Isolation and characterization of herpes simplex virus type 1 resistant to aminothiazolylphenyl-based inhibitors of the viral helicase-primase.

The aminothiazolylphenyl-containing compounds BILS 179 BS and BILS 45 BS are novel inhibitors of the herpes simplex virus helicase-primase with antiviral activity in vitro and in animal models of HSV disease. To verify the mechanism of antiviral action, resistant viruses were selected by serial passage or by single-step plaque selection of HSV-1 KOS in the presence of inhibitors. Three resistant isolates K138r3, K22r5, and K22r1 were found to be 38-, 316-, and 2500-fold resistant to BILS 22 BS, a potent analog of BILS 45 BS. All three viruses had growth properties in vitro similar to wild-type HSV-1 KOS but they were sensitive to acyclovir. Cutaneous and intra-cerebral inoculation of mice with K22r1 or K22r5 resulted in pathogenicity equivalent to that of HSV-1 KOS. Both isolates were fully competent for reactivation from latency following corneal inoculation. Helicase-primase purified from cells infected with resistant viruses showed decreased inhibition in an in vitro DNA-dependent ATPase assay that correlated well with antiviral resistance. Marker transfer experiments and DNA sequence analysis identified single base pair mutations clustered in the N-terminus of the UL5 gene that resulted in single amino acid changes in the UL5 protein. Taken together, the results indicate that helicase-primase inhibitors prevent HSV growth by inhibiting HSV helicase-primase through specific interaction with the UL5 protein.