[show abstract][hide abstract] ABSTRACT: The success of targeting kinases in cancer with small molecule inhibitors has been tempered by the emergence of drug-resistant kinase domain mutations. In patients with chronic myeloid leukemia treated with ABL inhibitors, BCR-ABL kinase domain mutations are the principal mechanism of relapse. Certain mutations are occasionally detected before treatment, suggesting increased fitness relative to wild-type p210 BCR-ABL. We evaluated the oncogenicity of eight kinase inhibitor-resistant BCR-ABL mutants and found a spectrum of potencies greater or less than p210. Although most fitness alterations correlate with changes in kinase activity, this is not the case with the T315I BCR-ABL mutation that confers clinical resistance to all currently approved ABL kinase inhibitors. Through global phosphoproteome analysis, we identified a unique phosphosubstrate signature associated with each drug-resistant allele, including a shift in phosphorylation of two tyrosines (Tyr253 and Tyr257) in the ATP binding loop (P-loop) of BCR-ABL when Thr315 is Ile or Ala. Mutational analysis of these tyrosines in the context of Thr315 mutations demonstrates that the identity of the gatekeeper residue impacts oncogenicity by altered P-loop phosphorylation. Therefore, mutations that confer clinical resistance to kinase inhibitors can substantially alter kinase function and confer novel biological properties that may impact disease progression.
Proceedings of the National Academy of Sciences 01/2007; 103(51):19466-71. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Imatinib (Gleevec/STI-571/CGP57148B, Novartis) is a small-molecule, tyrosine kinase inhibitor developed to target BCR-ABL, c-Kit, and PDGF-R. Through inhibition of these oncogenic kinases, imatinib is effective in the treatment of BCR-ABL-positive leukemia, gastrointestinal stromal tumor, and hypereosinophilic syndrome, respectively. However, clinical success of imatinib is hampered by acquired resistance that may occur through several mechanisms including kinase domain mutation, target amplification, and activation of alternate signaling pathways. Strategies to overcome resistance have included targeting BCR-ABL stability and downstream signaling pathways important for tumor growth. Additional work has shown that new BCR-ABL kinase inhibitors with increased potency or alternate conformation-binding properties can target imatinib resistance. This review focuses on the mechanisms of imatinib resistance and the strategies currently being developed to overcome clinical resistance.
The Scientific World Journal 02/2006; 6:918-30. · 1.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Structural studies suggest that most point mutations in the BCR-ABL kinase domain cause resistance to the ABL kinase inhibitor imatinib by impairing the flexibility of the kinase domain, restricting its ability to adopt the inactive conformation required for optimal imatinib binding, rather than by directly interfering with drug contact residues. BMS-354825, currently in clinical development for imatinib-resistant chronic myelogenous leukemia, is a dual SRC/ABL kinase inhibitor that binds ABL in both the active and inactive conformation. To examine the potential role of conformational binding properties in drug resistance, we mapped the mutations in BCR-ABL capable of conferring resistance to BMS-354825. Through saturation mutagenesis, we identified 10 such BCR-ABL mutations, 8 of which occurred at drug contact residues. Some mutants were unique to BMS-354825, whereas others also conferred imatinib resistance. Remarkably, the identity of the amino acid substitution at either of two contact residues differentially affects sensitivity to imatinib or BMS-354825. The combination of imatinib plus BMS-354825 greatly reduced the recovery of drug-resistant clones. Our findings provide further rationale for considering kinase conformation in the design of kinase inhibitors against cancer targets.
Proceedings of the National Academy of Sciences 04/2005; 102(9):3395-400. · 9.74 Impact Factor