Scientists at Sophion Bioscience and Johnson & Johnson Pharmaceutical Research and Development have published what could be among the first papers to present data from many different assays run on Sophion's QPatch system.
According to the paper, published this month in Combinatorial Chemistry and High-Throughput Screening, the researchers observed a 10-fold increase in throughput using the QPatch compared to conventional patch clamp done using the same cells, while maintaining a comparable success rate of gigaseals, formation of the whole-cell configuration, and usable cells.
J&J co-authors Michael Finley and Yi Liu declined to comment for this article.
Automated patch clamp for drug discovery research has been around since about 2002, with the launch of the IonWorks HT system from Molecular Devices (now a part of MDS).
As an automated patch clamp system, the QPatch has several advantages over conventional patch clamp, according to Chris Mathes, vice president and general manager for Sophion Bioscience in North America.
Before automated patch clamp technology was available, it took a highly trained PhD-level scientist to measure the electrical currents in the ion channels of a cell, one cell at a time. "It was very low throughput," Mathes said.
With automated machines like the QPatch, a technician, rather than a PhD-level scientist, can measure electrical currents in as many as 16 or 48 cells at a time.
So, automated patch clamp is "four to 10 times faster than conventional patch clamp," Mathes said. It is also about four to 10 times less expensive than conventional patch clamp, depending on the assay.
"We are also talking about time savings," said Mathes. The actual cost, if one considers the supplies, is more expensive than conventional patch clamp, he said. The average cost of conventional patch clamp is $1 per cell, and automated patch clamp like the QPatch costs about $5 to $10 per cell.
However, Mathes said, "Drug companies are willing to spend that, because it speeds up the drug-discovery process so much. They are also saving on the employee cost, so it ends up saving them money overall."
The QPatch can screen hundreds of compounds per day, compared to the usual definition of high throughput, which is perhaps, thousands of compounds per day, said Mathes. Thus, QPatch is more of a secondary screen. "This is why the paper is called 'The Missing Link between HTS and Ion-Channel Discovery,'" he said.
Drug-discovery companies have been using true high-throughput screening, and after that, there was no technique to do secondary screening, so they would have perhaps 5,000 compounds after a primary screening campaign, Mathes said.
"However, they could not test those further with a PhD scientist doing one cell at a time," he said. "But now, with technology like the QPatch, they can do that."
Otherwise, automated patch clamp data have the same quality as conventional patch clamp data. "One thing that the pharmaceutical industry has struggled with is that they have been using indirect methods, such as fluorescent methods, to evaluate ion channel function, and they have been getting a lot of false negatives and false positives," said Mathes.
He went on to say that patch clamp is the only direct way to measure ion channel function, "so it is important for a machine like the QPatch to have the same high quality as conventional patch clamp."
The QPatch system has been on the market since 2004. It takes cells that are in suspension, and it squirts them into a very small chamber, said Mathes. The cells go through a microfluidic tunnel, and a single cell is pulled through a hole that is about 2 µm in diameter, and a piece of the cell membrane is ruptured.
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Under the hole is a salt solution that mimics the intracellular solution in the cell. Above the hole, on the outside of the cell, is a salt solution that mimics the external environment. Once the whole-cell configuration is achieved, because of where the electrodes are placed, "we have electrical control of each of the cells," Mathes said.
The cells that are used on the QPatch are typically cells that are genetically engineered to have an ion channel protein of interest. "You can change the voltage to open or close that ion channel protein, and watch the currents flowing through," Mathes said.
In that way, investigators can obtain a baseline measurement. The machine robotically pipettes the compound of interest onto the cell, enabling scientists to see if it has an effect.
"The exciting thing about [automated patch clamp] is that it has opened up the door for ion-channel drug discovery," said Mathes. He added that until the early part of this decade, drug companies really shied away from ion channels as targets, even though they are important targets, because as proteins, they sit in the plasma membrane of cells. Ion channels have pieces that are on the outside of the cells, "perfectly situated to be affected by drugs/small molecules," said Mathes.
"In the next 10 years or so, we should start to see drugs that hit the market based on these kinds of technology, and hopefully it won't be too late for the pharma industry, which is really struggling right now," Mathes said.
Another important element is safety testing. Since the late 1990s, because of some problems with drugs that hit the market, particularly antihistamines, the FDA has strongly recommended that any drug that goes to market needs to be tested using patch clamp.
"Now with technology like the QPatch, a drug company can start doing safety testing earlier on in the drug-discovery process," Mathes said. Instead of waiting to see if they have a candidate in clinical trials, pharma companies can start doing safety testing earlier on.
The 48-well QPatch can screen from several hundred up to 3,000 compounds per day. The next step is to develop a truly high-throughput automated patch clamp system, "something that can do 10,000 to 20,000 compounds per day," Mathes said. That will allow automated patch clamp to be done in the primary screening step instead of just the secondary screening step, and will improve the quality of the R&D process.
Right now, pharma companies are still using binding assays or fluorescence assays in the primary screening step, and "they are probably missing some things," said Mathes. He added that if they had used automated patch clamp in that primary screening step, then "they would have had higher quality drug candidates going forward."
When asked about a timeline for developing such a high-throughput patch clamp machine, Mathes replied, "It is not this year for sure. The main thing is cost, because we are competing against primary screening assays that cost about 20 cents per data point, so we need to get [the cost per data point of automated patch clamp] down into the range for drug companies to be able to afford it." Sophion is currently focused on reducing the cost of the electrode array down to where it could be used for primary screening.
"We could make a machine right now with existing technology, but it would be too expensive to use to screen millions of compounds," Mathes explained.
In the meantime, Sophion is bolstering its international footprint and workforce. Mathes said that Sophion has hired a scientist in Japan to head up its branch office there, and although it is not Sophion's first foray into the Asian automated patch clamp market, it is "a big step" for the company.
"We have systems in China and a distributor in China. We have a distributor in India, and are trying to break into that developing market," said Mathes.
He added that all told, Sophion, which employees about 40 people worldwide, will probably hire about five people this year.