In vitro activity of R 61837, a new antirhinovirus compound

R 61837 or 3-methoxy-6-[4-(3-methylphenyl)-1-piperazinyl]pyridazine is a new and potent inhibitor of rhinoviruses at concentrations not inhibitory to HeLa cell growth. Different rhinovirus serotypes varied widely in their susceptibility to the antiviral agent. The MICs for 50% CPE reduction ranged from 0.004 to 15 micrograms/ml. The yields of the most susceptible serotypes were reduced by a factor of 1,000 to 10,000 after single round high multiplicity infections in presence of low concentrations of the compound. The inactivation of some but not all serotypes in a time-, concentration- and temperature-dependent way by R 61837 indicated a direct interaction between the drug and the viral particles. The antiviral activity of the compound was confirmed in the human target cells for rhinoviruses by experiments using nasal polyp explant cultures.