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

## TL;DR

Small antibody fragments called minibodies, when linked to drugs, show similar cancer-fighting power to traditional antibodies in mice, despite being smaller and clearing faster from the body.

## Contribution

GD2-targeted minibody–drug conjugates demonstrate in vivo efficacy comparable to IgG-based ADCs despite smaller size and faster clearance.

## Key findings

- Minibody–drug conjugates achieved 74% and 55% tumor growth inhibition, matching ADCs with higher drug load.
- Minibodies showed superior tumor-to-blood ratio (TBR) at all timepoints compared to IgG-based ADCs.
- In vitro ADCs were more cytotoxic than FDCs, but this did not translate to better in vivo performance.

## Abstract

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-CH3 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.