NEW YORK (GenomeWeb) – The market for circulating tumor cell (CTC) capture and detection grew significantly in 2018 as several companies pushed toward clinical implementation of their technologies for diagnosing multiple cancers, while new firms spun out of academic institutions with their own technologies.
In order to diagnose cancer clinicians have traditionally performed tissue biopsies, which can be invasive, expensive, and time-consuming for patients. Over the last decade, however, liquid biopsy tools have emerged as a way to address these issues and perhaps provide a more accurate picture of individual patients' disease.
"We are seeing more techniques that are able to analyze genotypic and phenotypic properties of CTCs at the single-cell level," University of Toronto biochemistry professor Shana Kelley, whose lab specializes in CTC capture and analysis, said in an email. "This is critically important given the heterogeneity of these cells and the importance of seeing trace levels of target subpopulations within patient samples."
Kelley added that "liquid biopsy will enable a radical paradigm shift, [since] patients can be continuously monitored non-invasively as they are being treated. This presents the opportunity to monitor the dynamic properties of tumors and enable more systemic choice[s] of therapy [as] tissue biopsy does not allow for this given its risks and invasiveness."
In principle, CTCs can be positively or negatively enriched using their biologic or physical properties, such as gene expression, size, density, deformability, or electric charges. The cells can then be detected using immunologic, molecular, or functional assays.
While the promise of CTC enrichment and capture technologies is great, researchers have encountered challenges compared to liquid biopsy techniques that use cell-free DNA collection for potential clinical benefit.
In a 2017 study published in Cancer Discovery, corresponding author Klaus Pantel and his team at the University Medical Centre Hamburg-Eppendof in Hamburg, Germany, examined the clinical applications of CTCs in the liquid biopsy space. In terms of limitations, the group noted that hundreds of CTCs are often needed to establish a cancer cell line or xenograft, which they believe "limits this approach to few patients with advanced disease."
The study authors also pointed out that the focus on new technical developments based on CTC biology discoveries has often slowed CTC assay introduction into clinical diagnostics.
However, the researchers noted that new insights into CTC biology are beginning to yield platforms for "combined enrichment, detection, and characterization of CTCs."
The technical challenges and barriers to the clinical implementation of CTCs depend on how the cells are being used, said Kristen Amanti, VP of San Francisco-based healthcare and life sciences consulting firm Health Advances.
"Companies will struggle more when they attempt to use CTCs for cancer screening than if they are using them to monitor therapy of a patient who's already been diagnosed with a specific cancer," Amanti said. "If there's no screening mechanism for the particular cancer type ... the evidence bar is going to be really high in terms of demonstrating clinical evidence that you're actually diagnosing people with good sensitivity and specificity."
However, Amanti also pointed out that "if you have an indication when there is already a screening mechanism that's in place, you're going to have to prove that you're better than that or that you offer some sort of economic advantage."
Amanti also argued that the biggest financial hurdle companies will deal with is convincing payors to cover the CTC assays, as they may worry about the frequency and cost of each CTC assay that needs to be administered to provide a benefit.
According to Health Advances Director Arushi Agarwal, payors are currently cautious of CTC assays because the technology initially "failed a little miserably" to deliver on promises for diagnostic and therapeutic purposes when it was first introduced. However, she believes that as technology around capturing and analyzing single CTCs improves, payors will be more willing to cover the assays.
"A lot of companies have to go through this sort of exercise of figuring out how to price the test reasonably but understand [how to offer] a test they want done multiple times because it's less invasive and a blood draw," Amanti said. "That's where the payors start to get nervous."
Amanti noted that even though companies may show that a CTC assay is prognostic for a type of cancer, they will need to demonstrate a meaningful change in clinical management in order to receive coverage.
"It is one thing to say 'Okay you're not responding to your therapy, but is there anything else to put these patients on?'" Amanti explained. "Also, are physicians actually switching therapies based on that, and are there change in patients' outcomes?"
Commercial progress
Despite the many regulatory and financial roadblocks to clinical implementation, the commercial prospects for CTC enrichment and detection remain strong. In 2018, several companies in particular made major strides to push their CTC capture and detection technologies toward clinical use.
Epic Sciences saw a number of positive developments for its technology in 2018. In June, Epic and its collaborators published a multi-institutional cohort study that validated its CTC-based AR-V7 assay that runs on its "No Cell Left Behind" CTC platform, now marketed by Genomic Health as Oncotype DX AR-V7 Nucleus Detect. According to Epic, the study is one of the first to validate that a liquid biopsy test can predict therapeutic response and show a survival benefit for patients. Medicare Administrative Contractor Palmetto GBA then issued a positive final local coverage determination for the assay in October.
In addition, Epic raised $52 million in a Series E financing round earlier this year and is now applying its technology to investigate how integrated analysis of tumor cells in the blood and human immune cells could be used in immunotherapy drug development and companion diagnostics. In November, the firm partnered with four major Canadian breast cancer centers in a clinical trial to see if its technology can predict the risk of recurrence in patients with metastatic breast cancer
Meanwhile, Michigan-based liquid biopsy firm Celsee Diagnostics is also making progress on commercializing its circulating tumor cell enrichment tools. After collaborating with IncellDx on a feasibility study, the firms signed a co-commercialization agreement in January for a range of products including a CTC-based screening test for breast, colorectal, prostate, and other cancers that run on its Celsee C-Prep Genesis platform.
