Inhibition Of Adenosine Deaminase Activity Research Articles

Inhibition of Adenosine Deaminase Activity Results in Cytotoxicity to T Lymphoblasts In Vivo

Abstract We have treated a patient with refractory T-cell acute lymphoblastic leukemia with 2′-deoxycoformycin, a potent inhibitor of the enzyme adenosine deaminase. Inhibition of adenosine deaminase activity resulted in (1) an abrupt rise in plasma deoxyadenosine, but not adenosine, concentrations; (2) accumulation of deoxyadenosine triphosphate by lymphoblasts; (3) inhibition of the enzyme S- adenoylhomocysteine hydrolase; and (4) rapid lysis of the leukemic cells. The patient died suddenly 3 days after therapy was discontinued, and postmortem examination revealed a complete absence of leukemic cells in all organs. Pharmacologic inhibition of adenosine deaminase activity can result in the lysis of T lymphoblasts in vivo, and this effect appears to be mediated by deoxyadenosine.

Effect of theophylline and other drugs on rabbit renal cyclic nucleotide phosphodiesterase, 5′-nucleotidase and adenosine deaminase

The effect of theophylline and several other drugs on cyclic AMP and cyclic GMP phosphodiesterase, 5′-nucleotidase and adenosine deaminase was tested in homogenates of rabbit renal cortex and medulla. Theophylline was a competitive inhibitor of cyclic nucleotide phosphodiesterase, a non-competitive inhibitor of 5′-nucleotidase and alkaline phosphatase but did not influence adenosine deaminase. Cyclic AMP and cyclic GMP hydrolysis were inhibited to an equal extent by theophylline, furosemide, caffeine, 3-isobutyl-methylxanthine, and SQ 20006. Dipyridamol, ZK 62.711, Ro 20-1724 and ICI 63.197 inhibited cyclic AMP hydrolysis in at least ten times lower concentrations than cyclic GMP hydrolysis. Conversely, M & B 22948 and dilazep were more potent as inhibitors of cyclic GMP than of cyclic AMP hydrolysis. All the diuretic agents tested (furosemide, ethacrynic acid, chlorthalidone, cyclopentiazide and theophylline) inhibited 5′-nucleotidase at 1 mM concentration or lower. Of the drugs tested at 1 mM concentration only dipyridamol and chlorthalidone produced significant (30 per cent) inhibition of adenosine deaminase activity.

Adenosine metabolism in phytohemagglutinin-stimulated human lymphocytes.

The association of a human genetic deficiency of adenosine deaminase activity with combined immunodeficiency prompted a study of the effects of adenosine and of inhibition of adenosine deaminase activity on human lymphocyte transformation and a detailed study of adenosine metabolism throughout phytohemagglutinin-induced blastogenesis. The adenosine deaminase inhibitor, coformycin, at a concentration that inhibited adenosine deaminase activity more than 95%, or 50 muM adenosine, did not prevent blastogenesis by criteria of morphology or thymidine incorporation into acid-precipitable material. The combination of coformycin and adenosine, however, substantially reduced both the viable cell count and the incorporation of thymidine into DNA in phytohemagglutinin-stimulated lymphocytes. Incubation of lymphocytes with phytohemagglutinin for 72 h produced a 12-fold increase in the rate of deamination and a 6-fold increase in phosphorylation of adenosine by intact lymphocytes. There was no change in the apparent affinity for adenosine with either deamination or phosphorylation. The increased rates of metabolism, apparent as early as 3 h after addition of mitogen, may be due to increased entry of the nucleoside into stimulated lymphocytes. Increased adenosine metabolism was not due to changes in total enzyme activity; after 72 h in culture, the ratios of specific activities in extracts of stimulated to unstimulated lymphocytes were essentially unchanged for adenosine kinase, 0.92, and decreased for adenosine deaminase, 0.44. As much as 38% of the initial lymphocyte adenosine deaminase activity accumulated extracellularly after a 72-h culture with phytohemagglutinin. In phytohemagglutinin-stimulated lymphocytes, the principal route of adenosine metabolism was phosphorylation at less than 5 muM adenosine, and deamination at concentrations greater than 5 muM. In unstimulated lymphocytes, deamination was the principal route of adenosine metabolism over the range of adenosine concentrations studied (0.5-250 muM). These studies demonstrate the dependence of both the unstimulated and stimulated lymphocyte on adenosine and may account for the observed sensitivity of mitogen-stimulated lymphocytes to the toxic effects of exogenously supplied adenosine in the presence of the adenosine deaminase inhibitor coformycin. A single case of immunodeficiency disease has been reported in association with purine nucleoside phosphorylase deficiency. The catabolism of guanosine was also found to be enhanced in stimulated normal lymphocytes; phosphorolysis of guanosine to guanine by intact lymphocytes increased six fold after 72-h culture with phytohemagglutinin. The specific activity of purine nucleoside phosphorylase in extracts, with guanosine as substrate, was essentially the same in stimulated and unstimulated lymphocytes after 72 h of culture.