Mosliciguat's Phase 2 PVR Signal Is Real — But Phase 3 and Mechanism Gaps Define the Bet

Roivant's Mosliciguat Shows Remarkable Efficacy in PH-ILD Phase 2 PHocus Study

Roivant announced positive results from its Phase 2 PHocus clinical trial evaluating mosliciguat for pulmonary hypertension associated with interstitial lung disease (PH-ILD). The study successfully met its primary endpoint, demonstrating a clinically meaningful and statistically significant placebo-adjusted reduction in pulmonary vascular resistance (PVR) of -56.3% at Week 16. Additionally, key secondary endpoints showed significant improvements, including a +35.2-meter increase in six-minute walk distance (6MWD) and a -53.2% reduction in the cardiac biomarker NT-proBNP. Exploratory Week 24 results further indicated sustained and strengthened treatment effects. Mosliciguat was observed to be well tolerated with a favorable safety profile, notably presenting a lower incidence of cough compared to placebo. Following these encouraging findings, Roivant has initiated the Phase 3 PHrontier study for mosliciguat in PH-ILD.

• The PHocus study achieved its primary endpoint with a remarkable -56.3% placebo-adjusted reduction in pulmonary vascular resistance (PVR) at Week 16 (p<0.0001), marking the highest PVR reduction reported in any randomized controlled PH trial. Additionally, secondary endpoints showed clinically meaningful improvements, including a +35.2-meter increase in six-minute walk distance (6MWD, p=0.0027) and a -53.2% reduction in the cardiac biomarker NT-proBNP (p=0.0002) at Week 16.
• Pre-specified exploratory analyses at Week 24 demonstrated continued strengthening of treatment effects, with 6MWD improving to +52.7 meters (nominal p<0.0001) and NT-proBNP reducing by -75.9% (nominal p<0.0001). Mosliciguat exhibited a favorable safety profile, being well tolerated with adverse events consistent with PH-ILD. Notably, the incidence of cough, a common issue with inhaled prostacyclins, was lower in the mosliciguat group (12.1%) compared to placebo (18.2%).
• Mosliciguat is a potential first-in-class, once-daily, inhaled sGC activator designed for targeted pulmonary vasodilation. Its differentiated mechanism of action, activating sGC independently of NO/heme status, positions it to address oxidative-stress-associated diseases like PH-ILD where native sGC function is impaired. These results support mosliciguat's potential to fill a significant treatment gap for PH-ILD patients, a population with high mortality and limited approved options.
• Building on the robust Phase 2 PHocus results, Roivant has initiated the Phase 3 PHrontier clinical trial for mosliciguat in PH-ILD. This rapid progression underscores the company's commitment to expedite the development of mosliciguat, aiming to bring this potential single-agent or combination therapy to patients battling this severe and life-threatening condition, which currently has sparse treatment options.

Addressing the Significant Unmet Needs in PH-ILD Treatment

PH-ILD represents one of the most therapeutically challenging intersections in pulmonary medicine, where the complexity of concurrent vascular and parenchymal disease has consistently undermined the efficacy of standard PAH-directed strategies. Investigations of targeted WHO Group 1 PAH therapies have largely failed to improve functional capacity, hemodynamics, oxygenation, quality of life, or survival in PH-ILD, underscoring a substantial unmet need in this population.

• Failure of conventional PAH-targeted therapies in PH-ILD: Therapeutic agents developed to combat vascular remodeling in WHO Group 1 PAH have not translated into meaningful clinical benefit when applied to PH-ILD, with no demonstrated improvements across functional, hemodynamic, or survival endpoints in this distinct patient group.

• V/Q mismatch as a dose-limiting barrier to systemic prostacyclin therapy: In patients with concurrent interstitial lung disease, escalation of intravenous prostacyclin analogues such as epoprostenol is constrained by the development of severe ventilation-perfusion (V/Q) mismatch. As illustrated in a reported case of systemic sclerosis-associated pulmonary hypertension complicated by ILD, efforts to escalate epoprostenol dose were limited by the development of severe V/Q mismatch, precluding further dose increases.

