Efficacy and mechanism of action of the proteasome inhibitor PS-341 in T-cell lymphomas and HTLV-I associated adult T-cell leukemia/lymphoma

Inhibiting HTLV-1 Protease: A Viable Antiviral Target

Human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that can cause severe paralytic neurologic disease and immune disorders as well as cancer. An estimated 20 million people worldwide are infected with HTLV-1, with prevalence reaching 30% in some parts of the world. In stark contrast to HIV-1, no direct acting antivirals (DAAs) exist against HTLV-1. The aspartyl protease of HTLV-1 is a dimer similar to that of HIV-1 and processes the viral polyprotein to permit viral maturation. We report that the FDA-approved HIV-1 protease inhibitor darunavir (DRV) inhibits the enzyme with 0.8 μM potency and provides a scaffold for drug design against HTLV-1. Analogs of DRV that we designed and synthesized achieved submicromolar inhibition against HTLV-1 protease and inhibited Gag processing in viral maturation assays and in a chronically HTLV-1 infected cell line. Cocrystal structures of these inhibitors with HTLV-1 protease highlight opportunities for future inhibitor design. Our results show promise toward developing highly potent HTLV-1 protease inhibitors as therapeutic agents against HTLV-1 infections.

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.

Striving to cure adult T-cell leukaemia/lymphoma: a role for allogeneic stem cell transplant?

Adult T-cell leukaemia/lymphoma (ATL) is an aggressive HTLV-1-related malignancy, rare outside of regions where the retrovirus is endemic. Although the use of antiviral therapy has improved outcomes, particularly for indolent forms of ATL, response to combination chemotherapy is poor and outcomes for aggressive subtypes remains dismal. Consolidation with allogeneic stem cell transplant (alloSCT) has an increasing role in the management of ATL in eligible patients, offering favourable long-term remission rates. However, relatively high-transplant-related mortality and issues with donor recruitment for certain ethnicities remain problematic. In this review, we discuss the rationale for and issues surrounding alloSCT in ATL in the context of conventional and emerging therapies.

Bortezomib for the treatment of mantle cell lymphoma: an update

Bortezomib is a first in class proteasome inhibitor, initially approved by the US Food and Drug Administration for the treatment of plasma cell myeloma. Bortezomib has been approved for the treatment of relapsed and refractory mantle cell lymphoma (MCL) and, more recently, in the upfront setting as well. Treatment algorithms for MCL have rapidly evolved over the past two decades, and the optimal regimen remains to be defined. The choice of treatment regimen is based on disease risk stratification models, the expected toxicity of antineoplastic agents, the perceived patient ability to tolerate the planned treatments and the availability of novel agents. As new drugs with novel mechanisms of action and variable toxicity profiles come into use, treatment decisions for a given patient have become increasingly complex. This article provides an overview of the evolving use of bortezomib in the rapidly changing management landscape of MCL.

A phase II study of bortezomib in patients with relapsed or refractory aggressive adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATL) is a malignancy of peripheral T-lymphocytes with a poor prognosis. This multicenter, two-stage, single-arm, phase II study assessed the efficacy and safety of bortezomib in patients with relapsed/refractory ATL who received at least one regimen of chemotherapy. The primary endpoint was the best overall response rate (ORR), and secondary endpoints included safety, the best response by lesions, and progression-free survival (PFS). Fifteen patients were enrolled in the first stage of this study. One partial remission (PR) and five stable disease (SD) were observed as the best overall responses, and ORR was 6.7% (95% confidence interval (C.I.) 0.17-31.95%). Responses according to disease sites were one complete remission (CR) in peripheral blood, two PR in measurable targeted lesions, and two PR in skin lesions. Progression-free survival (PFS) was 38 (95% CI; 18-106) days. All patients developed ≥1 adverse events (AEs), and 80% of patients had ≥1 grade 3/4 AEs; however, no new safety findings were obtained. Although these results fulfilled the planned settings to proceed to the second stage, the coordinating committee decided to terminate this study because single agent activity did not appear to be very promising for this cohort of patients.

Bortezomib for the treatment of non-Hodgkin's lymphoma

INTRODUCTION

Bortezomib , the first proteasome inhibitor (PI) to be evaluated in humans, is approved in the USA and Europe for the treatment of patients with multiple myeloma, and in the USA for patients with relapsed mantle cell lymphoma (MCL).

AREAS COVERED

This review examines the role of bortezomib in the therapy of non-Hodgkin's lymphoma (NHL). Bortezomib may be particularly effective against the NF-κB-dependent activated B-cell subtype of diffuse large B-cell lymphoma. The combination of bortezomib with rituximab and dexamethasone represents a standard approach for the treatment of Waldenström's macroglobulinemia, and that with bendamustine and rituximab has demonstrated excellent efficacy in follicular lymphoma. Combinations with other novel agents, such as inhibitors of cyclin-dependent kinases or histone deacetylases, also hold substantial promise in NHL. Unmet needs in NHL, competitor compounds, chemistry, pharmacokinetics, pharmacodynamics and safety and tolerability of bortezomib are also discussed.

EXPERT OPINION

The success of bortezomib in MCL has validated the proteasome as a therapeutic target in NHL. Rational combinations, for example, with Bruton's tyrosine kinase inhibitors or BH3-mimetics, may hold the key to optimizing the therapeutic potential of PIs in NHL. Future trials are likely to involve newer agents with improved pharmacodynamic (e.g., carfilzomib, marizomib) or pharmacokinetic (e.g., ixazomib, oprozomib) properties.

Overview of proteasome inhibitor-based anti-cancer therapies: perspective on bortezomib and second generation proteasome inhibitors versus future generation inhibitors of ubiquitin-proteasome system

Over the past ten years, proteasome inhibition has emerged as an effective therapeutic strategy for treating multiple myeloma (MM) and some lymphomas. In 2003, Bortezomib (BTZ) became the first proteasome inhibitor approved by the U.S. Food and Drug Administration (FDA). BTZ-based therapies have become a staple for the treatment of MM at all stages of the disease. The survival rate of MM patients has improved significantly since clinical introduction of BTZ and other immunomodulatory drugs. However, BTZ has several limitations. Not all patients respond to BTZ based therapies and relapse occurs in many patients who initially responded. Solid tumors, in particular, are often resistant to BTZ. Furthermore, BTZ can induce dose-limiting peripheral neuropathy (PN). The second generation proteasome inhibitor Carfizomib (CFZ; U.S. FDA approved in August 2012) induces responses in a minority of MM patients relapsed from or refractory to BTZ. There is less PN compared to BTZ. Four other second-generation proteasome inhibitors (Ixazomib, Delanzomib, Oprozomib and Marizomib) with different pharmacologic properties and broader anticancer activities, have also shown some clinical activity in bortezomib-resistant cancers. While the mechanism of resistance to bortezomib in human cancers still remains to be fully understood, targeting the immunoproteasome, ubiquitin E3 ligases, the 19S proteasome and deubiquitinases in pre-clinical studies represents possible directions for future generation inhibitors of ubiquitin-proteasome system in the treatment of MM and other cancers.

