Microtubule-Targeting Agents: Strategies To Hijack the Cytoskeleton

Structural biology has allowed the identification and detailed characterization of six distinct ligand-binding sites on tubulin. Two sites are targeted by microtubule-stabilizing agents (MSAs); four sites are targeted by microtubule-destabilizing agents (MDAs). MSAs stabilize microtubules by strengthening lateral and/or longitudinal tubulin contacts in microtubules. MDAs destabilize microtubules by either inhibiting the formation of native tubulin contacts or by hindering the curved-to-straight conformational change of tubulin accompanying microtubule formation. Different types of anticancer agents that were initially developed against kinases were found to bind also to tubulin as an off-target. Microtubule-targeting agents (MTAs) such as paclitaxel and the vinca alkaloids are among the most important medical weapons available to combat cancer. MTAs interfere with intracellular transport, inhibit eukaryotic cell proliferation, and promote cell death by suppressing microtubule dynamics. Recent advances in the structural analysis of MTAs have enabled the extensive characterization of their interactions with microtubules and their building block tubulin. We review here our current knowledge on the molecular mechanisms used by MTAs to hijack the microtubule cytoskeleton, and discuss dual inhibitors that target both kinases and microtubules. We further formulate some outstanding questions related to MTA structural biology and present possible routes for future investigations of this fascinating class of antimitotic agents. Microtubule-targeting agents (MTAs) such as paclitaxel and the vinca alkaloids are among the most important medical weapons available to combat cancer. MTAs interfere with intracellular transport, inhibit eukaryotic cell proliferation, and promote cell death by suppressing microtubule dynamics. Recent advances in the structural analysis of MTAs have enabled the extensive characterization of their interactions with microtubules and their building block tubulin. We review here our current knowledge on the molecular mechanisms used by MTAs to hijack the microtubule cytoskeleton, and discuss dual inhibitors that target both kinases and microtubules. We further formulate some outstanding questions related to MTA structural biology and present possible routes for future investigations of this fascinating class of antimitotic agents. a biochemical process leading to cell death. the process by which proteins transmit the effect of binding at one site to another, often distal, site. complex molecules composed of an antibody linked to a cytotoxic agent, which are used in targeted anticancer therapy. transmission EM carried out at cryogenic temperatures. The method allows the structural analysis of vitrified macromolecules at high resolution. a complex network of interlinked protein filaments that extend throughout the cytoplasm of a cell, from the nucleus to the plasma membrane. switching behavior between growth and shrinkage of microtubules. a discontinuity in the helical lattice of some microtubules where an α-tubulin subunit from one protofilament contacts a β-tubulin subunit of the neighboring protofilament. the slow-growing end of a microtubule exposing α-tubulin subunits. microtubule-based cytoskeletal structure of eukaryotic cells that forms during mitosis to separate and distribute sister chromatids equally between daughter cells. the phase of the cell cycle when replicated chromosomes are distributed between daughter cells. enzymes that catalyze the transfer of phosphate groups from ATP to a specific substrate. the fast-growing end of a microtubule exposing β-tubulin subunits. an extremely powerful source of X-rays that are produced by high-energy electrons as they move along a circular path. method to determine the atomic structure of macromolecules in a crystal. The atoms in the crystal cause a beam of incident X-rays to diffract in many specific directions, and this can be exploited to produce a 3D picture of the density of electrons of the macromolecules within the crystal. ultra-high-energy X-ray laser consisting of ultra-high-speed electrons moving freely through a magnetic structure. The methods can be used to perform, for example, time-resolved crystallography experiments.