Abstract
Salvicine, a structurally modified diterpenoid quinone derived from Salvia prionitis, is a nonintercalative 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 topo IIα (htopo IIα), including 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 classic topo II poison etoposide (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 a surface plasmon resonance binding assay, salvicine exhibited higher affinity for the ATPase domain of htopo IIα than ATP and ADP. Competitive inhibition tests demonstrated that ATP competitively and dose-dependently blocked the interactions between salvicine and ATPase domain of htopo IIα. 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 nonintercalative eukaryotic topo II poison. These findings collectively support the potential value of an ATP competitor of htopo IIα in tumor chemotherapy.
Footnotes
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This work was supported by grants from the National Natural Science Foundation of China (NSFC) (30330670), the Chinese Academy of Sciences (KSCX2-SW-202), and the Ministry of Science and Technology of China (2002AA2Z346A).
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ABBREVIATIONS: htopo IIα, human topoisomerase IIα; topo II, topoisomerase II; MDR, multidrug resistance; ICRF-187, dextrazoxan; SPR, surface plasmon resonance; DMSO, dimethyl sulfoxide; kDNA, kinetoplast DNA; TAE, Tris-acetate/EDTA; HsATPase, human topoisomerase IIα ATPase domain; ADPNP, 5′-adenylyl β,γ-imidodiphosphate; ICRF-193, 4-[(2R,3S)-3-(3,5-dioxopiperazin-1-yl)butan-2-yl]piperazine-2,6-dione.
- Received June 8, 2006.
- Accepted August 15, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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