p53 and Ceramide as Collaborators in the Stress Response

The sphingolipid ceramide mediates various cellular processes in response to several extracellular stimuli. Some genotoxic stresses are able to induce p53-dependent ceramide accumulation leading to cell death. However, in other cases, in the absence of the tumor suppressor protein p53, apoptosis proceeds partly due to the activity of this "tumor suppressor lipid", ceramide. In the current review, we describe ceramide and its roles in signaling pathways such as cell cycle arrest, hypoxia, hyperoxia, cell death, and cancer. In a specific manner, we are elaborating on the role of ceramide in mitochondrial apoptotic cell death signaling. Furthermore, after highlighting the role and mechanism of action of p53 in apoptosis, we review the association of ceramide and p53 with respect to apoptosis. Strikingly, the hypothesis for a direct interaction between ceramide and p53 is less favored. Recent data suggest that ceramide can act either upstream or downstream of p53 protein through posttranscriptional regulation or through many potential mediators, respectively.

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.

Animal models on HTLV-1 and related viruses: what did we learn?

Retroviruses are associated with a wide variety of diseases, including immunological, neurological disorders, and different forms of cancer. Among retroviruses, Oncovirinae regroup according to their genetic structure and sequence, several related viruses such as human T-cell lymphotropic viruses types 1 and 2 (HTLV-1 and HTLV-2), simian T cell lymphotropic viruses types 1 and 2 (STLV-1 and STLV-2), and bovine leukemia virus (BLV). As in many diseases, animal models provide a useful tool for the studies of pathogenesis, treatment, and prevention. In the current review, an overview on different animal models used in the study of these viruses will be provided. A specific attention will be given to the HTLV-1 virus which is the causative agent of adult T-cell leukemia/lymphoma (ATL) but also of a number of inflammatory diseases regrouping the HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), infective dermatitis and some lung inflammatory diseases. Among these models, rabbits, monkeys but also rats provide an excellent in vivo tool for early HTLV-1 viral infection and transmission as well as the induced host immune response against the virus. But ideally, mice remain the most efficient method of studying human afflictions. Genetically altered mice including both transgenic and knockout mice, offer important models to test the role of specific viral and host genes in the development of HTLV-1-associated leukemia. The development of different strains of immunodeficient mice strains (SCID, NOD, and NOG SCID mice) provide a useful and rapid tool of humanized and xenografted mice models, to test new drugs and targeted therapy against HTLV-1-associated leukemia, to identify leukemia stem cells candidates but also to study the innate immunity mediated by the virus. All together, these animal models have revolutionized the biology of retroviruses, their manipulation of host genes and more importantly the potential ways to either prevent their infection or to treat their associated diseases.

Localization and sub-cellular shuttling of HTLV-1 tax with the miRNA machinery

The innate ability of the human cell to silence endogenous retroviruses through RNA sequences encoding microRNAs, suggests that the cellular RNAi machinery is a major means by which the host mounts a defense response against present day retroviruses. Indeed, cellular miRNAs target and hybridize to specific sequences of both HTLV-1 and HIV-1 viral transcripts. However, much like the variety of host immune responses to retroviral infection, the virus itself contains mechanisms that assist in the evasion of viral inhibition through control of the cellular RNAi pathway. Retroviruses can hijack both the enzymatic and catalytic components of the RNAi pathway, in some cases to produce novel viral miRNAs that can either assist in active viral infection or promote a latent state. Here, we show that HTLV-1 Tax contributes to the dysregulation of the RNAi pathway by altering the expression of key components of this pathway. A survey of uninfected and HTLV-1 infected cells revealed that Drosha protein is present at lower levels in all HTLV-1 infected cell lines and in infected primary cells, while other components such as DGCR8 were not dramatically altered. We show colocalization of Tax and Drosha in the nucleus in vitro as well as coimmunoprecipitation in the presence of proteasome inhibitors, indicating that Tax interacts with Drosha and may target it to specific areas of the cell, namely, the proteasome. In the presence of Tax we observed a prevention of primary miRNA cleavage by Drosha. Finally, the changes in cellular miRNA expression in HTLV-1 infected cells can be mimicked by the add back of Drosha or the addition of antagomiRs against the cellular miRNAs which are downregulated by the virus.

Proteasome inhibition and combination therapy for non-Hodgkin's lymphoma: from bench to bedside

Although patients with B-cell non-Hodgkin's lymphoma (NHL) usually respond to initial conventional chemotherapy, they often relapse and mortality has continued to increase over the last three decades in spite of salvage therapy or high dose therapy and stem cell transplantation. Outcomes vary by subtype, but there continues to be a need for novel options that can help overcome chemotherapy resistance, offer new options as consolidation or maintenance therapy postinduction, and offer potentially less toxic combinations, especially in the elderly population. The bulk of these emerging novel agents for cancer treatment target important biological cellular processes. Bortezomib is the first in the class of proteasome inhibitors (PIs), which target the critical process of intracellular protein degradation or recycling and editing through the proteasome. Bortezomib is approved for the treatment of relapsed or refractory mantle cell lymphoma. The mechanisms of proteasome inhibition are very complex by nature (because they affect many pathways) and not fully understood. However, mechanisms of action shared by bortezomib and investigational PIs such as carfilzomib, marizomib, ONX-0912, and MLN9708 are distinct from those of other NHL treatments, making them attractive options for combination therapy. Preclinical evidence suggests that the PIs have additive and/or synergistic activity with a large number of agents both in vitro and in vivo, from cytotoxics to new biologicals, supporting a growing number of combination studies currently underway in NHL patients, as reviewed in this article. The results of these studies will help our understanding about how to best integrate proteasome inhibition in the management of NHL and continue to improve patient outcomes.

Human T-cell lymphotropic virus: a model of NF-κB-associated tumorigenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATL), whereas the highly related HTLV-2 is not associated with ATL or other cancers. In addition to ATL leukemogenesis, studies of the HTLV viruses also provide an exceptional model for understanding basic pathogenic mechanisms of virus-host interactions and human oncogenesis. Accumulating evidence suggests that the viral regulatory protein Tax and host inflammatory transcription factor NF-κB are largely responsible for the different pathogenic potentials of HTLV-1 and HTLV-2. Here, we discuss the molecular mechanisms of HTLV-1 oncogenic pathogenesis with a focus on the interplay between the Tax oncoprotein and NF-κB pro-oncogenic signaling. We also outline some of the most intriguing and outstanding questions in the fields of HTLV and NF-κB. Answers to those questions will greatly advance our understanding of ATL leukemogenesis and other NF-κB-associated tumorigenesis and will help us design personalized cancer therapies.

