cell lymphoma (PTCL) is a rare and heterogeneous group of clinically aggressive diseases associated with poor prognosis. Except for ALK + anaplastic large-cell lymphoma (ALCL), most peripheral T-cell lymphomas are highly malignant and have an aggressive disease course and poor clinical outcomes, with a poor remission rate and frequent relapse after first-line treatment. Aberrant epigenetic alterations play an important role in the pathogenesis and development of specific types of peripheral T-cell lymphoma, including the regulation of the expression of genes and signal transduction. The most common epigenetic alterations are DNA methylation and histone modification. Histone modification alters the level of gene expression by regulating the acetylation status of lysine residues on the promoter surrounding histones, often leading to the silencing of tumour suppressor genes or the overexpression of proto-oncogenes in lymphoma. DNA methylation refers to CpG islands, generally leading to tumour suppressor gene transcriptional silencing. Genetic studies have also shown that some recurrent mutations in genes involved in the epigenetic machinery, including TET2, IDH2-R172, DNMT3A, RHOA, CD28, IDH2, TET2, MLL2, KMT2A, KDM6A, CREBBP, and EP300, have been observed in cases of PTCL. The aberrant expression of miRNAs has also gradually become a diagnostic biomarker. These provide a reasonable molecular mechanism for epigenetic modifying drugs in the treatment of PTCL. As epigenetic drugs implicated in lymphoma have been continually reported in recent years, many new ideas for the diagnosis, treatment, and prognosis of PTCL originate from epigenetics in recent years. Novel epigenetic-targeted drugs have shown good tolerance and therapeutic effects in the treatment of peripheral T-cell lymphoma as monotherapy or combination therapy. NCCN Clinical Practice Guidelines also recommended epigenetic drugs for PTCL subtypes as second-line therapy. Epigenetic mechanisms provide new directions and therapeutic strategies for the research and treatment of peripheral T-cell lymphoma. Therefore, this paper mainly reviews the epigenetic changes in the pathogenesis of peripheral T-cell lymphoma and the advancement of epigenetic-targeted drugs in the treatment of peripheral T-cell lymphoma (PTCL).

Contemporary strategies to improve outcomes for peripheral T-cell lymphoma patients following the failure of first-line therapy

INTRODUCTION

T cell lymphomas are a heterogeneous group, with varying incidences, geographic patterns, and risk factors. Although until recently approached in a manner similar to B cell lymphomas, the treatment outcomes are poor and this disease is characterized by high relapse rates. The treatment advances in PTCL have been slow compared to B cell lymphomas. The outcomes of patients who progress following stem cell transplantation are worse.

AREAS COVERED

This review focuses on the novel targeted agents that are approved and/or are under investigation for patients with relapsed/refractory PTCL. We conducted an electronic literature search of the studies using PubMed, clincaltrials.gov, MEDLINE, using the key words 'PTCL,' 'second line therapy,' and 'targeted agents.' Studies published before January 2020 were included in the search criteria.

EXPERT OPINION

Development of newer therapies such as HDAC inhibitors and kinases are promising new agents with activity in relapsed/refractory PTCL. Combination therapy using novel agents may be the future for treatment of PTCL. Therapies in the next few years may take a more personalized approach taking into consideration not just the histology, but also the epigenomic landscape.

Oral 5-azacytidine and romidepsin exhibit marked activity in patients with PTCL: a multicenter phase 1 study

The peripheral T-cell lymphomas (PTCLs) are uniquely sensitive to epigenetic modifiers. Based on the synergism between histone deacetylase inhibitors and hypomethylating agents that we established in preclinical PTCL models, we conducted a phase 1 study of oral 5-azacytidine (AZA) and romidepsin (ROMI) in patients with advanced lymphoid malignancies, with emphasis on PTCL. According to a 3 + 3 design, patients were assigned to 1 of 7 cohorts with AZA doses ranging from 100 mg daily on days 1 to 14 to 300 mg daily on days 1 to 21, ROMI doses ranging from 10 mg/m2 on days 8 and 15 to 14 mg/m2 on days 8, 15, and 22, with cycles of 21 to 35 days. Coprimary end points included maximum tolerated dose (MTD) and dose-limiting toxicity (DLT). We treated a total of 31 patients. The MTD was AZA 300 mg on days 1 to 14 and ROMI 14 mg/m2 on days 8, 15, and 22 on a 35-day cycle. DLTs included grade 4 thrombocytopenia, prolonged grade 3 thrombocytopenia, grade 4 neutropenia, and pleural effusion. There were no treatment-related deaths. The combination was substantially more active in patients with PTCL than in those with non-T-cell lymphoma. The overall response rate in all, non-T-cell, and T-cell lymphoma patients was 32%, 10%, and 73%, respectively, and the complete response rates were 23%, 5%, and 55%, respectively. We did not find an association between response and level of demethylation or tumor mutational profile. This study establishes that combined epigenetic modifiers are potently active in PTCL patients. This trial was registered at www.clinicaltrials.gov as NCT01998035.

