Clinical pharmacology of deoxycoformycin.
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Deoxycoformycin (DCF) is an inhibitor of adenosine deaminase (ADA). Twenty-one courses of DCF were administered to 13 patients ranging in age from 15 to 78 yr. Eight patients had T-cell disorders, and five patients had non-T-cell malignancies. The i.v. bolus dose was escalated from 5 to 30 mg/sq m/day, and the duration of the courses ranged from 1 to 5 days. The DCF plasma half-life ranged from 4.9 to 6.2 hr and was independent of dose. The dose-limiting toxicities involved the central nervous system (CNS) and the kidneys. Other toxicities included bronchitis, decreases in hematocrit, arthralgias, and myalgias. Mortality was encountered in three patients. These toxic effects may have been secondary to the accumulation of the metabolites adenosine and deoxyadenosine. Deoxyadenosine and adenosine were both detectable in plasma (10(-6) M) and in urine (10(-3) M). Two partial remissions were observed: one in a patient with T-cell ALL and another in a patient with mycosis fungoides. Minimal responses characterized by either declines in peripheral blast counts or partial resolution of adenopathy were observed in five other patients. No responses were observed in six patients. These observations suggest that DCF is effective in the treatment of T-cell lymphoid malignancies. (+info)
Adenosine production inside rat polymorphonuclear leucocytes.
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Adenosine synthesis was studied during 2-deoxyglucose-induced ATP catabolism in intact rat polymorphonuclear leucocytes. When both adenosine kinase (EC 2.7.1.20) and adenosine deaminase (EC 3.5.4.4) were selectively inhibited, adenosine accumulated. Adenosine formation took place inside the intact cells by a metabolic pathway independent of the ecto-5'-nucleotidase (EC 3.1.3.5). Distinct metabolic pathways are proposed for adenosine production from intracellular or extracellular nucleotides. (+info)
Mechanism of deoxyadenosine-induced catabolism of adenine ribonucleotides in adenosine deaminase-inhibited human T lymphoblastoid cells.
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Loss of ATP accompanying accumulation of dATP has recently been reported to occur in the erythrocytes and lymphoblasts of patients with T lymphocytic leukemia during treatment with deoxycoformycin, an inhibitor of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) that causes the accumulation of deoxyadenosine. We have studied the mechanisms responsible for adenine ribonucleotide depletion in cultured human CEM T lymphoblastoid cells treated with deoxycoformycin and deoxyadenosine. Accumulation of dATP was accompanied by depletion of total soluble adenine ribonucleotides without change in the adenylate energy charge, by the route ATP --> AMP --> IMP --> inosine --> hypoxanthine; conversion of IMP to AMP and de novo purine synthesis were inhibited in these cells. ATP degradation did not occur in a mutant of CEM that was incapable of phosphorylating deoxyadenosine, or in a B cell line with very limited ability to accumulate dATP. We found that dATP and ATP were both able to stimulate markedly the deamination of AMP by lymphoblast AMP deaminase; dAMP was a poor substrate for this enzyme (K(m) = 2.4 mM, vs. 0.4 mM for AMP). Similarly, dATP as well as ATP caused marked activation of IMP dephosphorylation by a lymphoblast cytoplasmic nucleotidase. Inhibition of intracellular AMP deaminase with coformycin prevented degradation of adenine ribonucleotides without affecting dATP accumulation. We propose that ATP-dependent phosphorylation of deoxyadenosine generates ADP and AMP. Simultaneously, dATP accumulation stimulates deamination of AMP, but not dAMP, and the dephosphorylation of IMP to inosine. Coupling of AMP degradation to ATP utilization in deoxyadenosine phosphorylation maintains the adenylate energy charge despite net depletion of cellular ATP. (+info)
Differential effect of coformycin on the cell cycle traverse of normal and simian virus 40-transformed human fibroblasts.
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Normal and simian virus 40-transformed human embryonic lung fibroblasts in culture were exposed to 3.5 microM coformycin (CF). This treatment resulted in almost complete inhibition of adenosine deaminase activity in both cell lines and retarded the progress of the fibroblasts through the cell cycle, as measured by the rate of cell proliferation. There was a marked difference, however, in the effect of CF on the traverse of different segments of the cell cycle. In normal fibroblasts, CF rapidly but transiently inhibited cell entry into visible stages of mitosis and delayed the progress through S and G2. In transformed fibroblasts, the effects of CF on the cell cycle included an early acceleration of the cell entry into visible mitosis and prolongation of this phase of the cell cycle. These results indicate that inhibition of adenosine deaminase can have different effects on the traverse of the critical segments of the cell cycle in normal and transformed cells. (+info)
Effects of deoxyadenosine on the activation of ADA inhibited T & B cells.
