Multi-tyrosine Kinase Inhibitor Sunitinib Research Articles

The Efficacy of Sunitinib Treatment of Renal Cancer Cells Is Associated with the Protein PHAX In Vitro.

Anti-angiogenic agents, such as the multi-tyrosine kinase inhibitor sunitinib, are key first line therapies for metastatic clear cell renal cell carcinoma (ccRCC), but their mechanism of action is not fully understood. Here, we take steps towards validating a computational prediction based on differential transcriptome network analysis that phosphorylated adapter RNA export protein (PHAX) is associated with sunitinib drug treatment. The regulatory impact factor differential network algorithm run on patient tissue samples suggests PHAX is likely an important regulator through changes in genome-wide network connectivity. Immunofluorescence staining of patient tumours showed strong localisation of PHAX to the microvasculature consistent with the anti-angiogenic effect of sunitinib. In normal kidney tissue, PHAX protein abundance was low but increased with tumour grade (G1 vs. G3/4; p < 0.01), consistent with a possible role in cancer progression. In organ culture, ccRCC cells had higher levels of PHAX protein expression than normal kidney cells, and sunitinib increased PHAX protein expression in a dose dependent manner (untreated vs. 100 µM; p < 0.05). PHAX knockdown in a ccRCC organ culture model impacted the ability of sunitinib to cause cancer cell death (p < 0.0001 untreated vs. treated), suggesting a role for PHAX in mediating the efficacy of sunitinib.

Imaging of Tumor-Specific Hypoxia Dynamics and Its Significance in Radiation Biology

Hypoxia has been known to be a feature associated with tumor radioresistance. So far, clinical strategies to overcome chronic hypoxia due to the limitation of the oxygen diffusion have been designed. However, intermittent or acute/cycling hypoxia, whose frequency can range between a few cycles per minutes to hours, is receiving increased attention, because this type of hypoxia has been reported to have an influence on tumor malignancy as well as treatment resistance via increased expression of pro-survival pathways. Therefore, a priori information on fluctuating hypoxia can be important in clinical treatment planning, but complicated dynamics makes it difficult to elucidate biological significance of intermittent hypoxia.Here, we illustrate the use of pulsed electron spin resonance imaging (ESRI) as a novel imaging method to directly monitor fluctuating oxygenation i.e. cycling hypoxia in transplanted tumors. A common resonator platform for both ESRI and magnetic resonance imaging (MRI) provided pO2 maps with anatomical guidance without positional movement. Oxygen images every 3 min in pO2 could visualize the rapid oxygen fluctuation and distinguish the cycling hypoxia and chronic hypoxia. Furthermore, we have examined the vascular renormalization process by longitudinally pO2 mapping during treatments with a multi-tyrosine kinase inhibitor sunitinib. Transient improvement in tumor oxygenation and the decrease of cycling tumor hypoxia were visualized by ESRI 2 to 4 days following antiangiogenic treatments. Radiation treatment during this time period of improved oxygenation by antiangiogenic therapy resulted in a synergistic delay in tumor growth.In conclusion, this ESRI technique combined with MRI, may offer a powerful clinical tool to noninvasively detect variable hypoxic status in tumors and to identify a window of vascular renormalization to maximize the effects of combination therapy with antiangiogenic drugs.