The rapidly changing landscape in mature T-cell lymphoma (MTCL) biology and management

Historical advances in the care of patients with non-Hodgkin lymphoma (NHL) have been restricted largely to patients with B-cell lymphoma. The peripheral T-cell lymphomas (PTCLs), which are rare and heterogeneous in nature, have yet to experience the same degree of improvement in outcome over the past 20 to 30 years. It is estimated that there are approximately 80,000 and 14,000 cases, respectively, of NHL and Hodgkin lymphoma per year in the United States. As a subgroup of NHL, the PTCLs account for 6% to 10% of all cases of NHL, making them exceedingly rare. In addition, the World Health Organization 2017 classification describes 29 distinct subtypes of PTCL. This intrinsic diversity, coupled with its rarity, has stymied progress in the disease. In addition, most subtypes carry an inferior prognosis compared with their B-cell counterparts, an outcome largely attributed to the fact that most treatment paradigms for patients with PTCL have been derived from B-cell neoplasms, a radically different disease. In fact, the first drug ever approved for patients with PTCL was approved only a decade ago. The plethora of recent drug approvals in PTCL, coupled with a deeper understanding of the molecular pathogenesis of the disease, has stimulated the field to pursue new avenues of research that are now largely predicated on the development of novel, targeted small molecules, which include a host of epigenetic modifiers and biologics. There is an expectation these advances may begin to favorably challenge the chemotherapy paradigms that have been used in the T-cell malignancies.

T-cell therapies for T-cell lymphoma

T-cell lymphomas represent a subpopulation of non-Hodgkin lymphomas with poor outcomes when treated with conventional chemotherapy. A variety of novel agents have been introduced as new treatment strategies either as first-line treatment or in conjunction with chemotherapy. Immunotherapy has been demonstrated to be a promising area for new therapeutics, including monoclonal antibodies and adoptive cellular therapeutics. T-cell therapeutics have been shown to have significant success in the treatment of B-cell malignancies and are rapidly expanding as potential treatment options for other cancers including T-cell lymphomas. Although treating T-cell lymphomas with T-cell therapeutics has unique challenges, multiple targets are currently being studied both preclinically and in clinical trials.

Development of new agents for peripheral T-cell lymphoma

INTRODUCTION

Peripheral T-cell lymphoma (PTCL) is a relatively rare, heterogeneous group of mature T-cell neoplasms generally associated with poor prognosis, partly because of refractoriness against conventional cytotoxic chemotherapies. To improve the outcome of patients with PTCL, the clinical development of several novel agents is currently under investigation.

AREAS COVERED

Since the first approval of pralatrexate (dihydrofolate reductase inhibitor) by the US Food and Drug Administration, belinostat, romidepsin (histone deacetylase inhibitors), and brentuximab vedotin (anti-CD30 antibody-drug conjugate) have been approved in the US, and many other countries. In addition, mogamulizumab (anti-CC chemokine receptor 4 antibody), chidamide (histone deacetylase inhibitor), and forodesine (purine nucleoside phosphorylase inhibitor) have been approved in Asian countries, including China, and Japan. In this review, we have summarized the available data regarding these approved agents and new agents currently under development for PTCL.

EXPERT OPINION

Novel agents will be a promising therapeutic option in selected patients with relapsed/refractory PTCL and will change the daily clinical practice in the treatment of PTCL. However, these are not a curative option when used as a single agent. Further clinical developments are expected, comprising 1) combination therapies of new agents with cytotoxic chemotherapies; 2) 'novel-novel' combinations; 3) immune therapies, including chimeric antigen receptor T-cell therapy; and 4) predictive marker analysis.

The Future of Combination Therapies for Peripheral T Cell Lymphoma (PTCL)

PURPOSE OF REVIEW

Peripheral T cell lymphoma is a rare heterogeneous group of diseases which are characterized by poor outcomes to treatment and short overall survival. In the past decade, several new therapies targeting T cell biology have been approved in the relapsed setting. These new therapies, such as pralatrexate, romidepsin, belinostat, and brentuximab vedotin, have begun to make their way into practice. Despite these advances, outcomes have not changed dramatically. In recent years, efforts have been made to incorporate these new therapies into combination strategies to treat this challenging disease entity. Herein we will review some of the latest developments.