Controversies in targeted therapy of adult T cell leukemia/lymphoma: ON target or OFF target effects?

Adult T cell leukemia/lymphoma (ATL) represents an ideal model for targeted therapy because of intrinsic chemo-resistance of ATL cells and the presence of two well identified targets: the HTLV-I retrovirus and the viral oncoprotein Tax. The combination of zidovudine (AZT) and interferon-alpha (IFN) has a dramatic impact on survival of ATL patients. Although the mechanism of action remains unclear, arguments in favor or against a direct antiviral effect will be discussed. Yet, most patients relapse and alternative therapies are mandatory. IFN and arsenic trioxide induce Tax proteolysis, synergize to induce apoptosis in ATL cells and cure Tax-driven ATL in mice through specific targeting of leukemia initiating cell activity. These results provide a biological basis for the clinical success of arsenic/IFN/AZT therapy in ATL patients and suggest that both extinction of viral replication (AZT) and Tax degradation (arsenic/IFN) are needed to cure ATL.

The HTLV-1 Tax protein inhibits formation of stress granules by interacting with histone deacetylase 6

Human T cell leukemia virus type-1 (HTLV-1) is the causative agent of a fatal adult T-cell leukemia. Through deregulation of multiple cellular signaling pathways the viral Tax protein has a pivotal role in T-cell transformation. In response to stressful stimuli, cells mount a cellular stress response to limit the damage that environmental forces inflict on DNA or proteins. During stress response, cells postpone the translation of most cellular mRNAs, which are gathered into cytoplasmic mRNA-silencing foci called stress granules (SGs) and allocate their available resources towards the production of dedicated stress-management proteins. Here we demonstrate that Tax controls the formation of SGs and interferes with the cellular stress response pathway. In agreement with previous reports, we observed that Tax relocates from the nucleus to the cytoplasm in response to environmental stress. We found that the presence of Tax in the cytoplasm of stressed cells prevents the formation of SGs and counteracts the shutoff of specific host proteins. Unexpectedly, nuclear localization of Tax promotes spontaneous aggregation of SGs, even in the absence of stress. Mutant analysis revealed that the SG inhibitory capacity of Tax is independent of its transcriptional abilities but relies on its interaction with histone deacetylase 6, a critical component of SGs. Importantly, the stress-protective effect of Tax was also observed in the context of HTLV-1 infected cells, which were shown to be less prone to form SGs and undergo apoptosis under arsenite exposure. These observations identify Tax as the first virally encoded inhibitory component of SGs and unravel a new strategy developed by HTLV-1 to deregulate normal cell processes. We postulate that inhibition of the stress response pathway by Tax would favor cell survival under stressful conditions and may have an important role in HTLV-1-induced cellular transformation.

Guidelines for the management of mature T-cell and NK-cell neoplasms (excluding cutaneous T-cell lymphoma)

The peripheral T-cell neoplasms are a biologically and clinically heterogeneous group of rare disorders that result from clonal proliferation of mature post-thymic lymphocytes. Natural killer (NK) cell neoplasms are included in this group. The World Health Organization classification of haemopoietic malignancies has divided this group of disorders into those with predominantly leukaemic (disseminated), nodal, extra-nodal or cutaneous presentation. They usually affect adults and are more commonly reported in males than in females. The median age at diagnosis is 61 years with a range of 17-90 years. Although some subtypes may follow a relatively benign protracted course most have an aggressive clinical behaviour and poor prognosis. Excluding anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL), which has a good outcome, 5-year survival for other nodal and extranodal T-cell lymphomas is about 30%. Most patients present with unfavourable international prognostic index scores (>3) and poor performance status. The rarity of these diseases and the lack of randomized trials mean that there is no consensus about optimal therapy for T- and NK-cell neoplasms and recommendations in this guideline are therefore based on small case series, phase II trials and expert opinion.

Resveratrol protects leukemic cells against cytotoxicity induced by proteasome inhibitors via induction of FOXO1 and p27Kip1

BACKGROUND

It was reported recently that resveratrol could sensitize a number of cancer cells to the antitumoral effects of some conventional chemotherapy drugs. The current study was designed to investigate whether resveratrol could sensitize leukemic cells to proteasome inhibitors.

METHODS

Leukemic cells were treated with MG132 alone or in combination with resveratrol. Cell viability was investigated using MTT assay, and induction of apoptosis and cell cycle distribution was measured using flow cytometry. Western blot and real-time RT-PCR were used to investigate the expression of FOXO1 and p27Kip1. CHIP was performed to investigate the binding of FOXO1 to the p27 Kip1 promoter.

RESULTS

Resveratrol strongly reduced cytotoxic activities of proteasome inhibitors against leukemic cells. MG132 in combination with resveratrol caused cell cycle blockade at G1/S transition via p27Kip1 accumulation. Knockdown of p27Kip1 using siRNA dramatically attenuated the protective effects of resveratrol on cytotoxic actions of proteasome inhibitors against leukemic cells. Resveratrol induced FOXO1 expression at the transcriptional level, while MG132 increased nuclear distribution of FOXO1. MG132 in combination with resveratrol caused synergistic induction of p27Kip1 through increased recruitment of FOXO1 on the p27Kip1 promoter.

CONCLUSIONS

Resveratrol may have the potential to negate the cytotoxic effects of proteasome inhibitors via regulation of FOXO1 transcriptional activity and accumulation of p27Kip1.

Apoptosis induction through proteasome inhibitory activity of cucurbitacin D in human T-cell leukemia

BACKGROUND

Human T-cell leukemia is an aggressive malignancy of T lymphocytes. T-cell leukemia has a very poor prognosis, even with intensive chemotherapy, indicating the need for development of new drugs to treat the disease. Triterpenoid cucurbitacins have been shown to have antitumor activity, but the mechanism of this activity is not fully understood.

METHODS

The effects of cucurbitacin D on the proliferation and apoptotic induction of T-cell leukemia cells using the Cell viability assay and Annexin V staining were evaluated. To investigate the mechanisms of apoptosis, antiapoptotic protein, NF-κB, and the proteasome activity of leukemia cells treated with cucurbitacin D were evaluated by Western blotting both in vitro and in vivo.

RESULTS

In this study, cucurbitacin D was found to inhibit proliferation and to induce apoptosis of T-cell leukemia cells. Constitutively activated NF-κB was inhibited by cucurbitacin D in the nucleus, which resulted in accumulation of NF-κB in the cytoplasm, leading to down-regulation of the expression of antiapoptotic proteins Bcl-xL and Bcl-2. Furthermore, cucurbitacin D induced the accumulation of inhibitor of NF-κB (IκB)α by inhibition of proteasome activity. Low doses of cucurbitacin D synergistically potentiated the antiproliferative effects of the histone deacetylase inhibitor VPA. Finally, the proapoptotic and proteasome inhibitory activities of cucurbitacin D also were demonstrated using SCID mice in an in vivo study.

