Researchers have developed a highly sensitive blood test capable of early detection by identifying a key protein produced by cancer cells, according to a novel study published by Taylor et al in Cancer Discovery.
Background
Many tumors become deadly by remaining asymptomatic until they’re too advanced to treat. Ovarian cancer and gastroesophageal cancer are known to progress undetected, often leading to late-stage diagnoses.
Cancer biomarker detection is a young and growing field. Although there are a number of cancer biomarkers, they can come with drawbacks. Some of them require surgical biopsies while others are employed only after the emergence of symptoms—which can be too late for an effective intervention. Most of the biomarkers are normal human proteins that have variability between patients, making a single value hard to interpret. Yet, many are targeted to a specific cancer, which further narrows their range.
Previous studies have identified the LINE-1 ORF1p protein as an important new biomarker for the early detection of cancer. LINE-1 is a retrotransposon, a virus-like element present in every human cell that replicates through a copy-and-paste mechanism, resulting in a new copy in a new position in the genome. ORF1p is a protein it produces at high levels in cancer.
“Transposons are normally expressed in sperm and eggs [as well as] during embryogenesis, so there are some circumstances where you have nonpathobiological expression of transposons,” explained co–study author John LaCava, PhD, Research Associate Professor at The Rockefeller University. “But otherwise, these ‘jumping genes’ are silenced within the genome, because their activity creates stress and insults in the cell,” he continued.
Most of the time, the body keeps LINE-1 in check.
“There are layers of mechanisms that prevent LINE-1 from being expressed and producing ORF1p, so we can use the presence of the protein as a proxy for an unhealthy cell that no longer has control over its transcriptome. You shouldn’t find ORF1p in the bloodstream of a healthy person,” Dr. LaCava emphasized. “[Over the past 5 years], it’s become abundantly clear that these proteins become highly elevated in most cancers,” including esophageal cancer, colorectal cancer, lung cancer, breast cancer, prostate cancer, ovarian cancer, endometrial cancer, pancreatic cancer, and head and neck cancer, he revealed.
Because carcinoma cells make ORF1p from the onset of disease, researchers have long sought a sensitive, accurate test to detect ORF1p as early as possible. The ability to spot it in patients before a cancer has had a chance to spread could potentially save lives.
Study Methods and Results
In the new study, the researchers used the single-molecule–based detection technology Simoa—developed by coauthor David R. Walt, PhD, of Brigham and Women's Hospital—and contributed custom nanobodies derived and developed from llamas to act as capture reagents that ensnare the ORF1p protein and as sensitive probes to detect it.
“We developed these reagents as part of our mission to capture and describe the molecular associations of ORF1p with other proteins in colorectal cancers. We knew that most colorectal cancers have an abundance of LINE-1 proteins, so we reasoned that the interactions they form could be dysregulating normal cell functions in ways that benefit cancer. Isolating LINE-1 particles allowed us to have a closer look at these interactions. Later, it was clear that our collaborators at Harvard could make use of the same reagents for their developing biomarker assay, so we shared them,” detailed Dr. LaCava.
With this technology, the researchers engineered a fast-working assay capable of detecting the ORF1p protein in the plasma.
The researchers found that the assay was highly accurate at detecting ORF1p in the blood samples of patients with a variety of cancer types—including ovarian cancer, gastroesophageal cancer, and colorectal cancer.
Unlike many cancer tests that are limited in scope, expensive, or reliant on invasive tissue sampling, the researchers highlighted that the novel blood test is a low-cost multicancer detector that can pick up the presence of the protein in a tiny amount of blood in less than 2 hours. Notably, the test costed less than $3 to produce and return fast results.
The researchers also analyzed the plasma of 400 healthy individuals aged 20 to 90 years who had donated blood to the Mass General Brigham Biobank. ORF1p was undetectable in 97% to 99% of them. Among the 5 individuals who did have detectable ORF1p, the individual with the highest level was found 6 months later to have advanced prostate cancer.
“We were shocked by how well this test worked across cancer types,” stated lead study author Martin Taylor, MD, PhD, of the Department of Pathology at Massachusetts General Hospital.
Conclusions
“The assay has groundbreaking potential as an early diagnostic test for lethal cancers,” stressed co–study author Michael P. Rout, PhD, Head of the Laboratory of Cellular and Structural Biology at The Rockefeller University. “These kinds of ultrasensitive detection instruments are poised to improve patient outcomes in transformative ways,” he added.
The researchers noted that another potential use of the assay may be to monitor how a patient is responding to cancer therapy. If a treatment is effective, the ORF1p levels in the patient’s blood should drop. In one part of the study, the researchers assessed 19 patients receiving treatment for gastroesophageal cancer. In the 13 patients who responded to therapy, levels of ORF1p fell below the detection limit of the assay. In this way, tracking the protein could potentially be incorporated into routine health care.
“During a healthy time in your life, you could have your ORF1p levels measured to establish a baseline. Then your [physician] would just keep an eye out for any spikes in ORF1p levels, which could be indicative of a change in your state of health. While there might be some minor ORF1p fluctuations here and there, a spike would be a cause for a deeper investigation,” Dr. LaCava suggested.
The new findings also illustrated the immense potential of nanobody reagents generated through the study of interactomics—which seeks to understand the dynamic interactions of the millions of individual components in a cell, particularly its proteins and nucleic acids. These interactions form macromolecular complexes that transmit information and control cellular behaviors. Pathogenic changes in these interactions underlie all diseases.
“There’s an essential need for much better tools to reveal and dissect interactomes that’s only beginning to be met,” Dr. Rout underscored. “To that end, we often collaborate with other institutions on the development of reagents such as our llama-derived nanobodies. The resulting products are not mere research tools, they have enormous potential in the hands of [physicians],” he concluded.
Kathleen Burns, MD, PhD, of Dana-Farber Cancer Institute, is the corresponding author for the Cancer Discovery article.
Disclosure: For full disclosures of the study authors, visit aacrjournals.org.
