Antiproliferative mechanism of action of cryptophycin-52: kinetic stabilization of microtubule dynamics by high-affinity binding to microtubule ends.
Cryptophycin-52 (LY355703) is a new synthetic member of the cryptophycin family of antimitotic antitumor agents that is currently undergoing clinical evaluation. At high concentrations (>/=10 times the IC50), cryptophycin-52 blocked HeLa cell proliferation at mitosis by depolymerizing spindle microtubules and disrupting chromosome organization. However, low concentrations of cryptophycin-52 inhibited cell proliferation at mitosis (IC50 = 11 pM) without significantly altering spindle microtubule mass or organization. Cryptophycin-52 appears to be the most potent suppressor of microtubule dynamics found thus far. It suppressed the dynamic instability behavior of individual microtubules in vitro (IC50 = 20 nM), reducing the rate and extent of shortening and growing without significantly reducing polymer mass or mean microtubule length. Using [3H]cryptophycin-52, we found that the compound bound to microtubule ends in vitro with high affinity (Kd, 47 nM, maximum of approximately 19.5 cryptophycin-52 molecules per microtubule). By analyzing the effects of cryptophycin-52 on dynamics in relation to its binding to microtubules, we determined that approximately 5-6 molecules of cryptophycin-52 bound to a microtubule were sufficient to decrease dynamicity by 50%. Cryptophycin-52 became concentrated in cells 730-fold, and the resulting intracellular cryptophycin-52 concentration was similar to that required to stabilize microtubule dynamics in vitro. The data suggest that cryptophycin-52 potently perturbs kinetic events at microtubule ends that are required for microtubule function during mitosis and that it acts by forming a reversible cryptophycin-52-tubulin stabilizing cap at microtubule ends.
Department of Molecular Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, CA 93106, USA.
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D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001704:Biopolymers; D002455:Cell Division / Q000187:drug effects*; D047630:Depsipeptides; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D007769:Lactams / Q000494:pharmacology*; D007783:Lactones / Q000494:pharmacology*; D008870:Microtubules / Q000187:drug effects* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000494:pharmacology*
D000970:Antineoplastic Agents; D001704:Biopolymers; D047630:Depsipeptides; D007769:Lactams; D007783:Lactones; D010456:Peptides, Cyclic; C088419:cryptophycin; C114033:cryptophycin 52