In vitro Evaluation der antitumoralen Effekte und des Redifferenzierungspotentials von Histondeacetylaseinhibitoren in Schilddrüsenkarzinomen

Thyroid cancer is the most common malignancy of the endocrine glands with a globally increasing incidence since decades. With the help of entrenched therapeutical regimes, differentiated thyroid carcinomas usually have an excellent prognosis, whereas those therapies fail in poorly differentiated and anaplastic thyroid carcinomas. New therapeutical options to ameliorate the prognosis of these very de-differentiated tumors, that could improve their responsiveness to conventional therapies, are needed. In addition to genetic mutations, also epigenetic aberrations have a great influence on the malignant degeneration of thyroid tissue. The potential reversibility of epigenetic changes highlights its importance for the future of cancer treatment. In the present study, the effects of the HDACi Panobinostat, SAHA and Trichostatin A (TSA) were investigated by using a cell viability analysis, furthermore their influence on NIS, HMGA2, the miRNAs hsa-let-7b-5p and hsa-let-7f-5p, the lncRNA H19 and TTF1 was analysed by qRT-PCR, Western blot and gamma counter in vitro. The effects of the treatment with HDACi were analysed in five established thyroid cancer cell lines: TPC1 (PTC), BCPAP (PTC), 8505C (PDTC), C643 (ATC) and FTC133 (FTC). All HDACi had a strong inhibitory effect on the cell proliferation in all of the cell lines tested. Panobinostat, with an inhibitory concentration of 10nM, was the most potent agent among the substances evaluated. SAHA inhibited the cell proliferation at an concentration of 10μM, TSA between 100nM and 1μM. In all of the cell lines, a strong over-expression of NIS mRNA was observed. Moreover, an induction of NIS protein was found in the cell lines BCPAP, C643 and FTC133 and increased Radioiodine uptake characterised the cells FTC133 and C643, proving an intact function of the NIS protein in these cells. Both members of the miRNA let7 family, hsa-let-7b-5p and hsa-let-7f-5p, were stable and/or over-expressed after treatment with the HDACi and did not inversely correlate with their predicted target NIS. However, an inverse correlation between let7 miRNAs and the HMGA2 oncogene was shown, since HMGA2 was overall suppressed in the cell lines. Together with the increased Radioiodine uptake, HMGA2 suppression could reflect the redifferentiation of the cells mediated by treatment with HDACi. The role of the controversely discussed lncRNA H19 was analysed, too. In the cancerous tissues of patients with PTC, FTC and ATC, the expression of lncRNA H19 was heterogeneous. H19 was over-expressed in the cell-lines after the treatment with the HDACi. Without further investigations a specific statement about a tumorsuppressive or oncogene function as well as about a causal connection regarding its expression and the treatment with HDACi cannot be made. The differentiation marker TTF1 displayed a very heterogeneous expression in both the human cancer tissues and the cell lines. Interestingly, RET/PTC mutations and BRAF mutations have a possible influence on the TTF1 expression. Based on this in vitro analysis, the potential cytotoxic efficacy of three independently investigated HDACi in thyroid carcinomas, as well as their potential to redifferentiate degenerated thyroid tissue becomes evident. Thus, future in vivo experiments for further evaluation of the possible use of HDACi in thyroid cancer therapy are urgently needed.