Abstract

   Developing safe and effective new drugs is a difficult and
expensive process that can take 10 years and cost $1-$2 billion. Implicit in
these calculations are the cost of failed drug candidates, which in industry
surveys over the last two decades are attributed to lack of efficacy (~50%) followed
by safety issues (~30%). Cardiac toxicity and neurological side-effects are the
leading causes of new drug attrition (Valentin & Redfern, 2017), and in
many cases such toxicity involves voltage- and ligand-gated ion channels (e.g.
hERG, GABA). Drug attrition occurs in all phases of drug development, and the
later it occurs the greater the cost. The current challenge in our industry is
therefore to improve the performance of early stage safety assays to filter out
risky compounds earlier in the drug discovery process. The FDA and other drug
regulatory agencies have recognised this need and devised new initiatives such
as the Comprehensive in vitro Pro-arrhythmia assay (CiPA) and NeuTox working groups that look to move the focus away from ex vivo and in vivo
animal testing towards in vitro
assays using heterologous cells, native tissue and human induced pluripotent
stem cells (iPSC). Whereas industry publications indicate moderate predictivity
of traditional animal models (e.g. 60-70% for cardiac safety screening), these new
humanised in vitro approaches can
predict clinical risk with 75-90% accuracy.
   We present an overview of new in vitro CiPA cardiac safety and NeuTox neurotoxicity assays we
have developed and validated that achieve excellent reproduction and prediction
of human clinical side-effects. The CiPA assays are divided into three pillars:
 1. Pillar 1 comprises a core (hERG,
Nav1.5, Cav1.2) and extended panel (KvLQT1, Kv4.3, Kir2.1) of high quality human
cardiac ion channel electrophysiology assays, as well as dynamic hERG and LQT3
mutant late Nav1.5 assays run on QPatch. 2. Pillar 2 involves use of this high
quality in vitro data in the FDA’s
official in silico models of cardiac
action potentials and arrhythmia risk. 3. Pillar 3 tests the predictions from
these assays in human iPSC cardiomyocytes, using patch clamp, multi-electrode
array (MEA) and impedance electrophysiology platforms. Metrion validated all CiPA
assays using the core and Phase 1 reference compound toolbox. For NeuTox we validated
the current industry-standard rat cortical neuron seizure excitability assay on
the Axion Maestro MEA platform using a reference panel of compounds with known
ion channel and receptor activities and seizure risk. Further work will extend
this assay to include human iPSC neurons.
   Our cardiac safety and neurotoxicity cell-based assays
accurately predict known clinical risk of reference compounds, and deliver high
quality data required of a preclinical CRO drug discovery service provider.