Selective efficacy of depsipeptide in a xenograft model of Epstein-Barr virus-positive lymphoproliferative disorder

GAP31 from an ancient medicinal plant exhibits anti-viral activity through targeting to Epstein-Barr virus nuclear antigen 1

Since it was discovered as the first human tumor virus in 1964, Epstein-Barr Virus (EBV) is now implicated in several types of malignancies. Accordingly, certain aspects of EBV pathobiology have shown promise in anti-cancer research in developing virus-targeting methods for EBV-associated cancers. The unique role of EBV nuclear antigen 1 (EBNA1) in triggering episome-dependent functions has made it as the only latent gene to be expressed in most EBV+ neoplasms. Dimeric EBNA1 binds to the replication origin (oriP) to display its biological impact on EBV-driven cell transformation and maintenance. Hence, EBNA1/oriP has been made an ideal drug target site for anti-EBV protocol development. GAP31 protein was originally isolated from the seeds of an ancient medicinal plant Gelonium multiflorum. Although GAP31 has been shown to exhibit both anti-viral and anti-tumor activity, current understanding of the mechanistic picture underlying GAP31 functioning is not clear. Herein, we identify the EBNA1 DNA-binding domain as a core for GAP31 binding by performing affinity pulldown assays. Recombinant GAP31 (rGAP31) was shown to impair EBNA1-induced dimerization; consequently, it abrogated both EBNA1/oriP-mediated binding and transcription. Importantly, the therapeutic effects of GAP31 showed its capability to abrogate EBV-driven cell transformation and proliferation, and EBV-dependent tumorigenesis in xenograft animal models. Notably, the EBNA1 binding-mutant rGAP31_R166A/R169A simply exhibits defective phenotypes in the above-mentioned studies. Our data suggest rGAP31 is a potential anti-viral drug which can be applied to the development of therapeutic strategies against EBV-related malignancies.

Romidepsin alone or in combination with anti-CD20 chimeric antigen receptor expanded natural killer cells targeting Burkitt lymphoma in vitro and in immunodeficient mice

Facilitating the development of alternative targeted therapeutic strategies is urgently required to improve outcome or circumvent chemotherapy resistance in children, adolescents, and adults with recurrent/refractory de novo mature B-cell (CD20) non-Hodgkin lymphoma, including Burkitt lymphoma (BL). Romidepsin, a histone deacetylase inhibitor (HDACi), has been used to treat cutaneous T-cell lymphoma. We have demonstrated the significant anti-tumor effect of anti-CD20 chimeric antigen receptor (CAR) modified expanded peripheral blood natural killer (exPBNK) against rituximab-sensitive and -resistant BL. This study examined the anti-tumor activity of romidepsin alone and in combination with anti-CD20 CAR exPBNKs against rituximab-sensitive and -resistant BL in vitro and in vivo. We found that romidepsin significantly inhibited both rituximab-sensitive and -resistant BL cell proliferation in vitro (P < 0.001) and induced cell death in rituximab-sensitive Raji (P < 0.001) and cell cycle arrest in rituximab-resistant Raji-2R and Raji-4RH (P < 0.001). Consistent with in vitro observations, we also found romidepsin significantly inhibited the growth of rituximab-sensitive and -resistant BL in BL xenografted NSG mice. We also demonstrated that romidpesin significantly induced the expression of Natural Killer Group 2, Member D (NKG2D) ligands MICA/B in both rituximab-sensitive and -resistant BL cells (P < 0.001) resulting in enhancement of exPBNK in vitro cytotoxicity through NKG2D. Finally, we observed the combination of romidepsin and anti-CD20 CAR exPBNK significantly induced cell death in BL cells in vitro, reduced tumor burden and enhanced survival in humanized BL xenografted NSG mice (p < 0.05). Our data suggests that romidepsin is an active HDAC inhibitor that also potentiates expanded NK and anti-CD20 CAR exPBNK activity against rituximab-sensitive and -resistant BL.

