Sunitinib: bridging present and future cancer treatment

Tyrosine kinase receptors (RTKs) are a heterogeneous group of transmembrane proteins involved in signal transduction. These receptors are expressed in many different cells and regulate cellular growth, differentiation and angiogenesis. Overexpression and/or the structural alteration of different RTKs classes are generally associated to cancer and, when RTKs-mediated signal transduction pathways are abnormally activated, generate cancer growth, angiogenesis and metastatization. Therapeutic intervention targeting RTKs concerns antagonist drugs as little molecules or monoclonal antibodies. Sunitinib malate is a little molecule able to block intracellular tyrosine kinase domain of RTKs, which has both direct anticancer and antiangiogenetic activity. Sunitinib targets selectively vascular endothelial growth factor, KIT, Flt3 and platelet-derived growth factor receptors and the receptor encoded by the ret proto-oncogene. This drug is used in the treatment of gastrointestinal stromal cancer (GIST) resistant to imatinib and metastatic renal cell carcinoma (RCC). In this review, we report preclinical data of sunitinib, even about synergism with chemotherapy and radiotherapy, data relative to phase III trials of sunitinib in the treatment of GIST and RCC, and we try to plan what will be future applications of sunitinib in different types of cancer, even in association to chemotherapy, radiotherapy and monoclonal antibodies.