In May, Sunnyvale, California-based CellMax Life began a US clinical trial to validate its CTC colorectal cancer screening assay as it aims to support a regulatory submission to the US Food and Drug Administration. The firm's CMx platform, only currently available in Asia, trelies on a "chaotic mixing microfluidic chip" that isolates CTCs present at a fraction of one to 10 CTCs in a background of 1 billion normal cells. In addition, CellMax partnered with IncellDx in April to jointly develop and market CTC tests across several solid tumors and indications, including personalized therapy selection and monitoring.
Announced this week, CellMax said that it has partnered with Taiwan-based Medigen Biotech as part of the firm's cell therapy clinical trials. Medigen will combine Cellmax's Cmx circulating CTC platform with its liquid biopsy panel to determine patient treatment selection and response.
Another company looking to expand into CTC-focused liquid biopsy is Precision for Medicine. In September the company acquired ApoCell and its ApoStream CTC enrichment technology, which uses dielectric charge differences to separate tumor and normal cells. Precision for Medicine's Senior VP Darren Davis explained at the time that the firm bought ApoCell because it had developed novel liquid biopsy technology based on immunohistochemistry and immunofluorescence imaging.
Vortex Biosciences has also begun making strides to commercialize its VTX-1 liquid biopsy CTC platform. In March, the firm partnered with BioView to develop an integrated workflow to identify clinical biomarkers on CTCs. In November, Vortex struck a supply agreement deal with Stratec Consumables to develop a microfluidic chip for Vortex's platform. While initially developed at UCLA, the new version of the chip will help adapt the platform for commercial scale production, the firm said.
Earlier this year, Menarini Silicon Biosystems announced that it has combined recently acquired technologies into a cell-based liquid biopsy workflow, which includes its CellSearch CTC purification tool. According to the firm, CellSearch pulls tumor cells from blood samples using extracellular epitopes and immunomagnetic enrichment in "an automated way."
Menarini had previously received approval from the FDA to use CellSearch to identify and enumerate CTCs in metastatic prostate, breast, and colorectal cancers. The firm is now working to increase CellSearch's cell isolation abilities beyond epithelial cells by developing further markers and capture agents to select other cancer types from blood.
"There are a handful of new tests that are being adopted, but we [will] see many more in the next few years, and as the data comes out supporting their utility, liquid biopsy should become more routine," Kelly added.
Newer kids on the block
Michigan-based startup Akadeum also aims to enter the liquid biopsy space with its microbubble platform, which the firm said can identify and isolate CTCs and other molecules. In contrast to microfluidic chips, the firm's research-use-only tool uses low-density glass-shelled, air-filled bubbles with specific antibodies on the surface that bind to the target cell, which then "float to the surface."
According to Akadeum CEO Brandon McNaughton, the firm aims to deploy its products across the US and possibly abroad in the next two to three years.
Capio BioSciences, a spinout from the University of Wisconsin, has also developed similar technology — called CapioCyte — that integrates cell rolling and multivalent binding mediated by surface-immobilized nanoparticles to capture CTCs.
In an email, Capio BioSciences founder Seungpyo Hong explained that CapioCyte distinguishes itself from other CTC capture technology because it combines biomimicry and nanotechnology. While cancer screening and early diagnosis is emerging as a large market, Hong noted that the highly variable numbers and phenotypes of CTCs from individual patients suggest that the prognostic values of CTCs will more likely be explored in the future.
In May, University of Kansas researchers published a study on a microfluidic platform that can detect circulating plasma cells in patients diagnosed with clonal plasma cell disorders including multiple myeloma. Led by KU chemistry and mechanical engineering professor Stephen Soper, the researchers founded San Diego-based startup Biofluidica in 2016 to further develop a diagnostic tool that uses the sinusoidal microfluidic technology, and they now plan to apply for FDA 510(k) clearance.
Academic endeavors
At the University of British Columbia, researchers developed a CTC enrichment system that they believe overcomes limitations of current liquid biopsy techniques by integrating biophysical enrichment and laser capture microdissection (LCM). In the study, the group enriched CTCs in prostate cancer blood samples by lysing red blood cells and used a microfluidic "ratchet-based cell sorting method" to separate white blood cells and CTCs.
To extract single CTCs for LCM, the team selected tumor cells by fixation-free staining and embedded the cell samples in a hydrogel matrix, immobilizing the cells. The group then extracted the embedded cells by using a short-defocused UV laser to launch the embedded cells onto an adhesive cap in a collection tube.
In April, a research team led by Kelley at the University of Toronto published a study regarding a mRNA cytometry approach that integrates both CTC isolation and gene expression analysis. In the study, the researchers used two types of magnetic particles that selectively hybridize different regions of mRNA in a tumor cell, allowing the team to separate cells and assess the amount of RNA in each cell.
Looking at metastatic castration-resistant prostate cancer, the group identified CTCs in parallel using immunofluorescence and either its mRNA method or an EpCAM-based capture. The researchers found that the mRNA cytology method offered both a CTC count and an accurate readout of the absence or presence of clinically relevant mRNAs.
However, Kelley and her team said that they will have to test the method on earlier stage cancer patients with lower amounts of CTCs. While the researchers have not started discussing commercial test development, they hope that other groups or firms will be interested in using the platform.