Rapid immunoPET detection of neuroblastoma metastases using an engineered antibody

Objectives Neuroblastoma (NB) patients frequently relapse with widespread disease. Liver is a common site of metastatic spread, and the characterization of these metastases presents a significant challenge using conventional techniques. We previously demonstrated that the ⁶⁴Cu-labeled anti-GD2 antibody ch14.18 could be used to target a subcutaneous NB model, but the slow clearance of the antibody causes a significant delay between tracer injection and imaging. Here we report the evaluation of ⁶⁴Cu-labeled ch14.18-∆C_H2, a derivative of ch14.18 in which the C_H2 domains were removed to provide more rapid clearance, in an orthotopic model of NB.

Methods Intrahepatic metastases were established by injecting human NB cells (IMR32) into nude mice 3 weeks before the imaging study. The ch14.18-∆C_H2 antibody was radiolabeled with ⁶⁴Cu using NOTA and injected via the tail vein. PET data were collected at 1, 4, 24 and 48 h post injection. Frozen samples of liver were sectioned and the ⁶⁴Cu distribution within the tissue was measured using digital autoradiography.

Results Small animal PET imaging revealed foci of high ⁶⁴Cu uptake in the liver at all time points. The labeled antibody cleared rapidly from normal tissues leading to high tumor-to-normal tissue ratios of, for example, 12:1 for kidney and 34:1 for gut at 4 hours post injection. Autoradiographic and histological analysis of liver sections revealed that radionuclide uptake was focused in metastases of approximately 1 mm diameter with tumor-to-liver ratios of 10-20:1.

Conclusions The ⁶⁴Cu-labeled ch14.18-∆C_H2 antibody showed rapid clearance from non-target tissues allowing detection of liver metastases as early as 4 h post-injection. Furthermore, in contrast to previous studies with ⁶⁴Cu-labeled antibodies, accumulation of the labeled antibody in normal liver was low, improving visualization of liver metastases. Translation of these results to the clinic would facilitate evaluation of NB patients, especially with respect to recurrent metastatic disease.