Heightened JNK Activation and Reduced XIAP Levels Promote TRAIL and Sunitinib-Mediated Apoptosis in Colon Cancer Models.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis that may be a promising agent in cancer therapy due to its selectivity toward tumor cells. However, many cancer cells are resistant to TRAIL due to defects in apoptosis signaling or activation of survival pathways. We hypothesized that a disruption of pro-survival signaling cascades with the multi-tyrosine kinase inhibitor sunitinib would be an effective strategy to enhance TRAIL-mediated apoptosis. Here we demonstrate that sunitinib significantly augments the anticancer activity of TRAIL in models of colon cancer. The therapeutic benefit of the TRAIL/sunitinib combination was associated with increased apoptosis marked by enhanced caspase-3 cleavage and DNA fragmentation. Overexpression of the anti-apoptotic factor B-cell lymphoma 2 (BCL-2) in HCT116 cells reduced TRAIL/sunitinib-mediated apoptosis, further supporting that sunitinib enhances the anticancer activity of TRAIL via augmented apoptosis. Analysis of pro-survival factors identified that the combination of TRAIL and sunitinib significantly downregulated the anti-apoptotic protein X-linked inhibitor of apoptosis protein (XIAP) through a c-Jun N-terminal kinase (JNK)-mediated mechanism. Short hairpin RNA (shRNA)-mediated knockdown of JNK confirmed its key role in the regulation of sensitivity to this combination as cells with suppressed JNK expression exhibited significantly reduced TRAIL/sunitinib-mediated apoptosis. Importantly, the therapeutic benefit of the TRAIL/sunitinib combination was validated in the HCT116-Luc and HCT15 colon cancer xenograft models, which both demonstrated significant anti-tumor activity in response to combination treatment. Collectively, our data demonstrate that sunitinib enhances TRAIL-mediated apoptosis by heightened JNK activation, diminished XIAP levels, and augmented apoptosis.

Dual modulation of MCL-1 and mTOR determines the response to sunitinib.

Most patients who initially respond to treatment with the multi-tyrosine kinase inhibitor sunitinib eventually relapse. Therefore, developing a deeper understanding of the contribution of sunitinib's numerous targets to the clinical response or to resistance is crucial. Here, we have shown that cancer cells respond to clinically relevant doses of sunitinib by enhancing the stability of the antiapoptotic protein MCL-1 and inducing mTORC1 signaling, thus evoking little cytotoxicity. Inhibition of MCL-1 or mTORC1 signaling sensitized cells to clinically relevant doses of sunitinib in vitro and was synergistic with sunitinib in impairing tumor growth in vivo, indicating that these responses are triggered as prosurvival mechanisms that enable cells to tolerate the cytotoxic effects of sunitinib. Furthermore, higher doses of sunitinib were cytotoxic, triggered a decline in MCL-1 levels, and inhibited mTORC1 signaling. Mechanistically, we determined that sunitinib modulates MCL-1 stability by affecting its proteasomal degradation. Dual modulation of MCL-1 stability at different dose ranges of sunitinib was due to differential effects on ERK and GSK3β activity, and the latter also accounted for dual modulation of mTORC1 activity. Finally, comparison of patient samples prior to and following sunitinib treatment suggested that increases in MCL-1 levels and mTORC1 activity correlate with resistance to sunitinib in patients.

In VivoImaging of Tumor Physiological, Metabolic, and Redox Changes in Response to the Anti-Angiogenic Agent Sunitinib: Longitudinal Assessment to Identify Transient Vascular Renormalization

The tumor microenvironment is characterized by a highly reducing redox status, a low pH, and hypoxia. Anti-angiogenic therapies for solid tumors frequently function in two steps: the transient normalization of structurally and functionally aberrant tumor blood vessels with increased blood perfusion, followed by the pruning of tumor blood vessels and the resultant cessation of nutrients and oxygen delivery required for tumor growth. Conventional anatomic or vascular imaging is impractical or insufficient to distinguish between the two steps of tumor response to anti-angiogenic therapies. Here, we investigated whether the noninvasive imaging of the tumor redox state and energy metabolism could be used to characterize anti-angiogenic drug-induced transient vascular normalization. Daily treatment of squamous cell carcinoma (SCCVII) tumor-bearing mice with the multi-tyrosine kinase inhibitor sunitinib resulted in a rapid decrease in tumor microvessel density and the suppression of tumor growth. Tumor pO2 imaging by electron paramagnetic resonance imaging showed a transient increase in tumor oxygenation after 2-4 days of sunitinib treatment, implying improved tumor perfusion. During this window of vascular normalization, magnetic resonance imaging of the redox status using an exogenously administered nitroxide probe and hyperpolarized (13)C MRI of the metabolic flux of pyruvate/lactate couple revealed an oxidative shift in tumor redox status. Redox-sensitive metabolic couples can serve as noninvasive surrogate markers to identify the vascular normalization window in tumors with imaging techniques. A multimodal imaging approach to characterize physiological, metabolic, and redox changes in tumors is useful to distinguish between the different stages of anti-angiogenic treatment.

