PAPILLARY THYROID CANCER IS CHARACTERIZED BY ALTERED EXPRESSION OF GENES INVOLVED IN THE SUMOYLATION PROCESS.

Small Ubiquitin–like MOdifier (SUMO) proteins are small protein modifiers capable of regulating cellular localization and function of target proteins. Over the last few years, a relevant role has been demonstrated for sumoylation in the modulation of important cellular processes, including gene transcription, DNA repair, cell-cycle regulation and apoptosis. Components of the sumoylation machinery have been found deregulated in different human cancers, and are thought to significantly affect cancer cell progression. In the present study we sought to analyze the expression of all the components of the sumoylation machinery in a case study comprising 77 papillary thyroid cancers (PTC) and normal matched tissues. In particular, we evaluated the expression of the SENP1 to SENP8 (SENtrin-specific proteases), SAE1 (SUMO1 activating enzyme subunit 1), UBA2 (UBiquitin-like modifier activating enzyme 2), UBC9 (UBiquitin conjugating enzyme 9), RanBP2 (RAN binding protein 2), MSMCE2 (Non- SMC element 2), CBX4 (ChromoBoX homolog 4), PIAS1 to PIAS4 (protein inhibitor of activated STAT), ZMIZ1 (zinc finger, MIZ-type containing 1) and ZMIZ2 (Zinc finger, MIZ-type containing 2) by means of quantitative RT-PCR. In most of the PTC examined we observed a significant alteration in the mRNAs of SENP8, ZMIZ1, SAE1, PIAS1 and PIAS2. These tended to be reduced in about 50 to 66% of cases, and unchanged or increased in the remaining ones. Univariate and Kaplan-Mayer analyses documented the lack of association between the expression of the above 5 genes and clinicopathological parameters. Only SAE1 was significantly higher in female PTC tissues, in respect to male PTC tissues (p=0.021), and SENP8 was significantly lower in TNM stages III-V, with respect to stages I-II (p=0.047). In conclusion, we demonstrated that the expression of SENP8, SAE1, PIAS1, PIAS2 and ZMIZ1 is deregulated in the majority of PTC tissues, likely contributing to the PTC phenotype. However, differently from other human cancers, their mRNA level does not represent a prognostic biomarker in PTC patients.

Selective inhibitors of aurora kinases inhibit proliferation, reduce cell viability and impair cell cycle progression in papillary thyroid carcinoma cells.

The three members of the Aurora kinase family, Aurora-A, -B and -C, regulate several aspects of the mitotic process, and their aberrant expression and/or function causes mitotic abnormalities leading either to cell death or aneuploidy. They are found overexpressed in several human malignancies, including the papillary thyroid carcinoma (PTC). In the present study, we sought to establish whether Aurora kinase inhibition could be of any therapeutic value in the treatment of aggressive forms of PTC, enduring to radioactive iodide (RAI) ablation. To this end, the effects of selective inhibitors of Aurora-A (MLN8237) and Aurora-B (AZD1152) were analyzed on 3 human PTC cell lines expressing either wild-type (K1 and TPC1) or mutant p53 (BCPAP). The two inhibitors were capable of reducing cell proliferation in a time- and dose-dependent manner, with IC50 comprised between 65.4 and 114.9 nM for MLN8237, and between 26.6 and 484.6 nM for AZD1152. Immunofluorescence experiments confirmed that AZD1152 inhibited Aurora-B phosphorylation of histone H3 on Ser10, however, it did not affect Aurora-A autophosphorylation. MLN8237 inhibited Aurora-A autophosphorylation as expected, but at concentrations required to achieve the maximum antiproliferative effects it also abolished H3 (Ser10) phosphorylation. Time-lapse videomicroscopy evidenced that both inhibitors prevented the completion of cytokinesis, and cytofluorimetric analysis showed accumulation of cells in G2/M phase and/or polyploidy. Apoptosis was induced in all the cells by both inhibitors independently from the p53 status. In conclusion, in the present preclinical study MLN8237 and AZD1152 have emerged as promising drug candidates for RAI-insensitive PTC.

The dual Aurora kinase inhibitor ZM447439 prevents anaplastic thyroid cancer cell growth and tumorigenicity.

The anaplastic thyroid cancer (ATC) is among the most aggressive human tumors which fail to respond to all the currently available therapeutic approaches. As a consequence most patients die within a few months from diagnosis. In the present preclinical study, the effects of the ZM447439, a functional inhibitor of Aurora kinases, on the growth and tumorigenicity of a panel of ATC derived cell lines (CAL-62, 8305C, 8505C and BHT-101) were evaluated. The treatment of the different ATC cells with ZM447439 inhibited proliferation in a time- and dose-dependent manner, with IC50 comprised between 0.5 mM and 5 mM. Moreover, the drug remarkably impaired the formation of colonies in soft agar of all the cell lines. Consistently with Aurora inhibition, immunofluorescence and immunoblotting experiments demonstrated that Aurora auto-phosphorylation following drug treatment was completely abrogated, and treated cells were characterized by the presence of multiple spindles with short microtubules. In the same experiments we observed the loss of histone H3 phosphorylation on Ser10, specifically due to Aurora-B, after ZM447439 treatment. Time-lapse videomicroscopy and flow cytometric analysis demonstrated that in presence of ZM447439 the cells were able to enter mitosis but not to complete it, becoming polyploid. Almost all the ATC cell lines studied showed increased apoptosis after only 48 h of treatment. In conclusion, our data demonstrate that ZM447439 is effective in reducing cell growth and tumorigenicity of different ATC derived cell lines, and further investigations are needed to exploit its potential therapeutic value for ATC treatment.