The Epstein-Barr Virus (EBV) in T Cell and NK Cell Lymphomas: Time for a Reassessment

While Epstein-Barr virus (EBV) was initially discovered and characterized as an oncogenic virus in B cell neoplasms, it also plays a complex and multifaceted role in T/NK cell lymphomas. In B cell lymphomas, EBV-encoded proteins have been shown to directly promote immortalization and proliferation through stimulation of the NF-κB pathway and increased expression of anti-apoptotic genes. In the context of mature T/NK lymphomas (MTNKL), with the possible exception on extranodal NK/T cell lymphoma (ENKTL), the virus likely plays a more diverse and nuanced role. EBV has been shown to shape the tumor microenvironment by promoting Th2-skewed T cell responses and by increasing the expression of the immune checkpoint ligand PD-L1. The type of cell infected, the amount of plasma EBV DNA, and the degree of viral lytic replication have all been proposed to have prognostic value in T/NK cell lymphomas. Latency patterns of EBV infection have been defined using EBV-infected B cell models and have not been definitively established in T/NK cell lymphomas. Identifying the expression profile of EBV lytic proteins could allow for individualized therapy with the use of antiviral medications. More work needs to be done to determine whether EBV-associated MTNKL have distinct biological and clinical features, which can be leveraged for risk stratification, disease monitoring, and therapeutic purposes.

Preclinical Pharmacokinetics Study of R- and S-Enantiomers of the Histone Deacetylase Inhibitor, AR-42 (NSC 731438), in Rodents

AR-42, a new orally bioavailable, potent, hydroxamate-tethered phenylbutyrate class I/IIB histone deacetylase inhibitor currently is under evaluation in phase 1 and 2 clinical trials and has demonstrated activity in both hematologic and solid tumor malignancies. This report focuses on the preclinical characterization of the pharmacokinetics of AR-42 in mice and rats. A high-performance liquid chromatography-tandem mass spectrometry assay has been developed and applied to the pharmacokinetic study of the more active stereoisomer, S-AR-42, when administered via intravenous and oral routes in rodents, including plasma, bone marrow, and spleen pharmacokinetics (PK) in CD2F1 mice and plasma PK in F344 rats. Oral bioavailability was estimated to be 26 and 100% in mice and rats, respectively. R-AR-42 was also evaluated intravenously in rats and was shown to display different pharmacokinetics with a much shorter terminal half-life compared to that of S-AR-42. Renal clearance was a minor elimination pathway for parental S-AR-42. Oral administration of S-AR-42 to tumor-bearing mice demonstrated high uptake and exposure of the parent drug in the lymphoid tissues, spleen, and bone marrow. This is the first report of the pharmacokinetics of this novel agent, which is now in early phase clinical trials.

The translation inhibitor silvestrol exhibits direct anti-tumor activity while preserving innate and adaptive immunity against EBV-driven lymphoproliferative disease

Treatment options for patients with Epstein-Barr Virus-driven lymphoproliferative diseases (EBV-LPD) are limited. Chemo-immunotherapeutic approaches often lead to immune suppression, risk of lethal infection and EBV reactivation, thus it is essential to identify agents that can deliver direct anti-tumor activity while preserving innate and adaptive host immune surveillance. Silvestrol possesses direct anti-tumor activity in multiple hematologic malignancies while causing minimal toxicity to normal mononuclear cells. However, the effects of silvestrol on immune function have not been described. We utilized in vitro and in vivo models of EBV-LPD to simultaneously examine the impact of silvestrol on both tumor and normal immune function. We show that silvestrol induces direct anti-tumor activity against EBV-transformed lymphoblastoid cell lines (LCL), with growth inhibition, decreased expression of the EBV oncogene latent membrane protein-1, and inhibition of the downstream AKT, STAT1 and STAT3 signaling pathways. Silvestrol promoted potent indirect anti-tumor effects by preserving expansion of innate and EBV antigen-specific adaptive immune effector subsets capable of effective clearance of LCL tumor targets in autologous co-cultures. In an animal model of spontaneous EBV-LPD, silvestrol demonstrated significant therapeutic activity dependent on the presence of CD8-positive T-cells. These findings establish a novel immune-sparing activity of silvestrol, justifying further exploration in patients with EBV-positive malignancies.

