Wolfgang Lerch, CEO of Iongate Biosciences, reports on an exciting technological development, in use for just over a year, which accesses the transporters using cell-free electrophysiology.

All biological processes depend on the specific interaction of molecules with carefully adjusted affinities. Transporters are a particularly important class of molecules. These are electrogenic membrane proteins, which play a fundamental role in the regulation of cell activities.

All cells are compartmentalised to allow a strictly controlled metabolism. These compartments are formed through lipid bilayers that are impermeable to most ions and solutes. Specific membrane proteins transport solutes that are important for maintaining the cell metabolism, and thus function as ‘gatekeepers’ for the cell.

The transporters are responsible for the generation and maintenance of ion gradients, the transport of metabolites, the uptake of vitamins and nutrients, the re-uptake of signalling molecules, and the disposal of toxic and waste compounds. In many cases drug pharmacokinetics are influenced by transporters, too. On this account transporters are emerging targets of increasing importance to the pharmaceutical industry.

Turnover rate

Transporters have significant physiological relevance to a wide range of numerous indicators, including for cardiovascular, metabolic, inflammatory diseases and CNS disorders such as epilepsy and depression. Even so, transporters are highly valuable targets; no high throughput-capable assays for this class of membrane proteins have been available to date. The main difficulty is in detecting the low turnover rate of ion transporters of about 1-1000 molecules per second, about 104 times less than most ion channels.

Traditional transporter assay technologies such as radioactive assays, fluorescence-based assays and manual or semi-manual patch clamping suffer from a lack of sensitivity and robustness and are time-consuming and costly. These methods have always rendered high-throughput screening impossible or impractical.

Surface electrogenics

A new technology evades these disadvantages, however, by using cell-free electrophysiology, which is now made possible with the Surface Electrogenic Event Reader (SURFE2R) technology platform. Most transporters shift electrical charges while going through their transport cycle, and this charge displacement is the basic principle for the new technology platform. The method mainly focuses on transporter-containing membrane fragments or vesicles, mechanically and electrically coupled to a gold-coated biochip.

The membrane fragments adsorb to the surface, which carries a modified lipid layer, and form cavities that are able to maintain ion gradients across the membranes. The system, characterised by a high robustness, allows fast buffer changes. By rapidly changing from solutions containing no substrates for the transporter to solutions containing a substrate, the transporter can be activated and a transient current can be measured. Because many transporters are measured in parallel, the signal-to-noise ratio is optimised. While this technique is interesting for the investigation of basic research, it also contains the potential for industrial high-throughput applications as well.

Faster research

A 96-sensor array plate is the central part of a fully automated platform technology called SURFE2R Workstation. The new automated technique results in a throughput up to 100 times higher than before, as roughly 500 measurements can be carried out per day. This new development in automated cell and label-free transporter research clears the way for a cheaper and easily accessible tool to achieve the desired results in drug discovery and development. This solution meets the commercial needs of the pharmaceutical industry and in contrast to manual patch clamping, can easily be integrated in a standard screening laboratory. Using this technique will enable biotechnology and pharmaceutical companies to perform efficient drug discovery in the highly interesting but hitherto idle area of transporters.

Just one year after the initial development of the SURFE2R Workstation, pharmaceutical companies working with the pre-production model are very excited. This is rooted in the robustness of the system, the high data quality gained from the experiments and the fast access to long-needed information about transporters with a slow turnover rate.