Background: The GD2-targeting monoclonal antibody dinutuximab was the first FDA approved immunotherapy specifically for high-risk neuroblastoma. While dinutuximab therapy improved event-free survival rates, therapy is associated with severe pain caused by on-target activity on nerve cells, highlighting the need to consider other cell surface molecules as candidate targets for immunotherapy. CD56 is robustly over-expressed in many cancers including neuroblastoma.
Methods: We developed a fully human IgG1 targeting CD56 (m906-IgG) following phage-display-based isolation and optimization of CD56-specific binders. Using antibody glycan sites on m906-IgG1 for conjugation, we synthesized an antibody drug conjugate (ADC) with the DNA intercalating agent pyrrolobenzodiazepine dimer (m906-PBD) and tested for anti-neuroblastoma activity in both in vitro and in vivo preclinical models.
Results: Using immunofluorescence and flow cytometry, we showed that m906-IgG is rapidly internalized in a panel of 20 neuroblastoma cell lines. We next demonstrated potent cytotoxicity across this cell line panel (median IC50 = 1.48nM, range 10.5pM to 4.1nM) Somatic TP53 mutation was a biomarker for resistance to the ADC in the panel (p=0.03; median IC50 .for cell line models with wild-type TP53 = 211pM with a range from 10.5pM to 1.5nM vs median IC50 for mutated lines = 260nM, range 2.7nM to 4.1uM). Antibody-competition studies confirmed the specificity of m906-PBD. In an initial dose finding experiment using the NB-1643 patient-derived xenograft model and a twice weekly for a total of 4 doses schedule, we showed significant tumor regression at 1 mg/kg/dose, with eventual tumor regrowth at a median of 40 days. At 3mg/kg/dose, there were sustained regressions without regrowth out to 110 days.
Conclusions: The CD56-targeting m906-PBD ADC shows potent cytotoxicity in models of high-risk neuroblastoma.