1,10-phenanthroline and its non-chelating isomer, 1,7-phenanthroline were used to inhibit the replication of vaccinia virus (VV). Serial passage of VV in the presence of various concentrations of either 1,10-phenanthroline or 1,7-phenanthroline was carried out. No drug resistant mutants were isolated, suggesting that the observed inhibition was due to a cellular...