Abstract Prostate cancer (PrCa) is the most common malignancy and the second leading cause of cancer death in men. Although localized PrCa can be successfully cured, advanced hormone refractory tumors are resistant to current therapeutic regimes. Therefore, novel approaches for effective malignancy control are still required. Molecular targeted therapies have emerged as promising alternatives to classical chemo/radiotherapy. The clinical benefit of the multi-tyrosine kinase inhibitor Sunitinib, which blocks the activity of receptors such as PDGFR, VEGFR1/2, FLT3, and c-KIT has been proven in renal carcinoma, GIST, and neuroblastoma. In this work, we have tested the therapeutical efficacy of sunitinib against PrCa both in vitro and in vivo, using the androgen-independent cell line PC-3. These cells express target receptors PDGFRa/b, and VEGFR1/2. Sunitinib dramatically reduced cell proliferation in vitro (P<0.0001) in a dose-dependent manner (with an IC50 of 1-2 micro-M) and colony formation (P<0.0001), through an autocrine mechanism. Moreover, when combined with doses of 2 and 4 Gy ionizing radiation, sunitinib enhanced the inhibitory activity of radiotherapy in colony formation assays. In vivo experiments revealed that PC3 tumor-bearing mice treated with 80 mg/Kg/day sunitinib had significantly smaller tumors (63% reduction) than controls. A single dose of 6 Gy caused tumor shrinkage by 80%, whereas the combination of both therapies resulted in more than 90% tumor reduction, suggesting that sunitinib could be used as a radiosensitizer. Positron emission tomography (PET) analyses with 18-FDG, FMISO, and FLT tracers showed a decrease in glucose uptake, hypoxia, and cell proliferation, respectively, in sunitinib-treated mice, as compared to controls. Immunohistochemical analysis for CD-31 revealed an expected reduction in tumor angiogenesis in sunitinib-treated tumors in comparison with untreated tumors. Overall, these data support the use of sunitinib as a clinically relevant drug for the treatment of PrCa. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3621.