Abstract 339: Development of 212Pb-based Radio-DARPin therapy (RDT) for the treatment of mesothelin (MSLN)-positive solid tumors

Radioligand therapies have emerged as promising treatment modality for certain cancers. This therapeutic approach relies on a suitable tumor-targeting moiety labelled with a radioactive payload to allow the delivery of the radionuclide to cancer cells with high specificity. Due to its expression profile in tumor vs healthy tissues, MSLN is an attractive protein for targeted therapies. MSLN is a GPI-anchored membrane protein which is overexpressed in many tumor types, including ovarian cancer and pancreatic adenocarcinoma. Therapeutic approaches targeting MSLN have encountered obstacles due to the high levels of its proteolytically cleaved soluble form (sMSLN), which can sequester anti-MSLN therapeutics and potentially diminish their efficacy. To circumvent this caveat, we sought to generate a Designed Ankyrin Repeat Protein (DARPin) that binds to a membrane proximal epitope of MSLN and therefore avoids binding to sMSLN. Thanks to their small size and high affinity, DARPins are ideal vectors for targeted radiotherapies, dubbed as Radio-DARPin therapies (RDT). As radioactive payload we used 212Pb, an alpha particle-emitting radionuclide with a short half-life and a favorable decay profile which allows high energy deposition on tumor in a short time frame. Herein we report for the first time the development and initial preclinical characterization of our anti-MSLN 212Pb-RDT approach. In vitro assays revealed that the membrane proximal MSLN targeting DARPin specifically interacts with MSLN expressed on cancer cells with high affinity, and cell binding was not affected by the presence of sMSLN. The DARPin was then labelled with 212Pb and its preclinical pharmacokinetic and biodistribution profile was evaluated in MSLN-expressing xenograft tumor models. In these tumor bearing mice, the anti-MSLN 212Pb Radio-DARPin demonstrated substantial uptake into MSLN-positive tumors, while other organs only showed limited accumulation. We designed an approach to specifically target MSLN expressed on cancer cells employing DARPin technology combined with 212Pb. Our early preclinical results indicative of a favorable biodistribution profile of the 212Pb labelled MSLN DARPin motivate further development of this RDT for the treatment of patients with MSLN-positive solid tumors. Citation Format: Stephan Wullschleger,Amal Saidi,Delphine Buffet,Tania Stallons,Stefanie Riesenberg,Amy Wong,Maria Paladino,Federico Rojas,Mischa Müller,Christel Herzog,Justin Walter,Denis Villemagne,Yvonne Kaufmann,Nicole Pina,Henri Fernandez,Tamara Lekishvili,Eleni Tselempi,Jacqueline Blunschi,Liridon Abduli, Chloe Iss,Amelie Croset,Clara Domke,Aaron Schatzmann,Anne Goubier,Julien Torgue,Daniel Steiner. Development of 212Pb-based Radio-DARPin therapy (RDT) for the treatment of mesothelin (MSLN)-positive solid tumors [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 339.