Peloruside A does not bind to the taxoid site on β-tubulin and retains its activity in multidrug-resistant cell lines

Peloruside A (peloruside), a microtubule-stabilizing agent from a marine sponge, is less susceptible than paclitaxel to multidrug res stance arising from overexpression of the P-glycoprotein efflux pump an is not affected by mutations that affect the taxoid binding site of beta-tubulin. In vitro studies with purified tubulin indicate that peloruside directly induces tubulin polymerization in the absence of microtubule-associated proteins. Competition for binding between peloruside, paclitaxel, and laulimalide revealed that peloruside binds to a different site on tubulin to paclitaxel. Moreover, laulimalide was able to displace peloruside, indicating that peloruside and laulimalide may compete for the same or overlapping binding sites. It was concluded that peloruside and laulimalide have binding properties that are distinct from other microtubule-stabilizing compounds currently under investigation.