Apoptosis induced by the histone deacetylase inhibitor FR901228 in human T-cell leukemia virus type 1-infected T-cell lines and primary adult T-cell leukemia cells

Recent Updates on Viral Oncogenesis: Available Preventive and Therapeutic Entities

Human viral oncogenesis is a complex phenomenon and a major contributor to the global cancer burden. Several recent findings revealed cellular and molecular pathways that promote the development and initiation of malignancy when viruses cause an infection. Even, antiviral treatment has become an approach to eliminate the viral infections and prevent the activation of oncogenesis. Therefore, for a better understanding, the molecular pathogenesis of various oncogenic viruses like, hepatitis virus, human immunodeficiency viral (HIV), human papillomavirus (HPV), herpes simplex virus (HSV), and Epstein-Barr virus (EBV), could be explored, especially, to expand many potent antivirals that may escalate the apoptosis of infected malignant cells while sparing normal and healthy ones. Moreover, contemporary therapies, such as engineered antibodies antiviral agents targeting signaling pathways and cell biomarkers, could inhibit viral oncogenesis. This review elaborates the recent advancements in both natural and synthetic antivirals to control viral oncogenesis. The study also highlights the challenges and future perspectives of using antivirals in viral oncogenesis.

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

PURPOSE OF THE REVIEW

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

RECENT FINDINGS

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

Novel Treatments of Adult T Cell Leukemia Lymphoma

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

Mcl-1 inhibitors: a patent review

INTRODUCTION

The myeloid cell leukemia-1 (MCL-1) protein is one of the key anti-apoptotic members of the B-cell lymphoma-2 (BCL-2) protein family. Over-expression of MCL-1 has been closely related to tumor progression as well as to resistance, not only to traditional chemotherapies but also to targeted therapeutics including BCL-2 inhibitors such as ABT-263. Therefore, there has been extensive research and development in the last decade in both academic and industrial settings to address this unmet medical need. Areas covered: This review covers the research and patent literature of the past 10 years in the field of discovery and development of small-molecule inhibitors of the MCL-1 anti-apoptotic protein. Expert opinion: Small-molecule strategies to disrupt the protein-protein interactions between MCL-1 and its pro-apoptotic counterparts, such as BAK and BIM, have recently emerged. Several small-molecules based on different scaffolds describe promising in vitro data as MCL-1 selective inhibitors. While many lead compounds remain at the in vitro preclinical development stage, the two most recent patent applications describe promising in vivo data, and one small molecule inhibitor has recently entered into clinical development. It is such an exciting moment that the long awaited clinical studies will generate some insight into the therapeutic potential of this anti-cancer approach, and possibly facilitate the further development of other early stage inhibitors.

Treatment of adult T-cell leukemia

Adult T-cell Leukemia (ATL) is an aggressive malignant disease of CD4+ T-cells associated with human T-cell leukemia virus type I (HTLV-I). Prognosis of ATL patients is directly correlated to the subtype of ATL. Treatment of the aggressive forms (acute and lymphoma types) of ATL remains inadequate, as most ATL patients receive conventional chemotherapy without stem cell rescue. At present, LSG15 is the standard chemotherapy for the treatment of aggressive ATL, but the efficacy of LSG15 in most patients is transient. To prolong median survival time, additional therapies for maintenance of complete response (CR) are needed after achieving CR by induction chemotherapy. Improved outcome after allogeneic stem cell transplantation (allo-SCT), despite a high incidence of graft-versus-host disease, has been reported. Thus, allogeneic bone marrow transplantation and allogeneic peripheral blood SCT may have great potential for eradication of HTLV-1 and cure of ATL. Recently, reduced-intensity conditioning stem cell transplantation was also reported to be effective for ATL. Although several issues, including selection criteria for patients and sources of stem cells remain to be resolved, allo-SCT may be considered as a treatment option for patients with aggressive ATL. To evaluate whether allo-SCT is more effective than the standard chemotherapy (LSG15) for aggressive ATL, an up front phase II clinical trial of JCOG-LSG is now being planned. Novel innovative targeted strategies, such as antiretroviral therapy, arsenic trioxide, nuclear factor-kappaB inhibitors, proteasome inhibitors, histone deacetylase inhibitors, several monoclonal antibodies including anti-CC chemokine receptor 4, anti-folate, purine nucleotide phosphorylase inhibitor, mTOR (mammalian target of rapamycin) inhibitor, bendamustine, small molecule Bcl-2 inhibitors and Tax-targeted immunotherapy, should be promptly studied in order to develop curative treatments for ATL in the near future.

