Background: Anaplastic Thyroid Cancer (ATC) is one of the most lethal and aggressive human
malignancies. Studies have shown that Cancer Stem-Cell (CSC) phenotype is mainly responsible for ATC aggressiveness.
Cytostatic compounds are mostly ineffective because of multidrug resistance mechanisms driven
by the CSC phenotype. Taxanes have limited efficacy. Recently, CSC inhibition using plant-derived, less toxic
compounds, which have anti-cancer efficacy, has become a novel treatment modality. The aim of the study was
to evaluate the anti-cancer activity of two natural compounds (curcumin and deguelin) on ATC cells and their
CSC properties. In addition, the efficacies of these compounds were compared with that of docetaxel.
Methods: Besides control, five treatment groups were formed. ATC cells (CAL-62) were treated with curcumin,
deguelin, docetaxel, and their combinations (curcumin+docetaxel, deguelin+docetaxel) at previously determined
IC50 doses. Stemness was analyzed by quantitative estimation of sphere formation in matrigel, expression of
several cell surface markers (CD133, CD90, Nanog, and OCT3/4) using flow cytometry, and quantification of
the hypoxic status [Oxidative Stress Index (OSI) and Superoxide Dismutase (SOD) activity]. The anti-cancer
efficacies of these compounds and their combinations were evaluated by determining the alterations in the cell
cycle, apoptosis, and tumoral cell migration.
Results: Both the natural compounds (particularly curcumin) significantly suppressed the spheroid formation
and cellular motility in matrigel as well as suppressed the accumulation of cells in the G0/1 phase, in which the
maximum CSC activity is observed. The compounds did not suppress the expression of CSC markers, but twothirds
of the cells expressed CD90. Deguelin was found to be particularly effective in inducing apoptosis similar
to docetaxel at IC50 concentrations. Curcumin reduced the OSI and deguelin enhanced the SOD activity, even in
docetaxel pre-treated cells.
Conclusion: A large proportion of anaplastic tumors might consist of heterogeneous CSC population. Curcumin
and deguelin have anti-cancer and several anti-stem cell activities against ATC cells. These natural compounds
are capable of altering the aggressive behavior of ATC cells through the inhibition of the CSC phenotype. As a
novel therapeutic target, CD90 should be investigated in other ATC cell lines and in vivo models.