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Dissecting paclitaxel-microtubule association: quantitative assessment of the 2'-OH group.

ABSTRACT: Paclitaxel (PTX) is a microtubule-stabilizing agent that is widely used in cancer chemotherapy. This structurally complex natural product acts by binding to ?-tubulin in assembled microtubules. The 2'-hydroxyl group in the flexible side chain of PTX is an absolute requirement for activity, but its precise role in the drug-receptor interaction has not been specifically investigated. The contribution of the 2'-OH group to the affinity and tubulin-assembly efficacy of PTX has been evaluated through quantitative analysis of PTX derivatives possessing side chain deletions: 2'-deoxy-PTX, N-debenzoyl-2'-deoxy-PTX, and baccatin III. The affinity of 2'-deoxy-PTX for stabilized microtubules was more than 100-fold lower than that of PTX and only ~3-fold greater than the microtubule affinity of baccatin III. No microtubule binding activity was detected for the analogue N-debenzoyl-2'-deoxy-PTX. The tubulin-assembly efficacy of each ligand was consistent with the microtubule binding affinity, as was the trend in cytotoxicities. Molecular dynamics simulations revealed that the 2'-OH group of PTX can form a persistent hydrogen bond with D26 within the microtubule binding site. The absence of this interaction between 2'-deoxy-PTX and the receptor can account for the difference in binding free energy. Computational analyses also provide a possible explanation for why N-debenzoyl-2'-deoxy-PTX is inactive, in spite of the fact that it is essentially a substituted baccatin III. We propose that the hydrogen bonding interaction between the 2'-OH group and D26 is the most important stabilizing interaction that PTX forms with tubulin in the region of the C-13 side chain. We further hypothesize that the substituents at the 3'-position function to orient the 2'-OH group for a productive hydrogen bonding interaction with the protein.

SUBMITTER: Sharma S

PROVIDER: S-EPMC3685414 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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Dissecting paclitaxel-microtubule association: quantitative assessment of the 2'-OH group.

Sharma Shubhada S Lagisetti Chandraiah C Poliks Barbara B Coates Robert M RM Kingston David G I DG Bane Susan S

Biochemistry 20130319 13

Paclitaxel (PTX) is a microtubule-stabilizing agent that is widely used in cancer chemotherapy. This structurally complex natural product acts by binding to β-tubulin in assembled microtubules. The 2'-hydroxyl group in the flexible side chain of PTX is an absolute requirement for activity, but its precise role in the drug-receptor interaction has not been specifically investigated. The contribution of the 2'-OH group to the affinity and tubulin-assembly efficacy of PTX has been evaluated through ...[more]

PMID: 23473345

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Project description:BackgroundTumor promoters enhance tumor yield in experimental animals without directly affecting the DNA of the cell. Promoters may play a role in the development of cancer, as humans are exposed to them in the environment. In work based on computer-assisted microscopy and sophisticated classification methods, we showed that cells could be classified by reference to a database of known normal and cancerous cell phenotypes. Promoters caused loss of properties specific to normal cells and gain of properties of cancer cells. Other compounds, including colchicine, had a similar effect. Colchicine given together with paclitaxel, however, caused cells to adopt properties of normal cells. This provided a rationale for tests of microtubule inhibitor combinations in cancer patients. The combination of a depolymerizing and a stabilizing agent is a superior anti-tumor treatment. The biological basis of the effect is not understood.ResultsA single compound containing both colchicine and paclitaxel structures was synthesized. Colchicine is an alkaloid with a trimethoxyphenyl ring (ring A), a ring with an acetamide linkage (ring B), and a tropolone ring (ring C). Although rings A and C are important for tubulin-binding activity, the acetamide linkage on ring B could be replaced by an amide containing a glutamate linker. Alteration of the C-7 site on paclitaxel similarly had little or no inhibitory effect on its biological activity. The linker was attached to this position. The coupled compound, colchitaxel (1), had some of the same effects on microtubules as the combination of starting compounds. It also caused shortening and fragmentation of the + end protein cap.ConclusionSince microtubule inhibitor combinations give results unlike those obtained with either inhibitor alone, it is important to determine how such combinations affect cell shape and growth. Colchitaxel shows a subset of the effects of the inhibitor combination. Thus, it may be able to bind the relevant cellular target of the combination. It will be useful to determine the basis of the shape reversal effect and possibly, the reasons for therapeutic efficacy of microtubule inhibitor combinations.

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Dissecting paclitaxel-microtubule association: quantitative assessment of the 2'-OH group.

Publications

Dissecting paclitaxel-microtubule association: quantitative assessment of the 2'-OH group.

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