Biological effects of thyroxine in experimental carcinogenesis

The study was undertaken to examine the in vitro and in vivo effects ofthyroxine Т₄ at the concentrations of 10ˉ⁴ M, 10ˉ⁶ M, 10ˉ M on the proliferative capacity and apoptosis of tumor cells of various pathogenesis. During the investigations, the authors used the unicellular suspension prepared from the surgical material obtained from 2 patients operated on for thyroid nodules (n = 1) and breast tumors in gynecomastia (n = 1) and evaluated the in vivo antitumor and antiproliferative activities of Т₄, by using the melanoma B-16 inoculated in C57B1 mice. In the in vitro experiments, Т₄ given in a dose of 10ˉ М produced the highest cytotoxic activity against benign thyroid tumor cells (70±4.58%; p < 0.05). When used in this dose, T₄ induced the greatest apoptotic death of the cells (9.0±0.90%; p < 0.05) as compared with the controls (1.0±0.30%). The in vitro effect of T₄ in doses of 10ˉ⁴ M, 10ˉ⁶ M, 10ˉ M on breast tumor cells in the presence of gynecomastia led to a decrease in levels of the oncogenic protein HER2/neu by an average of 27.25±1.14% (p < 0.001). In the in vivo experiments on a model of the tumor strain of melanoma B-16, T₄ at the concentrations of 10ˉ⁴ M, 10ˉ⁶ M, 10ˉ M showed a high antitumor activity (59.00±5.54%; p < 0.001 of tumor growth suppression by mass and 74.12±0.26%; p < 0.001 by volume). When given in a dose of 10ˉ M, T₄ displayed the highest antiproliferative activity (MI, 1.3±0.16%o, p < 0.001; AI, 10.65±1.39%, p < 0.001) as compared with the control group (MI, 4.96±0.43%o; AI, 4.43+0.40%).

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