BAY-6096: A Potent, Selective, and Highly Water-Soluble Adrenergic α2B Antagonist.

After acute myocardial infarction, early reperfusion is the most effective strategy for reducing cardiac damage and improving clinical outcome. However, restoring blood flow to the ischemic myocardium can paradoxically induce injury by itself (reperfusion injury), with microvascular dysfunction being one contributing factor. α2B adrenergic receptors have been hypothesized to be involved in this process. To assess α2B-related pharmacology, we identified a novel α2B antagonist by HTS. The HTS hit showed limited α2A selectivity as well as low solubility and was optimized toward BAY-6096, a potent, selective, and highly water-soluble α2B antagonist. Key aspects of the optimization were the introduction of a permanently charged pyridinium moiety to achieve very good aqueous solubility and the inversion of an amide to prevent genotoxicity. BAY-6096 dose-dependently reduced blood pressure increases in rats induced by an α2B agonist, demonstrating the role of α2B receptors in vascular constriction in rats.

"Digital biomarkers" in preclinical heart failure models - a further step towards improved translational research.

Innovations in the development of novel heart failure therapies are essential to further increase the predictive value of early research findings. Animal models are still playing a pivotal role in 'translational research'. In recent years, the transferability from animal studies has been more and more critically discussed due to persistent high attrition rates in clinical trials. However, there is an increasing trend to implement mobile health devices in preclinical studies. These devices can increase the predictive value of animal models by providing more accurate and translatable data and protect from confounding factors. This review outlines the current prevalence and opportunities of these techniques in preclinical heart failure research studies to accelerate the integration of these important tools. A literature screening for preclinical heart failure studies in large animals implementing telemetry devices over the last decade was performed. Twelve out of 43 publications were included. A variety of different hemodynamic and cardiac parameters can be recorded in conscious state by means of telemetry devices in both, the animal model and the patient. The measurement quality is consistently rated as valid and robust. Mobile health technologies functioning as digital biomarkers represent a more predictive approach compared to the traditionally used invasive measurement techniques, due to the possibility of continuous data collection in the conscious animal. Furthermore, they help to implement the 3R concept (reduction, refinement, replacement) in animal research. Despite this, the use of these techniques in preclinical research has been restrained to date.

Inhaled mosliciguat (BAY 1237592): targeting pulmonary vasculature via activating apo-sGC.

BACKGROUND: Oxidative stress associated with severe cardiopulmonary diseases leads to impairment in the nitric oxide/soluble guanylate cyclase signaling pathway, shifting native soluble guanylate cyclase toward heme-free apo-soluble guanylate cyclase. Here we describe a new inhaled soluble guanylate cyclase activator to target apo-soluble guanylate cyclase and outline its therapeutic potential. METHODS: We aimed to generate a novel soluble guanylate cyclase activator, specifically designed for local inhaled application in the lung. We report the discovery and in vitro and in vivo characterization of the soluble guanylate cyclase activator mosliciguat (BAY 1237592). RESULTS: Mosliciguat specifically activates apo-soluble guanylate cyclase leading to improved cardiopulmonary circulation. Lung-selective effects, e.g., reduced pulmonary artery pressure without reduced systemic artery pressure, were seen after inhaled but not after intravenous administration in a thromboxane-induced pulmonary hypertension minipig model. These effects were observed over a broad dose range with a long duration of action and were further enhanced under experimental oxidative stress conditions. In a unilateral broncho-occlusion minipig model, inhaled mosliciguat decreased pulmonary arterial pressure without ventilation/perfusion mismatch. With respect to airway resistance, mosliciguat showed additional beneficial bronchodilatory effects in an acetylcholine-induced rat model. CONCLUSION: Inhaled mosliciguat may overcome treatment limitations in patients with pulmonary hypertension by improving pulmonary circulation and airway resistance without systemic exposure or ventilation/perfusion mismatch. Mosliciguat has the potential to become a new therapeutic paradigm, exhibiting a unique mode of action and route of application, and is currently under clinical development in phase Ib for pulmonary hypertension.

The sGC stimulator BAY-747 and activator runcaciguat can enhance memory in vivo via differential hippocampal plasticity mechanisms.

