Sunitinib Exerts Only Limited Effects on the Proliferation and Differentiation of Anaplastic Thyroid Cancer Cells Maria D’Agostino, 1, * Pasquale Voce, 2, * Marilena Celano, 1 Marialuisa Sponziello, 3 Sonia Moretti, 2 Valentina Maggisano, 1 Antonella Verrienti, 3 Cosimo Durante, 3 Sebastiano Filetti, 3 Efisio Puxeddu, 2 and Diego Russo 1 Background: Novel molecularly targeted drugs are undergoing preclinical and clinical testing to assess their efficacy against refractory thyroid carcinomas. The multikinase inhibitor Sunitinib has been shown to inhibit the kinase activity of the RET oncogene and reduce proliferation in differentiated thyroid cancer cells harboring the RET/PTC rearrangement. In this study, we evaluated its effects in human cell lines derived from differentiated (TPC-1) and anaplastic (8505C, CAL–62, and C643) thyroid cancers. Methods: The cells exposed to various concentrations of Sunitinib were examined for: (1) cell viability and presence of apoptosis, analyzed by cell counts, MTT assay, trypan blue exclusion assay, western blotting, and immunofluorescence; (2) expression of cyclin D1 and phosphorylated and nonphosphorylated extracellular signal-regulated kinase (ERK) and Akt proteins, analyzed by western blotting; and (3) transcription of genes encoding thyrocyte differentiation markers (thyroid-stimulating hormone receptor, sodium/iodide symporter, thyroglobulin, and thyroperoxidase) and proangiogenic factors (vascular endothelial growth factor A, platelet- derived growth factors A and B), measured by quantitative reverse transcriptase–polymerase chain reaction. Results: Exposure to nanomolar concentrations of Sunitinib significantly reduced cell viability in only TPC-1 cells, and this effect was paralleled by reduction of cyclin D1 levels. Western blotting revealed reduced phos- phorylation of ERK and Akt after 3 and 6 hours of drug exposure. In contrast, the growth of 8505C, CAL-62, and C-643 cells was significantly reduced only by micromolar concentrations of Sunitinib, mainly due to induced necrotic rather than apoptotic death. In these cells, Sunitinib exerted a few significant effects on the transcription of angiogenic factors or thyrocyte differentiation markers. Conclusions: Sunitinib has little or no effect on the growth or differentiation of anaplastic thyroid cancer cells, thus suggesting that it is unlikely to be effective in the treatment of anaplastic thyroid cancer. Introduction F inding effective treatments for poorly differentiated and anaplastic thyroid carcinomas continues to be a major challenge. The loss of capability in concentrating the radio- iodine, mainly due to reduced/absent expression of the sodium/iodide symporter (NIS) in recurrent and/or meta- static tissue (1,2), does not permit the use of radioiodine, the most effective targeted therapy for thyroid malignancies (3). As for multimodal treatment regimens based on aggres- sive surgery, external beam radiation, and chemotherapy, they rarely succeed in ameliorating the prognosis for these patients (4,5). Promising results have recently been obtained in some patients with combined therapies that include novel molec- ularly targeted agents (6–8). Those directed against the pro- tein tyrosine kinases (PTKs) are among the most promising. Thyrocyte growth regulation involves the activation of vari- ous PTKs, including growth factor receptors and elements of signal transduction pathways whose deregulation seems to be responsible for the cells’ neoplastic transformation (9). Suni- tinib, one of the several PTK inhibitors currently being tested in clinical trials, has produced encouraging results in patients whose carcinomas derived from thyroid follicular epithelial cells, including those with the more aggressive Hurthle-cell histotype (10–12), but no information has been published on 1 Department of Pharmacobiological Sciences, University of Catanzaro ‘Magna Graecia’, Catanzaro, Italy. 2 Department of Internal Medicine, University of Perugia, Perugia, Italy. 3 Department of Clinical Sciences, University of Rome ‘‘Sapienza,’’ Rome, Italy. *These authors contributed equally to this work. THYROID Volume 22, Number 2, 2012 ª Mary Ann Liebert, Inc. DOI: 10.1089/thy.2011.0060 138