A compound’s QT risk cannot be determined by an evaluation of hERG effects alone. Instead, an evaluation must be performed using assays included in the TSP. Compound X’s results are as follows:

1. hERG Trafficking (HERG-Lite®)
   Some compounds that inhibit hERG current also prevent the hERG channel from reaching the membrane surface, thus increasing their QT risk.
• Compound X does not inhibit trafficking of the hERG ion channel.
  
2. Cardiac Channel Panel™
   A compound that is a selective, potent hERG blocker will most likely prolong the QT interval. However, the QT prolonging effect of hERG inhibition may be “offset” if a compound also inhibits depolarizing ion channel currents (calcium and sodium). The Cardiac Channel Panel™ results for Compound X can be seen below.
   
   

   

• hERG (Kv11.1):
  • Compound X is a very potent hERG blocker with an IC₅₀ in the nanomolar range (IC₅₀ = 0.3 μM).
• Calcium (Cav1.2):
  • Compound X is also a potent inhibitor of calcium channel current with an IC₅₀ of 3.5 μM (Cav1.2).
• Sodium (Nav1.5)
  • Compound X also inhibits Nav1.5 with an IC₅₀ of 30 μM (Nav1.5) but with less potency than Cav1.2 inhibition.
• The Cardiac Channel Panel™ confirms that Compound X is not a selective hERG blocker. It inhibits depolarizing ion channel currents (Cav1.2 and Nav1.5) that may offset the hERG effect.
  
3. Stem Cell-Derived Human Cardiomyocyte (SC-hCM) APD
   In order to confirm that inhibition of calcium and sodium currents offset the hERG inhibition, the effects of Compound X on the action potential duration in stem cell-derived human cardiomyocytes were determined.

   

   • Compound X prolonged the APD₉₀, shortened the APD₃₀ and did not affect the APD₆₀, confirming that inhibition of the depolarizing currents (Cav1.2 and Nav1.5) offsets the effects of hERG inhibition.
4. in vivo QT
   • No QT prolongation was observed in an in vivo canine QT assay which also confirmed that hERG effects were offset by inhibition of depolarizing currents.

TSP Conclusion:

Results from the TSP suggest that Compound X is not a QT risk.

Confirmation of the TSP:

Compound X is Verapamil and has been used for more than 30 years with no incidence of QT prolongation or TdP at clinical plasma concentrations in humans.

In today’s world, a positive hERG signal (i.e. hERG inhibition) can terminate drug progression. Augmenting the hERG assay with inexpensive assessments of other key cardiac ion channels, protein trafficking and AP duration with confirmation in vivo provide a more thorough and comprehensive view into a compound’s true cardiac risk. Use of the TSP can help prevent rejection of potentially promising compounds, guide IND-enabling study selection, and provide complete compound performance data and advice for IND submissions and discussions with regulatory agencies. In addition, the TSP allows for early identification of compounds that pose true cardiac risk by resolving discordances often seen with standard S7B assays alone, and preventing undesirable compounds from progressing into costly clinical trials.