The anticytomegaloviral activity of raltitrexed is abrogated in quiescent mouse fibroblasts that overexpress thymidylate synthase

Cytomegalovirus (CMV) replication in non-proliferating cells requires the coordinated expression of the host enzymes responsible for deoxyribonucleotide synthesis. Thymidylate synthase (TS) is an essential cellular enzyme that catalyzes de novo synthesis of thymidylic acid (dTMP). In this report we show that murine CMV (MCMV) replication and DNA synthesis are inhibited in quiescent 3T6 fibroblasts by raltitrexed, a quinazoline-based folate analog that specifically inhibits TS. This antiviral activity was abrogated in LU3-7 cells, a 3T6 derivative that overproduces TS by about 50-fold. These observations indicate that the anticytomegaloviral activity of raltitrexed is associated with TS inhibition and suggest that cellular TS activity is required for efficient CMV replication in quiescent cells.