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1.
Blood ; 2024 04 21.
Article in English | MEDLINE | ID: mdl-38643492

ABSTRACT

Secondary kinase domain mutations in BCR::ABL1 represent the most common cause of resistance to tyrosine kinase inhibitor (TKI) therapy in chronic myeloid leukemia patients. The first five approved BCR::ABL1 TKIs target the ATP-binding pocket. Mutations confer resistance to these ATP-competitive TKIs and those approved for other malignancies by decreasing TKI affinity and/or increasing ATP affinity. Asciminib, the first highly active allosteric TKI approved for any malignancy, targets an allosteric regulatory pocket in the BCR::ABL1 kinase C-lobe. As a non-ATP-competitive inhibitor, the activity of asciminib is predicted to be impervious to increases in ATP affinity. Here we report several known mutations that confer resistance to ATP-competitive TKIs in the BCR::ABL1 kinase N-lobe that are distant from the asciminib binding pocket yet unexpectedly confer in vitro resistance to asciminib. Among these is BCR::ABL1 M244V, which confers clinical resistance even to escalated asciminib doses. We demonstrate that BCR::ABL1 M244V does not impair asciminib binding, thereby invoking a novel mechanism of resistance. Molecular dynamics simulations of the M244V substitution implicate stabilization of an active kinase conformation through impact on the -C helix as a mechanism of resistance. These N-lobe mutations may compromise the clinical activity of ongoing combination studies of asciminib with ATP-competitive TKIs.

2.
Cancer Res ; 79(16): 4283-4292, 2019 08 15.
Article in English | MEDLINE | ID: mdl-31270078

ABSTRACT

KIT is a type-3 receptor tyrosine kinase that is frequently mutated at exon 11 or 17 in a variety of cancers. First-generation KIT tyrosine kinase inhibitors (TKI) are ineffective against KIT exon 17 mutations, which favor an active conformation that prevents these TKIs from binding. The ATP-competitive inhibitors, midostaurin and avapritinib, which target the active kinase conformation, were developed to inhibit exon 17-mutant KIT. Because secondary kinase domain mutations are a common mechanism of TKI resistance and guide ensuing TKI design, we sought to define problematic KIT kinase domain mutations for these emerging therapeutics. Midostaurin and avapritinib displayed different vulnerabilities to secondary kinase domain substitutions, with the T670I gatekeeper mutation being selectively problematic for avapritinib. Although gatekeeper mutations often directly disrupt inhibitor binding, we provide evidence that T670I confers avapritinib resistance indirectly by inducing distant conformational changes in the phosphate-binding loop. These findings suggest combining midostaurin and avapritinib may forestall acquired resistance mediated by secondary kinase domain mutations. SIGNIFICANCE: This study identifies potential problematic kinase domain mutations for next-generation KIT inhibitors midostaurin and avapritinib.


Subject(s)
Antineoplastic Agents/pharmacology , Drug Resistance, Neoplasm/genetics , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-kit/genetics , Pyrazoles/pharmacology , Pyrroles/pharmacology , Staurosporine/analogs & derivatives , Triazines/pharmacology , Cell Line , Drug Resistance, Neoplasm/drug effects , Exons , Humans , Molecular Docking Simulation , Molecular Dynamics Simulation , Mutation , Proto-Oncogene Proteins c-kit/chemistry , Proto-Oncogene Proteins c-kit/metabolism , Staurosporine/chemistry , Staurosporine/pharmacology
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