Uloga mTOR i MAPK signalnih puteva u rezistenciji karcinoma štitaste žlezde na hemioterapiju
The role of mTOR and MAPK signaling pathways in resistance of thyroid carcinoma to chemotherapy.
Doctoral thesis (Published version)
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Thyroid carcinoma is the most common malignancy of the endocrine system. Thyroid malignancies are classified according to their histopathological characteristic as papillary, follicular, medullary and anaplastic thyroid carcinoma (ATC). Most thyroid malignancies (papillary thyroid carcinoma and follicular thyroid carcinoma) are well differentiated and have favorable prognosis. On the other hand, ATC is one of the most aggressive human cancers, with an intrinsic resistance and dismal prognosis despite various therapeutic modalities. Changes in components of RAS/MAPK/ERK and PI3K/AKT/mTORpathways are common in thyroid cancer genesis which are resistant to classic chemotherapy agents. Changes in the activity of RAS/MAPK/ERK and PI3K/AKT/mTORsignaling pathways can lead to drug resistance. Besides these changes, possible cause of chemotherapy resistance is also multi-drug resistance (MDR). The most common cause of MDR is high expression of P-gp and BCRP proteins. The aim of this study was to investigate the role of the key components of RAS/MAPK/ERK and PI3K/AKT/mTOR pathways in the pathogenesis and chemoresistance of ATC. We analyzed gene and protein changes in set of ATC patient samples. We also investigated the role of inhibition of RAS/MAPK/ERK and PI3K/AKT/mTOR pathways in ATC chemosensitization using human ATC cell lines. The role of P-gp and BCRP proteins in ATC chemoresistance was also investigated. Analysis of alterations in RAS/MAPK/ERK and PI3K/AKT/mTOR pathways in ATC patients indicated that both pathways cooperate in the development of ATC. Our results revealed a negative correlation between the activity of RAS/MAPK/ERK and PI3K/AKT/mTOR pathways in the samples of ATC patients. NRAS oncogene and p53 tumor suppressor are mutated with high frequency in our set of ATC samples. NRAS is dominantly mutated gene, indicating the importance of this gene in ATC development. All detected mutations in NRAS gene, and two mutations in p53 gene, have never been reported in ATC genesis before. In vitro results suggest that the inhibition of either RAS/MAPK/ERK or PI3K/AKT/mTOR components may confer sensitivity of ATC cells to classic chemotherapeutics. Treatment with dual mTOR inhibitor, AZD2014, alone or in combination with paclitaxel (PTX) or doxorubicin (DOX) was shown to be the most effective. Immunohistochemical analysis showed high P-gp and BCRP expression in our ATC samples, which indicates the role of these proteins in ATC chemoresistance. We sorted ATC cells with the low Rhodamin123 (Rho123) accumulation which is substrate of P-gp protein and established new ATC cell line. In this way we obtained in vitro model system more similar to the patients’ phenotype, then comercial ATC cell lines used in this study. We investigated the potential of dual mTOR inhibitor, AZD2014 combined with PTX to sensitize this new ATC cell line. It was showed that treatment with AZD2014 not only sensitizes ATC cells to PTX, but also combined with this cytostatic, efficiently inhibits ATC cell migration and invasion. Taking into account that chemoresistance and invasiveness of ATC are the main causes of poor outcome, the application of dual mTOR inhibitor combined with PTX, seems to be a logical therapeutic strategy for patients with ATC.
Keywords:Anaplastic thyroid cancer (ATC); RAS/MAPK/ERK pathway; PI3K/AKT/mTOR pathway; ATC chemoresistance; ATC invasiveness; Dual mTOR; Inhibitor; AZD2014; Paclitaxel (PTX)
Source:University of Belgrade, Faculty of Biology, 2014, 1-122
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