Histone deacetylase inhibitors induce growth arrest and apoptosis of HTLV-1-infected T-cells via blockade of signaling by nuclear factor κB

Therapeutic advances for the management of adult T cell leukemia: Where do we stand?

Adult T cell leukemia (ATL) is an aggressive blood malignancy secondary to chronic infection with the human T cell leukemia virus type I (HTLV-1) retrovirus. ATL encompasses four subtypes (acute, lymphoma, chronic, and smoldering), which exhibit different clinical characteristics and respond differently to various treatment strategies. Yet, all four subtypes are characterized by a dismal long-term prognosis and a low survival rate. While antiretroviral therapy improves overall survival outcomes in smoldering and chronic subtypes, survival remains poor in lymphoma subtypes despite their good response to intensive chemotherapy. Nonetheless, acute ATL remains the most aggressive form associated with profound immunosuppression, chemo-resistance and dismal prognosis. Targeted therapies such as monoclonal antibodies, epigenetic therapies, and arsenic/IFN, emerged as promising therapeutic approaches in ATL. Allogeneic hematopoietic cell transplantation is the only potentially curative modality, alas applicable to only a small percentage of patients. The recent findings demonstrating the expression of the viral oncoprotein Tax in primary ATL cells from patients with acute or chronic ATL, albeit at low levels, and their dependence on continuous Tax expression for their survival, position ATL as a virus-addicted leukemia and validates the rationale of anti-viral treatment strategies. This review provides a comprehensive overview on conventional, anti-viral and targeted therapies of ATL, with emphasis on Tax-targeted therapied in the pre-clinical and clinical settings.

The roles of HDAC with IMPDH and mTOR with JAK as future targets in the treatment of rheumatoid arthritis with combination therapy

Various studies have shown that cytokines are important regulators in rheumatoid arthritis (RA). In synovial inflammation alteration of the enzyme HDAC, IMPDH enzyme, mTOR pathway, and JAK pathway increase cytokine level. These increased cytokine levels are responsible for the inflammation in RA. Inflammation is a physiological and normal reaction of the immune system against dangerous stimuli such as injury and infection. The cytokine-based approach improves the treatment of RA. To reach this goal, various researchers and scientists are working more aggressively by using a combination approach. The present review of combination therapy provides essential evidence about the possible synergistic effect of combinatorial agents. We have focused on the effects of HDAC inhibitor with IMPDH inhibitor and mTOR inhibitor with JAK inhibitor in combination for the treatment of RA. Combining various targeted strategies can be helpful for the treatment of RA.

Therapeutic approaches for HTLV-1-associated adult T-cell leukemia/lymphoma: a comprehensive review

Adult T-cell leukemia/lymphoma (ATLL), an infrequent malignancy resultant from human T-cell lymphotropic virus type I (HTLV-1), exhibits a spectrum of phenotypes, encompassing acute, smoldering, lymphomatous, and chronic variants, each bearing distinct clinical presentations. The preponderant acute manifestation is characterized by hypercalcemia, systemic manifestations, organomegaly, and dermatological eruptions. Conversely, the chronic phenotype is typified by lymphocytosis and/or cutaneous eruptions, while smoldering ATLL assumes an asymptomatic course. Immunocompromise afflicts ATLL patients, heightening their vulnerability to opportunistic infections that frequently intricately intertwine with disease progression. Therefore, an early diagnosis is crucial to manage the disease appropriately. While conventional chemotherapeutic regimens have shown limited success, especially in acute and lymphoma types, recent studies suggest that allogeneic stem cell transplantation might enhance treatment results because it has shown promising outcomes in some patients. Novel therapeutics, such as interferon and monoclonal antibodies, have also shown promise, but more research is needed to confirm their efficacy. Moreover, the identification of biomarkers for ATLL and genetic changes in HTLV-1 infected cells has led to the development of targeted therapies that have shown remarkable success in clinical trials. These targeted therapies have the potential to offer a more personalized approach to the treatment of ATLL. The aim of our review is to elaborate on conventional and novel therapies and the efficiency of mentioned treatments.

Oncogenic Viruses and the Epigenome: How Viruses Hijack Epigenetic Mechanisms to Drive Cancer

Globally, viral infections substantially contribute to cancer development. Oncogenic viruses are taxonomically heterogeneous and drive cancers using diverse strategies, including epigenomic dysregulation. Here, we discuss how oncogenic viruses disrupt epigenetic homeostasis to drive cancer and focus on how virally mediated dysregulation of host and viral epigenomes impacts the hallmarks of cancer. To illustrate the relationship between epigenetics and viral life cycles, we describe how epigenetic changes facilitate the human papillomavirus (HPV) life cycle and how changes to this process can spur malignancy. We also highlight the clinical impact of virally mediated epigenetic changes on cancer diagnosis, prognosis, and treatment.

HDAC inhibitors Panobinostat and Romidepsin enhance tax transcription in HTLV-1-infected cell lines and freshly isolated patients’ T-cells

The viral transactivator Tax plays a key role in HTLV-1 reactivation and de novo infection. Previous approaches focused on the histone deacetylase inhibitor (HDACi) Valproate as a latency-reversing agent to boost Tax expression and expose infected cells to the host’s immune response. However, following treatment with Valproate proviral load decreases in patients with HAM/TSP were only transient. Here, we hypothesize that other compounds, including more potent and selective HDACi, might prove superior to Valproate in manipulating Tax expression. Thus, a panel of HDACi (Vorinostat/SAHA/Zolinza, Panobinostat/LBH589/Farydak, Belinostat/PXD101/Beleodaq, Valproate, Entinostat/MS-275, Romidepsin/FK228/Istodax, and MC1568) was selected and tested for toxicity and potency in enhancing Tax expression. The impact of the compounds was evaluated in different model systems, including transiently transfected T-cells, chronically HTLV-1-infected T-cell lines, and freshly isolated PBMCs from HTLV-1 carriers ex vivo. We identified the pan-HDACi Panobinostat and class I HDACi Romidepsin as particularly potent agents at raising Tax expression. qRT-PCR analysis revealed that these inhibitors considerably boost tax and Tax-target gene transcription. However, despite this significant increase in tax transcription and histone acetylation, protein levels of Tax were only moderately enhanced. In conclusion, these data demonstrate the ability of Panobinostat and Romidepsin to manipulate Tax expression and provide a foundation for further research into eliminating latently infected cells. These findings also contribute to a better understanding of conditions limiting transcription and translation of viral gene products.

