Quantitative studies of monoclonal antibody targeting to disialoganglioside G_D2 in human brain tumors

Iodine-131 3F8, a murine IgG₃ monoclonal antibody that targets to G_D2-bearing tumors, was administered intravenously to 12 patients with brain tumors. Six patients received 2 mCi (0.74 Bq) of¹³¹I-3F8, five patients 10 mCi (3.7 Bq)/1.73 m² of¹³¹I-3F8, and one patient 2.6 mCi (0.96 Bq) of¹²⁴I-3F8, with no side-effects. Nine of 11 malignant gliomas and the single metastatic melanoma showed antibody localization, with the best tumor delineation on single-photon emission tomography (SPET) following 10 mCi (3.7 Bq)/1.73 m² dose. No nonspecific uptake in the normal craniospinal axis was detected. There was no difference in the pharmacokinetics of low-dose versus the higher-dose antibody groups; plasma and total-body half-lives were 18 h and 49 h, respectively. Surgical sampling and time-activity curves based on quantitative imaging showed peak uptake in high-grade glioma at 39 h, with a half-life of 62 h. Tumor uptake at time of surgery averaged 3.5×10^-3 %ID/g and peak activity by the conjugate view method averaged 9.2×10^-3 %ID/g (3.5-17.8). Mean radiation absorption dose was 3.9 rad per mCi injected (range 0.7-9.6) or 10.5 cGy/Bq (range 1.9-26). There was agreement on positive sites when immunoscintigraphy was compared with technetium-99m glucoheptonate/diethylene triamine penta-acetic acid planar imaging, thallium-201 SPET, and fluorine-18 fluorodeoxyglucose positron emission tomography. Taken together, these data suggest that quantitative estimates of antibody targeting to intracranial tumors can be made using the modified conjugate view method.