[Experimental study of bio-distribution and tumor imaging of 131I in nude mice bearing human breast cancer].

Background & Objective: Previous study showed that about 85% of local and metastatic tissues of the estrogen-receptor-positive breast cancer express a large number of sodium/iodide symporter (NIS), which transfers the iodide from blood into cancer cells, leading to much higher cellular concentration in breast cancer than normal tissues. This study was designed to investigate the specific affinity of (131)I to the estrogen-receptor-positive breast cancer cells through the biodistribution and tumor imaging of the nude mice bearing breast cancer.

Methods: MCF-7/ER(+) and MCF-7/ER(-) nude mice bearing human breast cancer were prepared for the experiments. The animals were intraperitoneally injected with 37-55.5 MBq (131)I when the tumor grew to 0.8-1.0 cm. The tissue distribution of (131)I was determined at 6, 12, and 24 h after injection. The percentage of absorbed (131)I per gram of tissue (%ID/g) and the ratio of (131)I in tumor and non-tumor tissues (T/NT) were calculated. Meanwhile, the nude mice were imaged at different time.

Results: The (131)I was mainly concentrated in tumor, thyroid, blood, liver, stomach, and kidney at 6 h, and the concentration of (131)I in tumor of MCF-7/ER(+) group was significantly higher than that of MCF-7/ER(-) group at 6 h. At 12 h, the T/NT ratio of blood, heart, lung, intestine, and muscle were 2.39, 3.06, 3.94, 7.69, and 7.60, respectively, and increased to 5.15, 5.47, 5.29, 11.44, and 10.99 at 24 h. The T/NT ratio of MCF-7/ER(-) group was significantly lower than that of MCF-7/ER(+) group (P< 0.05). The imaging results showed that there was localized radioactivity in tumor tissue in the MCF-7/ER(+) group mice at 12 h, while no in MCF-7/ER(-) group mice.

Conclusion: (131)I could be concentrated particularly in the estrogen-receptor-positive nude mice bearing breast cancer tissue.