The lytic DNA replication of Kaposi's sarcoma-associated herpesvirus (KSHV) initiates at an origin (ori-Lyt) and requires trans-acting elements, both viral and cellular. We recently demonstrated that several host cellular
proteins, including topoisomerases I and II (
Topo I and II), are involved in KSHV lytic DNA replication (Y. Wang, H. Li, Q. Tang, G. G. Maul, and Y. Yuan. J. Virol. 82: 2867-2882, 2008). To assess the importance of these topoisomerases in viral lytic replication,
shRNA-mediated gene silencing was used. Depletion of
Topo I and II severely inhibited viral lytic DNA replication as well as virion production, suggesting essential roles of these cellular
proteins in
viral DNA replication. The discovery of
Topo I and II as
enzymes indispensable for KSHV DNA replication raises a possibility that these cellular
proteins could be new targets of therapeutic approaches to halt KSHV replication and treat KSHV-associated diseases. In this report, we examined one
Topo I inhibitor and several
Topo II inhibitors (inclusive of
Topo II
poison and catalytic inhibitors) as potential therapeutic agents for blocking KSHV replication. The
Topo II catalytic inhibitors in general exhibited marked inhibition on KSHV replication and minimal cytotoxicity. In particular,
novobiocin, with the best selectivity index (SI = 31.62) among the inhibitors tested in this study, is effective in inhibiting KSHV DNA replication and virion production but shows little adverse effect on cell proliferation and cycle progression in its therapeutic concentration, suggesting its potential to become an effective and safe
drug for the treatment of human diseases associated with KSHV
infection.