Received for publication September 7, 2005.
Revised December 4, 2005.
Accepted for publication December 5, 2005.

Biochemistry and Pharmacology of Novel Anthranilic Acid Derivatives Activating Heme-Oxidized Soluble Guanylyl Cyclase

Abstract

The heme-enzyme soluble guanylyl cyclase (sGC) is an ubiquitous nitric oxide (NO) receptor, which mediates NO downstream signaling by generation of cyclic GMP. We studied the mechanism of action of the anthranilic acid derivatives HMR1766 (proposed international non-proprietary name: ataciguat sodium) and S3448 as a new class of sGC agonists. Both compounds activated different sGC preparations (purified from bovine lung, or crude from human corpus cavernosum) in a concentration-dependent and quickly reversible fashion (EC₅₀ 0.5-10 µM), with mixed-type activation kinetics. Activation of sGC by these compounds was additive to activation by NO donors, but instead of being inhibited was potentiated by the heme-iron oxidants ODQ and NS2028, suggesting that the new compounds target the ferric heme sGC isoform. Protoporphyrin IX acted as a competitive activator and zinc-protoporphyrin IX inhibited activation of heme-oxidized sGC by HMR1766 and S3448, whereas heme-depletion of sGC by Tween 20-treatment reduced activation. Both compounds increased cGMP levels in cultured rat aortic smooth muscle cells, induced vasorelaxation of isolated endothelium-denuded rat aorta, porcine coronary arteries, and human corpus cavernosum (EC₅₀ 1 to 10 µM), and elicited phosphorylation of the cGMP kinase substrate vasodilator-stimulated phosphoprotein (P-VASP) at serine239. HMR1766 i.v. bolus injection decreased arterial blood pressure in anaesthetized pigs. All these pharmacological responses to the new compounds were enhanced by ODQ and NS2028. Our findings suggest that HMR1766 and S3448 preferentially activate the NO-insensitive heme-oxidized form of sGC, which exists to a variable extent in vascular tissues, and is a pharmacological target for these new vasodilator drugs.

Key words: Guanylyl cyclase, Nitric oxide

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