Background: Medullary thyroid cancer (MTC), which makes up 5-10% of all thyroid cancers, is a highly aggressive and chemotherapeutically resistant cancer originating from parafollicular C cells of the thyroid. In recent years, testing of new biological, chemical or natural compounds as an alternative to existing agents used in cancer treatment has been a popular research topic. One of these compounds is boric acid originating from the element boron, and studies have shown that it has anti-carcinogenic, anti-osteoporotic and anti-oxidant effects. Purpose: The aim of this study is to determine the therapeutic effects of boric acid on cell proliferation, invasion, migration, colony formation, cell cycle and apoptosis mechanisms in TT medullary thyroid cancer cell line under in vitro conditions.Methodology: The effects of boric acid on cell viability was determined by XTT assay. Total RNA was isolated by Trizol reagent. Gene and miRNA expressions were analyzed by RT-PCR. Effects of boric acid on apoptosis were analyzed by TUNEL assay and genotoxicity was performed by comet assay. Effects of boric acid on cell invasion, colony formation and cell migration were detected by matrigel-chamber, colony formation assay and wound healing assay, respectively. Results: In order to determine the effect of boric acid on cell viability and 50% lethal dose, the XTT method was employed and IC50 dose was found to be 35 μM at 48th hour. A real-time PCR test was used to investigate changes in cell cycle and apoptosis related genes and proteins and identified miRNAs under the addition of boric acid. In addition, miR-21 was significantly reduced in medullary thyroid cancer associated with cancer aggressiveness and poor prognosis. Using the Tunnel test, the apoptosis rate in the dose group cells were found as 14%. Matrigel invasion test showed a 30.8% decrease in invasion in the dose group and colony formation test decreased 67.9% in the dose group. Using the wound healing assay, it has been found that migration was reduced, and the Comet assay has shown that DNA fractures increased after treatment with boric acid.Conclusion: In conclusion, the findings of this study have shown that boric acid can be used as a potential anticancer agent in medullary thyroid cancer and other cancers caused by similar mechanisms.

Background Medullary thyroid cancer (MTC) is an aggressive, chemoresistant form originating from the thyroid parafollicular C cells, has spurred interest in alternative treatments like boric acid, a boron-based compound has demonstrated anti-carcinogenic effects. Materials and Methods Cell viability were determined using 2,3-bis(2-methoxy-4 nitro-5- sulfophenyl- 2H-tetrazolium- 5-carboxanilide (XTT) assay.. Total RNA was isolated with Trizol reagent for gene and miRNA analysis via reverse transcription polymerase chain reaction (RT-PCR). Terminal deoxynucleotidyl transferase dUTP nick end labeling assay (TUNEL) and comet assays evaluated boric acid's impact on apoptosis and genotoxicity, respectively. We also examined its influence on cell invasion, colony formation, and migration using matrigel- chamber, colony formation, and wound healing assays. Results 50% lethal dose (IC50) of boric acid was 35 µM at 48 hours. Real-time PCR showed changes at apoptosis-related genes, and miRNAs post-treatment. Significant increases in the expression of NOXA, apoptotic protease activating factor 1 (APAF-1), Bcl-2-associated X protein (Bax), caspase-3, and caspase-9, which are associated with apoptosis, were observed. Additionally, the expression of B-cell lymphoma 2 (bcl2), B- cell lymphoma‐ extra-large (bcl-xl), and microRNA-21 (miR-21), which are linked to the aggressiveness of MTC, was significantly reduced. The TUNEL assay revealed a 14% apoptosis rate, while assays showed a 30.8% decrease in cell invasion, a 67.9% decrease in colony formation, reduced cell migration, and increased DNA breaks post-treatment. Conclusions In conclusion, our findings suggest that boric acid may have potential as an anticancer agent in medullary thyroid cancer and other cancers with similar mechanisms.