Mosliciguat [INN]

Mosliciguat is an inhaled, once-daily soluble guanylate cyclase (sGC) activator that Pulmovant, a subsidiary of Roivant Sciences (ROIV), is developing for pulmonary hypertension associated with interstitial lung disease (PH-ILD). The lead Phase 2 trial PHocus (NCT06635850) enrolled approximately 120 patients (below its original 135-patient target) against placebo, with change in pulmonary vascular resistance at week 16 as the primary endpoint; enrollment completed in February 2026 with topline guided to H2 2026 [1][9]. The program's thesis rests on two independent bets. First, delivering an sGC-activating molecule by inhalation targets ventilated lung regions and avoids the systemic vasodilation that killed the class in this indication when given orally. Riociguat, an approved oral sGC stimulator, was tested in idiopathic interstitial pneumonia-associated PH in the RISE-IIP trial and stopped early for excess mortality and serious adverse events [2]. Second, mosliciguat is an activator, not a stimulator: it binds oxidized, heme-free sGC directly and works independently of nitric oxide, which is exactly the enzyme state that predominates in the oxidatively stressed pulmonary vasculature of ILD. Phase 1b ATMOS proof-of-concept in PAH and CTEPH patients showed mean peak PVR reductions of up to 38% after a single inhaled dose, one of the largest acute hemodynamic effects reported in PH [10]. The molecule was licensed out of Bayer (originally BAY 1237592). A separate Phase 2 PHactor study (NCT07333183) is testing mosliciguat added on to inhaled treprostinil, currently the only drug approved for PH-ILD following the INCREASE trial [3][4]. Japan granted orphan drug designation in 2025; no FDA breakthrough or fast track designation has been publicly disclosed [11].

Novel compound, first-in-class inhaled sGC activator, currently Phase 2. Mosliciguat was originally developed at Bayer as BAY 1237592 before Pulmovant in-licensed the program; the specific milestone and royalty economics owed back to Bayer have not been publicly disclosed. Phase 1 work in healthy volunteers characterized inhaled pharmacokinetics and lung deposition (Saleh et al., Clin Pharmacokinet 2025), showing pulmonary exposure with limited systemic levels [5]. The Phase 1b ATMOS study, an open-label, dose-escalation, single-dose study in patients with WHO Group 1 PAH and Group 4 CTEPH, reported a mean peak PVR reduction of up to 38% after a single inhaled dose. This is the most concrete efficacy signal for the program in the public record and is a strong positive prior that the current PoS model does not capture [10]. The key Phase 2 PHocus trial (NCT06635850) in PH-ILD is active, not recruiting; Pulmovant announced completion of enrollment on 2026-02-06 with approximately 120 patients (original target 135), completed in under 12 months from first patient dosed. Topline is officially guided to H2 2026 [1][9]. A second Phase 2 study, PHactor (NCT07333183), is recruiting up to 20 patients to test mosliciguat on top of inhaled treprostinil, the only FDA-approved therapy for PH-ILD [3]. A Phase 1 absolute bioavailability study using an IV [14C]-microtracer completed with n=8 (NCT07185321) [6]. Dosing is one puff once daily via dry powder inhaler, a material patient-burden advantage over inhaled treprostinil, which requires multiple puffs several times per day [9]. Japan granted orphan drug designation for PH-ILD in 2025 [11]; no FDA breakthrough therapy, fast track, or orphan designation has been publicly disclosed. If PHocus is positive on PVR, Pulmovant would still need a Phase 3 trial with a functional or clinical worsening endpoint before approval. Roivant retains a majority stake in Pulmovant and would capture the equity value of a positive readout.

