Riociguat: Clinical research and evolving role in therapy

Riociguat is a first-in-class soluble guanylate cyclase stimulator, approved for the treatment of adults with pulmonary arterial hypertension (PAH), inoperable chronic thromboembolic pulmonary hypertension (CTEPH), or persistent or recurrent CTEPH after pulmonary endarterectomy. Approval was based on the results of the phase III PATENT-1 (PAH) and CHEST-1 (CTEPH) studies, with significant improvements in the primary endpoint of 6-minute walk distance vs placebo of +36 m and +46 m, respectively, as well as improvements in secondary endpoints such as pulmonary vascular resistance and World Health Organization functional class. Riociguat acts as a stimulator of cyclic guanosine monophosphate synthesis rather than as an inhibitor of cGMP metabolism. As with other approved therapies for PAH, riociguat has antifibrotic, antiproliferative and anti-inflammatory effects, in addition to vasodilatory properties. This has led to further clinical studies in patients who do not achieve a satisfactory clinical response with phosphodiesterase type-5 inhibitors. Riociguat has also been evaluated in patients with World Health Organization group 2 and 3 pulmonary hypertension, and other conditions including diffuse cutaneous systemic sclerosis, Raynaud\u27s phenomenon and cystic fibrosis. This review evaluates the results of the original clinical trials of riociguat for the treatment of PAH and CTEPH, and summarises the body of work that has examined the safety and efficacy of riociguat for the treatment of other types of pulmonary hypertension

Pulmonary Capillary Recruitment and Distention in Mammalian Lungs: Species Similarities

Pulmonary arterial pressure rises minimally during exercise. The pulmonary microcirculation accommodates increasing blood flow via recruitment of pulmonary capillaries and, at higher flows, by distention of already perfused capillaries. The flow transition range between recruitment and distention has not been studied or compared across mammalian species, including humans. We hypothesised that the range would be similar. Functional pulmonary capillary surface area (FCSA) can be estimated using validated metabolic techniques. We reviewed data from previous studies in three mammalian species (perfused rabbit lungs and dog lung lobes, and exercising humans) and generated blood flow-FCSA curves over a range of flows. We noted where the curves diverged from the theoretical line of pure recruitment (Recruitment) and determined the flow where the curve slope equalled 50% that of Recruitment, or equalled that of a theoretical curve representing full capillary distention (Distention). The three mammalian species have similar flow ranges for the transition from predominantly recruitment to predominantly distention, with dogs having the highest transition point. Within the physiological range of most daily activity, the species are similar and accommodate increasing blood flow mainly via recruitment, with progressive distention at higher flows. This is highly relevant to pulmonary physiology during exercise

The Paradox of Pulmonary Vascular Resistance: Restoration of Pulmonary Capillary Recruitment as a \u3ci\u3eSine Qua Non\u3c/i\u3e for True Therapeutic Success in Pulmonary Arterial Hypertension

Exercise-induced increases in pulmonary blood flow normally increase pulmonary arterial pressure only minimally, largely due to a reserve of pulmonary capillaries that are available for recruitment to carry the flow. In pulmonary arterial hypertension, due to precapillary arteriolar obstruction, such recruitment is greatly reduced. In exercising pulmonary arterial hypertension patients, pulmonary arterial pressure remains high and may even increase further. Current pulmonary arterial hypertension therapies, acting principally as vasodilators, decrease calculated pulmonary vascular resistance by increasing pulmonary blood flow but have a minimal effect in lowering pulmonary arterial pressure and do not restore significant capillary recruitment. Novel pulmonary arterial hypertension therapies that have mainly antiproliferative properties are being developed to try and diminish proliferative cellular obstruction in precapillary arterioles. If effective, those agents should restore capillary recruitment and, during exercise testing, pulmonary arterial pressure should remain low despite increasing pulmonary blood flow. The effectiveness of every novel therapy for pulmonary arterial hypertension should be evaluated not only at rest, but with measurement of exercise pulmonary hemodynamics during clinical trials

Use of clinically relevant responder threshold criteria to evaluate the response to treatment in the Phase III PATENT-1 study

