Monobody NS1 binds to H-RAS or K-RAS protein and blocks RAS function by disrupting the protein's ability to form active molecular pairs. [John P. O'Bryan, et al./Nature Chemical Biology.]
Monobody NS1 binds to H-RAS or K-RAS protein and blocks RAS function by disrupting the protein’s ability to form active molecular pairs. [John P. O’Bryan, et al./Nature Chemical Biology.]

Heterogeneity among cancers plays a significant role in making the disease difficult to treat from patient to patient. Yet, there is one gene that disproportionately affects tumors and has been found to be mutated in nearly 30% of all cancer cases—providing researchers with a therapeutic opportunity to treat a large number of patients with a variety of different cancer subtypes.     

The prevalence of RAS mutations in human cancers and the dependence of tumors on RAS for survival has made it a prime target for cancer research and drug discovery. Scientists and drug developers have long studied RAS oncogenes hoping to find a new treatment for cancer, but they have yet to be able to identify drugs that safely inhibit the oncogene's activity.

Now, investigators at the University of Illinois at Chicago (UIC) have identified a new way to block the action of genetic mutations for the RAS family of proteins—K-RAS, H-RAS, and N-RAS. Mutations in the RAS gene are found in 90% of pancreatic cancers, as well as highly prevalent in colon cancer, lung cancer, and melanoma, the most lethal form skin cancer.

The UIC researchers took a different approach than others in the past when studying RAS, and created a synthetic binding protein they call “NS1 monobody,” that can block the activity of the RAS proteins.

“We did not look for a drug or specifically for an inhibitor,” explained senior study author John O'Bryan, associate professor of pharmacology in the UIC College of Medicine and a member of the University of Illinois Cancer Center. “We used monobody technology, a type of protein engineering technology, to identify regions of RAS that are critical for its function.”

Unlike conventional antibodies, monobodies are not dependent on their environment and can be readily used as genetically encoded inhibitors. Dr. O’Bryan added that “the beauty of the technology is that when a monobody binds a protein, it usually works as an inhibitor of that protein.”

In the new study, the authors described finding a critical allosteric region of RAS that could be targeted for inhibition. The findings from this study were published recently in Nature Chemical Biology in an article entitled “Inhibition of RAS Function through Targeting an Allosteric Regulatory Site.”

“We developed NS1, a synthetic binding protein (monobody) that bound with high affinity to both GTP- and GDP-bound states of H-RAS and K-RAS but not N-RAS,” the authors wrote. “NS1 potently inhibited growth factor signaling and oncogenic H-RAS- and K-RAS-mediated signaling and transformation but did not block oncogenic N-RAS, BRAF or MEK1.”

The researchers found that the NS1 monobody binds to an area of the RAS protein molecule that was not previously known to be important for its oncogenic activity. NS1 strongly inhibits oncogenic K-RAS and H-RAS function by blocking the ability of the protein to interact with an identical one to form a molecular pair.

“NS1 bound the α4-β6-α5 region of RAS, which disrupted RAS dimerization and nanoclustering and led to blocking of CRAF–BRAF heterodimerization and activation,” the authors penned. “These results establish the importance of the α4-β6-α5 interface in RAS-mediated signaling and define a previously unrecognized site in RAS for inhibiting RAS function.”

The UIC team are optimistic that these new insights will help guide the development of new therapeutic approaches to treating cancer by interfering with mutant RAS function in cancer cells.

“Development of effective RAS inhibitors represents a 'holy grail' in cancer biology,” Dr. O'Bryan said. “We now have a powerful tool we can use to further probe RAS function. While future studies and trials are needed before these findings can be leveraged outside the lab, this study provides new insight into how we can potentially inhibit RAS to slow tumor growth.”

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