Soluble Guanylate Cyclase as an Emerging Therapeutic Target in Cardiopulmonary Disease

doi:10.1161/CIRCULATIONAHA.110.981738

Circulation. Author manuscript; available in PMC 2012 May 24.

Published in final edited form as:

Circulation. 2011 May 24; 123(20): 2263–2273.

doi: 10.1161/CIRCULATIONAHA.110.981738

PMCID: PMC3103045

NIHMSID: NIHMS294586

Soluble Guanylate Cyclase as an Emerging Therapeutic Target in Cardiopulmonary Disease

Johannes-Peter Stasch, PhD, PharmD,^* Pál Pacher, MD, PhD, FAPS, FAHA,^* and Oleg V. Evgenov, MD, PhD^*

Institute of Pharmacy (J.-P.S.), Martin Luther University, Halle, and the Cardiology Research, Bayer HealthCare AG, Wuppertal, Germany; the Laboratory of Physiological Studies (P.P.), National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD; Department of Anesthesia, Critical Care and Pain Medicine (O.V.E.), Massachusetts General Hospital, Harvard Medical School, Boston, MA.

^*All authors contributed equally to this review.

Correspondence to Oleg V. Evgenov, MD, PhD, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Gray/Bigelow 444, Boston, MA 02114; Phone: 617-726-3030; Fax: 617-724-8500; Email: oevgenov/at/partners.org; Email: johannes-peter.stasch/at/bayer.com; Email: pacher/at/mail.nih.gov

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Keywords: cardiovascular diseases, hypertension, pulmonary, soluble guanylate cyclase, nitric oxide, riociguat

Soluble guanylate cyclase (sGC), a key enzyme of the nitric oxide (NO) signaling pathway, is attracting a rapidly growing interest as a therapeutic target in cardiopulmonary disease, with several sGC agonists currently in clinical development. Upon binding of NO to a prosthetic heme group on sGC, the enzyme catalyzes synthesis of the second messenger cyclic guanosine monophosphate (cGMP), which produces vasorelaxation and inhibits smooth muscle proliferation, leukocyte recruitment and platelet aggregation through a number of downstream mechanisms.^1,2

Impaired NO and cGMP signaling has been implicated in the pathogenesis of cardiovascular disease, including systemic arterial and pulmonary hypertension (PH), coronary artery disease, peripheral vascular disease (including erectile dysfunction), and atherosclerosis.^1,3–5 Organic nitrates that target the NO signaling pathway have been used to treat cardiovascular disease for more than 150 years. More recently, gaseous NO administered by inhalation has been approved for the treatment of persistent PH of the newborn.^3,6 These agents nonetheless have several important limitations. Cardiovascular disease is associated with resistance to NO and organic nitrates.⁷ This may be due to the oxidative-stress-induced alteration of the redox state of the prosthetic heme on sGC (from ferrous to ferric) that weakens the binding of heme to the enzyme and renders sGC unresponsive to NO.^1,8 Furthermore, the long-term efficacy of organic nitrates is limited by the development of tolerance.⁹ Nitric oxide may also have numerous cytotoxic effects, mostly attributed to the reactive oxidant peroxynitrite (formed from the diffusion-controlled reaction of NO with superoxide).^3,10 Peroxynitrite interacts with proteins and lipids, altering cellular signaling, disrupting mitochondrial function, and damaging DNA, which can eventually culminate in cellular dysfunction and/or death.³

As the beneficial effects of NO appear to be mediated through the sGC-cGMP-dependent downstream mechanisms, whereas most of its detrimental effects occur independently,¹¹ recent efforts have centered on identifying pharmacological agents that could target sGC-cGMP signaling directly. Compounds that act directly on sGC can be divided into two categories based on their modes of action – sGC stimulators and sGC activators. Stimulators sensitize sGC to low levels of bioavailable NO by stabilizing the nitrosyl-heme complex and thus maintaining the enzyme in its active configuration, and they can also increase sGC activity in the absence of NO.^11,12 Their action is dependent on the presence of a reduced (ferrous) prosthetic heme.^13–15 By contrast, sGC activators preferentially and effectively activate sGC when it is in an oxidized or, finally, a heme-free state (Figure 1).^11,16,17 Oxidation of the heme group on sGC results in its dissociation from the enzyme and the generation of NO-insensitive sGC with only basal levels of activity.¹⁸ Levels of oxidized or heme-free sGC are increased in animal models of hypertension and hyperlipidemia, as well as in certain cardiovascular diseases and type 2 diabetes in humans.^19,20 The detrimental effects of high levels of heme-free sGC were recently demonstrated in a study of genetically modified mice that express only the heme-free version of the enzyme. The mice had systemic hypertension with a loss of smooth muscle relaxation responses to NO and a shortened lifespan.²¹ The two categories of sGC agonists may thus have utility in different groups of diseases, depending on the relative importance of synergistic action with NO (sGC stimulators) compared with ability to act preferentially in conditions associated with oxidative stress (sGC activators).

Figure 1

Soluble guanylate cyclase (sGC) stimulators and activators target two different redox states of sGC, the nitric oxide (NO)-sensitive reduced (ferrous) sGC and NO-insensitive oxidized (ferric) sGC, respectively. Stimulators of sGC stabilize the nitrosyl-heme (more ...)

The first sGC activator, an amino dicarboxylic acid known as cinaciguat (BAY 58-2667), was discovered in a high-throughput screening less than a decade ago.²² Cinaciguat enabled scientists to demonstrate the presence of heme-free sGC in vivo for the first time.²⁰ It activates oxidized/heme-free sGC by binding in the sGC heme pocket and mimicking the heme group; it also protects heme-free sGC from oxidation-induced proteasomal degradation. Cinaciguat therefore opens up the possibility of new mechanism-based therapies for cardiovascular diseases associated with oxidative stress,^8,23 and is currently in clinical development for the treatment of acute decompensated heart failure.^24–26 A more recently discovered sGC activator, the anthranilic acid derivative ataciguat (HMR 1766),²⁷ has also been studied in clinical trials in healthy volunteers,²⁸ in patients with intermittent claudication due to peripheral arterial disease and in patients with neuropathic pain. However, its clinical development in these patients appears to have been stopped.^29,30 Another activator of sGC, BAY 60-2770, has been newly characterized in preclinical studies.³¹

The development of sGC stimulators began in the mid-1990s with the synthetic benzylindazole compound YC-1.^32–34 Binding of YC-1 to sGC is thought to stabilize the enzyme in its active configuration by maintaining stability of the nitrosyl-heme complex.^35,36 YC-1 increases the activity of purified sGC by approximately 10-fold, an effect that is enhanced by approximately one-to-two orders of magnitude in the presence of NO.^33,34,37 Although the precise mechanism by which YC-1 stimulates sGC remains to be elucidated, evidence to date suggests that YC-1 interacts with the catalytic domain of sGC and implicates both subunits of sGC in the action of YC-1.¹² YC-1 has been shown to have additional, cGMP-independent effects^38–40 and to inhibit phosphodiesterase (PDE) 5,^41,42 thus limiting its usefulness as a sGC stimulator. A structurally unrelated class of sGC stimulators (the acrylamide analogs A-350619, A-344905 and A-778935) was also discovered in recent years, but the vast majority of publications have focused on YC-1 and its successors (the indazole family).^12,43–45 Another sGC stimulator, CFM-1571, was developed based on YC-1 as a lead structure,⁴⁶ but has low oral bioavailability and potency.

A separate chemical and pharmacological optimization program yielded the pyrazolopyridine derivatives BAY 41-2272 and BAY 41-8543.^13,14,47 The mode of action of these two compounds is similar to that of YC-1, but they have greater potency and specificity for sGC than YC-1. BAY 41-2272 stimulates the activity of sGC by approximately 20-fold¹³ and BAY 41-8543 stimulates it by up to 92-fold,¹⁴ and both compounds strongly synergize with NO to stimulate sGC activity by up to 200-fold.¹⁵ Unlike YC-1, BAY 41-8543 is devoid of PDE5 inhibition¹⁴ and BAY 41-2272 does not cause any significant inhibition of PDE5 at the concentrations needed to stimulate sGC.^13,48–50 In addition, BAY 41-2272 and BAY 41-8543 do not inhibit other cGMP-specific or cGMP-metabolizing PDEs, such as PDE1, PDE2 and PDE9.^13,14,51

Further pharmacokinetic optimization with an investigation of over 800 pyrimidine derivatives finally yielded the orally bioavailable sGC stimulator riociguat (BAY 63-2521).⁵² Riociguat increases the activity of sGC in vitro by up to 73-fold and acts in synergy with NO to increase sGC activity up to 122-fold.⁵³ It does not inhibit cGMP-specific or cGMP-metabolizing PDEs, such as PDE1, PDE2, PDE5 and PDE9, at concentrations up to 10 μM.⁵³ It has vasodilator properties similar to BAY 41-2272 and BAY 41-8543, and is the first sGC stimulator to make the transition into clinical research, showing promising results in patients with PH in uncontrolled trials.^54,55

While clinical research is focusing on PH at present, disrupted NO signaling is a common pathogenic feature in many forms of cardiovascular disease, and the therapeutic potential of sGC stimulators has been and continues to be explored in a wide range of animal models. Research to identify and optimize new compounds in this drug class (e.g. the aminopyrimidines)⁵⁶ is also ongoing. The remainder of this review will evaluate the potential of sGC stimulation across the broad spectrum of cardiovascular disease, explain the rationale behind the current clinical focus on PH, and discuss the implications of the initial clinical results.

