October 18, 2023 | A group of researchers at the University of California Santa Cruz, University of Arizona, and University of Illinois at Chicago have identified a candidate biomarker that may help lead to earlier detection of ovarian cancer without the need for a biopsy. They hope that gynecologists could someday look for the presence of this biomarker while performing a routine Pap smear, but additional research involving more patients is still needed.
Generally, this type of cancer doesn’t reveal itself until it has already spread, Judith Su, associate professor of biomedical engineering and optical sciences at the University of Arizona, told Diagnostics World. Known as a “silent killer,” it tends to go undiagnosed until a late stage. Currently, there are no reliable ways to screen for ovarian cancer in women who do not show any signs or symptoms.
Existing methods either do not detect the disease early on or lack the specificity and sensitivity needed to be used routinely, Su and colleagues explained in a paper published in Molecular & Cellular Proteomics (DOI: 10.1016/j.mcpro.2023.100590). As such, they say there remains “an urgent need” for reliable biomarkers, methodologies to detect those biomarkers, and novel sampling methods.
Because the most lethal form, high-grade serous ovarian cancer, is thought to often originate in the fallopian tubes, the researchers noted that “sampling from the vaginal environment provides more proximal sources for tumor detection.” As they carried out their experiments, they planted human ovarian cancer tumors in mice, performed vaginal lavages on the mice, and looked at the proteins that were upregulated or downregulated as time went on in cancerous mice compared to non-cancerous mice.
The experiments led to the identification of what they call “a promising candidate ovarian cancer biomarker” in the enzyme cystatin A. It has previously been associated with the body’s immune response to cancer. It has also been shown to play a role in various cancers and diseases, such as colorectal, breast, and non-small-cell lung cancer, as well as psoriasis and glaucoma.
The researchers used tampons that women wore before gynecologic surgery to test this signal in human patients. They tracked tumor progression by measuring cystatin A and found higher levels of this biomarker in the samples that came from patients diagnosed with ovarian cancer. “We were able to correctly pick out which samples were from the cancerous patients and which ones weren’t using our ultra-sensitive optical sensing technology,” Su said.
She sees promise in this ability to detect a biomarker at low concentrations without needing a biopsy. The whole concept behind this paper revolves around the notion of early detection before the physical presentation of symptoms, she added, so the underlying goal of their approach is to help save lives.
“I think that’s going to be a very important thing to think about because if we want to detect tumors early, they should be small, maybe even so small that they wouldn’t be detectable if you were just looking for the cancer cell,” said Joanna Burdette, professor of pharmaceutical sciences at the University of Illinois at Chicago. Exploring the environment surrounding a tumor could offer a “more robust signal that we could detect earlier,” added Burdette, who is also a member of the University of Illinois Cancer Center.
“One of the interesting things that we’ve shown is that the mouse model does translate to the human disease to some extent, although there’s always caveats and limitations to every scientific study,” Laura Sanchez, associate professor of chemistry and biochemistry at the University of California Santa Cruz, told Diagnostics World.
Collaborative Science: Coupling Technologies to Overcome Limitations
To arrive at their findings, the researchers developed an untargeted mass spectrometry microprotein profiling method coupled with a tech approach meant to overcome the inherent limitations of mass spectrometry.
Mass spectrometry is a powerful tool for discovering changes in signal from highly complex mixtures, Sanchez explained. However, if the signal is not yet abundant, mass spectrometry has some clear limitations.
“We have to have enough copy numbers of a certain analyte in order to even detect the analyte to begin with,” she said, noting that she and colleagues didn’t see a lot of these signals in the early time points in the mouse study.
While attending a conference, she and Su got to talking and soon realized that coupling the mass spec expertise of the Sanchez lab with Su’s FLOWER (frequency locked optical whispering evanescent resonator) technology geared toward detecting biomarkers in small quantities could be beneficial.
“I thought one of the coolest things about Judy’s work was that this FLOWER technology is so sensitive,” Sanchez said. “She could see things way sooner than we could.”
Tech, Time, and Sample-Related Challenges Remain
The big vision is that gynecologists could eventually look for the presence of this biomarker while performing routine Pap smears. Or perhaps someday, women could even mail tampons into a lab for testing. Despite these sorts of exciting possibilities, the researchers acknowledged that there are still sizable challenges that need to be overcome.
“Our technology is still a research platform,” Su said, “so it’s not really a turnkey system.” However, efforts are underway to make this technique translatable out of the laboratory setting.