Romidepsin for the treatment of non-Hodgkin's lymphoma

INTRODUCTION

Patients with relapsed or refractory lymphoma remain a population with unmet medical needs. Histone deacetylase inhibitors (HDACIs) represent a novel class of anticancer drugs currently in development in several malignancies. Inhibition of HDACs leads to acetylation of histone and non-histone proteins, which in turn results in epigenetic modification of gene expression that leads to a plethora of effects, such as cell cycle arrest, apoptosis and inhibition of angiogenesis. Romidepsin is a novel HDACI that has demonstrated preclinical and clinical activity.

AREAS COVERED

This review discusses the different HDACs and epigenetic regulation with a particular focus on the preclinical and clinical development of romidepsin in lymphoma. The review of romidepsin includes: the mechanism of action, its synergistic interaction with novel agents, pivotal clinical trials that lead to its US FDA approval in cutaneous T-cell lymphoma and peripheral T-cell lymphoma as well as active combinations currently in clinical trials.

EXPERT OPINION

Romidepsin is a potent HDACI with clinical activity in T-cell lymphoma where novel agents and combinations are desperately needed. A deeper understanding of the molecular characteristics of this class of agents will allow the design of more potent drugs with improved toxicity profiles and future rational combinations that will expand the indication and benefit from these novel agents.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

A focus on the preclinical development and clinical status of the histone deacetylase inhibitor, romidepsin (depsipeptide, Istodax(®))

Romidepsin (Istodax(®), depsipeptide, FR901228, FK228, NSC 630176) is a cyclic peptide, broad-spectrum, potent histone deacetylase inhibitor, with activity mainly against class I histone deacetylase enzymes. In this article, we give an overview of the putative modes of action, such as effects on gene expression, cell cycle regulation, apoptosis induction, DNA repair, protein acetylation and induction of autophagy. Romidepsin has mainly been developed as a therapy for hematologic malignancies and is approved by the US FDA for the treatment of cutaneous T-cell lymphomas. This report outlines the laboratory and clinical development of the compound as a single agent that has more recently been evaluated in combination with other anticancer therapeutics, such as proteasome inhibitors.

Novel IkB kinase inhibitors for treatment of nuclear factor-kB-related diseases

INTRODUCTION

NF-kB is a key regulator of inflammation and immunity in cancer development. The IkB kinase (IKK) is a multisubunit complex containing catalytic subunits termed IKK-α, -β and -γ. It is well known that many pro-inflammatory stimuli require the IKK-β subunit for NF-kB activation.

AREAS COVERED

NF-kB affects the progression of inflammation-related diseases,such as myocardial ischemia, bronchial asthma, arthritis, cancer and other diseases. We review the characteristics and effects of these inhibitors on inflammatory and other diseases.

EXPERT OPINION

Various synthesized IKK inhibitors have been developed and they will be used clinically in the near future.

Investigational histone deacetylase inhibitors for non-Hodgkin lymphomas

IMPORTANCE OF THE FIELD

Histone deacetylase inhibitors (HDIs) have been shown effective as single agents for cutaneous T-cell lymphomas, peripheral T-cell lymphomas, and B-cell lymphomas, such as follicular lymphoma and mantle cell lymphoma. Of interest, HDIs in combination with other drugs can be a treatment for Epstein-Barr virus-associated lymphoproliferative disorders. Our data of gene expression profiles in PBMCs of responders to vorinostat was discussed.

AREAS COVERED IN THIS REVIEW

This review summarizes recent clinical trials of HDIs in non-Hodgkin lymphomas, the effects of HDIs in in vitro and mouse models, and the possibility of future combination treatments.

