The efficacy of BAY 57–1293, a novel non-nucleosidic inhibitor of herpes simplex virus 1 and 2 (HSV-1 and HSV-2), bovine herpesvirus and pseudorabies virus, was studied in the guinea pig model of genital herpes in comparison with the licensed drug valaciclovir (Valtrex™). Early therapy with BAY 57–1293 almost completely suppressed the symptoms of acute HSV-2 infection, and reduced virus shedding and viral load in the sacral dorsal root ganglia by up to three orders of magnitude, resulting in decreased latency and a greatly diminished frequency of subsequent recurrent episodes. In contrast, valaciclovir showed only moderate effects in this set of experiments. When treatment was initiated late during the course of disease after symptoms were apparent, that is, a setting closer to most clinical situations, the efficacy of therapy with BAY 57–1293 was even more pronounced. Compared with valaciclovir, BAY 57–1293 halved the time necessary for complete healing. Moreover, the onset of action was fast, so that only very few animals developed new lesions after treatment commenced. Finally, in a study addressing the treatment of recurrent disease in animals whose primary infection had remained untreated BAY 57–1293 was efficient in suppressing the episodes. In summary, superior potency and efficacy of BAY 57–1293 over standard treatment with valaciclovir was demonstrated in relevant animal models of human genital herpes disease in terms of abrogating an HSV infection, reducing latency and the frequency of subsequent recurrences. Furthermore, BAY 57–1293 shortens the time to healing even if initiation of therapy is delayed.

The vast majority of the world population is infected with at least one member of the human herpesvirus family. Herpes simplex virus (HSV) infections are the cause of cold sores and genital herpes as well as life-threatening or sight-impairing disease mainly in immunocompromized patients, pregnant women and newborns. Since the milestone development in the late 1970s of acyclovir (Zovirax), a nucleosidic inhibitor of the herpes DNA polymerase, no new non-nucleosidic anti-herpes drugs have been introduced. Here we report new inhibitors of the HSV helicase-primase with potent in vitro anti-herpes activity, a novel mechanism of action, a low resistance rate and superior efficacy against HSV in animal models. BAY 57-1293 (N-[5-(aminosulfonyl)-4-methyl-1,3-thiazol-2-yl]-N-methyl-2-[4- (2-pyridinyl)phenyl]acetamide), a well-tolerated member of this class of compounds, significantly reduces time to healing, prevents rebound of disease after cessation of treatment and, most importantly, reduces frequency and severity of recurrent disease. Thus, this class of drugs has significant potential for the treatment of HSV disease in humans, including those resistant to current medications.

3-Hydroxy-2,2-dimethyl-N-[4([[5-(dimethylamino)-1-naphthyl]sulfonyl]amino)-phenyl]propanamide (BAY 38-4766) is a novel selective nonnucleoside inhibitor of cytomegalovirus (CMV) replication with an excellent safety profile. This compound and structural analogues inhibit neither viral DNA synthesis nor viral transcription and translation. Accumulation of dense bodies and noninfectious enveloped particles coincides with inhibition of both concatemer 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) isolate with 566-fold-decreased drug sensitivity, were selected in vitro. Sequencing 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 combinations of murine homologues of mutant UL56, UL89, and UL104 and analysis of drug susceptibilities clearly demonstrated that mutant ORFs UL89 exon II (M360I) 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 vitro mutant. These findings are consistent with genetic mapping of resistance to TCRB (2,5,6-trichloro-1-beta-D-ribofuranosyl benzimidazole) (P. M. Krosky et al., J. Virol. 72:4721-4728, 1998) and provide further indirect evidence that proteins encoded by UL89 and UL56 function as two subunits of the CMV terminase. While these studies also suggest that the molecular mechanism of BAY 38-4766 is distinct from that of benzimidazole ribonucleosides, they also offer an explanation for the excellent specificity and tolerability of BAY 38-4766, since mammalian DNA does not undergo comparable maturation steps.

For two decades it has been impossible to develop drugs with novel mechanisms of action against herpesviruses, and treatment has been confined largely to the use of inhibitors of viral DNA polymerase. As a representative of a novel inhibitory approach, the non-nucleosidic BAY 38-4766 was identified as a highly selective inhibitor of human cytomegalovirus (HCMV). The compound selectively inhibits not only HCMV strains, including ganciclovir-resistant, ganciclovir/foscarnet and ganciclovir/cidofovir double-resistant clinical isolates, but also a number of monkey and rodent cytomegaloviruses. In a murine cytomegalovirus (MCMV) pathogenicity model in mice, antiviral efficacy and excellent tolerability were demonstrated. BAY 38-4766-resistant HCMV and MCMV strains are not cross-resistant to the nucleoside analogues ganciclovir and cidofovir or the pyrophosphate analogue foscarnet, indicating a different mode of action. Mechanistic studies demonstrated that the high selectivity of this drug class is most likely due to the inhibition of a late stage of the viral replication cycle. Sequence analyses of resistant HCMV and MCMV strains revealed mutations in UL89 and UL104, proteins known to be involved in viral DNA cleavage and packaging. Consequently, the drug is highly specific for the viral as opposed to cellular functions, since UL89 is related to a bacteriophage terminase and no human equivalent exists. In addition, because some of the genes of the viral DNA cleavage and packaging complex are highly conserved among herpesviruses, development of broad-spectrum agents covering additional human herpesviruses might be possible using this approach.

Novel non-nucleosidic compounds have recently been identified as potent inhibitors of the human cytomegalovirus (HCMV) and murine cytomegalovirus (MCMV) in vitro. We have now investigated the antiviral activity of these compounds in MCMV-infected NOD/LtSz-scid/j mice that lack functional T, B and, in contrast to C.B-17/Icr scid/scid mice, natural killer cells, and represent a novel model for cytomegalovirus infection in immunocompromised hosts. BAY 38-4766 (3-hydroxy-2,2-dimethyl-N-[4({[5-(dimethylamino)-1-naphthyl]sulfonyl}amino)-phenyl]propanamide) was identified as the most potent representative of this class of antiviral compounds. Per os administration of BAY 38-4766 at dosages ≥10 mg/kg body weight led to antiviral effects that were comparable to ganciclovir 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (Cymevene®) as measured by survival and levels of viral DNA in organs of infected mice. In order to assess the anti-HCMV activity of BAY 38-4766 in vivo, we used a model, in which HCMV-infected human cells were entrapped in hollow fibers and subsequently transplanted into immunodeficient mice. Using this model, we demonstrated antiviral activity of BAY 38-4766 similar to that of ganciclovir. We conclude that BAY 38-4766 shows potential as an anti-HCMV drug.