A Bigger Picture:
Peter Kuhn Looks at Circulating Tumor Cells

By Eric Sauter and Mika Ono

Cancer tumor cells are known to move around—and that's the problem. In the peripheral blood of patients with carcinomas, they circulate in minute amounts, about one cancer cell for every ten million normal blood cells. In certain patients, those circulating cells can lead to lethal metastases, cancer resulting from the spread of the original tumor.

At that concentration in the blood, detecting these cells, let alone finding useful information about them, would appear to border on the miraculous.

But Peter Kuhn, an associate professor in cell biology at Scripps Research, has led a collaboration with the Palo Alto Research Center (PARC) that uses a method of detection called fiber-optic array screening technology (FAST) that can directly scan 50 million cells to identify likely rare cancer cells in less than two minutes (500 times faster than other cell-based scan approaches). The research team in the Kuhn lab—including Scripps Clinic pathologist and Scripps Research adjunct faculty member Kelly Bethel, graduate student Dena Marrinucci, Scripps Clinic oncologist and Skaggs Translational Science Fellow Jenny Fisher, and Research Assistants Daniel Lazar, Peter Clark, and Maddy Luttgen—is also working on new clinically relevant tools that will determine where these rare cancer cells come from, where they're headed, and whether or not they have the potential to cause further harm.

Although he has a ways to go, Kuhn's work offers the long-term possibility of further leveling the playing field in the war against cancer and making early detection—when treatment can be most effective—a common and relatively simple process. The work should also facilitate monitoring of patients who need ongoing therapy management, to catch any cancer recurrences at the earliest possible juncture.

Over the past two years, Kuhn and his colleagues have used FAST to accurately detect circulating tumor cells in blood samples obtained from patients with metastatic breast and lung cancer.

"This is the evolution of our technology over time," he said. "We developed the basic technology by 2004. By 2006, we ran a study with a small group of patients that showed the sensitivity and specificity of that technology. Our 2006 study on breast cancer established for first time that cells we found in circulation were very similar to the cell types in the primary tumor."

All of this falls under the scientific umbrella of what Kuhn, who joined Scripps Research in 2002, calls true translational science—the kind of research that leads to advances in medicine, not just knowledge. In addition to his cancer work, he has identified and characterized a number of proteins of the SARS virus. He was also instrumental in bringing a new synchrotron, a particle accelerator that creates high intensity x-ray light, to Scripps Research this year, a major milestone. Together with the laboratory of Professor Ray Stevens at Scripps Research and their collaborators Brian Kobilka and company at Stanford University, Kuhn also helped solve the first human GPCR structure, which was selected as one of the top ten scientific breakthroughs of 2007 in Science magazine.

Kuhn has made a commitment to thinking about potential applications for patients, in addition to basic science, and this has changed the very nature of how he approaches his work. He stresses that his colleagues from Scripps Clinic have to be able to use his concepts in their daily clinical work if the concepts are to ever have any practical meaning outside of the laboratory.

"If I jump up and down, and say, 'Here's a cell and because of this particular protein we found, we think it's a circulating breast cancer cell,' that's not good enough. A pathologist needs to be able to say, 'Because of this data about the cell, we can prove that this cell originated in the breast.' Our 2006 case study is the first example of this kind of work. Now we're doing the same thing for other cancer types."

Cells Gone Wild

Like escaped prisoners out on a crime spree, breast cancer (and other types of tissue/organ cancer like lung, colon/rectal, and prostate) tumor cells escape from the primary tumor mass into the bloodstream, and these migrating cells are the source of the lethal metastases that kill patients. These cells can be identified using immunofluorescence assays via monoclonal antibodies directed against cytokeratins; cytokeratins, part of the cytoskeleton, are fibrous proteins found only in epithelial cells and not in normal blood cells. A number of clinical trials have established that cytokeratin-positive cells with certain boundary conditions are of cancerous origin, and that their presence in blood corresponds with poor outcome and lower survival rate in patients. 