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

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

Augmented efficacy with the combination of blockade of the Notch-1 pathway, bortezomib and romidepsin in a murine MT-1 adult T-cell leukemia model

Adult T-cell leukemia (ATL) is an aggressive malignancy caused by human T-cell lymphotropic virus-1. There is no accepted curative therapy for ATL. We have reported that certain ATL patients have increased Notch-1 signaling along with constitutive activation of the nuclear factor-κB pathway. Physical and functional interaction between these two pathways provides the rationale to combine the γ-secretase inhibitor compound E with the proteasome inhibitor bortezomib. Moreover, romidepsin, a histone deacetylase inhibitor, has demonstrated major antitumor action in leukemia/lymphoma. In this study, we investigated the therapeutic efficacy of the single agents and the combination of these agents in a murine model of human ATL, the MT-1 model. Single and double agents inhibited tumor growth as monitored by tumor size (P<0.05), and prolonged survival of leukemia-bearing mice (P<0.05) compared with the control group. The combination of three agents significantly enhanced the antitumor efficacy as assessed by tumor size, tumor markers in the serum (human soluble interleukin-2 receptor-α and β2-microglobulin) and survival of the MT-1 tumor-bearing mice, compared with all other treatment groups (P<0.05). Improved therapeutic efficacy obtained by combining compound E, bortezomib and romidepsin supports a clinical trial of this combination in the treatment of ATL.

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

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

Cotranscriptional Chromatin Remodeling by Small RNA Species: An HTLV-1 Perspective

Cell type specificity of human T cell leukemia virus 1 has been proposed as a possible reason for differential viral outcome in primary target cells versus secondary. Through chromatin remodeling, the HTLV-1 transactivator protein Tax interacts with cellular factors at the chromosomally integrated viral promoter to activate downstream genes and control viral transcription. RNA interference is the host innate defense mechanism mediated by short RNA species (siRNA or miRNA) that regulate gene expression. There exists a close collaborative functioning of cellular transcription factors with miRNA in order to regulate the expression of a number of eukaryotic genes including those involved in suppression of cell growth, induction of apoptosis, as well as repressing viral replication and propagation. In addition, it has been suggested that retroviral latency is influenced by chromatin alterations brought about by miRNA. Since Tax requires the assembly of transcriptional cofactors to carry out viral gene expression, there might be a close association between miRNA influencing chromatin alterations and Tax-mediated LTR activation. Herein we explore the possible interplay between HTLV-1 infection and miRNA pathways resulting in chromatin reorganization as one of the mechanisms determining HTLV-1 cell specificity and viral fate in different cell types.

Efficacy of novel histone deacetylase inhibitor, AR42, in a mouse model of, human T-lymphotropic virus type 1 adult T cell lymphoma

Human T-lymphotropic virus type 1 (HTLV-1) causes a variety of forms of adult T-cell leukemia/lymphoma (ATL), a refractory CD4+/CD25+ T-cell malignancy. Novel approaches to treat ATL patients are required due to the resistance of ATL to conventional chemotherapies. Histone deacetylase inhibitors (HDACi), which induce histone hyperacetylation leading to chromatin remodeling and reactivation of transcriptionally repressed genes have shown efficacy against a variety of cancers. Herein, we tested if valproic acid and the novel orally bioavailable HDACi, AR-42 reduced the proliferation of ATL cell lines by promoting apoptosis and histone hyperacetylation. Both compounds were cytotoxic and elicited a dose dependent increase in cytochrome C and cleaved Poly (ADP-ribose) polymerase (PARP) indicating the induction of cell death by apoptosis and promoted acetylation of histone H3 in both MT-2 and C8166 cell lines. We then evaluated the effects of AR-42, for survival in an ATL NOD/SCID mouse model. A dietary formulation of AR-42 prolonged survival of ATL engrafted mice compared to controls. Our data provide new directions for the treatment of ATL and support the further development of AR-42 against HTLV-1-associated lymphoid malignancies.

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

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

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

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

New targets of therapy in T-cell lymphomas

T-cell lymphomas (TCL) are characterized by poor response to chemotherapy and generally poor outcome. While molecular profiling has identified distinct biological subsets and therapeutic targets in B-cell lymphomas, the molecular characterization of TCL has been slower. Surface markers expressed on malignant T-cells, such as CD2, CD3, CD4, CD25, and CD52 were the first TCL-specific therapeutic targets to be discovered. However, the presence of these receptors on normal T-cells means that monoclonal antibody (mAb)- or immunotoxin (IT)-based therapy in TCL inevitably results in variable degrees of immunosuppression. Thus, although some mAbs/IT have significant activity in selected subsets of TCL, more specific agents that target signaling pathways preferentially activated in malignant T-cells are needed. One such novel class of agents is represented by the histone deacetylase (HDAC) inhibitors. These molecules selectively induce apoptosis in a variety of transformed cells, including malignant T-cells, both in vitro and in vivo. Several HDAC inhibitors have been studied in TCL with promising results, and have recently been approved for clinical use. Immunomodulatory drugs, such as interferons and Toll Receptor (TLR) agonists have significant clinical activity in TCL, and are particularly important in the treatment of primary cutaneous subtypes (CTCL). Although most classical cytotoxic drugs have limited efficacy against TCL, agents that inhibit purine and pyrimidine metabolism, known as nucleoside analogues, and novel antifolate drugs, such as pralatrexate, are highly active in TCL. With improved molecular profiling of TCL novel pharmacological agents with activity in TCL are now being discovered at an increasingly rapid pace. Clinical trials are in progress and these agents are being integrated in combination therapies for TCL, both in the relapsed/refractory setting as well as front line.

