Sitaxsentan: an endothelin-A receptor antagonist for the treatment of pulmonary arterial hypertension

Comparative efficacy and acceptability of endothelin receptor antagonists for pulmonary arterial hypertension: A network meta-analysis

BACKGROUND

Endothelin receptor antagonists (ERAs) such as ambrisentan, sitaxsentan, bosentan and macitentan are primary drug therapies for pulmonary arterial hypertension (PAH) patients. However, the optimal drugs for PAH remained controversial due to heterogeneous nature of randomized control trials (RCTs).

METHODS

Apart from traditional meta-analysis, network meta-analysis (NMA) was performed in this study for multiple comparisons among PAH therapies. The 6 minute walking distance (6MWD) and clinical worsening were efficacy outcomes whereas serious adverse effects (SAE) and all-cause discontinuation were acceptability outcomes. The weighted mean difference (WMD) and odds ratio (OR) along with their 95% confidence interval (95% CI) or 95% credible interval (95% CrI) were used to evaluate the positive and negative effects of these therapies on PAH patients.

RESULTS

By synthesizing direct evidence from 10 studies with a total number of 2172 patients, we discovered that all of the four PAH therapies significantly increased the average 6MWD in comparison to the placebo (P-value<0.05). Moreover, bosentan and ambrisentan both showed significant association with a decrease in the risk of clinical worsening compared to placebo. Regarding of all-cause discontinuation, ambrisentan is the only therapy which was significantly associated with a risk decrease compared to placebo. However, there was no sufficient evidence suggesting significant difference in any efficacy or acceptability outcomes between any two of the PAH therapies (P-value>0.05).

CONCLUSION

Ambrisentan could be considered as the most appropriate therapy among the four ERAs for PAH patients. Bosentan also behaved well, but it is not as safe as ambrisentan.

Sitaxsentan for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening, progressive condition that eventually leads to right heart failure. Endothelin receptor antagonists (ETRAs) have been shown to be a safe and efficacious treatment for PAH. Sitaxsentan is a highly selective oral ETRA that, in clinical trials, has demonstrated significant improvements in exercise capacity, functional class and pulmonary hemodynamics in PAH. Sitaxsentan has been shown to be a well tolerated and effective agent with a durable response for the treatment of PAH, and is associated with a low incidence of liver toxicity.

Endothelin-A receptor inhibition after cardiopulmonary bypass: cytokines and receptor activation

BACKGROUND

Basic studies have suggested that cross-talk exists between the endothelin-A receptor (ET-AR) and tumor necrosis factor signaling pathway. This study tested the hypothesis that administration of an ET-AR antagonist at the separation from cardiopulmonary bypass would alter the tumor necrosis factor activation in the early postoperative period.

METHODS

Patients (n = 44) were randomly allocated to receive bolus infusion of vehicle, 0.1, 0.5, 1, or 2 mg/kg of the ET-AR antagonist (sitaxsentan), at the separation from cardiopulmonary bypass (n = 9, 9, 9, 9, and 8, respectively). Plasma levels of tumor necrosis factor-alpha and soluble tumor necrosis factor receptor 1 and 2 were measured.

RESULTS

Compared with the vehicle group at 24 hours, plasma levels of tumor necrosis factor-alpha and tumor necrosis factor receptor 2 (indicative of receptor activation) were reduced in the 1 mg/kg ET-AR antagonist group (by approximately 13 pg/mL and approximately 0.5 ng/mL, respectively; p < 0.05). Plasma tumor necrosis factor receptor I levels also decreased (by approximately 1 ng/mL) after infusion of the higher doses of the ET-AR antagonist and remained lower (by approximately 3 ng/mL) at 24 hours after infusion (p < 0.05). In addition, a dose effect was observed between the ET-AR antagonist and these indices of tumor necrosis factor activation (p < 0.01).

CONCLUSIONS

This study demonstrated a mechanistic relationship between the ET-AR and tumor necrosis factor receptor activation in the post-cardiac surgery period. Thus, in addition to the potential cardiovascular effects, a selective ET-AR antagonist can modify other biological processes relevant to the post-cardiac surgery setting.

