Evaluation of tyrosine-kinase receptor c-KIT (c-KIT) mutations, mRNA and protein expression in canine leukemia: Might c-KIT represent a therapeutic target?

The tyrosine-kinase receptor c-KIT (c-KIT) plays an important role in proliferation, survival and 26 differentiation of progenitor cells in normal hematopoietic cells. In human hematological 27 malignancies, c-KIT is mostly expressed by progenitor cell neoplasia and seldom by those 28 involving mature cells. Tyrosine kinase inhibitors (TKIs) are actually licensed for the first- and 29 second-line treatment of human haematologic disorders. Aim of the present study was to evaluate c- 30 KIT mRNA and protein expression and complementary DNA mutations in canine leukemia. Eleven 31 acute lymphoblastic leukemia (ALL) and acute undifferentiated leukemia (AUL) and 12 chronic 32 lymphocytic leukemia (CLL) were enrolled in this study. The amounts of c-KIT mRNA and protein 33 were determined, in peripheral blood samples, by using quantitative Real Time RT-PCR, flow 34 cytometry and immunocytochemistry, respectively. The presence of mutations on c-KIT exons 8, 9, 35 10, 11 and 17 were investigated by cDNA sequencing. Higher amounts of c-KIT mRNA were found 36 in ALL/AUL compared to CLL, and this latter showed a lower pattern of gene expression. 37 Transcriptional data were confirmed at the protein level. No significant gain-of-function mutations 38 were ever observed in both ALL/AUL and CLL. Among canine hematological malignancies, 39 ALL/AUL typically show a very aggressive biological behavior, partly being attributable to the lack 40 of efficacious therapeutic options. The high level of c-KIT expression found in canine ALL/AUL 41 might represent the rationale for using TKIs in future clinical trials.