Point mutations induced by foscarnet (PFA) in the human cytomegalovirus DNA polymerase.

Background: In vitro selection of viruses with decreased drug susceptibility is a useful tool for mapping drug resistance-associated alterations, evaluating cross-resistance profiles, and elucidating molecular mechanisms of antiviral activity.

Objectives: To provide data on mechanisms of selective drug action and features of drug resistance that may be clinically important.

Study Design: Foscarnet (PFA) and ganciclovir (GCV) were used to induce mutants of the human cytomegalovirus (HCMV) Towne strain.

Results: Three new mutations, selected in the presence of PFA, were identified with single base substitutions resulting in T419M, Q578H, and L773V in conserved regions of the HCMV DNA polymerase. None of these mutations have been reported previously. These mutations conferred resistance to PFA but did not change the susceptibility to GCV. A mutant was selected in the presence of GCV. This GCV-selected mutant had no mutation in the UL54 but had an amino acid alteration at codon M460V of UL97, which conferred resistance to GCV. All the mutants had the same growth phenotype as the parental laboratory strain Towne.

Conclusions: We have determined three novel alterations in HCMV DNA polymerase inducing reduced susceptibility to PFA. None of these alterations changed the growth phenotype of the parental virus.