BRAF is a therapeutic target in aggressive thyroid carcinoma

Purpose: Oncogenic conversion of BRAF occurs in ∼ 44% of papillary thyroid carcinomas and 24% of anaplastic thyroid carcinomas. In papillary thyroid carcinomas, this mutation is associated with an unfavorable clinicopathologic outcome. Our aim was to exploit BRAF as a potential therapeutic target for thyroid carcinoma. Experimental Design: We used RNA interference to evaluate the effect of BRAF knockdown in the human anaplastic thyroid carcinoma cell lines FRO and ARO carrying the BRAF V600E ( ^V600EBRAF) mutation. We also exploited the effect of BAY 43-9006 [N-(3-trifluoromethyl-4-chlorophenyl)-N'-(4-(2-methylcarbamoyl pyridin-4-yl)oxyphenyl)urea], a multikinase inhibitor able to inhibit RAF family kinases in a panel of six ^V600EBRAF-positive thyroid carcinoma cell lines and in nude mice bearing ARO cell xenografts. Statistical tests were two sided. Results: Knockdown of BRAF by small inhibitory duplex RNA, but not control small inhibitory duplex RNA, inhibited the mitogen-activated protein kinase signaling cascade and the growth of ARO and FRO cells (P <0.0001 ). These effects were mimicked by thyroid carcinoma cell treatment with BAY 43-9006 (IC₅₀ = 0.5-1 μmol/L; P <0.0001), whereas the compound had negligible effects in normal thyrocytes. ARO cell tumor xenografts were significantly (P <0.0001) smaller in nude mice treated with BAY 43-9006 than in control mice. This inhibition was associated with suppression of phospho - mitogen-activated protein kinase levels. Conclusions: BRAF provides signals crucial for proliferation of thyroid carcinoma cells spontaneously harboring the ^V600EBRAF mutation and, therefore, BRAF suppression might have therapeutic potential in ^V600EBRAF-positive thyroid cancer.