Reactivated thyroid hormone receptor β attenuates anaplastic thyroid cancer (ATC) stem cell activity.

Anaplastic thyroid cancer (ATC) is one of the most aggressive solid cancers in humans, with limited treatment options. Recent studies suggest that cancer stem cell (CSC) activity contributes to therapeutic resistance and recurrence of ATC. We show that the expression of the endogenous thyroid hormone receptor β gene (THRB) is silenced in ATC and demonstrate that the exogenously expressed TRβ suppresses CSC activity. Decitabine is one of the demethylation agents to treat myelodysplastic syndrome and acute myeloid leukemia patients and is currently in clinical trials for hematopoietic malignancies and solid tumors. We aim to show that the re-expression of the endogenous THRB gene by decitabine can attenuate CSC activity to block ATC tumor growth. We treated ATC cell lines derived from human ATC tumors (11T and 16T cells) with decitabine and evaluated the effects of the reactivated endogenous TRβ on CSC activity in vitro and in vivo xenograft models. We found that treatment of 11T and 16T cells with decitabine reactivated the expression of endogenous TRβ, as evidenced by western blot and immunohistochemical analyses. The expressed TRβ inhibited cell proliferation by arresting cells at the S phase, increased apoptotic cell death by upregulation of cleaved caspase-3, and markedly suppressed the expression of CSC regulators, including cMYC, ALDH, SOX2, CD44, and β-catenin. Decitabine also inhibited xenograft tumor growth by suppressing CSC activity, inhibiting cancer cell proliferation, and increasing apoptosis. Our findings suggest that re-expression of the endogenous TRβ is a novel therapeutic approach for ATC via suppression of CSC activity.