Common inflammatory disorders such as ulcerative colitis and Crohn’s disease can be diagnosed or monitored by measuring the calprotectin protein in a stool sample, whereas serum calprotectin levels can be used to monitor the inflammatory status in rheumatoid arthritis.
The concentration of calprotectin in a patient sample is usually determined using an antibody that binds to and detects the protein, for example in a lateral flow test such as a typical home COVID-19 test kit.
But there’s a problem with the antibody-based calprotectin test: the results can vary depending on the type of antibody and the test used. This occurs because antibodies may bind to different sites on the protein, or may not have a uniform composition. Antibodies can also become inactivated over time due to exposure or precipitation.
One possible solution is to use peptides instead of antibodies to detect and measure disease markers such as calprotectin. Peptides are sequences of up to 50 amino acids that can bind to proteins with high affinity and selectivity, but unlike antibodies, they can be chemically produced with high purity and homogeneity. In addition, peptides are stable over time, cheaper to produce than antibodies and with lower inter-batch variability, and can be attached to specific sites on surfaces, significantly simplifying the development of diagnostic tests as they allow for more accuracy and control. how to detect biomarkers.
Good peptide candidates found for the test
With this idea in mind, Christian Gerhold, CTO of the diagnostic company BÜHLMANN, worked with Christian Heinis’ group at EPFL to develop a human calprotectin ligand based on a peptide. From a library of more than 500 billion different peptides, Cristina Diaz-Perlas, a post-doc in the Heinis group, isolated several calprotectin binders, and demonstrated that the peptides were suitable for calprotectin quantification in a simplified lateral flow assay. The best peptides have a dissociation constant of 26 nM – a measure of how tightly they bind to calprotectin – making them good candidates for diagnostic tests.
The peptide binds not only to the large surface area of calprotectin but also to the specific form of calprotectin which is the relevant species in patient samples. Benjamin Ricken at BÜHLMANN tested the peptide in a lateral flow cassette and found it suitable for accurate calprotectin detection and quantification. In a proof-of-concept study, this setting was used to measure the concentration of calprotectin in serum obtained from a patient’s blood sample.
The developed peptide is the first synthetic affinity reagent that can be generated against the calprotectin biomarker.
“The EPFL and BÜHLMANN teams are currently conducting more tests with the calprotectin-specific peptide to translate the assay into a product that can take the diagnostic power of this increasingly important biomarker to new levels to help patients suffering from inflammatory diseases,” said Heinis. .