WHAT THE READER WILL GAIN

The HDI dosing schedule is crucial to optimize outcomes and avoid irreversible adverse effects. Responses to HDIs are slow, highlighting the need to continue treatment until the maximum response is achieved. HDIs cause hyperacetylation of histone and nonhistone proteins, resulting in various effects on neoplastic cells and immune responses in their microenvironment.

TAKE HOME MESSAGE

Even though HDIs are not potent as single agents, they are likely to provide promising therapeutic options when combined with other agents, i.e., BCL2/BCL-XL antagonists and proteasome inhibitors. Future studies should seek to identify biomarkers that predict patient responses to HDIs.

Combination bortezomib and rituximab treatment affects multiple survival and death pathways to promote apoptosis in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a distinct histologic subtype of B cell non-Hodgkins lymphoma (NHL) associated with an aggressive clinical course. Inhibition of the ubiquitin-proteasome pathway modulates survival and proliferation signals in MCL and has shown clinical benefit in this disease. This has provided rationale for exploring combination regimens with B-cell selective immunotherapies such as rituximab. In this study, we examined the effects of combined treatment with bortezomib and rituximab on patient-derived MCL cell lines (Jeko, Mino, SP53) and tumor samples from patients with MCL where we validate reversible proteasome inhibition concurrent with cell cycle arrest and additive induction of apoptosis. When MCL cells were exposed to single agent bortezomib or combination bortezomib/rituximab, caspase dependent and independent apoptosis was observed. Single agent bortezomib or rituximab treatment of Mino and Jeko cell lines and patient samples resulted in decreased levels of nuclear NFkappaB complex(es) capable of binding p65 consensus oligonucleotides, and this decrease was enhanced by the combination. Constitutive activation of the Akt pathway was also diminished with bortezomib alone or in combination with rituximab. On the basis of in vitro data demonstrating additive apoptosis and enhanced NFkappaB and phosphorylated Akt depletion in MCL with combination bortezomib plus rituximab, a phase II trial of bortezomib-rituximab in patients with relapsed/refractory MCL is underway.

Reactivation of DNA viruses in association with histone deacetylase inhibitor therapy: a case series report

Histone deacetylase inhibitors are a class of anti-neoplastic agents that induce growth arrest, differentiation, and/or apoptotic cell death of transformed cells in vitro and in vivo. A phase II study exploring the efficacy of romidepsin, an histone deacetylase inhibitor, in patients with cutaneous or peripheral T-cell lymphomas was initiated at the National Cancer Institute. To date, over 120 patients with T-cell lymphoma have been treated on a multi-institutional phase II trial of romidepsin. Reactivation of latent DNA viruses including EBV, HBV, and VZV is well described as a consequence of the immune suppression associated with systemic chemotherapy. The incidence of viral reactivation in patients treated with histone deacetylase inhibitors is not yet known. We report the observation of EBV-associated illnesses in 2 patients and the reactivation of HBV in an additional patient treated with romidepsin. These cases may represent reactivation of DNA viruses due to histone deacetylase inhibitor induced immunosuppression, or direct promotion of viral replication via histone deacetylase inhibitor induced chromatin remodeling, or, alternatively, may be related to the underlying disease process. These observations suggest that vigilance for DNA virus reactivation is needed to quantify the risk in patients treated with histone deacetylase inhibitors.

Tubacin kills Epstein-Barr virus (EBV)-Burkitt lymphoma cells by inducing reactive oxygen species and EBV lymphoblastoid cells by inducing apoptosis

Tubacin is a small molecule inhibitor of histone deacetylase 6 and blocks aggresome activity. We found that Epstein-Barr virus (EBV)-positive Burkitt lymphoma (BL) cells were generally killed by lower doses of tubacin than EBV-transformed lymphoblastoid cells (LCLs) or EBV-negative BL cells. Tubacin induced apoptosis of LCLs, which was inhibited by pretreatment with a pancaspase inhibitor but not by butylated hydroxyanisole, which inhibits reactive oxygen species. In contrast, tubacin killed EBV-positive BL cells in a caspase-3-independent pathway that involved reactive oxygen species and was blocked by butylated hydroxyanisole. Previously, we showed that bortezomib, a proteasome inhibitor, induces apoptosis of EBV LCLs and that LCLs are killed by lower doses of bortezomib than EBV-positive BL cells. Here we found that the combination of bortezomib and tubacin acted in synergy to kill EBV-positive BL cells and LCLs. Tubacin or the combination of bortezomib and tubacin did not induce EBV lytic replication. These findings suggest that the combination of a proteasome inhibitor and an HDAC6 inhibitor may represent a useful strategy for the treatment of certain EBV-associated B cell lymphomas.

