TPO and thyroid gland follicular carcinoma: Thisin vitro method evaluates the peroxidase activity of TPO, a key enzyme for the synthesis of thyroid hormones. The method allows to identify TPO-inhibiting test items by assessing the enzyme activity in prepared extracts from FTC-238 human follicular thyroid carcinoma cells transfected with human recombinant TPO. TPO activity is measured through the oxidation of a commercially-available peroxidase substrate (Amplex UltraRed, AUR, ® LifeTech) and its conversion to a fluorescent product.