Tubulin Colchicine Binding Site Inhibitors as Vascular Disrupting Agents in Clinical Developments

Tumor vasculature is an important target in cancer treatment. Two distinct vascular-targeting therapeutic strategies are applied to attack cancer cells indirectly. The antiangiogenic approach intervenes in the neovascularization processes and blocks the formation of new blood vessels, while th e antivascular approach targets the established tumor blood vessels, making vascular shutdown and resulting in rapid haemorrhagic necrosis and tumor cell death. A number of compounds with diverse structural scaffolds have been designed to target tumor vasculature and they are called vascular disrupting agents (VDAs). The biological or ligand-directed VDAs utilize antibodies, peptides or growth factors to deliver toxins or pro-coagulants or proapoptotic affectors to tumor-related blood vessels, while the small-molecule VDAs selectively target tumor blood vessels and have little effects on the normal endothelium. Among the small-molecule VDAs, the tubulin colchicine binding site inhibitors have been extensively studied and many of them have entered the clinical trials, including CA-4P, CA-1P, AVE8062, OXi4503, CKD-516, BNC105P, ABT-751, CYT-997, ZD6126, NPI-2358, MN-029 and EPC2407. This review makes a summary of the small-molecule VDAs in clinical developments and highlights some potential VDA leads or candidates for the treatment of tumors.