Integrated Imaging Probe and Bispecific Antibody Development Enables <i>In Vivo</i> Targeting of Glypican-3–Expressing Hepatocellular Carcinoma

Glypican-3 (GPC3) is a proteoglycan with high sensitivity and specificity for hepatocellular carcinoma (HCC). We describe the integrated development and validation of a GPC3-targeting optical imaging probe and T cell-redirecting antibody (TRAB) as a theranostic strategy for the detection and treatment of HCC. A novel TRAB targeting GPC3 on HCC tumor cells and the CD3 T-cell receptor as well as a distinct GPC3-specific optical imaging probe were developed from a short peptide. The efficacy of GPC3/CD3 TRAB was evaluated in vitro using IFNγ release and calcein-AM assays. Patient-derived xenografts were used to assess the in vivo efficacy of GPC3/CD3 TRAB and the GPC3 imaging probe for the detection of GPC3+ HCC. GPC3/CD3 TRAB caused a dose-dependent escalation in IFNγ release from inactive peripheral blood T cells (P = 0.001) and higher tumor-cell lysis (P = 0.01) compared with controls in vitro. Intratumorally injected GPC3/CD3 TRAB resulted in significant prolongation of tumor doubling time in the GPC3+ tumors, with an associated reduction of tumor fluorescent signal from the HiLyte 488-conjugated GPC3-specific peptide on optical imaging. These data demonstrate that HCC cell targeting using a GPC3/CD3 TRAB derived from a small peptide enabled effective T-cell activation and induction of a cytotoxic response toward GPC3+ HCC tumor cells both in vitro and in vivo. GPC3-specific optical imaging enabled the detection of the GPC3+ HCC cells and noninvasive monitoring of tumor response to adoptive immunotherapy. The integrated development of a targeted therapeutic and molecular imaging probe provides a promising paradigm for the development of cancer theranostics.