Mouse models of human T lymphotropic virus type-1-associated adult T-cell leukemia/lymphoma

Human T-lymphotropic virus type-1 (HTLV-1), the first human retrovirus discovered, is the causative agent of adult T-cell leukemia/lymphoma (ATL) and a number of lymphocyte-mediated inflammatory conditions including HTLV-1-associated myelopathy/tropical spastic paraparesis. Development of animal models to study the pathogenesis of HTLV-1-associated diseases has been problematic. Mechanisms of early infection and cell-to-cell transmission can be studied in rabbits and nonhuman primates, but lesion development and reagents are limited in these species. The mouse provides a cost-effective, highly reproducible model in which to study factors related to lymphoma development and the preclinical efficacy of potential therapies against ATL. The ability to manipulate transgenic mice has provided important insight into viral genes responsible for lymphocyte transformation. Expansion of various strains of immunodeficient mice has accelerated the testing of drugs and targeted therapy against ATL. This review compares various mouse models to illustrate recent advances in the understanding of HTLV-1-associated ATL development and how improvements in these models are critical to the future development of targeted therapies against this aggressive T-cell lymphoma.

Long-term study of indolent adult T-cell leukemia-lymphoma

The long-term prognosis of indolent adult T-cell leukemia-lymphoma (ATL) is not clearly elucidated. From 1974 to 2003, newly diagnosed indolent ATL in 90 patients (65 chronic type and 25 smoldering type) was analyzed. The median survival time was 4.1 years; 12 patients remained alive for more than 10 years, 44 progressed to acute ATL, and 63 patients died. The estimated 5-, 10-, and 15-year survival rates were 47.2%, 25.4%, and 14.1%, respectively, with no plateau in the survival curve. Although most patients were treated with watchful waiting, 12 patients were treated with chemotherapy. Kaplan-Meier analyses showed that advanced performance status (PS), neutrophilia, high concentration of lactate dehydrogenase, more than 3 extranodal lesions, more than 4 total involved lesions, and receiving chemotherapy were unfavorable prognostic factors for survival. Multivariate Cox analysis showed that advanced PS was a borderline significant independent factor in poor survival (hazard ratio, 2.1, 95% confidence interval, 1.0-4.6; P = .06), but it was not a factor when analysis was limited to patients who had not received chemotherapy. The prognosis of indolent ATL in this study was poorer than expected. These findings suggest that even patients with indolent ATL should be carefully observed in clinical practice. Further studies are required to develop treatments for indolent ATL.

Susceptibility of human T-cell leukemia virus type I-infected cells to humanized anti-CD30 monoclonal antibodies in vitro and in vivo

Adult T-cell leukemia (ATL) is an aggressive malignancy of activated CD4(+) T cells associated with human T-cell leukemia virus type I (HTLV-I) infection. No conventional chemotherapy regimen has appeared successful in patients with ATL, thus establishing effective therapy is urgently required. In some cases, ATL tumor cells express CD30 on the cell surface, therefore, a therapy with mAb against CD30 would be beneficial. To investigate the effect of CD30-mediated therapy on ATL, we assessed SGN-30, a chimeric anti-CD30 mAb, and SGN-35, a monomethyl auristatin E-conjugated anti-CD30 mAb, in vitro and in vivo. Three HTLV-I-infected cell lines were co-cultured with SGN-30 or SGN-35, and the growth-inhibitory effects on the HTLV-I-infected cells were evaluated using an in vitro cell proliferation assay and cell cycle analysis. SGN-30 and SGN-35 showed growth-inhibitory activity against the HTLV-I-infected cell lines by apoptosis and/or cell growth arrest in vitro. To further investigate the effects of SGN-30 and SGN-35 on HTLV-I-infected cells in vivo, we used NOD/SCID mice subcutaneously engrafted with HTLV-I-infected cells. Both mAbs significantly inhibited the growth of HTLV-I-infected cell tumors in the NOD/SCID murine xenograft models. These data suggest that CD30-mediated therapy with SGN-30 or SGN-35 would be useful for patients with ATL.

Reduced levels of reactive oxygen species correlate with inhibition of apoptosis, rise in thioredoxin expression and increased bovine leukemia virus proviral loads

Background

Bovine Leukemia virus (BLV) is a deltaretrovirus that induces lymphoproliferation and leukemia in ruminants. In ex vivo cultures of B lymphocytes isolated from BLV-infected sheep show that spontaneous apoptosis is reduced. Here, we investigated the involvement of reactive oxygen species (ROS) in this process.

Results

We demonstrate that (i) the levels of ROS and a major product of oxidative stress (8-OHdG) are reduced, while the thioredoxin antioxidant protein is highly expressed in BLV-infected B lymphocytes, (ii) induction of ROS by valproate (VPA) is pro-apoptotic, (iii) inversely, the scavenging of ROS with N-acetylcysteine inhibits apoptosis, and finally (iv) the levels of ROS inversely correlate with the proviral loads.

Conclusion

Together, these observations underline the importance of ROS in the mechanisms of inhibition of apoptosis linked to BLV infection.

