Inhibition of lymphocyte function by 9-deazaadenosine

9-Deazaadenosine (c⁹Ado), a novel C-nucleoside, has been found to inhibit lymphocytemediated cytolysis (LMC) in a time-dependent manner. c⁹Ado inhibited LMC by 50% at concentrations of 10 and 0.07 μM after drug-pretreatment periods of 3 and 22 hr, respectively, although a 1-hr pretreatment of cytolytic lymphocytes with 100 μM c⁹Ado had no effect upon this lymphocyte function. c⁹Ado was metabolized rapidly and extensively to 9-deazaadenosine 5'-triphosphate (c⁹ATP) both by mouse cytolytic lymphocytes and by human erythrocytes. Adenosine kinase purified from rabbit liver phosphorylated c⁹Ado with a K_m of 200 μM and a V_max of 8% that for adenosine. The metabolic buildup of c⁹ATP in lymphocytes was accompanied by a large, time-dependent decrease in cellular ATP and by smaller percentage decreases in CTP, UTP and GTP. Among other biochemical effects examined, c⁹Ado was found to cause a decrease in lymphocyte cAMP content and appeared to be neither an inhibitor nor a substrate for S-adenosylhomocysteine hydrolase. Consistent with this latter result, l-homocysteine thiolactone had no effect on the inhibition of LMC by c⁹Ado. Neither the inhibition of LMC by c⁹Ado nor the metabolic formation of c⁹ATP in lymphocytes was affected by erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), indicating that c⁹Ado is not a substrate for adenosine deaminase. 5-Iodotubercidin, a non-competitive inhibitor (K₁₅ = 9 nM, K_ii = 20 nM) of adenosine kinase, prevented the above effects of c⁹Ado on lymphocyte function, c⁹ATP formation, and ATP levels. Either complete preservation (with coformycin) or partial replenishment (with adenosine plus EHNA) of ATP levels in c⁹Ado-treated lymphocytes resulted in partial restoration of cytolytic function to cells containing large amounts of c⁹ATP. These results suggest that c⁹Ado is inhibitory to LMC both because it causes a decrease in the absolute concentration of ATP within the cytolytic lymphocytes and because it permits the establishment within these cells of an unfavorable c⁹ATP: ATP ratio which impedes the utilization of ATP in a reaction essential to the execution of this lymphocyte function.