NEW YORK – Scout Health is aiming to expand the use of point-of-care molecular testing — perhaps even to consumers' homes — with a novel approach that enables sensitive and specific single-tube multiplexing of isothermal nucleic acid amplification.
Last week, the startup showed off its multiplexing capabilities, ability to rapidly develop new assays, and assay usability in home settings at Cambridge Healthtech Institute's Precision Medicine Tri-Con conference in San Diego.
Scout initially used a $14.9 million award from the National Institutes of Health's Rapid Acceleration of Diagnostics (RADx) initiative to develop an assay to detect SARS-CoV-2. Under its former name of Uh-Oh Labs, the firm obtained Emergency Use Authorization for its COVID test in 2022.
More recently, Scout was awarded $1 million from the Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X) to develop a low-cost, multiplex point-of-care molecular diagnostic test for the sexually transmitted infections Neisseria gonorrhoeae and Chlamydia trachomatis.
Isothermal nucleic amplification is typically more sensitive and specific than antigen testing yet less time-consuming and cheaper than PCR.
However, while they can attain the ideal point-of-care sweet spot of high accuracy and low cost, isothermal assays can be quite tricky to develop since they require six primers.
Multiplexing isothermal amplification assays have also previously demanded fluorescent chemistries, as the reactions are inhibited by high concentrations of primers and colorimetric readouts would be too dim to see. This has in turn necessitated more complex fluorescence reader devices for multiplex isothermal tests.
Cam Ball, cofounder and chief technology officer at Scout, said that the firm's patented solution — dubbed loop-de-loop — essentially eliminates the inhibition problem and increases the sensitivity of isothermal reactions, so they can be readily multiplexed using a less costly reader.
"We have some reactions with up to 70 primers," he said in an interview this week.
The loop-de-loop approach uses a looped primer attached to a quenched fluorophore, and it can insert itself into double-stranded DNA during a process known as DNA breathing, according to a poster the firm presented at Tri-Con.
Once incorporated into an amplicon, the reverse complement of the loop-de-loop primer is generated using a strand-displacing polymerase, which unquenches the fluorophore and yields a bright fluorescence.
Loop-de-loop primers melt open and fluoresce at approximately 10 degrees above the reaction temperature and also when incorporated into amplification products, according to the poster.
The method is adaptable to any type of isothermal amplification assay, including but not limited to loop-mediated isothermal amplification, Ball said.
Alex Jiao, cofounder and CEO of Scout, said in an interview that the loop-de-loop chemistry enables the Santa Clara, California-based firm to do its test development on standard lab equipment with very straightforward design transfer to the Scout system.
"We don't have to create like any complex consumables or cartridges, or do any verification or pilot production prototyping," he said, which means assay development can be quite rapid.
Proof of concept
Scout scientists also described several proof-of-concept studies in their poster.
Its triplex STI assay, called STI Scout, detects CT/NG as well as an internal molecular control target. It uses crude first-void urine or vaginal swab samples and reports results in 30 minutes using three spectrally separated fluorescence channels. The assay, which is also shelf-stable and lyophilized, showed a high sensitivity and specificity in preliminary studies of spiked-in samples.
With a four-target RT-LAMP respiratory panel, the team showed that loop-de-loop fluorescence brightness scales linearly with probe concentration but without any change in reaction speed. This property enables even higher multiplexing, Ball explained, because different targets can now be identified by color as well as by endpoint fluorescence brightness level.
The respiratory panel, called Respiratory Scout, detects influenza A, influenza B, SARS-CoV-2, and an internal control target in 30 minutes.
Meanwhile, a quadruplex rhinovirus assay called Rhino Scout, showed sensitivity comparable to the BioMérieux BioFire Spotfire respiratory panel. The test detects three types of rhinovirus plus an internal process control.