Evaluation of Potentially Predictive Markers for Anti-Angiogenic Therapy with Sunitinib in Recurrent Ovarian Cancer Patients

INTRODUCTION: In ovarian cancer, new therapeutic strategies are needed because the vast majority of patients develop a recurrence and resistance to platinum derivates. Attached to the AGO-OVAR2.11 study investigating the multityrosine kinase inhibitor sunitinib in recurrent platinum refractory ovarian cancers, this translational research project assesses the potential value of serum vascular endothelial growth factor (VEGF), soluble VEGF receptor-3 (sVEGFR-3), and angiopoietin-2 (Ang-2) levels for progression-free survival (PFS). MATERIALS AND METHODS: Longitudinal serum samples were taken while the patient was on study drugs. Serum concentration of VEGF, sVEGFR-3, and Ang-2 was determined by ELISA. The slope of the markers was correlated to the PFS. RESULTS: Patients showing a decrease in VEGF concentration had a median PFS of 10.5 months [confidence interval (CI), 2.89–12.25] compared to 2.9 months (CI, 1.48–5.32) in the case of an increase (P = .17). The stratified log-rank test showed a trend for longer PFS if a decrease of Ang-2 was observed (P = .089). Dichotomized in absolute decrease or increase, the PFS was 8.4 months (CI, 2.89–12.26) versus 2.7 months (CI, 1.05–5.32), respectively. Patients with a reduction of the sVEGFR-3 concentration had a median PFS of 4.76 months (CI 2.86–10.65) versus 8.61 months (CI, 1.05-not estimable) in patients with an increase of sVEGFR-3. This observation was statistically not significant in the log-rank test (P = .81). CONCLUSION: Ang-2 could potentially identify a patient population that might have a better PFS when under anti-angiogenic treatment, like the tyrosine kinase inhibitor sunitinib.

KRAS allel-specific activity of sunitinib in an isogenic disease model of colorectal cancer

To investigate the impact of different KRAS mutations on treatment with the tyrosine kinase inhibitor sunitinib in SW48 colorectal cancer cell line variants. Isogenic SW48 KRAS wt, G12A, G12C, G12D, G12R, G12S, G12 V, and G13D cells were evaluated for ERK phosphorylation with and without EGF stimulation. In addition, the respective cell lines were tested for the effect of sunitinib on ERK/ELK phosphorylation, cell cycle, and cytotoxicity. Compared to KRAS wt cells, all KRAS mutant variants were associated with resistance to sunitinib treatment. In the MTT chemosensitivity assay, the grade of resistance was less pronounced in G13D and highest in G12A, G12C, and G12S mutant cells. The reduction in ERK phosphorylation due to treatment with sunitinib was highest in G12V (89 %) mutant cells and lowest in G12A (24 %) mutant cells. ELK phosphorylation was less decreased in all KRAS mutant variants compared to KRAS wt cells following sunitinib treatment. The grade of resistance appears to correlate with the individual KRAS-dependent intrinsic activation of ERK. Our isogenic cell culture model suggests that KRAS mutations in SW48 colorectal cancer cells are linked to resistance to the multityrosine kinase inhibitor sunitinib. KRAS G13D mutant SW48 cells represented the KRAS subspecies with the lowest grade of resistance. Future studies will have to clarify whether KRAS can be used to guide sunitinib treatment or-in general-a treatment with a multityrosine kinase inhibitor in mCRC.

Neuroendokrine Neoplasiendes gastroenteropankreatischen Systems

Neuroendocrine neoplasms (NEN) occur in the entire gastrointestinal tract. The updated classification of the WHO (2010) and current TNM-classification provide a basis for the therapeutic decision and assess the prognosis. Endoscopy and different imaging techniques are important for the localization of the primary tumor as well as local and distant metastases. The most important diagnostic imaging technique is somatostatin receptor scintigraphy. Therapeutic strategy should be discussed within the scope of a multidisciplinary tumor board. Surgery of NEN is the sole curative option. The treatment options for liver metastases include surgical resection as well as radiofrequency ablation and hepatic artery embolization. In advanced stage, systemic therapy should be used. Recent studies demonstrated a significantly prolonged progression-free survival using octreotide in well differentiated NEN. Besides the well established steptozotocine based chemotherapy regimens for pancreatic NEN, novel agents such as the mTOR-inhibitor everolimus and multityrosine kinase inhibitor sunitinib have recently also shown a prolonged progression-free survival. Moreover, temozolomide-based chemotherapy appears to be effective in pancreatic NEN. Finally, somatostatin receptor targeted radionuclide therapy can be effective in progressing gastroenteropancreatic NEN.

