Flumatinib, a selective inhibitor of BCR-ABL/PDGFR/KIT, effectively overcomes drug resistance of certain KIT mutants.
Bottom Line: Interestingly, our in vitro study revealed that flumatinib effectively overcame the drug resistance of certain KIT mutants with activation loop mutations (i.e., D820G, N822K, Y823D, and A829P).Our in vivo study consistently suggested that flumatinib had superior efficacy compared with imatinib or sunitinib against 32D cells with the secondary mutation Y823D.Molecular modeling of flumatinib docked to the KIT kinase domain suggested a special mechanism underlying the capability of flumatinib to overcome the drug-resistance conferred by activation loop mutations.
Affiliation: Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.Show MeSH
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Mentions: The effects of flumatinib on the activation of KIT mutants and downstream signaling pathways were then investigated. In 32D-V559D cells, imatinib, flumatinib, and sunitinib treatment all effectively abolished the phosphorylation of KIT, ERK1/2, and STAT3 (Fig. 2), showing substantial shutdown of the KIT and downstream signaling pathways. In 32D-V559D + Y823D cells, the phosphorylation levels of KIT, ERK1/2, and STAT3 were strongly inhibited by flumatinib, but not imatinib or sunitinib (Fig. 2). Similar findings were observed in 32D-V559D + N822K and 32D-V559D + A829P cells (Fig. S1). The phosphorylation levels of these KIT mutants, as well as ERK1/2 and STAT3, were dose-dependent on each drug over a wide concentration range (1–1000 nM) and correlated with inhibition of cell growth. These results collectively show that flumatinib is capable of overcoming the imatinib and sunitinib resistance conferred by certain secondary activation loop mutations in vitro. We previously showed that flumatinib inhibits the tyrosine kinase activity of ABL 80-fold more effectively than imatinib in an ELISA (100.9 and 1.2 nM for imatinib and flumatinib, respectively). Furthermore, these ELISA results correlate with those from our previous cell-based proliferation assays.22 Given that our proliferation assays were all based on the same 32D cell line, we could exclude the possibility that the enhanced antiproliferative activity of flumatinib is presumably due to increased intracellular flumatinib concentrations. Taken together, our findings suggest that the enhanced antiproliferative activity of flumatinib against 32D cells transformed by certain KIT double mutants is because of its increased inhibitory activity against the kinase activation of these KIT mutants.
Affiliation: Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.