vascular-targeting agent vascular-targeting agent a vascular-targeting agent (vta) or vascular disrupting agent (vda) is a drug designed to damage the vasculature (blood vessels) of cancer tumors causing central necrosis. vtas can be small-molecule or ligand-based. small-molecule vtas include: microtubule destabilizing drugs such as combretastatin a-4 disodium phosphate (ca4p), zd6126, ave8062, oxi 4503 vadimezan (asa404) clinical trials phase ii : zd6126, ca4p, plinabulin (npi-2358) phase iii : dmxaa (asa404).