NEW YORK (GenomeWeb) – Sera Prognostics has published an analytical validation study investigating the performance of the company's mass spec assay for the PreTRM test for assessing risk of preterm birth.
The study, published this month in Clinical Mass Spectrometry, provides details on one of the first multi-protein MRM-based mass spec assays to make its way to the clinic. The company launched nationwide sales of the test in May through its agreement with Laboratory Corporation of America, which is the exclusive US distributor for the test and is the lead investor in Sera's $40 million Series C funding round.
The PreTRM test measures two proteins, insulin-like growth factors binding protein 4 (IBP4) and sex-hormone binding globulin (SHBG), to determine a patient's likelihood of preterm delivery. It is intended to be given at 19 weeks gestation and provides women and their doctors with their percent risk of giving preterm birth along with a comparison of their individual risk to that of the general population.
The Clinical Mass Spectrometry paper looked at the analytical performance of the test as Sera transferred it from its discovery platform, an Agilent 6490 triple quadrupole, to the newer, higher-performance Agilent 6495 triple quadrupole, which Sera will use for running the clinical version of the test. While LabCorp will handle much of the sales and sample collection for the test, Sera will perform the assays, running them out of its CLIA facility. The company announced this week that this lab has also received accreditation from the College of American Pathologists.
In moving from the 6490 to the 6495, the company aimed to cut the assay's LC gradient in half from 30 minutes to 15 minutes, while retaining the analytical performance of the original test. This cut in LC time will allow for improvements in assay throughput, which is a key consideration for clinical assays.
In addition to the increase in throughput, Sera decided to make the switch to the 6495 so it could start its commercialization process with a newer instrument that has a potentially longer life cycle, said Greg Critchfield, the company's chairman and CEO.
"We wanted to move to a newer generation piece of equipment because we knew that in the future we'd be buying more and more of them, and we would have a longer life cycle for those because Agilent, our supplier, would support them over a longer period of time into the future," he said.
Sera is the second company, following Integrated Diagnostics' Xpresys Lung cancer test, to launch a clinical test using a multi-protein MRM assay. While mass spec-based protein tests have made some headway in moving to the clinic in recent years, they remain relatively rare, and some proteomic firms that were initially enthusiastic about mass spec's clinical potential have struggled with actual clinical and commercial implementation.
For instance, Applied Proteomics planned to offer its SimpliPro Colon proteomic colon cancer test using MRM mass spec but shifted to an immunoassay format upon realizing it would be able to bring such a test to market more quickly. The company continues to explore mass spec as a clinical platform, including for testing from dried blood spots, but its next-generation SimpliPro Colon test will also be on an immunoassay platform.
Integrated Diagnostics has also discussed the possibility of moving Xpresys Lung to an immunoassay format if future generations of the test consist of a smaller number of proteins. Multiplexing ability is viewed as a notable advantage of mass spec over immunoassays, and one that naturally diminishes as the size of test panel decreases. That said, Indi plans this year to launch a second-generation version of that test consisting of two proteins, down from 11, and has said it will keep it on a mass spec platform.
Despite the small size of the PreTRM test panel, Sera has remained committed to the mass spec format from the company's early days.
"I think people have a misconception that mass spec is expensive and hard to do and everything else," Critchfield said. "That used to be the case, but it's getting better and there are ways to make it extremely efficient. It is a very good technology for multiplexing. We see the future [of clinical mass spec] as being very bright."
With regard to Sera's process in particular, Critchfield said the company currently sees the biggest gains in test quality and throughput coming from automating the upfront sample preparation steps.
The Clinical Mass Spectrometry study also suggested that techniques like affinity enrichment of the target analytes, either at the protein or peptide level, could reduce sample complexity and further cut down on separation times, boosting throughput. Critchfield said Sera is exploring these options, as well.
Currently, he said, it takes between one and two weeks from the time of a patient's blood draw to when results are returned to their doctor.
Critchfield declined to provide any information around sales of the test since LabCorp began offering it at the end of May, noting that the company "is in the very early stages of commercialization."
The test is not covered by insurance yet, but the company has launched health economic studies to generate data it can use in discussions with insurers, Critchfield said, adding that those studies will take around a year and a half to two years to finish.
Last year the company and its collaborators published a study in the American Journal of Perinatology Reports modeling potential health and economic outcomes of the PreTRM test. Their model found that at a price per test of $1,250 and a performance of predicting birth before 37 weeks with a sensitivity and specificity of 80 percent, the test could lead to a roughly 23 percent reduction in infant mortality and annual savings of more than $500 million in an annual population of 3.5 million births.
However, noted Scott Sullivan, a Medical University of South Carolina obstetrician and first author on a commentary in Proceedings in Obstetrics and Gynecology addressing the paper, Sera does not yet have data demonstrating the test's usefulness in such a broad population.
Sullivan has participated in clinical trials for the PreTRM test and uses it in his own practice, which specializes in preterm birth prevention. He said that around 20 percent to 25 percent of the patients in his practice are candidates for the test, though he said in a typical practice this rate would more likely be around 5 percent.