GD2-Targeted Minibody-Drug Conjugates Match the Potency of IgG-Based ADCs in a Mouse Cancer Model

Despite the clinical success of antibody-drug conjugates (ADCs), their efficacy in solid tumors remains constrained by limited tumor penetration of the IgG format. Smaller antibody fragment-drug conjugates (FDCs) present a compelling alternative, potentially offering superior intratumoral distribution and a wider therapeutic window driven by rapid systemic clearance. This study compares therapeutic activity of ganglioside GD2-specific minibody-drug conjugates against full-length ch14.18 antibody-drug conjugates, and biodistribution of the respective minibody (scFv-C_H3 homodimer) and IgG formats in the GD2-positive B78-D14 melanoma syngeneic mouse model. We conjugated the minibody and antibody with MMAE or MMAF via a cathepsin-cleavable linker, generating FDCs with drug-antibody ratio (DAR) of 2 and ADCs with DAR of 2 or 4. The biodistribution analysis showed no significant difference in tumor uptake for both formats early in the analysis (2-4 h) and a higher tumor uptake for the IgG at 24 h post-injection. However, the minibody achieved a superior tumor-to-blood ratio (TBR) at all timepoints, reaching a TBR > 1 compared to ~0.2 for the antibody by 24 h. In vitro studies demonstrated higher cytotoxicity for the ADCs regardless of drug load (DAR 2 or 4) compared to the FDCs, although the difference between conjugates with equal DAR was modest in B78-D14 cells. Critically, superior in vitro ADC potency did not translate in vivo. Minibody-MMAF and minibody-MMAE achieved 74% and 55% tumor growth inhibition, respectively, by the study endpoint-demonstrating comparable efficacy to ADCs with twice the drug load when administered to mice at equimass dosing. Stron/g in vivo efficacy of anti-GD2 FDCs, combined with the superior TBR for the minibody format, underscores the potential of minibody-drug conjugates for treating GD2-positive tumors, particularly when ADC-associated toxicity precludes high-dose regimens.