Activity of trifluorothymidine against cytomegalovirus

Trifluorothymidine (TFT) was tested for antiviral activity against mouse cytomegalovirus (MCMV) and human cytomegalovirus (HCMV) in one-step replication assays. The TFT concentration required to reduce virus yield by 50% (ID50) was 0.22 microM for MCMV and 0.012 microM for HCMV. The antiviral activity of TFT against MCMV was reversed by addition of equimolar thymidine, and no antiviral activity was demonstrable in a host cell line lacking thymidine kinase. Thus, TFT's anti-MCMV activity is dependent on a host cell TK since this herpesvirus lacks thymidine kinase. A continuous subcutaneous infusion of TFT achieving a serum concentration of 1 microM failed to protect mice from lethal MCMV infection, perhaps because serum levels of thymidine were comparable to the drug level. Comparison of the ID50 against HCMV and the ID50 against human bone marrow progenitor cells resulted in an in vitro therapeutic ratio of 108, suggesting that TFT might offer some promise as a clinically useful anti-HCMV agent.