Constitutive activation of c-kit by the juxtamembrane but not the catalytic domain mutations is inhibited selectively by tyrosine kinase inhibitors STI571 and AG1296

The c-kit receptor tyrosine kinase (KIT) is constitutively activated by 2 types of naturally occurring mutations, the Val559-->Gly (G559) mutation in the juxtamembrane domain and the Asp814-->Val (V814) mutation in the catalytic domain. We evaluated the effects of the tyrosine kinase inhibitors STI571 and AG1296 on BaF3 cells expressing wild-type KIT (KITWT) or activating mutants of KIT (KITG559 and KITV814) in the presence or absence of the KIT ligand, stem cell factor (SCF). Both STI571 and AG1296 inhibited SCF-dependent activation of KITWT and SCF-independent activation of KITG559 more efficiently, whereas SCF-independent activation of KITV814 was scarcely affected. Furthermore, both inhibitors inhibited SCF-dependent growth of BaF3-KITWT cells and, with higher potencies, SCF-independent growth of BaF3-KITG559 cells through the induction of apoptosis. In contrast, the inhibitors had little or no effect on SCF-independent growth of BaF3-KITV814 cells or on IL-3-dependent growth of BaF3-Mock cells. These results suggested that both inhibitors may be effective therapeutic agents for oncogenic KIT with the juxtamembrane domain mutation, but not with the catalytic domain mutation, and that the activation mechanism of the catalytic domain mutant KIT is complex and entirely different from that of the wild-type KIT or the juxtamembrane domain mutant KIT. (C)2002 The Japanese Society of Hematology.