Emerging drugs for pulmonary hypertension

Discovery and development of sGC stimulators for the treatment of pulmonary hypertension and rare diseases

The NO/sGC/cGMP signaling cascade plays a pivotal role in regulation of cardiovascular, cardiopulmonary and cardiorenal diseases and impairment of this cascade results in severe pathologies. Therefore, pharmacological interventions, targeting this pathway are promising strategies for treating a variety of diseases. Nitrates, supplementing NO and, PDE5 inhibitors preventing cGMP degradation, are used for angina pectoris treatment and the treatment of pulmonary arterial hypertension (PAH), respectively. More recently, a new class of drugs which directly stimulate the sGC enzyme and trigger NO-independent cGMP production was introduced and termed sGC stimulators. In 2013, the first sGC stimulator, riociguat, was approved for the treatment of PAH and chronic thromboembolic pulmonary hypertension (CTEPH). Since cGMP targets multiple intracellular downstream targets, sGC stimulators have shown - beyond the well characterized vasodilatation - anti-fibrotic, anti-inflammatory and anti-proliferative effects. These additional modes of action might extend the therapeutic potential of this drug class substantially. This review summarizes the NO/sGC/cGMP signaling cascades, the discovery and the mode of action of sGC stimulators. Furthermore, the preclinical evidence and development of riociguat for the treatment of PAH and CTEPH is reviewed. Finally, a summary of the antifibrotic effects of sGC stimulators, especially the most recent finding for skin fibrosis are included which may indicate efficacy in fibrotic diseases like Systemic Sclerosis (SSc).

Medical therapies for pulmonary arterial hypertension

Pulmonary Arterial hypertension (PAH) is a chronic and progressive disease characterized by an increase in pulmonary vascular resistance due to severe remodeling of the small pulmonary arteries. In PAH, the endothelial cells fail to maintain their homeostatic balance, with the consequent impaired production of vasodilators and over-expression of vasoconstrictors and proliferators. Current treatment of PAH is based on the discovery of three main pathways of endothelial dysfunction (prostacyclin, nitric oxide and endothelin-1), and includes drugs such as prostacyclin analogs, phosphodiesterase-5 inhibitors and endothelin receptor antagonists (ERAs). Recently approved drugs that act through these classic pathways include riociguat (cyclic GMP stimulator) and macitentan (a tissue specific dual ERA). However, several new drugs and new pathways are under study. New targeted therapies include tyrosine kinase inhibitors, Rho kinase inhibitors and serotonin receptor blockers. There are now ten drugs approved for the treatment of PAH that, alone or in combination, have changed the natural history of this disease. The new drugs will allow us to further modified the patients' life expectancy and move towards a cure.

Determination of riociguat and its major human metabolite M-1 in human plasma by stable-isotope dilution LCMS/MS

Background: Riociguat (BAY 63–2521) is an oral NO-independent as well as NO-synergistic stimulator of soluble guanylate cyclase (sGC) for the treatment of pulmonary hypertension. BAY 60–4552 (M-1) is its pharmacologically active major metabolite. An isotope dilution LC–ESI–MS/MS method has been developed and validated for the simultaneous determination of riociguat and M-1 in lithium heparinized human plasma. Results: The validated concentration range covers 0.500 μg/l (LLOQ) to 100 μg/l (ULOQ) for both analytes. Interassay accuracy and precision (%CV) for both analytes ranged from 92.7 to 111% and from 2.61 to 9.89%, respectively. Conclusion: The method proved to be selective, specific, sufficiently sensitive, highly reproducible and robust for the analysis of large numbers of samples.

Targeted approaches to the treatment of pulmonary hypertension

Pulmonary arterial hypertension is a progressive and incurable disease. Over the past two decades, significant advances have been made in understanding and thus managing this disease. Multiple therapeutic options are currently available and optimizing the treatment of pulmonary arterial hypertension has become complex. Patients who meet the American College of Chest Physicians criteria for vasoresponsiveness can be safely and effectively treated with high-dose calcium channel blockers but require close follow up to assure durability of response. Patients with World Health Organization (WHO) functional class IV status and those with determinants of high risk for progression and death should be treated with an infused prostanoid agent without delay. These patients should also be referred early after stabilization for transplant evaluation. Patients with WHO functional class II status benefit from early initiation of oral therapies. Those with WHO functional class III status and lower determinants of risk for progression may receive treatment with one or more oral or inhaled agents, though many experts would advise early use of infused prostanoids for these patients as well.

