Imatinib Responsiveness in Canine Mast Cell Tumors Carrying Novel Mutations of <i>c-KIT</i> Exon 11

Abstract

In 2 individual cases of canine mast cell tumors, we identified 2 novel c-KIT mutations in exon 11: a 9-base pair (bp) deletion (c.1663-1671del) and a point mutation (c.1676T>A). The 9-bp deletion mutation caused a loss of 3 amino acids, corresponding to p.Gln555_Lys557del, and the point mutation resulted in the substitution of valine by aspartic acid (p.Val559Asp) in the juxtamembrane domain of the protein. Imatinib mesylate, a therapeutic agent for canine mast cell tumors, was used to treat both tumors. Complete remission was achieved at 33 and 14 days after administration, respectively. However, in both cases, the therapeutic response subsequently tapered with the duration of remission lasting 66 and 255 days, respectively. Although these 2 novel c-KIT mutations in exon 11 were not confirmed to be gain-of-function mutations, a further study may help clarify relevance between mutations identified in this report and responsiveness.

Successful response to imatinib in two dogs with inoperable grade III infiltrating mast cell tumours: a case report

“…For the control of MCTs carrying c-kit exon 8 and 11 mutations, several previous studies have shown that TKIs can be effective, and imatinib has recently begun to be utilised for canine MCT as a novel targeted therapy (Kobayashi et al 2012;Nakano et al 2014). Imatinib is a commercially available drug targeting tyrosine kinases, and it inhibits downstream signalling of KIT by competing with adenosine triphosphate (ATP) for the ATP binding site (Buchdunger et al 2002).…”

“…Mutations consisting of internal tandem duplication (ITD) within c-kit exons 8 and 11, which causes ligand-independent phosphorylation of KIT, have been frequently found in highgrade MCT in dogs (London et al 1999;Downing et al 2002;Zemke et al 2002;Webster et al 2006;Kobayashi et al 2012). It has been reported that canine MCT with these mutations in the exon 8 and exon 11 regions regressed after treatment with imatinib in xenografted severe combined immunodeficiency (SCID) mice and dogs with spontaneous MCT (Kobie et al 2007;Kobayashi et al 2012;Nakano et al 2014). Moreover, other studies reported that several TKIs with different chemical structures from imatinib induced objective tumour regression in canine MCTs with these mutations Hahn et al 2008;London et al 2009).…”

“…Many previous studies have demonstrated that response to imatinib, which is a TKI, can be correlated with the presence of mutations in c-kit oncogene exons 8 and 11 found in canine MCT (Kobayashi et al 2012;Nakano et al 2014). Furthermore, these mutations occur in higher-grade tumours and their presence can be used to provide evidence of poor prognosis such as recurrence and metastasis (Downing et al 2002;Zemke et al 2002).…”

“…Tumour samples from FNA were washed three times with phosphate buffered saline (pH 7.2, Difco Laboratories Inc., Detroit, MI, USA), and genomic DNA was isolated using the DNeasy Blood & Tissue Kit (Qiagen, Valencia, CA, USA) according to the manufacturer's protocol and eluted in 50 μl of Tris-EDTA buffer. To screen for mutations in c-kit exons 8 and 11, the following primer sets developed by Nakano et al (2014) were used for amplifying c-kit exons 8 and 11: for exon 8, the forward primer was 5'-AGCCTTGGTGAGGTGTTCCA-3' and the reverse primer was 5'-CTACCCTGCT-GTCCTTCCCT-3'; for exon 11, the forward primer was 5'-CATTTGTTCTCTACCCTAAGTGCTA-3' and the reverse primer was 5'-GTTCCCTAAAGT-CATTGTTACACG-3'. The amplicons of exons 8 and 11 were 228 and 227 base pairs, respectively.…”

Dysregulation of tyrosine kinases and use of imatinib in small animal practice

“…In dogs, a total of 28 cases of MCTs treated with imatinib have been reported; of these, 25 cases were treated with imatinib (10-12.7 mg/kg daily), with examination of KIT mutation status (examination of entire KIT, KIT exons 8, 9 and 11, or KIT exon 11 alone) (Isotani et al, 2008;Yamada et al, 2011;Kobayashi et al, 2012;Nakano et al, 2014). In addition to these 25 cases, we have treated 13 cases with imatinib (10-12 mg/kg daily) with examination of KIT mutation status (KIT exons 8, 9, and 11) (unpublished data).…”