ICA-17043, a novel Gardos channel blocker, prevents sickled red blood cell dehydration in vitro and in vivo in SAD mice

A prominent feature of sickle cell anemia is the presence of dehydrated red blood cells (RBCs) in circulation. Loss of potassium (K+), chloride (Cl-), and water from RBCs is thought to contribute to the production of these dehydrated cells. One main route of K+ loss in the RBC is the Gardos channel, a calcium (Ca2+)-activated K+ channel. Clotrimazole (CLT), an inhibitor of the Gardos channel, has been shown to reduce RBC dehydration in vitro and in vivo. We have developed a chemically novel compound, ICA-17043, that has greater potency and selectivity than CLT in inhibiting the Gardos channel. ICA-17043 blocked Ca2+-induced rubidium flux from human RBCs with an IC50 value of 11+/-2 nM (CLT IC50=100+/-12 nM) and inhibited RBC dehydration with an IC50 of 30+/-20 nM. In a transgenic mouse model of sickle cell disease (SAD), treatment with ICA-17043 (10 mg/kg orally, twice a day) for 21 days showed a marked and constant inhibition of the Gardos channel activity (with an average inhibition of 90% +/-27%, P<.005), an increase in RBC K+ content (from 392 +/- 19.9 to 479.2 +/- 40 mmol/kg hemoglobin [Hb], P<.005), a significant increase in hematocrit (Hct) (from 0.435+/-0.007 to 0.509+/-0.022 [43.5%+/-0.7% to 50.9%+/-2.2%], P<.005), a decrease in mean corpuscular hemoglobin concentration (MCHC) (from 340 +/- 9.0 to 300 +/- 15 g/L [34.0 +/- 0.9 to 30 +/- 1.5 g/dL], P<.05), and a left-shift in RBC density curves. These data indicate that ICA-17043 is a potent inhibitor of the Gardos channel and ameliorates RBC dehydration in the SAD mouse.