Rapidly activating and desensitising ligand-gated ion channel receptors can provide a technical challenge on automated patch clamp electrophysiology platforms. This can affect their biophysics, pharmacology and assay reliability. We present data on an optimised and validated acid-activated receptor assay on the QPatch that is stable enough for drug discovery screening.
As an alternative to standard pharmacological procedures for NaV1.5(Late) assays, we present a more reliable and accurate NaV1.5(Late) assay on QPatch that removes the requirement for activators like veratridine and ATX-II and delivers improved cardiac safety screening reliability and cost.
There is growing interest in automated patch-clamp (APC) assays for ligand-gated targets which are expressed throughout the peripheral and central nervous system. The Acid-Sensing Ion Channel (ASIC) family comprises combinations of ASIC1-4 proteins that form acid-activated cation-selective channels.
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.
The cardiac late Na+ current (late INa) generates persistent inward currents throughout the plateau phase of the ventricular action potential and is an important determinant of repolarisation rate, EADs and arrythmia risk¹. As inhibition of late INa can offset drug effects on hERG and other repolarising K⁺conductances, it is one of the key cardiac channels in the Comprehensive in vitro Pro-arrythmia Assay (CiPA) panel being developed by the FDA to improve human clinical arrythmia risk assessment²̛ ³.
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.
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 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.
Acid-sensing ion channels (ASICs) are proton-gated ion channels which are highly sensitive to extracellular acidosis and are permeable to cations1, predominantly Na+. To date, six different ASIC subunits (1a, 1b, 2a, 2b, 3 and 4) encoded by four genes have been identified.