Endocrine Abstracts

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor arising from parafollicular C-cells. Differently to other neuroendocrine tumors, the information on MTC tumor microenvironment and its role in in therapy resistance are scanty, mainly because of the lack of reliable in vitro models. We hypothesized that, similarly to other cancers, MTC cells may have a certain degree of plasticity that could be modulated by variable microenvironmental factors. The main aim of this study was the establishment of patient-derived MTC in vitro models that can be grown in different tridimensional conditions and conserve the ability to shift toward a more mesenchymal stem-like phenotype. We successfully established 8 patient-derived primary MTC lines derived from tumors harboring different genetic backgrounds and with variable aggressiveness. We characterized their phenotype and response to different microenvironmental conditions and targeted therapies through Western Blot, Confocal Microscopy, ELISAs, ELDAs, RT-qPCR and proliferation assays. Interestingly, these cells may be grown at high passage numbers without losing their plasticity when cultivated in stem-promoting conditions. In differentiation media, they conserve the ability to secrete high levels of the MTC markers, calcitonin and CEA. When cultured in tridimensional conditions they all show a significant increase in the stem and neuroendocrine precursor markers such as SOX2, OCT4, EPAS1, TUJI and FOXA1 and a shift between the Epitelial-to-Mesenchimal Transition markers, E-cadherin and Vimentin, that occurs in a spatial-dependent manner. These variations in the behavior of MTC lines partially recapitulate several of the alterations that were detected in MTC tissue samples. Moreover, changes in culture conditions, as the induction of a pseudo-hypoxic state or growth in adhesion-free environment, have a great impact on the cell lines phenotypes and their response to the anticancer drugs available for MTC treatment, such as Pralsetinib, Selpercatinib, Cabozantinib, Lenvatinib and Vandetanib. In conclusion, we report here the generation of an unprecedented valid patient-derived in vitro model that can provide further insight in MTC biology complexity and will allow future translational studies, including those aiming to understand the mechanisms underlying the onset of therapy resistance.