A Glycine-based Tripeptide Linker for Maximizing the Therapeutic Index of Antibody–Drug Conjugates
Introduction
Valine-citrulline (VCit) is an industrial-standard protease-cleavable linker commonly used in antibody-drug conjugates (ADCs) for cancer therapy. However, its in vivo linker instability can cause various clinical adverse effects including neutropenia and hepatotoxicity. Here, we report that a glycine-based tripeptide linker sequence, glutamic acid-glycine-citrulline (EGCit), has the potential to solve these clinical issues without compromising the ability of traceless drug release and ADC therapeutic efficacy.
Methods
We analyzed the cleavage site mediated by human neutrophil proteases using LC-MS peptide mapping. To do this, we identified the cleavage site of the VCit linker. After that, we synthesized a new set of peptide linkers with various amino acids at the P2 position and tested their stability by incubating them with human neutrophil proteases and then analyzing their stability via LC-MS. The stable linkers were then used in the construction of ADCs. We evaluated ADCs' safety profile, and stability across multiple cell lines and xenograft models.
Results
We identified that the cleavage site was mediated by human neutrophil proteases between valine and citrulline in the VCit linker. Glutamic acid-glycine-citrulline (EGCit) was the most optimal and stable linker. We demonstrated that our EGCit ADC resisted human neutrophil protease-mediated degradation and spared differentiating human neutrophils. Notably, our anti-HER2 ADC showed almost no sign of blood and liver toxicity in healthy mice at 80 mg/kg. Our EGCit ADCs also exerted greater antitumor efficacy in multiple xenograft tumor models compared to the FDA-approved ADCs including Kadcyla® and Enhertu®.
Conclusion
We identified the cleavage site mediated by human neutrophil proteases of the clinically used VCit linker and demonstrated that our EGCit linker can broaden ADC therapeutic window. Because of the linker's simplicity, desirable physicochemical properties, and independence from conjugation modality and payload type, the EGCit linker is transferable to a wide range of ADC designs and other drug delivery agents. We believe that the EGCit linker technology will help expand the repertoire of effective, safe targeted drug delivery systems. This may provide clinicians and patients with cancer with access to otherwise unrealistic treatment options such as high-dose ADC therapy.