CONCLUSIONS

Cucurbitacin D induced apoptosis through suppression of proteasome activity both in vitro and in vivo, making cucurbitacin D a promising candidate for clinical applications in the treatment of T-cell leukemia.

Immunoglobulin light chains activate nuclear factor-κB in renal epithelial cells through a Src-dependent mechanism

One of the major attendant complications of multiple myeloma is renal injury, which contributes significantly to morbidity and mortality in this disease. Monoclonal immunoglobulin free light chains (FLCs) are usually directly involved, and tubulointerstitial renal injury and fibrosis are prominent histologic features observed in myeloma. The present study examined the role of monoclonal FLCs in altering the nuclear factor κ light chain enhancer of activated B cells (NF-κB) activity of renal epithelial cells. Human proximal tubule epithelial cells exposed to 3 different human monoclonal FLCs demonstrated Src kinase-dependent activation of the NF-κB pathway, which increased production of monocyte chemoattractant protein-1 (MCP-1). Tyrosine phosphorylation of inhibitor of κB kinases (IKKs) IKKα and IKKβ and a concomitant increase in inhibitor of κB (IκB) kinase activity in cell lysates were observed. Time-dependent, Src kinase-dependent increases in serine and tyrosine phosphorylation of IκBα and NF-κB activity were also demonstrated. Proteasome inhibition partially blocked FLC-induced MCP-1 production. These findings fit into a paradigm characterized by FLC-induced redox-signaling events that activated the canonical and atypical (IKK-independent) NF-κB pathways to promote a proinflammatory, profibrotic renal environment.

p53 and regulation of bioactive sphingolipids

Both the sphingolipid and p53 pathways are important regulators- and apparent collaborators-of cell-fate decisions. Whereas some investigations have suggested that ceramide and more complex sphingolipids function upstream of p53 or in a p53-independent manner, other studies propose that p53-dependent alterations in these sphingolipids can also contribute to apoptosis. Further studies focusing on sphingolipid metabolizing enzymes have revealed that they function similarly both upstream and downstream of p53 activation. However, whereas various components of the sphingolipid and p53 pathways may simultaneously function to elicit apoptosis and/or growth inhibition, SMase and SK1 may undergo explicit regulation by p53 that could contribute to ceramide-induced senescence in cells. Thus, we propose that regulation of bioactive sphingolipid signaling molecules could be of therapeutic benefit in the treatment of p53-dependent cancers.

Adult T-cell leukemia/lymphoma and HTLV-1

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) was the first oncogenic human retrovirus to be discovered, more than 25 years ago. HTLV-1 infects 15 to 20 million individuals worldwide. This oncoretrovirus can be transmitted in three ways: horizontally (sexually), vertically (mother to child), and via blood transfusion. HTLV-1 causes two major diseases: adult T-cell leukemia/lymphoma (ATLL) and tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM). ATLL can be classified into four major subtypes: a smoldering type, a chronic type, a lymphoma type, and a leukemic type. Because of intrinsic chemoresistance and severe immunosuppression, the survival rate of ATLL patients, especially those who develop the acute leukemic or lymphoma forms, is very poor, and such clonal malignant CD4 expansion remains one of the most severe lymphoproliferations. This article discusses a number of recent treatments including antiretroviral therapy, aggressive chemotherapy, and allogeneic bone-marrow transplantation, as well as new drugs.

Crystal structures of inhibitor complexes of human T-cell leukemia virus (HTLV-1) protease

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with several serious diseases, such as adult T-cell leukemia and tropical spastic paraparesis/myelopathy. For a number of years, the protease (PR) encoded by HTLV-1 has been a target for designing antiviral drugs, but that effort was hampered by limited available structural information. We report a high-resolution crystal structure of HTLV-1 PR complexed with a statine-containing inhibitor, a significant improvement over the previously available moderate-resolution structure. We also report crystal structures of the complexes of HTLV-1 PR with five different inhibitors that are more compact and more potent. A detailed study of structure-activity relationships was performed to interpret in detail the influence of the polar and hydrophobic interactions between the inhibitors and the protease.

Targeted therapy in T-cell malignancies: dysregulation of the cellular signaling pathways

T-cell malignancies, mainly known as T-cell acute lymphoblastic leukemia (T-ALL) and T-cell non-Hodgkin's lymphoma (T-NHL), are aggressive tumors. Although the clinical outcome of the patients has improved dramatically with combination chemotherapy, significant challenges remain, including understanding of the factors that contribute to the malignant behavior of these tumor cells and developing subsequently optimal targeted therapy. Aberrant cell signal transduction is generally involved in tumor progression and drug resistance. This review describes the pathogenetic role of multiple cellular signaling pathways in T-cell malignancies and the potential therapeutic strategies based on the modulation of these key signaling networks.

Different mutants of PSMB5 confer varying bortezomib resistance in T lymphoblastic lymphoma/leukemia cells derived from the Jurkat cell line

OBJECTIVE

To investigate the relationship between bortezomib resistance and mutations in the proteasome beta5 subunit (PSMB5) gene.

MATERIALS AND METHODS

Various bortezomib-resistant lymphoblastic lymphoma/leukemia lines were established by repeated cycles of bortezomib selection. Mutations were detected by sequencing the complementary DNA of the PSMB5 gene. Mutated clones were selected by limited dilution and cultured without bortezomib. Messenger RNA expression levels of PSMB5 in these mutated clones were measured by quantitative reverse transcription polymerase chain reaction. The degree of resistance was determined by cytotoxicity at various bortezomib concentrations. The chymotrypsin-like activities were assayed by measuring the release of the fluorescent 7-amido-4-methylcoumarin from the substrate N-succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin.

RESULTS

In addition to the previously reported PSMB5 G322A mutant (Ala49Thr), a C323T mutant (Ala49Val), and G322A, C326T conjoined mutant (Ala49Thr and Ala50Val) were selected and clones containing these mutations (JurkatB-G322A, JurkatB-C323T, and JurkatB-G322A/C326T) were obtained. After being cultured without bortezomib for >2 months, no significant difference in PSMB5 messenger RNA levels was detected between these JurkatB cells and parental Jurkat cells. JurkatB-G322A, JurkatB-C323T, and JurkatB-G322A/C326T clones displayed 22.0-fold, 39.4-fold, and 66.7-fold resistance, respectively, to bortezomib compared to Jurkat cells. There were no significant differences between the chymotrypsin-like activities of these mutants and Jurkat cells. The inhibitory effect of bortezomib on chymotrypsin-like activity was the weakest in JurkatB-G322A/C326T cells, and the strongest in JurkatB-G322A cells, with JurkatB-C323T cells falling in between.

