%0 Journal Article %A Catharina van Rij %A Cathelijne Frielink %A Robert Sharkey %A David Goldenberg %A W. McBride %A Edmund Rossi %A Chien-Hsing Chang %A Wim Oyen %A Otto Boerman %T Pretargeting of prostate cancer with an internalizing anti-EGP-1 x anti-HSG bispecific antibody %D 2011 %J Journal of Nuclear Medicine %P 1680-1680 %V 52 %N supplement 1 %X 1680 Objectives The monoclonal antibody RS7 (anti-EGP-1) effectively targets prostate cancer (PC), and because it internalizes, 111In-RS7 provides good tumor uptake. This study examined the prospects for using an anti-EGP-1 x anti-HSG bispecific antibody (bsMAb), TF12, for pretargeting. Methods Internalization of the anti-EGP1 antibody, RS7, and the bsMAb, TF12, by PC3 cells was determined in vitro in the presence or absence of di-HSG peptide (IMP288). Mice with s.c. human PC3 tumors were given 111In-TF12 and 125I-TF12 and necropsied 16 h later, while other mice were given 111In-IMP288 after the TF12 injection and then necropsied at 1, 2, 4, 24, 48, and 72 h p.i. Results RS7 and TF12 internalized at a comparable rate over 24 h, with evidence of early enhanced internalization in the presence of IMP288 (Table 1). 111In-TF12 uptake in PC3 cells was 7-fold higher than 125I-TF12 (4.9±0.6% ID/g vs. 0.7±0.2 %ID/g, respectively), indicating internalization also occurs in vivo. Nevertheless, TF12-pretargeted 111In-IMP288 uptake in the tumor was still high at 48 h after injection (50% of the %ID/g at 1 h). Conclusions Even though TF12 internalizes, it was highly effective for pretargeting prostate cancer. Due to the internalizing properties of the antibody, the radiolabel shows excellent retention in the tumorIn vitro internalization of TF12Fraction of the radiolabel that is internalized as % of the cell-associated activity %U