Discovery of triazolopyridine GS-458967, a late sodium current inhibitor (Late INai) of the cardiac NaV 1.5 channel with improved efficacy and potency relative to ranolazine.

We started with a medium throughput screen of heterocyclic compounds without basic amine groups to avoid hERG and β-blocker activity and identified [1,2,4]triazolo[4,3-a]pyridine as an early lead. Optimization of substituents for Late INa current inhibition and lack of Peak INa inhibition led to the discovery of 4h (GS-458967) with improved anti-arrhythmic activity relative to ranolazine. Unfortunately, 4h demonstrated use dependent block across the sodium isoforms including the central and peripheral nervous system isoforms that is consistent with its low therapeutic index (approximately 5-fold in rat, 3-fold in dog).

Discovery of triazolopyridinone GS-462808, a late sodium current inhibitor (Late INai) of the cardiac Nav1.5 channel with improved efficacy and potency relative to ranolazine.

Previously we disclosed the discovery of potent Late INa current inhibitor 2 (GS-458967, IC50 of 333nM) that has a good separation of late versus peak Nav1.5 current, but did not have a favorable CNS safety window due to high brain penetration (3-fold higher partitioning into brain vs plasma) coupled with potent inhibition of brain sodium channel isoforms (Nav1.1, 1.