S0859, an N‐cyanosulphonamide inhibitor of sodium‐bicarbonate cotransport in the heart

Abstract

Background and purpose: Intracellular pH (pH i ) in heart is regulated by sarcolemmal H þ -equivalent transporters such as Na þ -H þ exchange (NHE) and Na þ -HCO 3 À cotransport (NBC). Inhibition of NBC influences pH i and can be cardioprotective in animal models of post-ischaemic reperfusion. Apart from a rabbit polyclonal NBC-antibody, a selective NBC inhibitor compound has not been studied. Compound S0859 (C 29 H 24 ClN 3 O 3 S) is a putative NBC inhibitor. Here, we provide the drug's chemical structure, test its potency and selectivity in ventricular cells and assess its suitability for experiments on cardiac contraction. Experimental approach: pH i recovery from intracellular acidosis was monitored using pH-epifluorescence (SNARFfluorophore) in guinea pig, rat and rabbit isolated ventricular myocytes. Electrically evoked cell shortening (contraction) was measured optically. With CO 2 /HCO 3 À -buffered superfusates containing 30 mM cariporide (to inhibit NHE), pH i recovery is mediated by NBC. Key results: S0859, an N-cyanosulphonamide compound, reversibly inhibited NBC-mediated pH i recovery (K i ¼ 1.7 mM, full inhibition at B30 mM). In HEPES-buffered superfusates, NHE-mediated pH i recovery was unaffected by 30 mM S0859. With CO 2 /HCO 3 À buffer, pH i recovery from intracellular alkalosis (mediated by Cl À /HCO 3 À and Cl À /OH À exchange) was also unaffected. Selective NBC-inhibition was not due to action on carbonic anhydrase (CA) enzymes, as 100 mM acetazolamide (a membrane-permeant CA-inhibitor) had no significant effect on NBC activity. pH i recovery from acidosis was associated with increased contractile-amplitude. The time course of recovery of pH i and contraction was slowed by S0859, confirming that NBC is a significant controller of contractility during acidosis. Conclusions and implications: Compound S0859 is a selective, high-affinity generic NBC inhibitor, potentially important for probing the transporter's functional role in heart and other tissues.

Disrupting Hypoxia-Induced Bicarbonate Transport Acidifies Tumor Cells and Suppresses Tumor Growth

“…Like most pharmacologic inhibitors, recent data identified possible off-target effects of S0859 including inhibition of lactate transporters ectopically expressed in oocytes (31). Given the similarities in responses between S0859 and the NDBT knockdown studies, it is likely that the NDBT are the major targets here as described previously (7,29,30).…”

“…This small molecule inhibitor blocks the bulk of acid extrusion carried by sodium-driven bicarbonate transport (7,29,30), but other proteins have been shown to be sensitive to S0859 including lactate transporters ectopically expressed in oocytes (31). We used S0859 to explore the role of sodium driven bicarbonate transporters on 3D spheroid growth and intracellular pH regulation.…”

Characterization of the Na+/HCO3-Cotransport in Human Neutrophils

“…Figure 1C-D show the effect on basal pH i of the recently reported selective NBC blocker S0859 [16]. This compound did not significantly affect basal pH i .…”

“…The experiments presented herein reveal the existence of a bicarbonate and sodium-dependent mechanism, sensitive to SITS and S0859 that could participate in the recovery from acid loads and in the maintenance of steady basal pH i . Since SITS is a highly nonspecific inhibitor, S0859 (a putative NBC inhibitor) [16] has also been used to block bicarbonate transport. S0859 has no effect on acid-extruding NHE1 in the ventricular myocyte at doses that completely inhibit generic NBC [16].…”

“…Since SITS is a highly nonspecific inhibitor, S0859 (a putative NBC inhibitor) [16] has also been used to block bicarbonate transport. S0859 has no effect on acid-extruding NHE1 in the ventricular myocyte at doses that completely inhibit generic NBC [16]. These results demonstrate for the first time the presence of NBC in human neutrophils.…”