Received for publication June 9, 2006.
Revised August 15, 2006.
Accepted for publication August 15, 2006.

Salvicine Functions as Novel Topoisomerase II poison by Binding to ATP Pocket

Abstract

Salvicine, a structurally modified diterpenoid quinone derived from Salvia prionitis, is a non-intercalative topoisomerase II (topo II) poison. The compound possesses potent in vitro and in vivo antitumor activity with a broad spectrum of anti-multidrug resistance activity and is currently in Phase II clinical trials. To elucidate the distinct antitumor properties of salvicine and obtain valuable structural information of salvicine-topo II interactions, we characterized the effects of salvicine on human topoisomerase II (htopo II), the possible binding sites and molecular interactions. The enzymatic assays disclosed that salvicine mainly inhibits the catalytic activity with weak DNA cleavage action, in contrast to the classical topo II poison, VP16. Molecular modeling studies predicted that salvicine binds to the ATP pocket in the ATPase domain, and superimposes on the phosphate and ribose groups. In an SPR binding assay, salvicine exhibited higher affinity for the ATPase domain of htopo II than ATP and ADP. Competitive inhibition tests demonstrated that ATP competitively and dose-dependently blocked the interactions between salvicine and ATPase domain of htopo II. The data illustrate that salvicine shares a common binding site with ATP, and functions as an ATP competitor. To our knowledge, this is the first report to identify an ATP-binding pocket as the structural binding motif for a non-intercalative eukaryotic topo II poison. These findings collectively support the potential value of an ATP competitor of htopo II in tumor chemotherapy.

Key words: Structure-activity relationships and modeling, Topoisomerases

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