Antiretroviral activity of mechanism-based irreversible inhibitors of S-Adenosylhomocysteine hydrolase

S-Adenosylhomocysteine hydrolase (AdoHcy-nase) is a key enzyme in transmethylation reactions. The objective of the present study was to examine the potential antiretroviral activities of novel mechanism-based irreversible AdoHcy-nase inhibitors. (Z)-4′,5′-didehydro-5′-deoxy-5′-fluoroadenosine (ZDDFA), (E)-4′,5′-didehydro-5′-deoxy-5′-fluoroadenosine (EDDFA), (Z)-4′,5′-didehydro-5′-deoxy-5′-chloroadenosine (ZDDCA) and 5′-deoxy-5′-acetylenic adenosine (DAA) inhibited AdoHcy-nase activity with Ki values of 0.55, 1.04, > 10.0 and 3.30 μM, respectively. These four compounds were tested for antiviral activity in vitro against Moloney leukemia virus (MoLV) in the XC-plaque assay. MoLV replication in murine fibroblasts (SC-1) was inhibited by ZDDFA, EDDFA and DAA with IC 50 values of 0.05, 0.25 and 3.30 μg/ml, respectively. ZDDCA did not inhibit MoLV infection at the concentrations tested. Antiviral activity correlated with the ability of the individual compounds to maintain sustained elevations in intracellular S-adenosylhomocysteine (AdoHcy) concentrations in the SC-1 cells. ZDDFA, the most potent inhibitor of AdoHcy-nase and MoLV was also the most active in maintaining sustained elevations in intracellular AdoHcy levels. The antiviral activity of ZDDFA was also examined in murine C3H1OT 1 2 fibroblasts which constitutively produce MoLV. Pretreatment with ZDDFA (1.0 μg/ml) for 24 hr inhibited virus production by 88%. Similar to the SC-1 cells, and concomitant with enzyme inhibition, there was a 300-fold increase in AdoHcy levels in ZDDFA (1.0 μg/ml) treated C3H1OT 1 2 cells. Incorporation of a [ 3H]methyl group from tritiated S-adenosylmethionine into total RNA in C3H1OT 1 2 cells was inhibited by ZDDFA without affecting cell viability. These results suggest that mechanism-based inhibitors of AdoHcy-nase, such as ZDDFA, may have potential as antiretroviral agents.