Broad-spectrum antiviral activity of carbodine, the carbocyclic analogue of cytidine

Carbocyclic cytidine (C-Cyd) is a broad-spectrum antiviral agent active against DNA viruses [pox (vaccinia)], (+)RNA viruses [toga (Sindbis, Semliki forest), corona], (−)RNA viruses [orthomyxo (influenza), paramyxo (parainfluenza, measles), rhabdo (vesicular stomatitis)] and (±)RNA viruses (reo). The target enzyme of C-Cyd is supposed to be CTP synthetase that converts UTP to CTP. In keeping with this assumption are the observations that (i) C-Cyd effects a dose-dependent inhibition of RNA synthesis in both virus-infected and uninfected cells, and (ii) exogenous addition of either Urd or Cyd reverses both the antiviral and cytocidal activity of C-Cyd, whereas addition of dThd or dCyd fails to do so. The selectivity of C-Cyd against Sindbis, vesicular stomatitis and reo virus is markedly increased when C-Cyd is combined with Cyd (10 μg/mL). This combination may therefore be worth pursuing as a chemotherapeutic modality for the treatment of virus infections.