CONCLUSION

Mutations of the PSMB5 gene resulting in substitutions of Ala49 and Ala50 of PSMB5 protein can confer varying bortezomib resistance.

The effects of proteasome inhibitor bortezomib on a P-gp positive leukemia cell line K562/A02

The aim of this study is to clarify the efficacy of proteasome inhibitor bortezomib to multidrug resistant (MDR) acute leukemia cells. We observed the effects of bortezomib on a P-glycoprotein (P-gp) positive leukemia line K562/A02. The results showed that bortezomib has significant effects on P-gp positive K562/A02 cells including cytotoxicity (48 h IC(50): 171.36 nM), induction of apoptosis (31.71 +/- 1.07% apoptotic cells after 24 h treatment at 100 nM), and inhibition of proteasome chymotrypsin-like activity (relative activity to untreated controls: 20.07 +/- 0.66% at 24 h with 10 nM bortezomib). These effects were lower than those observed in K562 cells (IC(50), percentage of apoptotic cells, relative chymotrypsin-like activity to untreated controls were 56.28 nM, 77.95 +/- 0.35%, 5.35 +/- 2.05% after the same treatments, respectively). No synergy between daunorubicin and bortezomib was shown in the killing of K562/A02 cells (synergistic ratios were <1). P-gp expression levels did not decrease in K562/A02 cells after bortezomib treatment. Pretreatment with bortezomib does not improve the intracellular anthracycline concentration in K562/A02 cells. Bortezomib shows a promising effect for the treatment of refractory/relapsed leukemia, but it does not improve the effect of anthracycline to MDR leukemia cells.

Bortezomib-induced apoptosis in mature T-cell lymphoma cells partially depends on upregulation of Noxa and functional repression of Mcl-1

Bortezomib, a proteasome inhibitor that was originally developed as an inhibitor of nuclear factor-κB pathways, is currently used for the treatment of multiple myeloma (MM) and mantle cell lymphoma (MCL). The mechanisms of action of this antitumor agent have been studied by several investigators. Here, we explore the underlying mechanisms of bortezomib-induced apoptosis in cutaneous T-cell lymphoma (CTCL) and adult T-cell leukemia/lymphoma (ATLL) at the level of mitochondrial membrane injury. In all cell lines including (KMS-12-PE [MM], HUT78 [CTCL], ATN1 [ATLL], and MT4 [ATLL]), antiapoptotic factors such as c-Flip and XIAP were downregulated after exposure to bortezomib, probably via inhibition of nuclear factor-κB signaling. In addition, among the members of the BH3-only family, upregulation of Noxa was consistently seen at both the transcriptional and protein levels in a p53-independent manner after exposure to bortezomib. Repression of Noxa by small interfering RNA partially rescued CTCL and ATLL cells from bortezomib-induced apoptosis. Immunoprecipitation assays indicated time-dependent binding of Noxa and Mcl-1 in all cell types, suggesting that functional repression of Mcl-1 led to the loss of mitochondrial outer membrane potential. Similar results were also obtained in primary tumor cells from patients with ATLL. Taken together, we conclude that bortezomib-induced apoptosis in ATLL and CTCL cells at least partly depends on the upregulation of Noxa and functional repression of Mcl-1, as is also the case in MM and malignant melanoma.

Definition, prognostic factors, treatment, and response criteria of adult T-cell leukemia-lymphoma: a proposal from an international consensus meeting

Adult T-cell leukemia-lymphoma (ATL) is a distinct peripheral T-lymphocytic malignancy associated with a retrovirus designated human T-cell lymphotropic virus type I (HTLV-1). The diversity in clinical features and prognosis of patients with this disease has led to its subclassification into the following four categories: acute, lymphoma, chronic, and smoldering types. The chronic and smoldering subtypes are considered indolent and are usually managed with watchful waiting until disease progression, analogous to the management of some patients with chronic lymphoid leukemia (CLL) or other indolent histology lymphomas. Patients with aggressive ATL generally have a poor prognosis because of multidrug resistance of malignant cells, a large tumor burden with multiorgan failure, hypercalcemia, and/or frequent infectious complications as a result of a profound T-cell immunodeficiency. Under the sponsorship of the 13th International Conference on Human Retrovirology: HTLV, a group of ATL researchers joined to form a consensus statement based on established data to define prognostic factors, clinical subclassifications, and treatment strategies. A set of response criteria specific for ATL reflecting a combination of those for lymphoma and CLL was proposed. Clinical subclassification is useful but is limited because of the diverse prognosis among each subtype. Molecular abnormalities within the host genome, such as tumor suppressor genes, may account for these diversities. A treatment strategy based on the clinical subclassification and prognostic factors is suggested, including watchful waiting approach, chemotherapy, antiviral therapy, allogeneic hematopoietic stem-cell transplantation (alloHSCT), and targeted therapies.

NEMO-binding domain peptide inhibits proliferation of human melanoma cells

Melanoma is the most aggressive form of skin cancer, it originates from melanocytes and its incidence has increased in the last decade. Recent advances in the understanding of the underlying biology of the progression of melanoma have identified key signalling pathways that are important in promoting melanoma tumourigenesis, thus providing dynamic targets for therapy. One such important target identified in melanoma tumour progression is the Nuclear Factor-kappaB (NF-kappaB) pathway. In vitro studies have shown that NF-kappaB binding is constitutively elevated in human melanoma cultures compared to normal melanocytes. It has been found that a short cell-permeable peptide spanning the IKK-beta NBD, named NBD peptide, disrupted the association of NEMO with IKKs in vitro and blocked TNFalpha-induced NF-kappaB activation in vivo. In the present study we investigated the effect of the NBD peptide on NF-kappaB activity and survival of A375 human melanoma cells. We found that NBD peptide is able to inhibit the proliferation of A375 cells, which present constitutively elevated NF-kappaB levels. Inhibition of cell proliferation by NBD peptide was associated with direct inhibition of constitutive NF-kappaB DNA-binding activity and induction of apoptosis by activation of caspase-3 as confirmed by the cleavage and consequently inactivation of poly (ADP ribose) polymerase (PARP-1) known as the best marker of this process.

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.

Overexpression of the PSMB5 gene contributes to bortezomib resistance in T-lymphoblastic lymphoma/leukemia cells derived from Jurkat line

OBJECTIVE

To study the mechanism of bortezomib resistance in JurkatB lines derived from T-lymphoblastic lymphoma/leukemia Jurkat line.

