Histone deacetylase inhibitors induce thyroid cancer-specific apoptosis through proteasome-dependent inhibition of TRAIL degradation.

Anaplastic thyroid carcinoma (ATC) is considered one of the most aggressive malignancies, having a poor prognosis and being refractory to conventional chemotherapy and radiotherapy. Alteration in histone deacetylase (HDAC) activity has been reported in cancer, thus encouraging the development of HDAC inhibitors, whose antitumor action has been shown in both solid and hematological malignancies. However, the molecular basis for their tumor selectivity is unknown. To find an innovative therapy for the treatment of ATCs, we studied the effects of deacetylase inhibitors on thyroid tumorigenesis models. We show that HDACs 1 and 2 are overexpressed in ATCs compared with normal cells or benign tumors and that HDAC inhibitors induce apoptosis selectively in the fully transformed thyroid cells. Our results indicate that these phenomena are mediated by a novel action of HDAC inhibitors that reduces tumor necrosis factor-related apoptosis-inducing ligand protein degradation by affecting the ubiquitin-dependent pathway. Indeed, the combined treatment with HDAC and proteasome inhibitors results in synergistic apoptosis. These results strongly encourage the preclinical application of the combination deacetylase-proteasome inhibitors for the treatment of ATC.