Abstract B041: Deciphering the Mechanisms of Action of 212Pb-based PSMA-targeting Radioligand Therapies

Abstract Introduction: Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) with lutetium-177 (177Lu), a beta-emitter, with proven clinical benefit as treatment of prostate cancer (PC). Although emerging clinical data indicate better efficacy with alpha-emitters, the toxicities associated with actinium-225 (225Ac) may limit its broad application, and application in earlier lines of therapy. Lead-212 (212Pb), is a promising isotope for targeted alpha therapy with high linear energy transfer, a short half-life of 10.6 hours, and a simple decay scheme. These properties promote efficient killing of PSMA+ PC cells while limiting off-target toxicities. Here we present combined in vitro and in vivo models, omics approaches, and functional assays elucidating the intrinsic cellular mechanisms of response to 212Pb-PSMA RLT. Materials and Methods: 212Pb-ADVC001, a novel 212Pb-based PSMA-targeting RLT currently in Phase I/II clinical development (NCT05720130) for the treatment of metastatic PC, was used as 212Pb RLT. The cytotoxic activity in PC cell lines was measured by cell viability assays and in vivo studies. The kinetic mechanisms associated with 212Pb-ADVC001 mediated cell-death were assessed in vitro and ex vivo using transcriptomics and proteomics approaches, and their impact on the PC cell cycle by flow cytometry. Results: 212Pb-ADVC001 displayed potent cytotoxic activity with an average EC50 of 2.7, 7.2 and 3.3 kBq/mL in PC cell lines PC-3-PIP (PSMAhigh), C4-2 (PSMAint) and LNCaP (PSMAint), respectively. Transcriptomic analysis of in vitro treated PC cells and proteomic analysis of tumors harvested longitudinally revealed multiple mechanisms of action involving DNA damage, cell cycle arrest and cell death, and immune response modulation. In vitro cell cycle experiment further confirmed that 212Pb-ADVC001 caused significant DNA damage, and reduced DNA content in the S-phase of the cell cycle with a concomitant increase in the G1 and G2/M-phase arrest compared to 177Lu-PSMA-I&T (p<0.05). Conclusion: Transcriptomic and proteomic analyses indicate multiple 212Pb-PSMA treatment mechanisms of action collectively resulting in effective cancer cell kill. Mechanistic studies furthered the understanding of PC radiobiology and cellular responses to beta- and alpha-based RLT with the identification of a cell cycle arrest in PC specifically induced by 212Pb-PSMA. Citation Format: Feifei Liu, Melissa E. Monterosso, Didier Boucher, Anna Amiss, Stelle Shakti, Kwong Ching. Liu, Abby Sydes, Aneesha Jones, Jaimee Hesse, Chanwoo Kim, Aimee Horsfall, Kevin Kuan, William Tieu, Stephen Rose, Simon Puttick, Gary Li, Anna Karmann, Thomas Kryza. Deciphering the Mechanisms of Action of 212Pb-based PSMA-targeting Radioligand Therapies [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B041.