Anti-adult T-cell leukemia effects of brown algae fucoxanthin and its deacetylated product, fucoxanthinol

Adult T-cell leukemia (ATL) is a fatal malignancy of T lymphocytes caused by human T-cell leukemia virus type 1 (HTLV-1) infection and remains incurable. Carotenoids are a family of natural pigments and have several biological functions. Among carotenoids, fucoxanthin is known to have antitumorigenic activity, but the precise mechanism of action is not elucidated. We evaluated the anti-ATL effects of fucoxanthin and its metabolite, fucoxanthinol. Both carotenoids inhibited cell viability of HTLV-1-infected T-cell lines and ATL cells, and fucoxanthinol was approximately twice more potent than fucoxanthin. In contrast, other carotenoids, beta-carotene and astaxanthin, had mild inhibitory effects on HTLV-1-infected T-cell lines. Importantly, uninfected cell lines and normal peripheral blood mononuclear cells were resistant to fucoxanthin and fucoxanthinol. Both carotenoids induced cell cycle arrest during G(1) phase by reducing the expression of cyclin D1, cyclin D2, CDK4 and CDK6, and inducing the expression of GADD45alpha, and induced apoptosis by reducing the expression of Bcl-2, XIAP, cIAP2 and survivin. The induced apoptosis was associated with activation of caspase-3, -8 and -9. Fucoxanthin and fucoxanthinol also suppressed IkappaBalpha phosphorylation and JunD expression, resulting in inactivation of nuclear factor-kappaB and activator protein-1. Mice with severe combined immunodeficiency harboring tumors induced by inoculation of HTLV-1-infected T cells responded to treatment with fucoxanthinol with suppression of tumor growth, showed extensive tissue distribution of fucoxanthinol, and the presence of therapeutically effective serum concentrations of fucoxanthinol. Our preclinical data suggest that fucoxanthin and fucoxanthinol could be potentially useful therapeutic agents for patients with ATL.

Role for protein geranylgeranylation in adult T-cell leukemia cell survival

Adult T-cell leukemia (ATL) is a fatal lymphoproliferative disease that develops in human T-cell leukemia virus type I (HTLV-I)-infected individuals. Despite the accumulating knowledge of the molecular biology of HTLV-I-infected cells, effective therapeutic strategies remain to be established. Recent reports showed that the hydroxyl-3-methylglutaryl (HMG)-CoA reductase inhibitor statins have anti-proliferative and apoptotic effects on certain tumor cells through inhibition of protein prenylation. Here, we report that statins hinder the survival of ATL cells and induce apoptotic cell death. Inhibition of protein geranylgeranylation is responsible for these effects, since simultaneous treatment with isoprenoid precursors, geranylgeranyl pyrophosphate or farnesyl pyrophosphate, but not a cholesterol precursor squalene, restored the viability of ATL cells. Simvastatin inhibited geranylgeranylation of small GTPases Rab5B and Rac1 in ATL cells, and a geranylgeranyl transferase inhibitor GGTI-298 reduced ATL cell viability more efficiently than a farnesyl transferase inhibitor FTI-277. These results not only unveil an important role for protein geranylgeranylation in ATL cell survival, but also implicate therapeutic potentials of statins in the treatment of ATL.

Anti-adult T-cell leukemia effects of a novel synthetic retinoid, Am80 (Tamibarotene)

Clinical trials for treatment of adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type I (HTLV-I) using all-trans-retinoic acid (ATRA) have shown satisfactory therapeutic responses, although efficacies were limited. Recently, many synthetic retinoids have been developed and among them, a novel synthetic retinoid, Am80 (Tamibarotene) is an RARalpha- and RARbeta-specific retinoid expected to overcome ATRA resistance. The present study examined the inhibitory effects of Am80 on HTLV-I-infected T-cell lines and ATL cells. Am80 had negligible growth inhibition of peripheral blood mononuclear cells but marked growth inhibition of both HTLV-I-infected T-cell lines and ATL cells. Am80 arrested cells in the G1 phase of the cell cycle and induced apoptosis in HTLV-I-infected T-cell lines. It inhibited also the phosphorylation of IkappaBalpha and NF-kappaB-DNA binding, in conjunction with reduction of expression of proteins involved in the G1/S cell cycle transition and apoptosis. Am80 also inhibited the expression of JunD, resulting in suppression of AP-1-DNA binding. Furthermore, severe combined immunodeficient mice with tumors induced by subcutaneous inoculation of HTLV-I-infected T cells, responded to Am80 treatment with partial regression of tumors and no side-effects. These findings demonstrate that Am80 is a potential inhibitor of NF-kappaB and AP-1, and is a potentially useful therapeutic agent against ATL.

Effective treatment of a murine model of adult T-cell leukemia using depsipeptide and its combination with unmodified daclizumab directed toward CD25

Adult T-cell leukemia (ATL) is caused by human T-cell lymphotropic virus I (HTLV-1) and is an aggressive malignancy of CD4, CD25-expressing leukemia, and lymphoma cells. There is no accepted curative therapy for ATL. Depsipeptide, a histone deacetylase inhibitor, has demonstrated major antitumor effects in leukemias and lymphomas. In this study, we investigated the therapeutic efficacy of depsipeptide alone and in combination with daclizumab (humanized anti-Tac) in a murine model of human ATL. The Met-1 ATL model was established by intraperitoneal injection of ex vivo leukemic cells into nonobese diabetic/severe combined immunodeficiency mice. Either depsipeptide, given at 0.5 mg/kg every other day for 2 weeks, or daclizumab, given at 100 microg weekly for 4 weeks, inhibited tumor growth as monitored by serum levels of soluble IL-2R-alpha (sIL-2R-alpha) and soluble beta2-microglobulin (beta2mu) (P < .001), and prolonged survival of the leukemia-bearing mice (P < .001) compared with the control group. Combination of depsipeptide with daclizumab enhanced the antitumor effect, as shown by both sIL-2R-alpha and beta2mu levels and survival of the leukemia-bearing mice, compared with those in the depsipeptide or daclizumab alone groups (P < .001). The significantly improved therapeutic efficacy by combining depsipeptide with daclizumab supports a clinical trial of this combination in the treatment of ATL.