Abstract BACKGROUND: In PATENT-1, riociguat significantly improved 6-minute walking distance (6MWD) and a range of secondary end-points in patients with pulmonary arterial hypertension (PAH). We investigated whether riociguat increased the proportion of patients achieving clinically relevant responder thresholds compared with placebo during PATENT-1. METHODS: In PATENT-1, a randomized, double-blind study, treatment-naïve patients or patients on background PAH-targeted therapy with symptomatic PAH received 12 weeks of treatment with placebo, riociguat up to 2.5 mg 3 times daily, or riociguat up to 1.5 mg 3 times daily. Increases in 6MWD ≥40 m, 6MWD ≥380 m, cardiac index ≥2.5 liter/min/m(2), mixed venous oxygen saturation ≥65%, World Health Organization functional class I/II, N-terminal pro-brain natriuretic peptide <1,800 pg/ml, and right atrial pressure <8 mm Hg were chosen as threshold criteria of a positive response. RESULTS: Riociguat increased the proportion of treatment-naïve patients and patients on background PAH-targeted therapy with 6MWD ≥380 m at Week 12 (+21% and +15%, respectively), whereas there was a small reduction in 6MWD in placebo-treated patients for both sub-groups. Riociguat also increased the proportion of treatment-naïve patients and patients on background PAH-targeted therapy achieving World Health Organization functional class I/II (+12% and +19%, respectively) and cardiac index ≥2.5 liter/min/m(2) (+30% and +33%, respectively) at Week 12, whereas there was little change in the respective placebo groups. CONCLUSIONS: Compared with placebo, riociguat increased the proportion of treatment-naïve patients and patients on background PAH-targeted therapy who fulfilled criteria defining a positive response to therapy

EPITOME-2: An open-label study assessing the transition to a new formulation of intravenous epoprostenol in patients with pulmonary arterial hypertension.

Background Continuous infusion of epoprostenol is the treatment of choice in patients with pulmonary arterial hypertension in functional classes III to IV. However, this treatment's limitations include instability at room temperature. A new epoprostenol formulation offers improved storage conditions and patient convenience. Methods The EPITOME-2 trial was an open-label, prospective, multicenter, single-arm, phase IIIb study. Patients with pulmonary arterial hypertension on long-term, stable epoprostenol therapy were transitioned from epoprostenol with glycine and mannitol excipients (Flolan; GlaxoSmithKline, Durham, NC) to epoprostenol with arginine and sucrose excipients (Veletri; Actelion Pharmaceuticals Ltd, Allschwil, Switzerland). Patients were followed up for 3 months, and dose adjustments were recorded. Efficacy measures included the 6-minute walk distance, hemodynamics assessed by right heart catheterization, and New York Heart Association functional class. Safety and tolerability of the transition were also evaluated. Quality of life was assessed using the Treatment Satisfaction Questionnaire for Medication. Results Forty-two patients enrolled in the study, and 1 patient withdrew consent before treatment; thus, 41 patients received treatment and completed the study. Six patients required dose adjustments. There were no clinically relevant changes from baseline to month 3 in any of the efficacy end points. Adverse events were those previously described with intravenous prostacyclin therapy. Treatment Satisfaction Questionnaire for Medication scores showed an improvement from baseline to month 3 in the domain of treatment convenience. Conclusions Transition from epoprostenol with glycine and mannitol excipients to epoprostenol with arginine and sucrose excipients did not affect treatment efficacy, raised no new safety or tolerability concerns, and provided patients with an increased sense of treatment convenience

Oral anticoagulants (NOAC and VKA) in chronic thromboembolic pulmonary hypertension

EXPERT was an international, multicenter, prospective, uncontrolled, non-interventional cohort study in patients with pulmonary hypertension treated with riociguat. Patients were followed for 1-4 years, and the primary outcomes were adverse events (AEs) and serious AEs (SAEs), including embolic/thrombotic and hemorrhagic events. Here we report data on patients with chronic thromboembolic pulmonary hypertension (CTEPH) receiving a vitamin K antagonist (VKA; n = 683) or a non-vitamin K antagonist oral anticoagulant (NOAC; n = 198) at baseline. AEs and SAEs were reported in 438 patients (64.1%) and 257 patients (37.6%), respectively, in the VKA group, and in 135 patients (68.2%) and 74 patients (37.4%) in the NOAC group. Exposure-adjusted hemorrhagic event rates were similar in the two groups, while exposure-adjusted embolic and/or thrombotic event rates were higher in the NOAC group, although the numbers of events were small. Further studies are required to determine the long-term effects of anticoagulation strategies in CTEPH

Comparison of hemodynamic parameters in treatment-naïve and pre-treated patients with pulmonary arterial hypertension in the randomized phase III PATENT-1 study

Background Detailed hemodynamic data from the phase III PATENT-1 study of riociguat in patients with pulmonary arterial hypertension (PAH) were investigated. Methods Patients with PAH who were treatment naïve or pre-treated with endothelin receptor antagonists or non-intravenous prostanoids were randomly assigned to riociguat up to 2.5 mg 3 times a day or placebo. Hemodynamic parameters were assessed at baseline and week 12. Results Riociguat significantly decreased pulmonary vascular resistance in treatment-naïve (n = 221; least squares [LS] mean difference −266 dyne∙sec∙cm−5 [95% confidence interval (CI) −357 to −175; p < 0.0001]) and pre-treated (n = 222; LS mean difference −186 dyne∙sec ∙cm−5 [95% CI −252 to −120; p < 0.0001]) patients and significantly increased cardiac index (LS mean difference +0.7 [95% CI 0.5 to 0.8] and +0.5 [95% CI 0.3 to 0.7], respectively [both p < 0.0001]). Mean pulmonary artery pressure (p = 0.0056 and p = 0.0019 for treatment-naïve and pre-treated patients, respectively), mean arterial pressure (both p < 0.0001), and systemic vascular resistance (both p < 0.0001) were significantly reduced, and there was an increase in mixed venous oxygen saturation (p < 0.0001 and p = 0.0004, respectively). Results were similar in patients pre-treated with endothelin receptor antagonists and patients pre-treated with non-intravenous prostanoids. Improvements in 6-minute walking distance correlated very weakly with improvements in pulmonary vascular resistance (r = −0.21 [95% CI −0.30 to −0.11; p < 0.0001]) and cardiac index (r = 0.16 [95% CI 0.06 to 0.25; p < 0.0016]). Conclusions Riociguat significantly improved hemodynamic parameters in pre-treated and treatment-naïve patients with PAH