Adult T-Cell Leukemia: a Comprehensive Overview on Current and Promising Treatment Modalities

PURPOSE OF THE REVIEW

Adult T-cell leukemia (ATL) is an aggressive chemo-resistant malignancy secondary to HTLV-1 retrovirus. Prognosis of ATL remains dismal. Herein, we emphasized on the current ATL treatment modalities and their drawbacks, and opened up on promising targeted therapies with special focus on the HTLV-1 regulatory proteins Tax and HBZ.

RECENT FINDINGS

Indolent ATL and a fraction of acute ATL exhibit long-term survival following antiviral treatment with zidovudine and interferon-alpha. Monoclonal antibodies such as mogamulizumab improved response rates, but with little effect on survival. Allogeneic hematopoietic cell transplantation results in long-term survival in one third of transplanted patients, alas only few patients are transplanted. Salvage therapy with lenalidomide in relapsed/refractory patients leads to prolonged survival in some of them. ATL remains an unmet medical need. Targeted therapies focusing on the HTLV-1 viral replication and/or viral regulatory proteins, as well as on the host antiviral immunity, represent a promising approach for the treatment of ATL.

The Effect of a Histone Deacetylase Inhibitor (AR-42) and Zoledronic Acid on Adult T-Cell Leukemia/Lymphoma Osteolytic Bone Tumors

Simple Summary

Adult T-cell leukemia (ATL) Leukemia is an aggressive, peripheral blood (T-cell) neoplasm associated with human T-cell leukemia virus type 1 (HTLV-1) infection. Recent studies have implicated dysregulated histone deacetylases in ATL pathogenesis. ATL modulates the bone microenvironment of patients and activates osteoclasts (bone resorbing cells) that cause severe bone loss. The objective of this study was to assess the individual and dual effects of AR-42 (HDACi) and zoledronic acid (Zol) on the growth of ATL cells in vitro and in vivo. AR-42 and Zol reduced the viability of ATL cells in vitro. Additionally, Zol and Zol/AR-42 decreased ATL tumor growth and halted osteolysis in bone tumor xenografts in immunodeficient mice in vivo. Our study suggests that dual targeting of ATL cells (using HDACi) and bone osteoclasts (using bisphosphonates) may be exploited as a valuable approach to reduce bone tumor burden and improve the life quality of ATL patients.

Abstract

Adult T-cell leukemia/lymphoma (ATL) is an intractable disease affecting nearly 4% of Human T-cell Leukemia Virus Type 1 (HTLV-1) carriers. Acute ATL has a unique interaction with bone characterized by aggressive bone invasion, osteolytic metastasis, and hypercalcemia. We hypothesized that dual tumor and bone-targeted therapies would decrease tumor burden in bone, the incidence of metastasis, and ATL-associated osteolysis. Our goal was to evaluate dual targeting of both ATL bone tumors and the bone microenvironment using an anti-tumor HDACi (AR-42) and an osteoclast inhibitor (zoledronic acid, Zol), alone and in combination. Our results showed that AR-42, Zol, and AR-42/Zol significantly decreased the viability of multiple ATL cancer cell lines in vitro. Zol and AR-42/Zol decreased tumor growth in vivo. Zol ± AR-42 significantly decreased ATL-associated bone resorption and promoted new bone formation. AR-42-treated ATL cells had increased mRNA levels of PTHrP, ENPP2 (autotaxin) and MIP-1α, and TAX viral gene expression. AR-42 alone had no significant effect on tumor growth or osteolysis in mice. These findings indicate that Zol adjuvant therapy has the potential to reduce growth of ATL in bone and its associated osteolysis.

Latency Reversing Agents: Kick and Kill of HTLV-1?

Human T-cell leukemia virus type 1 (HTLV-1), the cause of adult T-cell leukemia/lymphoma (ATLL), is a retrovirus, which integrates into the host genome and persistently infects CD4⁺ T-cells. Virus propagation is stimulated by (1) clonal expansion of infected cells and (2) de novo infection. Viral gene expression is induced by the transactivator protein Tax, which recruits host factors like positive transcription elongation factor b (P-TEFb) to the viral promoter. Since HTLV-1 gene expression is repressed in vivo by viral, cellular, and epigenetic mechanisms in late phases of infection, HTLV-1 avoids an efficient CD8⁺ cytotoxic T-cell (CTL) response directed against the immunodominant viral Tax antigen. Hence, therapeutic strategies using latency reversing agents (LRAs) sought to transiently activate viral gene expression and antigen presentation of Tax to enhance CTL responses towards HTLV-1, and thus, to expose the latent HTLV-1 reservoir to immune destruction. Here, we review strategies that aimed at enhancing Tax expression and Tax-specific CTL responses to interfere with HTLV-1 latency. Further, we provide an overview of LRAs including (1) histone deacetylase inhibitors (HDACi) and (2) activators of P-TEFb, that have mainly been studied in context of human immunodeficiency virus (HIV), but which may also be powerful in the context of HTLV-1.