Antiangiogenic Agent Sunitinib Transiently Increases Tumor Oxygenation and Suppresses Cycling Hypoxia

Structural and functional abnormalities in tumor blood vessels impact the delivery of oxygen and nutrients to solid tumors, resulting in chronic and cycling hypoxia. Although chronically hypoxic regions exhibit treatment resistance, more recently it has been shown that cycling hypoxic regions acquire prosurvival pathways. Angiogenesis inhibitors have been shown to transiently normalize the tumor vasculatures and enhance tumor response to treatments. However, the effect of antiangiogenic therapy on cycling tumor hypoxia remains unknown. Using electron paramagnetic resonance imaging and MRI in tumor-bearing mice, we have examined the vascular renormalization process by longitudinally mapping tumor partial pressure of oxygen (pO(2)) and microvessel density during treatments with a multi-tyrosine kinase inhibitor sunitinib. Transient improvement in tumor oxygenation was visualized by electron paramagnetic resonance imaging 2 to 4 days following antiangiogenic treatments, accompanied by a 45% decrease in microvessel density. Radiation treatment during this time period of improved oxygenation by antiangiogenic therapy resulted in a synergistic delay in tumor growth. In addition, dynamic oxygen imaging obtained every 3 minutes was conducted to distinguish tumor regions with chronic and cycling hypoxia. Sunitinib treatment suppressed the extent of temporal fluctuations in tumor pO(2) during the vascular normalization window, resulting in the decrease of cycling tumor hypoxia. Overall, the findings suggest that longitudinal and noninvasive monitoring of tumor pO(2) makes it possible to identify a window of vascular renormalization to maximize the effects of combination therapy with antiangiogenic drugs.

The effect of a dimeric Affibody molecule (ZEGFR:1907)2 targeting EGFR in combination with radiation in colon cancer cell lines

The epidermal growth factor receptor (EGFR) is frequently overexpressed in colorectal cancer and is therefore an attractive target for treatment. (ZEGFR:1907)2 is a newly developed dimeric affibody molecule with high affinity to the extracellular part of EGFR. In this study, we evaluated the cytotoxic effects of (ZEGFR:1907)2 in combination with external radiation and the possible inhibitory effects in the EGFR signalling pathways in the colon cancer cell lines HT-29 and HCT116. The effects were compared with an EGFR antibody (cetuximab) and the tyrosine kinase inhibitors (erlotinib and sunitinib). These cell lines are genotypically different with respect to e.g. KRAS and BRAF mutational status, recently shown to be of clinical significance for therapeutic effects. Both cell lines express approximately 100,000-150,000 EGFRs per cell but differ in the radiation response (HCT116, SF2=0.28 and HT-29, SF2=0.70). Exposure to (ZEGFR:1907)2 produced a small, but significant, reduction in survival in HCT116 but did not affect HT-29 cells. Similar results were obtained after exposure to EGF and the EGFR antibody cetuximab. The EGFR tyrosine kinase targeting inhibitor erlotinib and the multi-tyrosine kinase inhibitor sunitinib reduced survival in both cell lines. However, none of the drugs had any significant radiosensitizing effects in combination with radiation. Akt and Erk are central proteins in the EGFR downstream signalling and in the cellular response to ionizing radiation. The activation of Akt (Ser 473) and Erk (Thr202/Tyr204) by radiation was both dose- and time-dependent. However the activation of EGFR was not clearly affected by radiation. Neither (ZEGFR:1907)2 nor any of the other drugs were able to completely inactivate Akt or Erk. On the contrary, erlotinib stimulated Akt phosphorylation in both cell lines and in HCT116 cells Erk was activated. Overall the results illustrate the complexity in response to radiation and drugs in cells with differential phenotypic status.

