Thyroid cancer (TC) is a frequent neoplasm in the endocrine system. Altered expression of miRNAs has been observed during TC evolution and progression. In particular, increased miR-221 and 222 expression has prognostic value in differentiated TC (DTC) and has been initially associated with deregulation of the cell cycle. Subsequently, in DTC cells, increase in miR-221 and 222 has been associated with the presence of extracellular HMGB1, a nuclear protein that is released by necrotic or stressed cells. Interestingly, cytosolic and extracellular accumulation of HMGB1 is favored by acetylation of lysines in the nuclear localization sequence (NLS). Moreover, deacetylation of these lysines is controlled by the nuclear NAD-dependent deacetylase SIRT1, member of the sirtuins family. Another interesting aspect is that SIRT1 is a target of miR-221 and 222 in chronic inflammation or prostate cancer. Based on these evidences, our hypothesis is that the presented aspects may be mechanistically connected forming, in DTC, a loop favoring cancer cells growth and invasion. For this reason our project aims to connect these separate aspects in a unifying mechanism consisting in a vicious loop in which increased miR-221 and 222 decrease SIRT1 expression that, in turn, increases acetylation of HMGB1. Acetylated HMGB1 accumulates into the cytosol where induces protective autophagy and in the extracellular space where it favors miR-221 and 222 increase in adjacent cells. Moreover, we also aim to treat DTC spheroids with functionalized graphene oxide nanoparticles combined with anti-miR-221 and 222, SIRT1 activators, HMGB1 or autophagy inhibitors in order to reach inner cancer cells to prevent or inhibit such loop.
In conclusion, our study will define a new molecular loop for DTC development and provide a strategy to limit such a mechanism and, finally, DTC growth and progression.
The single players described in this project and namely, miR-221 and 222, SIRT1, HMGB1 and autophagy have been described in different tumors and linked to cancer promotion or inhibition. However, a unifying mechanism connecting all of them to explain their role in cancer is still missing and it is exactly the aim of the present project. In particular, our new hypothesis is that, in thyroid carcinoma, there is a vicious loop in which the observed increase of miR-221 and 222 represses SIRT1 expression causing, in turn, acetylation of HMGB1. Acetylated HMGB1 moves from the nucleus to the cytosol where induces protective autophagy and/or it is released in the extracellular space. Finally, extracellular HMGB1 contributes to miR-221 and 222 synthesis in surrounding cells. Dissection of such a loop will allow us to understand molecularly how DTC cells modify their behavior during tumor progression and how they can co-opt adjacent cells to sustain tumor growth.
In addition, based on the results of this first part, we aim also to find or describe a strategy to inhibit or revert such a mechanism to block tumor growth and invasion. In particular, we will use inhibitors or treatments that have been already validated in other tumors or pathologies such as HMGB1 blocking antibodies or antagonist, SIRT1 activators or autophagy inhibitors. Importantly, as a new strategy, we propose to combine these substances with functionalized GO nanoparticles with the aim to reach the inner part of tumor spheroids and also to increase the efficacy of the treatment.