Cyclostreptin (FR182877), an Antitumor Tubulin-Polymerizing Agent Deficient in Enhancing Tubulin Assembly Despite Its High Affinity for the Taxoid Site

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• 作者：Michael C. Edler ; Rub&eacute ; n M. Buey ; Rick Gussio ; Adam I. Marcus ; Christopher D. Vanderwal ; Erik J. Sorensen ; J. Fernando Dí ; az ; Paraskevi Giannakakou ; and Ernest Hamel
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：August 30, 2005
• 年：2005
• 卷：44
• 期：34
• 页码：11525 - 11538
• 全文大小：669K
• 年卷期：v.44,no.34(August 30, 2005)
• ISSN：1520-4995

文摘

Cyclostreptin (FR182877), a bacterial natural product, was reported to have weak paclitaxel-like activity with tubulin but antitumor activity in vivo. We used synthetic cyclostreptin in studies of itsmechanism of action. Although less potent than paclitaxel in several human cancer cell lines, cyclostreptinwas active against cells resistant to paclitaxel and epothilone A. At equitoxic concentrations with paclitaxel,cyclostreptin was more effective in arresting MCF-7 cells in mitosis and equivalent in bundling microtubulesin PtK₂ cells. Tubulin assembly with paclitaxel occurs at low temperatures and in the absence of GTP ormicrotubule-associated proteins (MAPs). Brisk assembly with cyclostreptin required MAPs, GTP, andhigher reaction temperatures. On the basis of turbidimetry, cyclostreptin-induced microtubules were morestable in the cold than the paclitaxel-induced polymer. Moreover, at 37 s/entities/deg.gif">C cyclostreptin was a strongcompetitive inhibitor of the binding of radiolabeled paclitaxel to tubulin polymer, with an apparent K_ivalue of 88 nM. Competition studies versus a fluorescent taxoid across a temperature range, in comparisonwith paclitaxel and docetaxel, showed that only the binding of cyclostreptin to microtubules was markedlyreduced at 4 s/entities/deg.gif">C versus temperatures over 30 s/entities/deg.gif">C. The binding of cyclostreptin to microtubules wascharacterized by a relatively greater endothermic and entropic profile as compared with those of the taxoidbinding reactions, which are characterized more by exothermic and enthalpic interactions. Molecularmodeling showed that cyclostreptin formed a pharmacophore with taxoids but formed hydrogen bondsonly with the S9-S10 and M loops in the taxoid site. Initial studies also indicate that, relative to paclitaxel,cyclostreptin is more deficient in nucleation than elongation of polymer.