Two key issues for the pharmaceutical industry include accuracy of predicting in vivo drug interactions, including toxicity, and the time/cost of drug development. According to a 2007 report in Archives of Internal Medicine, the number of serious adverse and fatal drug events in the U.S., as reported to the FDA, increased threefold between 1998 and 2005.
One of the many advantages of 3-D cell culture is its ability to more accurately replicate physiological behavior, its proponents claim. Additional benefits are just beginning to be understood and utilized to enhance drug discovery, as well as bioprocess applications. Stem cells are also providing new opportunities in both of these areas.
When researchers in the laboratory of Robin Felder, Ph.D., at the University of Virginia, attempted to grow human renal proximal tubule cells on various 3-D technologies, they had problems.
“These are the leading cells in the kidney and have a definitive 3-D orientation,” noted Dr. Felder, professor of pathology and associate director of clinical chemistry. “If grown on a petri dish, it looks like a fried egg on a plate. It’s biologically confused.
“We decided to develop a microcarrier to get the cells oriented in the right polarity,” added Dr. Felder, who spoke on 3-D cell culture technology last month at CHI’s “Bioprocessing Summit” in Cambridge, MA.
Dr. Felder is also a cofounder and chairman of the board at Global Cell Solutions, which manufactures GEM™ (Global Eukaryotic Microcarrier). GEM contains alginate, a long, unbranched polysaccharide derived from brown seaweed, that acts like a “big electro-negative well that holds ions and molecules and allows the GEM to have a big sugar presence,” explained Brad Justice, director of research at Global Cell Solutions.
Justice said that this differs from previous 3-D technology that was based around proteins. The polysaccharide component seems to be important to the cells. Recent studies have also shown that alginate is biochemically sufficient to help maintain embryonic stem cells in an undifferentiated state.
Other advantages to GEM include the fact that it is optically clear and allows the incorporation of magnetic particles. This enables automated cell manipulation by an externally applied magnetic field and prevents cell damage and debris. “The magnets are essential to automation, to spatially control the cells’ location, which is required in a system with no human intervention,” explained Justice.
The main cells currently being used with GEM include: HEK293, CHO, and HeLa and, recently, a large variety of stem cells. In addition, GEM allows users to grow numerous cancer cell lines, neural cells, epithelial cells, and various primary cells right from human or animal sources by engineering certain coatings to improve cell growth, such as selective biomimetic coatings, antibodies, and various growth factors.
Automation Is Key
One of the challenges in bringing microcarriers into research is a lack of easy-to-use systems and small volume containers. This is what the BioLevitator™ was designed to address. Codeveloped by Global Cell Solutions and Hamilton, this unit is a compact benchtop incubator and bioreactor hybrid for handling four independent, high-density 3-D cell cultures. Engineered to magnetically maneuver the GEM, it facilitates nutrient and gas exchange, providing good growth rates and relevant phenotypes, said Justice.
“It also gives us absolute control over the inoculation culture conditions,” he added.
Up to four BioLevitators can be integrated on a liquid-handling platform to create the 3-D CellHost™, which is based on Hamilton’s STAR platform, and is intended for various applications including drug discovery.
“Cell-based assays are now part of all stages of drug discovery so that cell supply has become a major bottleneck,” said Clara Cavelier, Ph.D., senior product manager, cell biology at Hamilton Robotics. “Stem cells may provide a virtually unlimited source of specialized cells to all stages of the drug discovery process, including target discovery, lead identification, and validation.”
The 3-D CellHost permits scientists to take cryopreserved cells, automatically retrieve them from an automated freezer, and automatically introduce them directly into the system, according to Dr. Felder, who says that the system combines biorepository function, cell culture, and analytical technology.
Recent research by Life and Brain demonstrates that this system facilitates human ES cell derived neural stem cell growth, supports undifferentiated cell growth, and maintains morphological characteristics, noted Dr. Cavelier, who gave a presentation on 3-D cell culture at the SBS annual conference in Lille, France, earlier this year.
“Cell culture automation eliminates variability and provides immediate and significant improvements in downstream cell-based assays, i.e., cell-based HTS,” she added. “The big hope is that stem cells will provide better models for drug discovery.”