Melatonin synergizes BRAF-targeting agent dabrafenib for the treatment of anaplastic thyroid cancer by inhibiting AKT/hTERT signalling.

As a selective inhibitor of BRAF kinase, dabrafenib has shown potent anti-tumour activities in patients with BRAFV600E mutant anaplastic thyroid cancer. However, the resistance of thyroid cancer cells to dabrafenib limited its therapeutic effect. The effects of melatonin and dabrafenib as monotherapy or in combination on the proliferation, cell cycle arrest, apoptosis, migration and invasion of anaplastic thyroid cancer cells were examined. The molecular mechanism involved in drug combinations was also revealed. Melatonin enhanced dabrafenib-mediated inhibition of cell proliferation, migration and invasion, and promoted dabrafenib-induced apoptosis and cell cycle arrest in anaplastic thyroid cancer cells. Molecular mechanistic studies further uncovered that melatonin synergized with dabrafenib to inhibit AKT and EMT signalling pathways. Furthermore, melatonin and dabrafenib synergistically inhibited the expression of hTERT, and the inhibition of cell viability and the induction of cell cycle arrest mediated by the combination of these two drugs were reversed by hTERT overexpression. Taken together, our results demonstrated that melatonin synergized the anti-tumour effect of dabrafenib in human anaplastic thyroid cancer cells by inhibiting multiple signalling pathways, and provided new insights in exploring the potential therapeutic targets for the treatment of anaplastic thyroid cancer.