203Pb-DOTAM-GRPR1

203Pb-DOTAM-GRPR1 is a targeted radiopharmaceutical comprising lead-203 (^203Pb), the chelator DOTAM (1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane), and a peptide antagonist (GRPR1) that specifically binds the gastrin-releasing peptide receptor (GRPR). It is structurally and mechanistically analogous to 212Pb-DOTAM-GRPR1, which substitutes ^212Pb as the therapeutic alpha-emitting radionuclide, while ^203Pb often serves as a SPECT imaging surrogate for dosimetry and biodistribution studies due to its similar chemical properties and gamma emission profile. The compound targets cancers expressing GRPR—such as prostate, breast, lung, colorectal, cervical, and melanoma—enabling precise delivery of radioactivity for either diagnostic imaging (when labeled with ^203Pb) or therapy (when labeled with ^212Pb). The antagonist peptide component provides specific GRPR binding without activation, leading to selective localization and potential cytotoxicity when radioactivity is delivered. Primary developers include Orano Med, and the agent is being evaluated in early-phase trials for various advanced GRPR-positive malignancies[4][2][3].