Sunitinib Inhibits Cell Proliferation and Alters Steroidogenesis by Down-Regulation of HSD3B2 in Adrenocortical Carcinoma Cells.

The multi-tyrosine kinase inhibitor sunitinib is used in the treatment of several solid tumors. Animal experiments pointed to an adrenotoxic effect of sunitinib. Therefore, we evaluated the expression of key targets of sunitinib in human adrenocortical carcinoma (ACC) tumor samples and investigated its in vitro effects in ACC cell lines. We carried out immunohistochemistry for vascular endothelial growth factor (VEGF) and its receptor (VEGF-R2) in 157 ACC samples and nine normal adrenal glands. VEGF and VEGF-R2 protein were expressed in 72 and 99% of ACC samples, respectively. Using NCI-H295 and SW13 ACC cell lines, we investigated the effects of sunitinib on cell proliferation. Sunitinib reduced dose-dependently cell viability of both NCI-H295 and SW13 cells (SW13: 0.1 μM 96 ± 7%, 1 μM 90 ± 9%*, 5 μM 62 ± 6%*, controls 100 ± 9%; *p < 0.05). To determine sunitinib effects on steroidogenesis, we measured steroid hormones in cell culture supernatant by gas chromatography–mass spectrometry. We observed a pronounced decrease of cortisol secretion (1 μM 90.1 ± 1.5%*, 5 μM 57.2 ± 0.3%*, controls 100 ± 2.4%) and a concomitant increase in the DHEA/4-androstenedione and 17-hydroxypregnenolone/17-hydroxyprogesterone ratios, indicating specific inhibition of 3β-hydroxysteroid dehydrogenase (HSD3B2). In yeast microsomes transformed with HSD3B2, no direct inhibition of HSD3B2 by sunitinib was detected. Sunitinib induced down-regulation of HSD3B2 mRNA and protein in ACC cell lines (mRNA: 1 μM 44 ± 16%*; 5 μM 22 ± 2%*; 10 μM 19 ± 4%*; protein: 1 μM 82 ± 8%; 5 μM 63 ± 8%*; 10 μM 55 ± 9%*). CYP11B1 was down-regulated at mRNA but not at protein level and CYP11A1 remained unchanged. In conclusion, target molecules of sunitinib are expressed in the vast majority of ACC samples. Sunitinib exhibits anti-proliferative effects in vitro, and appears to specifically block adrenal steroidogenesis by down-regulation of HSD3B2, rendering it a promising option for treatment of ACC.

Cytotoxicity, drug combinability, and biological correlates of ABT‐737 against acute lymphoblastic leukemia cells with MLL rearrangement

ABT-737 is a BH3 mimetic small-molecule inhibitor that binds with high affinity to Bcl-2 to induce apoptosis in malignant cells and has shown promise as an effective anti-leukemic agent in pediatric preclinical tests. This study focuses on the effects of ABT-737 on leukemia cells with MLL rearrangement and identifies some of the biological correlates of its activity. Cells were cultured in the presence of increasing concentrations of ABT-737 alone or in combination with other agents. After 4 days in culture, cell growth inhibition was measured by Alamar blue assay. The expression and activation of potential intracellular targets of ABT-737 activity were determined by Western blot analysis. Significant Bcl-2 expression was detected in all infant leukemia cells investigated. ABT-737 induced cell death in all cell lines studied although the IC(50) values differed somewhat between cell lines. Western blot analysis identified the effects of ABT-737 on survival and apoptosis-regulatory proteins PARP, caspase-8, and cytochrome-c. Drug combination studies indicated synergy with distinct anti-neoplastic agents, including the multi-tyrosine kinase inhibitor sunitinib. This effective drug synergy appears to be mediated by the combined inhibition of Bcl-2 and intracellular signaling pathways. We describe the in vitro studies to demonstrate the activity and drug combinability of ABT-737 against MLL rearranged leukemia cells. In addition, identification of the molecular changes that occur in the presence of ABT-737 provides information regarding effective target validation and target modulation analyses in future clinical trials.

