Indolocarbazoles exhibit strong antiviral activity against human cytomegalovirus and are potent inhibitors of the pUL97 protein kinase

We have analyzed a panel of protein kinase inhibitors (PKIs) and found that some indolocarbazoles (Go6976, K252a, K252c) proved to be highly effective inhibitors of GCV-sensitive and -resistant human cytomegalovirus (HCMV) st rains, but did not show any effect against herpes simplex virus. Antiviral activity was determined by focus reduction assays (IC50 ranging from 0.009 to 0.4 muM). Other inhibitors of serine/threonine kinases (Go6850, H-7, ros covitine) were found to be ineffective. Virus yield at 5 days after infecti on was reduced by three orders of magnitude with nanomolar concentrations o f the indolocarbazoles. These compounds were fully effective when added up to 24 h post infection and showed reduced activity up to 72 h post infectio n. Cytotoxicity assays in proliferating and non-proliferating cells demonst rated that the effective antiviral concentration of these compounds was sig nificantly lower than either antiproliferative (IC50/CC50 ranging from 6.5 to 390) or cytotoxic (IC50/CC50 ranging from 72.5 to 1000) doses. The effec ts of PKIs on the virus-encoded protein kinase pUL97 were studied using rec ombinant vaccinia viruses. Indolocarbazoles strongly inhibited both pUL97 a utophosphorylation (IC50 ranging from 0.0012 to 0.013 muM) and pUL97-depend ent ganciclovir phosphorylation (IC50 ranging from 0.05 to 0.26 muM). Other inhibitors of serine/threonine kinases showed only weak (Go6850) or no (H- 7, roscovitine) effect on these pUL97 functions, while oxoflavone tyrosine kinase inhibitors had no effect at all. (C) 2000 Elsevier Science B.V. All rights reserved.