Recent Update of HDAC Inhibitors in Lymphoma

Modulating epigenetic modification has been recognized for over a decade as an effective therapeutic approach to cancer and many studies of histone deacetylase (HDAC), one of the best known epigenetic modulators, have been published. HDAC modulates cell proliferation and angiogenesis and plays an essential role in cell growth. Research shows that up-regulated HDACs are present in many cancer types and synthetic or natural HDAC inhibitors have been used to silence overregulated HDACs. Inhibiting HDACs may cause arrest of cell proliferation, angiogenesis reduction and cell apoptosis. Recent studies indicate that HDAC inhibitors can provide a therapeutic effect in various cancers, such as B-cell lymphoma, leukemia, multiple myeloma and some virus-associated cancers. Some evidence has demonstrated that HDAC inhibitors can increase the expression of immune-related molecules leading to accumulation of CD8 + T cells and causing unresponsive tumor cells to be recognized by the immune system, reducing tumor immunity. This may be a solution for the blockade of PD-1. Here, we review the emerging development of HDAC inhibitors in various cancer treatments and reduction of tumor immunity.

The Contribution of Epigenetics to Cancer Immunotherapy

Effective anticancer immunotherapy treatments constitute a qualitative leap in cancer management. Nonetheless, not all patients benefit from such therapies because they fail to achieve complete responses, suffer frequent relapses, or develop potentially life-threatening toxicities. Epigenomic signatures in immune and cancer cells appear to be accurate and promising predictors of patient outcomes with immunotherapy. In addition, combined treatments with epigenetic drugs can exploit the dynamic nature of epigenetic changes to potentially modulate responses to immunotherapy. Candidate epigenetic biomarkers may provide a rationale for patient stratification and precision medicine, thus maximizing the chances of treatment success while minimizing unwanted effects. We present a comprehensive up-to-date view of potential epigenetic biomarkers in immunotherapy and discuss their advantages over other indicators.

Novel Treatments of Adult T Cell Leukemia Lymphoma

Adult T cell leukemia-lymphoma (ATL) is an aggressive malignancy secondary to chronic infection with the human T cell leukemia virus type I (HTLV-I) retrovirus. ATL carries a dismal prognosis. ATL classifies into four subtypes (acute, lymphoma, chronic, and smoldering) which display different clinical features, prognosis and response to therapy, hence requiring different clinical management. Smoldering and chronic subtypes respond well to antiretroviral therapy using the combination of zidovudine (AZT) and interferon-alpha (IFN) with a significant prolongation of survival. Conversely, the watch and wait strategy or chemotherapy for these indolent subtypes allies with a poor long-term outcome. Acute ATL is associated with chemo-resistance and dismal prognosis. Lymphoma subtypes respond better to intensive chemotherapy but survival remains poor. Allogeneic hematopoietic stem cell transplantation (HSCT) results in long-term survival in roughly one third of transplanted patients but only a small percentage of patients can make it to transplant. Overall, current treatments of aggressive ATL are not satisfactory. Prognosis of refractory or relapsed patients is dismal with some encouraging results when using lenalidomide or mogamulizumab. To overcome resistance and prevent relapse, preclinical or pilot clinical studies using targeted therapies such as arsenic/IFN, monoclonal antibodies, epigenetic therapies are promising but warrant further clinical investigation. Anti-ATL vaccines including Tax peptide-pulsed dendritic cells, induced Tax-specific CTL responses in ATL patients. Finally, based on the progress in understanding the pathophysiology of ATL, and the risk-adapted treatment approaches to different ATL subtypes, treatment strategies of ATL should take into account the host immune responses and the host microenvironment including HTLV-1 infected non-malignant cells. Herein, we will provide a summary of novel treatments of ATL in vitro, in vivo, and in early clinical trials.

Targeting histone epigenetics to control viral infections

During the past decades, many studies have significantly broadened our understanding of complex virus-host interactions to control chromatin structure and dynamics.1, 2 However, the role and impact of such modifications during viral infections is not fully revealed. Indeed, this type of regulation is bidirectional between the virus and the host. While viral replication and gene expression are significantly impacted by histone modifications on the viral chromatin,³ studies have shown that some viral pathogens dynamically manipulate cellular epigenetic factors to enhance their own survival and pathogenesis, as well as escape the immune system defense lines.⁴ In this dynamic, histone posttranslational modifications (PTMs) appear to play fundamental roles in the regulation of chromatin structure and recruitment of other factors.⁵ Genuinely, those PTMs play a vital role in lytic infection, latency reinforcement, or, conversely, viral reactivation.⁶ In this chapter, we will examine and review the involvement of histone modifications as well as their potential manipulation to control infections during various viral life cycle stages, highlighting their prospective implications in the clinical management of human immunodeficiency virus (HIV), herpes simplex virus (HSV), human cytomegalovirus (HCMV), hepatitis B and C viruses (HBV and HCV, respectively), Epstein–Barr virus (EBV), and other viral diseases. Targeting histone modifications is critical in setting the treatment of chronic viral infections with both lytic and latent stages (HIV, HCMV, HSV, RSV), virus-induced cancers (HBV, HCV, EBV, KSHV, HPV), and epidemic/emerging viruses (e.g. influenza virus, arboviruses).

Histone Deacetylases (HDACs) Guided Novel Therapies for T-cell lymphomas

T-cell lymphomas are a heterogeneous group of cancers with different pathogenesis and poor prognosis. Histone deacetylases (HDACs) are epigenetic modifiers that modulate many key biological processes. In recent years, HDACs have been fully investigated for their roles and potential as drug targets in T-cell lymphomas. In this review, we have deciphered the modes of action of HDACs, HDAC inhibitors as single agents, and HDACs guided combination therapies in T-cell lymphomas. The overview of HDACs on the stage of T-cell lymphomas, and HDACs guided therapies both as single agents and combination regimens endow great opportunities for the cure of T-cell lymphomas.

