By Benjamin Ross
June 4, 2018 | In the process of late-stage cancer diagnosis, a lack of trained personnel and the high cost of MRIs and other detection methods are barriers limiting cancer screening in low-resource settings. Thomas Carey, a PhD candidate in Bioengineering at the University of California, Berkley, is developing a microfluidic-based platform to detect the presence of biomarkers present in virtually every fluid, particularly saliva.
Carey’s work caught the attention of judges at the recent Molecular Medicine Tri Conference, earning him the 2018 Early Innovator Award.
Carey told Diagnostics World that for decades blood has been the focal point of research on circulating tumor cells (CTCs), which Carey says can be isolated and characterized in order to noninvasively sample a tumor. Saliva as an exosome is not well explored in terms of being used as a noninvasive liquid biopsy.
“I’m interested in using saliva as a diagnostic fluid because the noninvasiveness of sample collection makes it especially well-suited for routine screening applications,” Carey said via email. “So it’s less about 'what might be found in saliva that isn’t in blood’ than ‘what might be found in saliva that’s also in blood but more readily accessible in saliva.’”
Carey enjoys the process of researching the unfamiliar territory of using exosomes for diagnostics, saying he feels like he’s on the leading edge in the field of exosome-based diagnostics.
“One of the most exciting parts of my project is how little is known about exosomes,” Carey wrote in his award entry form. “Presumably because they are so small, basic knowledge such as the concentration of tumor-derived exosomes in bodily fluids has not been reported. I also found it surprising that most other groups studying the diagnostic potential of exosomes are pursuing molecular assays rather than using surface markers, as molecular assays are less suitable for the point-of-care.”
Currently Carey’s platform is a theoretical proposal focusing on lung cancer, which he says is the subject of multiple studies that link certain microfluids commonly present in lung cancer with saliva.
The yet-to-be-named platform requires only 5ml of saliva to produce a result, which Carey says takes roughly 5 minutes to produce. From there the platform will provide a "yes/no" answer regarding the presence of tumor-derived exosomes as a proxy for a tumor. Carey believes this approach, which borrows signal-processing methods from cellular communications, will enable the platform to be used by untrained users.
“By physically encoding a series of nodes and pores of differing lengths (corresponding to a set of unique binary sequences called Barker codes), it’s possible to identify ‘events’, or particles passing through the pores, with high accuracy by using a matched filter bank and cross-correlation,” Carey said in an email. “This works even when multiple particles are present in the series of nodes and pores simultaneously. In cellular communications, similar technologies are used to separate signals such as from multiple phones connected to a single cell tower.”
In his entry for the award, Carey says that he and his colleagues have “so far demonstrated that our device is capable of distinguishing exosome-coated functionalized colloids relative to bare functionalized colloids when the exosome:colloid ratio is high.”
The next steps for Carey and his colleagues are to optimize their platform for specific capture of spiked cell-culture-derived exosomes in a large background of normal saliva-derived exosomes using tumor-specific markers before ultimately using their platform to detect tumor-derived exosomes specifically in the blood of Stage I lung cancer patients.
“Because of the exosome’s size, it’s hard to actually determine the number of exosomes that are present in a saliva sample from a lung cancer patient,” Carey says. “As of right now the platform is able to discriminate a sample of buffer-containing exosomes versus one that doesn’t or one that contains exosomes from a non-cancerous cell line.”
Looking ahead, Carey hopes that in two years he’ll be able to use the platform for clinical application. “The promise of being able to use a liquid biopsy and to get a definitive answer in half an hour on whether or not a patient has lung cancer, the ability to run your entire diagnostic and get the answer in the same doctor’s visit will be huge for diagnosis moving forward.”