Pladienolide B is the major analogue of a family of macrocyclic lactones isolated from Streptomyces platensis by researchers at Eisai Corp. Japan in 2004. Pladienolide B is a highly potent inhibitor of both hypoxia induced VEGF expression and cancer cell proliferation. Pladienolide B binds to SF3b complex blocking the spliceosome and is an important bioprobe for our understanding of the spiceosome, a highly selective target for next generation antitumor agents.