Identification of Selective Inhibitors of The Epithelial Sodium Channel ?.

Victoria Miller, a PhD student from the Drug Discovery Centre at the University of Sussex recently spent a few months working in the ApconiX ion channel laboratory as a part of her research. Her PhD project titled “Identification of Potent and Selective Inhibitors of the Epithelial Sodium Channel ?”, was supervised by Professors Martin Gosling and John Atack. Dr. Michael Morton of ApconiX was the external examiner of Victoria’s viva alongside the internal examiner Dr Ruth Murrell-Lagnado, the Acting Director of Sussex Drug Discovery Centre.

The epithelial sodium channel (ENaC) made up of the α, β and γ subunits, has been prominently studied and is well characterized in several epithelial tissues. However, the physiological relevance of the ENaC channel ? (made up of the ?, β and γ subunits), is less well understood due at least in part to the lack of selective tool compounds. The ENaC family of channels have been implicated in the neurodegeneration associated with a number of central nervous system (CNS) disease states.

Victoria’s research project followed the classic early drug discovery cascade. A baculoviral system was used to express ENaC d, b, g.

A membrane potential fluorescence assay was used to screen a library of biologically active compounds and hits were confirmed by conventional patch clamp. Only one compound showed activity against ENaC ? channel but showed no selectivity versus the epithelial channel.

Victoria came to ApconiX to repeat the primary screen by automated electrophysiology which is a direct functional measurement of ion channel activity and less prone to artefacts. Two libraries making up 9321 compounds were screened against ENaC ? on the IonWorks Quattro platform. Less hits were identified than the membrane potential assay, but many more hits were confirmed by subsequent electrophysiology. Chemical structure analysis revealed that that Victoria has characterized a novel group of compounds, not similar to amiloride, that are selective inhibitors of the ENaC ? channel.

Victoria’s project emphasizes the importance of high-throughput automated electrophysiology in drug discovery to eliminate false positives resulting in waste of time and resources. When working with ion channels the gold standard is electrophysiology, however the highly skilled and labour-intensive nature of manual patch clamp means it is not feasible to use early in the discovery process. Automated high throughput electrophysiology is accessible and cost effective and invaluable when studying ion channels as drug targets.

Congratulations to Dr Victoria Miller for successfully passing her viva! Good luck for your future career in patent law, from everyone at ApconiX!