Structural Basis and Cellular Consequences of Potent Inhibition of the Aurora Kinases, Wild Type Abl Kinase and a T315I Multi-Drug Resistant Mutant Form of Abl Kinase by MK-0457 (VX-680).

MK-0457 (VX-680) is a potent small molecule inhibitor of the Aurora-family of protein kinases that inhibits cell proliferation through aberrant mitosis and failed cytokinesis. Affected cells are subsequently deleted by apoptosis. Tumor regression and increased survival have been reported in multiple in-vivo models and in January 2005 MK-0457 entered Phase I clinical trials as the first in class Aurora inhibitor. Although MK-0457 demonstrates significant selectivity over the vast majority of kinases tested, it has been shown to potently inhibit Flt-3 and Abl, both of which are targets for anti-cancer therapies. Most notably MK-0457 potently inhibits a series of mutant Abl kinases including the multi-drug resistant T315I form that is commonly expressed in Gleevec refractory CML and ALL. We report here the first MK-0457 / Aurora co-complex crystal structure and show that it adopts a closed inactive conformation. By comparison with other reported kinase structures we provide a structural basis for the cross-reactivity with wild type and drug resistant mutants of the Abl kinase. We also show that MK-0457 blocks both Aurora and Abl cellular kinase activity and displays potent cytotoxic activity against a range of leukemic cell lines, including Gleevec resistant cells that are reliant on mutant Abl for growth and survival. Similar observations have recently been made in the clinic, where new data show that MK-0457 has activity in patients with BCR-ABL T315I mutant CML and Philadelphia positive ALL.