Stimulation of sGC in cardiovascular disease: preclinical evidence

Arterial hypertension

Impaired NO-sGC-cGMP signaling is a key feature of systemic arterial hypertension,^57,58 and studies of sGC stimulators in experimental models of hypertension have provided valuable insights regarding their therapeutic potential. Intravenous YC-1 produced a significant reduction of mean arterial pressure in a rat model of hypertension.⁵⁹ Oral BAY 41-2272 and BAY 41-8543 also produced dose-dependent vasodilation and markedly improved survival in rat models of hypertension, without causing tolerance.^13,60 Furthermore, studies in low NO rat models of hypertension demonstrated that BAY 41-8543 had a renal protective effect,⁶⁰ BAY 41-2272 attenuated cardiac fibrosis and hypertrophy,⁶¹ and riociguat provided significant protection against cardiac and renal damage, reducing glomerulosclerosis, cardiac and renal interstitial fibrosis, and the left ventricular weight.⁶² Riociguat also normalized blood pressure and demonstrated renal and cardiac protective effects in a rat model of chronic renal failure.⁶²

There is evidence from animal models of hypertension that sGC stimulation may protect against end-organ damage independently of its hemodynamic effects. A low dose of BAY 41-2272 that did not affect blood pressure attenuated cardiac fibrosis in rat models of hypertension induced by infusion of angiotensin II⁶³ and suprarenal aortic constriction.⁶⁴ BAY 41-2272 also inhibited angiotensin converting enzyme synthesis and myofibroblast transformation in cultured cardiac fibroblasts, suggesting a mechanism by which sGC stimulation might mediate a direct anti-fibrotic effect in the heart.⁶⁴ Finally, a recent study in aged spontaneously hypertensive rats showed that BAY 41-2272 could completely reverse established cardiac fibrosis and reduce cardiac hypertrophy at a dose that did not produce an antihypertensive effect.⁶⁵ The sGC activators cinaciguat and ataciguat have also shown pressure-independent anti-remodeling effects in the heart.^65,66 Taken together, these results indicate that sGC agonists can exert renal and cardiac protection, and that their antifibrotic effect in the heart may occur independently of their effect on vascular tone. This has important implications not only for the treatment of systemic arterial hypertension, but also for preventing its progression to cardiac dysfunction, heart failure, and renal failure.

Heart failure

The development and progression of heart failure involves both endothelial and myocardial dysfunction and dysregulation of a number of signaling pathways including the NO-sGC-cGMP pathway.^67,68 Agonists of sGC could have beneficial effects in heart failure with a reduced left ventricular ejection fraction by preventing the progression of, or even reversing, ventricular hypertrophy and fibrosis.^63–65 In addition, sGC agonists may have acute beneficial effects by decreasing right and left ventricular afterload through vasodilatation of both the pulmonary and systemic circulations. In a study using a canine model of heart failure induced by rapid ventricular pacing, administration of the sGC stimulator BAY 41-2272 reduced systemic pressure, pulmonary arterial pressure and pulmonary capillary wedge pressure, increased cardiac output, and preserved the glomerular filtration rate.⁶⁹ Activators of sGC have been researched more extensively in this disease. In a rat model of congestive heart failure, chronic treatment with ataciguat normalized endothelial function, improved sensitivity to NO and reduced platelet activation.⁷⁰ The sGC activator cinaciguat decreased blood pressure and unloaded the heart in anesthetized dogs, as well as in dogs with heart failure induced by rapid ventricular pacing.^22,71,72 In anesthetized dogs, cinaciguat and glyceryl trinitrate had similar arterial and venous vasodilatory effects but cinaciguat had a longer duration of action.²² In a phase IIa open-label study in patients with acute decompensated heart failure, intravenous cinaciguat titrated according to hemodynamic response had a favorable safety profile and potently unloaded the heart while also preserving renal function.²⁴

Atherosclerosis, restenosis, and thrombosis

Atherosclerosis is an inflammatory disease in which arterial lesions are formed via a complex process involving platelet adhesion, leukocyte infiltration and activation, and intimal migration and proliferation of smooth muscle cells. The resulting plaque may eventually rupture, causing thrombosis and ischemia.^73,74 Angioplasty and antiplatelet therapy can address the immediate obstruction and prevent distal thrombosis by debris from the ruptured plaque,⁷⁴ but angioplasty can also damage arterial walls, potentially leading to rethrombosis and/or neointimal hyperplasia (restenosis). Endothelial NO bioavailability is reduced in atherosclerosis as a result of oxidative stress,^4,75 and atherosclerotic lesions have reduced levels of sGC.⁷⁶ These changes contribute substantially to the development of atherosclerotic lesions, and preclinical studies have therefore explored the therapeutic potential of sGC stimulators.

YC-1 prolonged tail bleeding time and reduced mortality in a mouse model of fatal pulmonary thromboembolism.⁷⁷ In addition, YC-1 inhibited neointimal development in a rat model of carotid arterial balloon injury^78,79 and inhibited platelet aggregation and adhesion to collagen in vitro.⁸⁰ BAY 41-8543 also prolonged rat tail bleeding time, decreased FeCl₃-induced thrombosis, and inhibited collagen-mediated human platelet aggregation in plasma and washed platelets.^14,60 Moreover, BAY 41-2272 inhibited tissue factor expression and procoagulant activity in stimulated human monocytes and umbilical vein endothelial cells.⁸¹ In addition, BAY 41-2272 may have anti-inflammatory properties: it inhibited leukocyte recruitment in mouse mesenteric post-capillary venules,⁸² and attenuated the adhesive properties of leukocytes from patients with sickle cell disease in vitro.⁸³ The sGC activator ataciguat reduced thrombus formation in a canine model of coronary thrombosis, normalized platelet activation in streptozotocin-diabetic rats, and reduced atherosclerotic plaque formation in apolipoprotein E^−/− mice.⁸⁴ Finally, riociguat inhibited human coronary artery smooth muscle cell migration in vitro and decreased atherosclerosis in apolipoprotein E^−/− mice,¹² but it has not demonstrated antiplatelet effects in humans.⁸⁵ In summary, sGC stimulators may inhibit atherosclerosis and restenosis by virtue of their anti-inflammatory and anti-proliferative effects, but their effects on thrombosis in vivo need further investigation.

Protection against ischemia/reperfusion injury

The cGMP-protein kinase G pathway plays a key role in salvage signaling in ischemia/reperfusion and has been suggested as a therapeutic target.⁸⁶ Several very recent studies have investigated the role of sGC agonists in this field. The sGC stimulator BAY 41-2272 protected isolated intact rabbit lungs against ischemia/reperfusion injury.⁸⁷ The sGC activator cinaciguat reduced the myocardial infarction induced by isoproterenol in rats.⁸⁸ Cinaciguat also increased myocardial cGMP content and reduced infarct size in rabbit and rat hearts when administered prior to reperfusion,⁸⁹ and improved recovery of myocardial function in dogs undergoing cardiopulmonary bypass with hypothermic cardiac arrest.⁹⁰ Finally, the sGC activator ataciguat protected isolated rat hearts from reperfusion-induced edema.⁹¹

