The field of drug discovery is rapidly evolving, with new technologies emerging to streamline processes and enhance safety evaluations. One such breakthrough is the development of a non-invasive method combining electrical impedance tomography (EIT) with extracellular voltage activation (EVA). This innovative approach, pioneered by researchers at Chiba University, offers a cost-effective and accurate alternative for evaluating how drugs affect ion channels, particularly those related to cardiac function. This advancement not only simplifies the drug screening process but also plays a crucial role in understanding drug safety and potential cardiac risks.
Understanding Ion Channels and Their Importance in Drug Screening
Ion channels are vital proteins in cell membranes that regulate the flow of ions across the membrane, influencing various physiological processes. In particular, the human ether-a-go-go-related gene (hERG) ion channel, found in neurons and heart muscle cells, is critical for maintaining normal heart rhythms. Any disruption to hERG channel function can lead to severe cardiac conditions, including a potentially fatal arrhythmia known as torsade de pointes. Therefore, assessing how new drugs interact with these channels is a key component of drug safety evaluations.
Traditionally, techniques like the patch-clamp method and fluorescence microscopy have been used to measure ion channel activity. While effective, these methods are invasive, often altering cell properties and requiring specialized equipment and expertise. This complexity can increase costs and prolong the drug development timeline, making the search for more efficient methods a priority.
The Innovation: Combining Electrical Impedance Tomography with Extracellular Voltage Activation
To address these challenges, Assistant Professor Daisuke Kawashima and his team at Chiba University have developed a novel, non-invasive method for real-time evaluation of drug effects on hERG channels. Their approach integrates electrical impedance tomography (EIT) with extracellular voltage activation (EVA) within a printed circuit board (PCB) sensor. This method offers a promising alternative to traditional techniques, providing a faster, more cost-effective solution for drug screening.
Electrical Impedance Tomography (EIT): EIT is a technique that measures the impedance, or resistance, of a material by applying small electrical currents and monitoring the resulting voltage. In the context of drug screening, EIT can detect changes in ion flow across cell membranes, offering spatial information about extracellular ion distribution.
Extracellular Voltage Activation (EVA): EVA involves applying controlled voltages to the extracellular environment surrounding the cells, which can activate ion channels by altering the membrane potential. This activation allows researchers to observe how ion channels respond to different drugs in real time.
By combining these two techniques, the researchers created a sensor that can non-invasively monitor changes in ion flow through hERG channels when exposed to various drugs. This integrated EIT-EVA method allows for the continuous assessment of drug effects, providing a real-time understanding of how a drug interacts with ion channels.
How the EIT-EVA PCB Sensor Works
The EIT-EVA PCB sensor developed by the research team is made from a non-conductive epoxy glass fiber and measures 100 mm × 70 mm × 1.6 mm. It features 16 electrodes arranged around a central activation electrode, which plays a crucial role in the EVA process. Here’s how the system works:
- Cell Placement: Cells under investigation, typically genetically modified to express hERG channels, are placed on the sensor.
- Voltage Application: A step voltage is applied to the activation electrode, altering the potential distribution in the extracellular medium surrounding the cells. This change affects the cell membrane potential, leading to the activation of voltage-gated ion channels like hERG.
- Ion Flow Monitoring: As the hERG channels open, potassium ions move out of the cells, causing changes in extracellular resistance. These changes are measured by the EIT system, which provides real-time data on how the drug affects ion flow.
- Inhibition Assessment: The system calculates an inhibitory ratio (IR) by analyzing how quickly extracellular ion concentrations change over time. This index indicates the degree to which the drug inhibits hERG channel activity.
Case Study: Evaluating the Antiarrhythmic Drug E-4031
To validate their method, the researchers conducted experiments using the antiarrhythmic drug E-4031, which is known to block hERG channels. The study involved exposing genetically modified HEK 293 cells, expressing hERG channels, to varying concentrations of E-4031 (ranging from 0 nM to 100 nM).
Procedure:
- Baseline Measurement: The researchers conducted baseline EIT measurements for 20 seconds to establish the normal ion movement in the absence of the drug.
- Drug Exposure: The cells were then exposed to E-4031, and the researchers alternated between 20-second cycles of EVA activation and EIT measurements to observe changes in ion flow.
Results:
- When the hERG channels were activated by EVA, the extracellular resistance decreased, indicating an increase in potassium ion concentration outside the cells.
- However, as the concentration of E-4031 increased, the rate of potassium ion flow decreased, indicating that the drug was effectively blocking the hERG channels.
From the data, the researchers calculated the half-maximal inhibitory concentration (IC50) of E-4031, which was determined to be 2.7 nM. This result closely aligned with values obtained from traditional patch-clamp techniques, demonstrating the accuracy of the EIT-EVA method.
Advantages of the EIT-EVA Method in Drug Screening
The EIT-EVA method offers several key advantages over traditional techniques:
- Non-Invasive: Unlike patch-clamp methods, the EIT-EVA approach does not require direct contact with the cell membrane, preserving the natural state of the cells and reducing the risk of measurement artifacts.
- Cost-Effective: The use of a PCB sensor simplifies the setup, reducing the need for specialized equipment and lowering overall costs associated with drug screening.
- Real-Time Monitoring: The ability to monitor ion flow in real time allows for a more dynamic understanding of how drugs interact with ion channels, enabling quicker decision-making in the drug development process.
- Efficiency: The method’s fast response time and ease of use make it ideal for high-throughput screening, potentially shortening the preclinical testing phase and accelerating the drug discovery process.
The Future of Drug Safety and Cardiac Risk Assessment
The development of the EIT-EVA method represents a significant step forward in the field of drug discovery, particularly in the assessment of cardiac safety. By providing a non-invasive, cost-effective, and accurate tool for evaluating drug effects on ion channels, this technology has the potential to revolutionize preclinical testing and improve the efficiency of drug development.
As the pharmaceutical industry continues to seek faster and more reliable ways to bring new drugs to market, innovations like the EIT-EVA method will play a crucial role in ensuring that these drugs are both effective and safe. The ability to assess cardiac risks early in the development process could lead to safer medications and ultimately, better outcomes for patients.