Adult T-cell leukemia: molecular basis for clonal expansion and transformation of HTLV-1-infected T cells

Adult T-cell leukemia (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) that develops through a multistep carcinogenesis process involving 5 or more genetic events. We provide a comprehensive overview of recently uncovered information on the molecular basis of leukemogenesis in ATL. Broadly, the landscape of genetic abnormalities in ATL that include alterations highly enriched in genes for T-cell receptor-NF-κB signaling such as PLCG1, PRKCB, and CARD11 and gain-of function mutations in CCR4 and CCR7 Conversely, the epigenetic landscape of ATL can be summarized as polycomb repressive complex 2 hyperactivation with genome-wide H3K27 me3 accumulation as the basis of the unique transcriptome of ATL cells. Expression of H3K27 methyltransferase enhancer of zeste 2 was shown to be induced by HTLV-1 Tax and NF-κB. Furthermore, provirus integration site analysis with high-throughput sequencing enabled the analysis of clonal composition and cell number of each clone in vivo, whereas multicolor flow cytometric analysis with CD7 and cell adhesion molecule 1 enabled the identification of HTLV-1-infected CD4+ T cells in vivo. Sorted immortalized but untransformed cells displayed epigenetic changes closely overlapping those observed in terminally transformed ATL cells, suggesting that epigenetic abnormalities are likely earlier events in leukemogenesis. These new findings broaden the scope of conceptualization of the molecular mechanisms of leukemogenesis, dissecting them into immortalization and clonal progression. These recent findings also open a new direction of drug development for ATL prevention and treatment because epigenetic marks can be reprogrammed. Mechanisms underlying initial immortalization and progressive accumulation of these abnormalities remain to be elucidated.

Induction of apoptosis by HBI-8000 in adult T-cell leukemia/lymphoma is associated with activation of Bim and NLRP3

Adult T‐cell leukemia/lymphoma (ATL) is an aggressive T‐cell malignancy caused by human T‐cell lymphotropic virus 1. Treatment options for acute ATL patients include chemotherapy, stem cell transplantation, and recently the anti‐chemokine (C‐C motif) receptor 4 antibody, although most patients still have a poor prognosis and there is a clear need for additional options. HBI‐8000 is a novel oral histone deacetylase inhibitor with proven efficacy for treatment of T‐cell lymphomas that recently received approval in China. In the present study, we evaluated the effects of HBI‐8000 on ATL‐derived cell lines and primary cells obtained from Japanese ATL patients. In most cases HBI‐8000 induced apoptosis in both primary ATL cells and cell lines. In addition, findings obtained with DNA microarray suggested Bim activation and, interestingly, the contribution of the NLR family, pyrin domain containing 3 (NLRP3) inflammasome pathway in HBI‐8000‐induced ATL cell death. Further investigations using siRNAs confirmed that Bim contributes to HBI‐8000‐induced apoptosis. Our results provide a rationale for a clinical investigation of the efficacy of HBI‐8000 in patients with ATL. Although the role of NLRP3 inflammasome activation in ATL cell death remains to be verified, HBI‐8000 may be part of a novel therapeutic strategy for cancer based on the NLRP3 pathway.

Histone deacetylase inhibitor panobinostat induces calcineurin degradation in multiple myeloma

Multiple myeloma (MM) is a relapsed and refractory disease, one that highlights the need for developing new molecular therapies for overcoming of drug resistance. Addition of panobinostat, a histone deacetylase (HDAC) inhibitor, to bortezomib and dexamethasone improved progression-free survival (PFS) in relapsed and refractory MM patients. Here, we demonstrate how calcineurin, when inhibited by immunosuppressive drugs like FK506, is involved in myeloma cell growth and targeted by panobinostat. mRNA expression of PPP3CA, a catalytic subunit of calcineurin, was high in advanced patients. Panobinostat degraded PPP3CA, a degradation that should have been induced by inhibition of the chaperone function of heat shock protein 90 (HSP90). Cotreatment with HDAC inhibitors and FK506 led to an enhanced antimyeloma effect with a greater PPP3CA reduction compared with HDAC inhibitors alone both in vitro and in vivo. In addition, this combination treatment efficiently blocked osteoclast formation, which results in osteolytic lesions. The poor response and short PFS duration observed in the bortezomib-containing therapies of patients with high PPP3CA suggested its relevance to bortezomib resistance. Moreover, bortezomib and HDAC inhibitors synergistically suppressed MM cell viability through PPP3CA inhibition. Our findings underscore the usefulness of calcineurin-targeted therapy in MM patients, including patients who are resistant to bortezomib.

Roles of HTLV-1 basic Zip Factor (HBZ) in Viral Chronicity and Leukemic Transformation. Potential New Therapeutic Approaches to Prevent and Treat HTLV-1-Related Diseases

More than thirty years have passed since human T-cell leukemia virus type 1 (HTLV-1) was described as the first retrovirus to be the causative agent of a human cancer, adult T-cell leukemia (ATL), but the precise mechanism behind HTLV-1 pathogenesis still remains elusive. For more than two decades, the transforming ability of HTLV-1 has been exclusively associated to the viral transactivator Tax. Thirteen year ago, we first reported that the minus strand of HTLV-1 encoded for a basic Zip factor factor (HBZ), and since then several teams have underscored the importance of this antisense viral protein for the maintenance of a chronic infection and the proliferation of infected cells. More recently, we as well as others have demonstrated that HBZ has the potential to transform cells both in vitro and in vivo. In this review, we focus on the latest progress in our understanding of HBZ functions in chronicity and cellular transformation. We will discuss the involvement of this paradigm shift of HTLV-1 research on new therapeutic approaches to treat HTLV-1-related human diseases.

