Effects of 4-Aminopyridine on Cloned hERG Channels Expressed in Mammalian Cells.

Introduction.  Non-clinical evaluation of a medication's potential to induce cardiac toxicity is recommended by regulatory agencies. 4-Aminopyridine (fampridine) is a potassium channel blocker with the demonstrated ability to improve walking ability in patients with multiple sclerosis. We evaluated the in vitro effects of 4-aminopyridine on the human ether-a-go-go-related gene (hERG) channel current, since hERG current inhibition is associated with QT interval prolongation—a precursor to torsade de pointes (TdP). Methods.  4-Aminopyridine was evaluated in concentrations ranging from 0.1 mM to 30 mM in human embryonic kidney 293 cells stably transfected with the hERG gene; terfenadine 60 nM was used as a positive control. Results and Discussion.  We observed concentration-dependent inhibition of hERG current with 4-aminopyridine doses between 0.3 and 30 mM. The concentration of 3.8 mM resulting in 50% inhibition (IC50) is approximately three orders of magnitude higher than expected therapeutic plasma concentrations, suggesting 4-aminopyridine has low potential for prolonging QT interval or inducing TdP.