Regulation of oxidative stress and redox systems has important roles in carcinogenesis and cancer progression, and for this reason has attracted much attention as a new area of cancer therapeutic targets. Glutathione peroxidase 4 (GPX4), an antioxidant enzyme, has biological important functions such as signaling cell death by suppressing peroxidation of membrane phospholipids. However, few studies exist on the expression and clinical relevance of GPX4 in malignant lymphomas such as diffuse large B-cell lymphoma. In this study, we assessed the expression of GPX4 immunohistochemically. GPX4 was expressed in 35.5% (33/93) cases of diffuse large B-cell lymphoma. The GPX4-positive group had poor overall survival (P = 0.0032) and progression-free survival (P = 0.0004) compared with those of the GPX4-negative group. In a combined analysis of GPX4 and 8-hydroxydeoxyguanosine (8-OHdG), an oxidative stress marker, there was a negative correlation between GPX4 and 8-hydroxydeoxyguanosine (P = 0.0009). The GPX4-positive and 8-hydroxydeoxyguanosine-negative groups had a significantly worse prognosis than the other groups in both overall survival (P = 0.0170) and progression-free survival (P = 0.0005). These results suggest that the overexpression of GPX4 is an independent prognostic predictor in diffuse large B-cell lymphoma. Furthermore, in vitro analysis demonstrated that GPX4-overexpressing cells were resistant to reactive oxygen species-induced cell death (P = 0.0360). Conversely, GPX4-knockdown cells were sensitive to reactive oxygen species-induced cell death (P = 0.0111). From these data, we conclude that GPX4 regulates reactive oxygen species-induced cell death. Our results suggest a novel therapeutic strategy using the mechanism of ferroptosis, as well as a novel prognostic predictor of diffuse large B-cell lymphoma.

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Multidrug-resistant (MDR) multiple myeloma (MM) patients who fail chemotherapy frequently express MDR1 protein, which serves as an efflux pump that protects neoplastic cells. The expression of lung resistance protein (LRP), which mediates intercellular and nucleocytoplasmic transport, is also correlated with chemotherapy resistance and shorter survival of MM patients. Here, we investigated the chemotherapy-induced change of MDR expression in MM patients using quantitative RT-PCR. Overall expression levels of MDR1 and LRP in MM patients were significantly higher than those in control subjects and increased after chemotherapy. More than half of the patients exhibited increased expression of MDR1 (14/26) or LRP (17/26) after chemotherapy. Also, the expression of inhibitor of apoptosis proteins (IAP) was determined in association with the prognosis of the patients. Among patients with increased MDR1-expression after chemotherapy, those with a poor outcome exhibited significant increases in survivin, cIAP1, cIAP2, and XIAP expression by chemotherapy compared with those with a good prognosis. Similarly, in the LRP expression-increased group, patients with a poor outcome showed significant increases of cIAP1 and cIAP2 expression compared with those with longer survival. In patients with reduced-MDR1 or LRP expression after chemotherapy, changes in the expression of IAPs induced by chemotherapy did not correlate with their prognosis. These findings indicate that IAP family proteins might play a role in worsening the prognosis of MM patients in association with chemotherapy-induced overexpression of MDR1 or LRP. Am. J. Hematol. 81:824-831, 2006. V V C 2006 Wiley-Liss, Inc.

Telomerase is a ribonucleoprotein enzyme that maintains protective structures at the ends of eukaryotic chromosomes. We examined the impact of telomerase inhibition by the dominant-negative human catalytic subunit of telomerase (DN-hTERT) on the biological features of acute leukemia. We introduced vectors encoding dominant-negative (DN)-hTERT, wild-type (WT)-hTERT, or a control vector expressing only a drug-resistant marker into a telomerase-positive human acute lymphoblastic leukemia cell line, HAL-01. Expression of DNhTERT dramatically inhibited telomerase activity, leading to apoptotic cell death. Mutant telomerase expression also enhanced daunorubicin-induced apoptosis. Nude mice (n = 5 per group) received subcutanous implants of HAL-01 cells expressing the control vector or DN-hTERT or WT-hTERT. Implantation of HAL-01 cells expressing control vector (n = 5) rapidly produced tumors, whereas implantation of those expressing DN-hTERT (n = 5) did not. Thus, telomerase inhibition both growth of HAL-01 cells in vitro and tumorigenic capacity in vivo. Furthermore, the G-quadruplex-interactive telomerase-specific inhibitor, telomestatin, shortened the telomere length and induced apoptosis in freshly isolated primary acute leukemia cells. These results suggest that antitelomerase therapy may be useful in some acute leukemias in combination with antileukemic agents such as daunorubicin.

Epstein–Barr virus (EBV) has been detected in several T- and NK-cell neoplasms such as extranodal NK/T-cell lymphoma nasal type, aggressive NK-cell leukemia, EBV-positive peripheral T-cell lymphoma, systemic EBV-positive T-cell lymphoma of childhood, and chronic active EBV infection (CAEBV). However, how this virus contributes to lymphomagenesis in T or NK cells remains largely unknown. Here, we examined NF-κB activation in EBV-positive T or NK cell lines, SNT8, SNT15, SNT16, SNK6, and primary EBV-positive and clonally proliferating T/NK cells obtained from the peripheral blood of patients with CAEBV. Western blotting, electrophoretic mobility shift assays, and immunofluorescent staining revealed persistent NF-κB activation in EBV-infected cell lines and primary cells from patients. Furthermore, we investigated the role of EBV in infected T cells. We performed an in vitro infection assay using MOLT4 cells infected with EBV. The infection directly induced NF-κB activation, promoted survival, and inhibited etoposide-induced apoptosis in MOLT4 cells. The luciferase assay suggested that LMP1 mediated NF-κB activation in MOLT4 cells. IMD-0354, a specific inhibitor of NF-κB that suppresses NF-κB activation in cell lines, inhibited cell survival and induced apoptosis. These results indicate that EBV induces NF-κB-mediated survival signals in T and NK cells, and therefore, may contribute to the lymphomagenesis of these cells.