Synergistic Effects of Lenvatinib (E7080) and MEK Inhibitors against Anaplastic Thyroid Cancer in Preclinical Models

SIMPLE SUMMARY: Lenvatinib has been found to be effective against radioiodine-refractory thyroid cancer. However, compliance with lenvatinib therapy is poor due to cancer progression and adverse effects. To improve the success rate of lenvatinib treatment, we propose a combination of lenvatinib and another drug class that has a different target than lenvatinib. We tested the potential of this combination in preclinical models and found that it is effective in our models. The combination also does not cause significant adverse effects in our mouse model. Thus, our results suggest that the combination we propose in this study is a potential therapeutic approach for thyroid cancer that is not responsive to radiotherapy. ABSTRACT: E7080, known as lenvatinib, is an oral multitargeted tyrosine kinase inhibitor that has been shown to improve the survival rate of patients with radioiodine-refractory thyroid cancer. However, a majority of patients do not continue lenvatinib intake due to disease progression or significant toxicity. To improve treatment success rates, we propose the combination of lenvatinib with mitogen-activated protein kinase (MEK) inhibitors. To test this hypothesis, we tested the effects of lenvatinib with the MEK inhibitor U0126 in vitro using two human anaplastic thyroid cancer (ATC) cell lines, 8505C and TCO1, and with another MEK inhibitor, selumetinib (AZD6244), in an ATC mouse model. We found that the combination of lenvatinib with MEK inhibitors enhanced the antitumor effects of monotherapy with either agent in vitro and in vivo, and these effects may be through the AKT (Protein Kinase B) and extracellular signal-regulated kinase (ERK) signaling pathways. Furthermore, the combination does not have significant adverse effects in the ATC mouse models in terms of body weight, blood biochemical parameters, and histopathology. In conclusion, the combination of lenvatinib with an MEK inhibitor is a potentially viable therapeutic approach for ATC treatment.