Characteristics of Adult T-Cell Leukemia/Lymphoma Patients with Long Survival: Prognostic Significance of Skin Lesions and Possible Beneficial Role of Valproic Acid

We describe the clinical and biological features of ten patients with a survival superior to ten years (long survival), out of 175 patients diagnosed with Adult T-cell Leukemia/Lymphoma (ATL) in Martinique (1983–2013). There were 5 lymphoma and 5 chronic subtypes. Five of them (3 chronic, 2 lymphoma) had been treated with valproic acid (VA) for neurological disorders developed before or after ATL diagnosis, suggesting a beneficial role for VA as a histone deacetylase inhibitor (HDI) in ATL treatment. Total duration of uninterrupted VA treatment ranged from 8 to 37 years. Overall, the 175 incident ATL cases presented with a median survival of 5.43 months. The five VA-treated (VA⁺) patients presented with longer survival compared to VA treatment-free patients (VA⁻). For chronic subtypes, survival periods were of 213 months for 3 VA⁺ patients and of 33 months for 11 VA⁻ patients (p = 0.023). For lymphoma subtypes, survival periods were of 144 months for 2 VA⁺ patients versus 6 months for 49 VA⁻ patients (p = 0.0046). ATL cases with skin lesions, particularly lymphoma subtypes, had a longer survival (13.96 months) compared to those without skin lesions (6.06 months, p = 0.002). Eight out of the 10 patients presenting with long survival had skin lesions.

Recent advances in the treatment of adult T-cell leukemia-lymphomas

Recent advances in treatment for adult T-cell leukemia-lymphoma (ATL) are reviewed herein. It is currently possible to select a therapeutic strategy for ATL and predict prognosis by classification of patients by clinical subtypes and clinicopathological factors. Although the overall survival (OS) of patients with ATL has increased marginally because of advances in chemotherapy, further prolongation of survival might be difficult with conventional chemotherapy alone. Promising results have been reported for antiviral therapy using zidovudine and interferon-α, and, indeed, antiviral therapy is currently the standard treatment for patients with ATL in western countries. Remarkably, the 5-year OS rates are 100% for both the smoldering-type and chronic-type ATL. Recently, treatments for ATL have included allogeneic hematopoietic stem cell transplantation and molecular targeted therapies. Furthermore, the anti-CCR4 monoclonal antibody mogamulizumab has been shown to have marked cytotoxic effects on ATL cells, especially in the leukemic type of ATL. In the lymphoma type of ATL, the response rate may be improved by combining mogamulizumab with chemotherapy. It should be recognized that prevention of infection from carriers of human T-cell leukemia virus type-I and transfer of the virus from mother to infant are crucial issues for the eradication of ATL.

The histone deacetylase inhibitor vorinostat prevents TNFα-induced necroptosis by regulating multiple signaling pathways

Histone deacetylase (HDAC) inhibitors are novel anticancer reagents that have recently been reported to have anti-inflammatory and neuroprotective effects; however, the mechanisms underlying their activities are largely undefined. The data from this study show that the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) can protect L929 cells from TNFα-induced necroptosis. This effect involves multiple mechanisms, including the upregulation of cFLIPL expression, the enhanced activation of NFκB and p38 MAPK, and the inactivation of JNK. In addition, SAHA could initiate cell autophagy by inhibiting Akt and mTOR, which also play important roles in protecting cells from necroptosis. Because cell necroptosis is important for inflammation-related deterioration and neurodegenerative disease, our results indicate that preventing cell necrosis may be an important mechanism through which HDAC inhibitor compounds exert their anti-inflammatory or neuroprotective effects.

Protective roles of epithelial cells in the survival of adult T-cell leukemia/lymphoma cells

Adult T-cell leukemia/lymphoma (ATL) is a highly invasive and intractable T-cell malignancy caused by human T-cell leukemia virus-1 infection. We demonstrate herein that normal tissue-derived epithelial cells (NECs) exert protective effects on the survival of leukemic cells, which may partially account for high resistance to antileukemic therapies in patients with ATL. Viral gene-silenced, ATL-derived cell lines (ATL cells) dramatically escaped from histone deacetylase inhibitor-induced apoptosis by direct co-culture with NECs. Adhesions to NECs suppressed p21(Cip1) expression and increased a proportion of resting G0/G1 phase cells in trichostatin A (TSA)-treated ATL cells. ATL cells adhering to NECs down-regulated CD25 expression and enhanced vimentin expression, suggesting that most ATL cells acquired a quiescent state by cell-cell interactions with NECs. ATL cells adhering to NECs displayed highly elevated expression of the cancer stem cell marker CD44. Blockade of CD44 signaling diminished the NEC-conferred resistance of ATL cells to TSA-induced apoptosis. Co-culture with NECs also suppressed the expression of NKG2D ligands on TSA-treated ATL cells, resulting in decreased natural killer cell-mediated cytotoxicity. Combined evidence suggests that interactions with normal epithelial cells augment the resistance of ATL cells to TSA-induced apoptosis and facilitate immune evasion by ATL cells.

HTLV tax: a fascinating multifunctional co-regulator of viral and cellular pathways

Human T-cell lymphotropic virus type 1 (HTLV-1) has been identified as the causative agent of adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The virus infects between 15 and 20 million people worldwide of which approximately 2-5% develop ATL. The past 35 years of research have yielded significant insight into the pathogenesis of HTLV-1, including the molecular characterization of Tax, the viral transactivator, and oncoprotein. In spite of these efforts, the mechanisms of oncogenesis of this pleiotropic protein remain to be fully elucidated. In this review, we illustrate the multiple oncogenic roles of Tax by summarizing a recent body of literature that refines our understanding of cellular transformation. A focused range of topics are discussed in this review including Tax-mediated regulation of the viral promoter and other cellular pathways, particularly the connection of the NF-κB pathway to both post-translational modifications (PTMs) of Tax and subcellular localization. Specifically, recent research on polyubiquitination of Tax as it relates to the activation of the IkappaB kinase (IKK) complex is highlighted. Regulation of the cell cycle and DNA damage responses due to Tax are also discussed, including Tax interaction with minichromosome maintenance proteins and the role of Tax in chromatin remodeling. The recent identification of HTLV-3 has amplified the importance of the characterization of emerging viral pathogens. The challenge of the molecular determination of pathogenicity and malignant disease of this virus lies in the comparison of the viral transactivators of HTLV-1, -2, and -3 in terms of transformation and immortalization. Consequently, differences between the three proteins are currently being studied to determine what factors are required for the differences in tumorogenesis.

