Inflammatory disorders such as ulcerative colitis and Crohn’s disease can be diagnosed or monitored by measuring a protein called calprotectin in stool samples. Similarly, in rheumatoid arthritis, serum levels of calprotectin can be used to monitor inflammation. Currently, the measurement of calprotectin concentrations relies on antibody-based assays, like the ones found in home COVID-19 test kits.
However, there are limitations with these antibody-based calprotectin assays. The results can vary depending on the type of antibody and assay used. This variation occurs because antibodies may bind to different sites on the protein or have inconsistent compositions. Furthermore, antibodies can become inactivated over time due to unfolding or precipitation.
One potential solution to address these issues is to utilize peptides instead of antibodies for detecting and measuring disease markers such as calprotectin. Peptides are short sequences of up to 50 amino acids that can bind to proteins with high affinity and selectivity. Unlike antibodies, peptides can be chemically produced with high purity and homogeneity. They also exhibit stability over time, are more cost-effective to produce, and have lower inter-batch variability. Additionally, peptides can be attached to specific locations on a surface, which significantly simplifies the development of diagnostic assays. This controlled approach allows for a more accurate and precise detection of biomarkers.
Christian Gerhold, the Chief Technology Officer (CTO) of diagnostics company BÜHLMANN, collaborated with Professor Christian Heinis’ group at the Swiss Federal Institute of Technology Lausanne (EPFL) to develop human calprotectin ligands using peptide-based approaches. Their research involved screening a vast library of over 500 billion peptides, with postdoc Cristina Diaz-Perlas isolating several calprotectin binders. These peptides proved effective in simplified lateral flow assays for calprotectin quantification. The most promising peptide exhibited a dissociation constant of 26 nM, indicating strong binding affinity and making it a suitable candidate for diagnostic tests.
Notably, the developed peptide not only bound to a large surface region of calprotectin but also specifically recognized the relevant form of calprotectin found in patient samples. Working under Benjamin Ricken at BÜHLMANN, the peptide underwent rigorous testing in professionally assembled lateral flow cassettes. Results demonstrated its accuracy in detecting and quantifying calprotectin. In a proof-of-concept study, the peptide-based assay successfully measured calprotectin concentrations in serum obtained from patient blood samples.
This peptide represents the first synthetic affinity reagent generated against the biomarker calprotectin. Christian Heinis states that the EPFL and BÜHLMANN teams are currently conducting further tests on the calprotectin-specific peptide to refine the assay and bring its diagnostic capabilities to a new level, ultimately aiding patients with inflammatory diseases.
Christian Gerhold emphasizes the collaborative nature of the project, leveraging BÜHLMANN’s expertise in handling and producing the biomarker, along with the EPFL team’s proficiency in generating and screening large libraries of peptides using phage display techniques.