Control of pulmonary vascular tone during exercise in health and pulmonary hypertension

Despite the importance of the pulmonary circulation as a determinant of exercise capacity in health and disease, studies into the regulation of pulmonary vascular tone in the healthy lung during exercise are scarce. This review describes the current knowledge of the role of various endogenous vasoactive mechanisms in the control of pulmonary vascular tone at rest and during exercise. Recent studies demonstrate an important role for endothelial factors (NO and endothelin) and neurohumoral factors (noradrenaline, acetylcholine). Moreover, there is evidence that natriuretic peptides, reactive oxygen species and phosphodiesterase activity can influence resting pulmonary vascular tone, but their role in the control of pulmonary vascular tone during exercise remains to be determined. K-channels are purported end-effectors in control of pulmonary vascular tone. However, K(ATP) channels do not contribute to regulation of pulmonary vascular tone, while the role of K(V) and K(Ca) channels at rest and during exercise remains to be determined. Pulmonary hypertension is associated with alterations in pulmonary vascular function and structure, resulting in blunted pulmonary vasodilatation during exercise and impaired exercise capacity. Although there is a paucity of studies pertaining to the regulation of pulmonary vascular tone during exercise in idiopathic pulmonary hypertension, the few studies that have been performed in models of pulmonary hypertension secondary to left ventricular dysfunction suggest altered control of pulmonary vascular tone during exercise. Since the increased pulmonary vascular tone during exercise limits exercise capacity, future studies are needed to investigate the vasomotor mechanisms that are responsible for the blunted exercise-induced pulmonary vasodilatation in pulmonary hypertension.

The pharmacokinetic profile of sitaxsentan, a selective endothelin receptor antagonist, in varying degrees of renal impairment

AIM

To investigate the pharmacokinetic profile of a single 100-mg oral dose of sitaxsentan, a selective endothelin type A receptor antagonist, in subjects with normal and impaired renal function.

METHODS

This was an open label, single oral dose study in subjects with normal [creatinine clearance (CrCL) > or = 80 ml min(-1)] and impaired renal function (mild renal impairment CrCL 51-80 ml min(-1), moderate impairment CrCL 31-50 ml min(-1), severe impairment CrCL < or = 30 ml min(-1)). All subjects received a dose of 100 mg sitaxsentan.

RESULTS

Twenty-four subjects were enrolled, six in each of the normal and three renal impairment groups. The mean plasma sitaxsentan concentrations were comparable across the groups, as were the mean values for C(max) (10.3-13.9 microg ml(-1)), AUC(infinity) (18.7-22.5 h microg(-1) ml(-1)), oral clearance (CL/F, 82.3-94.9 ml min(-1)), volume of distribution (Vz/F, 64.8-69.6 l) and elimination half-life (t(1/2), 8.6-9.6 h). There was substantial overlap among the four groups in the individual subject values for CL/F and Vz/F and no relationship between either of these parameters and CrCL.

CONCLUSION

After a single 100-mg oral dose of sitaxsentan there were no differences in its pharmacokinetics among subjects with normal or impaired renal function.

Selective Endothelin-A Receptor Inhibition After Cardiac Surgery: A Safety and Feasibility Study

BACKGROUND

Increased synthesis and release of the bioactive peptide endothelin has been shown to change hemodynamics and postoperative recovery after cardiac surgery. However, the clinical effects of selective interruption of endothelin signaling have not been studied. Because the endothelin-A (ET-A) receptor subtype is the primary cardiovascular effector for endothelin, this study used the ET-A receptor antagonist sitaxsentan sodium (TBC11251Na) to evaluate: (1) dose-dependent changes in pulmonary artery pressure (PAP) and pulmonary (PVRI) and systemic (SVRI) vascular resistance index in patients undergoing on-pump coronary revascularization; and (2) whether ET-RA administration was associated with increased adverse events.

METHODS

Patients (n = 44, age, 62 +/- 1 years) were randomized to receive vehicle (n = 9) or different bolus infusions of ET-A receptor antagonist: 0.1 (n = 9), 0.5 (n = 9) 1.0 (n = 9), and 2.0 mg/kg (n = 8) at separation from cardiopulmonary bypass (CPB). Adverse events were tabulated until hospital discharge. Results were expressed as changes from a composite baseline value, or from time 0 due to a high degree of intrapatient measurement variability in the postoperative period.

RESULTS

PAP increased by 27% +/- 13% from baseline (19 +/- 1 mm Hg) in the vehicle group at 6 hours post-CPB (p < 0.05). PAP fell from this post-CPB vehicle value in a dose-dependent manner with the ET-A receptor antagonist; with a significant reduction observed at 2 mg/kg (7% +/- 8% increase from baseline, p < 0.05). PVRI was reduced by 28.6% +/- 16% from baseline (249 +/- 22 dyn x s x cm(-5) x m(-2)) in the 2 mg/kg ET-A receptor antagonist group at 30 minutes post-CPB and remained reduced up to 6 hours post-CPB (p < 0.05). SVRI was reduced from baseline (2770 +/- 106 dyn x s x cm(-5) x m(-2)) by 51% +/- 6% in the 2.0 mg/kg ET-A receptor antagonist group at 30 minutes post-CPB (p < 0.05) and remained reduced up to 6 hours post-CPB. A total of 203 adverse events were tabulated in the postoperative period and were equally distributed across the five treatment groups, with no direct attributions to ET-A receptor antagonist treatment.

