Lys(CO-C3-p-I-Ph)-O-tBu is a pharmacokinetic modifier (PK modifier) that can improve the PK properties of PSMA ligand molecules. Lys(CO-C3-p-I-Ph)-O-tBu can increase the residence time of PSMA ligand in plasma by increasing its binding capacity to albumin. Lys(CO-C3-p-I-Ph)-O-tBu also reduces salivary gland absorption, possibly extending the half-life of the active compound. Ac-PSMA-trillium is a suitable PSMA-targeting compound that has different biological applications after modification with different radioactive isotopes. If labeled with ¹¹¹In, it can be used as DOTA chelating agent and imaging agent. Or labeled with ²²⁵Ac as a Macropa chelator for targeted radionuclide therapy (TRT) in the study of metastatic castration-resistant prostate cancer (mCRPC)^[1][2].