Rationally designed anti-mitotic agents with pro-apoptotic activity

Agents that interact with cytoskeletal elements such as tubulin include syn thetic spiroketal pyrans (SPIKET), targeting the spongistatin binding site of beta -tubulin, and monotetrahydrofuran compounds (COBRA compounds), targ eting a unique binding cavity on alpha -tubulin. At nanomolar concentration s, the SPIKET compound SPIKET-P caused tubulin depolymerization and demonst rated potent cytotoxic activity against cancer cells. COBRA-1 inhibited GTP -induced tubulin polymerization. Treatment of human breast cancer and brain tumor cells with COBRA-1 caused destruction of microtubule organization an d apoptosis. Other agents that have shown promise for cancer treatment incl ude phorboxazoles, natural products that are extremely cytostatic towards t he National Cancer Institute's panel of 60 tumor cell lines. In standard MT T assays, synthetic phorboxazole A exhibited potent cytotoxicity against NA LM-6 acute lymphoblastic leukemia cells (IC50 = 1.7 nM), BT-20 breast cance r cells (IC50 = 3.4 nM), and U373 glioblastoma cells (IC50 = 6.7 nM). Struc ture-activity studies were reported for seven synthetic analogs of phorboxa zole A. Out of these, two showed potent anti-cancer activity. Phorboxazole analog 2 was active against NALM-6 cells (IC50 = 4.8 nM), BT-20 cells (IC50 12.6 nM) and U373 cells (IC50 = 27.4 nM), as was analog 3 (NALM-6 IC50 = 5 .2 nM, BT-20 IC50 11.3 nM, and U373 IC50 = 29.2 nM). Anticancer activity of the phorboxazole analogs was correlated to the presence of certain structu ral moieties such as portions of the macrolide group, the central oxazole g roup, and the polyene side chain, The requirement of more than one structur al element for activity suggested that at least bimodal interactions of the natural product with key cellular components may occur. Promising anti-mit otic agents with pro-apoptotic activity include inhibitors of the tyrosine kinase BTK. The leflunomide metabolite analog LFM-A13 inhibited BTK in leuk emia and lymphoma cells (IC50 = 17 muM). Consistent with the anti-apoptotic . function of BTK, treatment of leukemic cells with LFM-A13 enhanced their sensitivity to chemotherapy-induced apoptosis.