Synthesis and evaluation of technetium-99m-and rhenium-labeled inhibitors of the prostate-specific membrane antigen (PSMA)

The prostate- specific membrane antigen (PSMA) is increasingly recognized as a viable target for imaging and therapy of cancer. We prepared seven 99'Tc/Re-labeled compounds by attaching known Tc/Re chelating agents to an amino-functionalized PSMA inhibitor (lys-NHCONH-glu) with or without a variable length linker moiety. Ki values ranged from 0.17 to 199 nM. Ex vivo biodistribution and in vivo imaging demonstrated the degree of specific binding to engineered PSMA+ PC3 PIP tumors. PC3-PIP cells are derived from PO that have been transduced with the gene for PSMA. Despite demonstrating nearly the lowest PSMA inhibitory potency of this series, [99`Tc(COXLI)]+ (LI = (2-pyridylmethVI)2N(CH,,)4CH(COH)NHCO-(CH2)6CO-NH-lys-NHCONH-glu) showed the highest, most selective PIP tumor uptake, at 7.9 4.0% injected dose per gram of tissue at 30 min postinjection. Radioactivity cleared from nontarget tissues to produce a PIP to flu (PSMA-PC3) ratio of 44:1 at 120 min postinjection. PSMA can accommodate the steric requirements of 99"Tc/Re complexes within PSMA inhibitors, the best results achieved with a linker moiety between the e amine of the urea lysine and the chelator.