Researchers have developed a quick, cheap, and highly sensitive blood test to detect a telltale protein produced by cancer cells. The test can pick up a range of cancers before symptoms appear and could be key to early diagnosis of the disease.
Many cancers aren’t diagnosed until symptoms start to appear, by which time the disease may be widespread and difficult to treat effectively. Biomarkers are a way of detecting cancer, but, again, some only appear when cancer becomes symptomatic or are related to a specific cancer type.
In a new study, researchers from Rockefeller University have developed a highly sensitive blood test that detects a key protein produced by cancer cells that shows promise for early detection of a number of cancers.
LINE-1 ORF1p is a relatively new biomarker protein gaining attention in the scientific world. Long interspersed element-1 (LINE-1) is a retrotransposon, a virus-like element found in every human cell that replicates by a copy-and-paste mechanism, resulting in a new copy in a new position in the genome. Open reading frame 1 protein (ORF1p) is a protein LINE-1 produces at high levels in cancer, including many of the most common and lethal cancers of the esophagus, colon, lung, breast, prostate, ovaries, uterus, pancreas, and head and neck.
“Transposons are normally expressed in sperm and egg and during embryogenesis, so there are some circumstances where you have nonpathobiological expression of transposons,” said John LaCava, one of the study’s co-authors. “But otherwise, these ‘jumping genes’ are silenced within the genome because their activity creates stress and insults in the cell.”
Most of the time, the body keeps LINE-1 in check. But when it’s expressed and produces ORF1p, that’s an indicator that something may be wrong.
“There are 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,” LaCava said. “You shouldn’t find ORF1p in the bloodstream of a healthy person.”
It’s known that cancer cells produce ORF1p from the onset of the disease, so finding a way to accurately test for it would mean catching cancer in its early stages. The researchers set about engineering a fast, low-cost test to detect ORF1p in the blood plasma.
Because ORF1p is found in concentrations well below the detection limits of conventional clinical laboratory methods, the researchers used the single-molecule-based detection technology called Simoa, an ultrasensitive immunoassay platform for measuring biomarkers in small volumes of serum, plasma or cerebrospinal fluid. Custom nanobody reagents derived and engineered from llamas were used to detect and capture the ORF1p protein.
“We developed these reagents as part of our mission to capture and describe the molecular associations of ORF1p with other proteins in colorectal cancers,” LaCava said. “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.”
Using their newly developed assay, the researchers surveyed multiple cancer types and more than 400 ‘healthy’ control individuals without known cancer when they donated blood. Plasma ORF1p was undetectable in around 99% of controls, but of the five patients found to have detectable ORF1p, the one with the highest level was found, six months later, to have advanced prostate cancer. Four of eight stage I ovarian cancers in the cohort were positive for ORF1p, suggesting that the biomarker may be an indicator of early-stage disease.
Overall, the researchers found that the test was highly accurate at detecting ORF1p in the blood samples of patients with ovarian, gastroesophageal, and colorectal cancers. Moreover, the test costs less than US$3 and produces results in under two hours.
“We were shocked by how well this test worked across cancer types,” said Martin Taylor, lead author of the study.
In addition to detecting cancer, the test can also be used to evaluate how effective cancer treatment is. If a treatment is effective, it should cause a drop in the patient’s ORF1p levels. The researchers studied 19 patients being treated for gastroesophageal cancer and found that in the 13 who responded to treatment, ORF1p levels fell below the detection limit of the assay.
The researchers envision the test being incorporated into routine healthcare as an early warning system.
“During a healthy time in your life, you could have your ORF1p levels measured to establish a baseline,” said LaCava. “Then your doctor would just keep an eye our for any spikes in ORF1p levels, which would 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.”
Studies using larger cohorts are needed to further validate the test and to establish whether it picks up cancers other than carcinomas. And more research is needed to understand whether there is a normal baseline level of circulating ORF1p and what factors affect this level.
The study was published in the journal Cancer Discovery.
Source: Rockefeller University