Pulmonary hypertension

The vascular pathology of PH results from pulmonary endothelial cell dysfunction or injury⁹² accompanied by dysregulation of various signaling pathways,⁹³ including decreased production of NO and prostacyclin,^94–97 and increased levels of endothelin-1,⁹⁸ thromboxane A₂⁹⁶ and serotonin.⁹⁹ Specifically, the decreased production of NO has recently been linked to Golgi fragmentation (and may thus affect global protein trafficking) in human pulmonary arterial endothelial and smooth muscle cells.¹⁰⁰ Organic nitrates are unsuitable for treating PH because patients develop tolerance with long-term use. In addition, organic nitrates lack specificity for the pulmonary circulation and may, therefore, lead to adverse systemic effects such as hypotension, as well as hypoxemia due to impaired ventilation/perfusion matching. Although inhaled NO is used to treat newborns with persistent PH,⁶ a significant proportion of adult patients with PH do not respond to it,¹⁰¹ likely due to impaired sensitivity of sGC. Moreover, the duration of pulmonary vasodilation is very short and there is a frequent rebound pulmonary vasoconstriction after inhalation of NO is discontinued. When NO is inhaled at high concentrations, there is also a possibility of nonspecific interactions with various biomolecules.^3,102 Drugs that target the NO, endothelin, and prostacyclin signaling pathways to promote vasodilatation (PDE5 inhibitors, endothelin receptor antagonists and prostacyclins, respectively) have been developed for the treatment of one subcategory of PH – pulmonary arterial hypertension (PAH)¹⁰³ – and transiently improve quality of life, but outcomes remain poor and there is a need for more effective and durable therapies.¹⁰⁴ Furthermore, the majority of patients with PH (those with PH associated with interstitial lung disease [ILD], chronic obstructive pulmonary disease [COPD], or left heart disease, and those with chronic thromboembolic PH [CTEPH]) still have no proven pharmacological treatments.¹⁰⁵

An overview of preclinical studies of sGC stimulators in various models of PH is provided in Table 1. BAY 41-2272 produced marked, dose-dependent reductions in mean pulmonary arterial pressure and vascular resistance, as well as an increase in cardiac output, in an ovine model of acute PH.¹⁰⁶ BAY 41-2272 also reduced pulmonary vascular resistance in further studies in ovine and canine models of PH and in a canine model of acute pulmonary embolism.^107,113,114 Infusion of BAY 41-8543 reversed hypoxic pulmonary hypertension in anesthetized pigs.¹¹⁸ In addition, inhaling BAY 41-2272 and BAY 41-8543 resulted in selective pulmonary vasodilation in ovine and rat models of PH.^112,115 Inhibition of endogenous NO synthesis blunted (but did not completely block) the vasodilatory effect of intravenous BAY 41-8543 in rats,¹¹⁶ whereas the vasodilatory effect of BAY 41-2272 on the ovine pulmonary circulation was not affected.^106,108 Interestingly, the ability of BAY 41-2272 to function in conditions of low NO was also demonstrated very recently in a study of nitrergic relaxations in the corpus cavernosum of rats treated with an inhibitor of NO synthesis.¹¹⁹ Co-administration of BAY 41-8543 with sodium nitroprusside¹¹⁶ or inhaled NO¹⁰⁹ was more effective than administration of each compound alone, and the combination of BAY 41-8543 with inhaled NO caused selective pulmonary vasodilation and improved gas exchange in a rabbit model of acute lung injury.¹⁰⁹ BAY 41-2272, BAY 41-8543, and riociguat induced pulmonary vasodilation, and reversed vascular remodeling and right heart hypertrophy in rodent models of PH.^{53,110,111,115,117} BAY 41-2272 also displayed anti-proliferative properties in human pulmonary arterial smooth muscle cells in vitro,¹²⁰ and this effect may contribute to the reversal of structural changes observed in animal models of PH.

Table 1

Preclinical studies of soluble guanylate cyclase stimulators in experimental models of pulmonary hypertension.

Riociguat was recently evaluated in a mouse model of smoke-induced emphysema. Treatment with riociguat during six months of smoke exposure prevented the development of emphysema (unpublished data, Norbert Weissmann, PhD, personal communication). While preclinical studies of sGC stimulation in ILD are in progress, sGC activation has shown promise. Cinaciguat inhibited the conversion of human lung fibroblasts into myofibroblasts (a feature of pulmonary fibrosis) in vitro,¹²¹ suggesting that sGC agonists could have a dual effect in patients with PH in the context of lung fibrosis, reducing fibrosis as well as promoting pulmonary vasorelaxation.

From bench to bedside: riociguat in pulmonary hypertension

Rationale for clinical development

The extensive preclinical testing of sGC stimulators prompts the question: why was PH chosen as a first focus for clinical studies? The unmet need associated with this devastating disease is certainly an important factor. The therapeutic potential of the NO-sGC-cGMP signaling pathway has also not yet been fully exploited. Up to 60% of patients with PAH do not respond to therapy with the PDE5 inhibitor sildenafil, indicating that pulmonary cGMP production is severely impaired.^122,123 In patients with PAH, levels of asymmetric dimethylarginine (ADMA, an endogenous inhibitor of endothelial NO synthase) are elevated, most likely as a result of reduced expression of dimethylarginine dimethylaminohydrolase 2, which metabolizes ADMA.¹²⁴ Furthermore, expression of endothelial NO synthase decreases as the disease progresses.⁹⁴ Thus, NO bioavailability is limited in PAH, and preclinical data indicate that PDE5 inhibitors have limited efficacy in the presence of low levels of endogenous NO.^125,126 This is consistent with their mode of action: PDE5 inhibitors prevent the degradation of cGMP and thus rely on sufficient input at the start of the NO-sGC-cGMP pathway (Figure 2).^5,127 Interestingly, a preclinical study in a model of erectile dysfunction found that the efficacy of sildenafil was limited when NO levels were low, whereas the efficacy of BAY 41-2272 remained unaltered.¹²⁵ Long-term administration of BAY 41-2272 also ameliorated the impairment of corpus cavernosum relaxation in a NO-deficient rat model,¹¹⁹ and BAY 41-2272 caused more prolonged vasodilation than sildenafil in a study of pulmonary circulation in the ovine fetus.¹⁰⁸ Therefore, sGC stimulators may provide a more robust means of targeting the NO-sGC-cGMP pathway than PDE5 inhibitors. Finally, PAH is now recognized as a proliferative disease of the pulmonary vasculature,¹²⁸ and may thus respond to the antiproliferative properties ascribed to sGC stimulators in experimental studies. Experimental evidence for a direct pressure-independent anti-remodeling effect in the heart suggests that sGC stimulators could also help to reduce right heart hypertrophy independently of their effects on the vasculature.

Figure 2

Pharmacological targets in the nitric oxide (NO)-soluble guanylate cyclase (sGC) signaling pathway in pulmonary hypertension. Pulmonary hypertension is associated with reduced levels of endogenous NO, as a result of decreased bioavailability of L-arginine (more ...)

Clinical evidence

A summary of clinical studies of riociguat is provided in Table 2. In a phase I study in 58 healthy male volunteers,¹²⁹ oral riociguat was well tolerated. In a phase IIa study in 19 patients with PH,⁵⁴ riociguat demonstrated hemodynamic efficacy as well as favorable tolerability, causing improvement in all major pulmonary hemodynamic parameters to a greater extent than inhaled NO, without adversely affecting gas exchange or ventilation/perfusion matching. Following a 2.5 mg dose of riociguat, mean pulmonary arterial pressure (mPAP) fell by 14% on average.⁵⁴ The phase IIa study included 5 patients with CTEPH, who demonstrated an increase in cardiac index from baseline following a single dose of riociguat. These initial findings prompted a further open-label study of riociguat in 42 patients with CTEPH as well as 33 patients with PAH.⁵⁵ In this study, oral titration of riociguat (1–2.5 mg three-times daily for 12 weeks) according to systolic blood pressure was well tolerated and effective. At the end of the study, mPAP showed a median decrease of 4.5 mmHg from baseline. Dyspnea and functional class showed clinically meaningful improvements, accompanied by a marked median improvement in a 6-minute walking distance (6MWD): +55.0 m and +57.0 m from baseline in patients with CTEPH and PAH, respectively. Patients who completed the phase II study were eligible to enter a long-term extension phase, and an interim analysis (performed when the first patient had been in the extension phase for 2 years) suggested that long-term use of riociguat was generally well tolerated, and improvements in 6MWD and functional class were maintained.¹³⁰

Table 2

Clinical studies of the soluble guanylate cyclase stimulator riociguat.

These initial clinical results give cause for optimism, and phase III trials in CTEPH and PAH are ongoing. The results of the phase III trial in CTEPH will generate particular interest, because of the lack of approved pharmacotherapies for this disease. Pulmonary endarterectomy is currently the treatment of choice for CTEPH, but in some patients CTEPH is inoperable, and about one-third of patients who undergo pulmonary endarterectomy continue to have residual PH after the procedure.¹³² If positive data are obtained in the phase III studies, riociguat could provide these patients with a much-needed pharmacological treatment, as well as becoming a valuable addition to the therapeutic arsenal for PAH.

