NEW YORK (GenomeWeb) – Researchers focusing on lupus have known for a long time that certain RNAs trigger the inflammation that is characteristic of the disease. What had yet to be discovered was which exact RNAs correlated with lupus, and whether they were measurable in blood.
Now, in a new study published in The Journal of Immunology, two of those RNAs have been identified, which could lead to the development of a test to aid in the precise diagnosis of lupus and perhaps inform treatment decisions.
In lupus patients, RNAs turn on the Toll-like receptor TLR7, which defends cells against foreign RNAs and whose usual function is to use interferon to protect the body against viral infections. In the case of lupus, however, patients develop autoantibodies against nuclear proteins, many of which are involved in RNA regulation and are bound to RNA molecules. Therefore, when the autoantibodies bind to antigens that have RNA bound to them, the autoantibodies take RNA into various immune cells and turn on TLR7, which then turns on interferon production.
Resolve Therapeutics — a biotechnology company developing treatments for lupus and the related condition Sjögren's syndrome — is currently conducting a Phase II trial of a targeted nuclease therapeutic molecule designated RSLV-132. This molecule, Resolve CEO James Posada told GenomeWeb, digests circulating RNA that the company's researchers believe is the cause of chronic activation of interferon leading to inflammation in lupus patients.
Resolve, which largely paid for and participated in the new study, aimed to understand exactly how circulating RNAs activated the interferon pathway and what relation that might have to disease activity. The researchers found that many nuclear autoantigens are complexed with short, noncoding RNAs, such as U1 and Y1, so they used a custom RT-qPCR assay to measure the amount of U1 and Y1 RNA complexed with systemic lupus erythematosus (SLE) patient autoantibodies and immune complexes in 228 SLE patients. They found that the patients had significantly elevated levels of circulating U1 and/or Y1 RNA compared with healthy volunteers.
Further, the researchers noted, the circulating RNA molecules were correlated with SLE disease activity and increased expression of interferon-inducible genes. "To our knowledge, this study provides the first systematic examination of the role of circulating RNA in a large group of SLE patients and provides an important link with IFN dysregulation," the authors wrote.
"Basically the idea is to be able to quantitate the amount of RNA in the circulation and to what extent that is correlated with disease activity or turning on the interferon pathway," Posada, also the study's senior author, told GenomeWeb. "It wasn't known previously to what extent there was RNA floating around in the circulation. Now we've been able to quantify it and show that it's highly correlated with the expression of interferon-regulated genes and also with disease activity in lupus. It allows us to use that as a diagnostic in the sense that we can measure patients, look at their blood and measure the U1 or Y1 that's in there and see to what extent they'd be good candidates for therapy."
The study's results are not only useful to Resolve in refining its therapeutic molecule, but could also lead to the development of a companion diagnostic to go along with it. As of now, Resolve is using the assay it developed for the study in its clinical trial.
But Posada sees the potential for a diagnostic for a disease that clinicians now can largely diagnose only through clinical findings rather than through molecular tests. "For lupus right now, doctors rely on segregating patients by clinical findings, but it's really like using a sledgehammer," he said. "It's very imprecise because patients have all sorts of different manifestations like arthritis, or rash, or vasculitis. The disease affects different people in different ways and we don't have a molecular way of figuring out which patient has what pathology. So they just do it clinically, and that hasn't been working."
Precise diagnostics for lupus are "desperately" needed, he added.
Though the company has yet to start developing a diagnostic, Posada said such a test would be modeled on the study assay — the U1 and Y1 circulating RNAs quantified in the study would be the first molecules included on what would likely be a simple test using qPCR to measure RNAs in patient plasma. But Resolve is also planning to gather further data on larger groups of patients to see if there may be other RNAs that could allow for the further segregation of lupus patients into different clinical subgroups. Posada said that such information could also contribute to the refinement of a companion diagnostic — as other circulating RNAs are discovered to have a correlation with the disease, and with different subgroups, they could be added to the diagnostic assay to help clinicians determine which treatments would work best for which patients.
"It may end up that we measure six or eight or a dozen different RNAs, and an RNA fingerprint will allow us to determine what molecular subgroup that patient falls into and use the appropriate treatment," Posada said.
And although the company is conducting a clinical trial on its own therapeutic, the companion diagnostic is likely to be developed no matter what the results of that trial may be. Though he emphasized that Resolve had no plans beyond developing its own therapeutic, and later the companion diagnostic, Posada did say he was open to the idea of marketing the test to or co-marketing it with other companies who may have lupus therapeutics in their pipelines, should Resolve's treatment not succeed.
"All the information we're developing is useful and will be used one way or another," he added.