Soluble guanylate cyclase (sGC) requires a heme-group bound in order to produce cGMP, a second messenger involved in memory formation, while heme-free sGC is inactive. Two compound classes can increase sGC activity: sGC stimulators acting on heme-bound sGC, and sGC activators acting on heme-free sGC. In this rodent study, we investigated the potential of the novel brain-penetrant sGC stimulator BAY-747 and sGC activator runcaciguat to enhance long-term memory and attenuate short-term memory deficits induced by the NOS-inhibitor L-NAME. Furthermore, hippocampal plasticity mechanisms were investigated. In vivo, oral administration of BAY-747 and runcaciguat to male Wistar rats enhanced memory acquisition in the object location task (OLT), while only BAY-747 reversed L-NAME induced memory impairments in the OLT. Ex vivo, both BAY-747 and runcaciguat enhanced hippocampal GluA1-containing AMPA receptor (AMPAR) trafficking in a chemical LTP model for memory acquisition using acute mouse hippocampal slices. In vivo only runcaciguat acted on the glutamatergic AMPAR system in hippocampal memory acquisition processes, while for BAY-747 the effects on the neurotrophic system were more pronounced as measured in male mice using western blot. Altogether this study shows that sGC stimulators and activators have potential as cognition enhancers, while the underlying plasticity mechanisms may determine disease-specific effectiveness.

A novel approach for quantification of the future unmet medical need in right ventricular dysfunction.

Although 'unmet medical need' (UMN) is an increasingly used term in the healthcare sector instrumental to the approximate value of drug discovery projects relevant to portfolio management, no standardized approach exists for its quantification. Especially in diseases with different comorbidities, high patient heterogeneity, and incomplete epidemiological data, it is difficult to judge the need for new therapies. The approach presented here combines an expert assessment of key UMN indicators related to the individual patient with a literature search to collect epidemiological data describing the corresponding patient population with its underlying heterogeneity. This assessment supports decision-making within the portfolio management process in larger research and development organizations.

sGC stimulation lowers elevated blood pressure in a new canine model of resistant hypertension.

Therapy-resistant hypertension is a serious medical problem, causing end-organ damage, stroke, and heart failure if untreated. Since the standard of care fails in resistant hypertension patients, there is still a substantial unmet medical need for effective therapies. Active stimulation of soluble guanylyl cyclase via novel soluble guanylyl cyclase stimulators might provide an effective treatment option. To test this hypothesis, we established a new experimental dog model and investigated the effects of the soluble guanylyl cyclase-stimulator BAY 41-2272. In beagle dogs, a resistant hypertension phenotype was established by combining unilateral renal wrapping with the occlusion of the renal artery in the contralateral kidney. The most frequently used antihypertensive drugs were administered orally, either alone or in combination, and their acute effect on telemetric measured blood pressure was assessed and compared with that of BAY 41-2272. The chosen disease stimulus led to a moderate and stable increase in blood pressure. Even high doses of standard-of-care antihypertensives only slightly decreased blood pressure. In contrast, the administration of the soluble guanylyl cyclase stimulator BAY 41-2272 as standalone therapy led to a dose-dependent reduction in blood pressure (-14.1 ± 1.8 mmHg). Moreover, BAY 41-2272 could also further decrease blood pressure in addition to a triple combination of standard-of-care antihypertensives (-28.6 ± 13.2 mmHg). BAY 41-2272 was highly efficient as a standalone treatment in resistant hypertension but was also effective in addition to standard-of-care treatment. These data strongly suggest that soluble guanylyl cyclase stimulators might provide an effective pharmacologic therapy for patients with resistant hypertension.

Assessing the Use of the sGC Stimulator BAY-747, as a Potential Treatment for Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder, affecting one in 3500 to 5000 boys worldwide. The NO-sGC-cGMP pathway plays an important role in skeletal muscle function, primarily by improving blood flow and oxygen supply to the muscles during exercise. In fact, PDE5 inhibitors have previously been investigated as a potential therapy for DMD, however, a large-scale Phase III clinical trial did not meet its primary endpoint. Since the efficacy of PDE5i is dependent on sufficient endogenous NO production, which might be impaired in DMD, we investigated if NO-independent sGC stimulators, could have therapeutic benefits in a mouse model of DMD. Male mdx/mTRG2 mice aged six weeks were given food supplemented with the sGC stimulator, BAY-747 (150 mg/kg of food) or food alone (untreated) ad libitum for 16 weeks. Untreated C57BL6/J mice were used as wild type (WT) controls. Assessments of the four-limb hang, grip strength, running wheel and serum creatine kinase (CK) levels showed that mdx/mTRG2 mice had significantly reduced skeletal muscle function and severe muscle damage compared to WT mice. Treatment with BAY-747 improved grip strength and running speed, and these mice also had reduced CK levels compared to untreated mdx/mTRG2 mice. We also observed increased inflammation and fibrosis in the skeletal muscle of mdx/mTRG2 mice compared to WT. While gene expression of pro-inflammatory cytokines and some pro-fibrotic markers in the skeletal muscle was reduced following BAY-747 treatment, there was no reduction in infiltration of myeloid immune cells nor collagen deposition. In conclusion, treatment with BAY-747 significantly improves several functional and pathological parameters of the skeletal muscle in mdx/mTRG2 mice. However, the effect size was moderate and therefore, more studies are needed to fully understand the potential treatment benefit of sGC stimulators in DMD.