Chemoresistance to Valproate Treatment of Bovine Leukemia Virus-Infected Sheep; Identification of Improved HDAC Inhibitors

We previously proved that a histone deacetylase inhibitor (valproate, VPA) decreases the number of leukemic cells in bovine leukemia virus (BLV)-infected sheep. Here, we characterize the mechanisms initiated upon interruption of treatment. We observed that VPA treatment is followed by a decrease of the B cell counts and proviral loads (copies per blood volume). However, all sheep eventually relapsed after different periods of time and became refractory to further VPA treatment. Sheep remained persistently infected with BLV. B lymphocytes isolated throughout treatment and relapse were responsive to VPA-induced apoptosis in cell culture. B cell proliferation is only marginally affected by VPA ex vivo. Interestingly, in four out of five sheep, ex vivo viral expression was nearly undetectable at the time of relapse. In two sheep, a new tumoral clone arose, most likely revealing a selection process exerted by VPA in vivo. We conclude that the interruption of VPA treatment leads to the resurgence of the leukemia in BLV-infected sheep and hypothesize that resistance to further treatment might be due to the failure of viral expression induction. The development of more potent HDAC inhibitors and/or the combination with other compounds can overcome chemoresistance. These observations in the BLV model may be important for therapies against the related Human T-lymphotropic virus type 1.

Molecular hallmarks of adult T cell leukemia

The molecular hallmarks of adult T cell leukemia (ATL) comprise outstanding deregulations of signaling pathways that control the cell cycle, resistance to apoptosis, and proliferation of leukemic cells, all of which have been identified by early excellent studies. Nevertheless, we are now confronted the therapeutic difficulties of ATL that is a most aggressive T cell leukemia/lymphoma. Using next-generation strategies, emerging molecular characteristics such as specific surface markers and an additional catalog of signals affecting the fate of leukemic cells have been added to the molecular hallmarks that constitute an organizing principle for rationalizing the complexities of ATL. Although human T cell leukemia virus type 1 is undoubtedly involved in ATL leukemogenesis, most leukemic cells do not express the viral protein Tax. Instead, cellular gene expression changes dominate homeostasis disorders of infected cells and characteristics of ATL. In this review, we summarize the state of the art of ATL molecular pathology, which supports the biological properties of leukemic cells. In addition, we discuss the recent discovery of two molecular hallmarks of potential generality; an abnormal microRNA pattern and epigenetic reprogramming, which strongly involve the imbalance of the molecular network of lymphocytes. Global analyses of ATL have revealed the functional impact of crosstalk between multifunctional pathways. Clinical and biological studies on signaling inhibitory agents have also revealed novel oncogenic drivers that can be targeted in future. ATL cells, by deregulation of such pathways and their interconnections, may become masters of their own destinies. Recognizing and understanding of the widespread molecular applicability of these concepts will increasingly affect the development of novel strategies for treating ATL.

Prostaglandin E2 induces growth inhibition, apoptosis and differentiation in T and B cell-derived acute lymphoblastic leukemia cell lines (CCRF-CEM and Nalm-6)

Despite advances in the treatment of ALL, in most patients long-term survival rates remain unsatisfactory. The objective of the present study was to investigate the anti-cancer effects of Prostaglandin E2 (PGE2) in two different ALL cell lines (CCRF-CEM (T-ALL) and Nalm-6 (B-ALL)). The anti-leukemic effects of PGE2 were also compared with two epigenetic compounds (trichostatin A and 5-aza-2'-deoxycytidine). MTT assay was used to assess growth inhibition by anti-cancer drugs in these cells. All three compounds were shown to induce apoptosis in both ALL cell lines using flow cytometry and Western blotting. To evaluate the differentiation induction by these agents, the expressions of CD19 and CD38 markers on Nalm-6 cell line and CD7 marker on CCRF-CEM cell line were assayed. Surprisingly, the flow cytometric analysis showed a significant increase in CD markers expression in response to PGE2 treatments. We, for the first time, provide evidences that PGE2 has anti-leukemic effects and induces differentiation at micromolar ranges in both T- and B-cell derived ALL cell lines. Since T-ALL cells are insensitive to current chemotherapies, these findings may help the designing of new protocols for T-ALL differentiation therapy in the future.

Targeting triple-negative breast cancer cells with the histone deacetylase inhibitor panobinostat

INTRODUCTION

Of the more than one million global cases of breast cancer diagnosed each year, approximately fifteen percent are characterized as triple-negative, lacking the estrogen, progesterone, and Her2/neu receptors. Lack of effective therapies, younger age at onset, and early metastatic spread have contributed to the poor prognoses and outcomes associated with these malignancies. Here, we investigate the ability of the histone deacetylase inhibitor panobinostat (LBH589) to selectively target triple-negative breast cancer (TNBC) cell proliferation and survival in vitro and tumorigenesis in vivo.

METHODS

TNBC cell lines MDA-MB-157, MDA-MB-231, MDA-MB-468, and BT-549 were treated with nanomolar (nM) quantities of panobinostat. Relevant histone acetylation was verified by flow cytometry and immunofluorescent imaging. Assays for trypan blue viability, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation, and DNA fragmentation were used to evaluate overall cellular toxicity. Changes in cell cycle progression were assessed with propidium iodide flow cytometry. Additionally, qPCR arrays were used to probe MDA-MB-231 cells for panobinostat-induced changes in cancer biomarkers and signaling pathways. Orthotopic MDA-MB-231 and BT-549 mouse xenograft models were used to assess the effects of panobinostat on tumorigenesis. Lastly, flow cytometry, ELISA, and immunohistochemical staining were applied to detect changes in cadherin-1, E-cadherin (CDH1) protein expression and the results paired with confocal microscopy in order to examine changes in cell morphology.

