Radiolabeling of Fulvestrant with I-131

To prepare the ¹³¹I-fulvestrant, the fulvestrant was radiolabeled with ¹³¹I using an optimized Chloramine T (Ch-T) method. Initially, 50 µl of fulvestrant was combined with 100 µl of Chloramine T in a standard EP tube. Subsequently, 1 mCi of Na¹³¹I was added, followed by vigorous shaking for uniform mixing. This mixture was then allowed to incubate at room temperature for 5 min. To cease the iodination reaction, 200 µl of sodium metabisulfite was introduced into the tube. The solution was incubated again at room temperature, ensuring a pH of 7.5, for 5 min. This termination step was performed five times.