CONCLUSIONS

This unique study demonstrates that heightened endothelin-A receptor activation contributes to hemodynamic changes in patients after CPB. Selective inhibition of the endothelin receptor system can be successfully and safely performed in patients undergoing cardiac surgery and thereby reveals a potential, and clinically relevant therapeutic target.

Combination therapy and new types of agents for pulmonary arterial hypertension

This review assesses the available evidence supporting the use of drug combinations for the management of the various forms of pulmonary arterial hypertension (PAH). Ongoing and forthcoming randomized trials evaluating this strategy are also highlighted. Furthermore, new types of agents to treat PAH in the future are explored.

Sitaxsentan in the management of pulmonary arterial hypertension

PURPOSE

The pharmacology, pharmacokinetics, clinical trials, adverse effects, drug interactions, and dosing and administration of the endothelin receptor antagonist, sitaxsentan, and its role in the treatment of pulmonary arterial hypertension (PAH) are reviewed.

SUMMARY

PAH is a serious and potentially devastating chronic disorder of the pulmonary circulation. Bosentan is the first and only approved endothelin receptor antagonist for the treatment of PAH. Endothelin-1, a potent endogenous vasoconstrictor and smooth-muscle mitogen, has been shown to be overexpressed in the plasma and lung tissue of patients with PAH; the reduction or blockade of entothelin-1 may aid in disease symptomatology and progression. Activation of ET(A) leads to vasoconstriction and vascular smooth-muscle-cell proliferation. Sitaxsentan is an orally active, organic nonpeptide that binds competitively to the ET(A) receptor. Sitaxsentan, unlike bosentan, has a high affinity for the ET(A) receptor. In one trial, sitaxsentan was compared with placebo, and the results suggested that sitaxsentan was more effective than placebo. A 12-week, open-label trial demonstrated the safety and efficacy of sitaxsentan in 20 patients. The Sitaxsentan to Relieve Impaired Exercise (STRIDE-1) trial randomized patients to receive placebo, sitaxsentan 100 mg orally once daily, or sitaxsentan 300 mg orally once daily. Significant improvements in exercise capacity and cardiopulmonary hemodynamics were demonstrated. The results of STRIDE-2, the second randomized sitaxsentan trial, demonstrated the efficacy and safety of 100 mg sitaxsentan and the unacceptable safety profile of 300 mg sitaxsentan.

CONCLUSION

Sitaxsentan is an orally administered endothelin receptor blocker that offers the effective and safe treatment of patients with mild to moderate PAH.

Sitaxsentan: a selective endothelin-A receptor antagonist, for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive, life-threatening condition. Sitaxsentan, a selective endothelin-A receptor antagonist, is an effective, safe and well-tolerated endothelin receptor antagonist for the treatment of PAH in adult patients. Multi-center, randomized, placebo-controlled clinical trials have demonstrated that sitaxsentan has beneficial effects on exercise capacity (i.e., 6-min walk distance), functional class and hemodynamic parameters in PAH patients. Sitaxsentan has a low incidence of acute hepatotoxicity. Patients on concomitant warfarin require a decrease in warfarin dose to maintain a therapeutic international normalized ratio. The demonstration of clinical efficacy and low incidence of acute hepatotoxicity support the potential use of sitaxsentan for the treatment of PAH.

Effect of sitaxsentan treatment on quality of life in pulmonary arterial hypertension

In recent years new therapeutic options have been developed for the management of pulmonary arterial hypertension (PAH). Sitaxsentan is an oral, once daily, highly selective endothelin A receptor antagonist that recently demonstrated a positive effect on functional capacity and haemodynamics of PAH patients. The aim of this study is to evaluate the effect of sitaxsentan in the quality of life (QOL) of PAH patients. Twenty-three patients with idiopathic PAH or PAH associated to collagen vascular diseases were evaluated at baseline and after 16 weeks of treatment with sitaxsentan 100 mg orally, once daily. 6-min walk test distance (6MWD) and QOL questionnaire (QOLQ) (SF-36) were obtained at baseline and at week 16. There was a significant improvement in functional capacity evaluated by 6MWD (472 m vs. 490 m, p = 0.03) and also in the physical component of the QOLQ (p < 0.01). Evaluating each of the domains of the SF-36 QOLQ, those more related to physical capacity presented a significant increase while the domains related to the mental component presented a trend of improvement, without reaching statistical significance. Sitaxsentan improves QOL in patients with PAH mainly through the domains related to functional capacity.