Abstract
In patients with chronic myeloid leukemia (CML), kinase domain mutations account for imatinib resistance in the majority of cases. Mutations cause either a direct steric hindrance to drug binding or a conformational change that favors kinase activation, which therefore precludes imatinib binding. We have previously characterized the dual Src-Abl kinase inhibitor AP23464 and found it to effectively suppress the growth of cells expressing native and essentially all imatinib-resistant variants of BCR-ABL, with the notable exception of the gatekeeper T315I mutant (Azam et al., Proc. Natl. Acad. Sci. USA, 103: 9244, 2006). Following this work, we have used mutant panel screening and integrated structural analysis to further characterize key analogs designed to overcome T315I resistance, as exemplified by AP23846 and AP24163. Both molecules effectively inhibit the tyrosine kinase activity of wild type (WT) and T315I variants of BCR-ABL, and inhibit the proliferation of BaF3-derived cell lines expressing these enzymes (see Table below). AP24163 was further characterized against a broader panel of imatinib-resistant BCR-ABL-expressing cell lines and showed a promising profile of proliferation inhibition. Comparison of these data with structural models of the mutants provides insights into the basis for the ability of AP24163 to overcome imatinib resistance.
Refinement of small-molecule kinase inhibitors by the integration of sequential screening of panels of mutants coupled with structural analysis is a powerful drug discovery paradigm that is applicable to an increasing number of targeted therapeutic agents.
INHIBITION OF PROLIFERATION OF BAF3 CELLS EXPRESSING BCR-ABL AND ITS VARIANTS (IC50 in nM) IMATINIB AP23464 AP23846 AP24163 WT 600 14 500 7 T315I >20000 >1000 500 480 L248R >20000 92 ND 64 G250E 5000 25 ND 63 Q252H 3000 40 ND 42 Y253H 18000 32 ND 44 E255K 12000 74 ND 24 BAF3+IL3 >20000 >1000 500 >10000 Figure Figure
Structural Analysis of Small-Molecule Binding to the BAZ2A and BAZ2B Bromodomains
