Microtubule-stabilizing agents based on designed laulimalide analogues

Laulimalide is a potent, structurally unique microtubule-stabilizing agent originally isolated from the marine sponge Cacospongia mycofijiensis. Laulimalide exhibits an activity profile different from other microtubule-binding agents, notably including effectiveness against paclitaxel-resistant cells, but it is intrinsically unstable. Five analogues of laulimalide were designed to exhibit enhanced chemical stability yet retain its exceptional biological activities. Evaluations of these analogues showed that all are effective inhibitors of cancer-cell proliferation yet differ substantially in potency with an IC50 range of 0.12-16.5 muM. Although all of the analogues initiated cellular changes similar to laulimalide, including increased density of interphase microtubules, aberrant mitotic spindles, and ultimately apoptosis, differences among the analogues were apparent. The two most potent analogues, C-16-C-I7-des-epoxy laulimalide and C-20-methoxy laulimalide, appear to have a mechanism of action identical to laulimalide. The C-16-C-17-des-epoxy, C-20-methoxy laulimalide derivative, which incorporates both chemical changes of the most potent analogues, was significantly less potent and initiated the formation of unique interphase microtubules unlike the parent compound and other analogues. Two C-2-C-3-alkynoate derivatives had lower potency, and they initiated abnormal microtubule structures but did not cause micronucleation or extensive G(2)/M accumulation. Significantly, paclitaxel- and epothilone-resistant cell lines were less resistant to the laulimalide analogues. In summary, analogues of laulimalide designed to minimize or eliminate its intrinsic instability have been synthesized, and some have been found to retain the unique biological activities of laulimalide.