Cinaciguat

Cinaciguat, also known as BAY-58-2667, is a NO-independent activator for sGC with EC50 of ∼10 nM for heme-free/oxidized sGC.  [1]
Heme-related dysfunction can lead to cardiovascular diseases with the oxidation of the heme of soluble guanylate cyclase (sGC) critically implicated in some of these cardiovascular diseases. sGC, the main nitric oxide receptor, stimulates second messenger cGMP production, however reactive oxygen species are known to scavenge NO and oxidize/inactivate the heme leading to sGC degradation. Cinaciguat binding causes a rotation of the α- helix away from the heme pocket, as this helix is normally held in place via the inhibitory His105–heme covalent bond. [2]
Cinaciguat activates sGC with EC 50 and Kd values in the low nanomolar range. This renders the compound the most potent NO-independent sGC activator reported to date. Furthermore, cinaciguat produces an additive, non-synergistic effect when combined with NO donors. Cinaciguat could also relaxe blood vessels with a high potency which is several orders of magnitude greater than the NO-donors sodium nitroprusside (SNP) and 3-morpho-linosydnonimin. In addition, the compound reduces coronary perfusion pressure in the rat Langendorff heart preparation and remains active in tissues made tolerant to glyceryl trinitrate. [1]
Cinaciguat could protect cardiomyocytes against ischemia/reperfusion injuries. Cinaciguat caused 63 and 41% reduction of infarct size when given before I/R and at reperfusion in rabbits, respectively. In addition, cinaciguat pretreatment caused a more robust 80% reductionin infarct size vs. 63% reduction when given at reperfusion and preserved cardiac function following I/R in mice, through cGMP-PKG-dependent generation of H2S in the heart and cardiomyocytes.[3]
References:
[1] Evgenov, Oleg V., et al. "NO-independent stimulators and activators of soluble guanylate cyclase: discovery and therapeutic potential." Nature reviews Drug discovery 5.9 (2006): 755-768.
[2] Martin, Faye, et al. "Structure of cinaciguat (BAY 58–2667) bound to Nostoc H-NOX domain reveals insights into heme-mimetic activation of the soluble guanylyl cyclase." Journal of Biological Chemistry 285.29 (2010): 22651-22657.
[3] Salloum, Fadi N., et al. "Cinaciguat, a novel activator of soluble guanylate cyclase, protects against ischemia/reperfusion injury: role of hydrogen sulfide."American Journal of Physiology-Heart and Circulatory Physiology 302.6 (2012): H1347-H1354.

The soluble guanylate cyclase stimulator riociguat and the soluble guanylate cyclase activator cinaciguat exert no direct effects on contractility and relaxation of cardiac myocytes from normal rats.[Pubmed:26407652]

Eur J Pharmacol. 2015 Nov 15;767:1-9.

In cardiovascular diseases, reduced responsiveness of soluble guanylate cyclase (sGC) to nitric oxide (NO) upon long-term application has led to the development of NO-independent sGC stimulators (heme-dependent) and sGC activators (heme-independent). Any direct inotropic or lusitropic effects of these compounds on isolated cardiac myocytes, however, remain to be elucidated. Here, we analyzed the dose-dependent effects of clinical relevant concentrations (10(-10)-10(-5) M) of the sGC activator Cinaciguat and the sGC stimulator riociguat on the contraction, relaxation, and calcium transients of isolated field-stimulated cardiac myocytes from healthy rats. For comparison, we used isoproterenol, which induced a dose-dependent significant increase in cell contractility, relaxation, and calcium transients, verapamil that significantly decreased these parameters (both at 10(-9)-10(-5) M) and 8-(4-Chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (8-pCPT-cGMP) that induced a negative inotropic effect at 10(-5) M accompanied by a slight increase in relaxation. In contrast, neither Cinaciguat nor riociguat significantly influenced any measured parameters. Furthermore, isoproterenol significantly increased intracellular cAMP levels that were not influenced by Cinaciguat or riociguat (all at 10(-6) M). Otherwise, riociguat and Cinaciguat (both at 10(-6) M) significantly enhanced intracellular cGMP generation. This accumulation was significantly augmented by Cinaciguat in the presence of the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 25 microM), whereas ODQ blocked cGMP generation by riociguat. However, blocking of sGC did not influence cell contractility. Our results demonstrate that, in isolated cardiac myocytes from healthy rats, the increase in cGMP levels induced by Cinaciguat and riociguat at clinical relevant concentrations is not associated with acute direct effects on cell contraction and relaxation.

Influence of cinaciguat on gastrointestinal motility in apo-sGC mice.[Pubmed:25200007]

Neurogastroenterol Motil. 2014 Nov;26(11):1573-85.

