SUMMARY
Tyrosine kinases are critical regulators of normal cell signalling, because they
control several key processes. Tyrosine kinases are specific signalling molecules
playing an essential role in cell growth, survival, migration and differentiation.
Their receptors are located on the cell surface, delivering signals to the nuc leus through a phosphorylation cascade. Receptor tyrosine kinases are those
tyrosine kinases expressed on the cell surface that are stimulated by binding
of growth factors. Tyrosine kinases are also of paramount importance in angiog enesis, and thus, in the development of tumor vascularisation. The emergence
of abnormal signalling pathways due to the dysregulation of receptor tyrosine
kinases is a known feature in several tumour types, and is regarded as a nega tive prognostic factor, as it alters tumor growth, proliferation and metastatic
potential. Inhibition of tyrosine kinases is very important in human oncology,
and it is likely that many more tyrosine kinase inhibitors will become available
in the near future; and their biological activity will be enhanced as combination
regimens with standard treatment modalities are explored. The use of kinase
inhibitors in dogs and cats is relatively recent. There are now 2 small molecule
inhibitors approved for use in veterinary medicine: Palladia (toceranib) and Masi vet/Kinavet (masitinib). Their use is approved in mast cell tumours of dogs by the
Federal Drug Administration (USA). Gleevec (imatinib) is human tyrosine kinase
inhibitor used in the treatment of multiple human cancers (for example chronic
myelogenous leukaemia and GIST), but has been successfully used in dogs and
cats as well. The authors review the current knowledge on the biology of tyrosine
kinase dysfunction in human and animal cancers, and the application of specific
tyrosine kinase inhibitors to veterinary cancer patients