Characterization of the promoter region of the proto-oncogene c-Kit in canine mast cell tumour

In medicinal chemistry, G-quadruplex (G4) represents a promising chemotherapeutic target. The unveiling of telomerase role in cell cycle progression and the defi nition of its mechanism of action prompted the search of small molecule able to block it by promoting G4 formation at the telomere ends. More recently, the role of conformational equilibria of G-rich sequences as modulator of gene expression has been assessed and opened new perspectives. In particular, several oncogene promoters were found to contain G-rich sequences and have been considered as targets for anticancer therapy. Among them, we were interested in c-kit, due to its widespread relevance in tumorigenesis and tumor maintenance. Interestingly, two distinct G-rich sequences were identifi ed in c-kit promoter and both are now structurally characterized in their G4 conformation. The knowledge of the target is defi nitely a great advantage to the identifi cation and/or optimization of new ligands directed towards these genomic portions. However, we also need solid models to assess the pharmacological effi ciency of potential new drugs. In this context dog can represent a remarkable translational animal for human cancer. Indeed, mast cell tumour (MCT) is the most common (7% to 21%) cutaneous skin tumour of dogs and, interestingly, the MCT aggressive behaviour, (which results in poor outcome) is often characterized either by an overexpression or a mutational status of c-Kit. All this makes c-kit an important target for dog chemotherapy. Furthermore, c-kit mutations occurring in dog MCTs are similar to those found in human cancers, such as gastrointestinal stromal tumors (GIST), melanoma and mastocytosis. Therefore, canine MCT could represent a proper disease model to evaluate the functional consequences of c-kit abnormalities in cancer and the role of c-kit inhibitors in antitumor chemotherapy. To validate such an assumption, we started a detailed characterization of the promoter region of c-kit in dogs. The sequence of canine upstream promotorial sequence was cloned and sequenced in both healthy and MCT-suffering dogs. Then, the canine sequences were compared to the human ones. In particular, large attention was devoted to clarify the conformational equilibria occurring in physiologically relevant conditions. This work represents the required preliminary step for a better understanding of MCT biology, progression and treatment as well as to export this knowledge in the many c-Kit related human tumours.