Scout is currently working with Altesa BioSciences, according to the poster, to offer Rhino Scout for research-use-only clinical stage development. Altesa is currently in Phase IIb clinical trials for its novel antiviral, vapendavir, which can prevent rhinovirus from entering human cells, according to the firm's website.
Providing RUO custom testing to support pharma and vaccine research and development has actually helped the firm generate revenues to support its business to date, Jiao said.
Finally, with an assay called Avian Scout, the firm was able to prove it could go from a concept to a research-use-only RT-LAMP test ported onto the Scout platform in about six weeks.
Compared to a published fluorescent RT-LAMP assay specific for H5N1 clade 2.3.4.4b sequence, Scout showed that the loop-de-loop chemistry was twice as fast and between 10 to 100 times more sensitive, depending on viral titer. Similarly, an RT-LAMP assay using SYTO9 intercalating dye from researchers in France was recently shown to detect clade 2.3.4.4b H5 from pooled poultry samples in 30 minutes with sensitivity of 86 percent while, by comparison, the Avian Scout test showed a time to positivity of between 10 to 15 minutes in the firm's proof-of-concept studies.
Importantly, the Avian Scout test kit was able to be integrated with the firm's reader device and mobile app within the six-week pilot project.
Pros of a reader
The pandemic-era boom in the over-the-counter molecular testing space has shifted dramatically in the past year, and only a handful of over-the-counter molecular tests are currently commercially available. Similarly, firms focused on CLIA-waived, rapid point-of-care systems for use in urgent care clinics and physician offices also seem to be feeling the post-COVID pinch.
Among the POC MDx companies surviving the extinction event are Aptitude Medical, Visby Medical, PlusLife, Anavasi Diagnostics, Nuclein, and Detect Diagnostics. There are also innovative new molecular systems in development from Credo Diagnostics, Kryptos Biotechnologies, and Cubit Diagnostics, and a host of amplification-free technologies on the horizon.
On the other hand, some early beneficiaries of pandemic-era need for rapid molecular COVID testing have not fared as well. Talis Biomedical, for example, is no longer operating as a public company, while Cue Health declared bankruptcy, and Pfizer's Lucira Health subsidiary will be shuttering by the end of this year. Meanwhile, messages to 3EO Health are currently forwarded to a consultancy firm that offers bankruptcy and insolvency services.
For over-the-counter, at-home molecular tests, in particular, the incorporation of a reader device that customers need to purchase and keep in their homes has been considered a potential hurdle for adoption.
Michael Mina, an epidemiologist who publicly advocates for expanded decentralized testing and who serves as a scientific adviser to Scout Health, said in a recent interview that consumers seem hesitant to purchase a device that reminds them they may need to do infectious disease testing in the future. Still, molecular testing is highly accurate, and "it is really important to help curb transmission and keep people empowered over their health care," Mina said.
Jiao and Ball also believe that certain consumers who require frequent testing are more likely to be psychologically aligned with owning a reader, and Scout is currently pursuing niche assays that can cater to these potential users.
In the traditional point-of-care space, a reader is also a benefit, as it can connect to a health system's network or public health reporting site, Jiao said.
For the OTC space, the reader can also store and track a patient's test data and enable patients to send it to their clinicians.
Jiao said the firm was not yet in a position to cite a sales price for the reader, or hub, but noted the cost would be in the range of a co-pay and approximately twice the cost of the test consumables.
"We see the hub aspect as a net positive, because it opens up a lot of other opportunities," Jiao said. "It's part of what we think is coming for digital health in general," he added.
After proving itself through the US Food and Drug Administration EUA regulatory process and demonstrating it can develop new assays very rapidly, Scout is currently in initial conversations with potential investors and partners.
Investors may currently be more hesitant about molecular testing, given companies going under and a lack of IPO wins, Jiao said, and they may be looking for technical de-risking and perhaps partnerships.
However, investors are also aware of the power of point-of-care molecular testing. "They understand that this is where the future is headed," he said.