Voltage-gated k+ channel block by catechol derivatives: defining nonselective and selective pharmacophores

High-throughput screening led to the identification of a 3-norbornyl derivative of catechol called 48F10 (3-bicyclo[2.2.1]hept-2-yl-benzene-1,2-diol) as a Kv2.1 K(+) channel inhibitor. By virtue of the involvement of Kv2.1 channels in programmed cell death, 48F10 prevents apoptosis in cortical neurons and enterocytes. This uncharged compound acts with an apparent affinity of 1 muM at the tetraethylammonium (TEA) site at the external mouth of the Kv2.1 channel but is ineffective on Kv1.5. Here we investigated the basis of this selectivity with structure-activity studies. We find that catechol (1,2-benzenediol), unlike 48F10, inhibits Kv2.1 currents with a Hill coefficient of 2 and slows channel activation. Furthermore, this inhibition, which requires millimolar concentrations, is unaffected by external TEA or by mutation of the external tyrosine implicated in channel block by TEA and 48F10. In addition, catechol does not distinguish between Kv2.1 and Kv1.5. Thus, catechol acts at conserved sites that are distinct from 48F10. We also tested 11 catechol derivatives based on hydrocarbon adducts including norbornyl substructures, a 48F10 isomer, and a 48F10 diastereomer. These compounds are more potent than catechol, but none replicated the marked selectivity of 48F10 for Kv2.1 over Kv1.5. We conclude that the targeting of 48F10 to the TEA site at the external mouth of the Kv2.1 pore and away from other sites involved in nonselective Kv channel block by catechol requires the norbornyl group in a unique position and orientation on the catechol ring.