Eliana is a two-year-old from Canada with a de novo mutation (V434L) in her KCNC1 gene which encodes for the Kv3.1 channel in central nervous system neurons such as cerebellar neurons and GABAergic interneurons. The mutation manifests as a variety of neurological disorders which can include myoclonic epilepsy and ataxia due to K+ channel mutation, developmental epileptic encephalopathy (DEE), or hypotonia, depending on the specific variant. Although Eliana does not exhibit typical DEE, she suffers from hypotonia, cortical-visual impairment, vertical nystagmus, and global delays.

The endo-lysosomal system is a series of intracellular organelles responsible for recycling and degradation of macromolecules. Endo-lysosomes express several functionally diverse ion channels, crucial for regulating organelle trafficking and intracellular signalling as well as maintaining the acidic luminal pH for optimal enzymatic activity. Dysfunctions within the endo-lysosomal system are associated with multiple disorders including lysosomal storage disorders and neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. Lysosomal ion channels have therefore gained significant attention as potential targets for novel therapeutics.

Domainex and Metrion Biosciences have formed an alliance to identify new chemical hits against ion-channel targets. Key to this collaboration are Domainex’s experience in hit identification and Metrion Bioscience’s expertise in ion channel screening and pharmacology.

Cardiac toxicity remains the leading cause of new drug safety side-effects. Current preclinical cardiac safety assays rely on in vitro cell-based ion channel assays and ex vivo and in vivo animal models⁽¹⁾. These assays provide an indication of acute risk but they do not always predict the effect of chronic compound exposure, as recently seen with oncology drugs. Therefore, new assays are required to characterise chronic structural and functional effects in human cells earlier in drug discovery. Impedance-based technology can provide more accurate chronic cardiotoxicity measurements in an efficient manner using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs).

Ion channels represent 15 – 20% of historic drug approvals and recent drug discovery projects. Many ion channel families (Nav, Cav, TRPx and GABA) are validated as therapeutic targets based on human genetics, animal models and selective pharmacology. However, ion channels are challenging targets requiring specialist target class knowledge and screening technology such as automated patch clamp (APC) electrophysiology.

Ion channels play a key role in regulating resting membrane potential and cell excitability and are attractive targets for therapeutic intervention.
Thallium (Tl+) flux assays, which measure the flow of Tl+ through potassium channels, offer a high throughput method for the identification of potassium channel activators. However, these assays are a surrogate for channel function and it is important to have an appropriate panel of orthogonal and translational electrophysiology assays in place to confirm activity at the channel of interest.

The FDA’s Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative is designed to remove the over-reliance on hERG data to predict human clinical cardiac risk⁽¹⁾, with recent results suggesting that inclusion of additional cardiac ion channels and assays (e.g. peak and late Nav1.5, Cav1.2, dynamic hERG⁽²⁾) improve risk predictions of in silico action potential models⁽¹⁾. The CiPA working groups currently use a mixture of manual and automated patch clamp (APC) platform data, but future CiPA drug screening will likely rely on APC data.

New cardiac safety testing guidelines are being finalised, as part of the FDA’s Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative, which aim to remove the over-reliance on screening against the hERG channel by expanding the panel to include hNav1.5, hCav1.2, hKv4.3/KChiP2.2, hKir2.1 and hKv7.1/KCNE1 human cardiac ion channels. In addition, the CiPA working groups have recently identified two additional in vitro assays required for in silico models to reliably predict proarrhythmia. The first is a ‘late’ sodium current assay, as inhibition of persistent inward current can affect repolarisation and mitigate proarrhythmia (e.g. ranolazine). The second assay quantifies the degree of drug trapping in the hERG channel using the Milnes voltage protocol⁽¹⁾, which can improve the prediction of proarrhythmic risk⁽²⁾.