Effects of Finerenone Combined with Empagliflozin in a Model of Hypertension-Induced End-Organ Damage.

INTRODUCTION: The nonsteroidal mineralocorticoid receptor (MR) antagonist finerenone and sodium-glucose cotransporter-2 (SGLT2) inhibitors have demonstrated clinical benefits in CKD patients with type 2 diabetes. Clinical data analyzing the potential value of a combination therapy are currently limited. We therefore investigated cardiorenal protection of respective mono- and combination therapy in a preclinical model of hypertension-induced end-organ damage. METHODS: Cardiovascular (CV) morbidity and mortality were studied in hypertensive, N(ω)-nitro-L-arginine methyl ester-treated, renin-transgenic (mRen2)27 rats. Rats (10- to 11-week-old females, n = 13-17/group) were treated once daily orally for up to 7 weeks with placebo, finerenone (1 and 3 mg/kg), empagliflozin (3 and 10 mg/kg), or a combination of the respective low doses. Key outcome parameters included mortality, proteinuria, plasma creatinine and uric acid, blood pressure, and cardiac and renal histology. RESULTS: Placebo-treated rats demonstrated a 50% survival rate over the course of 7 weeks. Drug treatment resulted in variable degrees of survival benefit, most prominently in the low-dose combination group with a survival benefit of 93%. Monotherapies of finerenone or empagliflozin dose-dependently reduced proteinuria, while low-dose combination revealed an early, sustained, and over-additive reduction in proteinuria. Empagliflozin induced a strong and dose-dependent increase in urinary glucose excretion which was not influenced by finerenone coadministration in the combination arm. Low-dose combination but not respective low-dose monotherapies significantly reduced plasma creatinine and plasma uric acid after 6 weeks. Treatment with finerenone and the low-dose combination significantly decreased systolic blood pressure after 5 weeks. There was a dose-dependent protection from cardiac and kidney fibrosis and vasculopathy with both agents, while low-dose combination therapy was more efficient than the respective monotherapy dosages on most cardiorenal histology parameters. DISCUSSION/CONCLUSIONS: Nonsteroidal MR antagonism by finerenone and SGLT2 inhibition by empagliflozin confer CV protection in preclinical hypertension-induced cardiorenal disease. Combination of these 2 independent modes of action at low dosages revealed efficacious reduction in important functional parameters such as proteinuria and blood pressure, plasma markers including creatinine and uric acid, cardiac and renal lesions as determined by histopathology, and mortality indicating a strong potential for combined clinical use in cardiorenal patient populations.

Why translation from basic discoveries to clinical applications is so difficult for atrial fibrillation and possible approaches to improving it.

Atrial fibrillation (AF) is the most common sustained clinical arrhythmia, with a lifetime incidence of up to 37%, and is a major contributor to population morbidity and mortality. Important components of AF management include control of cardiac rhythm, rate, and thromboembolic risk. In this narrative review article, we focus on rhythm-control therapy. The available therapies for cardiac rhythm control include antiarrhythmic drugs and catheter-based ablation procedures; both of these are presently neither optimally effective nor safe. In order to develop improved treatment options, it is necessary to use preclinical models, both to identify novel mechanism-based therapeutic targets and to test the effects of putative therapies before initiating clinical trials. Extensive research over the past 30 years has provided many insights into AF mechanisms that can be used to design new rhythm-maintenance approaches. However, it has proven very difficult to translate these mechanistic discoveries into clinically applicable safe and effective new therapies. The aim of this article is to explore the challenges that underlie this phenomenon. We begin by considering the basic problem of AF, including its clinical importance, the current therapeutic landscape, the drug development pipeline, and the notion of upstream therapy. We then discuss the currently available preclinical models of AF and their limitations, and move on to regulatory hurdles and considerations and then review industry concerns and strategies. Finally, we evaluate potential paths forward, attempting to derive insights from the developmental history of currently used approaches and suggesting possible paths for the future. While the introduction of successful conceptually innovative new treatments for AF control is proving extremely difficult, one significant breakthrough is likely to revolutionize both AF management and the therapeutic development landscape.