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.

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.

Histone deacetylase inhibitors: mechanisms and clinical significance in cancer: HDAC inhibitor-induced apoptosis

Epigenic modifications, mainly DNA methylation and acetylation, are recognized as the main mechanisms contributing to the malignant phenotype. Acetylation and deacetylation are catalyzed by specific enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. While histones represent a primary target for the physiological function of HDACs, the antitumor effect of HDAC inhibitors might also be attributed to transcription-independent mechanisms by modulating the acetylation status of a series of non-histone proteins. HDAC inhibitors may act through the transcriptional reactivation of dormant tumor suppressor genes. They also modulate expression of several other genes related to cell cycle, apoptosis, and angiogenesis. Several HDAC inhibitors are currently in clinical trials both for solid and hematologic malignancies. Thus, HDAC inhibitors, in combination with DNA-demethylating agents, chemopreventive, or classical chemotherapeutic drugs, could be promising candidates for cancer therapy. Here, we review the molecular mechanisms and therapeutic potential of HDAC inhibitors for the treatment of cancer.

New insights into the pathogenesis, diagnosis and treatment of human T-cell leukemia virus type 1-induced disease

It has been over 25 years since the discovery of human T-cell leukemia virus type 1 (HTLV-1); however, the exact sequence of events that occur during primary infection, clinical latency or the development of disease remains unresolved. The advances in molecular virology and neuroimmunology have contributed significantly to our understanding of HTLV-1 pathogenesis, but also uncovered the complexity of the virus–host interaction both in the peripheral blood and the CNS. Here, we overview the general pathologic features of HTLV-1, molecular mechanisms of oncogenic transformation and characteristics of the host immune response during the associated neuroinflammatory process. We also discuss both current and new approaches in the diagnosis and therapy of HTLV-1 associated diseases – adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis. Finally, potentially important emerging areas of research that may have an impact on our understanding of the pathogenic mechanism have been briefly introduced.

Human T-cell leukemia virus type I induces adult T-cell leukemia: from clinical aspects to molecular mechanisms

BACKGROUND

Human T-cell leukemia virus type I (HTLV-I) is a causative virus of adult T-cell leukemia (ATL), HTLV-I-associated myelopathy/tropical spastic paraparesis, and HTLV-I-associated uveitis. ATL is a neoplastic disease of CD4-positive T lymphocytes that is characterized by pleomorphic tumor cells with hypersegmented nuclei, termed "flower cells." The mechanisms of leukemogenesis have not been fully clarified.

METHODS

The authors reviewed the virological, clinical, and immunological features of HTLV-I and ATL and summarized recent findings on the oncogenic mechanisms of ATL and therapeutic advances.

RESULTS

Multiple factors, such as viral genes, genetic and epigenetic alterations, and the host immune system, may be implicated in the leukemogenesis of ATL. Among them, viral genes, tax, and HBZ have been thought to play important roles. The prognosis of aggressive-type ATL remains poor, regardless of intensive chemotherapy. Effectiveness of allogeneic stem cell transplantation for ATL has been recently reported.

CONCLUSIONS

Although the precise mechanism of leukemogenesis of ATL remains unclear, recent progress provides important clues in oncogenesis by HTLV-I. Future research should focus on the composition of novel therapeutic strategies, including prevention, based on the evidence in the leukemogenic mechanisms.

Inhibition of heat shock protein-90 modulates multiple functions required for survival of human T-cell leukemia virus type I-infected T-cell lines and adult T-cell leukemia cells

The molecular chaperone Hsp90 is involved in the stabilization and conformational maturation of many signaling proteins that are deregulated in cancers. The geldanamycin derivative 17-AAG is currently tested in clinical trials and known to inhibit the function of Hsp90 and promote the proteasomal degradation of its misfolded client proteins. ATL is a fatal malignancy of T lymphocytes caused by HTLV-I infection and remains incurable. Since Hsp90 is overexpressed in HTLV-I-infected T-cell lines and primary ATL cells, we analyzed the effects of 17-AAG on cell survival, apoptosis and expression of signal transduction proteins. HTLV-I-infected T-cell lines and primary ATL cells were significantly more sensitive to 17-AAG in cell survival assays than normal PBMCs. 17-AAG induced the inhibition of cell cycle and apoptosis. These effects could be mediated by inactivation of NF-kappaB, AP-1 and PI3K/Akt pathways, as well as reduction of expression of proteins involved in the G1-S cell cycle transition and apoptosis. Proteasome inhibition interfered with 17-AAG-mediated signaling proteins depletion. Collectively, our results indicate that 17-AAG suppresses ATL cell survival through, at least in part, destabilization of several client proteins and suggest that 17-AAG is a potentially useful chemotherapeutic agent for ATL.

