In vitro effects of arsenic trioxide, interferon α and zidovudine in adult T cell leukemia/lymphoma cells.

Despite the efficacy of combination chemotherapy with arsenic trioxide (ATO), interferon α (IFN) and zidovudine (AZT) for adult T cell leukemia/lymphoma (ATL), the precise mechanism underlying this combination treatment effect is unknown. In the present study, ATO/IFN/AZT was examined in an ATL leukemic cell line (S1T, non-Tax expressing), a human T-lymphotropic virus 1 (HTLV-1)-infected cell line (MT2, Tax-expressing) and primary ATL cells from patients with acute and chronic ATL. IFN/AZT marginally inhibited MT2 cell proliferation, but substantially inhibited S1T cell proliferation. IFN/AZT increased the cleavage of numerous caspases and PARP in S1T cells, and regulated the signal transducer and activator of transcription 1 and nuclear factor-κB signaling pathway. These effects represent the potential anti-ATL mechanisms of INF/AZT in vitro. In addition, the combination of ATO and IFN/AZT demonstrated synergistic effects on S1T cells. Therefore, the Tax-independent mechanism underlying the anti-ATL effect of ATO must be further elucidated.

Angiotensin II type 1 receptor blocker telmisartan induces apoptosis and autophagy in adult T-cell leukemia cells.

Adult T-cell leukemia/lymphoma (ATL), an aggressive T-cell malignancy that develops after long-term infection with human T-cell leukemia virus (HTLV-1), requires new treatments. Drug repositioning, reuse of a drug previously approved for the treatment of another condition to treat ATL, offers the possibility of reduced time and risk. Among clinically available angiotensin II receptor blockers, telmisartan is well known for its unique ability to activate peroxisome proliferator-activated receptor-γ, which plays various roles in lipid metabolism, cellular differentiation, and apoptosis. Here, telmisartan reduced cell viability and enhanced apoptotic cells via caspase activation in ex vivo peripheral blood monocytes from asymptomatic HTLV-1 carriers (ACs) or via caspase-independent cell death in acute-type ATL, which has a poor prognosis. Telmisartan also induced significant growth inhibition and apoptosis in leukemia cell lines via caspase activation, whereas other angiotensin II receptor blockers did not induce cell death. Interestingly, telmisartan increased the LC3-II-enriched protein fraction, indicating autophagosome accumulation and autophagy. Thus, telmisartan simultaneously caused caspase activation and autophagy. A hypertension medication with antiproliferation effects on primary and leukemia cells is intriguing. Patients with an early diagnosis of ATL are generally monitored until the disease progresses; thus, suppression of progression from AC and indolent ATL to acute ATL is important. Our results suggest that telmisartan is highly effective against primary cells and leukemia cell lines in caspase-dependent and -independent manners, and its clinical use may suppress acute transformation and improve prognosis of patients with this mortal disease. This is the first report demonstrating a cell growth-inhibitory effect of telmisartan in fresh peripheral blood mononuclear cells from leukemia patients.

Clinical significance of CD70 expression on T cells in human T-lymphotropic virus type-1 carriers and adult T cell leukemia/ lymphoma patients.

Human T-lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATL). Miscellaneous host immune surveillance systems control T-cell growth/leukemogenesis during HTLV-1 infection. We characterized CD70 and CD27 expression on lymphocytes of HTLV-1 carriers and patients with ATL (study approved by the local Medical Ethical Committee). High CD70 expression was observed on CD4 + CD25+ T cells from patients with acute-type ATL, while patients with smoldering- or chronic-type ATL and HTLV-1 carriers exhibited lower expression. Furthermore, significantly higher CD27 expression was observed on HTLV-1-specific CTLs. We found an association between CD70 expression on CD4 + T cells and HTLV-1 infection; increased CD70 expression was observed after exposure to Tax. Moreover, addition of anti-CD70 antibodies enhanced the CD107a surface mobilization of HTLV-1 Tax-specific CTLs following Tax-peptide stimulation in the PBMCs of carriers. These data demonstrate the important role of the CD70/CD27 axis in immune responses in HTLV-1 carriers and ATL patients.

Novel small-molecule SIRT1 inhibitors induce cell death in adult T-cell leukaemia cells.

Adult T-cell leukaemia/lymphoma (ATL) is an aggressive T-cell malignancy that develops after long-term infection with human T-cell leukaemia virus (HTLV)-1. The identification of new molecular targets for ATL prevention and treatment is desired. SIRT1, a nicotinamide adenine dinucleotide(+) -dependent histone/protein deacetylase, plays crucial roles in various physiological processes, including aging and apoptosis. We previously reported that ATL patients had significantly higher SIRT1 protein levels than healthy controls. Here, we demonstrate that two novel small-molecule SIRT1 inhibitors, NCO-01/04, reduced cell viability and enhanced apoptotic cells in peripheral blood monocyte cells of patients with acute ATL, which has a poor prognosis. NCO-01/04 also reduced the cell viability with DNA fragmentation, Annexin V-positive cells, and caspase activation. However, a caspase inhibitor did not inhibit this caspase-dependent cell death. NCO-01/04 enhanced the endonuclease G level in the nucleus with loss of the mitochondrial transmembrane potential, which can promote caspase-independent death. Interestingly, NCO-01/04 increased the LC3-II-enriched protein fraction, indicating autophagosome accumulation as well as autophagy. Thus, NCO-01/04 simultaneously caused caspase activation and autophagy. These results suggest that NCO-01/04 is highly effective against ATL cells in caspase-dependent or -independent manners with autophagy, and that its clinical application might improve the prognosis of patients with this fatal disease.

A new ATL xenograft model and evaluation of pyrrolidine dithiocarbamate as a potential ATL therapeutic agent.

Adult T-cell leukemia/lymphoma (ATL) is caused by human T-lymphotrophic virus type 1 infection and is one of the most refractory malignant T-cell lymphomas. Improvement of ATL therapy options requires the establishment of appropriate ATL animal models. In this study, we successfully generated an ATL mouse model by xenotransplantation of primary peripheral blood mononuclear cells (PBMCs) isolated from ATL patients (ATL cells) into nonobese diabetic/severe combined immunodeficiency/Jak3-null mice (NOJ mice). To generate the model, the ATL S1T cell line was subcutaneously injected into mice. Primary ATL cells were then transplanted subcutaneously, intraperitoneally, or intravenously. ATL cells infiltrated multiple organs, and elevated human soluble interleukin 2 receptor (IL-2R) levels were detected in peripheral blood. Injection of one million primary ATL cells was needed for successful engraftment into host mice. Thawed cells, frozen long-term in liquid nitrogen, could also be transplanted; however, more cells were required to achieve similar results. The median mouse survival time was proportional to the number of cells injected. Successful secondary transplantation of ATL cells from one NOJ mouse into another was achieved and confirmed by T-cell receptor analysis. Finally, we examined the effects of the antioxide pyrrolidine dithiocarbamate (PDTC) as an antitumor agent in vivo. PDTC administration inhibited the increase of soluble IL-2R and improved mouse survival, suggesting that this compound has potential as an anti-ATL agent. We demonstrated that ATL cells could be stably xenotransplanted into NOJ mice using primary cells. This model will be useful in the establishment of novel therapies to treat ATL.