MATERIALS AND METHODS

Cytotoxicities of popular chemotherapeutic drugs to JurkatB cells were analyzed by trypan blue assay. Functional drug efflux in JurkatB cells was determined by flow cytometry utilizing daunorubicin and the expression of P-glycoprotein (P-gp) was detected by Western blot. mRNA expression levels of proteasome beta5 subunit (PSMB5) were measured by quantitation real-time reverse transcription polymerase chain reaction. In situ hybridization was performed to detect the amplification of PSMB5 gene. The chymotrypsin-like activities were assayed by measuring the release of the fluorescent 7-amido-4-methylcoumarin (AMC) from the substrate N-succinyl-Leu-Leu-Val-Tyr-AMC. Cytogenetic studies were performed using R-banded metaphases and fluorescence in situ hybridization (FISH) analysis. IkappaB-alpha levels were detected by Western blot.

RESULTS

No cross-resistance to daunorubicin, adriamycin, vindesine, and etoposide was found in JurkatB cells. No evidence of drug efflux was found in JurkatB cells and the expression of P-gp was negative. The PSMB5 mRNA was overexpressed in highly resistant JurkatB5 and JurkatB1 lines compared with parental Jurkat, corresponding well with the increase of chymotrypsin-like activity and a karyotype of i(14q). Amplification of PSMB5 gene was demonstrated by in situ hybridization and FISH. The decreased IkappaB-alpha level in JurkatB5 cells after bortezomib treatment indicating an upregulation of nuclear factor-kappaB (NF-kappaB) activity.

CONCLUSION

The mechanism of bortezomib resistance is different from that of multidrug resistance. Overexpression of PSMB5 is an important mechanism for bortezomib resistance in JurkatB lines. NF-kappaB may play a critical role in evading the apoptotic effects.

Emerging drugs for rarer chronic lymphoid leukemias

BACKGROUND

Rarer indolent lymphoid leukemias include well defined mature B-cell and T-cell neoplasm with widely varying natural history and specific morphological, immunophenotypic and molecular characteristics. Among these are prolymphocytic leukemia (PLL), hairy cell leukemia (HCL) and its variants, large granular lymphocyte leukemia (LGLL) and adult T-cell leukemia/lymphoma (ATLL).

OBJECTIVE

To present current therapies and emerging drugs potentially useful in the treatment of rarer chronic lymphoid leukemias.

METHODS

After searching MEDLINE, PubMed and the Current Contents database, and conference proceedings from the previous 3 years of the American Society of Hematology (ASH), the European Society of Hematology (EHA) and the American Society of Clinical Oncology (ASCO) were searched manually; articles written in English and additional relevant publications were then selected.

RESULTS/CONCLUSION

New drugs including monoclonal antibodies (mAbs), new purine analogs, small molecules targeting specific molecular targets and other agents are included. Future research should focus on the novel therapeutic strategies based on the molecular pathogenic mechanisms and the development of new targeted therapies for each distinct chronic lymphoid leukemia.

EAPB0203, a member of the imidazoquinoxaline family, inhibits growth and induces caspase-dependent apoptosis in T-cell lymphomas and HTLV-I-associated adult T-cell leukemia/lymphoma

Imiquimod is an immune response modifier currently used as a topical treatment of genital warts, basal cell carcinoma, cutaneous metastasis of malignant melanoma, and vascular tumors. We developed more efficient killers from the same family of compounds that can induce apoptosis without the prominent pro-inflammatory response associated with imiquimod. Among these new products, tk;4EAPB0203, a member of the imidazo[1,2-a]quinoxalines, exhibits an important cytotoxic activity in vitro. HTLV-I-associated adult T-cell leukemia (ATL) and HTLV-I-negative peripheral T-cell lymphomas are associated with poor prognosis. Using potentially achievable concentrations of EAPB0203, we demonstrate inhibition of cell proliferation, G2/M cell- cycle arrest, and induction of apoptosis in HTLV-I-transformed and HTLV-I-negative malignant T cells and fresh ATL cells, whereas normal resting or activated T lymphocytes were resistant. EAPB0203 treatment significantly down-regulated the antiapoptotic proteins c-IAP-1 and Bcl-XL and resulted in a significant loss of mitochondrial membrane potential, cytoplasmic release of cytochrome c, and caspase-dependent apoptosis. Moreover, in HTLV-I-transformed cells only, EAPB0203 treatment stabilized p21 and p53 proteins but had no effect on NF-kappaB activation. These results support a potential therapeutic role for EAPB0203 in ATL and HTLV-I-negative T-cell lymphomas, either as a systemic or topical therapy for skin lesions.

A novel bioluminescent mouse model and effective therapy for adult T-cell leukemia/lymphoma

Adult T-cell /lymphomaleukemia (ATLL) is caused by human T-cell lymphotropic virus type 1 (HTLV-1). Approximately 80% of ATLL patients develop humoral hypercalcemia of malignancy (HHM), a life-threatening complication leading to a poor prognosis. Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1 alpha (MIP-1 alpha) are important factors in the pathogenesis of HHM in ATLL and the expression of PTHrP can be activated by nuclear factor kappaB (NF-kappaB). NF-kappaB is constitutively activated in ATLL cells and is essential for leukemogenesis including transformation of lymphocytes infected by HTLV-1. Our goal was to evaluate the effects of NF-kappaB disruption by a proteasomal inhibitor (PS-341) and osteoclastic inhibition by zoledronic acid (Zol) on the development of ATLL and HHM using a novel bioluminescent mouse model. We found that PS-341 decreased cell viability, increased apoptosis, and down-regulated PTHrP expression in ATLL cells in vitro. To investigate the in vivo efficacy, nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice were xenografted with ATLL cells and treated with vehicle control, PS-341, Zol, or a combination of PS-341 and Zol. Bioluminescent imaging and tumor cell count showed a significant reduction in tumor burden in mice from all treatment groups. All treatments also significantly reduced the plasma calcium concentrations. Zol treatment increased trabecular bone volume and decreased osteoclast parameters. PS-341 reduced PTHrP and MIP-1 alpha expression in tumor cells in vivo. Our results indicate that both PS-341 and Zol are effective treatments for ATLL and HHM, which are refractory to conventional therapy.

Initial testing (stage 1) of the proteasome inhibitor bortezomib by the pediatric preclinical testing program

BACKGROUND

Bortezomib is a proteasome inhibitor that has been approved by FDA for the treatment of multiple myeloma and that has completed phase 1 testing in children. The purpose of the current study was to evaluate the antitumor activity of bortezomib against the in vitro and in vivo childhood cancer preclinical models of the Pediatric Preclinical Testing Program (PPTP).

PROCEDURES

Bortezomib was tested against the PPTP in vitro panel at concentrations ranging from 0.1 nM to 1.0 microM and was tested in vivo at a dose of 1 mg/kg for a planned duration of 6 weeks.

