In the direct labeling of antibodies with Re-186, 188, the lower redox
potential of ReO4- than TcO4- requires the addition of excess SnCl2 a
nd a medium-chelating agent for stabilizing the excess of SnCl2 in sol
ution. Through extensive tests, sodium glucoheptonate (GH) was chosen
as an excellent stabilizer for SnCl2 and also the reduced Re(V) from a
variety of chelators, such as citrate, cyclodextrin, tartrate, inosit
ol, glucose, glycine, etc. ReO4- solution was then quantitatively redu
ced for 2 h with newly prepared SnCl2(GH) solution. Then, we directly
incorporated the reduced Re to the antibodies IgG modified with 135 fo
rd of NaHSO3 and 3500 fold of 2-ME, and more than 90% of specific bind
ing was yielded in 100-150 min at room temperature. TLC analysis indic
ated that less than 5% of activity was in the colloid form. Radiolabel
ed antibodies IgG were stable to the challenging of 700 fold of DTPA,
and also showed fine in vivo stability.