MUTATIONS IN KIT PREDICT RESISTANCE TO SEVERAL TKI (SORAFENIB, SUNITINIB, AND MASATINIB) IN NEOPLASTIC HUMAN AND CANINE MAST CELL LINES
E Hadzijusufovic,1 B Peter,1 H Herrmann,1 K Schuch,1 T Thaiwong,2 V Yuzbasiyan-Gurkan,2 W Pickl,1 M Willmann,3 P Valent1
Advanced mast cell (MC) disorders are characterized by uncontrolled growth of neoplastic MC in various organs, resistance against cytoreductive drugs, and a poor prognosis. In most patients, transforming mutations in the KIT proto-oncogene are detectable and are considered to contribute to resistance. MC lines are an important model for analyzing drug resistance. We have established a novel canine mastocytoma cell line, NI-1 from a canine patient suffering from mast cell leukemia. NI-1 cells were found to harbour several homozygous KIT mutations including two single nucleotide mutations, one at nucleotide 107 (C to T, leading to a missense mutation, P36L) and another at 1187 (A to G, leading to a missense mutation, Q396R), a 12 bp duplication at nucleotide 1263, and a 12 bp deletion at nucleotide 1550, the latter reflecting a transcriptional variant. Drug response profiling revealed that NI-1 cells differ markedly from canine mastocytoma C2 cells harbouring an exon 11 KIT mutation, and the human mast cell lines HMC-1.1 (exon 11 mutation in KIT) and HMC-1.2 (exon 11 and exon 17 mutation). In contrast to C2 cells, NI-1 cells were found to be largely resistant against the apoptosis-inducing effects of masatinib, sorafenib, and sunitinib. Similarly, in contrast to HMC-1.1 cells, HMC-1.2 cells were found to be largely resistant against masatinib, sorafenib, and sunitinib. Drug resistance was specific for KIT tyrosine kinase blockers in that vorinostat, an HDAC inhibitor, produced growth-inhibitory and apoptosis-inducing effects with comparable IC50 and ED50 values in all MC lines tested. Together, these data provide further evidence that KIT mutations are associated with resistance to KIT-targeting drugs. The novel MC line NI-1 may serve as a valuable tool to investigate the mechanisms of drug resistance in canine mast cell tumors and the role of novel KIT mutations.