POLYPHENOLS AS A POTENTIAL STRATEGY IN OVERCOMING THERAPY RESISTANCE IN ANAPLASTIC THYROID CANCER THROUGH THE SOX2-SOX17 MOLECULAR SWITCH

Abstract

Anaplastic thyroid cancer (ATC) is a rare and undifferentiated endocrine tumor, without reliable therapies and poor prognosis. Due to severe early metastasis and the rapid fatal course, surgery is rarely performed, while radio and chemotherapy exhibit low efficacy. Therapy resistance is largely attributed to a loss of thyroid cell function due to the downregulation of thyroid terminal differentiation genes, among them sodium-iodide symporter (NIS), transcription termination factor (TTF-1), and thyroid peroxidase (TPO). Disrupting the circuit that sustains the acquisition of a dedifferentiated state in ATC, remains the main challenge in order to resensitize cells to conventional or novel therapies. We previously identified a cancer stem cell (CSC) subpopulation derived from ATC, characterized by high expression of several stem cell markers, such as SOX2, OCT4, and NANOG. We proposed a potential upstream role of SOX2 in regulating cell proliferation and tumor progression. In contrast, SOX17 displayed anti-tumoral properties in papillary thy- roid cancer (PTC). Its low expression positively correlates with increased PTC cell migration and invasion. However, the impact of the SOX family on thyroid cancer is unclear. Our previous in vitro studies shown that resveratrol (RSV), a natural polyphenol, could affect the stem cell features, promoting the differentiation towards the epithelial lineage by modulation of the SOX2/SOX17 balance in limbal primary mesenchymal stem cells. In this regard, two ATC cell lines, SW1736 and 8505c, were used to investigate the effects of RSV and two natural analogues, 3,4’,5-trans-trimethoxystil-bene (3-MET-OX) and isorhapontigenin (ISOR-H-PG). Polyphenol treatments did not induce apoptosis, whereas a slowdown in the cell cycle in anaplastic thyroid cells compared with normal thyroid cells (Nthy-ori) was observed. To better mimic tumor microenvironment, 3D cell culture sys- tems were employed along the traditional monolayer cultures. In 3D cultures, after 14 days of polyphenol treatments a gradual loss of spheroidal structure was observed, suggesting reduced self-renewal and enhanced differentiation. Moreover, at a molecular level, treatments resulted in a significant up-regulation of SOX17, along with the re-expres- sion of specific thyroid markers TTF-1, TPO, and NIS, indicating a possible function restoration. In conclusion, our work aims to provide new insight into upstream regulatory mechanisms in ATC dedifferentiation molecular processes by implementing a 3D cell culture model that more closely resembles the in vivo tumor environment. Our data highlight the potential antitumor effect of polyphenols as differentiation-inducing agent and a promising therapeutic agent or coadjutant component to existing treatments to overcome ATC drug resistance. Further investigation will focus on exploring the molecular upstream pathways involved in ATC dedifferentiation, as well as cytoskeletal remodeling patterns, which play a key role in the epithelial-mesenchymal transition (EMT) during the metastatic progression.