PD0084430: a non-nucleoside inhibitor of human cytomegalovirus replication in vitro

Abstract

Human cytomegalovirus (HCMV) is a major opportunistic pathogen in immunocompromised individuals. Current therapies target viral DNA replication and accumulate mutations that yield cross-resistance among the approved drugs. A novel, non-nucleoside inhibitor of HCMV replication, PD0084430, was identified in a screening assay using the HCMV β-galactosidase recombinant RC256. The EC 50 for PD0084430 by inhibition of β-galactosidase production is 1±0.7 μM. This antiviral activity was confirmed by yield reduction and plaque reduction assays using HCMV strain AD169. The TC 50 of PD0084430 as measured by 14C-thymidine incorporation is ∼30 μM and by XTT is ∼90 μM. The TC 50 for inhibition of cellular proliferation is ∼20 μM. Time of addition experiments displayed a similar drop in efficacy for both PD0084430 and GCV when added after the onset of viral DNA replication. The transcomplementation assay for viral DNA replication, using a transfected ori Lyt containing plasmid, confirmed that viral DNA synthesis was inhibited at the same concentrations that showed antiviral activity. Western blots showed no apparent block of immediate early or early gene expression. Two ganciclovir (GCV) resistant isolates of HCMV tested showed no cross-resistance to PD0084430. These data suggested a potentially promising novel compound that inhibited HCMV at or before viral DNA replication. However, in vivo testing in mice dosed either orally or intraperitoneally showed rapid glucuronidation on the –OH group. SAR studies on this backbone showed that the –OH group was essential for the antiviral activity in vitro.