Identification of C-6 as a New Site for Linker Conjugation to the Taccalonolide Microtubule Stabilizers

J Nat Prod. 2019 Mar 22;82(3):583-588. doi: 10.1021/acs.jnatprod.8b01036. Epub 2019 Feb 25.

Abstract

The taccalonolides are a class of microtubule stabilizers that circumvent clinically relevant forms of drug resistance due to their unique mechanism of microtubule stabilization imparted by the covalent binding of the C-22-C-23 epoxide moiety to tubulin. A taccalonolide (8) with a fluorescein group attached with a linker at C-6 was generated, and biochemical and cell-based assays showed that it bound directly to tubulin and stabilized microtubules. This pharmacological probe has allowed, for the first time, a direct visualization of a taccalonolide binding to microtubules, verifying their cellular binding site. This C-6-modified taccalonolide showed potency comparable to the untagged compound in biochemical experiments; however, its potency was lower in cellular assays, presumably due to decreased cellular permeability. These studies provide a valuable tool to facilitate the further understanding of taccalonolide pharmacology and demonstrate that C-6 is a promising site for a linker to be added to this novel class of microtubule stabilizers for targeted drug delivery.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Proliferation / drug effects
  • HeLa Cells
  • Humans
  • Microtubules / drug effects*
  • Molecular Structure
  • Steroids / chemistry*
  • Steroids / pharmacology*
  • Structure-Activity Relationship
  • Tubulin Modulators / chemistry
  • Tubulin Modulators / pharmacology*

Substances

  • Steroids
  • Tubulin Modulators