Combination <i> BRAF <sup>V600E</sup> </i> Inhibition with the Multitargeting Tyrosine Kinase Inhibitor Axitinib Shows Additive Anticancer Activity in <i> BRAF <sup>V600E</sup> </i> -Mutant Anaplastic Thyroid Cancer
Viswanath Gunda, Chandrayee Ghosh, Jiangnan Hu, Lisa Zhang, Ya -Qin Zhang, Min Shen, Electron Kebebew
Abstract
Background: Anaplastic thyroid cancer (ATC) is uniformly lethal. BRAF V600E mutation is present in 45% of patients with ATC. Targeted therapy with combined BRAF and MEK inhibition in BRAF V600E -mutant ATC can be effective, but acquired resistance is common because this combination targets the same pathway. Drug matrix screening, in BRAF V600E ATC cells, of highly active compounds in combination with BRAF inhibition showed multitargeting tyrosine kinase inhibitors (MTKIs) had the highest synergistic/additive activity. Thus, we hypothesized that the combination of BRAF V600E inhibition and an MTKI is more effective than a single drug or combined BRAF and MEK inhibition in BRAF V600E -mutant ATC. We evaluated the effect of BRAF V600E inhibitors in combination with the MTKI axitinib and its mechanism(s) of action. Methods: We evaluated the effects of BRAF V600E inhibitors and axitinib alone and in combination in in vitro and in vivo models of BRAF V600E -mutant and wild-type ATC. Results: The combination of axitinib and BRAF V600E inhibitors (dabrafenib and PLX4720) showed an additive effect on inhibiting cell proliferation based on the Chou–Talalay algorithm in BRAF V600E -mutant ATC cell lines. This combination also significantly inhibited cell invasion and migration ( p < 0.001) compared with the control. Dabrafenib and PLX4720 arrested ATC cells in the G0/G1 phase. Axitinib arrested ATC cells in the G2/M phase by decreasing phosphorylation of aurora kinase B (Thr232) and histone H3 (Ser10) proteins and by upregulating the c-JUN signaling pathway. The combination of BRAF inhibition and axitinib significantly inhibited tumor growth and was associated with improved survival in an orthotopic ATC model. Conclusions: The novel combination of axitinib and BRAF V600E inhibition enhanced anticancer activity in in vitro and in vivo models of BRAF V600E -mutant ATC. This combination may have clinical utility in BRAF V600E -mutant ATC that is refractory to current standard therapy, namely combined BRAF and MEK inhibition.