RECENT FINDINGS

With the new WHO classification, discrete entities of PTCL are now being identified by molecular and phenotypic markers. This new classification is critical to our ability to define disease entities which may respond to certain classes of targeted therapy. Some such mutations include genes controlling epigenetics (TET2, IDH2, DNMT3A, RHOA, CD28). As such, epigenetic therapies such as histone deacetylase (HDAC) inhibitors have become the platform to which other novel therapies or chemotherapy has been added. Early phase clinical studies have demonstrated that combination therapy with romidepsin plus other agents known to have activity in T cell lymphoma have enhanced clinical benefit for this group of diseases. In addition, the antibody drug conjugate, brentuximab vedotin has been shown to have potent activity in T cell lymphomas expressing CD30. This drug is being studied as well with other targeted therapies and chemotherapy in an effort to improve response rates and progression-free survival. Although T cell lymphomas remain a highly challenging group of diseases to treat, new efforts to leverage drugs that discretely target the biology that drives T cell lymphomagenesis in combination provide hope that improved outcomes may be realized in the near future.

Advances and Challenges of HDAC Inhibitors in Cancer Therapeutics

Since the identification and cloning of human histone deacetylases (HDACs) and the rapid approval of vorinostat (Zolinza®) for the treatment of cutaneous T-cell lymphoma, the field of HDAC biology has met many initial successes. However, many challenges remain due to the complexity involved in the lysine posttranslational modifications, epigenetic transcription regulation, and nonepigenetic cellular signaling cascades. In this chapter, we will: review the discovery of the first HDAC inhibitor and present discussion regarding the future of next-generation HDAC inhibitors, give an overview of different classes of HDACs and their differences in lysine deacylation activity, discuss different classes of HDAC inhibitors and their HDAC isozyme preferences, and review HDAC inhibitors' preclinical studies, their clinical trials, their pharmacokinetic challenges, and future direction. We will also discuss the likely reason for the failure of multiple HDAC inhibitor clinical trials in malignancies other than lymphoma and multiple myeloma. In addition, the potential molecular mechanism(s) that may play a key role in the efficacy and therapeutic response rate in the clinic and the likely patient population for HDAC therapy will be discussed.

Histone modifier gene mutations in peripheral T-cell lymphoma not otherwise specified

Due to heterogeneous morphological and immunophenotypic features, approximately 50% of peripheral T-cell lymphomas are unclassifiable and categorized as peripheral T-cell lymphomas, not otherwise specified. These conditions have an aggressive course and poor clinical outcome. Identification of actionable biomarkers is urgently needed to develop better therapeutic strategies. Epigenetic alterations play a crucial role in tumor progression. Histone modifications, particularly methylation and acetylation, are generally involved in chromatin state regulation. Here we screened the core set of genes related to histone methylation (KMT2D, SETD2, KMT2A, KDM6A) and acetylation (EP300, CREBBP) and identified 59 somatic mutations in 45 of 125 (36.0%) patients with peripheral T-cell lymphomas, not otherwise specified. Histone modifier gene mutations were associated with inferior progression-free survival time of the patients, irrespective of chemotherapy regimens, but an increased response to the histone deacetylase inhibitor chidamide. In vitro, chidamide significantly inhibited the growth of EP300-mutated T-lymphoma cells and KMT2D-mutated T-lymphoma cells when combined with the hypomethylating agent decitabine. Mechanistically, decitabine acted synergistically with chidamide to enhance the interaction of KMT2D with transcription factor PU.1, regulated H3K4me-associated signaling pathways, and sensitized T-lymphoma cells to chidamide. In a xenograft KMT2D-mutated T-lymphoma model, dual treatment with chidamide and decitabine significantly retarded tumor growth and induced cell apoptosis through modulation of the KMT2D/H3K4me axis. Our work thus contributes to the understanding of aberrant histone modification in peripheral T-cell lymphomas, not otherwise specified and the stratification of a biological subset that can benefit from epigenetic treatment.

