Asparagine-containing peptide linkers cleaved by legumain matched standard ADC potency while being completely resistant to neutrophil elastase — the enzyme blamed for blood-related side effects of current ADC drugs.
0% cleavage by neutrophil elastaseThe new Asn-containing peptide linkers were completely resistant to human neutrophil elastase — the enzyme thought to cause the neutropenia and thrombocytopenia side effects of current ValCit-based ADC drugs.
What the researchers found
From a screen of 75 peptide FRET pairs, asparagine-containing peptides emerged as being cleaved far more rapidly than traditional valine-citrulline linkers by lysosomal extracts while maintaining excellent plasma stability. These linkers were cleaved by legumain (an asparaginyl endopeptidase overexpressed in many cancers). MMAE-containing ADCs with the new linkers showed cytotoxicity comparable to standard ValCit ADCs. Critically, the Asn-containing linkers were completely stable to human neutrophil elastase (thought to cause ADC-related neutropenia and thrombocytopenia). Serum stability was excellent: >85% drug retention after 1 week in mouse and human serum, and <10% cleavage of FRET pairs after 18 hours.
Why it matters
ADC toxicity from off-target drug release is a major clinical problem limiting their use. Current valine-citrulline linkers are cut by neutrophil elastase and other enzymes in the blood, causing side effects. These new legumain-cleavable linkers could make ADC therapy significantly safer while maintaining cancer-killing potency, potentially broadening the patient population that can benefit from these drugs.
The numbers in context
75 peptides screened; Asn linkers; legumain-cleavable; MMAE ADCs; >85% drug retained 1wk serum; <10% cleavage 18h serum; 0% neutrophil elastase cleavage
How the study worked
Researchers designed 75 peptide FRET (fluorescence resonance energy transfer) pairs and screened them for cleavage by lysosomal extracts and plasma in an enzyme-agnostic approach (not targeting any specific enzyme). Hits were identified and the cleaving enzyme was determined through catabolism studies. Lead peptide linkers (particularly AsnAsn) were incorporated into MMAE-containing ADCs. These were tested for cytotoxicity against cancer cells, serum stability in mouse and human serum, and resistance to neutrophil elastase.
Who was studied
N/A (in vitro peptide screening and ADC characterization)
What this study cannot tell us
All data are in vitro and cell-based — no in vivo tumor efficacy studies were conducted. Legumain expression varies between cancer types, which could limit the broad applicability of these linkers. Manufacturing complexity of the new linkers compared to standard ValCit was not assessed. Long-term stability and pharmacokinetics in animal models remain untested.
How to read the evidence
This is an in vitro drug design study with thorough screening methodology and multiple validation experiments. While the data strongly support the linker concept, no in vivo efficacy or safety data were generated. The evidence is strong for proof-of-concept but preclinical.
When this study was published
Published in 2021, this study addresses an active challenge in ADC development. Legumain-cleavable linkers have continued to attract research interest since this publication.
The bigger picture
ADCs are one of the fastest-growing areas in cancer drug development, with over a dozen approved and hundreds in clinical trials. Improving linker technology is central to making these drugs safer and more effective. This study's shift from enzyme-specific to enzyme-agnostic screening represents a methodological advance that could yield new linker designs beyond what rational design alone would produce.
Questions still open
- Will legumain-cleavable ADCs show improved safety profiles (lower neutropenia/thrombocytopenia) in animal models and clinical trials?
- How does variable legumain expression across cancer types affect the efficacy of these linkers?
- Could the AsnAsn linker be combined with next-generation antibody platforms for even more targeted drug delivery?
Common questions
What are antibody-drug conjugates and why do peptide linkers matter?
How are these new linkers safer than current ones?
Read the original research
Enzyme-Agnostic Lysosomal Screen Identifies New Legumain-Cleavable ADC Linkers.
Bioconjugate chemistry, 32(4), 842-858
Citation
Miller, Jared T; Vitro, Caitlin N; Fang, Siteng; Benjamin, Samantha R; Tumey, L Nathan. (2021). Enzyme-Agnostic Lysosomal Screen Identifies New Legumain-Cleavable ADC Linkers.. Bioconjugate chemistry, 32(4), 842-858. https://doi.org/10.1021/acs.bioconjchem.1c00124