For years, doctors have looked at tissue biopsies and spotted unusual cells that seem to have early signs of cancer. The problem is that, until recently, doctors have never had the right tools to extract the cells from the tissue, leaving them with no good way to confirm their observation while the tumor is in its early stages and most treatable.
That situation changed recently with the publication of a report on a powerful new technique, called laser capture microdissection, that can pull out a small cluster of cells from a tissue sample in as little as 8 seconds.
By taking these cells directly from the tissue, National Institutes of Health (NIH) scientists say that they can immediately analyze the cells' gene and enzyme activity with other research tools. Currently, scientists must attempt to extract, or microdissect, cells either by trying to yank them free with a manual tool or through a convoluted process of isolating and culturing the cells. Most scientists consider both approaches to be tedious, time-consuming, and inefficient.
According to Lance Liotta, MD, PhD, a scientist at the National Cancer Institute (NCI) and senior author of the paper, published in the November 8, 1996, issue of Science, the direct access to cells should revolutionize the understanding of the molecular basis of cancer and other diseases, helping to lay the groundwork for earlier and more precise disease detection.
"Having this technique is the difference between being able to investigate a crime in progress and going back 2 weeks later to the scene of the crime when much of the evidence has vanished, as we typically do now," said Liotta. "Laser capture microdissection gives us access to the disease, in a sense, while the crime is still in the planning stages, and that's really powerful information to have in designing strategies to halt the disease process."
"Low-Tech," User-Friendly Procedure
Laser capture microdissection is a fully automated, one-step technique that, in today's high-tech world, has emerged as a remarkably low-tech creation. It integrates a standard laboratory microscope with a low-energy laser and a transparent ethylene vinyl acetate polymer thermoplastic film--the same plastic seal as is used in a container of yogurt.
Michael Emmert-Buck, MD, PhD, an NCI scientist and lead author of the paper, said the group's prototype device works on the same basic aim-and-shoot principle as a fully automated camera:
- Scientist looks through a microscope at a tissue biopsy, which typically contains hundreds of different types of cells.
- Upon spotting a group of tumor cells, for example, the scientist presses a button attached to the side of the microscope. The button activates the laser, which flashes a beam of light that has an intensity slightly greater than a laser pointer.
- The beam of light passes through the plastic film placed above the tissue sample and focuses onto the cells. In the process, the beam heats the plastic, giving it the thermal qualities of a piece of cellophane tape. The cells then stick to the plastic directly above them, whereupon the cells are immediately extracted and ready for analysis.
Emmert-Buck said he and his colleagues purposely designed their device with a camera in mind. "We wanted an instrument that any scientist could sit down and use immediately," he said. "That meant creating a fully automated, user-friendly device that was free of any tricky, manual manipulations to complicate its operation. A camera seemed like a device that is simple and familiar to most people. With this idea in mind, we spent about 2 years creating a viable, one-step technique."
In the Science paper, Emmert-Buck and colleagues report that laser capture microdissection has successfully extracted cells in all tissues in which it has been tested. These include kidney glomeruli, in situ breast carcinoma, atypical ductal hyperplasia of the breast, prostatic intraepithelial neoplasia, and lymphoid follicles.
They reported no limitation in their ability to amplify DNA or RNA from tumor cells extracted with laser capture microdissection. The scientists also found that they were able to recover enzymes from within the cells and test them for activity.
Robert F. Bonner, PhD, a coauthor on the paper and a scientist with NIH's National Center for Research Resources, said laser capture microdissection, like all emerging techniques, still has room for improvement. Bonner said with further refinement of the plastic film and activation of a finer laser beam, he could easily foresee the technique extracting single cells, rather than the two or three cells at a time that it now yields.
Technique May Prove Useful in Recording Gene Expression Patterns
Another likely role for the technique is in helping to record the patterns of gene expression in various cell types, an emerging issue in medical research. For instance, NCI's Cancer Genome Anatomy Project (CGAP) seeks, in part, to define the patterns of gene expression in normal, precancerous, and malignant cells.
In projects such as CGAP, laser capture microdissection fits in nicely at the front end of the process as the tool that procures pure cell samples from tissue, feeding the rest of the analytical process.
Given the technique's great potential to advance the study of biology and medicine, the NCI has made plans to make the device widely available to researchers and clinicians around the country. A demonstration project is already in the works with Steven Bova, MD, a scientist in the Departments of Urology and Pathology at The Johns Hopkins University School of Medicine. Liotta said the aim of this project is to receive input from fellow researchers on how the device might be simplified even more, while also achieving the highest standard of quality.
"As new information accrues about the genetics of cancer and other human diseases, it opens up new opportunities for discovery, which will ultimately lead to more targeted ways to diagnose and treat disease," said Richard Klausner, MD, NCI director. "The NCI recognizes that it has a commitment to place powerful, new research tools into the hands of scientists to catalyze the discovery process. And, the NCI will make every effort to do so with laser capture microdissection."