Preclinical Evaluation of Multistep Targeting of Diasialoganglioside GD2 Using an IgG-scFv Bispecific Antibody with High Affinity for GD2 and DOTA Metal Complex

Abstract

Bispecific antibodies (BsAb) have proven to be useful targeting vectors for pretargeted radioimmunotherapy (PRIT). We sought to overcome key PRIT limitations such as high renal radiation exposure and immunogenicity (e.g. of streptavidin-antibody fusions), to advance clinical translation of this PRIT strategy for diasialoganglioside GD2-positive (GD2(+)) tumors. For this purpose, a IgG-scFv BsAb was engineered using the sequences for the anti-GD2 humanized monoclonal antibody hu3F8 (1) and C825, a murine scFv antibody with high affinity for the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complexed with beta-particle emitting radiometals such as 177Lu and 90Y (2, 3). A three-step regimen including hu3F8-C825, a dextran-based clearing agent, and p-aminobenzyl-DOTA radiolabeled with 177Lu (as 177Lu-DOTA-Bn; t1/2 = 6.71 days (d)) was optimized in immunocompromised mice carrying subcutaneous (s.c.) human GD2(+) neuroblastoma (NB) xenografts. Absorbed doses for tumor and normal tissues were ∼85 cGy/MBq and ≤3.7 cGy/MBq, respectively, with therapeutic indicies (TI) of 142 for blood and 23 for kidney. A therapy study (n = 5 per group; tumor volume: 240 ± 160 mm3) with three successive PRIT cycles (total 177Lu: ∼33 MBq; tumor dose ∼3400 cGy), revealed complete tumor response in 5/5 animals, with no recurrence up to 28 d post-treatment. Tumor ablation was confirmed histologically in 4/5 mice, and normal organs showed minimal overall toxicities. All non-treated mice required sacrifice within 12 d (>1.0 cm3 tumor volume). We conclude that this novel anti-GD2 PRIT approach has sufficient TI to successfully ablate s.c. GD2(+)–NB in mice while sparing kidney and bone marrow.

Radioimmunotherapy of human tumours

“…For example, in a DOTA-PRIT approach using bifunctional antibody with antigen reactivity to GD2 ganglioside in neuroblastoma xenografts, therapeutic index (TI) for tumour to bone marrow was 50:1, while TI for kidney was 7, and CRs were observed with no detectable toxicity 112 .…”

GD2-Targeted Immunotherapy and Radioimmunotherapy

“…Generally, a tumor-specific antibody is conjugated to a ligand-binder, such as streptavidin (with high affinity for biotin) 113 or ligand-specific antibody (binding to metal chelators, such as diethylene triamine pentaacetic acid [DTPA] or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid [DOTA]). 105,112 In the first step, these bispecific antibodies (172–200 kD) are allowed to localize to tumors in vivo, and any excess is cleared from the blood. The small radiolabeled ligand (DOTA-radiometal or its biotinylated form) is then injected intravenously.…”

“…The proof of concept in animal studies was recently demonstrated using the hu3F8-C825 bispecific construct achieving a >20 AUC ratio for kidney and >100 ratio for blood, curing neuroblastoma without clinical or histologic toxicities. 112 …”

Proceedings of the Second NCI–SNMMI Workshop on Targeted Radionuclide Therapy

“…Compartmental intrathecal antibody-based radioimmunotherapy has shown promise in metastatic central nervous system neuroblastoma. Preclinical research is ongoing on multistep targeting, whereby bispecific antibodies serve as targeting vectors for pretargeted radioimmunotherapy (25).…”