New Non-Peptide Linkers for Antibody-Drug Conjugates Release Cancer Drugs More Selectively | Research

The takeaway

Researchers discovered a non-peptide linker for antibody-drug conjugates that is selectively cleaved by cathepsin B, potentially improving the safety of targeted cancer therapies.

Cathepsin B-selective cleavage
The new peptidomimetic linker is predominantly cleaved by one specific protease rather than multiple enzymes, potentially reducing off-target drug release

What the researchers found

The researchers discovered that a cyclobutane-1,1-dicarboxamide-containing linker is hydrolyzed predominantly by cathepsin B, unlike the standard valine-citrulline dipeptide linker which is cleaved by multiple proteases. Key results:

• The novel peptidomimetic linker showed enhanced protease specificity — preferentially cleaved by cathepsin B rather than multiple lysosomal enzymes

• ADCs with the new linker were equally efficacious in vivo as those with the standard valine-citrulline dipeptide linker

• Serum stability was maintained — the new linker did not break down prematurely in blood

• Structure-guided design using crystallography informed the linker optimization

• The approach opens a new chemical space beyond peptide-based linkers for controlling drug release selectivity

Why it matters

ADCs are one of the fastest-growing areas of cancer drug development, with three FDA-approved and over 60 in clinical trials at the time of this study. A major challenge is the therapeutic index — killing cancer cells while sparing healthy tissue. By making the linker more selective for tumor-specific enzymes, this technology could reduce the side effects of ADC therapies and expand the range of cancers that can be safely treated with these targeted drugs.

How the study worked

Using structure-guided drug design (including crystal structures of cathepsin B), researchers designed and synthesized novel non-peptide linkers based on a cyclobutane-1,1-dicarboxamide scaffold. They tested protease cleavage specificity in biochemical assays, measured serum stability, evaluated ADC efficacy in animal tumor models, and compared performance head-to-head against the standard valine-citrulline dipeptide linker used in FDA-approved ADCs.

What this study cannot tell us

The study demonstrated proof of concept but did not include human clinical trials. While the new linker matched the standard linker's efficacy, the theoretical safety advantage of cathepsin B selectivity was not directly demonstrated through improved therapeutic index in the animal models shown. The long-term stability and immunogenicity of the peptidomimetic linker in humans is unknown.

How to read the evidence

This is a preclinical drug discovery study published in the Journal of Medicinal Chemistry. It includes biochemical assays, structural biology, and in vivo animal tumor models. While the science is rigorous, no human data exists for this specific linker. This represents early-stage drug development evidence.

When this study was published

Published in 2018, this study is about 8 years old. The ADC field has advanced significantly since then, with several new approvals. The peptidomimetic linker concept introduced here has influenced ongoing ADC linker research and design strategies.

The bigger picture

This study is part of the broader effort to improve ADC technology — the linker is often called the most underappreciated component of these cancer drugs. Traditional valine-citrulline peptide linkers work but lack protease specificity, contributing to off-target toxicity. By moving beyond peptide chemistry to peptidomimetic structures, this work opens a new design space for ADC linkers. Since 2018, the ADC field has exploded, with drugs like trastuzumab deruxtecan and sacituzumab govitecan becoming blockbusters — making linker innovation even more relevant.

Questions still open

Does cathepsin B selectivity actually translate to fewer off-target side effects in human cancer patients?
Can this peptidomimetic linker approach be applied to next-generation ADCs carrying newer, more potent payloads?
How does this linker perform with different antibody targets beyond those tested in this study?

Common questions

What is an antibody-drug conjugate (ADC) and why does the linker matter?

An ADC is a cancer drug that attaches a toxic payload to an antibody that targets tumor cells. The linker is the chemical bridge between them — it must stay intact in blood but break apart inside cancer cells to release the drug. A more selective linker means the drug is released more precisely at the tumor, potentially reducing side effects.

Why is this peptidomimetic linker better than the standard peptide linker?

The standard valine-citrulline peptide linker is cleaved by multiple enzymes, which can cause premature drug release. The new cyclobutane-based peptidomimetic linker is predominantly cleaved by just cathepsin B, offering more selective drug release. In animal studies, it matched the standard linker's cancer-killing efficacy while offering the potential for improved safety.

Read the original research

Discovery of Peptidomimetic Antibody-Drug Conjugate Linkers with Enhanced Protease Specificity.

Journal of medicinal chemistry, 61(3), 989-1000

View on PubMed ↗Publisher’s paper ↗

Citation

Wei, BinQing; Gunzner-Toste, Janet; Yao, Hui; Wang, Tao; Wang, Jing; Xu, Zijin; Chen, Jinhua; Wai, John; Nonomiya, Jim; Tsai, Siao Ping; Chuh, Josefa; Kozak, Katherine R; Liu, Yichin; Yu, Shang-Fan; Lau, Jeff; Li, Guangmin; Phillips, Gail D; Leipold, Doug; Kamath, Amrita; Su, Dian; Xu, Keyang; Eigenbrot, Charles; Steinbacher, Stefan; Ohri, Rachana; Raab, Helga; Staben, Leanna R; Zhao, Guiling; Flygare, John A; Pillow, Thomas H; Verma, Vishal; Masterson, Luke A; Howard, Philip W; Safina, Brian. (2018). Discovery of Peptidomimetic Antibody-Drug Conjugate Linkers with Enhanced Protease Specificity.. Journal of medicinal chemistry, 61(3), 989-1000. https://doi.org/10.1021/acs.jmedchem.7b01430