Preclinical discovery of ixabepilone, a highly active antineoplastic agent

Cancer Chemother Pharmacol. 2008 Dec;63(1):157-66. doi: 10.1007/s00280-008-0724-8. Epub 2008 Mar 18.


The epothilones and their analogs constitute a novel class of antineoplastic agents, produced by the myxobacterium Sorangium cellulosum. These antimicrotubule agents act in a similar manner to taxanes, stabilizing microtubules and resulting in arrested tumor cell division and apoptosis. Unlike taxanes, however, epothilones and their analogs are macrolide antibiotics, with a distinct tubulin binding mode and reduced susceptibility to a range of common tumor resistance mechanisms that limit the effectiveness of taxanes and anthracyclines. While natural epothilones A and B show potent antineoplastic activity in vitro, these effects were not seen in preclinical in vivo models due to their poor metabolic stability and unfavorable pharmacokinetics. A range of epothilone analogs was synthesized, therefore, with the aim of identifying those with more favorable characteristics. Here, we describe the preclinical characterization and selection of ixabepilone, a semi-synthetic epothilone B analog, among many other epothilone analogs. Ixabepilone demonstrated superior preclinical characteristics, including high metabolic stability, low plasma protein binding and low susceptibility to multidrug resistance protein-mediated efflux, all of which were predictive of potent in vivo cell-killing activity. Ixabepilone also demonstrated in vivo antitumor activity in a range of human tumor models, several of which displayed resistance to commonly used agents such as anthracyclines and taxanes. These favorable preclinical characteristics have since translated to the clinic. Ixabepilone has shown promising phase II clinical efficacy and acceptable tolerability in a wide range of cancers, including heavily pretreated and drug-resistant tumors. Based on these results, a randomized phase III trial was conducted in anthracycline-pretreated or resistant and taxane-resistant metastatic breast cancer to evaluate ixabepilone in combination with capecitabine. Ixabepilone combination therapy showed significantly superior progression-free survival and tumor responses over capecitabine alone.

Publication types

  • Review

MeSH terms

  • Animals
  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents / therapeutic use*
  • Blood Proteins / metabolism
  • Cell Line, Tumor / drug effects
  • Clinical Trials as Topic
  • Drug Resistance, Neoplasm
  • Drug Screening Assays, Antitumor
  • Epothilones / chemical synthesis
  • Epothilones / chemistry
  • Epothilones / pharmacology
  • Epothilones / therapeutic use*
  • Female
  • Humans
  • Male
  • Mice
  • Neoplasms / drug therapy
  • Protein Binding
  • Taxoids / pharmacology
  • Tubulin / drug effects
  • Tubulin Modulators / pharmacology
  • Tubulin Modulators / therapeutic use
  • Xenograft Model Antitumor Assays


  • Antineoplastic Agents
  • Blood Proteins
  • Epothilones
  • Taxoids
  • Tubulin
  • Tubulin Modulators
  • ixabepilone