First acute haemodynamic study of soluble guanylate cyclase stimulator riociguat in pulmonary hypertension

Pulmonary hypertension (PH) is associated with impaired production of the vasodilator nitric oxide (NO). Riociguat (BAY 63-2521; Bayer Healthcare AG, Wuppertal, Germany) acts directly on soluble guanylate cyclase, stimulating the enzyme and increasing sensitivity to low NO levels. The present study evaluates riociguat safety, tolerability and efficacy in patients with moderate-to-severe PH (pulmonary arterial hypertension, distal chronic thromboembolic PH or PH with mild to moderate interstitial lung disease). The optimal tolerated dose was identified by incremental dosing in four patients with PH; pharmacodynamic and pharmacokinetic parameters were assessed following single-dose administration (2.5 mg or 1 mg) in 10 and five patients with PH, respectively. All subjects (n = 19) were analysed for safety and tolerability. Riociguat had a favourable safety profile at single doses < or =2.5 mg. It significantly improved pulmonary haemodynamic parameters and cardiac index in patients with PH in a dose-dependent manner, to a greater extent than inhaled NO. Although riociguat also had significant systemic effects and showed no pulmonary selectivity, mean systolic blood pressure remained >110 mmHg. The present report is the first to describe the use of riociguat in patients with pulmonary hypertension. The drug was well-tolerated and superior to nitric oxide in efficacy and duration. Riociguat, therefore, has potential as a novel therapy for pulmonary hypertension and warrants further investigation.

Inhibition of phosphodiesterase 4 enhances lung alveolarisation in neonatal mice exposed to hyperoxia

Bronchopulmonary dysplasia (BPD) is characterised by impaired alveolarisation, inflammation and aberrant vascular development. Phosphodiesterase (PDE) inhibitors can influence cell proliferation, antagonise inflammation and restore vascular development and homeostasis, suggesting a therapeutic potential in BPD. The aim of the present study was to investigate PDE expression in the lung of hyperoxia-exposed mice, and to assess the viability of PDE4 as a therapeutic target in BPD. Newborn C57BL/6N mice were exposed to normoxia or 85% oxygen for 28 days. Animal growth and dynamic respiratory compliance were reduced in animals exposed to hyperoxia, paralleled by decreased septation, airspace enlargement and increased septal wall thickness. Changes were evident after 14 days and were more pronounced after 28 days of hyperoxic exposure. At the mRNA level, PDE1A and PDE4A were upregulated while PDE5A was downregulated under hyperoxia. Immunoblotting confirmed these trends in PDE4A and PDE5A at the protein expression level. Treatment with cilomilast (PDE4 inhibitor, 5 mg.kg(-1).day(-1)) between days 14 and 28 significantly decreased the mean intra-alveolar distance, septal wall thickness and total airspace area and improved dynamic lung compliance. Pharmacological inhibition of phosphodiesterase improved lung alveolarisation in hyperoxia-induced bronchopulmonary dysplasia, and thus may offer a new therapeutic modality in the clinical management of bronchopulmonary dysplasia.

Phosphodiesterase inhibitors for the treatment of pulmonary hypertension

The pulmonary vascular bed is both a source of and target for a number of vasoactive factors. Among the most important for pulmonary vascular homeostasis are factors that utilise cyclic guanosine monophosphate (cGMP) as an intracellular second messenger. These include nitric oxide and the natriuretic peptide family (atrial, brain and C-type natriuretic peptides). In the search for therapeutic strategies that engage the cGMP signalling pathway for the treatment of pulmonary arterial hypertension (PAH), inhibition of cGMP metabolism by phosphodiesterase type 5 (PDE5)-targeted compounds has proven most successful to date. One PDE5 inhibitor, sildenafil, has been shown to improve pulmonary haemodynamics and exercise capacity in patients with PAH and is now an approved treatment. Others are under investigation. An interesting, although still tentative, observation is the potential of sildenafil to reduce pulmonary vascular resistance without adversely affecting ventilation-perfusion matching. Another is the expression of phosphodiesterase type 5 in the hypertrophied right ventricle. These data suggest that phosphodiesterase type 5 inhibitors may have effects that distinguish them from other treatments for pulmonary hypertension and merit further study.

Intravenous injection of siRNA directed against hypoxia-inducible factors prolongs survival in a Lewis lung carcinoma cancer model

Different routes for the in vivo administration of synthetic siRNA complexes targeting lung tumors were compared, and siRNA complexes were administered for the inhibition of hypoxia-inducible factor (HIF-1alpha and HIF-2alpha). Intravenous jugular vein injection of siRNA proved to be the most effective means of targeting lung tumor tissue in the Lewis lung carcinoma (LLC1) model. In comparison, intraperitoneal injection of siRNA was not suitable for targeting of lung tumor and intratracheal administration of siRNA exclusively targeted macrophages. Inhibition of HIF-1alpha and HIF-2alpha by siRNA injected intravenously was validated by immunohistofluorescent analysis for glucose-transporter-1 (GLUT-1), a well-established HIF target protein. The GLUT-1 signal was strongly attenuated in the lung tumors of mice treated with siRNA-targeting HIF-1alpha and HIF-2alpha, compared with mice treated with control siRNA. Interestingly, injection of siRNA directed against HIF-1alpha and HIF-2alpha into LLC1 lung tumor-bearing mice resulted in prolonged survival. Immunohistological analysis of the lung tumors from mice treated with siRNA directed against HIF-1alpha and HIF-2alpha displayed reduced proliferation, angiogenesis and apoptosis, cellular responses, which are known to be affected by HIF. In conclusion, intravenous jugular vein injection of siRNA strongly targets the lung tumor and is effective in gene inhibition as demonstrated for HIF-1alpha and HIF-2alpha.