GE Healthcare and MDS Pharma Services this week announced the availability of a new micronucleus assay protocol for GE Healthcare's IN Cell 1000 and 3000 high-content screening platforms that is expected to more accurately predict genotoxicity in early-stage drug discovery.
The assay will be available as part of MDS Pharma's contract pharmaceutical research offerings and is a key component of its growing portfolio of early-stage, cell-based assays for assessing the potential toxicity of drug candidates.
Meanwhile, for GE Healthcare, the new assay could stimulate sales for its IN Cell platforms both indirectly and directly through possible additional instrument purchases by MDS Pharma.
The formation of micronuclei in cells is an indicator of genetic toxicity, and is used by the pharmaceutical industry to identify potentially genotoxic drug candidates early in the development process. Advances in high-content imaging and laser-scanning cytometry have made high-throughput, automated assessment of micronuclei formation possible.
"We realized that there were bugs in their software, and that it wasn't working the way it should have been."
GE officially launched a micronucleus formation software application module for its IN Cell Analyzer 1000 and 3000 platforms in November 2005 (see CBA News, 11/21/2005). Around the same time that GE was developing the new module, MDS Pharma was looking to expand its high-content screening capabilities and chose to go with an IN Cell 1000 "because it best met our needs," David Kirk, director of cell biology for MDS Pharma, told CBA News this week.
At the time, MDS Pharma was also seeking to build up its cell-based toxicity profiling portfolio, and GE Healthcare was looking for customers to validate the micronucleus assay. The collaboration was a "perfect fit," Kirk said, and MDS Pharma became a beta-tester for the new software module.
While MDS Pharma found the application to be "much faster than similar assays on the market" due to the IN Cell's fast laser auto-focus feature, Kirk said the new module had some kinks that needed to be worked out in terms of sensitivity, and MDS Pharma drew on its in-house assay-development expertise to make improvements in this area.
"GE made the IN Cell analyzer and micronuclei analysis routine commercially available to … MDS," Ger Brophy, general manager of GE Healthcare Discovery Sciences wrote in an e-mail to CBA News. "We then worked with them to establish the MDS assay offering for the assessment of compound genotoxicity, which MDS are now rolling out to their customers.
"This is a great example of how we are supporting our IN Cell customers by collaboratively developing assay technology for emerging applications," Brophy added. "The value to GE customers is the continued commitment to working with them to develop new applications, and the knowledge that the IN Cell technology suite can be applied successfully to demanding drug discovery programs."
"[GE] provided the hardware and software, of course, and gave us a very rudimentary protocol for the micronucleus assay that they had worked up, and we improved on that significantly," MDS' Kirk said. "We realized that there were bugs in their software, and that it wasn't working the way it should have been.
"We put that together with experimental variables that we put in to increase the sensitivity of the assay, and we have come up with an assay that I'm convinced is the best on the market, at this point, in terms of sensitivity and speed," he added.
Specifically, other commercial micronucleus detection assays use a compound called cytochalasin B to inhibit microfilament assembly, cytokinesis, and splitting into daughter cells, which results in binucleate cells. But this compound also causes background noise, and is not necessary in all cell lines, in particular the ones MDS Pharma uses in its assays.
"OECD Guidelines require [the use] of cytochalasin B for primary human lymphocytes, but it is not mandatory to use CB when using other lines that they recommend," Kirk elaborated in a later email to CBA News. "Micronuclei are only formed during mitosis; therefore, it is critical that micronuclei are scored only in proliferating cells. In lymphocytes, the micronuclei are scored only in binucleate cells to ensure evaluation in proliferating cells. Lymphocytes have a low growth fraction and only CB-generated binucleates are scored to guarantee that the cell was proliferating.
"However, the use of CB has carried over to assays using the continuous cell lines," Kirk added. "We find this to be unnecessary in our assay since CB itself causes a low level of micronuclei formation. CHO cells have a high growth fraction and so CB is unnecessary to ensure cells are proliferating. Under conditions of rapid growth … miconuclei are scored in all cells. Without CB, our background micronuclei formation is lower. Hence, the assay is more sensitive."
Kirk stressed that the company does run protocols both ways for clients "because some people are locked into using cytochalasin B."
"We have come up with an assay that I'm convinced is the best on the market, at this point, in terms of sensitivity and speed."
In addition, Kirk said, genotoxicity assays depend very heavily upon monitoring growth inhibition of cells "because you usually have to subject the cells to fairly high concentrations of toxicity without killing them. We actually concurrently measure growth inhibition … so we can look at the micronucleus development as a specific percentage of growth inhibition."
Focusing on Toxicity
The micronucleus assay is a key component in MDS Pharma's portfolio for assessing cell-based toxicity, which the company has been looking to build out over the past year.
"One of the biggest problems in drug discovery right now is toxicity," Krik said. "Two or three years ago there was a pharmacokinetics or ADME problem, where people were trying to anticipate ADME before they actually got to the animal-testing stage. But the next big bottleneck is toxicity; we need to [assess] toxicity in early discovery," Kirk said.
MDS Pharma recently adopted a cell-based functional hERG assay using Molecular Devices' PatchXpress platform to assess cardiac liabilities. In addition, MDS Pharma's ADME group has increased its use of hepatocyte-based assays to assess liver toxicity.
"So this genotoxicity assay fit in beautifully, and sort of fills the gap for us, and broadens out our portfolio," Kirk said.
Furthermore, MDS Pharma specifically targeted high-content screening as a way to beef up its functional cell-based assay capabilities, which the company was "a little bit thin on," Kirk said.
"Cell-based assays provide higher quality leads than ligand-binding assays do," he added. "That's pretty much accepted in the industry now, and every large pharma has got a high-content system working. So we're trying to take all of our ligand-binding assays and get parallel functional cell-based assays."
Other recent examples of cell-based assays adopted by MDS Pharma include its line of PathTrak assays, which are based on BioSource's phosphoELISA detection methodology, and used to measure changes in phospho-protein levels resulting from kinase inhibition in signaling pathways; and a panel of multiplexed cytokine profiling assays based on human peripheral blood mononuclear cells.
In addition, MDS Pharma has tapped internal resources, adopting sister company MDS Sciex's recently launched CellKey system, which uses a non-imaging, label-free technique known as cellular dielectric spectroscopy to measure, among other things, GPCR activation in live cells (see CBA News, 8/15/2005).
And the company may not be done working with GE Healthcare. According to Kirk, MDS Pharma has got one IN Cell 1000 in house, and is "currently negotiating with [GE] to buy a second instrument because the demand is so high, and [because] you always need backup.
"We find that we're using it all the time … and the work is actually out there to keep two systems busy at this point," he added.
Ben Butkus ([email protected])