Synthesis and Evaluation of Imidazo[2,1‐b]thiazoles as Iodide Efflux Inhibitors in Thyrocytes

The Na⁺/I^? symporter (NIS) mediates iodide uptake in the thyroid gland as well as in other NIS‐expressing cells. This transport is the basis for an emerging approach to selective cancer cell destruction by using radioiodide after targeted NIS gene transfer. Therapeutic efficacy requires that radioiodide retention be maximized in tumor cells. A first generation of forty imidazo[2,1‐b]thiazole derivatives as iodide efflux inhibitors is described along with the evaluation of their biological properties. Structure–activity relationship studies by using radioiodide uptake in rat thyroid‐derived cells (FRTL5) revealed that the 5,6‐dihydroimidazo[2,1‐b]thiazole heterocycle is required for activity. Introduction of electron‐donor substituents on the 3‐biphenyl moiety led to the discovery of novel potent compounds. A compound was identified with enhanced potency compared to reference 1 . These molecules give the possibility to increase the cellular retention of radioiodide in NIS‐expressing tumors, leading to higher absorbed doses and killing efficacy.     

Enhanced iodide sequestration by 3-biphenyl-5,6-dihydroimidazo[2,1-b]thiazole in sodium/iodide symporter (NIS)-expressing cells

The ability of the sodium/iodide symporter (NIS) to take up iodide has long provided the basis for cytoreductive gene therapy and cancer treatment with radioiodide. One of the major limitations of this approach is that radioiodide retention in NIS-expressing cells is not sufficient for their destruction. We identified and characterized a small organic molecule capable of increasing iodide retention in HEK293 cells permanently transfected with human NIS cDNA (hNIS-HEK293) and in the rat thyroid-derived cell line FRTL-5. In the presence of 3-biphenyl-4'-yl-5,6-dihydroimidazo[2,1-b]thiazole (ISA1), the transmembrane iodide concentration gradient was increased up to 4.5-fold. Our experiments indicate that the imidazothiazole derivative acts either by inhibiting anion efflux mechanisms, or by promoting the relocation of iodide into subcellular compartments. This new compound is not only an attractive chemical tool to investigate the mechanisms of iodide flux at the cellular level, but also opens promising perspectives in the treatment of cancer after NIS gene transfer.