• Impaired hypoxic pulmonary vasoconstriction compounding perfusion dysregulation: In conditions involving diffuse alveolar damage and atelectasis — features shared with severe pulmonary inflammation — inadequate perfusion of hypoventilated areas is a primary driver of hypoxaemia. High perfusion in relation to ventilation (V/Q <1) and shunting (V/Q = 0) is not only caused by impaired hypoxic pulmonary vasoconstriction but also redistribution of perfusion from obstructed lung vessels, making rebalancing of pulmonary vascular tone a therapeutic challenge.

• Limited evidence base and need for larger cohort studies: The combination of inhaled treprostinil with intravenous epoprostenol has shown promise in individual cases of SSc-PH with ILD, but further investigation is warranted to establish the efficacy and feasibility of this combination therapy in larger cohorts of patients with SSc-PH and associated ILD, reflecting the broader evidentiary gap in PH-ILD management.

• Inhaled treprostinil as the sole agent with demonstrated benefit: In contrast to the broader failure of PAH-targeted therapies in PH-ILD, inhaled treprostinil demonstrated efficacy in the INCREASE Trial — a placebo-controlled study in which patients treated with inhaled treprostinil showed a 31-meter placebo-corrected improvement in the primary endpoint, 6-minute walk distance — positioning it as a narrow but meaningful exception within an otherwise limited therapeutic landscape.

Mosliciguat's Positive Phase 2 PHocus Study Outcomes

Two pivotal studies stand out in the recent PH-ILD evidence base. The INCREASE Trial evaluated inhaled treprostinil in patients with group 3 pulmonary hypertension associated with interstitial lung disease. On the efficacy side, patients receiving inhaled treprostinil demonstrated a 31-meter placebo-corrected improvement in the primary endpoint of 6-minute walk distance. Treatment was also associated with improvement in time to clinical worsening, fewer exacerbations of underlying lung disease, a decrease in N-terminal pro-B-type natriuretic protein (NT-proBNP) levels, and improvement in forced vital capacity compared to placebo. These favorable significant changes in 6-minute walk distance, NT-proBNP level, clinical worsening events, and forced vital capacity were maintained in the open-label extension study.

A second area of investigation highlighted in the literature involves a placebo-controlled pilot trial using escalated doses of inhaled nitric oxide in ILD-PH patients, which yielded promising results. Beyond these interventional studies, the broader regulatory and clinical context has evolved: inhaled treprostinil solution and a newer formulation — treprostinil dry powder inhaler — have both received FDA approval for group 3 PH-ILD, with the dry powder formulation's approval supported by the BREEZE study for both group 1 pulmonary arterial hypertension and group 3 PH-ILD. The BREEZE study is referenced in the literature as the basis for this approval, though granular efficacy and safety outcome data from BREEZE are not detailed beyond its role in supporting the regulatory decision.

The knowledge base does not have sufficient information on this aspect.

The Differentiated sGC Activator MoA and Future Potential

The sGC activator mechanism of action — which enables NO-independent activation of the oxidised, heme-free form of sGC to restore cGMP signalling under conditions of oxidative stress and hypoxia — is being explored across several indications beyond PH-ILD. The trials below reflect the breadth of therapeutic areas where this pharmacological principle is under active clinical investigation.

The knowledge base does not have sufficient information on this aspect.

The available literature does address the broader sGC activator class across multiple indications, summarised below:

The knowledge base does not have sufficient information on this aspect. regarding mosliciguat specifically — the drug is not named in the available literature, and the trial details and intervention models above pertain to the sGC activator class more broadly rather than to mosliciguat as a named compound.

Mosliciguat's Potential in the PH-ILD Treatment Landscape

Inhaled treprostinil stands as the only approved therapy for PH-ILD and has demonstrated consistent hemodynamic and functional benefits across multiple study designs. In a multicenter, non-randomized, open-label, single-arm trial of Japanese patients with PH-ILD, inhaled treprostinil administered at 3 breaths (18 μg)/session four times daily — titrated to a maximum of 12 breaths (72 μg)/session — produced a -40.1% change in pulmonary vascular resistance index (95% CI, -53.1 to -27.2) and a 13.0 m increase in peak 6-minute walking distance (95% CI, -15.0 to 49.0) from baseline to week 16. A broader meta-analysis of six randomized controlled trials (791 patients total) confirmed that PAH-specific therapy significantly improved 6-minute walking distance versus placebo (mean difference 23.09 m; 95% CI, 12.07–34.12; P < 0.0001), but when the inhaled treprostinil study was excluded, this improvement was no longer statistically significant (MD 11.01, 95% CI -6.43–28.46; P = 0.22), underscoring that the aggregate benefit of PAH-specific therapy in PH-ILD is driven predominantly by inhaled treprostinil. No significant improvements in lung function, hemodynamic parameters, clinical worsening, all-cause death, or serious adverse effects were observed across the remaining PAH-specific therapies compared to placebo.

