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New Generation of CTC Platforms Moves Toward the Clinic


NEW YORK (360Dx) – Multiple new technologies have emerged in recent years for isolating circulating tumor cells, some of which are now making more definitive moves towards the clinic.

Angle, a UK-based firm with a label-free system called Parsortix, announced last week, for example, that it has enrolled the first patient in its ANG-002 breast cancer clinical study, which is intended to support submission of Parsortix to the US Food and Drug Administration.

Unlike platforms that use antibodies or molecular probes to bind CTCs, Parsortix is what is known as an unbiased or label-free technology, in which CTCs are extracted using things like magnetic depletion of other blood cells, microfluidics, physical filtering systems, centrifugation, and other systems.

Angle aims to become the first to receive a class II clearance from the US Food and Drug Administration for this type of product, but it is not alone in pushing such technologies toward clinical use. Vortex Biosciences, for example, is also commercializing a label-free CTC instrument.

Meanwhile, although label-free detection platforms are being promoted as lacking the biases that might lead antibody methods to miss CTCs, researchers and new companies are also now advancing platforms that combine fluidic and nanoscale technologies with more standard label-based approaches that they believe might work even better in certain clinical niches.

In an email this week, Angle CEO Andrew Newland reiterated that his company's goal in bringing its platform through the FDA is to make available a technology that allows isolation of CTCs in as many patients as possible, through a regulatory pathway that allows it to be used by clinical labs in a decentralized manner.

The company called the start of its study, which is being led by MD Anderson Cancer Center and will recruit 200 metastatic breast cancer patients and 200 healthy controls, a "culmination of an enormous amount of work."

The primary endpoint is to show that the Parsortix system can sensitively isolate CTCs from metastatic breast cancer patients but does not detect them in healthy volunteers. In his email, Newland said that there is no particular sensitivity or specificity levels that the company is targeting in the study. "Even one patient that can benefit from a blood-based biopsy would be positive," he wrote.

In addition to testing the basic principle of CTC isolation, collaborators at different institutions will also analyze the harvested cells using quantitative PCR, FISH, and RNA-Seq. Angle said in February that it had signed an agreement with Abbott to use its proprietary PathVysion HER-2 DNA FISH Probe kits in the study, and added that a positive result from this part of the trial could provide an impetus for Abbott to someday offer a Parsortix-based product for HER-2 analysis from a routine blood test.

The company expects both the clinical study and the associated analytical studies to finish during the second half of this year.

Ideally, Angle will demonstrate a high sensitivity in detecting CTCs in breast cancer patients, with comparable, or better performance than what other groups working with label-free capture platforms have shown, though Newland said that from a business perspective, the performance measures for other technologies that haven't been commercialized or are not going through FDA are not really relevant.

That said, data does already exist on other platforms — both investigational and recently commercialized. Last April, for example, a team from Massachusetts General Hospital reported on an assay they have developed using a microfluidic CTC enrichment platform called the CTC-iChip, coupled with a highly sensitive and specific multi-gene RNA biomarker panel.

The chip uses microfluidics and magnetic beads to deplete red and white blood cells from a sample, leaving a mix that includes any CTCs present, along with some remaining white blood cells — fewer than 500 per milliliter of processed whole blood, according to developers.

In the experiments in breast cancer patients, the assay successfully identified a CTC signal in 50-70 percent of metastatic and 20-40 percent of localized, pretreatment patient samples.

In the commercial field, Vortex Sciences' VTX-1 instrument uses a microfluidic chip to capture CTCs in what the company describes as "micro-scale vortices" based on physical properties like cell size and deformability. CTCs are trapped in these microscopic currents and eddies, while red and white blood cells flow past.

Last November, researchers from Stanford University working with Vortex published a study showing that the VTX-1 system could isolate CTCs with high enough purity to allow successful whole-genome amplification and targeted sequencing of a pooled sample of cells.

More recently, the firm released a paper describing the development and laying out more basic parameters of the platform's performance, including that it could recover spiked breast and lung cancer cell lines at a rate of up to about 75 percent while reducing contaminating white blood cells down to less than 100 per milliliter of blood processed.

Vortex has received a CE mark for its system and registered it as a Class I medical device with the FDA but has not discussed any plans to try to establish the system as a Class II device.

Despite the attention of various companies on label-free CTC isolation, others in the liquid biopsy space have also started to show that, depending on the application, it may not be all that important to have a platform that segregates CTCs without the use of a molecular biomarker or antibody. Focusing on subsets of CTCs that express a certain surface marker could be sufficiently sensitive, or in some cases even more effective in detecting or monitoring disease, despite challenges that have been seen with earlier platforms like Menarini Silicon Biosystems' FDA-approved CellSearch.

A research team from the University of Toronto, for example, recently developed and published a "two birds with one stone" approach that enables both isolation of CTCs and analysis of their gene expression, or messenger RNA content.

And startup CytoLumina, is advancing its "NanoVelcro" approach in a system it calls CytoTrapNano, which combines both physical engineering analogous to the fluidic approaches of Vortex and Angle, as well as capture antibodies in the manner of CellSearch.

According to CytoLumina's website, the system is currently aimed at CTC enumeration, not necessarily the extraction of CTCs for follow-on analyses, as in with Angle's Parsortix or Vortex's VTX-1.

But the company has noted research studies awaiting publication that suggest its approach can allow not just detection of cells, but also their further characterization.

Researchers from another new firm, Capio Biosciences, are also hoping to commercialize a CTC platform that combines structural and antibody capture features. Their technology, called CapioCyte, involves a chip whose surface is treated to induce CTCs to roll slowly along it while other blood components float swiftly by.

Once captured, CTCs can either be recovered for post-capture analysis like RNA-Seq or can be automatically stained for enumeration and fluorescent imaging analysis.

The group published a study last month in Clinical Cancer Research showing that CapioCyte was able to pick up CTCs in each of 24 patients undergoing radiation treatment for head-and-neck, prostate, rectal, or cervical cancer. Results showed a correlation between a reduction of cells and successful results of radiation therapy.

Seungpyo Hong, cofounder of Capio and a professor or pharmaceutical sciences at the University of Wisconsin, Madison, said in an email that while unbiased or label-free CTC platforms do have advantages in allowing potential capture of CTCs that don't express a particular biomarker, there is also no guarantee that label-free methods might not also miss cancer cells, for example those with an abnormally small size.

The Capio approach potentially allows for the use of multiple antibodies or capture agents, which would hopefully minimize the chance of missing specific populations of CTCs, he added.

According to Hong, Capio is also planning to submit its own platform to the FDA — although not for two or three years — as well offering analyses through a CLIA lab setting. "We are currently building a commercial prototype that will serve as a platform for the two tracks" he said.

And despite label-free technologies like Parsortix and VTX-1 now positioning themselves as alternatives, the field's main legacy antibody-based technology, Menarini's CellSearch, also does not look like it is shying away from competitors. In fact, Menarini recently said that it might seek regulatory approval for its existing CellSearch platform not just as a CTC enumerator, but as part of a larger pipeline that includes CTC purification; isolation of cells with the company's DEPArray platform; whole-genome amplification, and library preparation to support both Ion Torrent and Illumina sequencing.