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, diminishes lymphoproliferation in the Fas -deficient MRL/lpr(-/-) murine model of autoimmune lymphoproliferative syndrome (ALPS)

OBJECTIVE

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of apoptosis, often presenting in childhood. Similarly, MRL/lpr(-/-) mice homozygous for Fas mutations develop an ALPS-like disease with autoimmunity, lymphadenopathy, splenomegaly, and expansion of double-negative T cells. Currently, there are no proven therapies with adequate safety margins for sustained abolition of the lymphoproliferation associated with ALPS. We sought to test the ability of valproic acid (VPA), a histone deacetylase inhibitor, to induce apoptosis and inhibit lymphoproliferation.

MATERIALS AND METHODS

Human peripheral blood mononuclear cells from patients with ALPS and normal controls were tested in vitro to determine the efficacy of VPA at inducing cell death. VPA was used in vivo to control lymphoproliferation in MRL/lpr(-/-) mice, a model for ALPS.

RESULTS

VPA induced cell death in vitro, and was partially inhibited by the pan caspase inhibitor, Z-VAD-FMK. MRL/lpr(-/-) mice treated with VPA for 8 weeks showed significant reductions in spleen and lymph node weights and cellularity compared to controls. A concomitant decrease in double-negative T cells was observed in the spleen, lymph nodes, and peripheral blood. Serum levels of VPA peaked 1 hour after injection, and a 2.5-fold increase in histone acetylation was observed in the spleen at 4 hours after injection.

CONCLUSION

Based on our data, VPA is effective at reducing lymphoproliferation in mice, and is currently being studied in a clinical trial as a lympholytic agent in patients with ALPS.

Over-expression of BMP4 and BMP5 in a child with axial skeletal malformations and heterotopic ossification: a new syndrome

Bone morphogenetic proteins (BMPs) are a highly conserved class of signaling molecules that induce ectopic cartilage and bone formation in vivo. Dysregulated expression of bone morphogenetic protein 4 (BMP4) is found in the cells of patients who have fibrodysplasia ossificans progressiva (FOP), a genetic disorder of axial and appendicular skeletal malformation and progressive heterotopic ossification. Loss of function mutations in the bone morphogenetic protein 5 (bmp5) gene leading to under-expression of BMP5 cause the murine short ear syndrome, characterized by small malformed ears and a broad range of axial skeletal malformations. We found features reminiscent of both the short ear mouse and FOP in a child with malformed external ears, multiple malformations of the axial skeleton, and progressive heterotopic ossification in the neck and back. We examined BMP mRNA expression in transformed lymphocytes by semi-quantitative RT-PCR and protein expression by ELISA assays and immunohistochemistry. Elevated levels of BMP4 and BMP5 mRNA and protein were detected in the patient's cells while levels of BMP2 mRNA were unchanged. Our data suggest that dysregulated expression of BMP4 and BMP5 genes is associated with an array of human axial skeletal abnormalities similar to the short ear mouse and FOP.

