The Stable Isotope Labeling Kinetics (SILK™) Platform

For the stable isotope labeling kinetic (SILK™) platform, we infuse a stable, non-radioactive isotope labeled amino acid into human subjects. In C2N’s flagship product, the SILK-Aβ® assay, 13C6 leucine is used, since it is an essential amino acid and readily crosses the blood brain barrier. The stable isotope incorporates into newly synthesized proteins in the brain, which we sample through serial collection of various biological fluids. C2N offers a number of SILK™ and SISAQ™ platforms for measuring specific proteins in both CSF and plasma.


Advantages of the SILK™ platform:

Highly sensitive:

Highly sensitive biomarker measurements allow for fewer subjects and better powered studies to detect important biologic differences between drug study arms. The SILK-Aβ® assay is highly sensitive for identifying drug-induced changes of Aβ metabolism.

Target validation:

The SILK™ method directly measures the metabolism of the biomolecule of interest, even if multiple isoforms are present. This dynamic endpoint is notably more informative than static measurements of the concentration of proteins. The SILK™ assay allows for novel therapeutic target validation and new insights into the mechanism by which drugs exert their biologic effects.

Speed and lowered cost:

Measurements of protein metabolism allow for quick endpoint read-outs and the identification of drug activity signals more rapidly than clinical and imaging endpoints (i.e., days versus months or years). In collaboration with industry partners, we seek to terminate undeserving compounds early and streamline promising candidates rapidly into later-stage clinical development. The results are improved efficiency and lowered overall costs of clinical drug development.

Stable Isotope Spike Absolute Quantification (SISAQ™ Platform)

The Stable Isotope Spike Absolute Quantitation (SISAQ™) platform is a proprietary C2N technique that enables the measurement of the absolute concentration of peptides in biological fluids. This mass spectrometry (MS) based technique identifies peptides with a very high degree of specificity and precision in the concentration measurement. The proteomic applications for this technique are numerous and an important complement to and can be performed concurrently with the kinetic SILK™ assay, eliminating the need for separate ELISA assays. Studies performed at C2N have shown that the SISAQ™ assays have less variability in the measurement of Aβ compared to ELISAs.


The concentration of total Aβ was measured in 272 CSF samples using both ELISA and SISAQ™ (left). The Spearman correlation was 0.874 and p value was < 0.0001 between the ELISA and SISAQ™ results. Individual plots of changes in Aβ concentration from the mean concentration in CSF samples collected for 36 hours, showed that the SISAQ™ measurements (red line, right) had lower variation than the ELISA measurements (blue line, right).