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SAT Developing Longitudinal Protein Panel Using Mass Spec, Dried Blood Spots

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NEW YORK (GenomeWeb) – Clinical proteomics firm SISCAPA Assay Technologies is developing a 12-protein panel for longitudinal tracking of cardiovascular disease, kidney disease, and diabetes.

The panel will use mass spec-based analysis of dried blood spot samples, which should improve patient convenience and lower costs, SAT CEO Leigh Anderson told GenomeWeb. He added that the company is currently in discussions with several large clinical reference labs about possibly implementing the panel as a CLIA test.

Dried blood spots have been a main area of interest for Anderson and SAT due to their potential as a more convenient, less expensive alternative to conventional blood draws. Typically consisting of microliter volumes of blood spotted and dried on filter paper, dried blood spots can be stored and shipped without refrigeration, meaning they could be sent through standard mail. Conventional blood draws, on the other hand, require rapid, cold shipping via services like FedEx.

Additionally, because dried blood spots require only a finger prick, patients can do them at home without having to go to a doctor's office to have blood taken.

Due to their limited sample volume, dried blood spots generally can't be used for large panels of immunoassays. Mass spec, on the other hand, is well suited to measuring relatively large multiplexes in dried blood spot samples, Anderson said.

For instance, in a study published last week in Bioanalysis, Anderson and his SAT colleagues managed to multiplex in a single mass spec assay measurements of 22 proteins and one post-translational modification from dried blood spots. He noted that other studies have shown similar assays to be capable of multiplexing up to 50 proteins. In a paper published last year in Molecular & Cellular Proteomics, researchers at the University of Victoria-Genome British Columbia Proteomics Centre developed a mass spec assay for simultaneously quantifying 97 proteins in dried blood spots.

"There doesn't appear to be a major limitation there," Anderson noted. Assay sensitivity, on the other hand, is currently a limitation. The SAT researchers were able with their assay to measure proteins in as low as the nanogram per ml range, which, Anderson said, covers around 80 percent of the proteins currently offered as part of standard clinical menus.

SAT's SISCAPA technology improves assay sensitivity by using antibody enrichment of target peptides upfront of mass spec analysis. However, even with this increase in sensitivity, certain proteins, including cancer markers like thyroglobulin, remain out of reach in dried blood spot samples.

Anderson suggested that one way to address this issue would be to simply use more of the sample present on a typical blood spot. Typically, people collect 100 microliters or more of plasma in a dried blood spot sample, but this is usually not all used in one analysis, he said. Were that full amount to be used, though, it "would extend the range pretty much to the bottom range of things that are clinically useful to measure," he noted.

In the Bioanalysis paper, the SAT researchers looked at the potential of mass spec analysis of dried blood spots for tracking individuals longitudinally. Longitudinal biomarker measurements are an attractive idea in that they would allow physicians to use individuals as their own baselines, which could prove a more sensitive and accurate approach than traditional population-based cut-offs, Anderson said.

He and his colleagues followed the 22 proteins in fourteen individuals over periods of up to 6.5 years, collecting data on a total of 784 dried blood spot samples. They found that the measured proteins were highly stable within individuals, allowing them to generate personalized baselines and then track changes in response to events including a normal pregnancy, a kidney infection, colds, and pneumonia.

"The key thing we have demonstrated at this point is that there are interesting physiologically important biomarker changes on a whole variety of timescales from hours to days to weeks to months and years," Anderson said. "The idea of [measuring markers] longitudinally is very well established at this point, I think."

Now the question becomes what might be commercially viable applications of such an approach, he said, adding that the company believes the most obvious would be a panel covering cardiovascular disease and related conditions like kidney disease and diabetes.

With this in mind, SAT is building a 12-plex protein panel covering analytes linked to these conditions. Unlike much biomarker work, the company is not looking to develop new markers, but rather aims to convert established markers to the mass spec and dried blood spot format and market them for more regular testing as part of longitudinal monitoring of individuals.

Because the proteins they plan to measure are already well established clinical markers, the company doesn't have to work to convince physicians of their value — a step where many proteomic diagnostics firms have faltered. That said, SAT does aim to change physician behavior by increasing the frequency with which these tests are ordered.

"Generally, it would be a good idea to collect this data on a quarterly basis," Anderson said, acknowledging that this is more frequent than is typical at present. "So from a business point of view, this [issue of changing current medical practice] is obviously a really important question."

He said that one factor that led him to believe there was momentum for the idea is the trend towards regular, personal collection of health data via electronic trackers like FitBits. "The whole electronic health, mobile health revolution going on is super compatible" with the idea of frequent, longitudinal monitoring of biomarker data, he suggested.

This is a trend that some of the large clinical reference labs SAT hopes to partner with on its panel are taking note of and investing in. For instance, Quest Diagnostics offers two direct-to-consumer biomarker monitoring services, its Blueprint for Wellness and Blueprint for Athletes products. Last month, the company announced plans to offer diagnostic testing services in 12 Safeway grocery stores in California, Colorado, Texas, Virginia, and Maryland in order to make the process more convenient for customers.

Mass spec-based analysis of dried blood spots could make testing even more convenient still, Anderson noted, as it would, in theory, allow patients to generate and mail in blood samples from their own home. Highly multiplexed mass spec tests could also be less expensive than conventional immunoassays, he said, estimating that a 10-plex mass spec panel could cost between half and a quarter of what the equivalent immunoassays would run.

Anderson said that with the technical hurdles now largely overcome, he is seeing increased interest in SAT's approach from large labs.

"Two years ago they weren't very interested, primarily for technical reasons," he said. "So that has been the focus, to prove that that barrier can be overcome. And now that it can be overcome, the interest has rapidly increased. The question now is what is the right point at which a big lab commits to trying to do a significant menu in a new sample type. That requires a lot of soul searching, and I believe that is the stage we are at right now."

Anderson said that while SAT hopes to work with a clinical lab on the cardio-kidney-diabetes panel, the company will take it to market on its own if it is unable to find a suitable partner.

"It is a matter of speed," he said. "The discussions are aimed at locating a partner with whom we could get it to market sooner than if we did it ourselves."

With a partner SAT could launch the panel in around a year, while on its own it would take closer to two years, Anderson said.

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