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Using an in vitro model of adenosine deaminase deficiency, we have shown that the triggering of T lymphocyte proliferation by PHA is inhibited by concentrations of deoxyadenosine likely to occur in the plasma of ADA deficient children with severe combined immunodeficiency (ADA-SCID). Prostaglandin E1 increases the sensitivity of T cells to this inhibition, suggesting that derangement of cyclic nucleotide metabolism underlies the profound T lymphopaenia seen in ADA-SCID and in patients treated with the ADA inhibitor, deoxycoformycin. The proliferation and Ig synthesis of ADA inhibited B cells stimulated with protein A and EBV is in general less sensitive to the inhibitory effects of deoxyadenosine. However, this sensitivity varies widely between experiments suggesting that other cells present in the cultures may modify the inhibitory effect of deoxyadenosine. This may help explain the variability in B cell numbers and function in patients with ADA-SCID. (+info)
Susceptibility of phosphonoformic acid-resistant herpes simplex virus variants to arabinosylnucleosides and aphidicolin.
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A plaque-reduction assay was used to examine the susceptibility of five phosphonoformic acid-resistant variants of herpes simplex virus type 1 to arabinosylnucleosides and aphidicolin. These viruses were cross-resistant to arabinosylhypoxanthine and to arabinosyladenine when tested in the absence of deoxycoformycin, a deaminase inhibitor. In the presence of deoxycoformycin, no cross-resistance between arabinosyladenine and phosphonoformic acid was observed. The two variants tested were cross-resistant to arabinosylthymine, and all five variants were collaterally susceptible to aphidicolin inhibition. (+info)
Adenosine: a physiological modulator of superoxide anion generation by human neutrophils.
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The effects of adenosine were studied on human neutrophils with respect to their generation of superoxide anion, degranulation, and aggregation in response to soluble stimuli. Adenosine markedly inhibited superoxide anion generation by neutrophils stimulated with N-formyl methionyl leucyl phenylalanine (FMLP), concanavalin A (Con A), calcium ionophore A23187, and zymosan-treated serum; it inhibited this response to PMA to a far lesser extent. The effects of adenosine were evident at concentrations ranging from 1 to 1,000 microM with maximal inhibition at 100 microM. Cellular uptake of adenosine was not required for adenosine-induced inhibition since inhibition was maintained despite the addition of dipyridamole, which blocks nucleoside uptake. Nor was metabolism of adenosine required, since both deoxycoformycin (DCF) and erythro-9-(2-hydroxy-3-nonyl) adenine did not interfere with adenosine inhibition of superoxide anion generation. The finding that 2-chloroadenosine, which is not metabolized, resembled adenosine in its ability to inhibit superoxide anion generation added further evidence that adenosine metabolism was not required for inhibition of superoxide anion generation by neutrophils. Unexpectedly, endogenously generated adenosine was present in supernatants of neutrophil suspensions at 0.14-0.28 microM. Removal of endogenous adenosine by incubation of neutrophils with exogenous adenosine deaminase (ADA) led to marked enhancement of superoxide anion generation in response to FMLP. Inactivation of ADA with DCF abrogated the enhancement of superoxide anion generation. Thus, the enhancement was not due to a nonspecific effect of added protein. Nor was the enhancement due to the generation of hypoxanthine or inosine by deamination of adenosine, since addition of these compounds did not affect neutrophil function. Adenosine did not significantly affect either aggregation or lysozyme release and only modestly affected beta-glucuronidase release by neutrophils stimulated with FMLP. These data indicate that adenosine (at concentrations that are present in plasma) acting via cell surface receptors is a specific modulator of superoxide anion generation by neutrophils. (+info)
Neplanocin A. A cyclopentenyl analog of adenosine with specificity for inhibiting RNA methylation.
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The mechanism of action of the adenosine analog, neplanocin A (NPC), was investigated in human colon carcinoma cell line HT-29. Cell viability was reduced to 38 and 17% of control by 24-h exposure to 10(-5) and 10(-4) M NPC, respectively. Cytocidal activity was not affected by inhibition of adenosine deaminase with 2'-deoxycoformycin. Concomitant with decreased cell viability was the reduced incorporation of [14C]dThd and [3H]Leu, and to a lesser extent [3H]Urd, into acid-precipitable material. Labeling of rRNA and tRNA during drug treatment for 24 h with [methyl-3H]Met and [14C]Urd revealed that NPC primarily inhibited RNA methylation, and to a lesser extent, RNA synthesis. RNase T2 digests of total RNA indicated that base and 2'-O-methylation were inhibited to approximately the same degree. Metabolites of NPC were measured by reverse-phase high-performance liquid chromatography and it was found that the major drug metabolite was the drug analog of S-adenosylmethionine with little formation of the respective, S-adenosylhomocysteine metabolite. NPC was utilized to a very small degree for RNA synthesis where only 2 and 30 pmol of NPC/A260 were incorporated into rRNA and tRNA after 24-h exposure to 10(-5) and 10(-4) M NPC, respectively. These results indicate that NPC is metabolized to a metabolite of S-adenosylmethionine which is a poor methyl donor for RNA methyltransferases, and that the accompanying decrease in RNA methylation and protein synthesis appears to be related to its cytocidal activity. (+info)