RESULTS

Bortezomib was uniformly active against the PPTP's in vitro panel, with a median IC(50) of 23 nM and with a steep dose-response curve. The four acute lymphoblastic leukemia (ALL) cell lines had significantly lower IC(50) values compared to the remaining lines of the in vitro panel. Limited in vivo activity was observed for bortezomib against the solid tumor xenografts tested, with one line meeting criteria for intermediate activity for the time to event measure and with the remaining lines showing low activity for this measure. Bortezomib demonstrated in vivo activity against the ALL panel, inducing two complete and two partial responses among seven evaluable lines.

CONCLUSIONS

Administered at its MTD in mice, bortezomib demonstrated activity against selected lines of the PPTP's ALL in vivo panel. Further studies are indicated to determine the activity of bortezomib when combined with standard agents to treat childhood ALL.

Treatment of adult T-cell leukemia/lymphoma: past, present, and future

Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell malignancy caused by human T-cell lymphotrophic virus type I. Clinical manifestations of ATLL range from smoldering to chronic, lymphoma and acute. Patients with acute and lymphoma type ATLL require therapeutic intervention. Conventional chemotherapeutic regimens used against other malignant lymphoma have been administered to ATLL patients, but the therapeutic outcomes of acute and lymphoma type ATLL remain very poor. Promising results of allogeneic stem cell transplantation (SCT) for ATLL patients have recently been reported and the treatment outcome might be improved for some ATLL patients. Besides conventional chemotherapy and SCT, interferon, zidovudine, arsenic trioxide, targeted therapy against surface molecule on ATLL cells, retinoid derivatives, and bortezomib have been administered to ATLL patients in pilot or phase I/II studies. Further studies are required to confirm the clinical benefits of these novel therapeutics. This article reviews the current status and future directions of ATLL treatment.

Induction of heme oxygenase-1 by cobalt protoporphyrin enhances the antitumour effect of bortezomib in adult T-cell leukaemia cells

Adult T-cell leukaemia (ATL) is a lethal neoplasia derived from HTLV-1-infected T lymphocytes frequently exhibiting nuclear factor-κB (NF-κB) activation. Despite the use of various treatment regimens, the prognosis of ATL is poor, and new treatment strategies are urgently needed. We therefore explored the effect and the molecular mechanism of a proteasome inhibitor, bortezomib, in ATL cells. We found bortezomib-induced cell death, and bortezomib suppressed constitutive NF-κB activation via I-κB stabilisation in three ATL cell lines (TaY, MT-2 and MT-4). An oligonucleotide DNA microarray analysis of TaY cells revealed upregulation of genes encoding heat shock proteins (HSPA1A, STIP1, HSPA1B, and HSPCA), genes related to protein folding (CDC37 and ANAPC5), Fas-associated factor 1(FAF1) and an oxidative stress-related gene, heme oxygenase-1(HMOX-1), known to be a target gene of hypoxia-inducible gene-1 alpha (HIF-1 alpha). Cobalt protoporphyrin induced HMOX-1, instead of HIF-1 alpha expression and increased bortezomib-induced apoptosis in the presence of pharmacologically effective doses of bortezomib. In contrast, zinc protoporphyrin downregulated HMOX-1 expression, thereby partially inhibiting bortezomib-induced cell death. This indicates that HMOX-1 may modulate anticancer effects of bortezomib in ATL cells, and could be a molecular target in treating ATL patients.

Phase II trial of proteasome inhibitor bortezomib in patients with relapsed or refractory cutaneous T-cell lymphoma

PURPOSE

To determine the antitumor activity of the proteasome inhibitor bortezomib in patients with cutaneous T-cell lymphoma (CTCL) or peripheral T-cell lymphoma unspecified (PTCLU) with isolated skin involvement.

PATIENTS AND METHODS

From May 2005 to June 2006 at our institute, we treated patients with previously pretreated CTCL or PTCLU using bortezomib as a single agent, at a dose of 1.3 mg/m2 intravenously on days 1, 4, 8, and 11, every 21 days for a total of six cycles.

RESULTS

Fifteen patients were registered, of whom 12 (10 CTCL, all mycosis fungoides, and two PTCLU with isolated skin involvement) were assessable. The overall response rate was 67%, with two (17%) complete remissions and six (50%) partial remissions. The remaining four patients had disease progression. Histologically, the responder patients were seven with CTCL and one with PTCLU with isolated skin involvement. All responses were durable, lasting from 7 to 14 or more months. Overall, the drug was well tolerated, with no grade 4 toxicity. The most common grade 3 toxicities were neutropenia (n = 2), thrombocytopenia (n = 2), and sensory neuropathy (n = 2).

CONCLUSION

This study suggests that bortezomib was well tolerated and has significant single-agent activity in patients with cutaneous T-cell lymphoma.

PS-341 or a combination of arsenic trioxide and interferon-α inhibit growth and induce caspase-dependent apoptosis in KSHV/HHV-8-infected primary effusion lymphoma cells

Kaposi's sarcoma (KS)-associated herpes virus (KSHV) is the causative agent of primary effusion lymphoma and of KS. Primary effusion lymphoma (PEL) is an aggressive proliferation of B cells. Conventional chemotherapy has limited benefits in PEL patients, and the prognosis is very poor. We previously reported that treatment of human T-cell leukemia virus type 1 (HTLV-1)-associated adult T-cell leukemia/lymphoma cells either with arsenic trioxide (As) combined to interferon-alpha (IFN-alpha) or with the bortezomib (PS-341) proteasome inhibitor induces cell cycle arrest and apoptosis, partly due to the reversal of the constitutive nuclear factor-kappaB (NF-kappaB) activation. PEL cells also display an activated NF-kappaB pathway that is necessary for their survival. This prompted us to investigate the effects of PS-341, or of the As/IFN-alpha combination on PEL cells. A dramatic inhibition of cell proliferation and induction of apoptosis was observed in PS-341 and in As/IFN-alpha treated cells. This was associated with the dissipation of the mitochondrial membrane potential, cytosolic release of cytochrome c, caspase activation and was reversed by the z-VAD caspase inhibitor. PS-341 and As/IFN-alpha treatment abrogated NF-kappaB translocation to the nucleus and decreased the levels of the anti-apoptotic protein Bcl-X(L). Altogether, these results provide a rational basis for a future therapeutic use of PS-341 or combined As and IFN-alpha in PEL patients.

p53 status dictates responses of B lymphomas to monotherapy with proteasome inhibitors

