Sunitinib: A Multitargeted Receptor Tyrosine Kinase Inhibitor in the Era of Molecular Cancer Therapies

Sunitinib is an oral oxindole multitargeted kinase inhibitor that inhibits certain receptor tyrosine kinases (RTKs). These include vascular endothelial growth factor receptors (VEGFR type 1 and 2), platelet-derived growth factor receptors (PDGFR-α and PDGFR-β), stem cell factor receptor (KIT), FMS-like tyrosine kinase-3 (FLT3), glial cell-line derived neurotrophic factor receptor (RET) and the receptor of macrophagecolony stimulating factor (CSF1R). Examination of the antitumor effect of sunitinib in a variety of cell lines in vitro suggested an antiproliferative activity that is dependent on the presence of constitutively active RTK targets. The use of sunitinib as first-line therapy in advanced renal cell carcinoma (RCC) has improved the overall survival compared with that observed after cytokine therapy, while its administration in patients with gastrointestinal stromal tumors (GISTs) after progression or intolerance to imatinib achieved an objective response of 7%. Sunitinib is currently approved for the treatment of GISTs in this setting, and as first-line therapy for the treatment of advanced RCC. The relatively long half-life of sunitinib and its major metabolite allow for a once-daily dosing schedule. An interesting antitumor activity of sunitinib was reported in phase II studies of patients with a variety of malignancies, such as hepatocellular cancer, pancreatic neuroendocrine tumors, and non-small cell lung cancer; results of phase III studies are urgently anticipated. Fatigue is one of the most common adverse effects of sunitinib, as 50–70% of patients with advanced RCC and GIST complained of this adverse effect. Other adverse effects are diarrhea, anorexia, nausea and vomiting, oral changes and bleeding events. Most toxicities are reversible and should not result in discontinuation of sunitinib. If necessary, dose adjustments or interruptions should be made. Hypothyroidism has been described in the first 2 weeks of sunitinib therapy and its incidence increases progressively with the duration of therapy. Sunitinib may exert its hypertensive activity through a direct effect on the vasculature, while its most important cardiac adverse effect is left ventricular dysfunction. A variety of skin adverse effects have been described with the use of sunitinib such as hand-foot syndrome, yellow discoloration of the skin, dry skin, subungual splinter hemorrhages, acral erythema, and generalized skin rashes. Administration of sunitinib in the adjuvant and