Glypican-3-Targeted 227 Th α -Therapy Reduces Tumor Burden in an Orthotopic Xenograft Murine Model of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is a significant cause of morbidity and mortality worldwide, with limited therapeutic options for advanced disease. Targeted α-therapy is an emerging class of targeted cancer therapy in which α-particle-emitting radionuclides, such as ²²⁷ Th, are delivered specifically to cancer tissue. Glypican-3 (GPC3) is a cell surface glycoprotein highly expressed on HCC. In this study, we describe the development and in vivo efficacy of a ²²⁷ Th-labeled GPC3-targeting antibody conjugate ( ²²⁷ Th-octapa-αGPC3) for treatment of HCC in an orthotopic murine model. Methods: The chelator p -SCN-Bn-H ₄ octapa-NCS (octapa) was conjugated to a GPC3-targeting antibody (αGPC3) for subsequent ²²⁷ Th radiolabeling (octapa-αGPC3). Conditions were varied to optimize radiolabeling of ²²⁷ Th. In vitro stability was evaluated by measuring the percentage of protein-bound ²²⁷ Th by γ-ray spectroscopy. An orthotopic athymic Nu/J murine model using HepG2-Red-FLuc cells was developed. Biodistribution and blood clearance of ²²⁷ Th-octapa-αGPC3 were evaluated in tumor-bearing mice. The efficacy of ²²⁷ Th-octapa-αGPC3 was assessed in tumor-bearing animals with serial measurement of serum α-fetoprotein at 23 d after injection. Results: Octapa-conjugated αGPC3 provided up to 70% ²²⁷ Th labeling yield in 2 h at room temperature. In the presence of ascorbate, at least 97.8% of ²²⁷ Th was bound to αGPC3-octapa after 14 d in phosphate-buffered saline. In HepG2-Red-FLuc tumor-bearing mice, highly specific GPC3 targeting was observed, with significant ²²⁷ Th-octapa-αGPC3 accumulation in the tumor over time and minimal accumulation in normal tissue. Twenty-three days after treatment, a significant reduction in tumor burden was observed in mice receiving a 500 kBq/kg dose of ²²⁷ Th-octapa-αGPC3 by tail-vein injection. No acute off-target toxicity was observed, and no animals died before termination of the study. Conclusion: ²²⁷ Th-octapa-αGPC3 was observed to be stable in vitro; maintain high specificity for GPC3, with favorable biodistribution in vivo; and result in significant antitumor activity without significant acute off-target toxicity in an orthotopic murine model of HCC.
(© 2022 by the Society of Nuclear Medicine and Molecular Imaging.)