Antibody–Drug Conjugate Efficacy in Neuroblastoma: Role of Payload, Resistance Mechanisms, Target Density, and Antibody Internalization

mutation are significantly more resistant to tubulin and DNA/DNA topoisomerase 1 binding payloads, respectively. Next, we utilized the GPC2-specific D3-GPC2-IgG1 antibody to show that neuroblastomas internalize this antibody/GPC2 complex at significantly different rates and that these antibody internalization kinetics correlate significantly with GPC2 cell surface density. However, sensitivity to pyrrolobenzodiazepine (PBD) dimers primarily dictated sensitivity to the corresponding D3-GPC2-PBD ADC, overall having a larger influence on ADC efficacy than GPC2 cell surface density or antibody internalization. Finally, we utilized GPC2 isogenic Kelly neuroblastoma cells with different levels of cell surface GPC2 expression to define the threshold of target density required for ADC efficacy. Taken together, DNA binding ADC payloads should be prioritized for development for neuroblastoma given their superior efficacy and considering that ADC payload sensitivity is a major determinant of ADC efficacy.