Inhibition of wild-type and mutant Bcr-Abl by AP23464, a potent ATP-based oncogenic protein kinase inhibitor: implications for CML

Abstract

IntroductionThe initial, chronic stage of chronic myeloid leukemia (CML) is strictly dependent on signals emanating from the deregulated protein tyrosine kinase Bcr-Abl. 1 Although the Bcr-Abl signaling cascade is incompletely understood, the premise that CML can be treated by selective inhibition of Bcr-Abl kinase activity has been validated in the clinic. [2][3][4] Imatinib mesylate (Gleevec, STI571), a protein tyrosine kinase inhibitor with a narrow specificity profile (Abl, ARG, Kit, and platelet-derived growth factor receptor [PDGFR]), has remarkable single agent activity in patients with CML and is now the first-line treatment for the disease. 5,6 In addition, this molecular-targeted therapy is effective against other cancers that depend on signaling through imatinib mesylatesensitive protein tyrosine kinases. [7][8][9][10][11][12] An important clinical concern pertaining to imatinib mesylate therapy is relapse after an initial response, particularly in patients with advanced phase CML. For example, among patients with accelerated phase enrolled in a phase 2 clinical trial, the incidence of disease progression at 24 months was 50%. 13 Between 60% and 90% of patients who acquire imatinib mesylate resistance harbor one or more specific mutations in the kinase domain of Bcr-Abl that impair the ability of imatinib mesylate to inhibit Bcr-Abl kinase activity. These mutations presumably affect drug binding without eliminating adenosine 5Ј-triphosphate (ATP) binding or kinase activity. [14][15][16][17][18][19] Clinically observed mutations have been identified within several regions of the Bcr-Abl kinase domain. In this study, we examined 6 common kinase domain variants that collectively account for at least 60% of reported Bcr-Abl mutations in relapsed patients: Q252H, Y253F, E255K, T315I, M351T, and H396P. The panel spans a range of residual imatinib mesylate sensitivities (IC 50 ϭ 900-4400 nM) 20 and encompasses several functionally distinct kinase domain regions, including the nucleotide binding P-loop (Q252H, Y253F, E255K), 2 imatinib mesylate contact residues (Y253F and T315I), the base supporting the activation loop (M351T), and the activation loop (H396P). 21,22 Currently, there is considerable interest in developing alternative Abl kinase inhibitors capable of inhibiting the Bcr-Abl kinase domain mutants observed in relapsed patients. Using structurebased drug design and focused synthetic libraries of trisubstituted purine analogs, we identified AP23464 as a potent inhibitor of Abl and Src-family kinases. AP23464 displayed potent inhibitory activity against Src-family kinases and Abl kinase (IC 50 Յ 1 nM), Supported by grants from the National Cancer Institute, the Leukemia and Lymphoma Society, the Doris Duke Charitable Foundation, and the Howard Hughes Medical Institute (B.J.D.).Several of the authors (R.P., J.A.K., V.M.R., H.T., C.A.M., R.S.B., Y.W., R.S., W.C.S., D.D., T.C., and T.K.S.) are employed by ARIAD Pharmaceuticals Inc, whose potential product was studied in the present work. For personal us...

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