Structure-Activity Analysis of the Interaction of Curacin A, the Potent Colchicine Site Antimitotic Agent, with Tubulin and Effects of Analogs on the Growth of MCF-7 Breast Cancer Cells

Abstract

Originally purified as a major lipid component of a strain of the cyanobacterium Lyngbya majuscula isolated in Curaçao, curacin A is a potent inhibitor of cell growth and mitosis, binding rapidly and tightly at the colchicine site of tubulin. Because its molecular structure differs so greatly from that of colchicine and other colchicine site inhibitors, we prepared a series of curacin A analogs to determine the important structural features of the molecule. These modifications include reduction and E-to-Z transitions of the olefinic bonds in the 14-carbon side chain of the molecule; disruption of and configurational changes in the cyclopropyl moiety; disruption, oxidation, and configurational reversal in the thiazoline moiety; configurational reversal and substituent modifications at C13; and demethylation at C10. Inhibitory effects on tubulin assembly, the binding of colchicine to tubulin, and the growth of MCF-7 human breast carcinoma cells were examined. The most important portions of curacin A required for its interaction with tubulin seem to be the thiazoline ring and the side chain at least through C4, the portion of the side chain including the C9-C10 olefinic bond, and the C10 methyl group. Only two modifications totally eliminated the tubulin-drug interaction. The inactive compounds were a segment containing most of the side chain, including its two substituents, and analogs in which the methyl group at the C13 oxygen atom was replaced by a benzoate residue. Antiproliferative activity comparable with that observed with curacin A was only reproduced in compounds that were potent inhibitors of the binding of colchicine to tubulin. Molecular modeling and quantitative structure-activity relationship studies demonstrated that most active analogs overlapped extensively with curacin A but failed to provide an explanation for the apparent structural analogy between curacin A and colchicine.

Development of two novel benzoylphenylurea sulfur analogues and evidence that the microtubule-associated protein tau is predictive of their activity in pancreatic cancer

“…Binding Studies Tubulin assays with SG410 and SG430 were done as previously described (20,21). Briefly, tubulin polymerization was followed turbidimetrically at 350 nm in Beckman model DU7400 and DU7500 recording spectrophotometers equipped with electronic temperature controllers.…”

Docking and hydropathic scoring of polysubstituted pyrrole compounds with antitubulin activity

“…In contrast, paclitaxel and its analogues actually promote microtubule polymer formation [3][4][5], albeit by acting at a different site on tubulin than colchicine. A variety of small molecules with diverse molecular scaffolds have been shown to bind tubulin at the colchicine site [6][7][8][9]. One class of these compounds receiving particular attention has been that based on the natural product combretastatin A-4 discovered by Pettit [10,11].…”

Terminal Alkene Formation by the Thioesterase of Curacin A Biosynthesis

“…Curacin A, from the marine cyanobacterium Lyngbya majuscula, is a mixed polyketide/non-ribosomal peptide with antimitotic properties (3). The hybrid PKS/NRPS assembly line pathway for curacin A (4) generates several unusual chemical groups in addition to the terminal alkene, including a cyclopropyl ring, a thiazoline ring, and a cis double bond.…”

“…Gene clusters encoding assembly line biosynthetic pathways for polyketide and polypeptide natural products are ubiquitous in bacterial and fungal genomes. Polyketide synthase (PKS) 3 and non-ribosomal peptide synthetase (NRPS) pathways have a common modular organization in which intermediates tethered to carrier domains by a thioester linkage pass sequentially through modules of the assembly line. The final step in the assembly line is typically a thioesterasecatalyzed off-loading from the final carrier domain to produce a carboxylate, macrolactone, or cyclic peptide.…”