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First published on August 3, 2006; DOI: 10.1124/mol.106.027847

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Received for publication June 14, 2006.
Revised July 31, 2006.
Accepted for publication August 1, 2006.

Synergistic effects of peloruside A and laulimalide with taxoid site drugs, but not with each other, on tubulin assembly

Ernest Hamel 1*, Billy W Day 2, John H Miller 3, M Katherine Jung 4, Peter T Northcote 3, Arun K Ghosh 5, Dennis P Curran 2, Mark Cushman 5, K C Nicolaou 6, Ian Paterson 7, Erik J Sorensen 8

1 National Cancer Institute 2 University of Pittsburgh 3 Victoria University of Wellington 4 SAIC-Frederick Inc. 5 Purdue University 6 Scripps Research Institute 7 University of Cambridge 8 Princeton University

* Address correspondence to: E-mail: hamele{at}mail.nih.gov

Abstract

Previous studies on the drug content of pelleted tubulin polymers suggest that peloruside A binds in the laulimalide site, which is distinct from the taxoid site. In a tubulin assembly system containing microtubule-associated proteins and GTP, however, peloruside A was significantly less active than laulimalide, inducing assembly in a manner that was most similar to sarcodictyins A and B. Since peloruside A thus far appears to be the only compound that mimics the action of laulimalide, we examined combinations of microtubule-stabilizing agents for synergistic effects on tubulin assembly. We found that peloruside A and laulimalide showed no synergism but that both compounds could act synergistically with a number of taxoid site agents (paclitaxel, epothilones A/B, discodermolide, dictyostatin, eleutherobin, the steroid derivative 17{beta}-acetoxy-2-ethoxy-6-oxo-B-homo-estra-1,3,5(10)-trien-3-ol, and cyclostreptin). None of the taxoid site compounds showed any synergism with each other. From an initial study with peloruside A and cyclostreptin, we conclude that the synergism phenomenon derives, at least in part, from an apparent lowering of the tubulin critical concentration with drug combinations as compared with single drugs. The apparent binding of peloruside A in the laulimalide site led us to attempt construction of a pharmacophore model based on superposition of an energy-minimized structure of peloruside A on the crystal structure of laulimalide. Although the different sizes of the macrocycles limited our ability to superimpose the two molecules, atom correspondences that were observed were consistent with the difficulty so far experienced in creation of fully active analogues of laulimalide.


Key words: Structure-activity relationships and modeling, Structure/function/mechanism, Cytoskeletal targets


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Home page
 Clin. Cancer Res.Home page
P. G. Morris and M. N. Fornier
Microtubule Active Agents: Beyond the Taxane Frontier
Clin. Cancer Res., November 15, 2008; 14(22): 7167 - 7172.
[Abstract] [Full Text] [PDF]


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