Insights into ET(A) subtype selectivity of benzodiazepine endothelin receptor antagonists by 3D-QSAR approaches

ET(A) subtype selective antagonists constitute a novel and potentially important class of agents for the treatment of pulmonary hypertension, heart failure, and other pathological conditions. In this paper, 60 benzodiazepine derivatives displaying potent activities against ET(A) and ET(B) subtypes of endothelin receptor were selected to establish the 3D-QSAR models using CoMFA and CoMSIA approaches. These models show excellent internal predictability and consistency, external validation using test-set 19 compounds yields a good predictive power for antagonistic potency. Statistical parameters of models were obtained with CoMFA-ET(A) (q (2) = 0.787, r (2) = 0.935, r (2) ( pred ) = 0.901), CoMFA-ET(B) (q (2) = 0.842, r (2) = 0.984, r (2) ( pred ) = 0.941), CoMSIA-ET(A) (q (2) = 0.762, r (2) = 0.971, r (2) ( pred ) = 0.958) and CoMSIA-ET(B) (q (2) = 0.771, r (2) = 0.974, r (2) ( pred ) = 0.953) respectively. Field contour maps (CoMFA and CoMSIA) corresponding to the ET(A) and ET(B) subtypes reflects the characteristic similarities and differences between these types. The results of this paper provide valuable information to facilitate structural modifications of the title compounds to increase the inhibitory potency and subtype selectivity of endothelin receptor.

Connexins as therapeutic targets in lung disease

INTRODUCTION

The lung is a mechanically active system exposed to the external environment and is particularly sensitive to injury and inflammation. Studies have identified intercellular communication pathways that promote proper lung function in response to injury and disease. These pathways involve connexins (Cxs) and gap junctional intercellular communication (GJIC).

AREAS COVERED IN THIS REVIEW

The functional expression of Cxs in airway epithelium and vasculature, under normal and pathological conditions, is reviewed. Inhibition of GJIC and/or silencing of Cxs have been shown to modulate the course of disease development. Cx-based channels: i) coordinate ciliary beating and fluid transport to promote clearance of particulates, ii) regulate secretion of pulmonary surfactant, in response to deep inhalation by interconnecting type I and type II alveolar epithelial cells, and iii) are key mediators of pro- and anti-inflammatory signalling by the pulmonary endothelium, in order to modulate leukocyte recruitment from the circulation.

EXPERT OPINION

Cx-based channels play several central roles in promoting a regulated inflammatory response and facilitating lung repair, thus enabling the pulmonary epithelium and vasculature to behave as integrated systems. Several pathologies can disrupt the normal communication pathways required for proper lung function, including acute lung injury, asthma, cystic fibrosis, pulmonary fibrosis and cancer.

Peptide-directed highly selective targeting of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary vasculature associated with elevated pulmonary vascular resistance. Despite recent advances in the treatment of PAH, with eight approved clinical therapies and additional therapies undergoing clinical trials, PAH remains a serious life-threatening condition. The lack of pulmonary vascular selectivity and associated systemic adverse effects of these therapies remain the main obstacles to successful treatment. Peptide-mediated drug delivery that specifically targets the vasculature of PAH lungs may offer a solution to the lack of drug selectivity. Herein, we show highly selective targeting of rat PAH lesions by a novel cyclic peptide, CARSKNKDC (CAR). Intravenous administration of CAR peptide resulted in intense accumulation of the peptide in monocrotaline-induced and SU5416/hypoxia-induced hypertensive lungs but not in healthy lungs or other organs of PAH rats. CAR homed to all layers of remodeled pulmonary arteries, ie, endothelium, neointima, medial smooth muscle, and adventitia, in the hypertensive lungs. CAR also homed to capillary vessels and accumulated in the interstitial space of the PAH lungs, manifesting its extravasation activity. These results demonstrated the remarkable ability of CAR to selectively target PAH lung vasculature and effectively penetrate and spread throughout the diseased lung tissue. These results suggest the clinical utility of CAR in the targeted delivery of therapeutic compounds and imaging probes to PAH lungs.