Abstract

We investigated the pharmacological properties and interaction domains of N-(3-aminobenzyl)-6-{4-[(3-fluorobenzyl)oxy]phenoxy} nicotinamide (YM-244769), a novel potent Na⁺/Ca²⁺ exchange (NCX) inhibitor, using various NCX-transfectants and neuronal and renal cell lines. YM-244769 preferentially inhibited intracellular Na⁺-dependent ⁴⁵Ca²⁺ uptake via NCX3 (IC₅₀ = 18 nM); the inhibition was 3.8- to 5.3-fold greater than for the uptake via NCX1 or NCX2, but it did not significantly affect extracellular Na⁺-dependent ⁴⁵Ca²⁺ efflux via NCX isoforms. We searched for interaction domains with YM-244769 by NCX1/NCX3-chimeric analysis and determined that the α-2 region in NCX1 is mostly responsible for the differential drug response between NCX1 and NCX3. Further cysteine scanning mutagenesis in the α-2 region identified that the mutation at Gly833 markedly reduced sensitivity to YM-244769. Mutant exchangers that display either undetectable or accelerated Na⁺-dependent inactivation, had markedly reduced sensitivity or hypersensitivity to YM-244769, respectively. YM-244769, like 2-[2-[4-(4-nitrobenzyloxyl)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943), protected against hypoxia/reoxygenation-induced cell damage in neuronal SH-SY5Y cells, which express NCX1 and NCX3, more efficiently than that in renal LLC-PK₁ cells, which exclusively express NCX1, whereas 2-[4-(4-nitrobenzyloxy)benzyl]thiazolidine-4-carboxylic acid ethyl ester (SN-6) suppressed renal cell damage to a greater degree than neuronal cell damage. These protective potencies consistently correlated well with their inhibitory efficacies for the Ca²⁺ uptake via NCX isoforms existing in the corresponding cell lines. Antisense knockdown of NCX1 and NCX3 in SH-SY5Y cells confirmed that NCX3 contributes to the neuronal cell damage more than NCX1. Thus, YM-244769 is not only experimentally useful as a NCX inhibitor that preferentially inhibits NCX3, but also has therapeutic potential as a new neuroprotective drug.