S-adenosylhomocysteine hydrolase inhibition in deoxyadenosine-treated human T-lymphoblasts and resting peripheral blood lymphocytes.

The pattern of inhibition and recovery of intracellular Sadenosylhomocysteine hydrolase (AdoHcyase) activity in duced by cytotoxic concentrations of 2'-deoxyadenosine (dAdo) in the presence of the adenosine deaminase inhibitor erythro-9-[3-(2-hydroxynonyl)]adenine was studied in cultured human T-lymphoblasts (CCRF-CEM and -HSB), Epstein-Barr virus-transformed B-lymphoblasts (JP and RDG), and resting peripheral blood lymphocytes. In the presence of 5 /ÌM erythro9-{3-(2-hydroxynonyl)]adenine the AdoHcyase activity was in hibited 50% after 1 hr of incubation by 3, 10, and 30 jtiM dAdo for B-lymphoblasts, T-lymphoblasts, and peripheral blood lym phocytes, respectively, while cytotoxicity (to 50% of controls) was effected by 600,3, and 1 fiM dAdo, respectively. Cytostatic concentrations of dAdo, which induce G,-phase arrest in Tlymphoblasts, inhibited AdoHcyase to 30% of control at 4 hr, after which recovery to normal levels occurred over 24 hr. Coincubation with 50 ¡IM2'-deoxycytidine, which protects these cells from both Gi-phase arrest and growth inhibition by dAdo, had no effect on the pattern of inhibition of AdoHcyase activity. Epstein-Barr virus-transformed B-lymphoblasts ex posed to the same concentrations of dAdo were not growth inhibited but displayed patterns of AdoHcyase inhibition closely similar to those seen in T-lymphoblasts. Coincubation with 20 fiM 2'-deoxycytidine, despite its protective effect againt dAdo cytotoxicity, had no effect on the pattern of AdoHcyase inhi bition in resting peripheral blood lymphocytes induced by 10 JIMdAdo and 5 UMerythro-9-[3-(2-hydroxynonyl)]adenine over a 72-hr period. The lack of correlation between cytotoxicity and AdoHcyase inhibition in human lymphoid cells suggest that other mechanisms may account for the toxic effects of dAdo in these cells.