A phase 1 study of romidepsin and pralatrexate reveals marked activity in relapsed and refractory T-cell lymphoma

Peripheral T-cell lymphomas (PTCL) are a group of rare malignancies characterized by chemotherapy resistance and poor prognosis. Romidepsin and pralatrexate were approved by the US Food and Drug Administration for patients with relapsed/refractory PTCL, exhibiting response rates of 25% and 29% respectively. Based on synergy in preclinical models of PTCL, we initiated a phase 1 study of pralatrexate plus romidepsin in patients with relapsed/refractory lymphoma. This was a single institution dose-escalation study of pralatrexate plus romidepsin designed to determine the dose-limiting toxicities (DLTs), maximum tolerated dose, pharmacokinetic profile, and response rates. Patients were treated with pralatrexate (10 to 25 mg/m²) and romidepsin (12 to 14 mg/m²) on 1 of 3 schedules: every week × 3 every 28 days, every week × 2 every 21 days, and every other week every 28 days. Treatment continued until progression, withdrawal of consent, or medical necessity. Twenty-nine patients were enrolled and evaluable for toxicity. Coadministration of pralatrexate and romidepsin was safe, well tolerated, with 3 DLTs across all schedules (grade 3 oral mucositis × 2; grade 4 sepsis × 1). The recommended phase 2 dose was defined as pralatrexate 25 mg/m² and romidepsin 12 mg/m² every other week. Twenty-three patients were evaluable for response. The overall response rate was 57% (13/23) across all patients and 71% (10/14) in PTCL. The phase 1 study of pralatrexate plus romidepsin resulted in a high response rate in patients with previously treated PTCL. A phase 2 study in PTCL will determine the efficacy of the combination. This trial was registered at www.clinicaltrials.gov as #NCT01947140.

Decitabine Priming Enhances Mucin 1 Inhibition Mediated Disruption of Redox Homeostasis in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous neoplasm and patients with relapsed/refractory disease exhibit resistance to standard therapies. We have previously demonstrated that the Mucin 1 C-terminal subunit (MUC1-C) plays a critical role in protection from oxidative stress in CTCL cells. Targeting of MUC1-C with a pharmacologic inhibitor, GO-203, was associated with apoptosis in CTCL. However, disease responses were incomplete underscoring the need for combinatorial strategies that could exploit the vulnerability of CTCL cells to oxidative signals. Cell lines, primary samples, and xenograft models of CTCL were used to assess synergy of GO-203 with decitabine, a hypomethylating agent. Present studies demonstrate that exposure of CTCL cells to decitabine in combination with GO-203, increased the generation of reactive oxygen species (ROS) levels and decreased levels of scavenger molecules, NADP, NADPH, glutathione, and TIGAR, critical to intracellular redox homeostasis. Dual exposure to GO-203 and decitabine resulted in marked downregulation of DNA methyl transferases demonstrating significant synergy of these agents in inducing global and gene specific hypomethylation. Accordingly, treatment with decitabine and GO-203 upregulated the ROS generating enzymes, NADPH oxidase 4 and dual oxidase 2 potentially due to their effect on epigenomic regulation of these proteins. In concert with these findings, exposure to decitabine and GO-203 resulted in heightened apoptotic death in CTCL cell lines, patient-derived primary samples and in a murine xenograft model. These findings indicate that decitabine intensifies MUC1-C inhibition induced redox imbalance and provides a novel combination of targeted and epigenetic agents for patients with CTCL. Mol Cancer Ther; 16(10); 2304-14. ©2017 AACR.

Complete remission with romidepsin in a patient with T-cell acute lymphoblastic leukemia refractory to induction hyper-CVAD

T‐cell acute lymphoblastic leukemia (T‐ALL) and T‐cell lymphoblastic lymphoma (T‐LBL) are neoplasms that originate from T‐cell precursors. Outcomes in adult patients with T‐ALL/LBL remain unsatisfactory; early relapse following intensive induction chemotherapy is a concern, and patients with relapsed or refractory disease have a poor prognosis. Romidepsin is a potent, class 1 selective histone deacetylase inhibitor approved for the treatment of patients with peripheral T‐cell lymphoma who have had ≥1 prior therapy and patients with cutaneous T‐cell lymphoma who have had ≥1 prior systemic therapy. Here, we report the case of an adult patient with T‐ALL refractory to induction hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (hyper‐CVAD). Treatment with romidepsin was initiated, and romidepsin in combination with hyper‐CVAD resulted in complete remission, with mild tumor lysis syndrome as the only detectable additional toxicity. The patient eventually underwent allogeneic stem cell transplant while in first complete remission. Prior studies have shown that romidepsin is capable of inducing durable responses with manageable toxicities in patients with mature T‐cell lymphomas. This case study describes the successful use of romidepsin in combination with hyper‐CVAD in an adult patient with refractory T‐ALL and highlights the activity of romidepsin in the T‐cell lineage. The potential of romidepsin‐containing regimens in patients with T‐ALL/LBL deserves further study.