Riociguat is also being investigated in patients with PH associated with ILD or chronic COPD. Maintenance of gas exchange is a challenge in PH associated with these lung diseases, because indiscriminate pulmonary vasodilation can increase perfusion of poorly ventilated parts of the lungs. In a 12-week, uncontrolled study in 21 patients with PH associated with ILD, riociguat was well tolerated and produced improvements from baseline in cardiac output (+1.3 L/min) and pulmonary vascular resistance (−122 dyn^.s/cm⁵), and an increase in 6MWD (+21 m).¹³¹ In an uncontrolled single-dose study in 22 patients with PH associated with COPD, 2.5 mg riociguat caused significant improvements in pulmonary vascular resistance (−124 dyn^.s/cm⁵), without deterioration in lung function or gas exchange (unpublished data, Ardeschir Ghofrani, MD, personal communication). Large randomized controlled studies are now warranted to shed further light on the clinical effects of sGC stimulation in these patient populations.

Patients with left heart disease often develop PH, which worsens their prognosis.^133,134 There is growing evidence to consider the use of PH therapies in patients with congestive heart failure.^{6,133,135–137} The principle of targeting the NO pathway gained support from a pivotal study of a combined administration of isosorbide dinitrate with hydralazine, which showed a considerable reduction in mortality; however, a high frequency of adverse reactions limits its clinical use.^138,139 The sGC stimulator BAY 60-4552 (a close chemical analog of riociguat) improved pre- and after-load leading to a significant increase in cardiac index in 42 patients with PH and biventricular heart failure,¹⁴⁰ and a randomized controlled trial of riociguat in patients with left heart disease and PH is currently ongoing.

Summary

The concept of sGC stimulation as a treatment for cardiopulmonary disease has developed rapidly since its inception in the mid-1990s, and preclinical studies continue to shed new light on the properties of this drug class in a wide range of cardiopulmonary diseases (Figure 3). Riociguat is the first sGC stimulator to enter clinical development and has shown promising phase II results in CTEPH, PAH, and PH associated with ILD and COPD, while a phase II study of BAY 60-4552 has suggested that sGC stimulation may also have potential as a treatment for PH associated with biventricular heart failure. The ongoing phase III randomized controlled trials of riociguat in CTEPH and PAH will hopefully be the first of many clinical studies of sGC stimulators. If successful, these studies will herald a new generation of treatments for cardiopulmonary disease.

Figure 3

Timeline of key events in the preclinical and clinical development of soluble guanylate cyclase stimulators. The discovery and first characterization of each compound is shown below the timeline. Key publications and trials are summarized above the timeline. (more ...)

Acknowledgments

Funding Sources Supported, in part, by departmental funds and the NIH Intramural Research Program.

Footnotes

Disclosures J.P.S. is a co-inventor in several patent applications on sGC agonists and an employee of Bayer HealthCare AG. P.P. has no financial interests related to the subject matter of the article. O.V.E. has received test drugs from Bayer HealthCare AG.

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References

1. Murad F. Shattuck Lecture. Nitric oxide and cyclic GMP in cell signaling and drug development. N Engl J Med. 2006;355:2003–2011. [PubMed]

2. Bryan NS, Bian K, Murad F. Discovery of the nitric oxide signaling pathway and targets for drug development. Front Biosci. 2009;14:1–18. [PubMed]

3. Pacher P, Beckman JS, Liaudet L. Nitric oxide and peroxynitrite in health and disease. Physiol Rev. 2007;87:315–424. [PMC free article] [PubMed]

4. Lubos E, Handy DE, Loscalzo J. Role of oxidative stress and nitric oxide in atherothrombosis. Front Biosci. 2008;13:5323–5344. [PMC free article] [PubMed]

5. Tsai EJ, Kass DA. Cyclic GMP signaling in cardiovascular pathophysiology and therapeutics. Pharmacol Ther. 2009;122:216–238. [PMC free article] [PubMed]

6. McLaughlin VV, Archer SL, Badesch DB, Barst RJ, Farber HW, Lindner JR, Mathier MA, McGoon MD, Park MH, Rosenson RS, Rubin LJ, Tapson VF, Varga J. ACCF/AHA 2009 Expert Consensus Document on Pulmonary Hypertension. A Report of the American College of Cardiology Foundation Task Force on Expert Consensus Documents and the American Heart Association. Circulation. 2009;119:2250–2294. [PubMed]

7. Chirkov YY, Horowitz JD. Impaired tissue responsiveness to organic nitrates and nitric oxide: a new therapeutic frontier? Pharmacol Ther. 2007;116:287–305. [PubMed]

8. Hobbs AJ, Stasch JP. Soluble guanylate cyclase: allosteric activation and redox regulation. In: Ignarro LJ, editor. Nitric oxide: biology and pathobiology. 2nd edn. Academic Press; 2010. pp. 301–326.

9. Munzel T, Daiber A, Mulsch A. Explaining the phenomenon of nitrate tolerance. Circ Res. 2005;97:618–628. [PubMed]

10. Szabo C, Ischiropoulos H, Radi R. Peroxynitrite: biochemistry, pathophysiology and development of therapeutics. Nat Rev Drug Discov. 2007;6:662–680. [PubMed]

11. Evgenov OV, Pacher P, Schmidt PM, Hasko G, Schmidt HH, Stasch JP. NO-independent stimulators and activators of soluble guanylate cyclase: discovery and therapeutic potential. Nat Rev Drug Discov. 2006;5:755–768. [PMC free article] [PubMed]

12. Stasch JP, Hobbs AJ. NO-independent, haem-dependent soluble guanylate cyclase stimulators. Handb Exp Pharmacol. 2009:277–308. [PubMed]

13. Stasch JP, Becker EM, Alonso-Alija C, Apeler H, Dembowsky K, Feurer A, Gerzer R, Minuth T, Perzborn E, Pleiss U, Schroder H, Schroeder W, Stahl E, Steinke W, Straub A, Schramm M. NO-independent regulatory site on soluble guanylate cyclase. Nature. 2001;410:212–215. [PubMed]

14. Stasch JP, Alonso-Alija C, Apeler H, Dembowsky K, Feurer A, Minuth T, Perzborn E, Schramm M, Straub A. Pharmacological actions of a novel NO-independent guanylyl cyclase stimulator, BAY 41-8543: in vitro studies. Br J Pharmacol. 2002;135:333–343. [PubMed]

15. Schmidt P, Schramm M, Schroder H, Stasch JP. Mechanisms of nitric oxide independent activation of soluble guanylyl cyclase. Eur J Pharmacol. 2003;468:167–174. [PubMed]

16. Schmidt HHHW, Schmidt PM, Stasch JP. NO- and heme-independent sGC activators. In: Hofmann F, editor. cGMP: generators, effectors and therapeutic implications. Springer-Verlag; Berlin Heidelberg: 2009. pp. 309–339.

17. Martin F, Baskaran P, Ma X, Dunten PW, Schaefer M, Stasch JP, Beuve A, van den Akker F. Structure of cinaciguat (BAY 58-2667) bound to nostoc H-NOX domain reveals insights into heme-mimetic activation of the soluble guanylyl cyclase. J Biol Chem. 2010;285:22651–22657. [PubMed]

18. Roy B, Mo E, Vernon J, Garthwaite J. Probing the presence of the ligand-binding haem in cellular nitric oxide receptors. Br J Pharmacol. 2008;153:1495–1504. [PubMed]

19. Gladwin MT. Deconstructing endothelial dysfunction: soluble guanylyl cyclase oxidation and the NO resistance syndrome. J Clin Invest. 2006;116:2330–2332. [PMC free article] [PubMed]

20. Stasch JP, Schmidt PM, Nedvetsky PI, Nedvetskaya TY, H SA, Meurer S, Deile M, Taye A, Knorr A, Lapp H, Muller H, Turgay Y, Rothkegel C, Tersteegen A, Kemp-Harper B, Muller-Esterl W, Schmidt HH. Targeting the heme-oxidized nitric oxide receptor for selective vasodilatation of diseased blood vessels. J Clin Invest. 2006;116:2552–2561. [PMC free article] [PubMed]

21. Thoonen R, Buys E, Sips P, Nimmegeers S, Van den Hemel M, Hochepied T, Van de Voorde J, Brouckaert P. Targeting the NO – cGMP pathway: phenotyping of NO-insensitive sGCbeta1 H105F knockin mice. BMC Pharmacol. 2007;7:P60. abstract.

