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, greater than 10.0 and 3.30 microM, 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 IC50 values of 0.05, 0.25 and 3.30 micrograms/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 C3H1OT1/2 fibroblasts which constitutively produce MoLV. Pretreatment with ZDDFA (1.0 microgram/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 microgram/ml) treated C3H1OT1/2 cells. Incorporation of a [3H]methyl group from tritiated S-adenosylmethionine into total RNA in C3H1OT1/2 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.