Cardiac output improvement by pecavaptan: a novel dual-acting vasopressin V1a/V2 receptor antagonist in experimental heart failure.

AIMS: Arginine vasopressin (AVP) mediates deleterious effects via vascular V1a and renal V2 receptors in heart failure (HF). Despite positive short-term decongestive effects in phase II HF studies, selective V2 receptor antagonism has shown no long-term mortality benefit, potentially related to unopposed V1a receptor activation. We compared the novel dual V1a/V2 receptor antagonist pecavaptan with the selective V2 receptor antagonist tolvaptan in pre-clinical HF models. METHODS AND RESULTS: In vitro IC50 determination in recombinant cell lines revealed similar receptor selectivity profiles (V2:V1a) of tolvaptan and pecavaptan for human and dog AVP receptors, respectively. Two canine models were used to compare haemodynamic and aquaretic effects: (i) anaesthetised dogs with tachypacing-induced HF, and (ii) conscious telemetric dogs with a non-invasive cardiac output (CO) monitor. Tolvaptan and pecavaptan exhibited no differences in urinary output. In HF dogs, pecavaptan counteracted the AVP-induced increase in afterload and decrease in CO (pecavaptan: 1.83 ± 0.31 L/min; vs. tolvaptan: 1.46 ± 0.07 L/min, P < 0.05). In conscious telemetric animals, pecavaptan led to a significant increase in CO (+0.26 ± 0.17 L/min, P = 0.0086 vs. placebo), in cardiac index (+0.58 ± 0.39 L/min/m2 , P = 0.009 vs. placebo) and a significant decrease in total peripheral resistance (-5348.6 ± 3601.3 dyn × s/cm5 , P < 0.0001 vs. placebo), whereas tolvaptan was without any significant effect. CONCLUSIONS: Simultaneous blockade of vascular V1a and renal V2 receptors efficiently induces aquaresis and counteracts AVP-mediated haemodynamic aggravation in HF models. Dual V1a/V2 antagonism may lead to improved outcomes in HF.

A New Therapeutic Framework for Atrial Fibrillation Drug Development.

Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia and cause of significant morbidity and mortality. Its increasing prevalence in aging societies constitutes a growing challenge to global healthcare systems. Despite substantial unmet needs in AF prevention and treatment, drug developments hitherto have been challenging, and the current pharmaceutical pipeline is nearly empty. In this review, we argue that current drugs for AF are inadequate because of an oversimplified system for patient classification and the development of drugs that do not interdict underlying disease mechanisms. We posit that an improved understanding of AF molecular pathophysiology related to the continuous identification of novel disease-modifying drug targets and an increased appreciation of patient heterogeneity provide a new framework to personalize AF drug development. Together with recent innovations in diagnostics, remote rhythm monitoring, and big data capabilities, we anticipate that adoption of a new framework for patient subsegmentation based on pathophysiological, genetic, and molecular subsets will improve success rates of clinical trials and advance drugs that reduce the individual patient and public health burden of AF.

Vascular Protection and Decongestion Without Renin-Angiotensin-Aldosterone System Stimulation Mediated by a Novel Dual-Acting Vasopressin V1a/V2 Receptor Antagonist.

Increased plasma vasopressin levels have been shown to be associated with the progression of congestive heart failure. Vasopressin mediates water retention by renal tubular V2 receptor activation as well as vasoconstriction, cardiac hypertrophy, and fibrosis through V1a receptor activation. Therefore, we developed a novel, dual-acting vasopressin receptor antagonist, BAY 1753011, with almost identical Ki-values of 0.5 nM at the human V1a receptor and 0.6 nM at the human V2 receptor as determined in radioactive binding assays. Renal V2 antagonism by BAY 1753011 was compared with the loop diuretic furosemide in acute diuresis experiments in conscious rats. Similar diuretic efficacy was found with 300-mg/kg furosemide (maximal diuretic response) and 0.1-mg/kg BAY 1753011. Furosemide dose-dependently induced plasma renin and angiotensin I levels, while an equiefficient diuretic BAY 1753011 dose did not activate the renin-angiotensin system. BAY 1753011 dose-dependently decreased the vasopressin-induced expression of the profibrotic/hypertrophic marker plasminogen activator inhibitor-1 and osteopontin in rat cardiomyocytes, while the selective V2 antagonist satavaptan was without any effect. The combined vascular V1a-mediated and renal V2-mediated properties as well as the antihypertrophic/antifibrotic activity enable BAY 1753011 to become a viable treatment option for oral chronic treatment of congestive heart failure.

