KIT kinase mutants show unique mechanisms of drug resistance to imatinib and sunitinib in gastrointestinal stromal tumor patients

Abstract

Most gastrointestinal stromal tumors (GISTs) exhibit aberrant activation of the receptor tyrosine kinase (RTK) KIT. The efficacy of the inhibitors imatinib mesylate and sunitinib malate in GIST patients has been linked to their inhibition of these mutant KIT proteins. However, patients on imatinib can acquire secondary KIT mutations that render the protein insensitive to the inhibitor. Sunitinib has shown efficacy against certain imatinib-resistant mutants, although a subset that resides in the activation loop, including D816H/V, remains resistant. Biochemical and structural studies were undertaken to determine the molecular basis of sunitinib resistance. Our results show that sunitinib targets the autoinhibited conformation of WT KIT and that the D816H mutant undergoes a shift in conformational equilibrium toward the active state. These findings provide a structural and enzymologic explanation for the resistance profile observed with the KIT inhibitors. Prospectively, they have implications for understanding oncogenic kinase mutants and for circumventing drug resistance.kinase inhibitor ͉ signal transduction ͉ targeted therapy ͉ resistance mechanism ͉ cancer

Gastrointestinal stromal tumors: what do we know now?

“…34,38,127,128 This mutation favors the active conformation of the kinase domain and consequently disfavors imatinib binding. 34,129,130 This is corroborated by clinical results, as patients with PDGFRA D842V-mutant GIST have low response rates and very short progression-free and overall survivals during imatinib treatment. Crenolanib is a TKI that has activity versus D842V and is now being tested in a clinical trial.…”

Imatinib resistance and microcytic erythrocytosis in a Kit V558Δ;T669I/+ gatekeeper-mutant mouse model of gastrointestinal stromal tumor

“…Although in vitro the autoactivation of the KIT V558Δ kinase is unchanged compared with the KIT V558Δ;T669I kinase, the kinase activity of the KIT V558Δ;T669I kinase is nearly doubled and could explain the KIT hyperactivity observed in the ICC, mast cell, and erythrocyte lineages in Kit V558Δ;T669I/+ mice (32). However, at this time we cannot rule out the possibility that the T669I second-site mutation alters oncogenic Kit signaling in a qualitative fashion.…”

Molecular conformations, interactions, and properties associated with drug efficiency and clinical performance among VEGFR TK inhibitors

“…Just before the classical kinase domain, the plus-JM residues 820-826 extend over the α-helix C. The density for residues 813-819 was not wellordered, and therefore, positions for these residues are not included in the crystal structure coordinates. Residues 801-812 were well-ordered, packing into the RDP to participate in many interactions that stabilize an autoinhibitory conformation, analogous to the JM segment of FMS-related tyrosine kinase 3 (FLT3) (18) and cKit (17,19,20). The crystal structure of pazopanib shows insufficient electron density to support assignment of specific JM residues, but partial density is consistent with a mobile JM that transiently adopts a JM in conformation similar to the conformation seen with axitinib and sunitinib.…”

“…These complexes all show the activation loop adopting a DFG out position, similar to previously described inhibitor complexes of the nonphosphorylated VEGFR2 catalytic domain (minus-JM), including an axitinib complex (12). The plus-JM complexes with inhibitors axitinib and sunitinib show the JM to fold into the portion of the kinase interdomain space adjacent to α-helix C(JM in ), analogous to autoinhibitory JM in conformations reported for other PDGFR kinase family members (16)(17)(18)(19) and very similar to apo cKit (20) (Fig. 1A).…”