Beyond the approved inhaled route, oral PAH-targeted therapy has also been evaluated retrospectively. In a registry-based analysis of 37 PH-ILD patients — 27 (73%) receiving monotherapy and 9 (24%) receiving dual therapy — treatment was associated with a statistically significant decrease in pulmonary vascular resistance (8 vs. 5 Wood units; P < 0.001), an increase in cardiac output (4 vs. 5 L/min; P = 0.014), and a reduction in NT-proBNP levels (1,421 vs. 842 ng/dL; P = 0.045). Separately, a retrospective study of six patients with severe PH-ILD demonstrated that rapid inpatient uptitration of inhaled treprostinil — starting at 3 breaths four times daily and increasing by 2 additional breaths every 12–24 hours — achieved target dosing in all six patients without dose reduction or interruption. At three-month follow-up, mean pulmonary artery pressure decreased from 42 ± 5.5 to 35.2 ± 4.5 mmHg, pulmonary vascular resistance from 8.0 ± 1.2 to 6.0 ± 0.9 Wood units, and cardiac index increased from 2.05 ± 0.13 to 2.15 ± 0.12 L/min/m², with no readmissions within 90 days.

In the context of acute exacerbations of ILD (AE-ILD), antifibrotic therapy — specifically nintedanib — has emerged as a potentially meaningful adjunct to standard corticosteroid-based care. A systematic review of four observational studies comprising 6,321 patients found that nintedanib was associated with significantly reduced in-hospital mortality (7.1% vs. 15.1%; P < 0.001) and shorter hospitalization duration (30.7 ± 13.7 vs. 37.5 ± 19.0 days; P < 0.001) in one large study (n = 6,235), and lower 90-day mortality (36.36% vs. 54.55%; P = 0.048) with delayed time to subsequent exacerbations in a second study. Pirfenidone showed trends toward improved 90-day survival that did not reach statistical significance (64.3% vs. 52.9%, P = 0.72; 44% vs. 34%, P = 0.391). The knowledge base does not have sufficient information on this aspect regarding how a specific investigational agent such as mosliciguat compares within this treatment landscape.

Inhaled Mosliciguat: A Targeted Advance for PH-ILD

Pulmonary hypertension associated with interstitial lung disease (PH-ILD) remains a devastating condition, characterized by a poor prognosis and significant unmet medical need. Current therapeutic strategies often focus on managing the underlying lung disease, with limited targeted options for the pulmonary vascular component. The recent positive Phase 2 results for mosliciguat, an inhaled soluble guanylate cyclase (sGC) activator, offer a beacon of hope for this challenging patient population.

Mosliciguat's mechanism of action, by directly activating sGC, leverages the nitric oxide-sGC-cGMP pathway to promote vasodilation and inhibit vascular remodeling, which are critical in mitigating the progression of pulmonary hypertension. What makes mosliciguat particularly compelling is its inhaled delivery, designed to provide targeted drug exposure to the pulmonary vasculature while minimizing systemic side effects. This approach appears to be bearing fruit, with the Phase 2 PHocus trial demonstrating a significant reduction in pulmonary vascular resistance (PVR), a key hemodynamic endpoint, alongside meaningful improvements in six-minute walk distance (6MWD) and the cardiac biomarker NT-proBNP. Furthermore, the drug exhibited a favorable safety profile, notably with a lower incidence of cough compared to placebo, which could be a significant advantage for patients already suffering from respiratory compromise.

However, the path forward is not without its challenges. While the Phase 2 data are robust, the larger and longer Phase 3 PHrontier study will be critical in confirming these benefits and establishing long-term safety. Mosliciguat will also need to differentiate itself from existing systemic sGC stimulators, such as riociguat, which is already approved for PH-ILD. The inhaled route and potentially superior tolerability could be key differentiators, but sustained clinical benefit and a clear safety advantage will be paramount for widespread adoption. If successful, mosliciguat could redefine the treatment landscape for PH-ILD, offering a targeted, effective, and well-tolerated option for patients in desperate need.