Abstract LB281: A preclinical therapeutic study of minibody 177Lu-DOTAGA-IAB56 targeting αVβ6 for the treatment of pancreatic cancer

Abstract Pancreatic cancer represents 3% of all cancers and 7% of all cancer deaths in the USA, with a majority of cases diagnosed late and with limited treatment efficacy. Radiopharmaceutical Therapy (RPT) using antibodies (Abs) is emerging as a new approach for the treatment of solid cancers. Due to the long circulation time in blood, full-length antibodies bear concerns for hematological exposure to radioactivity. Antibody fragments with lower molecular weight like minibodies (Mb, 80 kDa) show rapid blood clearance, thus reducing off-target exposure, while maintaining the high target affinity typical of immunoglobulins. Mbs consist of two scFv antigen-binding domains fused to the CH3 domain of human IgG. Integrin αVβ6 is mainly absent in healthy adult tissues but upregulated in a variety of carcinomas, including pancreatic cancer. In this preclinical proof of concept study, we evaluated a Mb targeting human αVβ6 (IAB56) as an RPT agent for the treatment of pancreatic cancer. To this end we first evaluated the β-emitter Mb 177Lu-DOTAGA-IAB56 in a dosimetry study in mice and extrapolated the organ exposures to humans. Then we tested its therapeutic efficacy in female Nu/J mice bearing the subcutaneous ductal adenocarcinoma xenograft CFPAC-1. The IAB56 Mb was conjugated with DOTAGA and radiolabeled with 177Lu. Doses of 1.48 MBq/animal were administered intravenously (iv) in non-tumor bearing mice and biodistributions collected at 0.5, 3, 6, 24, 48, 120 and 192 hours postinjection (p.i.) to quantify time course uptake at major organs. Dosimetry data extrapolated from these biodistributions showed that exposure in humans at clearance organs (kidneys and liver), had an average dose of 3.1 and 5.0 Gy which is 8 times and 6 times below the published dosimetry thresholds of 23 Gy and 32 Gy respectively. Bone marrow and the lungs, two additional radiation sensitive sites, show doses of 0.04 and 0.4 Gy, 50.0 times and 67.5 times below the tox thresholds (2 Gy for bone marrow and 27 Gy for the lungs). The spleen had an average dose of 2.2 Gy, which is 18.2 times below the threshold of 40 Gy. Preclinical RPT studies were conducted in CFPAC-1 xenografts. A pancreatic carcinoma cell-line reported to have intermediate-to-low expression level of human αVβ6 (4-fold lower than BxPC3 pancreatic adenocarcinoma). When the tumor size reached 100-150 mm3 mice were randomized into three groups: vehicle, single dose of 18.5 MBq, or two doses 11.1 MBq and 8.1 MBq 7 days apart of 177Lu radiolabeled DOTAGA-IAB56. A rapid tumor growth inhibition response for up to 36 days was observed in both RPT groups which evoked a significant improvement in survival compared to control. Overall, our data indicate the anti-αvβ6 Mb, IAB56 is efficacious for the treatment of pancreatic cancer supporting the use of this agent as a RPT approach for solid tumors. Citation Format: Leticia M. De Souza Cordeiro, Kelley C. Atkinson, Fang Jia, Argin Aivazian, Gareth E. Smith, Ian Wilson, Alessandro Mascioni. A preclinical therapeutic study of minibody 177Lu-DOTAGA-IAB56 targeting αVβ6 for the treatment of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB281.