22. Stasch JP, Schmidt P, Alonso-Alija C, Apeler H, Dembowsky K, Haerter M, Heil M, Minuth T, Perzborn E, Pleiss U, Schramm M, Schroeder W, Schroder H, Stahl E, Steinke W, Wunder F. NO- and haem-independent activation of soluble guanylyl cyclase: molecular basis and cardiovascular implications of a new pharmacological principle. Br J Pharmacol. 2002;136:773–783. [PubMed]

23. Hoffmann LS, Schmidt PM, Keim Y, Schaefer S, Schmidt HH, Stasch JP. Distinct molecular requirements for activation or stabilization of soluble guanylyl cyclase upon haem oxidation-induced degradation. Br J Pharmacol. 2009;157:781–795. [PubMed]

24. Lapp H, Mitrovic V, Franz N, Heuer H, Buerke M, Wolfertz J, Mueck W, Unger S, Wensing G, Frey R. Cinaciguat (BAY 58-2667) improves cardiopulmonary hemodynamics in patients with acute decompensated heart failure. Circulation. 2009;119:2781–2788. [PubMed]

25. Erdmann E, Semigran MJ, Nieminen MS, Agrawal R, Mitrovic V, Mebazaa A. Cinaciguat, a soluble guanylate cyclase activator, unloads the heart in acute decompensated heart failure. J Am Coll Cardiol. 2010;55:A16, E147. abstract.

26. Tamargo J, Duarte J, Caballero R, Delpon E. Cinaciguat, a soluble guanylate cyclase activator for the potential treatment of acute heart failure. Curr Opin Investig Drugs. 2010;11:1039–1047. [PubMed]

27. Schindler U, Strobel H, Schonafinger K, Linz W, Lohn M, Martorana PA, Rutten H, Schindler PW, Busch AE, Sohn M, Topfer A, Pistorius A, Jannek C, Mulsch A. Biochemistry and pharmacology of novel anthranilic acid derivatives activating heme-oxidized soluble guanylyl cyclase. Mol Pharmacol. 2006;69:1260–1268. [PubMed]

28. Oberwittler H, Hirschfeld-Warneken A, Wesch R, Willerich H, Teichert L, Lehr KH, Ding R, Haefeli WE, Mikus G. Significant pharmacokinetic and pharmacodynamic interaction of warfarin with the NO-independent sGC activator HMR1766. J Clin Pharmacol. 2007;47:70–77. [PubMed]

29. Sanofi-aventis delivers double-digit EPS growth in 2009 as the transformation program progresses. Paris: 2010. [Accessed March 14, 2011]. Available from: http://en.sanofi-aventis.com/press/press_releases/2010/ppc_27174.asp.

30. Sanofi-aventis delivers 2008 results above guidance. Paris: 2009. [Accessed March 14, 2011]. Available from: http://en.sanofi-aventis.com/binaries/20090211_res2008_en_tcm28-23953.pdf.

31. Pankey EA, Bhartiya M, Badejo AM, Jr., Haider U, Stasch JP, Murthy SN, Nossaman BD, Kadowitz PJ. Pulmonary and systemic vasodilator responses to the soluble guanylyl cyclase activator, BAY 60-2770, are not dependent on endogenous nitric oxide or reduced heme. Am J Physiol Heart Circ Physiol. 2011;300:H792–802. [PubMed]

32. Ko FN, Wu CC, Kuo SC, Lee FY, Teng CM. YC-1, a novel activator of platelet guanylate cyclase. Blood. 1994;84:4226–4233. [PubMed]

33. Friebe A, Schultz G, Koesling D. Sensitizing soluble guanylyl cyclase to become a highly CO-sensitive enzyme. EMBO J. 1996;15:6863–6868. [PubMed]

34. Mulsch A, Bauersachs J, Schafer A, Stasch JP, Kast R, Busse R. Effect of YC-1, an NO-independent, superoxide-sensitive stimulator of soluble guanylyl cyclase, on smooth muscle responsiveness to nitrovasodilators. Br J Pharmacol. 1997;120:681–689. [PubMed]

35. Friebe A, Koesling D. Mechanism of YC-1-induced activation of soluble guanylyl cyclase. Mol Pharmacol. 1998;53:123–127. [PubMed]

36. Russwurm M, Mergia E, Mullershausen F, Koesling D. Inhibition of deactivation of NO-sensitive guanylyl cyclase accounts for the sensitizing effect of YC-1. J Biol Chem. 2002;277:24883–24888. [PubMed]

37. Lee YC, Martin E, Murad F. Human recombinant soluble guanylyl cyclase: expression, purification, and regulation. Proc Natl Acad Sci U S A. 2000;97:10763–10768. [PubMed]

38. Tsai IF, Lin CY, Huang CT, Lin YC, Yang CM, Liao CH. Modulation of human monocyte-derived dendritic cells maturation by a soluble guanylate cyclase activator, YC-1, in a cyclic nucleotide independent manner. Int Immunopharmacol. 2007;7:1299–1310. [PubMed]

39. Hwang TL, Wu CC, Guh JH, Teng CM. Potentiation of tumor necrosis factor-alpha expression by YC-1 in alveolar macrophages through a cyclic GMP-independent pathway. Biochem Pharmacol. 2003;66:149–156. [PubMed]

40. Wang JP, Chang LC, Huang LJ, Kuo SC. Inhibition of extracellular Ca(2+) entry by YC-1, an activator of soluble guanylyl cyclase, through a cyclic GMP-independent pathway in rat neutrophils. Biochem Pharmacol. 2001;62:679–684. [PubMed]

41. Friebe A, Mullershausen F, Smolenski A, Walter U, Schultz G, Koesling D. YC-1 potentiates nitric oxide- and carbon monoxide-induced cyclic GMP effects in human platelets. Mol Pharmacol. 1998;54:962–967. [PubMed]

42. Galle J, Zabel U, Hubner U, Hatzelmann A, Wagner B, Wanner C, Schmidt HH. Effects of the soluble guanylyl cyclase activator, YC-1, on vascular tone, cyclic GMP levels and phosphodiesterase activity. Br J Pharmacol. 1999;127:195–203. [PubMed]

43. Miller LN, Nakane M, Hsieh GC, Chang R, Kolasa T, Moreland RB, Brioni JD. A-350619: a novel activator of soluble guanylyl cyclase. Life Sci. 2003;72:1015–1025. [PubMed]

44. Nakane M, Kolasa T, Chang R, Miller LN, Moreland RB, Brioni JD. Acrylamide analog as a novel nitric oxide-independent soluble guanylyl cyclase activator. J Pharmacol Sci. 2006;102:231–238. [PubMed]

45. Zhang HQ, Zhiren X, Teodozyj K, Dinges J. A concise synthesis of ortho-substituted arylacrylamides - potent activators of soluble guanylate cyclase. Tetrahedron Lett. 2003;44:8661–8663.

46. Selwood DL, Brummell DG, Budworth J, Burtin GE, Campbell RO, Chana SS, Charles IG, Fernandez PA, Glen RC, Goggin MC, Hobbs AJ, Kling MR, Liu Q, Madge DJ, Meillerais S, Powell KL, Reynolds K, Spacey GD, Stables JN, Tatlock MA, Wheeler KA, Wishart G, Woo CK. Synthesis and biological evaluation of novel pyrazoles and indazoles as activators of the nitric oxide receptor, soluble guanylate cyclase. J Med Chem. 2001;44:78–93. [PubMed]

47. Straub A, Stasch JP, Alonso-Alija C, Benet-Buchholz J, Ducke B, Feurer A, Furstner C. NO-independent stimulators of soluble guanylate cyclase. Bioorg Med Chem Lett. 2001;11:781–784. [PubMed]

48. Mullershausen F, Russwurm M, Friebe A, Koesling D. Inhibition of phosphodiesterase type 5 by the activator of nitric oxide-sensitive guanylyl cyclase BAY 41-2272. Circulation. 2004;109:1711–1713. [PubMed]

49. Hobbs AJ, Moncada S. Antiplatelet properties of a novel, non-NO-based soluble guanylate cyclase activator, BAY 41-2272. Vascul Pharmacol. 2003;40:149–154. [PubMed]

50. Koglin M, Stasch JP, Behrends S. BAY 41-2272 activates two isoforms of nitric oxide-sensitive guanylyl cyclase. Biochem Biophys Res Commun. 2002;292:1057–1062. [PubMed]

51. Bischoff E, Stasch JP. Effects of the sGC stimulator BAY 41-2272 are not mediated by phosphodiesterase 5 inhibition. Circulation. 2004;110:e320–321. [PubMed]

52. Mittendorf J, Weigand S, Alonso-Alija C, Bischoff E, Feurer A, Gerisch M, Kern A, Knorr A, Lang D, Muenter K, Radtke M, Schirok H, Schlemmer KH, Stahl E, Straub A, Wunder F, Stasch JP. Discovery of riociguat (BAY 63-2521): a potent, oral stimulator of soluble guanylate cyclase for the treatment of pulmonary hypertension. ChemMedChem. 2009;4:853–865. [PubMed]

53. Schermuly R, Stasch JP, Pullamsetti SS, Middendorff R, Mueller D, Schlüter KD, Dingendorf A, Hackemack S, Kolosionek E, Kaulen C, Dumitrascu R, Weissmann N, Mittendorf J, Klepetko W, Seeger W, Ghofrani HA, Grimminger F. Expression and function of soluble guanylate cyclase in pulmonary arterial hypertension. Eur Respir J. 2008;32:881–891. [PubMed]

54. Grimminger F, Weimann G, Frey R, Voswinckel R, Thamm M, Bölkow D, Weissmann N, Mück W, Unger S, Wensing G, Schermuly RT, Ghofrani HA. First acute haemodynamic study of soluble guanylate cyclase stimulator riociguat in pulmonary hypertension. Eur Respir J. 2009;33:785–792. [PubMed]

55. Ghofrani HA, Hoeper MM, Halank M, Meyer FJ, Staehler G, Behr J, Ewert R, Weimann G, Grimminger F. Riociguat for chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension: a phase II study. Eur Respir J. 2010;36:792–799. [PubMed]

56. Brockunier LL, Guo J, Parmee ER, Raghavan S, Rosauer K, Stelmach JE, Schmidt DR. Soluble guanylate cyclase activators. Merck Sharp & Dohme Corp.; 2009. Patent application number: PCT/US2009/064570.

