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Thymidine high concentrations

Cytotoxic effect. Gas phase of mainstream cigarette smoke, in monolayer culture of mouse lung epithelial cells, produced an increase in cytotoxicity in a dose-dependent manner. Cell viability of cultures exposed to gas phase with only the nonorganic components was equivalent to controls. Removal of volatile organic constituents resulted in almost elimination of cytotoxicity of the smoke . Smoke condensate and tobacco extract, at high concentrations in Lewis lung adenocarcinoma cells and mice spleen lymphocytes, were cytotoxic. Smaller doses increased thymidine incorporation in both cell types. Lymphocytes were more susceptible to the toxic effect of tobacco prod-... [Pg.302]

Cells lacking thymidine kinase (TK- cells) can be isolated by treating cell cultures with high concentrations (30 jug/ml) of 5-bromodeoxyuridine, which kills cells containing the enzyme thymidine kinase due to incorporation of large amounts of the analogue into the cells DNA. [Pg.264]

The in vivo metabolism of capecitabine (1) to the active tumor cytotoxic substance 5-fluorouracil (5) is now fairly well understood. When capecitabine is administered orally it is delivered to the small intestine, where it is not a substrate for thymidine phosphorylase in intestinal tissue, and so passes through the intestinal mucosa as an intact molecule and into the bloodstream. When 1 reaches the liver, the carbamate moiety is hydrolyzed through the action of carboxylesterase enzymes, liberating 5 -deoxy-5-fluorocytidine (5 -DFCR, 10). DFUR is partially stable in systemic circulation, but eventually diffuses into tumor cell tissue where it is transformed into 5 -deoxy-5-fluorouridine (5 -DFUR, 9) by cytidine deaminase, an enzyme present in high concentrations in various types of human cancers compared to adjacent healthy cells (although it is present in significantly lower levels in the liver). Within the tumor, 5-... [Pg.61]

Several processes in the immune response are affected by lithium in vivo and in vitro 139). The proliferative responses of hamster lymphoid cells to concanavalin A or phytohemagglutinin, which stimulate mitosis in T cells, were enhanced by lithium in a serum-free culture system. Proliferative stimulation also was obtained with lithium using the B cell mitogen lipopolysaccharide, but the B cell mitogens dextran sulfate and trypsin had no effect 140-143). Lithium increased the effects of suboptimal concentrations of stimulants, but had smaller effects on stimulation by optimal concentrations. With concanavalin A, the response to optimal stimulatory concentrations was inhibited 140). Paradoxical results such as these may be due to inhibitory effects of lithium on adenylate cyclase, or to effects on membrane transport systems 141). Most of these experiments used very high concentrations of lithium, considerably in excess of normal therapeutic doses (maximal inhibitory concentrations were 10 mM with hamster cells and 5 mM with human lymphocytes). At therapeutic levels of lithium, increased incorporation of [ H]thymidine was seen in human peripheral blood mononuclear cells. [Pg.61]

Comparison of the uptake of(III.147) and MTXin cultured L1210 cells [45] confirmed that the quinazoline was able to accumulate to a higher level than MTX when the cells were exposed to the same concentration of drug (4 M) for 40 min. Competitive uptake experiments suggested that (III. 147) shares a common active transport mechanism with MTX and folinic acid. As expected, high concentrations of folinic acid (50 juM) fully protected the cells from the effects of (III. 147). At lower folinic acid concentrations, however, there was only partial protection thus, 5 juM folinic acid (a 100-fold molar excess) was fully protected the cells from 0.05 juM (III. 147), whereas 0.5 /tM folinic acid (only a 10-fold excess) did not. Cells were also completely protected from 0.05 juM (III. 147) with 100 pM thymidine and 100/tM hypoxanthine, and greater protection was achieved with 5 /tM folinic and 100 /iM thymidine than with 5 iM folinic acid alone. It was concluded from these results that (III. 147) does not kill cells solely via DHFR inhibition, but rather via concomitant inhibition of DHFR and TS. [Pg.37]

L D. The conversion of penciclovir to its active form requires initial monophosphorylation by viral thymidine kinases, then conversion to its active triphosphate form by cellular enzymes. Thus, the concentration of penciclovir triphosphate is particularly high in cells infected with its target viruses (e.g., HSV, VZV, HBV). Foscarnet is a pyrophosphate analogue that does not require activation. Oseltamivir is a neuraminidase inhibitor that is con-... [Pg.582]

The less basic purines generate different adducts. Both a C-8 adduct 107 and an 0-6 adduct 108 are produced in the presence of I, while the exclusive product of the reaction of A with 75n and 75o is the unique benzene imine 109. ° These purines also exhibit lower selectivity for trapping of the nitre-nium ions (Table 3). The pyrimidine nucleosides thymidine (T), uridine (U), and cytosine (C) showed negligible reactivity with these two nitrenium ions. ° The selectivity ratios for T, U, and C given in Table 3 are upper limits based on the decrease in the yield of the hydrolysis products at high nucleoside concentration (ca. 50mM). ° Since no adducts were isolated it is not clear that these selectivities represent nucleophilic trapping by the pyrimidines. [Pg.219]

The thymidine analog stavudine (d4T) (Figure 49-2) has high oral bioavailability (86%) that is not food-dependent. The serum half-life is 1.1 hours, the intracellular half-life is 3.0-3.5 hours, and mean cerebrospinal fluid concentrations are 55% of those of plasma. Excretion is by active tubular secretion and glomerular filtration (Table 49-... [Pg.1078]

For quantitative work it is important to use a high enough concentration of thymidine such that it remains constant throughout the incubation. [Pg.242]


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See also in sourсe #XX -- [ Pg.232 ]




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