Generation of Novel Thyroid Cancer Stem-Like Cell Clones: Effects of Resveratrol and Valproic Acid

Abstract

Anaplastic thyroid cancer is an aggressive and highly lethal cancer for which conventional therapies have proved ineffective. Cancer stem-like cells (CSCs) represent a small fraction of cells in the cancer that are resistant to chemotherapy and radiation therapy and are responsible for tumor reoccurrence and metastasis. We characterized CSCs in thyroid carcinomas and generated clones of CSC lines. Our study showed that anaplastic thyroid cancers had significantly more CSCs than well-differentiated thyroid cancers. We also showed that Aldefluor-positive cells revealed significantly higher expression of stem cell markers, self-renewal properties, thyrosphere formation, and enhanced tumorigenicity. In vivo passaging of Aldefluor-positive cells resulted in the growth of larger, more aggressive tumors. We isolated and generated two clonal spheroid CSC lines derived from anaplastic thyroid cancer that were even more enriched with stem cell markers and more tumorigenic than the freshly isolated Aldefluor-positive cells. Resveratrol and valproic acid treatment of one of the CSC lines resulted in a significant decrease in stem cell markers, Aldefluor expression, proliferation, and invasiveness, with an increase in apoptosis and thyroid differentiation markers, suggesting that these cell lines may be useful for discovering new adjuvant therapies for aggressive thyroid cancers. For the first time, we have two thyroid CSC lines that will be useful tools for the study of thyroid CSC targeted therapies.

Figure 1

Flow cytometric data of THJ-16T Aldefluor and stage-specific embryonic antigen 1 (SSEA1) content. Aldefluor panel of THJ-16T Aldefluor staining with or without DEAB (aldehyde dehydrogenase inhibitor) and the selection of Aldefluor (ALD)⁺ cells at 4.6%. SSEA1 panel of THJ-16T showing SSEA1-positive staining at 6% and the isotype control. FL1-H, aldefluor; SSC-H, side scatter.

Figure 2

Aldefluor (ALD)⁺ sphere formation. A: Sphere formation capacity of ALD⁻ and ALD⁺ sorted THJ-16T cells. B: Sphere-forming efficiency of two ATC lines (THJ-16T and FRO) comparing the percentage of spheres formed from ALD⁻ cells sorted at 10 cells per well (ALD− 10), ALD⁺ sorted at 10 cells per well (ALD+ 10), and ALD⁺ cells sorted at one cell per well (ALD+ 1). Scale bar = 50 μm (A).

Figure 3

Induction of epithelial-mesenchymal transition (EMT) in ATC. A: Growth curve of THJ-16T treated with or without (control) 2 ng/mL transforming growth factor (TGF-β)-1 for 21 days showing TGF-β exposure exhibits growth inhibition. B: RT-PCR results of ECAD down-regulation and Slug up-regulation by TGF-β treatment on THJ-16T cells normalized to 18S. C: RT-PCR results of stem cell markers NANOG, OCT4, and SOX2 up-regulation from TGF-β treatment of THJ-16T cells normalized to 18S. D: Western blot of EMT markers Slug, Twist, and Snail expression effect by TGF-β treatment of THJ-16T cells. β-Actin used as loading control. ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001 versus the control on the same day. C, control; T, TGF-β.

Figure 4

Aldefluor (ALD)⁺ xenograft tumor growth. A: Tumor growth rate of ALD⁺ and ALD⁻ THJ-16T cells injected s.c. into nude mice at 1 × 10⁵ cells per injection site. B: Tumor weights of ALD⁺, ALD⁻, and unsorted parental THJ-16T cells injected s.c. into nude mice.

Figure 5

Tumorigenicity increases with in vivo passaging. A: Tumor growth rate of Aldefluor (ALD)⁺ THJ-16T cells passaged in vivo. B: RT-PCR results for stem cell marker expression of ALD⁻ and in vivo passaged ALD⁺ (ALD⁺ P1-ALD⁺ P3) tumors. Samples normalized to 18S. C: RT-PCR results of CMET and epidermal growth factor receptor (EGFR) expression of in vivo passaged (P1 to P3) ALD⁺ tumors compared with unsorted parental THJ-16T cells grown in RPMI 1640 media with 10% fetal bovine serum (10% P1). Samples normalized to 18S. D: Western blot of Oct4 and Nanog expression from ALD⁻ tumors compared with in vivo passaged ALD⁺ tumors. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was used as a loading control. ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001. ^†P < 0.05 and ^†††P < 0.001 versus the 10% tumor.