57. Schlaich MP, Parnell MM, Ahlers BA, Finch S, Marshall T, Zhang WZ, Kaye DM. Impaired L-arginine transport and endothelial function in hypertensive and genetically predisposed normotensive subjects. Circulation. 2004;110:3680–3686. [PubMed]

58. Taddei S, Virdis A, Mattei P, Ghiadoni L, Sudano I, Salvetti A. Defective L-arginine-nitric oxide pathway in offspring of essential hypertensive patients. Circulation. 1996;94:1298–1303. [PubMed]

59. Rothermund L, Friebe A, Paul M, Koesling D, Kreutz R. Acute blood pressure effects of YC-1-induced activation of soluble guanylyl cyclase in normotensive and hypertensive rats. Br J Pharmacol. 2000;130:205–208. [PubMed]

60. Stasch JP, Dembowsky K, Perzborn E, Stahl E, Schramm M. Cardiovascular actions of a novel NO-independent guanylyl cyclase stimulator, BAY 41-8543: in vivo studies. Br J Pharmacol. 2002;135:344–355. [PubMed]

61. Zanfolin M, Faro R, Araujo EG, Guaraldo AM, Antunes E, De Nucci G. Protective effects of BAY 41-2272 (sGC stimulator) on hypertension, heart, and cardiomyocyte hypertrophy induced by chronic L-NAME treatment in rats. J Cardiovasc Pharmacol. 2006;47:391–395. [PubMed]

62. Sharkovska Y, Kalk P, Lawrenz B, Godes M, Hoffmann LS, Wellkisch K, Geschka S, Relle K, Hocher B, Stasch JP. Nitric oxide-independent stimulation of soluble guanylate cyclase reduces organ damage in experimental low-renin and high-renin models. J Hypertens. 2010;28:1666–1675. [PubMed]

63. Masuyama H, Tsuruda T, Kato J, Imamura T, Asada Y, Stasch JP, Kitamura K, Eto T. Soluble guanylate cyclase stimulation on cardiovascular remodeling in angiotensin II-induced hypertensive rats. Hypertension. 2006;48:972–978. [PubMed]

64. Masuyama H, Tsuruda T, Sekita Y, Hatakeyama K, Imamura T, Kato J, Asada Y, Stasch JP, Kitamura K. Pressure-independent effects of pharmacological stimulation of soluble guanylate cyclase on fibrosis in pressure-overloaded rat heart. Hypertens Res. 2009;32:597–603. [PubMed]

65. Jones ES, Kemp-Harper B, Stasch JP, Schmidt H, Widdop RE. Cardioprotective effects in aged spontaneously hypertensive rats due to chronic stimulation/activation of sGC without hypotension. BMC Pharmacol. 2009;9:P29. abstract.

66. Benz K, Orth SR, Simonaviciene A, Linz W, Schindler U, Rutten H, Amann K. Blood pressure-independent effect of long-term treatment with the soluble heme-independent guanylyl cyclase activator HMR1766 on progression in a model of noninflammatory chronic renal damage. Kidney Blood Press Res. 2007;30:224–233. [PubMed]

67. Mitrovic V, Hernandez AF, Meyer M, Gheorghiade M. Role of guanylate cyclase modulators in decompensated heart failure. Heart Fail Rev. 2009;14:309–319. [PubMed]

68. Pacher P, Schulz R, Liaudet L, Szabo C. Nitrosative stress and pharmacological modulation of heart failure. Trends Pharmacol Sci. 2005;26:302–310. [PMC free article] [PubMed]

69. Boerrigter G, Costello-Boerrigter LC, Cataliotti A, Tsuruda T, Harty GJ, Lapp H, Stasch JP, Burnett JC., Jr. Cardiorenal and humoral properties of a novel direct soluble guanylate cyclase stimulator BAY 41-2272 in experimental congestive heart failure. Circulation. 2003;107:686–689. [PubMed]

70. Schafer A, Fraccarollo D, Werner L, Bauersachs J. Guanylyl cyclase activator ataciguat improves vascular function and reduces platelet activation in heart failure. Pharmacol Res. 2010;62:432–438. [PubMed]

71. Hoffmann M, Thuss U. Cardiovascular effects of the soluble guanylate cyclase activator BAY 58-2667 in anaesthetized dogs. BMC Pharmacology. 2007;7:P28. abstract.

72. Boerrigter G, Costello-Boerrigter LC, Cataliotti A, Lapp H, Stasch JP, Burnett JC., Jr. Targeting heme-oxidized soluble guanylate cyclase in experimental heart failure. Hypertension. 2007;49:1128–1133. [PubMed]

73. Hansson GK. Inflammation, atherosclerosis, and coronary artery diseasea. N Engl J Med. 2005;352:1685–1695. [PubMed]

74. Libby P, Theroux P. Pathophysiology of coronary artery disease. Circulation. 2005;111:3481–3488. [PubMed]

75. Yang Z, Ming XF. Recent advances in understanding endothelial dysfunction in atherosclerosis. Clin Med Res. 2006;4:53–65. [PubMed]

76. Melichar VO, Behr-Roussel D, Zabel U, Uttenthal LO, Rodrigo J, Rupin A, Verbeuren TJ, Kumar HSA, Schmidt HH. Reduced cGMP signaling associated with neointimal proliferation and vascular dysfunction in late-stage atherosclerosis. Proc Natl Acad Sci U S A. 2004;101:16671–16676. [PubMed]

77. Teng CM, Wu CC, Ko FN, Lee FY, Kuo SC. YC-1, a nitric oxide-independent activator of soluble guanylate cyclase, inhibits platelet-rich thrombosis in mice. Eur J Pharmacol. 1997;320:161–166. [PubMed]

78. Tulis DA, Durante W, Peyton KJ, Chapman GB, Evans AJ, Schafer AI. YC-1, a benzyl indazole derivative, stimulates vascular cGMP and inhibits neointima formation. Biochem Biophys Res Commun. 2000;279:646–652. [PubMed]

79. Wu CH, Chang WC, Chang GY, Kuo SC, Teng CM. The inhibitory mechanism of YC-1, a benzyl indazole, on smooth muscle cell proliferation: an in vitro and in vivo study. J Pharmacol Sci. 2004;94:252–260. [PubMed]

80. Tulis DA, Bohl Masters KS, Lipke EA, Schiesser RL, Evans AJ, Peyton KJ, Durante W, West JL, Schafer AI. YC-1-mediated vascular protection through inhibition of smooth muscle cell proliferation and platelet function. Biochem Biophys Res Commun. 2002;291:1014–1021. [PubMed]

81. Sovershaev MA, Egorina EM, Hansen JB, Østerud B, Stasch JP, Evgenov OV. Soluble guanylate cyclase agonists inhibit expression and procoagulant activity of tissue factor. Arterioscl Thromb Vasc Biol. 2009;29:1578–1586. [PMC free article] [PubMed]

82. Ahluwalia A, Foster P, Scotland RS, McLean PG, Mathur A, Perretti M, Moncada S, Hobbs AJ. Antiinflammatory activity of soluble guanylate cyclase: cGMP-dependent down-regulation of P-selectin expression and leukocyte recruitment. Proc Natl Acad Sci U S A. 2004;101:1386–1391. [PubMed]

83. Canalli AA, Franco-Penteado CF, Saad ST, Conran N, Costa FF. Increased adhesive properties of neutrophils in sickle cell disease may be reversed by pharmacological nitric oxide donation. Haematologica. 2008;93:605–609. [PubMed]

84. van Eickels M, Wassmann S, Schäfer A, Bauersachs J, Strobel H, Rütten H. Role of the sGC activator ataciguat sodium (HMR1766) in cardiovascular disease. BMC Pharmacol. 2007;7:S4. abstract.

