A novel nonnucleoside inhibitor specifically targets cytomegalovirus DNA maturation via the UL89 and UL56 gene products

3-Hydroxy-2,2-dimethyl-N-[4({[5-(dimethylamino)-1-naphthyl]sulfonyl}amino)- phenyl]propanamide (BAY 38-4766) is a novel selective nonnucleoside inhibit or of cytomegalovirus (CMV) replication with an excellent safety profile. T his compound and structural analogues inhibit neither viral DNA synthesis n or viral transcription and translation. Accumulation of dense bodies and no ninfectious enveloped particles coincides with inhibition of both concateme r processing and functional cleavage at intergenomic transitions, pointing to interference with viral DNA maturation and packaging of monomeric genome lengths. Resistant virus populations, including a murine CMV (MCMV) isolat e with 566-fold-decreased drug sensitivity, were selected in vitro. Sequenc ing of the six open reading frames (ORFs) known to be essentially involved in viral DNA cleavage and packaging identified mutations in ORFs UL56, UL89 , and UL104. Construction of MCMV recombinants expressing different combina tions of murine homologues of mutant UL56, UL89, and UL104 and analysis of drug susceptibilities clearly demonstrated that mutant ORFs UL89 exon II (M 360I) and M56 (P202A I208N) individually confer resistance to BAY 38-4766. A combination of both mutant proteins exhibited a strong synergistic effect on resistance, reconstituting the high-resistance phenotype of the in vitr o mutant. These findings are consistent with genetic mapping of resistance to TCRB (2,5,6-trichloro-1-beta -D-ribofuranosyi benzimidazole) (P.M. Krosk y et al., J. Virol. 72:4721-4728, 1998) and provide further indirect eviden ce that proteins encoded by UL89 and UL56 function as two subunits of the C MV terminase. While these studies also suggest that the molecular mechanism of BAY 38-4766 is distinct from that of benzimidazole ribonucleosides, the y also offer an explanation for the excellent specificity and tolerability of BAY 38-4766, since mammalian DNA does not undergo comparable maturation steps.