Histone deacetylase inhibitors increase virus gene expression but decrease CD8+ cell antiviral function in HTLV-1 infection

The dynamics of human T-lymphotropic virus type-1 (HTLV-1) provirus expression in vivo are unknown. There is much evidence to suggest that HTLV-1 gene expression is restricted: this restricted gene expression may contribute to HTLV-1 persistence by limiting the ability of the HTLV-1–specific CD8+ cell immune response to clear infected cells. In this study, we tested the hypothesis that derepression of HTLV-1 gene expression would allow an increase in CD8+ cell–mediated lysis of HTLV-1–infected cells. Using histone deacetylase enzyme inhibitors (HDIs) to hyperacetylate histones and increase HTLV-1 gene expression, we found that HDIs doubled Tax expression in naturally infected lymphocytes after overnight culture. However, the rate of CD8+ cell–mediated lysis of Tax-expressing cells ex vivo was halved. HDIs appeared to inhibit the CD8+ cell–mediated lytic process itself, indicating a role for the microtubule-associated HDAC6 enzyme. These observations indicate that HDIs may reduce the efficiency of cytotoxic T-cell (CTL) surveillance of HTLV-1 in vivo. The impact of HDIs on HTLV-1 proviral load in vivo cannot be accurately predicted because of the widespread effects of these drugs on cellular processes; we therefore recommend caution in the use of HDIs in nonmalignant cases of HTLV-1 infection.

The Histone Deacetylase Inhibitor FK228 Distinctly Sensitizes the Human Leukemia Cells to Retinoic Acid-Induced Differentiation

FK228 (depsipeptide) is a novel histone deacetylase inhibitor (HDACI) that has shown therapeutical efficacy in clinical trials for malignant lymphoma. In this article, we examined in vitro effects of FK228 on human leukemia cell lines, NB4 and HL-60. FK228 alone (0.2-1 ng/mL) inhibited leukemia cell growth in a dose-dependent manner and induced death by apoptosis. FK228 had selective differentiating effects on two cell lines when used for 6 h before induction of granulocytic differentiation by retinoic acid (RA) or in combination with RA. These effects were accompanied by a time- and dose-dependent histone H4 hyper-acetylation or histone H3 dephosphorylation and alterations in DNA binding of NF-kappaB in association with cell death and differentiation. Pifithrin-alpha (PFT), an inhibitor of p53 transcriptional activity, protected only NB4 cells with functional p53 from FK228-induced apoptosis and did not interfere with antiproliferative activity in p53-negative HL-60 cells. In NB4 cells, PFT inhibited p53 binding to the p21 (Waf1/Cip1) promotor and induced DNA binding of NF-kappaB leading to enhanced cell survival. Thus, beneficial effects of FK228 on human promyelocytic leukemia may be exerted through the induction of differentiation or apoptosis via histone modification and selective involvement of transcription factors, such as NF-kappaB and p53.

HBZ, a new important player in the mystery of adult T-cell leukemia

Adult T-cell leukemia (ATL) was first described in 1977. A link between ATL and human T-cell leukemia virus type 1 (HTLV-1) was clearly established in the early 1980s. Over the years, many aspects of HTLV-1-induced cellular dysfunctions have been clarified. However, the detailed mechanism behind ATL occurrence remains unsolved. Presently, we are still unable to explain the absence of viral Tax protein (thought to play a central role in T-cell transformation) in more than 50% of ATL cells. A novel HTLV-1 HBZ protein, encoded on the negative strand, was characterized by our group and is currently the subject of intensive research efforts to determine its function in viral replication and/or pathophysiology. Recently, 4 studies reported on the existence of different HBZ isoforms and have investigated on their function in both ATL cells or animal models. One report suggests that the HBZ gene might have a bimodal function (at the mRNA and protein levels), which could represent an uncharacterized strategy to regulate viral replication and proliferation of infected T cells.

NIK-333 inhibits growth of human T-cell leukemia virus type I-infected T-cell lines and adult T-cell leukemia cells in association with blockade of nuclear factor-kappaB signal pathway

Adult T-cell leukemia (ATL) is caused by human T-cell leukemia virus type I (HTLV-I) and remains incurable. NIK-333, a novel synthetic retinoid, prevents the recurrence of human hepatoma after surgical resection of primary tumors. We explored the effects of NIK-333 on HTLV-I-infected T-cell lines and ATL cells. NIK-333 inhibited cell proliferation, induced G1 arrest, and resulted in massive apoptosis in all tested HTLV-I-infected T-cell lines and ATL cells, whereas little effect was observed on normal peripheral blood mononuclear cells. NIK-333 treatment decreases the levels of cyclin D1, cyclin D2, cIAP2, and XIAP proteins. Further analysis showed that NIK-333 inactivated nuclear factor-kappaB in HTLV-I-infected T-cell lines. In animal studies, treatment with NIK-333 (100 mg/kg given orally every other day) produced partial inhibition of growth of tumors of a HTLV-I-infected T-cell line transplanted s.c. in severe combined immunodeficient mice. Our results indicate that NIK-333 is a potentially useful therapeutic agent for patients with ATL.