85. Frey R, Muck W, Kirschbaum N, Kratzschmar J, Weimann G, Wensing G. Riociguat (BAY 63-2521) and warfarin: a pharmacodynamic and pharmacokinetic interaction study. J Clin Pharmacol. 2010 Aug 27; Epub ahead of print. [PubMed]

86. Burley DS, Ferdinandy P, Baxter GF. Cyclic GMP and protein kinase-G in myocardial ischaemia-reperfusion: opportunities and obstacles for survival signaling. Br J Pharmacol. 2007;152:855–869. [PubMed]

87. Egemnazarov B, Sydykov A, Schermuly RT, Weissmann N, Stasch JP, Sarybaev AS, Seeger W, Grimminger F, Ghofrani HA. Novel soluble guanylyl cyclase stimulator BAY 41-2272 attenuates ischemia/reperfusion induced lung injury. Am J Physiol Lung Cell Mol Physiol. 2009;296:L462–469. [PubMed]

88. Korkmaz S, Radovits T, Barnucz E, Hirschberg K, Neugebauer P, Loganathan S, Veres G, Pali S, Seidel B, Zollner S, Karck M, Szabo G. Pharmacological activation of soluble guanylate cyclase protects the heart against ischemic injury. Circulation. 2009;120:677–686. [PubMed]

89. Krieg T, Liu Y, Rutz T, Methner C, Yang XM, Dost T, Felix SB, Stasch JP, Cohen MV, Downey JM. BAY 58-2667, a nitric oxide-independent guanylyl cyclase activator, pharmacologically post-conditions rabbit and rat hearts. Eur Heart J. 2009;30:1607–1613. [PubMed]

90. Radovits T, Korkmaz S, Miesel-Groschel C, Seidel B, Stasch JP, Merkely B, Karck M, Szabo G. Pre-conditioning with the soluble guanylate cyclase activator Cinaciguat reduces ischaemiareperfusion injury after cardiopulmonary bypass. Eur J Cardiothorac Surg. 2011;39:248–255. [PubMed]

91. Kasseckert SA, Schafer C, Kluger A, Gligorievski D, Tillmann J, Schluter KD, Noll T, Sauer H, Piper HM, Abdallah Y. Stimulation of cGMP signalling protects coronary endothelium against reperfusion-induced intercellular gap formation. Cardiovasc Res. 2009;83:381–387. [PubMed]

92. Farber HW, Loscalzo J. Pulmonary arterial hypertension. N Engl J Med. 2004;351:1655–1665. [PubMed]

93. Morrell NW, Adnot S, Archer SL, Dupuis J, Lloyd Jones P, MacLean M, McMurtry I, Stenmark KR, Thistlethwaite P, Weissmann N, Yuan JX, Weir EK. Cellular and molecular basis of pulmonary arterial hypertension. J Am Coll Cardiol. 2009;54:S20–S31. [PMC free article] [PubMed]

94. Giaid A, Saleh D. Reduced expression of endothelial nitric oxide synthase in the lungs of patients with pulmonary hypertension. N Engl J Med. 1995;333:214–221. [PubMed]

95. Tuder RM, Cool CD, Geraci MW, Wang J, Abman SH, Wright L, Badesch D, Voelkel NF. Prostacyclin synthase expression is decreased in lungs from patients with severe pulmonary hypertension. Am J Respir Crit Care Med. 1999;159:1925–1932. [PubMed]

96. Christman BW, McPherson CD, Newman JH, King GA, Bernard GR, Groves BM, Loyd JE. An imbalance between the excretion of thromboxane and prostacyclin metabolites in pulmonary hypertension. N Engl J Med. 1992;327:70–75. [PubMed]

97. Zakrzewicz D, Eickelberg O. From arginine methylation to ADMA: a novel mechanism with therapeutic potential in chronic lung diseases. BMC Pulm Med. 2009;9:5. [PMC free article] [PubMed]

98. Giaid A, Yanagisawa M, Langleben D, Michel RP, Levy R, Shennib H, Kimura S, Masaki T, Duguid WP, Stewart DJ. Expression of endothelin-1 in the lungs of patients with pulmonary hypertension. N Engl J Med. 1993;328:1732–1739. [PubMed]

99. Eddahibi S, Guignabert C, Barlier-Mur AM, Dewachter L, Fadel E, Dartevelle P, Humbert M, Simonneau G, Hanoun N, Saurini F, Hamon M, Adnot S. Cross talk between endothelial and smooth muscle cells in pulmonary hypertension: critical role for serotonin-induced smooth muscle hyperplasia. Circulation. 2006;113:1857–1864. [PubMed]

100. Lee JE, Patel K, Almodovar S, Tuder R, Flores SC, Sehgal PB. Dependence of Golgi apparatus integrity on nitric oxide in vascular cells: implications in pulmonary arterial hypertension. Am J Physiol Heart Circ Physiol. 2011 Jan 7; Epub ahead of print. [PubMed]

101. Sitbon O, Humbert M, Jagot JL, Taravella O, Fartoukh M, Parent F, Herve P, Simonneau G. Inhaled nitric oxide as a screening agent for safely identifying responders to oral calcium-channel blockers in primary pulmonary hypertension. Eur Respir J. 1998;12:265–270. [PubMed]

102. Bloch KD, Ichinose F, Roberts JD, Jr., Zapol WM. Inhaled NO as a therapeutic agent. Cardiovasc Res. 2007;75:339–348. [PMC free article] [PubMed]

103. Barst RJ, Gibbs JS, Ghofrani HA, Hoeper MM, McLaughlin V, Rubin LJ, Sitbon O, Tapson V, Galie N. Updated evidence-based treatment algorithm in pulmonary arterial hypertension. J Am Coll Cardiol. 2009;54:S78–84. [PubMed]

104. Girgis RE. Emerging drugs for pulmonary hypertension. Expert Opin Emerg Drugs. 2010;15:71–85. [PubMed]

105. Hoeper MM, Albert Barbera J, Channick RN, Hassoun PM, Lang IM, Manes A, Martinez FJ, Naeije R, Olschewski H, Pepke-Zaba J, Redfield MM, Robbins IM, Souza R, Torbicki A, McGoon M. Diagnosis, assessment, and treatment of non-pulmonary arterial hypertension pulmonary hypertension. J Am Coll Cardiol. 2009;54:S85–S96. [PubMed]

106. Evgenov OV, Ichinose F, Evgenov NV, Gnoth MJ, Falkowski GE, Chang Y, Bloch KD, Zapol WM. Soluble guanylate cyclase activator reverses acute pulmonary hypertension and augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs. Circulation. 2004;110:2253–2259. [PubMed]

107. Deruelle P, Grover TR, Abman SH. Pulmonary vascular effects of nitric oxide-cGMP augmentation in a model of chronic pulmonary hypertension in fetal and neonatal sheep. Am J Physiol Lung Cell Mol Physiol. 2005;289:L798–806. [PubMed]

108. Deruelle P, Grover TR, Storme L, Abman SH. Effects of BAY 41-2272, a soluble guanylate cyclase activator, on pulmonary vascular reactivity in the ovine fetus. Am J Physiol Lung Cell Mol Physiol. 2005;288:L727–733. [PubMed]

109. Weidenbach A, Stasch JP, Ghofrani HA, Weissmann N, Grimminger F, Seeger W, Schermuly RT. Inhaled NO and the guanylate cyclase stimulator BAY 41-2272 in oleic acid induced acute lung injury in rabbits. BMC Pharmacol. 2005;5:P61. abstract.

