Making Epothilones Fluoresce: Design, Synthesis, and Biological Characterization of a Fluorescent N12-Aza-Epothilone (Azathilone)

✍ Scribed by Jürg Gertsch ; Fabian Feyen ; Alexander Bützberger; Barbara Gerber; Bernhard Pfeiffer; Karl-Heinz Altmann

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 907 KB
• Volume: 10
• Category: Article
• ISSN: 1439-4227
• DOI: 10.1002/cbic.200900376

✦ Synopsis

Abstract

A green fluorescent 12‐aza‐epothilone (azathilone) derivative has been prepared through the attachment of the 4‐nitro‐2,1,3‐benzoxadiazole (NBD) fluorophore to the 12‐nitrogen atom of the azamacrolide core structure. While less potent than natural epothilones or different N12‐acylated azathilone derivatives, NBD‐azathilone (3) promotes tubulin assembly, inhibits cancer cell proliferation in vitro and arrests the cell cycle at the G2/M transition. Most significantly, the binding of 3 to cellular microtubules (MTs) could be directly visualized by confocal fluorescence microscopy. Based on competition binding experiments with laulimalide‐stabilized MTs in vitro, the N12‐Boc substituted azathilone 1, Epo A, and NBD‐azathilone (3) all interact with the same tubulin‐binding site. Computational studies provided a structural model of the complexes between β‐tubulin and 1 or 3, respectively, in which the NBD moiety of 3 or the BOC moiety of 1 directly and specifically contribute to MT binding. Collectively, these data demonstrate that the cellular effects of 3 and, by inference, also of other azathilones are the result of their interactions with the cellular MT network.