Novel HSP90 inhibitors effectively target functions of thyroid cancer stem cell preventing migration and invasion.

Background: Thyroid cancer stem cells (CSCs) with ALDH and CD44 markers contribute to tumor growth and aggressiveness. We hypothesized that novel HSP90 inhibitors (KU711, WGA-TA) and 17-AAG can effectively target the function of thyroid CSCs in vitro and prevent migration and invasion.
Methods: Validated papillary (TPC1), follicular (FTC238,WRO), and anaplastic (ACT1) human thyroid cancer cell lines were treated with 3 HSP90 inhibitors. CSCs were quantified for aldehyde dehydrogenase by flow cytometry, CD44 expression by Western blot, and thyrosphere formation assay. Cellular pathway proteins were analyzed by Western blot and migration/invasion by Boyden-chambers.
Results: WGA-TA and 17-AAG induced HSP70 compensation (not observed with KU711) on Western blot in all cell lines (>1,000 fold vs controls). Only WGA-TA degraded HSP90-Cdc37 complexing by 60-70% versus controls. Expression of HSP90 clients β-catenin, BRAF, Akt, and phospho-Akt were significantly inhibited by WGA-TA treatment (50-80%, 50-90%, >80%, and >90%) compared with controls, KU711, and 17-AAG treatment. KU711 and WGA-TA decreased CD44 expression in all cell lines (25-60% vs controls/17-AAG), decreased ALDEFLOR activity by 69-98% (P < .005), and decreased sphere formation by 64-99% (P < .05 each). Finally, cell migration was decreased by 31-98%, 100%, and 30-38%, and invasion by 75-100%, 100%, and 47% by KU711,WGA-TA, and 17-AAG treatment (P < .05) each, respectively.
Conclusion: KU711 and WGA-TA are novel HSP90 inhibitors targeting CSC function and inhibiting cell migration/invasion in differentiated and anaplastic thyroid cancers, warranting further translational evaluation in vivo.
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