Resistance to Ara-C up-regulates the activation of NF-kappaB, telomerase activity and Fas expression in NALM-6 cells.

Cytosine arabinoside (1-beta-D-arabinofuranosylcytosine; Ara-C) is the most important antimetabolite used to induce remission in acute leukemia, but cellular resistance to Ara-C reflects a poor prognosis in cancer chemotherapy. To further investigate the mechanisms of resistance to Ara-C, we have established Ara-C-resistant NALM-6 cells. The activation of nuclear factor kappaB (NF-kappaB) was accompanied by the acquisition of Ara-C resistance. Telomerase activity has also increased with the acquisition of Ara-C resistance. The expression of Bid, Bax, or p53 proteins have been shown to increase correlated with the acquisition of Ara-C resistance. In contrast to the increase in these proteins, Bcl-2, Bcl-x, and Bag-1 proteins remained unchanged with the acquisition of Ara-C resistance. Fas expression increased with the acquisition of Ara-C resistance in the late stage. The induction of apoptosis and reduction of cell viability by cytotoxic anti-Fas antibody was more susceptible in resistant cells than parental cells. In conclusion, this report has shown that resistance to Ara-C up-regulates the activation of NF-kappaB, telomerase activity and Fas expression.

Characterization of resistance to cytosine arabinoside (Ara-C) in NALM-6 human B leukemia cells.

BACKGROUND: Cytosine arabinoside (1-beta-D-arabinofuranosylcytosine;Ara-C) is the most important antimetabolite used for acute leukemia. We established Ara-C (0.003-1 micromol/l)-resistant NALM-6 leukemia cells, and attempted the characterization of their resistance. METHODS: The Ara-C-resistant cell lines were developed by stepwise increases in the drug. The mRNA expressions were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The uptake of Ara-C, deoxycytidine kinase (dCK) activity and cytidine deaminase (CDA) activity were measured using radioisotope methods. Cytotoxicity was evaluated using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. RESULTS: The mRNA expression of human equilibrative nucleoside transporter-1 (hENT-1), which is an uptake transporter of Ara-C, was initially decreased during the acquisition of resistance to Ara-C. The expression of dCK, an activation enzyme, and of CDA, an inactivation enzyme, was decreased and increased in the late phase, respectively. The cytotoxic effect of Ara-C on parental NALM-6 cells was ameliorated by hENT-1 inhibitors. There were no differences in the cytotoxic effect of other anticancer drugs, but there was similar resistance to nucleoside analogues via hENT-1 between the parental and resistant cells. CONCLUSIONS: Decreased hENT-1 expression and function is causatively responsible for the acquisition of Ara-C resistance and alterations in dCK and CDA contribute to the higher concentration range.

Melatonin protects on toxicity by acetaminophen but not on pharmacological effects in mice.

The pineal gland and its main hormone, melatonin (MLT), are involved in a variety of physiological processes. MLT is a member of the indolamine family and has significant antioxidative activity. Acetaminophen (AA) is the most widely used medication in the world, both by prescription and over the counter. In large doses, AA is hepatotoxic causing oxidative stress and lipid peroxidation. Therefore, antioxidants have been used to protect against the toxicity of AA. Here, we examined in vitro and in vivo the protective effects of MLT against AA-induced toxicity in mice. MLT (100 microM) had a significant protective effect on the AA (7 mM)-induced loss of cell viability in mouse primary cultured hepatocytes as determined using the 3H-thymidine incorporation assay and MTT assay. The AA-induced generation of reactive oxygen species (ROS) peaked at 6 h and was followed by an increase in lipid peroxidation at 12 h in hepatocytes. MLT (0.1, 1, 10 or 100 microM) dose-dependently attenuated the increase in both production of ROS and lipid peroxidation by AA. Similarly, in vivo, AA (400, 600 or 800 mg/kg, intraperitoneally)-induced mortality and hepatotoxicity were significantly decreased by MLT (10 mg/kg, subcutaneously). Pretreatment with MLT had a greater protective effect on the hepatotoxicity of AA than post-treatment. However, MLT had no protective effect on the antipyretic effect or antinociception caused by AA. These results suggest that MLT is potentially useful for preventing AA-induced toxicity, but not the antipyretic effect or antinociception caused by AA.

Trimidox induces apoptosis via cytochrome c release in NALM-6 human B cell leukaemia cells.