Time is another notable challenge. “We want to be very careful when we’re trying to tell someone they have cancer or not, and so we want to really do our due diligence in terms of making sure we test this on a large cohort of patients to make sure this is a good biomarker,” she said.
It is possible that the best screening tool may rely on multiple biomarkers. As novel biomarkers continue to be found, they could be used along with or as a replacement for existing biomarkers in multimarker panels, so more research will be helpful in this regard.
Su emphasized that the recently published study was conducted using a relatively limited number of samples, so the next logical step would be to carry out this work on a much larger group of patients. Yet the lack of available samples is a major hurdle, said Sanchez, especially considering they want to focus on samples that are not overly invasive.
Sanchez pointed out that samples taken from female patients and stored in biorepositories, such as serum or tissues, are a great resource, but they are also invasive. She sees value in repurposing Pap smears, which are routinely taken during women’s health exams, for screening purposes. “But those samples are not really stored anywhere, ever,” she added.
Up Next: Different Model, Additional Proteins
Looking ahead, Sanchez said that a pilot grant award from the Foundation for Women’s Cancer, supported by the Laura Crandall Brown Foundation, will help build upon the work detailed in the Molecular & Cellular Proteomics paper with two main aims.
One is to use a different mouse model. She explained that the mouse model used in the recently published paper represents aggressive end-stage disease because the cancer cells were put right next to the ovaries. As a result, the time points all stayed within an eight-week timeframe.
Because ovarian cancer likely develops over the course of many years, there is a desire to use a model where the mice develop cancer over many months to find different signals that could be used in earlier screening.
The other main focus is to go through and validate other proteins, beyond just cystatin A, to see if they could be used to develop a multimodal fingerprinting approach.
“I think we have a high barrier to overcome with trying to implement early screening for this disease, but I also feel like since there is nothing that currently is available, the bar is on the ground,” said Sanchez. “Hopefully, we can correctly jump over it,” she added.
Profiling the Metabolome of Uterine Fluid
In other ovarian cancer-focused research, scientists at Peking University in China set out to profile the metabolome of uterine fluid to screen biomarkers for the early diagnosis of ovarian cancer. They see promise in gathering information from this fluid, which is located in the pelvic cavity, rather than focusing on blood that circulates throughout the body.
Although liquid biopsies are increasingly used in clinical settings for patients with ovarian cancer, the researchers explained that there is a growing body of evidence showing that many ovarian cancers originate in the fallopian tubes. Considering the anatomical ties to the uterine cavity, the Peking University researchers see uterine fluid as a better option for detecting abnormal changes taking place as this form of cancer begins to set in.
This form of fluid is made up of a range of molecules, such as proteins, amino acids, and ions. The researchers hypothesized that abnormal metabolites of malignant cells from the ovaries and fallopian tubes would pool in the uterine cavity—and that the metabolomics of uterine fluid could help enable the early diagnosis of ovarian cancer.
To explore further, they performed metabolomics analysis on a training set of uterine fluid from 96 gynecological patients. Over 1,200 metabolites were identified in the fluid samples. The researchers developed a seven-metabolite-marker panel (made up of phenylalanine, beta-alanine, tyrosine, NE, VMA, 12S-HHT, and crithmumdiol) and validated it using an independent set of samples from 123 patients.
“Using the biomarker panel, we successfully distinguished most early-stage patients in the validation set,” the researchers said in a study published in Cell Reports Medicine (DOI: 10.1016/j.xcrm.2023.101061). The panel distinguished early ovarian cancer from controls with an area under the curve (AUC) of 0.957.
The Peking University researchers concluded that their work “not only characterizes metabolic profiles of uterine fluid in different gynecological patients but also provides an accurate and sensitive strategy” for early diagnosis.
Predicting Which Patients Won’t Respond to Chemotherapy
In still other ovarian cancer-focused work, Amanda Paulovich at the Fred Hutchinson Cancer Center and colleagues have used mass spectrometry to identify a 64-protein signature that aims to predict patients with high-grade serous ovarian cancer who are unlikely to respond to chemotherapy.
As Bio-IT World previously reported, work is underway on proteomics-based assays that could enable precision medicine for ovarian cancer. One is expected to point out the chance of chemorefractory disease whereas the other will be devoted to identifying cases with higher expression of metabolic pathways.
Paul Nicolaus is a freelance writer specializing in science, nature, and health. Learn more at www.nicolauswriting.com.