Histone deacetylase inhibitors in cancer therapy

Histones are a family of nuclear proteins that interact with DNA, resulting in DNA being wrapped around a core of histone octamer within the nucleosome. Acetylation/deacetylation of histones is an important mechanism that regulates gene expression and chromatin remodeling. Histone deacetylase (HDAC) inhibitors are a new class of chemotherapeutic drugs that regulate gene expression by enhancing the acetylation of histones, and thus inducing chromatin relaxation and altering gene expression. HDAC inhibitors have been shown in preclinical studies to have potent anticancer activities. A range of structurally diverse HDAC inhibitors have been purified as natural products or synthetically produced. Due to the promising preclinical activity of these agents, numerous clinical trials have been initiated. In this review, the results of published data of single agent and combination trials of these drugs are reviewed, with a focus on dosing, scheduling and toxicity. Although still early in drug development, there is a picture that is starting to develop as to the common toxicities and which tumors seem to be the most susceptible to this class of drugs.

A phase 1/2 trial of arginine butyrate and ganciclovir in patients with Epstein-Barr virus-associated lymphoid malignancies

Malignancies associated with latent Epstein-Barr virus (EBV) are resistant to nucleoside-type antiviral agents because the viral enzyme target of these antiviral drugs, thymidine kinase (TK), is not expressed. Short-chain fatty acids, such as butyrate, induce EBV-TK expression in latently infected B cells. As butyrate has been shown to sensitize EBV(+) lymphoma cells in vitro to apoptosis induced by ganciclovir, arginine butyrate in combination with ganciclovir was administered in 15 patients with refractory EBV(+) lymphoid malignancies to evaluate the drug combination for toxicity, pharmacokinetics, and clinical responses. Ganciclovir was administered twice daily at standard doses, and arginine butyrate was administered by continuous infusion in an intrapatient dose escalation, from 500 mg/(kg/day) escalating to 2000 mg/(kg/day), as tolerated, for a 21-day cycle. The MTD for arginine butyrate in combination with ganciclovir was established as 1000 mg/(kg/day). Ten of 15 patients showed significant antitumor responses, with 4 CRs and 6 PRs within one treatment cycle. Complications from rapid tumor lysis occurred in 3 patients. Reversible somnolence or stupor occurred in 3 patients at arginine butyrate doses of greater than 1000 mg/(kg/day). The combination of arginine butyrate and ganciclovir was reasonably well-tolerated and appears to have significant biologic activity in vivo in EBV(+) lymphoid malignancies which are refractory to other regimens.

Epigenetic modulation of endogenous tumor suppressor expression in lung cancer xenografts suppresses tumorigenicity

Epigenetic changes involved in cancer development, unlike genetic changes, are reversible. DNA methyltransferase and histone deacetylase inhibitors show antiproliferative effects in vitro, through tumor suppressor reactivation and induction of apoptosis. Such inhibitors have shown activity in the treatment of hematologic disorders but there is little data concerning their effectiveness in treatment of solid tumors. FHIT, WWOX and other tumor suppressor genes are frequently epigenetically inactivated in lung cancers. Lung cancer cell clones carrying conditional FHIT or WWOX transgenes showed significant suppression of xenograft tumor growth after induction of expression of the FHIT or WWOX transgene, suggesting that treatments to restore endogenous Fhit and Wwox expression in lung cancers would result in decreased tumorigenicity. H1299 lung cancer cells, lacking Fhit, Wwox, p16(INK4a) and Rassf1a expression due to epigenetic modifications, were used to assess efficacy of epigenetically targeted protocols in suppressing growth of lung tumors, by injection of 5-aza-2-deoxycytidine (AZA) and trichostatin A (TSA) in nude mice with established H1299 tumors. High doses of intraperitoneal AZA/TSA suppressed growth of small tumors but did not affect large tumors (200 mm(3)); lower AZA doses, administered intraperitoneally or intratumorally, suppressed growth of small tumors without apparent toxicity. Responding tumors showed restoration of Fhit, Wwox, p16(INKa), Rassf1a expression, low mitotic activity, high apoptotic fraction and activation of caspase 3. These preclinical studies show the therapeutic potential of restoration of tumor suppressor expression through epigenetic modulation and the promise of re-expressed tumor suppressors as markers and effectors of the responses.

