Glypican-3 Targeted Human Heavy Chain Antibody as a Drug Carrier for Hepatocellular Carcinoma Therapy

Glypican-3 (GPC3) represents an attractive target for hepatocellular carcinoma (HCC) therapy because it is highly expressed in HCC but not in adult normal tissue. Recently, high affinity anti-GPC3 antibodies have been developed; however, full antibodies may not penetrate evenly into tumor parenchyma, reducing their effectiveness. In this study, we compared a whole IgG antibody, anti-GPC3 YP7, with an anti-GPC3 human heavy chain antibody, HN3, with regard to their relative therapeutic effects. Both YP7 and HN3 bound to GPC3-positive A431/G1 cells and were internalized by the cells by in vitro evaluation with (125)I- and (111)In-radiolabeling antibodies. In vivo biodistribution and tumor accumulation was performed with (111)In-labeled antibodies, and intratumoral microdistribution was evaluated using fluorescently labeled antibodies (IR700). HN3 showed similar high tumor accumulation but superior homogeneity within the tumor compared with YP7. Using the same IR700 conjugated antibodies photoimmunotherapy (PIT) was performed in vitro and in a tumor-bearing mouse model in vivo. PIT with IR700-HN3 and IR700-YP7 demonstrated that comparable results could be achieved despite of low reaccumulation 24 h after the first NIR light exposure. These results indicated that a heavy-chain antibody, HN3, showed more favorable characteristics than YP7, a conventional IgG, as a therapeutic antibody platform for designing molecularly targeted agents against HCC.