Imaging of experimental prostate cancer with pretargeted immunoPET and FDG-PET

112 Objectives TROP2 (epithelial glycoprotein-1, EGP-1) is a pancarcinoma marker that is expressed at high levels on virtually all prostate carcinomas (PC). The bispecific antibody TF12 (anti-TROP2 x anti-HSG (Histamine-Succinyl-Glycine)) effectively targets PC, and provides good tumor uptake of the radiolabeled di-HSG-peptide. In this study the potential of pretargeted immunoPET with TF12 and 68Ga-labeled diHSG-hapten (IMP288) is studied in mice with s.c. PC3 tumors, using 18F-FDG-PET as a reference. Methods Two groups of athymic mice (n=5) bearing s.c. PC3 xenografts were examined. The first group was injected first with 18F-FDG (5 MBq) followed 2 days later by a pretargeting study using 2.5 nmol (462 μg) TF12 followed 16 h later with 0.1 nmol (160 ng, 5 MBq) of 68Ga -labeled di-HSG. The second group was examined first with pretargeting followed 2 days later by 18F-FDG-PET. In each group, animals were imaged 1 h after injection using a microPET/CT scanner, with all animals necropsied after the second imaging session to quantify tissue uptake. Results The pretargeting system revealed high uptake in the PC3 tumors (7.2±1.1% ID/g) and rapid blood clearance, resulting in excellent tumor-to-blood ratios (17.4±11.2) of 68Ga-IMP288 as early as 1 h after injection. Pretargeted immunoPET images nicely visualized the s.c. tumor with minimal activity in the kidneys (1.8±0.5% ID/g). Tumor uptake of 18F-FDG was significantly lower (3.4±0.9% ID/g, p Conclusions Pretargeting with TF12 in combination with 68Ga-IMP288 is an excellent system for specific pretargeted immunoPET of prostate cancer