Dual-labeled anti-GD2 targeted probe for intraoperative molecular imaging of neuroblastoma

Background: Surgical resection is integral for the treatment of neuroblastoma, the most common extracranial solid malignancy in children. Safely locating and resecting primary tumor and remote deposits of disease remains a significant challenge, resulting in high rates of complications and incomplete surgery, worsening outcomes. Intraoperative molecular imaging (IMI) uses targeted radioactive or fluorescent tracers to identify and visualize tumors intraoperatively. GD2 was selected as an IMI target, as it is highly overexpressed in neuroblastoma and minimally expressed in normal tissue.

Methods: GD2 expression in neuroblastoma cell lines was measured by flow cytometry. DTPA and IRDye^® 800CW were conjugated to anti-GD2 antibody to generate DTPA-αGD2-IR800. Binding affinity (Kd) of the antibody and the non-radiolabeled tracer were then measured by ELISA assay. Human neuroblastoma SK-N-BE(2) cells were surgically injected into the left adrenal gland of 3.5-5-week-old nude mice and the orthotopic xenograft tumors grew for 5 weeks. ¹¹¹In-αGD2-IR800 or isotype control tracer was administered via tail vein injection. After 4 and 6 days, mice were euthanized and gamma and fluorescence biodistributions were measured using a gamma counter and ImageJ analysis of acquired SPY-PHI fluorescence images of resected organs (including tumor, contralateral adrenal, kidneys, liver, muscle, blood, and others). Organ uptake was compared by one-way ANOVA (with a separate analysis for each tracer/day combination), and if significant, Sidak's multiple comparison test was used to compare the uptake of each organ to the tumor. Handheld tools were also used to detect and visualize tumor in situ, and to assess for residual disease following non-guided resection.

Results: ¹¹¹In-αGD2-IR800 was successfully synthesized with 0.75-2.0 DTPA and 2-3 IRDye^® 800CW per antibody and retained adequate antigen-binding (K_d = 2.39 nM for aGD2 vs. 21.31 nM for DTPA-aGD2-IR800). The anti-GD2 tracer demonstrated antigen-specific uptake in mice with human neuroblastoma xenografts (gamma biodistribution tumor-to-blood ratios of 3.87 and 3.88 on days 4 and 6 with anti-GD2 tracer), while isotype control tracer did not accumulate (0.414 and 0.514 on days 4 and 6). Probe accumulation in xenografts was detected and visualized using widely available operative tools (Neoprobe^® and SPY-PHI camera) and facilitated detection ofputative residual disease in the resection cavity following unguided resection.

Conclusions: We have developed a dual-labeled anti-GD2 antibody-based tracer that incorporates In-111 and IRDye^® 800CW for radio- and fluorescence-guided surgery, respectively. The tracer adequately binds to GD2, specifically accumulates in GD2-expressing xenograft tumors, and enables tumor visualization with a hand-held NIR camera. These results encourage the development of ¹¹¹In-αGD2-IR800 for future use in children with neuroblastoma, with the goal of improving patient safety, completeness of resection, and overall patient outcomes.