Effects of AMN107, a Novel Aminopyrimidine Tyrosine Kinase Inhibitor, on Human Mast Cells Bearing Wild-Type or Mutated Codon 816 c-kit.

Background. Majority of adult patients with systemic mastocytosis (SM) have activating mutation in codon 816 of c-kit (CD117), a receptor on the surface of mast cells. This abnormality is responsible for the pathogenesis of the disease.

Methods. We investigated the effects of a newly designed tyrosine kinase inhibitor, AMN107, by comparing its in vitro inhibitory potency on c-kit mutated mast cell lines and patient samples with that of imatinib mesylate, another tyrosine kinase inhibitor, effective in some patients with SM. Two cell lines, subclones of HMC-1 cells, were used: HMC-1⁵⁶⁰ carrying juxtamembrane domain mutation in codon 560 of c-kit, and HMC-1^{560, 816} carrying both codon 560 mutation and tyrosine kinase domain mutation in codon 816 of c-kit.

Results. In HMC-1⁵⁶⁰ mast cell line carrying wild-type codon 816, AMN107 was as potent as imatinib in inhibiting cellular proliferation, with IC₅₀ values of 108 and 74 nM respectively, while in HMC-1^{560, 816} cell line carrying 816 mutation, neither medication had an effect. AMN107 was also as effective as imatinib in inhibiting phosphorylation of c-kit tyrosine kinase in HMC-1⁵⁶⁰ cells. The inhibition of cellular proliferation was associated with induction of apoptosis in HMC-1⁵⁶⁰ cells. AMN107 in concentrations up to 1 uM had no effect on bone marrow mast cells carrying D816V c-kit mutation obtained from patients with mastocytosis.

Conclusions. Our results suggest similar potency of AMN107 and imatinib in mast cells that carry wild-type codon 816, but no activity against codon 816 mutation carrying cells.