Dynamics of Clinically Important Proteins: Measuring Turnover of Drug Targets and Biomarkers

Improved Sensitivity for Protein Turnover Quantification by Monitoring Immonium Ion Isotopologue Abundance

We describe an analytical strategy allowing for the direct quantification of stable isotope label incorporation in newly synthesized proteins following administration of the stable isotope tracer deuterium oxide. We present a demonstration of coupling high-resolution mass spectrometry, metabolic stable isotope labeling, and MS/MS-based isotopologue quantification for the measurement of protein turnover. Stable isotope labeling with deuterium oxide, followed by immonium ion isotopologue quantification, is a more sensitive strategy for determining protein fractional synthesis rates compared to peptide centric mass isotopomer distribution analysis approaches when labeling time and/or stable isotope tracer exposure is limited and, as such, offers a great advantage for human studies.

Standardized Immunomonitoring: Separating the Signals from the Noise

Classical immunoassays are routinely performed in the clinic for disease diagnosis and monitoring. Recent advances in phenotyping technologies offer huge potential in expanding the breadth of immune response monitoring. Challenges remain, however, in translating many of these tools to routine clinical practice. This Opinion focuses on two strategies that may advance the clinical adoption of immune-based biomarkers: protein-based assays employing digital readouts can reduce nonspecific signals that limit more classical assays; and approaches that stimulate immune responses in more standardized ways can help to reveal disease-specific immune response signatures by elevating the signal above the background. The integration of such immune response phenotypes is a critical step for the increased implementation of precision medicine-based strategies.