Osteosarcoma (OS) is the most frequently diagnosed bone tumor in children in the United States. The prognosis for metastatic or recurrent OS has remained poor (5-year survival<30%) with no new effective therapies developed during the past 30 years. The high expression of tumor antigen, ganglioside GD2, on a variety of tumors, including OS, with its restricted expression on normal tissue makes GD2 an ideal target for anti-OS radiopharmaceutical therapy. Since human and canine OS shares many biological and molecular features and the prevalence of OS in dogs is 27 times higher than that in humans, spontaneously occurring OS in dogs has been shown to be an ideal model for testing new treatments for human translation. In this study, we evaluated a humanized GD2 antibody, hu3F8, that was developed for neuroblastoma therapy, as a potential delivery vector for targeted radiopharmaceutical therapy of human and canine OS.The cross immunoreactivity of hu3F8 with canine OS cells (OSCA78) and tissue, and human OS cells was confirmed by immunohistochemistry staining and flow cytometry. The binding affinity of hu3F8 to GD2 was assessed in vitro in OSCA78 and IMR32 (a human neuroblastoma cell line known expressing GD2) cell lines using 111In-DTPA-hu3F8. The dissociation constant Kd was 7.4 ± 1.0 nM for OSCA78, and 6.2 ± 1.9 nM for IMR32. Biodistribution study was performed in Nu/Nu mice bearing either OSCA78 tumor or IMR32 tumor. At 24 h after 111In-DTPA-hu3F8 injection, the highest uptake was observed in the tumor, followed by the blood, spleen, lung, and kidneys. The mean tumor uptake was 12.0% ID/g for OSCA78 tumors and 15.0% ID/g for IMR32 tumors, with a tumor-to-muscle ratio of 10.6 and 21.1, and a tumor-to-blood ratio of 1.1 and 2.4, for OSCA78 and IMR32 tumors, respectively. The 72 h biodistribution study revealed the highest uptake of 111In-DTPA-hu3F8 in both OSCA78 (28.0% ID/g) and IMR32 (51.6% ID/g ) tumors, with a tumor-to-muscle ratio of 93.3 and 206.6, and a tumor-to-blood ratio of 6.7 and 8.4, for OSCA78 tumors and IMR32 tumors, respectively. The improved uptake of 111In-DTPA-hu3F8 in tumors at 72 h was indicative of selective binding of 111In-DTPA-hu3F8 to GD2 expressing tumors. SPECT imaging showed that both OSCA78 and IMR32 tumors with 111In-DTPA-hu3F8 had superior contrast to the background, while 111In-DTPA-Rituximab (an irrelevant antibody) injected OSCA78-bearing mouse only showed moderate contrast to the background in the kidney.The cross immunoreactivity and high binding affinity of hu3F8 to canine OS cells/tissue and its ability to deliver an imaging payload (111In) suggest that conjugating hu3F8 with a radionuclide, such as alpha-emitter, 225Ac, may provide a potent radiopharmaceutical therapy for human and canine OS.

Citation Format: Yingli Fu, Jing Yu, Ioanna Liatsou, Anders Josefsson, Yong Du, Jeffrey Bryan, Dara L. Kraitchman, George Sgouros. Humanized GD2 antibody for targeted radiopharmaceutical therapy of human and canine osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1395.