An orally active diketopiperazine derivative with potential antineoplastic activity. Plinabulin selectively binds to the colchicine-binding site of tubulin, thereby interrupting equilibrium of microtubule dynamics; mitotic spindle assembly is disrupted, resulting in cell cycle arrest at the M phase and blockage of cell division in tumor cells. In addition, this agent induces tubulin depolymerization in vascular endothelial cells, resulting in the disruption of tumor blood vessel architecture and a selective collapse of tumor vasculature. or A cyclic depsipeptide isolated from the marine tunicate Aplidium albicans. Plitidepsin displays a broad spectrum of antitumor activities, inducing apoptosis by triggering mitochondrial cytochrome c release, initiating the Fas/DC95, JNK pathway and activating caspase 3 activation. This agent also inhibits elongation factor 1-a, thereby interfering with protein synthesis, and induces G1 arrest and G2 blockade, thereby inhibiting tumor cell growth.