The effects of Aurora Kinase inhibition on thyroid cancer growth and sensitivity to MAPK-directed therapies.

Thyroid cancer is one of the deadliest endocrine cancers, and its incidence has been increasing. While mutations in BRAF are common in thyroid cancer, advanced PTC patients currently lack therapeutic options targeting the MAPK pathway, and despite the approved combination of BRAF and MEK1/2 inhibition for BRAF-mutant ATC, resistance often occurs. Here, we assess growth and signaling responses to combined BRAF and MEK1/2 inhibition in a panel of BRAF-mutant thyroid cancer cell lines. We first showed that combined BRAF and MEK1/2 inhibition synergistically inhibits cell growth in four out of six of the -BRAF-mutant thyroid cancer cell lines tested. Western blotting showed that the MAPK pathway was robustly inhibited in all cell lines. Therefore, to identify potential mechanisms of resistance, we performed RNA-sequencing in cells sensitive or resistant to MEK1/2 inhibition. In response to MEK1/2 inhibition, we identified a downregulation of Aurora Kinase B (AURKB) in sensitive but not resistant cells. We further demonstrated that combined MEK1/2 and AURKB inhibition slowed cell growth, which was phenocopied by inhibiting AURKB and ERK1/2. Finally, we show that combined AURKB and ERK1/2 inhibition induces apoptosis in BRAF-mutant thyroid cancer cell lines, together suggesting a potential combination therapy for BRAF-mutant thyroid cancer patients.