RESULTS

Panobinostat treatment increased histone acetylation, decreased cell proliferation and survival, and blocked cell cycle progression at G2/M with a concurrent decrease in S phase in all TNBC cell lines. Treatment also resulted in apoptosis induction at 24 hours in all lines except the MDA-MB-468 cell line. MDA-MB-231 and BT-549 tumor formation was significantly inhibited by panobinostat (10 mg/kg/day) in mice. Additionally, panobinostat up-regulated CDH1 protein in vitro and in vivo and induced cell morphology changes in MDA-MB-231 cells consistent with reversal of the mesenchymal phenotype.

CONCLUSIONS

This study revealed that panobinostat is overtly toxic to TNBC cells in vitro and decreases tumorigenesis in vivo. Additionally, treatment up-regulated anti-proliferative, tumor suppressor, and epithelial marker genes in MDA-MB-231 cells and initiated a partial reversal of the epithelial-to-mesenchymal transition. Our results demonstrate a potential therapeutic role of panobinostat in targeting aggressive triple-negative breast cancer cell types.

High expression of the longevity gene product SIRT1 and apoptosis induction by sirtinol in adult T-cell leukemia cells

Adult T-cell leukemia-lymphoma (ATL) is an aggressive peripheral T-cell neoplasm that develops after long-term infection with human T-cell leukemia virus (HTLV-1). SIRT1, a nicotinamide adenine dinucleotide(+)-dependent histone/protein deacetylase, plays a crucial role in various physiological processes, such as aging, metabolism, neurogenesis and apoptosis, owing to its ability to deacetylate numerous substrates, such as histone and NF-κB, which is implicated as an exacerbation factor in ATL. Here, we assessed how SIRT1 is regulated in primary ATL cells and leukemic cell lines. SIRT1 expression in ATL patients was significantly higher than that in healthy controls, especially in the acute type. Sirtinol, a SIRT1 inhibitor, induced significant growth inhibition or apoptosis in cells from ATL patients and leukemic cell lines, especially HTLV-1-related cell lines. Sirtinol-induced apoptosis was mediated by activation of the caspase family and degradation of SIRT1 in the nucleus. Furthermore, SIRT1 knockdown by SIRT1-specific small interfering RNA caused apoptosis via activation of caspase-3 and PARP in MT-2 cells, HTLV-1-related cell line. These results suggest that SIRT1 is a crucial antiapoptotic molecule in ATL cells and that SIRT1 inhibitors may be useful therapeutic agents for leukemia, especially in patients with ATL.

Induction of caspase mediated apoptosis and down-regulation of nuclear factor-κB and Akt signaling are involved in the synergistic antitumor effect of gemcitabine and the histone deacetylase inhibitor trichostatin A in human bladder cancer cells

PURPOSE

Previously we reported that the histone deacetylase inhibitor trichostatin A (Sigma®) synergistically potentiates the antitumor effects of cisplatin in human bladder cancer cells. In the current study we explored the synergistic interaction between trichostatin A and gemcitabine (Novartis Korea, Seoul, Korea), the other mainstay chemotherapeutic regimen for advanced bladder cancer.

MATERIALS AND METHODS

The bladder cancer cell lines HTB5, HTB9, T24, J82, UMUC14 and SW1710 (ATCC®) were exposed to gemcitabine and/or trichostatin A. Synergism between the 2 drugs was determined by the combination index based on the Cell Counting Kit-8 assay (Dojindo Molecular Technologies, Rockville, Maryland) and by a clonogenic assay. Flow cytometry was used to evaluate cell cycle distribution and apoptosis. The expression of cell cycle (p21(WAF1/CIP1), cyclin A, B1 and D1, p-CDC2C, CDC2C, p-CDC25C, CDC25C and pRb), apoptosis (caspase-3, 8 and 9, PARP, Bcl-2, Bad and Bax), NF-κB (NF-κB, p-IκBα, IκBα, p-IKKα, IKKα, cIAP1, cIAP2 and XIAP) and survival (p-Akt, Akt, p-mTOR, mTOR and PTEN) related proteins was analyzed by Western blot.

RESULTS

Isobolic analysis of the Cell Counting Kit-8 assay revealed strong synergism between gemcitabine and trichostatin A, which caused a 4.6 to 25.4-fold gemcitabine dose reduction and a 1.9 to 41.4-fold trichostatin A dose reduction while killing an estimated 90% of bladder cancer cells. The underlying mechanisms could be synergistic cell cycle arrest, induction of caspase mediated apoptosis, and down-regulation of the antiapoptotic NF-κB and Akt signaling pathways.

CONCLUSIONS

Results show that trichostatin A may synergistically enhance gemcitabine mediated cell cycle arrest and apoptosis, suggesting the potential of using histone deacetylase inhibitors as combination agents to enhance the antitumor effect of gemcitabine for advanced bladder cancer.

Targeting HTLV-1 activation of NFκB in mouse models and ATLL patients

Of the millions of HTLV-1 infected carriers worldwide, 3-5% will develop an aggressive T-cell neoplasm that is highly refractory to conventional therapy. The virus carries the Tax oncogene which constitutively activates the NFκB pathway. This co-option of signaling through NFκB provides for the HTLV-1 infected cell an escape from cell cycle arrest and apoptosis, a steady source of growth factors, and a mechanism by which the virus can activate its own target cell. Therapies that target the NFκB pathway sensitize adult T-cell leukemia/lymphoma (ATLL) cells to apoptosis. A focus on translational interrogation of NFκB inhibitors in animal models and ATLL patients is needed to advance NFκB-targeted ATLL therapies to the bedside.