The proapoptotic function of p53 is thought to underlie most anticancer modalities and is also activated in response to oncogenic insults, such as overexpression of the Myc oncoprotein. Here we generated tractable B lymphomas using retroviral transduction of the MYC oncogene into hematopoietic cells with 2 knock-in alleles encoding a fusion between p53 and 4-hydroxytamoxifen (4OHT) receptor (p53ER(TAM)). In these polyclonal tumors, Myc is the only oncogenic lesion, and p53ER(TAM) status can be rapidly toggled between "off" and "on" with 4OHT, provided that the Trp53 promoter has been independently activated. Although 4OHT can trigger widespread apoptosis and overt tumor regression even in the absence of DNA-damaging agents, in tumors with high levels of Mdm2 these responses are blunted. However, cotreatment with proteasome inhibitors fully restores therapeutic effects in vivo. Similarly, human Burkitt lymphomas with wild-type p53 and overexpression of Hdm2 are highly sensitive to proteasome inhibitors, unless p53 levels are reduced using the HPV-E6 ubiquitin ligase. Therefore, proteasome inhibitors could be highly effective as a monotherapy against Myc-induced lymphomas, with no need for adjuvant chemotherapy or radiation therapy. On the other hand, their efficacy is crucially dependent on the wild-type p53 status of the tumor, placing important restrictions on patient selection.

High-dose chemotherapy and autologous stem cell transplantation for peripheral T-cell lymphoma: complete response at transplant predicts survival

Although the role of high dose chemotherapy (HDT) and autologous stem cell transplantation (ASCT) in the treatment of aggressive lymphoma has been established in several large prospective studies, its effectiveness in patients with peripheral T cell lymphoma (PTCL) has not been defined. We aimed to evaluate the efficacy of HDT and ASCT and prognostic factors for survival in patients with PTCL. We retrospectively analyzed the results of 40 PTCL patients treated with HDT and ASCT at Asan Medical Center between January 1995 and December 2005. Twenty patients had PTCL-U (peripheral T cell lymphoma, unspecified), 10 had extranodal natural killer/T cell lymphoma, 5 had anaplastic large cell lymphoma, 3 had angioimmunoblastic T cell lymphoma, 1 had hepatosplenic gammasigma T cell lymphoma, and 1 had disseminated mycosis fungoides. Disease status at transplant was complete response (CR)1 in 3 patients, CR2 or greater in 8, partial remission in 25, and refractory in 4. At a median follow-up of 16 months (range, 5 to 135 months) for surviving patients, the median overall survival (OS) was 11.5 months and the 1-year probability of survival was 46.1%. The median event free survival (EFS) was 3.6 months (95% confidence interval, 2.5 to 4.8 months). Ten patients (25%) remain alive without evidence of disease. The median OS of 11 patients with CR at ASCT was not reached; of these, 7 patients (63.6%) were alive with CR. In multivariate analysis, CR at ASCT was a prognostic factor for EFS (P = 0.025) and OS (P = 0.027) and normal lactate dehydrogenase (LDH) at ASCT was a prognostic factor for improved OS (P = 0.025). Chemosensitive patients with PTCL who achieved CR before ASCT seem to benefit from HDT and ASCT. Pretransplant values of LDH had potential to predict the survival.

NF-κB–independent down-regulation of XIAP by bortezomib sensitizes HL B cells against cytotoxic drugs

The proteasome inhibitor bortezomib has been shown to possess promising antitumor activity and significant efficacy against a variety of malignancies. Different studies demonstrated that bortezomib breaks the chemoresistance in different tumor cells basically by altering nuclear factor–κB (NF-κB) activity. NF-κB has been shown to be constitutively active in most primary Hodgkin-Reed-Sternberg (H-RS) cells in lymph node sections and in Hodgkin lymphoma (HL) cell lines and was suggested to be a central molecular switch in apoptosis resistance in HL. Here we report a bimodal effect of bortezomib in HL cells. Whereas high-dose bortezomib induced direct cytotoxicity that correlated with decreased NF-κB activity, low-dose bortezomib sensitized HL cells against a variety of cytotoxic drugs without altering NF-κB action. Strikingly, bortezomib induced marked XIAP down-regulation at the posttranslational level that was independent of the NF-κB status. Similarly, RNA interference (RNAi)–mediated XIAP down-regulation generated susceptibility to cytostatic agents. The results identify XIAP as an NF-κB–independent target of bortezomib action that controls the chemoresistant phenotype of HL cells.

EGF receptor activity modulates apoptosis induced by inhibition of the proteasome of vascular smooth muscle cells

The observation that intracellular protein turnover rates participate directly in cell viability led to the development and clinical use of potent proteasome inhibitors. This study determined that the mechanism of apoptosis that is induced by inhibition of the proteasome of vascular smooth muscle cells (VSMC) was related to the intracellular accumulation of Bad, a BH3-only member of the Bcl-2 family of apoptosis regulators. Experiments confirmed that the apoptotic process was mitochondria- and caspase-dependent. Ubiquitination and accumulation of Bad in VSMC followed inhibition of the proteasome, and depletion of Bad using RNA interference prevented apoptosis that was induced by proteasome inhibition with PS-341. EGF receptor (EGFR) activation produced posttranslational modifications of Bad, providing the pro-survival signals that prevented apoptosis of smooth muscle cells during proteasome inhibition. Antagonists of the EGFR potentiated the apoptotic rate. In summary, the activities of the EGFR and the proteasome focused on Bad and the intrinsic apoptotic pathway and were involved integrally in determining viability of VSMC. These findings might prove useful in the management of diseases in which proliferation of vascular smooth muscle cells plays a central role.

Nuclear factor-κB and inhibitor of κB kinase pathways in oncogenic initiation and progression

Abundant data support a key role for the transcription factor nuclear factor-kappaB (NF-kappaB) signaling pathway in controlling the initiation and progression of human cancer. NF-kappaB and associated regulatory proteins such as IkappaB kinase (IKK) are activated downstream of many oncoproteins and there is much evidence for the activation of NF-kappaB-dependent target genes in a variety of solid tumors and hematologic malignancies. This review focuses on the mechanisms by which the NF-kappaB pathway is activated in cancer and on the oncogenic functions controlled by activated NF-kappaB. Additionally, the effects of NF-kappaB activation in tumors relative to cancer therapy are also discussed.

NF-κB in solid tumors

Cancer is a multistep process during which cells acquire genetic alterations that drive the progressive transformation of normal cells into highly malignant cells. Self-sufficiency in growth, insensitivity to anti-growth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, tissue invasion and metastasis, are signatures of transformed cells. NF-kappaB is a key actor in tumorigenesis given its ability to control the expression and the function of a number of genes involved in these processes. Indeed, constitutive activation of NF-kappaB is a common feature of many human tumors, while its sustained activation during inflammation predisposes normal cells to neoplastic transformation. Since suppression of NF-kappaB has been shown to inhibit oncogenic potential of transformed cells, targeting it should be effective in the prevention and treatment of cancer.