Recently, scientists at Chiba University introduced a new non-invasive technique that merges electrical impedance tomography (EIT) and extracellular voltage activation (EVA) to assess how drugs influence ion channels. This innovative printed circuit board (PCB) sensor enables real-time observation of how cutting-edge medications impact ion flow in channels, offering a more cost-effective and precise alternative to conventional approaches like patch-clamp techniques. This advancement could streamline and shorten preclinical evaluations in the drug development pipeline.
Recently, scientists at Chiba University introduced a new non-invasive technique that merges electrical impedance tomography (EIT) and extracellular voltage activation (EVA) to assess how drugs influence ion channels. This innovative printed circuit board (PCB) sensor enables real-time observation of how cutting-edge medications impact ion flow in channels, offering a more cost-effective and precise alternative to conventional approaches like patch-clamp techniques. This advancement could streamline and shorten preclinical evaluations in the drug development pipeline.
In the process of creating new drugs, it is crucial to comprehend their effects on ion channels within the body, such as the human ether-a-go-go-related gene (hERG) ion channel found in neurons and heart muscle. Blocking hERG channels can interfere with the heart’s normal rhythm, potentially leading to a life-threatening condition known as torsades de pointes. Traditional methods used to evaluate these effects often involve invasive procedures like patch-clamp techniques or fluorescence microscopy. These techniques can inadvertently alter cell characteristics and may skew measurement accuracy, necessitating specialized equipment and expertise, which raises costs and complexity.
To overcome these issues, a team led by Daisuke Kawashima, an Assistant Professor at Chiba University’s Graduate School of Engineering, has introduced an innovative, non-invasive method for real-time assessment of drug impacts on hERG channels. They have developed a PCB sensor that integrates EIT with EVA. EIT detects changes in impedance due to ion movement, providing spatial details about the extracellular distribution of ions. EVA entails applying controlled voltages to the extracellular environment to initiate changes in ion channel activity. This combined method enables scientists to non-invasively stimulate hERG channels and track real-time alterations in ion flow caused by drug exposure.
The findings were published in the journal Lab on A Chip on May 23, 2024, with contributions from Assistant Professor Songshi Li and Professor Masahiro Takei from the Graduate School of Engineering, Chiba University, along with Associate Professor Satoshi Ogasawara and Professor Takeshi Murata from the Graduate School of Science, Chiba University.
Dr. Kawashima remarked, “This imaging technique is anticipated to establish a new platform for measurement and evaluation in medical and drug discovery.”
The EIT-EVA PCB sensor measures 100 mm × 70 mm × 1.6 mm, constructed from non-conductive epoxy glass fiber (FR-4 TG130) and equipped with 16 electrodes for EIT, arranged around a central electrode that facilitates EVA activation. Here’s the operation process: Cells being examined for their drug response are placed on the sensor. A step voltage is applied to the activation electrode, altering the potential distribution in the surrounding extracellular medium. This adjustment impacts the cell membrane potential, activating voltage-gated ion channels such as the hERG channels. When these channels are opened, potassium ions exit the cells, resulting in measurable changes to extracellular resistance via the EIT system.
The drug’s impact on the ion channels is monitored by observing variations in extracellular conductivity. If the hERG channels remain unobstructed by the drug, potassium ion concentration outside the cells will quickly rise. Conversely, if the drug obstructs the channels, this increase is significantly slowed. The system derives an inhibitory ratio index (IR) that quantifies the rate of extracellular ion concentration changes over time, revealing the extent of the drug’s inhibitory effects on the hERG channels.
To validate their approach, the researchers exposed genetically modified HEK 293 cell suspensions, which express hERG channels, to varying concentrations of the antiarrhythmic drug E-4031 (0 nM, 1 nM, 3 nM, 10 nM, 30 nM, and 100 nM). After preparing the drug-cell mix on the sensor with a micropipette, they conducted baseline EIT measurements over a 20-second period to establish a reference for ion movement. Next, they alternated between 20-second cycles of EVA activation and EIT measurements.
Upon activation of the hERG channels through EVA, extracellular resistance lowered in comparison to the established baseline (due to a rise in potassium ion concentration). However, as the concentration of E-4031 increased and began to inhibit the hERG channels, the transportation of potassium ions from inside to outside the cells decreased, slowing the decline in extracellular resistance.
From the resulting IR response curve, the researchers determined that the half-maximal inhibitory concentration—the amount of drug needed to diminish hERG channel function by 50%—was 2.7 nM. This measurement demonstrated a strong correlation (R2 = 0.85) with results obtained from the conventional patch-clamp approach, indicating significant agreement between both methods. Compared to traditional practices in hERG channel evaluation, this proposed technique is non-invasive, offers a rapid response time, and doesn’t require specialized training. Dr. Kawashima concluded, “This can lead to more efficient and shorter preclinical testing in the drug discovery process.”
