125i iodide

Chemicals and solvents were purchased from Sigma‐Aldrich (St. Louis, MO) and Merck (Germany) or otherwise as indicated. All reagents and solvents were of the highest commercially available purity grade. No‐carrier‐added (n.c.a.) sodium [¹²⁵I]‐iodide was obtained from PerkinElmer international, [¹²³I]‐iodide was from GE Healthcare international. The precursor of ^123,125I‐ITdU, precursor 5‐(trimethylstannyl)‐4′‐thio‐2′‐deoxyuridine, CAS no. 444586‐71‐4, and the unlabeled reference standard, 5‐iodo‐4′‐thio‐2′‐deoxyuridine (ITdU) CAS no. 134699‐95‐9, were synthesized as previously reported 12. Used water and acetonitrile for reagents were from Merck. ¹⁸F‐FLT was purchased from Max Planck Institute for Neurological Research (Cologne, Germany). Chloramine T (sodium N‐chloro‐p‐toluenesulfonamide trihydrate, CAS no. 7080‐50‐4) was from Sigma‐Aldrich. For concentration of the radionucleosides, a SPE cartridge (Sep‐Pak C18 Plus Short Cartridge, 360 mg sorbent, 55−105 μm particle size, part no. WAT020515, Waters, MA) was applied, conditioned by 2 mL EtOH, followed by flushing with 15 mL water. For analytical and semipreparative chromatography the following column was used: MultoKrom 100–5 C4 (250 × 4 mm, reversed‐phase column, CS‐Chromatography, Langerwehe, Germany).

FRTL-5 cells were incubated in growth media containing 20 μM iodide supplemented with 50 μCi/mmol ¹²⁵I-iodide (PerkinElmer, Waltham, MA, USA) for 30 min at 37 °C. NIS-specific iodide uptake was assessed in the presence of 80 μM K-perchlorate, a competitive inhibitor of NIS-mediated iodide transport. The accumulated radioiodide was extracted with ice-cold ethanol and then quantified in a Triathler Gamma Counter (Hidex, Turku, Finland). The amount of DNA was determined by the diphenylamine method after trichloroacetic acid precipitation [23 (link)].

Forty micrograms of HRG, 0.5 µg/µl in PBS, was mixed with ¹²⁵I-iodide (15–80 MBq; Perkin Elmer) in an IodoGen coated tube (Pierce), incubated for 30 min and purified on NAP-5 columns (GE Healthcare). The yield and radiochemical purity was analyzed using 150–771 DARK GREEN, Tec-Control Chromatography strips (Biodex Medical Systems) and eluted using 80% acetone. Bovine (Fraction V, fatty acid free, Roche) was similarly radioiodinated. Before labeling with ¹²⁴I for microPET imaging, ¹²⁴I-sodium iodide (19 MBq) was mixed with 0.04 nmol of non-radioactive sodium iodide and incubated for 20 min. Further labeling was performed as described above.