Remote Left Ventricular Hemodynamic Monitoring Using a Novel Intracardiac Sensor.

BACKGROUND: Heart failure (HF) remains the most common reason for hospital admission in patients aged >65 years. Despite modern drug therapy, mortality and readmission rates for patients hospitalized with HF remain high. This necessitates further research to identify early patients at risk for readmission to limit hospitalization by timely adjustment of medical therapy. Implantable devices can monitor left ventricular (LV) hemodynamics and remotely and continuously detect the early signs of decompensation to trigger interventions and reduce the risk of hospitalization for HF. Here, we report the first preclinical study validating a new batteryless and easy to implant LV-microelectromechanical system to assess LV performance. METHODS AND RESULTS: A miniaturized implantable wireless pressure sensor was adapted for implantation in the LV apex. The LV-microelectromechanical system sensor was tested in a canine model of HF. The wireless pressure sensor measurements were compared with invasive left heart catheter-derived measurements at several time points. During different pharmacological challenge studies with dobutamine or vasopressin, the device was equally sensitive compared with invasive standard procedures. No adverse events or any observable reaction related to the implantation and application of the device for a period of 35 days was observed. CONCLUSIONS: Our miniaturized wireless pressure sensor placed in the LV (LV-microelectromechanical system) has the potential to become a new telemetric tool to earlier identify patients at risk for HF decompensation and to guide the treatment of patients with HF.

New pulmonary hypertension model in conscious dogs to investigate pulmonary-selectivity of acute pharmacological interventions.

PURPOSE: Testing of investigational drugs in animal models is a critical step in drug development. Current models of pulmonary hypertension (PH) have limitations. The most relevant outcome parameters such as pulmonary artery pressure (PAP) are measured invasively which requires anesthesia of the animal. We developed a new canine PH model in which pulmonary vasodilators can be characterized in conscious dogs and lung selectivity can be assessed non-invasively. METHODS: Telemetry devices were implanted to measure relevant hemodynamic parameters in conscious dogs. A hypoxic chamber was constructed in which the animals were placed in a conscious state. By reducing the inspired oxygen fraction (FiO2) to 10%, a hypoxic pulmonary vasoconstriction was induced leading to PH. The PDE-5 inhibitor sildenafil, the current standard of care was compared to atrial natriuretic peptide (ANP). RESULTS: The new hypoxic chamber provided a stable hypoxic atmosphere during all experiments. The mean PAP under normoxic conditions was 15.8 ± 1.8 mmHg. Hypoxia caused a reliable increase in mean PAP (+ 12.2 ± 3.2 mmHg, p < 0.0001). Both, sildenafil (- 6.8 ± 4.4 mmHg) and ANP (- 6.4 ± 3.8 mmHg) significantly (p < 0.05) decreased PAP. Furthermore sildenafil and ANP showed similar effects on systemic hemodynamics. In subsequent studies, the in vitro effects and gene expression pattern of the two pathways were exemplified. CONCLUSIONS: By combining the hypoxic environment with the telemetric approach, we could successfully establish a new acute PH model. Sildenafil and ANP demonstrated equal effects regarding pulmonary selectivity. This non-invasive model could help to rapidly screen pulmonary vasodilators with decreased animal burden.

Transcutaneous glomerular filtration rate measurement in a canine animal model of chronic kidney disease.

