Identification of novel and highly potent deiodinase type 1 selective inhibitors via a non-radioactive high throughput screening assay

German. Deiodinase type 1 (DIO1), a selenocysteine-containing enzyme belonging to the deiodinase (DIO) family, plays an essential role in the systemic and local modulation of thyroid hormone (TH) availability. However, DIO1 not only converts the prohormone thyroxine (T4) to the active triiodothyronine (T3) but also degrades T3 to the inactive 3,3'-diiodothyronine (3,3'-T2). In the liver, T3 concentrations affect glucose, lipid, and cholesterol metabolism. Alterations to the local TH concentrations play a role in the progression of hepatic diseases; e.g., subclinical hypothyroidism is associated with the development of non-alcoholic fatty liver and its sequelae. Therefore, DIO1, a prominent hepatic deiodinase, is a critical target to decipher and modulate hepatic T3 contractions in exerting beneficial, antisteatotic effects. We used a High Throughput Screening (HTS) approach to identify novel and potent DIO1-selective inhibitors by screening 69344 small molecular weight compounds. The HTS assay is based on the iodide-catalysed Sandell-Kolthoff reaction and was used to screen large substance libraries consisting of FDA-approved drugs and pharmacologically active compounds. The HTS screen flagged known DIO1 inhibitors like propylthiouracil (PTU), aurothioglucose and genistein, corroborating its efficacy. After a validation screen with the most potent 352 compounds, we prioritised 28 compounds to characterise the DIO1-selective inhibition comprehensively. We identified 16 highly potent and DIO1-selective compounds, not interfering with DIO2 or DIO3 at their IC50s < 1µM. These inhibitors are more effective than PTU, the bonafide DIO1-selective inhibitor, which also blocks thyroperoxidase. We aim to assess these novel DIO1-selective inhibitors in DIO1-expressing cell lines. Unravelling the role of hepatic T3 in lipid and energy metabolism and modulating T3 concentrations via DIO1 inhibitors may provide novel avenues for therapeutic intervention and exerting antisteatotic effects.