Clinical Application of Exomes
Said the tumor to its neighbor: “You’ve got mail”

Cells have their own miniaturized postal service in the shape of vesicles, or tiny bubbles through which molecules crucial for biological processes like communication and food intake are sorted, packaged and delivered. Outside of the 2013 Nobel Prize in Medicine going to the discoverers of this highly organized transport system, scientific interest in a particular group of vesicles called exosomes has accelerated over the last several years. Andrew K. Godwin, Ph.D., of Drug Discovery, Delivery and Experimental Therapeutics, is among the researchers studying the potential clinical applications of these specialized structures.

exomes 
 Electron microscopy image (magnification: 45,000x) showing immunopurified exosomes in the center, surrounded by larger microvesicles.

Exosomes are found in blood, urine and many other biological fluids, with contents that, while varied according to the cells from which they bud off, generally comprise proteins, DNA and assorted RNA molecules. The latter include messenger RNA, or transcripts dictating protein production; and microRNAs, short strings of bases that help regulate gene expression. Typically no more than 100 nanometers in size, these vesicles may be minute – about one-thousandth of a human hair’s average width – but they pack a punch.

Until recently, scant attention was paid to the existence of exosomes derived from tumor cells, much less any nefarious purposes they might harbor. Godwin, long interested in the biology underlying gastrointestinal stromal tumors (GISTs), decided to find out what exosomes might be up to in this malignant environment. Once metastasized, GISTs – which hail from interstitial cells of Cajal, normally involved in smooth muscle contraction along the digestive tract – are difficult to treat. The drug Gleevec may work well for the majority of these patients, but a relapse is more common than not, and about 15 percent don’t respond the first time around.

An early clue surfaced when Godwin and his laboratory group observed that mutated c-KIT, a gene central to GIST development, counts among the components of tumor-derived exosomes. The researchers began looking at whether exosomes bearing oncogenic c-KIT might influence interactions between GIST cells and the surrounding support structure of stromal cells that eventually caves before the tumor’s outward spread.

“We’ve seen normal stromal cells, in taking up these exosomes, get converted into GIST cells; they express similar proteins and induce many of the same signaling pathways,” Godwin says. It’s akin to drinking Polyjuice Potion (which allows a person to assume a different form) in the magical world of Harry Potter – except in the case of GIST-derived exosomes, it’s not fiction.  

“Tumor cells also actively release higher numbers of exosomes, and we’ve found that normal recipient cells end up copying this maneuver, so there’s a snowball effect,” Godwin observes. “It’s another means for metastasis, at least locally. These exosomes are somehow able to modify other cells in the tumor microenvironment, which stimulates the production of additional factors that allow the host tumor cells to keep promoting themselves through growth and invasion.”

While exosomes are difficult to detect in biological fluids, Godwin and his crew are concurrently trying to utilize tumor productivity – in terms of active exosome release – as a potential way to track disease early on. “Exosomes are Nature’s way of compacting an enrichment of biomarkers, and in tumors, there’s natural amplification of the signal to make detection easier,” he explains. “We just need to figure out how to separate all that cargo in the carrier, so we’re able to closely analyze the different components.”

The researchers are fine-tuning a diagnostic tool for this purpose, harnessing the power of microfluidics, a technology inspired by integrated semiconductor electronics and developed in the 1990s. Essentially, it allows precise manipulation of minuscule volumes of fluids and tiny objects – in this instance, blood and exosomes – analogous to moving electrons in integrated circuits. Godwin and his group have developed microfluidic platforms to capture and analyze tumor-derived exosomes, starting with non-small cell lung cancer. “Basically, it’s a lab-on-a-chip device that goes beyond detecting exosomes to profiling the biomarkers within,” he says.

“Think of it as a non-invasive liquid biopsy that would require mere microliters of blood from patients. Besides early detection, it could be used to monitor disease during treatment. For instance, by isolating exosomes and measuring their contents, we could see if the levels of specific proteins are dropping in response to targeted therapy.” 

In December 2012, Godwin was awarded a grant from the Mary Kay Foundation to characterize new and more reliable biomarkers in ovarian cancer, also using microfluidics. Between the likely involvement of exosomes in ovarian cancer and the fact that current clinical tests for one biomarker, CA-125, have proven less than effective (it can be elevated by conditions other than cancer), there are good reasons for the foundation’s keen interest in what Godwin’s research brings to the table. 

“Ours is a broad-range lab; we cover a range of investigations from genetic risk factors and cancer therapeutics to molecular profiling and even drug repurposing,” he says. “So we’re very much bench-to-bedside, in terms of actually taking discoveries into clinical trials. It’s early days yet, but we hope to do the same with what we learn about exosomes in non-small cell lung cancer, GIST and ovarian cancer.”

Funding sources for this research

  • Mary Kay Foundation 2012 Cancer Research Grant: “High-Throughput Microfluidic Exosome Profiling Platform for Early Detection of Ovarian Cancer” 

  • NIH RO1 CA140323: “Exploiting Biological Networks to Improve Clinical Treatment of Ovarian Cancer” 

  • Biomedical Research Training Program Fellowship, 40088X6: “Evaluation of the Impact of Ovarian Ascites-Derived Exosomes in the Induction of Tumor Associated Macrophages”

  • Kansas Bioscience Authority Eminent Scholar Award

  • The OVERRUN Ovarian Cancer Postdoctoral Fellowship 

  • University of Kansas Medical Center Auxiliary: “Diagnostic Device for Lung Cancer”