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AstraZeneca Finds CellKey CDS System Precisely Characterizes Gi-Coupled GPCRs

Investigators from AstraZeneca recently found that MDS Analytic Technologies’ CellKey platform is “versatile” for secondary screening — important validation for MDS, which launched CellKey in late 2005 with the goal of targeting it toward secondary screening of GPCR drug targets in living cells.
CellKey is a label-free cellular-analysis platform based on a technique called cellular dielectric spectroscopy in which cells are grown on electrodes embedded in microwell plates and exposed to a constant low-level voltage.
In their evaluation of the instrument, which appears in the April issue of the Journal of Biomolecular Screening, the AstraZeneca researchers used three different Gi-coupled G-protein coupled receptors to assess CellKey’s ability to support structure-activity relationship studies.
“We liked the [CellKey] technology for a number of reasons,” Matthew Peters, a principal scientist in the lead generation department at AstraZeneca and lead author of the study, told CBA News this week. “We think it has a lot of power to do new pharmacological characterization of GPCRs. And essentially the combination of features that it offers is novel: it’s label-free, whole cell, and highly sensitive.”
The fact that CellKey is label-free means that researchers do not have to use dyes and radioactivity, Peters said. He also pointed out that the platform is not only label-free in terms of ligand detection, but it is also label-free in terms of the receptor.
“This means you do not have to clone the receptor and then put it into a cell,” Peters said. “It can be a receptor that is already in the cell line.”
Peters added that endogenously expressed receptors in the cell are readily detectable with the system — a valuable benefit because it eliminates the need to overexpress the receptor, which changes its pharmacology.
Peters said that CellKey has good correlation with existing assays. In the paper, the researchers compared CellKey to two other assays, cAMP and GTPγS, and found they could use the applications interchangeably.
In addition, he said, the data were extremely robust in terms of reproducibility and showed good correlation across a 1,000-fold range of compound potencies.
Future Plans
Now that the AstraZeneca researchers have proven that CellKey works as well as existing assays, “our next step is to look at more complex pharmacology using CellKey and see if it can beat technologies that are already working just fine,” Peters said.
For example, he said his team would like to look at inverse agonism.
Peters said that one difficulty when looking at inverse agonism is that high sensitivity is necessary to detect low levels of basal, constitutive, or spontaneous activity of the receptor. He said that he and his colleagues think that CellKey may work for this application, but did not give a timeline for future research plans.
CellKey has other applications as well, Peters said. For example, he mentioned an emerging school of thought in pharmacology that different drugs can act at the same receptor, but induce different downstream signals in the cell.
“A growing body of literature suggests that depending on how you hit receptor X, you get effect X or effect Y,” said Peters. This is known as “ligand-induced differential signaling.”
The CellKey instrument can distinguish the coupling of GPCRs, which could make it a useful tool for studying this signaling phenomenon, according to Peters. The instrument gives one profile when the receptor is Gi-coupled, another when it is Gs-coupled, and a third when it is Gq-coupled. Peters said it is conceivable that CellKey could be very powerful in this area of pharmacology, at least for the GPCR class of receptors.          
CDS has been around for a long time, Peters said, but the way that the technology is applied, in terms of software and hardware, can tune the technology to detect many different things.

“We think CellKey has a lot of power to do new pharmacological characterization of GPCRs. And essentially the combination of features that it offers is novel: it’s label-free, whole cell, and highly sensitive.”

San Diego-based Acea Biosciences has a similar technology, which it calls cell electronic sensing, which can detect longer-term responses, such as mitosis or cell proliferation, said Peters. CellKey, on the other hand, is set up to look at short-term responses, which would be more relevant to cell surface receptors that give quick responses. Such receptors include GPCRs and tyrosine kinase receptors.
Peters said that another difference between Acea’s cell electronic sensing system and CellKey is cost. CellKey costs approximately $300,000 and Acea’s system costs about $50,000.
Proof of Concept
AstraZeneca isn’t the only pharma to test drive CellKey. Ralph Garippa, a research leader in Roche Discovery Technologies’ cell-based HTS and robotics group, said his company performed a series of collaborative proof-of-concept experiments with MDS several years ago.
Garippa said that those experiments were designed around a known receptor. Roche supplied MDS with a number of small molecules and peptides that were agonists and antagonists, but did not tell the company what the effect was going to be, he said. Roche also gave MDS a cell line, and MDS ran the assay and plated it.
“When MDS got back to us, it had been perfectly able to predict what the activity of those compounds was,” Garippa said. “MDS also gave us a very good indication of what the coupling of the receptor was.”
Garippa added that Roche looked at the system because it was interested in orphan GPCRs. “With orphan receptors, one does not have a cognate ligand with which to stimulate the system, and because of that you are really unsure of what GPCR pathway might be triggered by having a ligand,” he said.
With one assay, CellKey will provide readout information as to whether the receptor coupling is through calcium flux, an increase in cAMP, or a decrease in cAMP, said Garippa. Other available assays can measure those individual components, but cannot provide an all-in-one assay readout, he said.
Garippa said that Roche has not yet purchased a CellKey, but is looking into getting one if MDS comes out with a higher throughput version with 384-well plates. The current version features 96-well plates.
He thinks the higher throughput system will come out in a year or two.

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