Antiproliferative and Apoptosis-Inducing Effects of Iodine Molecule in Differentiated Primary Thyroid Cancer Cells: In Vitro Study

Abstract

Thyroid cancer poses a persistent clinical challenge, particularly when conventional therapies fall short. Growing evidence suggests that molecular iodine (I₂) may exert direct antitumor effects beyond its classical role in thyroid hormone synthesis. This study evaluated the antiproliferative and apoptosis-inducing effects of I₂ on primary cell cultures derived from differentiated thyroid cancer tissue and established dose- and time-response relationships. Primary cultures were exposed to I₂ at concentrations of 5, 10, 20, 40, 80, and 100 µM for 24, 48, and 72 hours. Cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, with IC₅₀ calculated accordingly. Apoptosis was characterized by acridine orange/propidium iodide (AO/PI) double-staining, analyzed by fluorescence microscopy and ImageJ software. I₂ demonstrated clear antiproliferative and apoptotic activity in a dose- and time-dependent manner. The strongest effect appeared at 100 µM after 72 hours, reducing viability to 1.39% (p < 0.001). At the IC₅₀ of 2.09 µM, iodine significantly suppressed proliferation and induced apoptosis, with an apoptosis rate of 81.77% ± 12.24% (p = 0.004). These findings confirm the meaningful antineoplastic potential of I₂ against differentiated thyroid cancer cells. This study supports SDG 3 (Good Health and Well-Being), contributing to efforts to develop more equitable, effective cancer treatment options and to reduce cancer-related morbidity globally.