Trimidox (3,4,5-trihydroxybenzamidoxime) has been shown to reduce the activity of ribonucleotide reductase accompanied by growth inhibition and the differentiation of mammalian cells. Here we examine the induction of apoptosis by trimidox in several human leukaemia cell lines, focusing on the release of cytochrome c and the activation of caspase proteases in the human B cell line NALM-6. Induction of apoptosis by trimidox (300 microM) was detected in NALM-6, HL-60 (premyelocytic leukaemia cells), MOLT-4 (an acute lymphoblastic leukaemia cells), Jurkat (a T-cell leukaemia cells), U937 (expressing many monocyte-like characteristics), and K562 (erythroleukaemia). NALM-6 was most affected by trimidox among leukaemia cells; therefore, we employed NALM-6 cells in the subsequent experiments. The cells showed a time-dependent increase in DNA damage after trimidox (250 microM) treatment. A significant increase in the amount of cytochrome c release was detected after treatment with trimidox. Bcl-2 and Bax protein expressions were not changed by trimidox. Caspase-3 and -9 were activated by incubation with trimidox, whereas caspase-8 was not. Furthermore, trimidox-induced apoptosis was prevented by a broad-spectrum caspase inhibitor, a caspase-3, and a caspase-9 inhibitor, but not by a caspase-8 inhibitor. Inhibition of c-Jun NH2-terminal kinase (JNK) by SP600125 appreciably protected cells from trimidox-induced apoptosis, but no effect inhibition of p38 mitogen-activated protein kinase (MAPK) by SB203580. In contrast, extracellular signal-regulated kinase (ERK) inhibitors U0126 and PD98059 strongly potentiated the apoptotic effect of trimidox. This report shows that the induction of apoptosis by trimidox occurs through a cytochrome c-dependent pathway, which sequentially activates caspase-3 and caspase-9.

Inhibitory effect of naringin on lipopolysaccharide (LPS)-induced endotoxin shock in mice and nitric oxide production in RAW 264.7 macrophages.

Lipopolysaccharide (LPS) has been known to induce endotoxin shock via production of inflammatory modulators such as tumor necrosis factor alpha (TNF-alpha), or nitric oxide (NO). In this study, we have examined the effect of naringin (NG), one of the flavonoids, on LPS-induced endotoxin shock in mice and NO production in RAW 264.7 macrophages. For intraperitoneal (i.p., 20 mg/kg) injection of LPS at 48 h, the survival rate of mice administered with LPS alone (n=10) or pretreated with NG at 10, 30 and 60 mg/kg (i.p.) group (n=10) was 0% or 10%, 50% and 70%, respectively. NG dose-dependently suppressed LPS-induced production of TNF-alpha. LPS-induced production of NO at 6 h (125.89+/-16.35 microM), as measured by nitrite formation, was significantly reduced by NG at 30 or 60 mg/kg for 49.49+/-4.81 or 27.91+/-1.81 microM (P<0.01 vs. LPS alone), respectively. To further examine the mechanism by which NG suppresses LPS-induced endotoxin shock, we used an in vitro model, RAW 264.7 mouse macrophage cells. NG (1 mM) suppressed LPS (0.01, 0.1 or 1 microg/ml)-induced production of NO and the expression of inflammatory gene products such as inducible NO synthase (iNOS), TNF-alpha, inducible cyclooxygenase (COX-2) and interleukin-6 (IL-6) as determined by RT-PCR assay. NG was found to have blocked the LPS-induced transcriptional activity of NF-kappaB in electrophoretic mobility shift assay and reporter assay. These findings suggest that suppression of the LPS-induced mortality and production of NO by NG is due to inhibition of the activation of NF-kappaB.

Inhibitory effects of naringenin on tumor growth in human cancer cell lines and sarcoma S-180-implanted mice.

We have investigated the effect of naringenin (NGEN) on tumor growth in various human cancer cell lines and sarcoma S-180-implanted mice. NGEN showed cytotoxicity in cell lines derived from cancer of the breast (MCF-7, MDA-MB-231), stomach (KATOIII, MKN-7), liver (HepG2, Hep3B, Huh7), cervix (Hela, Hela-TG), pancreas (PK-1), and colon (Caco-2) as well as leukemia (HL-60, NALM-6, Jurkat, U937). NGEN-induced cytotoxicity was low in Caco-2 and high in leukemia cells compared to other cell lines. NGEN dose-dependently induced apoptosis, with hypodiploid cells detected in both Caco-2 and HL-60 by flow cytometric analysis. In vivo, NGEN inhibited tumor growth in sarcoma S-180-implanted mice, following intraperitoneal or peroral injection once a day for 5 d. Naringin (NG) also inhibited tumor growth by peroral injection but not intraperitoneal injection. NGEN, one of the most abundant flavonoids in citrus fruits, may have a potentially useful inhibitory effect on tumor growth.