Liquid chromatography mass spectrometry profiling of histones

Here we describe the use of reverse-phase liquid chromatography mass spectrometry (RPLC-MS) to simultaneously characterize variants and post-translationally modified isoforms for each histone. The analysis of intact proteins significantly reduces the time of sample preparation and simplifies data interpretation. LC-MS analysis and peptide mass mapping have previously been applied to identify histone proteins and to characterize their post-translational modifications. However, these studies provided limited characterization of both linker histones and core histones. The current LC-MS analysis allows for the simultaneous observation of all histone PTMs and variants (both replacement and bulk histones) without further enrichment, which will be valuable in comparative studies. Protein identities were verified by the analysis of histone H2A species using RPLC fractionation, AU-PAGE separation and nano-LC-MS/MS.

Nuclear factor-kappaB maintains TRAIL resistance in human pancreatic cancer cells

Although it displays promising activity in other tumor models, the effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on human pancreatic cancer cells have not been comprehensively explored. We report that a majority of human pancreatic cancer cell lines (seven of nine) underwent apoptosis when they were exposed to recombinant human TRAIL in vitro. Characterization of surface TRAIL receptors by fluorescence-activated cell sorting showed that TRAIL-resistant cells (Panc-1 and HS766T) expressed lower levels of DR4 and DR5 than did TRAIL-sensitive cells. The proteasome inhibitor bortezomib (PS-341, Velcade) further increased TRAIL responsiveness in the TRAIL-sensitive cells and synergized with TRAIL to reverse resistance in Panc-1 and HS776T cells. The effects of bortezomib were mimicked by transfection with a small interfering RNA construct specific for the p65 subunit of nuclear factor-kappaB (NF-kappaB) or exposure to a selective chemical inhibitor of IKK (PS-1145). Silencing IkappaBalpha prevented TRAIL sensitization by PS-1145, confirming that IkappaBalpha mediated the effects of PS-1145. NF-kappaB inhibition resulted in down-regulation of BCL-XL and XIAP, and silencing either restored TRAIL sensitivity in TRAIL-resistant cells. Finally, therapy with TRAIL plus PS-1145 reversed TRAIL resistance in vivo to produce synergistic growth inhibition in orthotopic Panc-1 tumors. Together, our results show that NF-kappaB inhibits TRAIL-induced apoptosis in human pancreatic cancer cells and suggest that combination therapy with TRAIL and NF-kappaB inhibitors, such as bortezomib, PS-1145, or curcumin, should be considered as a possible treatment strategy in patients with pancreatic cancer.

Update on the therapy of highly aggressive non-Hodgkin’s lymphoma

This review focuses on the current understanding of the biology of highly aggressive non-Hodgkin's lymphomas, such as Burkitt's lymphoma, lymphoblastic lymphoma and adult T cell lymphoma/leukaemia. Specifically, this review will examine how our increased understanding of the pathophysiology of these diseases can be used to develop new therapies.

Histone deacetylase inhibitors induce apoptosis with minimal viral reactivation in cells infected with Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) latently infects tumor cells in patients with Kaposi's sarcoma and primary effusion lymphoma (PEL). The purpose of this study was to determine whether histone deacetylase inhibitors (HDAI) could induce apoptosis, with minimal viral replication, in cells latently infected with KSHV. Four HDAI (depsipeptide, suberoylanilide hydroxamic acid, MS-275, and trichostatin A) were studied in two PEL B cell lines (BCBL-1, BC-3). As expected, histone hyperacetylation was readily induced in all PEL cells exposed to HDAI. HDAI also triggered KSHV reactivation in a time- and dose-dependent manner. Flow cytometric and transmission electron microscopic studies, however, revealed that reactivation occurred in only a minor percentage (3-14%) of treated cells. Importantly, and in contrast to viral reactivation, HDAI induced apoptotic cell death in a dose-dependent manner in a large percentage (up to 90%) of KSHV-infected cells. In summary, all four HDAI tested induced histone hyperacetylation in all cells, KSHV reactivation in a minority of cells, and apoptotic cell death in a majority of cells latently infected with KSHV. These findings suggest that HDAI may be a therapeutic option for patients with KSHV-mediated diseases by rendering cells infected with KSHV susceptible to apoptosis.