Sunitinib induces PTEN expression and inhibits PDGFR signaling and migration of medulloblastoma cells

We previously showed that inhibition of the platelet-derived growth factor receptor (PDGFR) blocks the survival and migration of medulloblastoma cells. Identification of in vitro PDGFR-targeting pharmacologic agents that are suitable for preclinical testing in medulloblastoma models in vivo will be critical for efficiently translating these agents to clinical investigation in children with medulloblastoma. In this study, we investigated whether the multi-tyrosine kinase inhibitor sunitinib, effectively inhibits PDGFR signaling required for medulloblastoma cell migration. Daoy and D556 human medulloblastoma cells pre-treated for 1 h with 0.2 μM sunitinib demonstrated induction of PTEN expression and significant inhibition of PDGFR signaling activity and transactivation of EGFR, in a RAS-independent manner, in response to PDGF-BB stimulation. Sunitinib pre-treatment markedly reduced medulloblastoma cell migration in response to both PDGF-BB and 10% serum at 4 and 24 h after treatment. Pre-treatment with sunitinib for 1 h also resulted in detachment and decreased viability of D556, but not Daoy, cells and only after 48 h following treatment. However, sunitinib did not induce apoptosis in either cell line at any time point, indicating that the anti-migratory effects of sunitinib were not due to impeding cell survival. Sunitinib similarly inhibited PDGFR signaling and migration of primary murine Smo/Smo medulloblastoma cells, suggesting that the Smo/Smo mouse is an appropriate model for preclinical testing of sunitinib. These results indicate that sunitinib may be an important pharmacologic agent for the treatment of invasive medulloblastoma, particularly given evidence of its ability to cross the blood-brain barrier to target tumor cells, and thus warrants further in vivo testing for confirmation of efficacy.

Activity of the multi-tyrosine kinase inhibitor sunitinib in neuroblastoma tumors.

e13640 Background: Neuroblastoma (NB) is the most commonly diagnosed extracranial solid malignancy during infancy. Although curable in its early stages, metastatic tumors are associated with a bad prognosis and a poor survival. Receptor tyrosine kinases have been associated with oncogenic transformation in many human tumors. Sunitinib is multityrosine kinase inhibitor (c-kit, PDGFR and VEGFR) that has shown antitumor activity in some solid tumors. It was our intention to evaluate the antitumor activity of the multityrosine kinase inhibitor sunitinib in NB in order to identify novel therapeutic options of treatment. Methods: Here, we tested the antitumor activity of sunitinib, using cancer cell lines and in vivo xenografted mouse models. MTT proliferation, apoptosis assays and biochemical experiments were performed to investigate the molecular bases of the action of sunitinib alone or in combination with standard chemotherapy. Results: Sunitinib exhibited a potent antitumor activity in vitro (IC50 0.8-2.6 μM) in a representative panel of NB cell lines (SH-SY5Y, SK-N-BE2 and SK-N-AS). It also showed a high therapeutic index when tested in the non-transformed cells 293T and MCF10A. When combined with chemotherapies (cisplatin and doxorubicin) used for the treatment of NB tumors sunitinib was synergistic at very low doses (0.1 μM). Sunitinib induced cell cycle arrest and stimulates apoptosis at different doses. Mechanistically sunitinib inhibited several receptor tyrosine kinase proteins and the downstream PI3-AKT pathway. In vivo xenograft studies revealed a significant antitumor activity of sunitinib compared with the control group in two types of cells lines (SH-SY5Y, p=0.02 and SK-N-BE, p=0.08). Sunitinib demonstrated an anti-angiogenic effect in vivo with a reduction of markers associated with angiogenesis (factor VIII). Conclusions: Sunitinib demonstrates antitumor activity in several in vitro and in vivo models. Theses results support the development of sunitinib in clinical studies alone or in combination with chemotherapy. No significant financial relationships to disclose.

Abstract 3621: The multi-tyrosine kinase inhibitor Sunitinib reduces prostate cancer growth through autocrine and paracrine mechanisms

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&amp;lt;0.0001) in a dose-dependent manner (with an IC50 of 1-2 micro-M) and colony formation (P&amp;lt;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.