Sorafenib inhibits vascular endothelial cell proliferation stimulated by anaplastic thyroid cancer cells regardless of BRAF mutation status

Anaplastic thyroid cancer (ATC) is a rare refractory disease, frequently associated with BRAF mutations and aberrant vascular endothelial growth factor (VEGF) secretion. The antitumor effects of sorafenib were evaluated, and its mechanisms of action were investigated. Four human ATC cell lines were used: OCUT-4, which possesses a BRAF mutation; OCUT-6 and ACT-1, which carry NRAS mutations; and OCUT-2, which possesses mutations in BRAF and PI3KCA. The viability of Sorafenib was evaluated by MTT assay. In order to examine the inhibitory effect of Sorafenib on intracellular signal transduction, expression of mitogen-activated protein kinase kinase was examined by western blotting. In addition, cell cycle analysis was performed using flow cytometry. The inhibitory effects of sorafenib on the growth of ATC cells and human umbilical vein endothelial cells (HUVECs) stimulated with conditioned media from ATC cells were examined. Sorafenib inhibited the viability of OCUT-4 more effectively than other ATC cell lines; these effects may have been mediated cytostatically by suppressing mitogen-activated protein kinase kinase phosphorylation. Conversely, similar suppression was not observed in OCUT-6 cells, which possess an NRAS mutation. The four cell lines secreted different quantities of VEGF, and the proliferation of HUVECs was differentially stimulated by their conditioned media. Both anti-VEGF antibody and sorafenib prevented this stimulation of proliferation. In conclusion, sorafenib more effectively inhibited RAF-generated growth signals in ATC cells compared with signals generated by its upstream gene, RAS. ATC cells stimulated the growth of HUVECs via humoral factors, including VEGF; this effect was clearly inhibited by sorafenib. The present findings highlighted the potential of sorafenib for the treatment of ATC and provided insight into its mechanism of action.