Background and purpose: Prolongation of the cardiac QRS complex is linked to increased mortality and may result from drug-induced inhibition of cardiac sodium channels (hNaV 1.5). There has been no systematic evaluation of preclinical and marketed drugs for their additional potential to cause QRS prolongation via gap junction uncoupling.
Experimental approach: Using the human cardiac gap junction connexin 43 (hCx43), a dye transfer 'parachute' assay to determine IC50 values for compound ranking was validated with compounds known to uncouple gap junctions. Uncoupling activity (and hNaV 1.5 inhibition by automated patch clamp) was determined in a set of marketed drugs and preclinical candidate drugs, each with information regarding propensity to prolong QRS.
Key results: The potency of known gap junction uncouplers to uncouple hCx43 was ranked (according to IC50 ) as phorbol ester>digoxin>meclofenamic acid>carbenoxolone>heptanol. Among the drugs associated with QRS prolongation, 29% were found to uncouple hCx43 (IC50 < 50 μM), whereas no uncoupling activity was observed in drugs not associated with QRS prolongation. In preclinical candidate drugs, hCx43 and hNaV 1.5 IC50 values were similar (within threefold). No consistent margin over preclinical Cmax (free) was apparent for QRS prolongation associated with Cx43 inhibition. However, instances were found of QRS prolonging compounds that uncoupled hCx43 with significantly less activity at hNaV 1.5.
Conclusion and implications: These results demonstrate that off-target uncoupling activity is apparent in drug and drug-like molecules. Although the full ramifications of Cx inhibition remain to be established, screening for hCx43 off-target activity could reduce the likelihood of developing candidate drugs with a risk of causing QRS prolongation.
© 2013 The British Pharmacological Society.