[In vivo and in vitro stability of ¹³¹I-Herceptin and its form of existence in the blood of rabbits].

Objective: To evaluate the in vivo and in vitro stability of (131)I-Herceptin and its form of existence in the blood.

Methods: Herceptin was labelled with iodine-131 using the Iodogen method. (131)I-Herceptin was stored at 4 degrees celsius for 3, 24, 48, 72 and 96 h, and the radiochemical purity (RCP) was measured by high performance liquid chromatography (HPLC). Five rabbits received injections of (131)I-Herceptin and at 1, 3, 6, 24, 48, 72, 96 and 120 h after the injection, blood samples were taken to measure the RCP of (131)I-Herceptin in the serum, and the radio count of the serum and blood cells was calculated.

Results: The baseline RCP of (131)I-Herceptin was (94.9±2.7)%. The RCP was stable after placement at 4 degrees celsius for not over 72 h (F=15.985, P<0.001), but was significantly lowered to (82.6±2.8)% after preservation for over 72 h (t=9.971, P<0.001). Within the time of 1.0 to 96 h after injection in rabbits, (131)I-Herceptin existed mainly in the serum with a radio count of 81%-87%; 24 h after the injection, the RCP of (131)I-Herceptin in the serum was significantly lowered to (75.4±3.9)% (t=6.564, P<0.001).

Conclusion: Storage at 4 degrees celsius for no more than 72 h does not obviously affect the activity of (131)I-Herceptin in terms of RCP. After injection in rabbits, (131)I-Herceptin exists mainly in the serum and its radiochemical purity remains stable within 24 h, after which obvious degradation occurs.