Figure 6

Recapitulation of parental tumor in Aldefluor (ALD)⁻ and in vivo passaged ALD⁺ THJ-16T cells. The histopathological features of the P1 to P3 were similar showing cells with large nuclei and prominent nucleoli and moderate amounts of eosinophilic cytoplasm. Hematoxylin and eosin staining of ALD- P1 (A), ALD⁺ P1 (B), ALD⁺ P2 (C), and ALD⁺ P3 (D) tumor. Prominent mitotic activity is present in P1, P2, and P3 (arrows). Scale bar = 100 μm (A–D).

Figure 7

Clonal sphere enriched for stem cell markers. A: Flow cytometric analysis of Aldefluor positivity with or without DEAB (aldehyde dehydrogenase inhibitor) of D3 clone. B: Graph indicating reversal of the percentage of Aldefluor (ALD) positive versus negative cells in the parental THJ-16T cell line compared with the D3 clone. C: RT-PCR results of stem cell markers comparing the parental THJ-16T cell line with freshly sorted ALD⁺ cells and the D3 clonal line. D: Percentage of Aldefluor and stage-specific embryonic antigen 1 (SSEA1) positivity of the D3 and D6 clonal lines compared with the parental THJ-16T cell line. ^∗∗P < 0.01, and ^∗∗∗P < 0.001 versus ALD⁻. ^†P < 0.05, ^††P < 0.01, and ^†††P < 0.001 versus the 16T parental line control group.

Figure 8

Symmetric versus asymmetric division. Live, unfixed D3 spheres stained with Aldefluor and counterstained with Hoechst; 1 × 10² single cells were incubated for 72 hours to allow for cell division and then analyzed for symmetric versus asymmetric division. The D3 clone shows predominantly symmetric division over asymmetric division (82% and 18%, respectively). Scale bar = 100 μm.

Figure 9

Spheroid differentiation with serum. Graph showing a significant decrease in Aldefluor activity over time in the D3 clonal line after culturing in normal media containing 10% fetal bovine serum.

Figure 10

Clonal spheres are highly tumorigenic. The D3 clonal spheres were dissociated into single cells and freshly sorted Aldefluor (ALD)⁺ THJ-16T cells were injected s.c. into nude mice at 1 × 10⁵ cells per injection site (3 injection sites, one in each flank and one in the back). A: The D3 clone forms larger tumors faster than the ALD⁺ tumors. B: RT-PCR results comparing stem cell marker expression of the D3 tumors and the ALD⁺ tumors. ^∗P < 0.05, ^∗∗P < 0.01 versus respective ALD⁺ tumor.

Figure 11

Resveratrol induces differentiation of cancer stem-like cells (CSCs). A: MTT assay showing 72 hours resveratrol treatment at 50 μmol/L significantly reduces proliferation of CSCs. B: Resveratrol significantly decreases the invasive potential of CSCs at both ×0.5 and ×0.1 basement membrane extract concentrations. C: Flow cytometric data indicating resveratrol significantly increases apoptosis and decreases Aldefluor activity of CSCs. D: RT-PCR results indicating resveratrol induces thyroid differentiation markers of CSCs. ^∗∗P < 0.01, and ^∗∗∗P < 0.001 versus controls. RFU, relative fluorescence unit.

Figure 12

Valproic acid (VPA) induces differentiation of cancer stem-like cells (CSCs). A: Seven day VPA in vitro treatment of CSCs greatly reduces proliferative properties, as shown by MTT assay. B: VPA decreases invasion slightly at a basement membrane extract concentration of ×0.1. C: Flow cytometric analysis showing that VPA treatment dramatically increases apoptosis and decreases Aldefluor positivity. D: RT-PCR data showing VPA induces thyroid differentiation markers in CSCs. ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001 versus controls. RFU, relative fluorescence unit.

Figure 13

Resveratrol and valproic acid (VPA) treatment affects the parental 16T, its Aldefluor (ALD)⁻ and ALD⁺ fractions, and the D3 clone. The unsorted 16T, freshly isolated ALD⁻ and ALD⁺ fractions, and the D3 clone were incubated with 1 mmol/L VPA, 50 μmol/L resveratrol, or control (dimethyl sulfoxide) in spheroid media for 3 days. A: Both VPA and resveratrol significantly reduce Aldefluor activity on all fractions of cells tested, with the exception of VPA on the parental 16T, which reduces the Aldefluor activity yet it is not significant. The ALD⁻ fraction was tested and remains negative for all treatments (data not shown). B: MTT assay showing significantly reduced proliferation in all cell fractions tested with the ALD⁻ fraction the least affected. The ALD⁻ fraction proliferation rate is severely affected by the serum-free nature of the spheroid media. C: Percentage of viable cells for all cell fractions and treatment groups showing the reduction of viable cells. This also shows the severity of the serum-free media effect on the ALD⁻ fraction. ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001 versus the control group. OD, optical density.