Synergistic effects of peloruside A and laulimalide with taxoid site drugs, but not with each other, on tubulin assembly.
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. Because peloruside A thus far seems 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 17beta-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 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 analogs of laulimalide.
Hamel
Ernest
E
Toxicology and Pharmacology Branch, Developmental Threapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute at Frederick, MD 21702, USA. hamele@mail.nih.gov
Day
Billy W
BW
Miller
John H
JH
Jung
M Katherine
MK
Northcote
Peter T
PT
Ghosh
Arun K
AK
Curran
Dennis P
DP
Cushman
Mark
M
Nicolaou
K C
KC
Paterson
Ian
I
Sorensen
Erik J
EJ
D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry / Q000494:pharmacology*; D004357:Drug Synergism; D018698:Glutamic Acid / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007783:Lactones / Q000737:chemistry / Q000494:pharmacology*; D018942:Macrolides; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008958:Models, Molecular; D017239:Paclitaxel / Q000494:pharmacology; D043823:Taxoids / Q000737:chemistry / Q000494:pharmacology*; D013696:Temperature; D014404:Tubulin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D019086:Bridged Bicyclo Compounds, Heterocyclic; D007783:Lactones; D018942:Macrolides; D008869:Microtubule-Associated Proteins; D043823:Taxoids; D014404:Tubulin; C117305:laulimalide; C414085:peloruside A; D018698:Glutamic Acid; D006160:Guanosine Triphosphate; D017239:Paclitaxel