Effects of valproate on Tax and HBZ expression in HTLV-1 and HAM/TSP T lymphocytes

A determinant of human T-lymphotropic virus-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) development is the HTLV-1-infected cell burden. Viral proteins Tax and HBZ, encoded by the sense and antisense strands of the pX region, respectively, play key roles in HTLV-1 persistence. Tax drives CD4(+)-T cell clonal expansion and is the immunodominant viral antigen recognized by the immune response. Valproate (2-n-propylpentanoic acid, VPA), a histone deacetylase inhibitor, was thought to trigger Tax expression, thereby exposing the latent HTLV-1 reservoir to immune destruction. We evaluated the impact of VPA on Tax, Gag, and HBZ expressions in cultured lymphocytes from HTLV-1 asymptomatic carriers and HAM/TSP patients. Approximately one-fifth of provirus-positive CD4(+) T cells spontaneously became Tax-positive, but this fraction rose to two-thirds of Tax-positive-infected cells when cultured with VPA. Valproate enhanced Gag-p19 release. Tax- and Gag-mRNA levels peaked spontaneously, before declining concomitantly to HBZ-mRNA increase. VPA enhanced and prolonged Tax-mRNA expression, whereas it blocked HBZ expression. Our findings suggest that, in addition to modulating Tax expression, another mechanism involving HBZ repression might determine the outcome of VPA treatment on HTLV-1-infected-cell proliferation and survival.

LBH589, a deacetylase inhibitor, induces apoptosis in adult T-cell leukemia/lymphoma cells via activation of a novel RAIDD-caspase-2 pathway

Adult T-cell leukemia/lymphoma (ATLL), an aggressive neoplasm etiologically associated with human T-lymphotropic virus type-1 (HTLV-1), is resistant to treatment. In this study, we examined the effects of a new inhibitor of deacetylase enzymes, LBH589, on ATLL cells. LBH589 effectively induced apoptosis in ATLL-related cell lines and primary ATLL cells and reduced the size of tumors inoculated in SCID mice. Analyses, including with a DNA microarray, revealed that neither death receptors nor p53 pathways contributed to the apoptosis. Instead, LBH589 activated an intrinsic pathway through the activation of caspase-2. Furthermore, small interfering RNA experiments targeting caspase-2, caspase-9, RAIDD, p53-induced protein with a death domain (PIDD) and RIPK1 (RIP) indicated that activation of RAIDD is crucial and an event initiating this pathway. In addition, LBH589 caused a marked decrease in levels of factors involved in ATLL cell proliferation and invasion such as CCR4, IL-2R and HTLV-1 HBZ-SI, a spliced form of the HTLV-1 basic zipper factor HBZ. In conclusion, we showed that LBH589 is a strong inducer of apoptosis in ATLL cells and uncovered a novel apoptotic pathway initiated by activation of RAIDD.

Highly active antiretroviral treatment against STLV-1 infection combining reverse transcriptase and HDAC inhibitors

Approximately 3% of all human T-lymphotropic virus type 1 (HTLV-1)–infected persons will develop a disabling inflammatory disease of the central nervous system known as HTLV-1–associated myelopathy/tropical spastic paraparesis, against which there is currently no efficient treatment. As correlation exists between the proviral load (PVL) and the clinical status of the carrier, it is thought that diminishing the PVL could prevent later occurrence of the disease. We have conducted a study combining valproate, an inhibitor of histone deacetylases, and azidothymidine, an inhibitor of reverse transcriptase, in a series of baboons naturally infected with simian T-lymphotropic virus type 1 (STLV-1), whose PVL was equivalent to that of HTLV-1 asymptomatic carriers. We show that the combination of drugs caused a strong decrease in the PVL and prevented the transient rise in PVL that is seen after treatment with histone deacetylases alone. We then demonstrate that the PVL decline was associated with an increase in the STLV-1–specific cytotoxic T-cell population. We conclude that combined treatment with valproate to induce viral expression and azidothymidine to prevent viral propagation is a safe and effective means to decrease PVL in vivo. Such treatments may be useful to reduce the risk of HAM/TSP in asymptomatic carriers with a high PVL.

Preliminary evidence of disease response to the pan deacetylase inhibitor panobinostat (LBH589) in refractory Hodgkin Lymphoma

There are few treatment options for patients with Hodgkin Lymphoma (HL) who relapse after conventional therapies. Panobinostat is an orally available pan deacetylase inhibitor with evidence of activity in myeloid malignancies and cutaneous T cell lymphoma. Thirteen HL patients were treated with escalating doses of this novel agent in a phase IA/II multicentre study. A computed tomography partial response was achieved in 5/13(38%), and a metabolic response by (18)F-fluoro-2-deoxy-D-glucose positron emission tomography scanning in 7/12 (58%) evaluable patients. This report describes the preliminary evidence of anti-tumour activity seen in the early phase of this study, which recently closed to accrual.

HTLV-1 and apoptosis: role in cellular transformation and recent advances in therapeutic approaches

A universal cellular defense mechanism against viral invasion is the elimination of infected cells through apoptotic cell death. To counteract host defenses many viruses have evolved complex apoptosis evasion strategies. The oncogenic human retrovirus HTLV-1 is the etiological agent of adult-T-cell leukemia/lymphoma (ATLL) and the neurodegenerative disease known as HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The poor prognosis in HTLV-1-induced ATLL is linked to the resistance of neoplastic T cells against conventional therapies and the immuno-compromised state of patients. Nevertheless, several studies have shown that the apoptotic pathway is largely intact and can be reactivated in ATLL tumor cells to induce specific killing. A better understanding of the molecular mechanisms employed by HTLV-1 to counteract cellular death pathways remains an important challenge for future therapies and the treatment of HTLV-1-associated diseases.