Data Sheet | August 17, 2026
Quantitative Protein Assays: Measuring the Proteins That Decide a Program
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Download NowDrug programs increasingly succeed or fail based on a single measurement. Teams must be able to accurately measure proteins of interest: the target itself, a marker of mechanism, or a pharmacodynamic readout that shows the drug is working. For novel modalities such as antisense oligonucleotides, siRNA, gene therapies, antibody-drug conjugates (ADCs), T-cell engagers, and radioligand therapies, that measurement is often the only direct evidence of target engagement a team has.
Most programs rely on antibody-based methods to obtain these critical protein measurements, but these approaches have limitations. Even when an validated antibody-based assay already exist for the protein of interest, it is still an indirect proxy measurement of the protein – and when no such assay exists, teams can wait months for development.
Sapient’s quantitative protein assays reframe targeted protein measurement from what an antibody happens to detect to a direct, absolute readout of the exact protein that matters using mass spectrometry.
Limitations of Traditional Targeted Protein Assays
Most targeted protein measurement still depends on a validated antibody or binding reagent. When one does not exist, or cannot resolve the protein form that matters, programs advance on incomplete data.
| Common Approach | Key Limitation |
|---|---|
| ELISA and ligand binding assays | Require a validated antibody pair that often does not exist for novel or newly drugged targets. Development is slow and can fail outright. |
| Multiplex immunoassays (MSD, Simoa) | Restricted to catalog analytes. Cross-reactivity and non-specific binding compromise specificity. |
| Immunohistochemistry (IHC) | Not quantitative. Cannot resolve isoforms or report absolute concentrations./td> |
| Antibody assays in general | Average isoforms, variants, and PTMs together. Rarely transfer cleanly across species. |
This often leaves development teams with gaps or the need to make trade-offs:
- If no validated antibody assay exists for the target, building one can take months with no guarantee of success.
- Antibodies cannot separate the isoform, variant, or transgene product that matters from the background of closely related proteins.
- A method validated in one species does not transfer to the next, so assays have to be rebuilt at preclinical and clinical stages.
- Cross-reactivity and non-specific binding erode confidence in the numbers, and few antibody assays report a true absolute concentration.
Sapient's Quantitative Protein Assays: Four Key Capabilities Enabled by Mass Spectrometry
Sapient’s quantitative protein assays measure proteotypic peptides that are unique to the protein or proteoform of interest by advanced mass spectrometry, using stable isotope-labeled internal standards for direct, absolute quantitation.
Because the readout is the protein sequence itself, no antibody is required, and the assay reports exactly what is measured.
Additionally, owing to innovations in sample processing and mass spectrometry instrumentation, sensitivity is no longer the tradeoff it once was. Label-free quantitation in plasma reaches ~20 pg/mL, within the range immunoassays have long owned, and optional enrichment extends this to single-digit pg/mL, all without an antibody in the core workflow.
Download the white sheet to explore how our quantitative protein assays compare to traditional targeted methods.
Sapient’s targeted assay approach:
1) Measures target proteins without the need for antibodies.
When no validated reagent exists, Sapient builds a sequence-specific assay directly against the target. For many programs this is the only way to prove target expression or engagement.
We offer a Protein Assay Menu with >12,000 proteins already represented. Any of these assays can undergo further qualification based on your specific study, sample type, and regulatory requirements, or we can develop bespoke assays for difficult-to-measure proteins outside of this existing menu.
2) Resolves the exact proteoform.
Working at the peptide level, Sapient quantifies a specific isoform, sequence variant, cleavage product, PTM, or transgene product, and distinguishes it from the endogenous protein it resembles. That means that we can readily build targeted assays for non-canonical proteins.
3) Allows for one method to be carried across species.
The same mass spectromety-based targeted assay transfers from mouse and non-human primate into human models, so a single validated method follows the program from preclinical toxicology through the clinic.
4) Reports absolute, standardized concentrations.
Labeled-peptide quantitation yields true concentrations that stay reproducible across sites, timepoints, and study phases.
Built for Every Phase and Sample Type
Sapient’s targeted assays are matrix agnostic. The same sequence-specific measurement can be made across solid tissue and every common biofluid, in both human and preclinical samples, so a program keeps one method as it moves from cells to tissue to circulating markers.
Workflows also quantify viral proteins, bacterial proteins, and drug levels. High-throughput systems process hundreds of samples per day, supporting large population studies and clinical trials, and assays can be taken to GCLP validation for regulated use.
Sapient’s Targeted Protein Assay Menu covers 12,000+ proteins, searchable by protein name or gene symbol, and each can be qualified to a study’s specific sample type and context of use.
De-Risk Development with Accurate, Quantitative Protein Data – Get Started Today
Historically, teams either waited months on antibody development or accepted a proxy measurement to quantify their proteins of interest. Sapient’s mass spectrometry-based quantitative protein assays provide direct, peptide-level data with high sensitivity, so you can be confident in quantitating the protein that is key to your program – whether part of target identification, PK, PD, and target engagement studies, or clinical biomarker monitoring.
Use the form to request a meeting or email discover@sapient.bio to set up a time to talk about your study needs.