-NH-Dansyl Isocolchicine Exhibits a Significantly Improved Tubulin-Binding Affinity and Microtubule Inhibition in Comparison to Isocolchicine by Binding Tubulin through Its A and B Rings

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• 作者：Lalita Das ; Ajit B. Datta ; Suvroma Gupta ; Asim Poddar ; Suparna Sengupta ; Mark E. Janik ; and Bhabatarak Bhattacharyya
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：March 8, 2005
• 年：2005
• 卷：44
• 期：9
• 页码：3249 - 3258
• 全文大小：435K
• 年卷期：v.44,no.9(March 8, 2005)
• ISSN：1520-4995

文摘

Structure-activity relationship studies have established that the A and C rings of colchicinecomprise the minimum structural feature necessary for high affinity drug-tubulin binding. Thus, colchicineacts as a bifunctional ligand by making two points of attachment to the protein. Furthermore, analoguesbelonging to the iso series of colchicine are virtually inactive in binding to tubulin and inhibiting microtubuleassembly. In the present study, we found that the substitution of a hydrophobic dansyl group on theB-ring side chain (C7 position) of isocolchicine reverses the structural alterations at the C ring and thenewly synthesized -NH-dansyl isocolchicine restores the lost biological activity of the compound. It inhibitsmicrotubule assembly efficiently with an IC₅₀ value of 10 es/entities/mgr.gif">M and competes with [³H]colchicine forbinding to tubulin. Moreover, although -NH-dansyl colchicine binding to tubulin involves two steps, the-NH-dansyl isocolchicine-tubulin interaction has been found to occur via a one-step process. Also, theaffinity constant of the -NH-dansyl isocolchicine-tubulin interaction is roughly only 3 times lower thanthat of the -NH-dansyl colchicine-tubulin interaction. These results suggest that the enhanced microtubuleinhibitory ability of -NH-dansyl isocolchicine is therefore related to the affinity of the drug-tubulininteraction and not to any conformational changes upon binding tubulin. We also observed that thecompetition of -NH-dansyl isocolchicine with [³H]colchicine for binding to tubulin was dependent on thetubulin concentration. In conclusion, this paper for the first time indicates that a biologically activebifuntional colchicine analogue can be designed where the drug binds tubulin through its A and B rings,while the C ring remains inactive.