Action mechanisms of histone deacetylase inhibitors in the treatment of hematological malignancies

Histone deacetylases (HDACs) critically regulate gene expression by determining the acetylation status of histones. Studies have increasingly focused on the activities of HDACs, especially involving non-histone proteins, and their various biological effects. Aberrant HDAC expression observed in several kinds of human tumors makes HDACs potential targets for cancer treatment. Several preclinical studies have suggested that HDAC inhibitors show some efficacy in the treatment of acute myelogenous leukemia with AML1-ETO, which mediates transcriptional repression through its interaction with a complex including HDAC1. Recurrent mutations in epigenetic regulators are found in T-cell lymphomas (TCLs), and HDAC inhibitors and hypomethylating agents were shown to act cooperatively in the treatment of TCLs. Preclinical modeling has suggested that persistent activation of the signal transducer and activator of transcription signaling pathway could serve as a useful biomarker of resistance to HDAC inhibitor in patients with cutaneous TCL. Panobinostat, a pan-HDAC inhibitor, in combination with bortezomib and dexamethasone, has achieved longer progression-free survival in patients with relapsed/refractory multiple myeloma (MM) than the placebo in combination with bortezomib and dexamethasone. Panobinostat inhibited MM cell growth by degrading protein phosphatase 3 catalytic subunit α (PPP3CA), a catalytic subunit of calcineurin. This degradation was suggested to be mediated by the blockade of the chaperone function of heat shock protein 90 due to HDAC6 inhibition. Aberrant PPP3CA expression in advanced MM indicated a possible correlation between high PPP3CA expression and the pathogenesis of MM. Furthermore, PPP3CA was suggested as a common target of panobinostat and bortezomib.

Use of class I histone deacetylase inhibitor romidepsin in combination regimens

Histone deacetylase (HDAC) inhibitors are epigenetic-modifying agents that have shown promise as anticancer therapies. Several HDAC inhibitors have been approved by the US Food and Drug Administration (FDA) as single-agent therapies to treat T-cell lymphoma. The synergistic combination of HDAC inhibitors with other anticancer agents has the potential to constitute treatment regimens with enhanced efficacy. Romidepsin is a structurally unique, potent, bicyclic class 1 selective HDAC inhibitor approved by the FDA for the treatment of patients with peripheral T-cell lymphoma who have had at least 1 prior therapy and patients with cutaneous T-cell lymphoma who have had at least 1 prior systemic therapy. Here, we review data that support the use of romidepsin in combination with other anticancer agents for the treatment of various malignancies. Promising results have emerged from early clinical studies, supporting the potential for romidepsin combination regimens to constitute safe and effective treatments for cancer.

Development of 5' LTR DNA methylation of latent HIV-1 provirus in cell line models and in long-term-infected individuals

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) latency represents the major barrier to virus eradication in infected individuals because cells harboring latent HIV-1 provirus are not affected by current antiretroviral therapy (ART). We previously demonstrated that DNA methylation of HIV-1 long terminal repeat (5' LTR) restricts HIV-1 reactivation and, together with chromatin conformation, represents an important mechanism of HIV-1 latency maintenance. Here, we explored the new issue of temporal development of DNA methylation in latent HIV-1 5' LTR.

RESULTS

In the Jurkat CD4(+) T cell model of latency, we showed that the stimulation of host cells contributed to de novo DNA methylation of the latent HIV-1 5' LTR sequences. Consecutive stimulations of model CD4(+) T cell line with TNF-α and PMA or with SAHA contributed to the progressive accumulation of 5' LTR DNA methylation. Further, we showed that once established, the high DNA methylation level of the latent 5' LTR in the cell line model was a stable epigenetic mark. Finally, we explored the development of 5' LTR DNA methylation in the latent reservoir of HIV-1-infected individuals who were treated with ART. We detected low levels of 5' LTR DNA methylation in the resting CD4(+) T cells of the group of patients who were treated for up to 3 years. However, after long-term ART, we observed an accumulation of 5' LTR DNA methylation in the latent reservoir. Importantly, within the latent reservoir of some long-term-treated individuals, we uncovered populations of proviral molecules with a high density of 5' LTR CpG methylation.

CONCLUSIONS

Our data showed the presence of 5' LTR DNA methylation in the long-term reservoir of HIV-1-infected individuals and implied that the transient stimulation of cells harboring latent proviruses may contribute, at least in part, to the methylation of the HIV-1 promoter.