INTRODUCTION: Quantitative assessment of renal function by measurement of glomerular filtration rate (GFR) is an important part of safety and efficacy evaluation in preclinical drug development. Existing methods are often time consuming, imprecise and associated with animal burden. Here we describe the comparison between GFR determinations with sinistrin (PS-GFR) and fluorescence-labelled sinistrin-application and its transcutaneous detection (TD-GFR) in a large animal model of chronic kidney disease (CKD). METHODS: TD-GFR measurements compared to a standard method using i.v. sinistrin were performed in a canine model. Animals were treated with one-sided renal wrapping (RW) followed by renal artery occlusion (RO). Biomarker and remote hemodynamic measurements were performed. Plasma sinistrin in comparison to transcutaneous derived GFR data were determined during healthy conditions, after RW and RW+RO. RESULTS: RW alone did not led to any significant changes in renal function, neither with PS-GFR nor TD-GFR. Additional RO showed a rise in blood pressure (+68.0mmHg), plasma urea (+28.8mmol/l), creatinine (+224,4µmol/l) and symmetric dimethylarginine (SDMA™; +12.6µg/dl). Plasma sinistrin derived data confirmed the expected drop (-44.7%, p<0.0001) in GFR. The calculated transcutaneous determined Fluorescein Isothiocyanate (FITC)-sinistrin GFR showed no differences to plasma sinistrin GFR at all times. Both methods were equaly sensitive to diagnose renal dysfunction in the affected animals. DISCUSSION: Renal function assessment using TD-GFR is a valid method to improve preclinical drug discovery and development. Furthermore, TD-GFR method offers advantages in terms of reduced need for blood sampling and thus decreasing animal burden compared to standard procedures.

Big pharma screening collections: more of the same or unique libraries? The AstraZeneca-Bayer Pharma AG case.

In this study, the screening collections of two major pharmaceutical companies (AstraZeneca and Bayer Pharma AG) have been compared using a 2D molecular fingerprint by a nearest neighborhood approach. Results revealed a low overlap between both collections in terms of compound identity and similarity. This emphasizes the value of screening multiple compound collections to expand the chemical space that can be accessed by high-throughput screening (HTS).

Functional cell-based assays in microliter volumes for ultra-high throughput screening.

Functional cell-based assays have gained increasing importance for microplate-based high throughput screening (HTS). The use of high-density microplates, most prominently 1536-well plates, and miniaturized assay formats allow screening of comprehensive compound collections with more than 1 million compounds at ultra-high throughput, i.e. in excess of 100,000 samples per day. uHTS operations with numerous campaigns per year should generally support this throughput at all different steps of the process, including the underlying compound logistics, the (automated) testing of the corporate compound collection in the bioassay, and the subsequent follow-up studies for hit confirmation and characterization. A growing number of reports document the general feasibility of cell-based uHTS in microliter volumes. In addition, full automation with integrated robotic systems allows the realization of also complex assay protocols with multiple liquid handling and signal detection steps. For this review, cell-based assays are categorized based on the kinetics of the cellular response to be quantified in the test and the readout method employed. Thus, assays measuring fast cellular responses with high temporal resolution, e.g., receptor mediated calcium signals or changes in membrane potential, are at one end of this spectrum, while tests quantifying cellular transcriptional responses mark the opposite end. Trends for cell-based uHTS assays developed at Bayer-Schering Pharma are, first, to incorporate assay integral reference signals allowing the experimental differentiation of target hits from non-specifically acting compounds, and second, to make use of kinetic, real-time readouts providing additional information on the mode-of-action of test compounds.

A cell-based nitric oxide reporter assay useful for the identification and characterization of modulators of the nitric oxide/guanosine 3',5'-cyclic monophosphate pathway.

Nitric oxide (NO) plays an important role in protection against the onset and progression of various cardiovascular disorders. Therefore, the NO/guanosine 3',5'-cyclic monophosphate (cGMP) pathway has gained considerable attention and has become a target for new drug development. We have established a rapid, homogeneous, cell-based, and highly sensitive reporter assay for NO generated by endothelial nitric oxide synthase (eNOS). In a coculture system, NO production is indirectly monitored in living cells via soluble guanylyl cyclase (sGC) activation and calcium influx mediated by the olfactory cyclic nucleotide-gated (CNG) cation channel CNGA2, acting as the intracellular cGMP sensor. Using this NO reporter assay, we performed a fully automated high-throughput screening campaign for stimulators of NO synthesis. The coculture system reflects most aspects of the natural NO/cGMP pathway, namely, Ca(2+)-dependent and Ca(2+)-independent regulation of eNOS activity by G protein-coupled receptor agonists, oxidative stress, phosphorylation, and cofactor availability as well as NO-mediated stimulation of cGMP synthesis by sGC activation. The NO reporter assay allows the real-time detection of NO synthesis within living cells and makes it possible to identify and characterize activators and inhibitors of enzymes involved in the NO/cGMP signaling pathway.