Implementing Thorough Safety Package Assays into your Workflow
ChanTest’s Thorough Preclinical Safety Package (TSP) was designed as a comprehensive preclinical cardiac safety assessment for full resolution of potential cardiac risk. This page summarizes our recommendations for adopting elements of the TSP into your drug discovery workflow to:
- most effectively move promising compounds through your pipeline
- save time, labor and costs by eliminating high risk compounds early
- provide comprehensive cardiac characterization for scientific and regulatory discussions
Rationale: at this stage, hits are further characterized in secondary screening/profiling assays to look for specificity and off-target effects. Inexpensive automated patch clamp screening of three key cardiac ion channels at this stage will help identify candidates with a strong degree of cardiac risk to either remove from consideration or to send back to chemistry for further development.
In contrast to selective hERG inhibitors, selective Nav1.5 or Cav1.2 blockers are not necessarily a safety risk. Use-dependent blockers (i.e. "phasic blockers"), for example, are effective treatments for pain, arrhythmia, seizure, and hypertension. However, strong blockade of resting Nav1.5 channels (i.e. "tonic block") could cause conduction delays and re-entrant arrhythmia. Our screen provides a qualitative indication of the strength of tonic vs. phasic blockade, but does not thoroughly characterize use-dependence.
Secondary screen hits against Nav1.5 or Cav1.2 should progress and be further characterized in Lead Optimization.
Inclusion of the hERG-Lite® assay is an inexpensive way to identify hERG trafficking inhibitors that are not detected in patch clamp assays.
Rationale: at this stage, compound IC50 values are required to quantify relative potency for the most critical cardiac channels (i.e. profile compounds according to rank order) in an iterative fashion. This is done to identify compounds with low hERG potency but that affect other critical channels that can influence the QT interval.
Compounds that clear this hurdle should be tested in an Action Potential Duration (APD) Assay to confirm the physiological relevance of ion channel results. We recommend stem-cell-derived human cardiomyocytes for APD testing because of their greater pharmacological sensitivity compared to animal tissue, lower cost and faster throughput. This assay is an excellent predictor of probable adverse cardiovascular effects in animal or human subjects at later stages of development. Positive APD effects can be further characterized with full cardiac ion channel panels to explore root causes.
Both hERG Concentration Response and in vivo QT assays under GLP conditions are highly recommended assays prior to IND submission according to S7B guidelines. Data from assays conducted throughout the drug discovery process also should be compiled with the IND-enabling data to clearly define a compound’s integrated cardiac risk.