High-payload trastuzumab–drug conjugates achieved through hydrophilic Y-shaped pendant PEG linkers for a potent and selective antitumor response

A high drug-to-antibody ratio (DAR) is a desirable attribute for enhancing the clinical performance of antibody-drug conjugates (ADCs). However, most approved ADCs are constrained to a DAR of 4 due to the high hydrophobicity of the cytotoxic drugs used. To overcome this limitation, alternative strategies rely on incorporating hydrophilic linkers to offset drug-borne hydrophobicity. Here, a novel linker comprising a Y-shaped PEG pedant is introduced to enable the generation of trastuzumab-based ADCs with a DAR of 8 while fully preserving the structural integrity of the clinically approved VC-pABC-MMAE payload. Systematic evaluation of PEG lengths reveals that the Y-shaped pendant architecture, when combined with PEG12 oligomers, is sufficient to effectively counterbalance the payload's hydrophobicity, yielding an ADC with excellent tumor accumulation and in vivo efficacy. This innovative hydrophilic configuration presented here expands the applicability of the VC-pABC-MMAE payload to high-DAR ADCs without altering its core structure, supporting a straightforward path toward clinical translation. • A Y-shaped PEG pendant linker offset the hydrophobicity of eight VC-pABC-MMAE cargos. • Systematic tuning of PEG length identified the PEG12 linker as the lead compound. • Highly hydrophilic ADC PEG12 (DAR8) showed long PK and excellent tumor accumulation. • The ADC with tailored hydrophilicity achieved near-complete tumor regression in vivo.