Histone Deacetylase Inhibitors Suppress the Inducibility of Nuclear Factor-κB by Tumor Necrosis Factor-α Receptor-1 Down-regulation

Recently, the inhibition of histone deacetylase (HDAC) enzymes has attracted attention in the oncologic community as a new therapeutic opportunity for hematologic and solid tumors including non-small cell lung cancer (NSCLC). In hematologic malignancies, such as diffuse large B-cell lymphoma, the HDAC inhibitor (HDI), suberoylanilide hydroxamic acid (SAHA), has recently entered phase II and III clinical trials. To further advance our understanding of their action on tumor cells, we investigated the possible effect of HDI treatment on the functionality of the nuclear factor-kappaB (NF-kappaB) pathway in NSCLC. We found that in the NSCLC cell lines, A549 and NCI-H460, the NF-kappaB pathway was strongly inducible, for example, by stimulation with tumor necrosis factor-alpha (TNF-alpha). Incubation of several NSCLC cell lines with HDIs resulted in greatly reduced gene expression of TNF-alpha receptor-1. HDI-treated A549 and NCI-H460 cells down-regulated TNF-alpha receptor-1 mRNA and protein levels as well as surface exposure, and consequently responded to TNF-alpha treatment with reduced IKK phosphorylation and activation, delayed IkappaB-alpha phosphorylation, and attenuated NF-kappaB nuclear translocation and DNA binding. Accordingly, stimulation of NF-kappaB target gene expression by TNF-alpha was strongly decreased. In addition, we observed that SAHA displayed antitumor efficacy in vivo against A549 xenografts grown on nude mice. HDIs, therefore, might beneficially contribute to tumor treatment, possibly by reducing the responsiveness of tumor cells to the TNF-alpha-mediated activation of the NF-kappaB pathway. These findings also hint at a possible use of HDIs in inflammatory diseases, which are associated with the overproduction of TNF-alpha, such as rheumatoid arthritis or Crohn's disease.

Cancer cells become susceptible to natural killer cell killing after exposure to histone deacetylase inhibitors due to glycogen synthase kinase-3-dependent expression of MHC class I-related chain A and B

We show that histone deacetylase (HDAC) inhibitors lead to functional expression of MHC class I-related chain A and B (MICA/B) on cancer cells, making them potent targets for natural killer (NK) cell-mediated killing through a NK group 2, member D (NKG2D) restricted mechanism. Blocking either apoptosis or oxidative stress caused by HDAC inhibitor treatment did not affect MICA/B expression, suggesting involvement of a separate signal pathway not directly coupled to induction of cell death. HDAC inhibitor treatment induced glycogen synthase kinase-3 (GSK-3) activity and down-regulation of GSK-3 by small interfering RNA or by different inhibitors showed that GSK-3 activity is essential for the induced MICA/B expression. We thus present evidence that cancer cells which survive the direct induction of cell death by HDAC inhibitors become targets for NKG2D-expressing cells like NK cells, gammadelta T cells, and CD8 T cells.

Continuing challenges in childhood non-Hodgkin's lymphoma

Non-Hodgkin's lymphoma in children includes a number of different pathological subtypes and, with improved diagnostic techniques and better understanding of the natural history of each type, treatment strategies have become more tumour-specific. Original staging systems are now less useful in determining treatment stratification and there is a need for careful analysis of large cohorts of patients, treated in the same manner, to determine the clinical and biological features that, with current therapies, are of prognostic value. Novel imaging techniques, such as positron emission tomography, and molecular techniques to detect low-level marrow involvement are likely to be incorporated into new risk grouping. These will be used to determine the extent of initial disease and evaluate more accurately the speed and quality of response to chemotherapy. With high cure rates, it becomes particularly important to minimize late effects of therapy and the introduction of monoclonal antibodies in combination with chemotherapy may provide a method for improving outcome in poor risk groups and reducing sequelae by allowing reduction in chemotherapy in good risk patients.