MON-513 Suppressing the Growth of Human Medullary Thyroid Cancer Cells Using FDA-Approved Drug

Abstract Medullary thyroid carcinoma (MTC) is a solid tumor of the parafollicular cells in the thyroid gland. MTC has worse prognosis, when compared with other differentiated thyroid cancers, and MTC patients with distant metastases have a low survival rate unless thyroidectomy is performed at an early stage. Furthermore, conventional treatments have only marginal benefits. Therefore, there is a need to develop novel therapeutics for MTC. Several drugs that are developed and tested in preclinical trials fail in clinical trials. Therefore, repurposing the already US Food and Drug Administration (FDA)-approved drugs towards the treatment of cancers may have potential benefits, like saving the lives of cancer patients and lowering the investment cost of drug development. Here, we explored a novel precision treatment for thyroid cancers by repurposing the FDA-approved small molecule anti-parasitic drug Nitazoxanide (NTZ). In our study, we examined the anticancer effects of NTZ on human MTC cells using the TT cell line. We treated the TT cells with different concentrations of NTZ and assessed the cell proliferation by water-soluble tetrazolium salt (WST-1) assay and oxygen consumption rate (OCR) by Seahorse extracellular flux analysis (Seahorse XFe24 Analyzer). Additionally, we determined the effects of NTZ on the protein expression of key signaling molecules that regulate MTC cell growth by western blot analysis. Our results indicated that NTZ significantly suppressed the growth of TT cells at 24 h treatment. Very importantly, NTZ reduced the basal OCR demonstrating the inhibition of mitochondrial respiration. Moreover, protein expression studies revealed that NTZ markedly reduced the key Hippo signaling pathway effector molecule TAZ and the oncogene c-myc. Interestingly, NTZ decreased the expression of epidermal growth factor receptor (EGFR) that plays an important role for RET activation in MTC. Importantly, NTZ increased the expression of p53 upregulated modulator of apoptosis (Puma). Taken together, our findings demonstrate for the first time that NTZ inhibits the growth of MTC cells and decreases the cancer cell metabolism. The mechanisms by which NTZ targets the MTC cells involve the suppression of key oncogenic proteins and upregulation of tumor suppressor molecule. Thus, our study highlights that repurposing this FDA-approved currently used drug may have a greater advantage of being tested in preclinical models of MTC, and therefore, for the rapid consideration of NTZ as a potential therapeutic drug to treat MTC patients in the near future.