February 11, 2003
Purdue center formed to create devices to speed drug discovery
WEST LAFAYETTE, Ind. A new state-funded research center at Purdue University will team up scientists and engineers for a project that could speed the discovery of drugs to treat numerous diseases, including cancer and cystic fibrosis.
The Center for Membrane Protein Biotechnology will be funded initially with a $1.3 million, two-year grant from the Indiana 21st Century Research and Technology Fund, established by the state to promote high-tech research and to help commercialize university innovations. Funding for the first half of 2003 was approved in January.
Research in the center will concentrate on developing a new class of miniature devices that use cell membranes to screen new drugs effectively recreating how cancer cells would react to the drugs. The goal is to produce "laboratories-on-a-chip," devices less than one half-inch square that contain up to 1 million test chambers, each capable of screening an individual drug, said Gil Lee, the project's leader and an associate professor of chemical engineering.
Purdue has filed a patent application for the devices.
Each of the chip's tiny chambers will be about one-tenth as wide as a human hair, and each chamber will be covered with a synthetic cell membrane.
Cell membranes are sack-like structures that surround cells and regulate the movement of molecules into and out of the cells. Cells contain a variety of membrane proteins, some of which are directly responsible for cancer's ability to resist anti-tumor chemotherapy drugs. The Purdue researchers will focus on developing devices that screen for a membrane protein called P-glycoprotein, which acts as a tiny pump that quickly removes chemotherapy drugs from tumor cells, said Christine Hrycyna, an assistant professor of chemistry who specializes in the field of multidrug resistance and is an expert on P-glycoprotein.
Cancer cells exposed to chemotherapy drugs produce a disproportionately large amount of P-glycoprotein, and they become progressively resistant to the anticancer drugs. About half of all cancers use P-glycoprotein, in addition to other mechanisms, to resist chemotherapy. Because the protein pumps remove the chemotherapy drugs from cancer cells, tumors are able to resist the toxic effects of those drugs, Hrycyna said.
However, if scientists could find drugs that inactivated the pumps, the chemotherapy drugs would be more effective in destroying the tumors.
Pharmaceutical companies now screen new drugs using conventional methods that are time-consuming and expensive. Such an advanced technology could be used to quickly screen millions of untested drug compounds that exist in large pharmaceutical "libraries."
"This project has enormous potential," said David Thompson, a professor of chemistry who specializes in cell-membrane research. "It could revolutionize drug discovery for membrane protein targets."
Thompson and Hrycyna originated the idea for the research on which the new center is based.
"Drug companies have the capacity to create huge libraries of compounds but no way to screen them rapidly against membrane proteins, in particular," Hrycyna said. "A fertile research area in biochemistry and cell biology is the study of membrane proteins. These proteins are notoriously difficult to work with, and there are not any effective assays to screen drug compounds in large quantities."
The new center will combine the expertise of a diverse range of researchers, from engineers to chemists, and pharmaceutical scientists to physicists.
"I don't think there are many places in the world where this really could happen where you have this many scientists who are specialists in such diverse areas coming together in a collaborative team," said Charles O. Rutledge, interim vice provost for research and director of Purdue's recently formed Discovery Park, a complex of facilities that will use a multidisciplinary approach to develop new technologies.
If the team is successful in creating the screening devices for drugs to control P-glycoprotein, the technology will be adaptable to test for many other membrane proteins. That means the devices would be able to screen drugs that affect other membrane proteins critical to numerous diseases, including cancer. The researchers would especially like to target a membrane protein called isoprenylcysteine methyl transferase, which is critical for the growth of about a third of all cancers.
"What a beautiful thing it would be if we could come up with a basic platform that could be used to screen drugs for numerous membrane-protein-based diseases," Hrycyna said. "We are thinking of this device as having modular components. If you replace the P-glycoprotein module with an isoprenylcysteine methyl transferase module, you can now screen for other kinds of anticancer agents."
Thompson said, "This would enable you to filter through thousands, or even millions, of different potential drugs and figure out the top 10 that you want to spend your time and money developing into real drugs. That's the value of the practical side of this project."
Cell membranes are made of a double layer of lipids, or fats. One reason the membrane proteins are so difficult to study is that they are embedded in the double-layer structure. When the proteins are removed from the membranes to be studied, they lose their function.
Meanwhile, the membranes of most cells are too weak to be fitted over the tiny test chambers. The Purdue researchers will have to create synthetic membranes for the job. To do this, they will borrow characteristics from organisms that have managed to survive for eons amid the high temperatures and pressures of hot, volcanic springs on the ocean floors.
The cells in these "thermophilic" organisms have much stronger membranes. Those membranes, however, are too rigid for the new devices, so Thompson will have to create a hybrid membrane that contains the rigidity of the deep-sea membranes but the flexibility of normal cell membranes.
The new synthetic membranes also will have to be made so that they lie flat, in sheets, as opposed to membranes in nature, which automatically form into round shapes. Then the membranes will have to be attached over the tiny chambers in such a way that the chambers do not leak.
Yet another challenge will be to create the synthetic membranes so that proteins like P-glycoproteins are arranged in the proper orientation.
"That's very important," Thompson said. "Whether the protein is pointed in one direction or another has a huge impact on how sensitive the device will be."
P-glycoprotein gets its pumping energy from a molecule called adenosine triphosphate, or ATP. In the process of using ATP for energy, the molecule is converted to adenosine diphosphate, or ADP, a reaction that changes the acidity of the cell. The researchers believe they will be able to design devices that detect this changing acidity and conversion to ADP, in effect indicating whether the protein is functioning. If a drug is successful in reducing or inactivating the protein's pumping mechanism, the device will detect this change in activity and send an electronic signal to a computer.
In addition to Hrycyna, Lee and Thompson, Purdue engineers and scientists on the team are: Osman Basaran, a professor of chemical engineering; Elias Franses, a professor in chemical engineering; Kinam Park, a professor of pharmaceutics and biomedical engineering; and Igal Szleifer, a professor of theoretical physical chemistry.
"Each person brings a critical component," Lee said. "The sum is much more than the individual parts."
Hrycyna and Thompson are members of the Purdue Cancer Center, which has provided funding for earlier, related research.
"These new devices will help scientists learn more about the basic functioning of virtually any membrane protein and to completely change the way we study and work with membrane proteins," Lee said.
Writer: Emil Venere, (765) 494-4709, email@example.com
Sources: Christine Hrycyna, (765) 494-7322, firstname.lastname@example.org
Gil Lee, (765) 494-0492, email@example.com
David Thompson, (765) 494-0386, firstname.lastname@example.org
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A publication-quality graphic is available at ftp://ftp.purdue. edu/pub/uns/lee.membranes.jpeg.
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A publication-quality photo is available at ftp://ftp. purdue.edu/pub/uns/hrycyna.membranes.jpeg.