110. Dumitrascu R, Weissmann N, Ghofrani HA, Dony E, Beuerlein K, Schmidt H, Stasch JP, Gnoth MJ, Seeger W, Grimminger F, Schermuly RT. Activation of soluble guanylate cyclase reverses experimental pulmonary hypertension and vascular remodeling. Circulation. 2006;113:286–295. [PubMed]

111. Deruelle P, Balasubramaniam V, Kunig AM, Seedorf GJ, Markham NE, Abman SH. BAY 41-2272, a direct activator of soluble guanylate cyclase, reduces right ventricular hypertrophy and prevents pulmonary vascular remodeling during chronic hypoxia in neonatal rats. Biol Neonate. 2006;90:135–144. [PubMed]

112. Evgenov OV, Kohane DS, Bloch KD, Stasch JP, Volpato GP, Bellas E, Evgenov NV, Buys ES, Gnoth MJ, Graveline AR, Liu R, Hess DR, Langer R, Zapol WM. Inhaled agonists of soluble guanylate cyclase induce selective pulmonary vasodilation. Am J Respir Crit Care Med. 2007;176:1138–1145. [PMC free article] [PubMed]

113. Freitas CF, Morganti RP, Annichino-Bizzacchi JM, De Nucci G, Antunes E. Effect of BAY 41-2272 in the pulmonary hypertension induced by heparin-protamine complex in anaesthetized dogs. Clin Exp Pharmacol Physiol. 2007;34:10–14. [PubMed]

114. Cau SB, Dias-Junior CA, Montenegro MF, de Nucci G, Antunes E, Tanus-Santos JE. Dose-dependent beneficial hemodynamic effects of BAY 41-2272 in a canine model of acute pulmonary thromboembolism. Eur J Pharmacol. 2008;581:132–137. [PubMed]

115. Egemnazarov B, Amirjanians V, Kojonazarov B, Sydykov A, Stasch JP, Weissmann N, Grimminger F, Seeger W, Schermuly RT, Ghofrani HA. Inhalative application of soluble guanylyl cyclase stimulator BAY 41-8543 for treatment of pulmonary arterial hypertension. Am J Respir Crit Care Med. 2010;181:A6307. abstract.

116. Badejo AM, Jr., Nossaman VE, Pankey EA, Bhartiya M, Kannadka CB, Murthy SN, Nossaman BD, Kadowitz PJ. Pulmonary and systemic vasodilator responses to the soluble guanylyl cyclase stimulator, BAY 41-8543, are modulated by nitric oxide. Am J Physiol Heart Circ Physiol. 2010;299:H1153–1159. [PubMed]

117. Thorsen LB, Eskildsen-Helmond Y, Zibrandtsen H, Stasch JP, Simonsen U, Laursen BE. BAY 41-2272 inhibits the development of chronic hypoxic pulmonary hypertension in rats. Eur J Pharmacol. 2010;647:147–154. [PubMed]

118. Hedelin P, Kylhammar D, Radegran G. The sGC stimulator BAY 41-8543 totally reverses hypoxia induced pulmonary hypertension. Eur Heart J. 2010;31:761. abstract.

119. Claudino MA, Da Silva FH, Monica FZ, Rojas-Moscoso JA, De Nucci G, Antunes E. Long-term oral treatment with BAY 41-2272 ameliorates impaired corpus cavernosum relaxations in a nitric oxide-deficient rat model. BJU Int. 2010 Oct 15; Epub ahead of print. [PubMed]

120. Wharton J, Strange JW, Moller GM, Growcott EJ, Ren X, Franklyn AP, Phillips SC, Wilkins MR. Antiproliferative effects of phosphodiesterase type 5 inhibition in human pulmonary artery cells. Am J Respir Crit Care Med. 2005;172:105–113. [PubMed]

121. Dunkern TR, Feurstein D, Rossi GA, Sabatini F, Hatzelmann A. Inhibition of TGF-beta induced lung fibroblast to myofibroblast conversion by phosphodiesterase inhibiting drugs and activators of soluble guanylyl cyclase. Eur J Pharmacol. 2007;572:12–22. [PubMed]

122. Chockalingam A, Gnanavelu G, Venkatesan S, Elangovan S, Jagannathan V, Subramaniam T, Alagesan R, Dorairajan S. Efficacy and optimal dose of sildenafil in primary pulmonary hypertension. Int J Cardiol. 2005;99:91–95. [PubMed]

123. Leuchte HH, Schwaiblmair M, Baumgartner RA, Neurohr CF, Kolbe T, Behr J. Hemodynamic response to sildenafil, nitric oxide, and iloprost in primary pulmonary hypertension. Chest. 2004;125:580–586. [PubMed]

124. Pullamsetti S, Kiss L, Ghofrani HA, Voswinckel R, Haredza P, Klepetko W, Aigner C, Fink L, Muyal JP, Weissmann N, Grimminger F, Seeger W, Schermuly RT. Increased levels and reduced catabolism of asymmetric and symmetric dimethylarginines in pulmonary hypertension. Faseb J. 2005;19:1175–1177. [PubMed]

125. Kalsi JS, Ralph DJ, Madge DJ, Kell PD, Cellek S. A comparative study of sildenafil, NCX-911 and BAY41-2272 on the anococcygeus muscle of diabetic rats. Int J Impot Res. 2004;16:479–485. [PubMed]

126. Nagayama T, Zhang M, Hsu S, Takimoto E, Kass DA. Sustained soluble guanylate cyclase stimulation offsets nitric-oxide synthase inhibition to restore acute cardiac modulation by sildenafil. J Pharmacol Exp Ther. 2008;326:380–387. [PubMed]

127. Kass DA, Takimoto E, Nagayama T, Champion HC. Phosphodiesterase regulation of nitric oxide signaling. Cardiovasc Res. 2007;75:303–314. [PubMed]

128. Adnot S, Eddahibi S. Lessons from oncology to understand and treat pulmonary hypertension. Int J Clin Pract Suppl. 2007:19–25. [PubMed]

129. Frey R, Mück W, Unger S, Artmeier-Brandt U, Weimann G, Wensing G. Single-dose pharmacokinetics, tolerability and safety of the soluble guanylate cyclase stimulator BAY 63-2521; an ascending-dose study in healthy male volunteers. J Clin Pharmacol. 2008;48:926–934. [PubMed]

130. Ghofrani HA, Hoeper MM, Halank M, Meyer FJ, Staehler G, Behr J, Ewert R, Binnen T, Weimann G, Grimminger F. Riociguat for chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension: first long-term extension data from a phase II study. Am J Respir Crit Care Med. 2010;181:A6770. abstract.

131. Hoeper MM, Halank M, Wilkens H, Günther A, Weimann G, Gebert I, Leuchte H, Behr J. Riociguat for patients with pulmonary hypertension associated with interstitial lung disease. Am J Respir Crit Care Med. 2010;181:A5262. abstract.

132. Hagan G, Treacy C, Mackenzie Ross R, Jenkins D, Sheares K, Pepke-Zaba J. Haemodynamics and functional outcome following pulmonary endarterectomy (PEA) - a single centre experience 2006 – 2009. Am J Respir Crit Care Med. 2010;181:A1942. abstract.

133. Bonderman D, Martischnig AM, Moertl D, Lang IM. Pulmonary hypertension in chronic heart failure. Int J Clin Pract Suppl. 2009:4–10. [PubMed]

134. Guazzi M, Arena R. Pulmonary hypertension with left-sided heart disease. Nat Rev Cardiol. 2010;7:648–659. [PubMed]

135. Lewis GD, Shah R, Shahzad K, Camuso JM, Pappagianopoulos PP, Hung J, Tawakol A, Gerszten RE, Systrom DM, Bloch KD, Semigran MJ. Sildenafil improves exercise capacity and quality of life in patients with systolic heart failure and secondary pulmonary hypertension. Circulation. 2007;116:1555–1562. [PubMed]

136. Guazzi M, Samaja M, Arena R, Vicenzi M, Guazzi MD. Long-term use of sildenafil in the therapeutic management of heart failure. J Am Coll Cardiol. 2007;50:2136–2144. [PubMed]

137. Behling A, Rohde LE, Colombo FC, Goldraich LA, Stein R, Clausell N. Effects of 5'-phosphodiesterase four-week long inhibition with sildenafil in patients with chronic heart failure: a double-blind, placebo-controlled clinical trial. J Card Fail. 2008;14:189–197. [PubMed]

138. Taylor AL, Ziesche S, Yancy C, Carson P, D'Agostino R, Jr., Ferdinand K, Taylor M, Adams K, Sabolinski M, Worcel M, Cohn JN. Combination of isosorbide dinitrate and hydralazine in blacks with heart failure. N Engl J Med. 2004;351:2049–2057. [PubMed]

139. Hunt SA, Abraham WT, Chin MH, Feldman AM, Francis GS, Ganiats TG, Jessup M, Konstam MA, Mancini DM, Michl K, Oates JA, Rahko PS, Silver MA, Stevenson LW, Yancy CW. 2009 Focused update incorporated into the ACC/AHA 2005 Guidelines for the Diagnosis and Management of Heart Failure in Adults A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines Developed in Collaboration With the International Society for Heart and Lung Transplantation. J Am Coll Cardiol. 2009;53:e1–e90. [PubMed]

140. Mitrovic V, Swidnicki B, Ghofrani A, Mück W, Kirschbaum N, Mittendorf J, Stasch JP, Wensing G, Frey R, Lentini S. Acute hemodynamic response to single oral doses of BAY 60-4552, a soluble guanylate cyclase stimulator, in patients with biventricular heart failure. BMC Pharmacology. 2009;9:P51. abstract.