Effects of selective aurora-a and aurora-b inhibitors on anaplastic thyroid cancer derived cell lines

Anaplastic thyroid carcinomas (ATC) are highly aggressive tumors unresponsive to any available radio- or chemotherapeutic protocol, with a median survival rate of 4-5 months from the time of diagnosis. We previously demonstrated that ATC are characterized by increased expression of the kinases Aurora-A, -B and -C, involved in the regulation of multiple steps of the mitotic phase, and that ATC cells are sensitive to Aurora kinase pan-inhibitors. In this study, we evaluated the efficacy of small molecule inhibitors selective for Aurora-A (MLN8237/Alisertib) and Aurora-B (AZD1152-HQPA/Barasertib) in suppressing cell growth and inducing apoptosis of four different ATC derived cell lines: CAL-62, 8305C, 8505C and BHT-101. The cells were treated with each inhibitor or with the sole vehicle DMSO, and examined by means of cell proliferation assay, immunofluorescence, cytofluorimetry, time lapse microscopy, and soft-agar colony formation. Both inhibitors were able to impair proliferation in a time- and dose-dependent manner, with IC50 comprised between 50 nM and 100 nM. Time-lapse video-microscopy performed on CAL-62 cells showed that the administration of either Alisertib or Barasertib prevented the completion of mitosis with cytokinesis leading to polyploidy. Immunofluorescence experiments evidenced in all the cells typical mitotic features of Aurora-A and Aurora-B inhibition, that is lack of histone H3 phosphorylation on Ser10, multipolar spindles with shorter microtubules, misalignment of chromosomes at the metaphase plate, and aberrant post-mitotic nuclei. The final outcome of such endoreplication was the induction of apoptosis, as demonstrated by the augmentation of sub-G0 cell population after 24 h exposition to each inhibitor. Finally, the two molecules were also capable to block anchorage-independent cell growth. In conclusion, our results demonstrated that cell proliferation and tumorigenicity of different ATC derived cell lines can be prevented by selective inhibitors of Aurora-A or -B. At present these inhibitors are both undergoing clinical trials for hematologic cancers, and they may represent a new therapeutic option for the ATC treatment.