In vitro and in vivo antitumor activity of the NF-κB inhibitor DHMEQ in the human T-cell leukemia virus type I-infected cell line, HUT-102

Adult T-cell leukemia (ATL) is an aggressive neoplasm caused by human T-cell leukemia virus type I (HTLV-I). The NF-kappaB pathway is activated in ATL cells and in virus-infected cells, and plays a central role in oncogenesis. We examined the effect of the novel NF-kappaB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), on a well-characterized HTLV-I-infected cell line, HUT-102, in vitro and in vivo. DHMEQ inhibited translocation of NF-kappaB p65 to the nucleus and induced apoptotic cell death in vitro. In vivo, DHMEQ inhibited the growth and infiltration of HUT-102 tumor cells transplanted subcutaneously in SCID mice lacking natural killer cell activity.

Histone deacetylase inhibitors reduce VEGF production and induce growth suppression and apoptosis in human mantle cell lymphoma

OBJECTIVES

Mantle cell lymphoma (MCL) is an incurable disease with an aggressive course and novel treatment strategies are urgently needed. The purpose of this study was to evaluate the effects of histone deacetylase (HDAC) inhibitors, a new group of antiproliferative agents, on human MCL cells.

METHODS

Three MCL cell lines (JeKo-1, Hbl-2 and Granta-519) were exposed to different concentrations of the HDAC inhibitors sodium butyrate (NaB) and suberoylanilide hydroxamic acid (SAHA) for 8-72 h. Their effects on cell viability, apoptosis induction and cell cycle proliferation were studied. Moreover, the influence of SAHA on the expression of cyclin D1, the cell cycle regulators p21 and p27 and the production of vascular endothelial growth factor (VEGF) were analyzed.

RESULTS

The HDAC inhibitors induced accumulation of acetylated histones in MCL cells. MTT assays and Annexin-V staining showed that they potently inhibited viability in a dose-dependent manner and induced apoptosis in all cell lines tested. Cell cycle analysis indicated that their exposure to SAHA or NaB decreased the proportion of cells in S phase and increased the proportion of cells in the G0/G1 and/or G2/M phases. Incubation with the two HDAC inhibitors resulted in downregulation of cyclin D1. SAHA lead to an upregulation of p21 in all cell lines and an upregulation of p27 in JeKo-1 and Granta-519 cells, while expression of p27 in Hbl-2 was not altered. In addition, SAHA inhibited the production of the angiogenic cytokine VEGF. Treatment with NaB increased the expression of p21 in JeKo-1 and Hbl-2 cells, while in Granta 519 cells no effect was noted. The expression of p27 remained constant in all three cell lines after exposure to NaB.

CONCLUSION

Based on these findings, we provide evidence that HDAC inhibitors have antiproliferative effects in MCL and may represent a promising therapeutic approach.

Natural history of adult T-cell leukemia/lymphoma and approaches to therapy

After cell-to-cell transmission, HTLV-I increases its viral genome by de novo infection and proliferation of infected cells. Proliferation of infected cells is clonal and persistent in vivo. During the carrier state, infected cells are selected in vivo by the host's immune system, the genetic and epigenetic environment of proviral integration sites, and other factors. In leukemic cells, tax gene expression is frequently impaired by genetic and epigenetic mechanisms. Such loss of Tax expression enables ATL cells to escape the host immune system. On the other hand, ATL cells acquire the ability to proliferate without Tax by intracellular genetic and epigenetic changes. Despite advances in support and the development of novel treatment agents, the prognosis for ATLL remains poor. A number of therapies, however, do appear to improve prognosis compared to CHOP (VEPA). These include interferon-alpha plus zidovudine (probably after 1-2 cycles of CHOP), intensive chemotherapy as in LSG-15 with G-CSF support and Allo-SCT (which includes the potential for cure). Emerging novel approaches include HDAC inhibitors, monoclonal antibodies, and proteasome inhibitors. Comparison between different therapeutic approaches is complicated by the range of natural history of ATLL, different recruitments of naïve-to-therapy, refractory or relapsed patients, and variations in the reporting of outcome that frequently excludes difficult-to-evaluate patients. Moreover, results from relatively small proof-of-principle studies have not been extended with randomized, controlled trials. As a result, currently, there is no clear evidence to support the value of any particular treatment approach over others. To avoid further unnecessary patient suffering and to identify optimal therapy as rapidly as possible, large randomized, controlled trials encompassing multicenter, international collaborations will be necessary.

Transcriptional and post-transcriptional gene regulation of HTLV-1

Adult T-cell leukemia (ATL) is an aggressive hematologic malignancy caused by human T-cell leukemia virus type I (HTLV-1). Tax, encoded by the HTLV-1 pX region, has been recognized by its pleiotropic actions to play a critical role in leukemogenesis. Three highly conserved 21-bp repeat elements located within the long terminal repeat, commonly referred to as Tax-responsive element 1 (TRE-1), are critical to Tax-mediated viral transcriptional activation through complex interaction with cyclic AMP-responsive element binding protein (CREB), CBP/p300 and PCAF. Tax has also been shown to activate transcription from a number of critical cellular genes through the NF-kappaB and serum-responsive factor pathways. Tax transactivation has been attributed to the protein's interaction with transcription factors, chromatin remodeling complexes, cell cycle and repair genes. In this review, we will discuss some of the latest findings on this fascinating viral activator and highlight its regulation of cellular factors including CREB, p300/CBP and their effect on RNA polymerase II and chromatin remodeling, as well as its role in cytoplasmic and nuclear function. We will highlight the possible contribution of each factor, discuss Tax's critical peptide domains and highlight its post-transcriptional modifications. It is quite obvious that, collectively, Tax's effects on a wide variety of cellular targets cooperate in promoting cell proliferation and leukemogenesis. In addition, the post-transcriptional effects of Rex play an important role in virus replication. Understanding these interactions at a molecular level will facilitate the targeted development of drugs to effectively inhibit or treat ATL.

