Chemical. CAS: 117048-59-6. Formula: C18H20O5. MW: 316.35. Combretastatin A4 is a natural stilbenoid phenol originally isolated from an African shrub, Combretum caffrum. It is a potent inhibitor of tubulin polymerization and displays strong inhibitory activity on tumor cell growth. It inhibits tubulin polymerization at the colchicine-binding site of beta-tubulin. CA4 was shown to impede tumor growth in several cell lines including IMR32 (neuroblastoma), Hs746T (gastric carcinoma), CFPAC-1 (pancreatic carcinoma) and MCF-7 (breast cancer). It has antitumor activity by inhibiting AKT function in human gastric cells. The inhibited AKT activation causes decreased cell proliferation, cell cycle arrest and reduced in vitro migration/invasiveness and in vivo metastatic ability. Combretastatin A-4 is the active component of combretastatin A-4 phosphate, a prodrug designed to damage the vasculature (blood vessels) of cancer tumors causing central necrosis.