- Eribulin mesylate (E7389) is a synthetic analog of Halichondrin B (HalB), a large polyether macrolide isolated from a marine sponge. Eribulin is a mechanistically unique antagonist of microtubule dynamics among tubulin-targeted agents, leading to inhibition of microtubule growth in the absence of effects on microtubule shortening, and formation of non- productive tubulin aggregates.