Wj. Waldman et al., Novel mechanism of inhibition of cytomegalovirus by the experimental immunosuppressive agent leflunomide, TRANSPLANT, 68(6), 1999, pp. 814-825
Background Despite progress in antiviral chemotherapy, cytomegalovirus (CMV
) remains a major cause of morbidity and mortality among pharmacologically
immunosuppressed organ transplant recipients, frequently engaging the clini
cian in a struggle to balance graft preservation with control of CMV diseas
e. Leflunomide, an inhibitor of protein kinase activity and pyrimidine synt
hesis, is an experimental immunosuppressive agent effective against acute a
nd chronic allograft rejection in animal models. Because a number of CMV pr
oteins are known to be phosphorylated, we tested the hypothesis that this a
gent might exert inhibitory activity against CMV.
Methods and results. Plaque assays demonstrated dramatic dose-dependent att
enuation of production of multiple clinical CMV isolates in leflunomide-tre
ated human fibroblasts and endothelial cells, common targets for CMV infect
ion in vivo. As shown by Northern blot analysis and immunohistochemical sta
ining, leflunomide neither interferes with transcription of immediate early
or late viral genes, nor with expression of corresponding proteins. CMV-sp
ecific DNA dot blots and biochemical enzyme assays indicated that, in contr
ast to currently approved anti-CMV drugs, leflunomide exerts no inhibitory
effect on the accumulation of viral DNA in infected tells, or on viral DNA
polymerase activity, Rather, as visualized by transmission electron microsc
opy, this agent appears to act at a late stage in virion assembly by preven
ting tegument acquisition by viral. nucleocapsids. Finally we have demonstr
ated equivalent inhibitory activity of leflunomide against multi-drug-resis
tant CMV isolates.
Conclusions. These findings imply that leflunomide, an effective immunosupp
ressive agent, shows potential to concurrently attenuate a major complicati
on of immunosuppression, CMV disease, by a novel mechanism of antiviral act
ivity.