Novel GPC3-targeting radiopharmaceutical therapy for hepatocellular carcinoma.

525 Background: Glypican-3 (GPC3) is a membrane-anchored oncofetal protein whose expression is largely absent in normal tissues. Significant upregulation of GPC3 protein has been observed in approximately 75% of hepatocellular carcinomas (HCC), and is associated with poor prognosis. The differential expression of GPC3 between tumor and normal tissues provides an opportunity for targeted radiopharmaceutical therapy (RPT) to treat HCC, a leading cause for cancer-related deaths worldwide. Methods: RAYZ-8009 comprises a novel macrocyclic peptide binder to GPC3, a linker, and a chelator that can be complexed with different radioisotopes. The affinity of peptide binders to GPC3 was determined by surface plasma resonance (SPR) and radioligand binding assays. Target-mediated cellular internalization was radiometrically measured at multiple time points. In vivo biodistribution, monotherapy and combination treatments with 177 Lu or 225 Ac were performed in HCC xenografts. Results: RAYZ-8009 showed high binding affinity (K D =0.7 nM) to human GPC3, with comparable affinity to GPC3 of human, mouse, canine and monkey origins, and no binding to other GPC family members. Potent cellular binding was confirmed in GPC3+ HepG2 cells, and was not affected by isotope switching. RAYZ-8009 achieved efficient internalization upon binding, with 42% internalized by 20 minutes in HepG2 cells. Biodistribution study of 177 Lu-RAYZ-8009 showed sustained tumor uptake and fast renal clearance, with minimal or no uptake in other normal tissues. Exquisite tumor-specific uptake was also demonstrated in orthotopic HCC tumors with no uptake in surrounding normal liver tissue. Therapeutically, significant and durable anti-tumor effect and survival benefit were achieved with 177 Lu- and 225 Ac-labeled RAYZ-8009, as monotherapy or in combination with lenvatinib, in GPC3+ HCC xenografts. Conclusions: Preclinical in vitro and in vivo data demonstrate the potential of RAYZ-8009 as a theranostic agent for the treatment of patients with GPC3+ HCC.