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1984-03-25Related article: YAMASHITA, Hirokazu; IWAI, Akira; SATOH, Mitsugi; KATOH, Toshio; VHF DIRECTION FINDER FOR LOCATING LIGHTNINGS AT CLOSE RANGES, Proceedings of the Research Institute of Atmospherics, Nagoya University. v.30, 1983, p.15-24, http://hdl.handle.net/2237/22159departmental bulletin pape

Fludarabine-Mediated Circumvention of Cytarabine Resistance Is Associated with Fludarabine Triphosphate Accumulation in Cytarabine-Resistant Leukemic Cells

The combination of cytarabine (ara-C) with fludarabine is a common approach to treating resistant acute myeloid leukemia. Success depends on a fludarabine triphosphate (F-ara-ATP)-mediated increase in the active intracellular metabolite of ara-C, ara-C 5'-triphosphate (ara-CTP). Therapy-resistant leukemia may exhibit ara-C resistance, the mechanisms of which might induce cross-resistance to fludarabine with reduced F-ara-ATP formation. The present study evaluated the effect of combining ara-C and fludarabine on ara-C-resistant leukemic cells in vitro. Two variant cell lines (R1 and R2) were 8-fold and 10-fold more ara-C resistant, respectively, than the parental HL-60 cells. Reduced deoxycytidine kinase activity was demonstrated in R1 and R2 cells, and R2 cells also showed an increase in cytosolic 5'-nucleotidase II activity. Compared with HL-60 cells, R1 and R2 cells produced smaller amounts of ara-CTP. Both variants accumulated less F-ara-ATP than HL-60 cells and showed cross-resistance to fludarabine nucleoside (F-ara-A). R2 cells, however, accumulated much smaller amounts of F-ara-ATP and were more F-ara-A resistant than R1 cells. In HL-60 and R1 cells, F-ara-A pretreatment followed by ara-C incubation produced F-ara-ATP concentrations sufficient for augmenting ara-CTP production, thereby enhancing ara-C cytotoxicity. No potentiation was observed in R2 cells. Nucleotidase might preferentially degrade F-ara-A monophosphate over ara-C monophosphate, leading to reduced F-ara-ATP production and thereby compromising the F-ara-A-mediated potentiation of ara-C cytotoxicity in R2 cells. Thus, F-ara-A-mediated enhancement of ara-C cytotoxicity depended on F-ara-ATP accumulation in ara-C-resistant leukemic cells but ultimately was associated with the mechanism of ara-C resistance.othe

Studies on the Vapour Phase Acetylation of Cellulose.(V):Homogeneous Liquid Phase Saponification of the Primary Cellulose Acetate by ZnCl2 Catalyser

The primary cellulose acetate made by the vapour phase method using ZnCl2 as a catalyser was dissolved in acetic acid containing various amounts of water and ZnCl2, and the solutions were then ripened at various temperatures.From those experiments were obtained the following results:(1) In order to dissolve the primary acetate it is necessary to use acetic acid containing ZnCl2 in at least 7.7% concentration and to increase ZnCl2-concentration as the water content of acetic acid rises. (2) The saponifion velocity is accelerted as the temperature or the concentrations of water and ZnCl2 rise. But the depolymerisation is accelerated with the rise of temperatre or the increase of ZnCl2, and retarded by water. (3) Addition of HCl promotes very much the saponification velocity, and even at room temperture the rpening proceeds with feasible velocity. But excess of HCl also promotes the depolymerisation. (4) When Zn-acetate is added to the ripening solution, it surpresses the action of ZnCl2 or HCl, both the saponification and depolymerisation are stopped, and thus the ripening solution can be kept at a stable state.departmental bulletin pape

Heteroepitaxial growth of gallium nitride on (111)GaAs substrates by radio frequency magnetron sputtering

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