Tracking circulating tumor cells is still accomplished primarily through immunocytochemical markers like cytokeratin and the use of nuclear staining. However successful the current method may be, pathologists have been unable to differentiate circulating tumor cells to tumor cells from other sites obtained through routine diagnostic procedures. Pathologists know circulating tumor cells are bad but cannot tell where they're from or where they are going to—a serious, even fatal gap in knowledge because, to a great degree, their origin and destination help determine treatment.

Kuhn and his team are trying to close that gap, and have moved a significant part of this proposition along over the last few years.

"We are running small clinical trials with breast, colon, and lung cancer patients—50 patients in all," Kuhn said, "and we hope to have data ready in the next six months. Even though this is just the first step, we have a scientifically sound vision for the future of this technology. These circulating tumor cells should have a sender, an address, and a delivery date—that's what we're looking for now."

Kuhn and his colleagues have three abstracts accepted at the 2008 annual meeting of the American Society of Clinical Oncology that, while still preliminary, confirm the concept of characterizing circulating cells from colon and lung cancers. They also add weight to the idea that patients with detectable circulating tumor cells are at much greater risk than even those patients with metastatic disease but no detectable circulating tumor cells.

Kuhn said cells that start metastatic disease have their origins in the primary tumor, but those cells have to go through significant reprogramming several times before they reach their permanent destination in different tissue to seed a new tumor. Determining exactly what type of cell that is would go a long to solving these mysteries, and to translating his research into therapeutic and diagnostic realities.

The Rise of Theranostics

Along with translational science, the other word that Kuhn uses most often these days is "theranostics"—the nexus of therapies and diagnostics—and the latest wave to hit the pharmaceutical/biotechnology industries.

Writing in the January 1, 2008 issue of Genetic Engineering & Biotechnology News, California attorney Lisa Haile, a lawyer for DLA Piper and member of a San Diego think tank, SHOUT, that Kuhn co-founded, described theranostics—and its future—this way: "In recent years, our knowledge of the genome, proteome, and metabolic pathways has increased exponentially, given improvements in research techniques and the population of databases. The field of theranostics thus allows us to use detailed information about a patient's genotype and to monitor the individual's particular therapeutic regimen and assess the patient's response to it… Theranostics and personalized medicine have the potential to transform the medical industry and the overall approach to healthcare. Clearly, widespread adoption of theranostics will eliminate unnecessary treatment of patients for whom the treatment is ineffective or even dangerous, with an end result being major drug cost savings for the patients and the entire healthcare industry."

Kuhn agrees with her.

"We are at a critical juncture and turning point where there are targeted efforts around the world in anti-cancer drug discovery," he said. "They involve Scripps Research, other academic institutions, and the pharmaceutical and biotech industries. But considering the fact that cancer really comprises more than 200 distinct diseases, it is also clear that we have to learn how to stratify patients on a personal basis, to customize diagnosis and treatment aimed at the way it presents in that individual."

For Kuhn that means advancing along the track he's been on since 2004—developing qualitative and quantitative diagnostic techniques that will be available for individual patients.

"You want to be able to provide initial therapy that is based on individual diagnosis and monitor that in real time," he said. "You want to say within a week or two if the patient is responding to the treatment. Then you need a way to monitor that same patient over a long period of time. I don't believe any one of these new methods will be the solution. What will be critical will be our ability to get individual data and correlate that in a clinically useful way—from circulating tumor cells to imaging to better genomic data. This will require real teamwork—not only among the members of my lab, who do an outstanding job, but also with other pioneering research groups."

For Kuhn, the science is part of a bigger picture

"At the end of the day, the clinician has to be really excited about what we do. It's important to educate the scientific community to think of the clinic, and vice versa. It helps to put ourselves in the position of the eternal student. We have so much still to learn and so much to learn from each other."

Send comments to: mikaono[at]scripps.edu

The research team in the Kuhn lab (including, left to right, Associate Professor Peter Kuhn, Graduate Student Dena Marrinucci, Research Assistant Daniel Lazar) is working on methods to detect rare circulating cancer cells and to learn where these cells come from, where they're headed, and whether or not they have the potential to cause further harm.