Abstract
Small-conductance (KCa2) and intermediate-conductance (KCa3.1) calcium-activated K+ channels are voltage-independent and share a common calcium/calmodulin-mediated gating mechanism. Existing positive gating modulators like EBIO, NS309 or SKA-31 activate both KCa2 and KCa3.1 channels with similar potency or, as in the case of CyPPA and NS13001, selectively activate KCa2.2 and KCa2.3 channels. We here performed a structure-activity relationship (SAR) study with the aim of optimizing the benzothiazole pharmacophore of SKA-31 towards KCa3.1 selectivity. We have identified SKA-111 (5-methylnaphtho[1,2-d]thiazol-2-amine), which displays 123-fold selectivity for KCa3.1 (EC50 111 ± 27 nM) over KCa2.3 (EC50 13.7 ± 6.9 μM), and SKA-121 (5-methylnaphtho[2,1-d]oxazol-2-amine), which displays 41-fold selectivity for KCa3.1 (EC50 109 nM ± 14 nM) over KCa2.3 (EC50 4.4 ± 1.6 μM). Both compounds are 200-400 fold selective over representative KV (KV1.3, KV2.1, KV3.1 and KV11.1), NaV (NaV1.2, NaV1.4, NaV1.5 and NaV1.7) as well as CaV1.2 channels. SKA-121 is a typical positive-gating modulator, which shift the calcium-concentration response curve of KCa3.1 to the left. In blood pressure telemetry experiments SKA-121 (100 mg/kg i.p.) significantly lowered mean arterial blood pressure in normotensive and hypertensive wild-type but not KCa3.1-/- mice. SKA-111, which was found in pharmacokinetic experiments to have a much longer half-live and to be much more brain penetrant than SKA-121 not only lowered blood pressure but also drastically reduced heart rate presumably through cardiac and neuronal KCa2 activation when dosed at 100 mg/kg. In conclusion, with SKA-121 we have generated a KCa3.1-specific positive gating modulator suitable for further exploring the therapeutically potential of KCa3.1 activation.
- Bradykinin
- Ion channel regulation
- Potassium channels
- Structure-activity relationships and modeling
- Func. analysis receptor/ion channel mutants
- Patch clamp methods
- The American Society for Pharmacology and Experimental Therapeutics