Abstract 314: Improved tumor penetration and cytotoxic payload release with TD001, a novel PSMA-targeting ADC with optimized linker-payload composition, in PSMA-expressing CRPC CDX castrated mouse models

Abstract Prostate-specific membrane antigen (PSMA), a type II transmembrane glycoprotein belonging to the folate receptor family, is highly expressed in metastatic castration-resistant prostate cancer (mCRPC), and increases following androgen deprivation therapy (ADT). PSMA is a validated diagnostic and therapeutic target for radioligands and antibody-drug conjugates (ADCs). TD001 is a novel ADC composed of a deimmunized anti-PSMA IgG1 monoclonal antibody (HuJ591) conjugated to a highly stable protease-cleavable proprietary linker and the potent Topo I inhibitor exatecan payload. The LD038 linker-payload leverages exatecan’s ability to stabilize Topo I-DNA complexes and induce DNA damage and cell death. We tested TD001 in 2D and 3D cell cultures and in vivo in human CRPC xenograft models with different levels of PSMA expression. We evaluated cell internalization, payload release, and drug activity by flow cytometry, immunohistochemistry, and immunofluorescence microscopy. Free payload levels were measured 24 h post treatment in plasma and tumors by LC-MS/MS. TD001 showed efficient binding and rapid internalization within 1-3 h followed by lysosomal localization and payload release in PSMA-expressing cells. Due to the quick and effective payload release, TD001 exhibited selective and potent activity with the induction of Topo I-mediated DNA damage (gamma-H2AX) and apoptosis (cleaved caspase 3). TD001 had no effect on PSMA-negative cells. This was supported by 3D cell culture models, which demonstrated rapid diffusion into the extracellular matrix, and rapid internalization of TD001 into PSMA-expressing tumor cells. TD001 was evaluated in vivo in three CRPC xenograft models with different PSMA expression patterns: the high/homogenous (∼104 ligands/cell) PSMA-expressing LNCaP-abl cell line-derived xenograft (CDX) castrated mouse model, the intermediate/heterogeneous (∼102-104 ligands/cell) PSMA-expressing 22Rv1 CDX castrated mouse model, and the AR-positive, high/homogenous (∼105 ligands/cell)-PSMA-expressing patient-derived xenograft (PDX) C5 mouse model. The LD038 linker-payload in TD001 resulted in high free payload release within tumor tissue, triggering DNA damage, cell death, and growth arrest. Notably, tumor uptake and a very high tumor/plasma ratio (70-100 fold) of exatecan were similar 24 h after IV administration in all three in vivo models despite substantial differences in PSMA expression and heterogeneity. These findings highlight the ability of TD001 to deliver effectively and selectively the payload exatecan to PSMA-positive prostate tumors, resulting in potent antitumor activity in different CRPC models, including those with intermediate and heterogenous PSMA expression. Citation Format: Daniela Impellizzieri, Elisa Storelli, Atik Balla, Simone Mosole, Cristina Dongilli, Federico Jauk, Roberta Frapolli, Lavinia Morosi, Maurizio D'Incalci, Jemila Houacine, Morris Rosenberg, Bérangère Deleglise, Esteban Cvitkovic, Carlo V. Catapano. Improved tumor penetration and cytotoxic payload release with TD001, a novel PSMA-targeting ADC with optimized linker-payload composition, in PSMA-expressing CRPC CDX castrated mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 314.