FOLH1 and neoplasm: Small animal PET studies using PSMA-positive PC-3 PIP and PSMA-negative PC-3 tumor-bearing nude mice revealed specific uptake of 21 (13%ID/g) and 22 (6%ID/g) in PC-3 PIP tumors at 60 min p.i. Highly remarkably, 21 had high uptake in the kidneys with very high retention (74 to 72%ID/g at 30 to 60 min p.i.), while 22 showed very low uptake in the kidneys of 7.5%ID/g at 30 min p.i. with rapid clearance (0.9%ID/g at 120 min p.i.).