Effect of riociguat on right ventricular function in patients with pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

BACKGROUND In the Phase III PATENT-1 (NCT00810693) and CHEST-1 (NCT00855465) studies, riociguat demonstrated efficacy vs placebo in patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Clinical effects were maintained at 2 years in the long-term extension studies PATENT-2 (NCT00863681) and CHEST-2 (NCT00910429). METHODS This post hoc analysis of hemodynamic data from PATENT-1 and CHEST-1 assessed whether riociguat improved right ventricular (RV) function parameters including stroke volume index (SVI), stroke volume, RV work index, and cardiac efficiency. REVEAL Risk Score (RRS) was calculated for patients stratified by SVI and right atrial pressure (RAP) at baseline and follow-up. The association between RV function parameters and SVI and RAP stratification with long-term outcomes was assessed. RESULTS In PATENT-1 (n = 341) and CHEST-1 (n = 238), riociguat improved RV function parameters vs placebo (p < 0.05). At follow-up, there were significant differences in RRS between patients with favorable and unfavorable SVI and RAP, irrespective of treatment arm (p < 0.0001). Multiple RV function parameters at baseline and follow-up were associated with survival and clinical worsening-free survival (CWFS) in PATENT-2 (n = 396; p < 0.05) and CHEST-2 (n = 237). In PATENT-2, favorable SVI and RAP at follow-up only was associated with survival and CWFS (p < 0.05), while in CHEST-2, favorable SVI and RAP at baseline and follow-up were associated with survival and CWFS (p < 0.05). CONCLUSION This post hoc analysis of PATENT and CHEST suggests that riociguat improves RV function in patients with PAH and CTEPH

Endothelin-Receptor Antagonists beyond Pulmonary Arterial Hypertension: Cancer and Fibrosis.

The endothelin axis and in particular the two endothelin receptors, ETA and ETB, are targets for therapeutic intervention in human diseases. Endothelin-receptor antagonists are in clinical use to treat pulmonary arterial hypertension and have been under clinical investigation for the treatment of several other diseases, such as systemic hypertension, cancer, vasospasm, and fibrogenic diseases. In this Perspective, we review the molecules that have been evaluated in human clinical trials for the treatment of pulmonary arterial hypertension, as well as other cardiovascular diseases, cancer, and fibrosis. We will also discuss the therapeutic consequences of receptor selectivity with regard to ETA-selective, ETB-selective, or dual ETA/ETB antagonists. We will also consider which chemical characteristics are relevant to clinical use and the properties of molecules necessary for efficacy in treating diseases against which known molecules displayed suboptimal efficacy

Results of an Expert Consensus Survey on the Treatment of Pulmonary Arterial Hypertension With Oral Prostacyclin Pathway Agents

Background Treatment of pulmonary arterial hypertension (PAH) has evolved substantially over the past two decades and varies according to etiology, functional class (FC), hemodynamic parameters, and other clinical factors. Current guidelines do not provide definitive recommendations regarding the use of oral prostacyclin pathway agents (PPAs) in PAH. To provide guidance on the use of these agents, an expert panel was convened to develop consensus statements for the initiation of oral PPAs in adults with PAH. Methods A systematic literature search was conducted using MEDLINE. The established RAND/University of California Los Angeles appropriateness method, which incorporates the Delphi method and the nominal group technique, was used to create consensus statements. Idiopathic, heritable, repaired congenital heart defect, and drug- or toxin-induced PAH (IPAH+) was considered as one etiologic grouping. The process was focused on the use of oral treprostinil or selexipag in patients with IPAH+ or connective tissue disease-associated PAH and FC II or III symptoms receiving background dual endothelin receptor antagonist/phosphodiesterase type 5 inhibitor therapy. Results The panel developed 14 consensus statements regarding the appropriate use of oral PPAs in the target population. The panel identified 13 clinical scenarios in which selexipag may be considered as a treatment option. Conclusions The paucity of clinical evidence overall, and particularly from randomized trials in this setting, creates a gap in knowledge. These consensus statements are intended to aid physicians in navigating treatment options and using oral PPAs in the most appropriate manner in patients with PAH