C-Myc Is a Major Determinant for Antitumor Activity of Aurora A Kinase Inhibitor MLN8237 in Thyroid Cancer

c-Myc is overexpressed in different types of cancer, including thyroid cancer, and has been considered undruggable. There is evidence showing that MLN8237, a type of aurora A kinase (AURKA) inhibitor, destabilizes c-Myc proteins in liver cancer cells through disruption of the c-Myc/AURKA complex. However, the role of MLN8237 in thyroid cancer remains largely unclear. The aims of this study were to test the therapeutic potential of MLN8237 in thyroid cancer, and to analyze determinant factors affecting the response of thyroid cancer cells to MLN8237 and clarify the corresponding mechanism. Methods: The phenotypic effects of MLN8237 in thyroid cancer cells were evaluated through a series of in vitro and in vivo experiments, and the mechanism of c-Myc affecting MLN8237 response were explored using Western blot, ubiquitination, and cycloheximide chase assays. Results: The data show that the levels of c-Myc protein were strongly associated with MLN8237 cellular response in thyroid cancer cells. Only the cells with high c-Myc expression exhibited growth inhibition upon MLN8237 treatment. However, MLN8237 barely affected the growth of those with low c-Myc expression. Mechanistically, MLN8237 dramatically promoted proteasomal degradation of c-Myc proteins through disruption of the c-Myc/AURKA complex in the cells with high c-Myc expression. A similar antitumor activity of MLN8237 was also found in xenograft tumor models. Conclusions: The data demonstrate that c-Myc is a major determinant for MLN8237 responsiveness in thyroid cancer cells. Thus, indirectly targeting c-Myc by MLN8237 may be an effective strategy for thyroid cancer overexpressing c-Myc.