NI-1: a novel canine mastocytoma model for studying drug resistance and IgER-dependent mast cell activation

BACKGROUND: Advanced mast cell (MC) disorders are characterized by uncontrolled growth of neoplastic MC in various organs, mediator-related symptoms, and a poor prognosis. Kit mutations supposedly contribute to abnormal growth and drug resistance in these patients. METHODS: We established a novel canine mastocytoma cell line, NI-1, from a patient suffering from MC leukemia. RESULTS: NI-1 cells were found to form mastocytoma lesions in NOD/SCID IL-2Rgamma(null) mice and to harbor several homozygous Kit mutations, including missense mutations at nucleotides 107(C→T) and 1187(A→G), a 12-bp duplication (nucleotide 1263), and a 12-bp deletion (nucleotide 1550). NI-1 cells expressed several MC differentiation antigens, including tryptase, Kit, and a functional IgE receptor. Compared to the C2 mastocytoma cell line harboring a Kit exon 11 mutation, NI-1 cells were found to be less responsive against the Kit tyrosine kinase inhibitors (TKI) masitinib and imatinib, but were even more sensitive against proliferation-inhibitory effects of the mammalian target of rapamycin (mTOR) blocker RAD001 and PI3-kinase/mTOR blocker NVP-BEZ235. The Kit-targeting multikinase inhibitors PKC412 and dasatinib were also found to override TKI resistance in NI-1 cells, and produced growth inhibition with reasonable IC(50) values (<0.1 μM). CONCLUSION: NI-1 may serve as a useful tool to investigate IgE-dependent reactions and mechanisms of abnormal growth and drug resistance in neoplastic MC in advanced mastocytosis.