BACKGROUND: Cinaciguat (BAY 58-2667), an NO- and heme-independent sGC activator, was shown to be more effective when the heme-group of sGC is oxidized in vascular tissue. In apo-sGC mice (sGCbeta1 (His105Phe) knockin) both sGC isoforms (sGCalpha1 beta1 and sGCalpha2 beta1 ) are heme-deficient and can no longer be activated by NO; these mice, showing decreased gastrointestinal nitrergic relaxation and decreased gastric emptying, can be considered as a model to study the consequence of heme-oxidation in sGC. Our aim was to compare the influence of Cinaciguat, on in vitro muscle tone of gastrointestinal tissues, and on gastric emptying in WT and apo-sGC mice. METHODS: Gastrointestinal smooth muscle strips were mounted in organ baths for isometric force recording and cGMP levels were determined by enzyme immunoassay. Protein levels of sGC subunits were assessed by immunoblotting. Gastric emptying was determined by phenol red recovery. KEY RESULTS: Although protein levels of the sGC subunits were lower in gastrointestinal tissues of apo-sGC mice, Cinaciguat induced concentration-dependent relaxations and increased cGMP levels in apo-sGC fundus and colon to a similar or greater extent than in WT mice. The sGC inhibitor ODQ increased Cinaciguat-induced relaxations and cGMP levels in WT fundus and colon. In apo-sGC antrum, pylorus and jejunum, Cinaciguat was not able to induce relaxations. Cinaciguat did not improve delayed gastric emptying in apo-sGC mice. CONCLUSIONS & INFERENCES: Cinaciguat relaxes the fundus and colon efficiently when sGC is in the heme-free condition; the non-effect of Cinaciguat in pylorus explains its inability to improve the delayed gastric emptying in apo-sGC mice.

The soluble guanylate cyclase activator cinaciguat prevents cardiac dysfunction in a rat model of type-1 diabetes mellitus.[Pubmed:26520063]

Cardiovasc Diabetol. 2015 Oct 31;14:145.

BACKGROUND: Diabetes mellitus (DM) leads to the development of diabetic cardiomyopathy, which is associated with altered nitric oxide (NO)--soluble guanylate cyclase (sGC)--cyclic guanosine monophosphate (cGMP) signalling. Cardioprotective effects of elevated intracellular cGMP-levels have been described in different heart diseases. In the current study we aimed at investigating the effects of pharmacological activation of sGC in diabetic cardiomyopathy. METHODS: Type-1 DM was induced in rats by streptozotocin. Animals were treated either with the sGC activator Cinaciguat (10 mg/kg/day) or with placebo orally for 8 weeks. Left ventricular (LV) pressure-volume (P-V) analysis was used to assess cardiac performance. Additionally, gene expression (qRT-PCR) and protein expression analysis (western blot) were performed. Cardiac structure, markers of fibrotic remodelling and DNA damage were examined by histology, immunohistochemistry and TUNEL assay, respectively. RESULTS: DM was associated with deteriorated cGMP signalling in the myocardium (elevated phosphodiesterase-5 expression, lower cGMP-level and impaired PKG activity). Cardiomyocyte hypertrophy, fibrotic remodelling and DNA fragmentation were present in DM that was associated with impaired LV contractility (preload recruitable stroke work (PRSW): 49.5 +/- 3.3 vs. 83.0 +/- 5.5 mmHg, P < 0.05) and diastolic function (time constant of LV pressure decay (Tau): 17.3 +/- 0.8 vs. 10.3 +/- 0.3 ms, P < 0.05). Cinaciguat treatment effectively prevented DM related molecular, histological alterations and significantly improved systolic (PRSW: 66.8 +/- 3.6 mmHg) and diastolic (Tau: 14.9 +/- 0.6 ms) function. CONCLUSIONS: Cinaciguat prevented structural, molecular alterations and improved cardiac performance of the diabetic heart. Pharmacological activation of sGC might represent a new therapy approach for diabetic cardiomyopathy.

Cinaciguat prevents the development of pathologic hypertrophy in a rat model of left ventricular pressure overload.[Pubmed:27853261]

Sci Rep. 2016 Nov 17;6:37166.

Pathologic myocardial hypertrophy develops when the heart is chronically pressure-overloaded. Elevated intracellular cGMP-levels have been reported to prevent the development of pathologic myocardial hypertrophy, therefore we investigated the effects of chronic activation of the cGMP producing enzyme, soluble guanylate cyclase by Cinaciguat in a rat model of pressure overload-induced cardiac hypertrophy. Abdominal aortic banding (AAB) was used to evoke pressure overload-induced cardiac hypertrophy in male Wistar rats. Sham operated animals served as controls. Experimental and control groups were treated with 10 mg/kg/day Cinaciguat (Cin) or placebo (Co) p.o. for six weeks, respectively. Pathologic myocardial hypertrophy was present in the AABCo group following 6 weeks of pressure overload of the heart, evidenced by increased relative heart weight, average cardiomyocyte diameter, collagen content and apoptosis. Cinaciguat did not significantly alter blood pressure, but effectively attenuated all features of pathologic myocardial hypertrophy, and normalized functional changes, such as the increase in contractility following AAB. Our results demonstrate that chronic enhancement of cGMP signalling by pharmacological activation of sGC might be a novel therapeutic approach in the prevention of pathologic myocardial hypertrophy.