Synthesis and Preclinical Evaluation of a Bispecific PSMA-617/RM2 Heterodimer Targeting Prostate Cancer

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have been used for diagnostic molecular imaging/therapy of prostate cancer (PCa). To address tumor heterogeneity, we synthesized and evaluated a bispecific PSMA/GRPR ligand (<b>3</b>) combining PSMA-617 (<b>1</b>) and the GRPR antagonist RM2 (<b>2</b>) with the radiometal chelator DOTA. <b>3</b> was radiolabeled with ⁶⁸Ga ([⁶⁸Ga]Ga-<b>3</b>) and ¹⁷⁷Lu ([¹⁷⁷Lu]Lu-<b>3</b>). [⁶⁸Ga]Ga-<b>3</b> was tested in the following PCa cell lines for receptor affinity, time kinetic cell-binding/specificity, and cell-internalization: PC-3 and LNCaP. Compared to the monomers (<b>1</b> and <b>2</b>), ligand <b>3</b> showed specific cell binding, similar receptor affinities, and higher lipophilicity, while its internalization rates and cell-binding were superior. Docking calculations showed that <b>3</b> can have binding interactions of PSMA-617 (<b>1</b>) inside the PSMA receptor funnel and RM2 (<b>2</b>) inside the GRPR. <i>In vivo</i> biodistribution studies for [⁶⁸Ga]Ga-<b>3</b> showed dual targeting for PSMA(+) and GRPR(+) tumors and higher tumor uptake, faster pharmacokinetic, and lower kidney uptake compared to <b>1</b> and <b>2</b>.