I-131-GD2-ch14.18 Scintigraphy to Evaluate Option for Radioimmunotherapy in Patients with Advanced Tumors

The tumor-selective ganglioside antigene GD2 is frequently expressed on neuroblastomas and to a lesser extent on sarcomas and neuroendocrine tumors. The aim of our study was to evaluate the tumor targeting and biodistribution of 131I-labeled chimeric GD2-antibody clone 14/18 (131I-GD2-ch14.18) in patients with late-stage disease in order to identify eligibility for radioimmunotherapy. Methods: Twenty patients (neuroblastoma, n = 9; sarcoma, n = 9; pheochromocytoma, n = 1; and neuroendocrine tumor, n = 1) were involved in this study. A 21- to 131-MBq dose (1-2 MBq/kg) of 131I-GD2-ch14.18 (0.5-1.0 mg) was injected intravenously. Planar scintigraphy was performed within 1 h from injection (day 0) and on days 1, 2, 3, and 6 or 7 to analyze tumor uptake and tracer biodistribution. Serial blood samples were collected in 4 individuals. Absorbed dose to tumor lesions and organs was calculated using OLINDA software. Results: The tumor-targeting rate on a per-patient base was 65% (13/20), with 6 of 9 neuroblastomas showing uptake of 131I-GD2-ch14.18. Tumor lesions showed maximum uptake at 20-64 h after injection (effective half-life in tumors, 33-192 h). The tumor-absorbed dose varied between 0.52 and 30.2 mGy/MBq (median, 9.08 mGy/MBq; n = 13). Visual analysis showed prominent blood-pool activity up to day 2 or 3 after injection. No pronounced uptake was observed in the bone marrow compartment or in the kidneys. Bone marrow dose was calculated at 0.09-0.18 mGy/MBq (median, 0.12 mGy/MBq), whereas blood dose was 1.1-4.7 mGy/MBq. Two patients (1 neuroblastoma and 1 pheochromocytoma) with particularly high tumor uptake underwent radioimmunotherapy using 2.3 and 2.9 GBq of 131I-GD2-ch14.18, both achieving stable disease. Overall survival was 17 and 6 mo, respectively. Conclusion: 131I-GD2-ch14.18 is cleared slowly from blood, not resulting in good tumor-to-background contrast until 2 d after application. With acceptable red marrow and organ dose, radioimmunotherapy is an option for patients with high tumor uptake. However, on pretherapeutic dosimetry.