Distinct IκB kinase regulation in adult T cell leukemia and HTLV-I-transformed cells

We have recently shown constitutive IkappaB kinase (IKK) activation and aberrant p52 expression in adult T cell leukemia (ATL) cells that do not express human T cell leukemia virus type I (HTLV-I) Tax, but the mechanism of IKK activation in these cells has remained unknown. Here, we demonstrate distinct regulation of IKK activity in ATL and HTLV-I-transformed T cells in response to protein synthesis inhibition or arsenite treatment. Protein synthesis inhibition for 4 h by cycloheximide (CHX) barely affects IKK activity in Tax-positive HTLV-I-transformed cells, while it diminishes IKK activity in Tax-negative ATL cells. Treatment of ATL cells with a proteasome inhibitor MG132 prior to protein synthesis inhibition reverses the inhibitory effect of CHX, and MG132 alone greatly enhances IKK activity. In addition, treatment of HTLV-I-transformed cells with arsenite for 1 h results in down-regulation of IKK activity without affecting Tax expression, while 8 h of arsenite treatment does not impair IKK activity in ATL cells. These results indicate that a labile protein sensitive to proteasome-dependent degradation governs IKK activation in ATL cells, and suggest a molecular mechanism of IKK activation in ATL cells distinct from that in HTLV-I-transformed T cells.

Treatment of thyroid cancer with histone deacetylase inhibitors and peroxisome proliferator-activated receptor-gamma agonists

Among the most promising new antineoplastic therapies for poorly differentiated or undifferentiated thyroid cancer are the histone deacetylase inhibitors and the peroxisome proliferator-activated receptor (PPAR)-gamma agonists. These two classes of drugs have been shown to inhibit growth and induce apoptosis and redifferentiation in a variety of hematologic and solid cancer cell lines and animal models. In this article we review the molecular mechanisms, in vitro and in vivo studies, and clinical applications of the histone deacetylase inhibitors and PPAR-gamma agonists in the treatment of thyroid cancer.

Apoptosis-based therapies for hematologic malignancies

Apoptosis is an intrinsic cell death program that plays critical roles in tissue homeostasis, especially in organs where high rates of daily cell production are offset by rapid cell turnover. The hematopoietic system provides numerous examples attesting to the importance of cell death mechanisms for achieving homeostatic control. Much has been learned about the mechanisms of apoptosis of lymphoid and hematopoietic cells since the seminal observation in 1980 that glucocorticoids induce DNA fragmentation and apoptosis of thymocytes and the demonstration in 1990 that depriving colony-stimulating factors from factor-dependent hematopoietic cells causes programmed cell death. From an understanding of the core components of the apoptosis machinery at the molecular and structural levels, many potential new therapies for leukemia and lymphoma are emerging. In this review, we introduce some of the drug discovery targets thus far identified within the core apoptotic machinery and describe some of the progress to date toward translating our growing knowledge about these targets into new therapies for cancer and leukemia.

Fucoidan extracted from Cladosiphon okamuranus Tokida induces apoptosis of human T-cell leukemia virus type 1-infected T-cell lines and primary adult T-cell leukemia cells

Adult T-cell leukemia (ATL) is caused by human T-cell leukemia virus type 1 (HTLV-1) and remains incurable. The highest endemic area of HTLV-1 carriers in Japan is located in Okinawa, and novel treatments are urgently needed in this area. We extracted fucoidan, a sulfated polysaccharide, from the brown seaweed Cladosiphon okamuranus Tokida cultivated in Okinawa, Japan and examined its tumor-suppression activity against ATL. Fucoidan significantly inhibited the growth of peripheral blood mononuclear cells of ATL patients and HTLV-1-infected T-cell lines but not that of normal peripheral blood mononuclear cells. Fucoidan induced apoptosis of HTLV-1-infected T-cell lines mediated through downregulation of cellular inhibitor of apoptosis protein-2 and survivin and G1 phase accumulation through the downregulation of cyclin D2, c-myc, and hyperphosphorylated form of the retinoblastoma tumor suppressor protein. Further analysis showed that fucoidan inactivated NF-kappaB and activator protein-1 and inhibited NF-kappaB-inducible chemokine, C-C chemokine ligand 5 (regulated on activation, normal T expressed and secreted) production, and homotypic cell-cell adhesion of HTLV-1-infected T-cell lines. In vivo use of fucoidan resulted in partial inhibition of growth of tumors of an HTLV-1-infected T-cell line transplanted subcutaneously in severe combined immune deficient mice. Our results indicate that fucoidan is a potentially useful therapeutic agent for patients with ATL.