The microtubule stabilizing agent laulimalide does not bind in the taxoid site, kills cells resistant to paclitaxel and epothilones, and may not require its epoxide moiety for activity.
Laulimalide is a cytotoxic natural product that stabilizes microtubules. The compound enhances tubulin assembly, and laulimalide is quantitatively comparable to paclitaxel in its effects on the reaction. Laulimalide is also active in P-glycoprotein overexpressing cells, while isolaulimalide, a congener without the drug's epoxide moiety, was reported to have negligible cytotoxic and biochemical activity [Mooberry et al. (1999) Cancer Res. 59, 653-660]. We report here that laulimalide binds at a site on tubulin polymer that is distinct from the taxoid site. We found that laulimalide, while as active as paclitaxel, epothilone A, and eleutherobin in promoting the assembly of cold-stable microtubules, was unable to inhibit the binding of radiolabeled paclitaxel or of 7-O-[N-(2,7-difluoro-4'-fluoresceincarbonyl)-L-alanyl]paclitaxel, a fluorescent paclitaxel derivative, to tubulin. Confirming this observation, we demonstrated that microtubules formed in the presence of both laulimalide and paclitaxel contained near-molar quantities, relative to tubulin, of both drugs. Laulimalide was active against cell lines resistant to paclitaxel or epothilones A and B on the basis of mutations in the M40 human beta-tubulin gene. We also report that a laulimalide analogue lacking the epoxide moiety, while less active than laulimalide in biochemical and cellular systems, is probably more active than isolaulimalide. Further exploration of the role of the epoxide in the interaction of laulimalide with tubulin is therefore justified.
Pryor
Donald E
DE
Screening Technologies Branch, Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute at Frederick, National Institutes of Health, Frederick, Maryland 21702, USA.
O'Brate
Aurora
A
Bilcer
Geoffrey
G
Díaz
J Fernando
JF
Wang
Yuefang
Y
Wang
Yong
Y
Kabaki
Mikio
M
Jung
M Katherine
MK
Andreu
José M
JM
Ghosh
Arun K
AK
Giannakakou
Paraskevi
P
Hamel
Ernest
E
D001665:Binding Sites; D019008:Drug Resistance, Neoplasm; D004852:Epoxy Compounds / Q000494:pharmacology*; D005454:Fluorescence Polarization; D018942:Macrolides; D008870:Microtubules / Q000187:drug effects* / Q000378:metabolism; D008958:Models, Molecular; D017239:Paclitaxel / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D043823:Taxoids; D014316:Tritium
D004852:Epoxy Compounds; D018942:Macrolides; D043823:Taxoids; C117305:laulimalide; D014316:Tritium; D017239:Paclitaxel