Frequently expressed glypican‐3 as a promising novel therapeutic target for osteosarcomas

Osteosarcoma (OS) is the most common bone malignancy without a reliable therapeutic target. Glypican‐3 (GPC3) mutation and upregulation have been detected in multidrug resistant OS, and anti‐GPC3 immunotherapy can effectively suppress the growth of organoids. Further profiling of GPC3 mutations and expression patterns in OS is of clinical significance. To address these issues, fresh OS specimens were collected from 24 patients for cancer‐targeted next‐generation sequencing (NGS) and three‐dimensional patient‐derived organoid (PDO) culture. A tumor microarray was prepared using 37 archived OS specimens. Immunohistochemical (IHC) staining was performed on OS specimens and microarrays to profile GPC3 and CD133 expression as well as intratumoral distribution patterns. RT‐PCR was conducted to semiquantify GPC3 and CD133 expression levels in the OS tissues. Anti‐GPC3 immunotherapy was performed on OS organoids with or without GPC3 expression and its efficacy was analyzed using multiple experimental approaches. No OS cases with GPC3 mutations were found, except for the positive control (OS‐08). IHC staining revealed GPC3 expression in 73.77% (45/61) of OSs in weak (+; 29/45), moderate (++; 8/45), and strong (+++; 8/45) immunolabeling densities. The intratumoral distribution of GPC3‐positive cells was variable in the focal (+; 10%–30%; 8/45), partial (++; 31%–70%; 22/45), and the most positive patterns (+++; >71%; 15/45), which coincided with CD133 immunolabeling (P = 9.89 × 10(−10)). The anti‐GPC3 antibody efficiently inhibits Wnt/β‐catenin signaling and induces apoptosis in GPC3‐positive PDOs and PDXs, as opposed to GPC3‐negative PDOs and PDXs. The high frequency of GPC3 and CD133 co‐expression and the effectiveness of anti‐wild‐type GPC3‐Ab therapy in GPC3‐positive OS models suggest that GPC3 is a novel prognostic parameter and a promising therapeutic target for osteosarcoma.