Soluble guanylate cyclase (sGC) is an enzyme inside vascular smooth muscle cells that makes cyclic GMP (cGMP), a small signaling molecule that tells the muscle to relax. When a blood vessel relaxes, it widens, local pressure drops, and blood flow improves. Normally nitric oxide (NO) binds to a reduced (Fe2+) heme group inside sGC, which triggers cGMP production. In pulmonary hypertension, NO signaling is broken: endothelial cells lining pulmonary vessels stop making enough NO, sGC sits idle, cGMP falls, and pulmonary arteries stay constricted. Chronic constriction plus vascular remodeling drives right heart failure. There are two distinct pharmacological approaches to fixing this: sGC stimulators and sGC activators. They are commonly confused but mechanistically different, and the difference is central to the mosliciguat thesis. sGC stimulators (riociguat, vericiguat) bind sGC that still has an intact, reduced heme. They amplify NO signaling and produce cGMP synergistically with NO. If heme is oxidized or lost, stimulators lose activity. sGC activators (mosliciguat, cinaciguat) bind the oxidized (Fe3+) or heme-free form of sGC and turn it on directly, independently of NO. In healthy tissue, most sGC is in the reduced, heme-containing state, so stimulators dominate. In diseased pulmonary vasculature, chronic inflammation and oxidative stress push a substantial fraction of sGC into the oxidized or apo (heme-free) state. Stimulators cannot bind that pool. Activators can. This gives activators a theoretical pharmacological advantage in exactly the disease microenvironment being targeted, on top of any advantage from inhaled delivery [12]. Riociguat has been approved for chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension since 2013 (Adempas, Bayer/Merck) [8], and vericiguat is approved for heart failure with reduced ejection fraction, so the target is well-validated broadly, but no activator has ever been approved. Cinaciguat, the first activator, was abandoned in acute decompensated heart failure for excessive hypotension when dosed intravenously. Inhaled mosliciguat is meant to preserve the activator's mechanistic advantage while confining exposure to the lung. The second axis of differentiation is anatomical. In ILD, some lung regions are scarred and no longer participate in gas exchange. Systemic pulmonary vasodilators (oral sGC stimulators, endothelin antagonists, PDE5 inhibitors) dilate vessels in both healthy and scarred regions, sometimes shunting blood into non-ventilated tissue. That worsens ventilation-perfusion matching and drops oxygen saturation. Inhaled delivery targets ventilated regions preferentially, matching perfusion to ventilation instead of scrambling it. Whether both advantages (activator mechanism plus inhaled delivery) hold up in real ILD lungs with distorted airway geometry is the open clinical question.

PHocus (NCT06635850) is a randomized, double-blind, placebo-controlled Phase 2 with approximately 120 PH-ILD patients enrolled (original target 135). Primary endpoint is change from baseline in pulmonary vascular resistance (PVR) at week 16, measured by right heart catheterization [1]. PVR directly quantifies how hard the right ventricle has to work to pump blood through the lungs, so it is a mechanistically clean hemodynamic surrogate. Regulators have accepted PVR change as a Phase 2 signal for PH programs, but Phase 3 typically requires a functional endpoint like six-minute walk distance, time to clinical worsening, or exercise capacity via cardiopulmonary exercise testing. The trial is active, not recruiting, meaning enrollment is complete and patients are on treatment [9]. Strengths of the design: it uses invasive hemodynamics rather than a soft functional readout at Phase 2, and the placebo control is appropriate given that inhaled treprostinil is the only approved therapy and add-on studies are being handled separately in PHactor. Weaknesses: ~120 patients is modest for a heterogeneous population, and coming in below the 135 target may erode statistical power modestly depending on the pre-specified assumptions. PH-ILD etiology can be idiopathic pulmonary fibrosis, connective tissue disease-associated ILD, chronic hypersensitivity pneumonitis, or other patterns, and each has different vascular biology. The proportional breakdown of ILD subtypes in the enrolled cohort has not been publicly disclosed and will materially affect interpretability; investors should look for that stratification in the topline release. Pre-specified subgroup analyses that isolate patients most likely to benefit anatomically are not visible in the public listing. PHactor (NCT07333183, n=20) tests add-on to inhaled treprostinil with safety and tolerability as the primary endpoint, effectively de-risking the combination positioning before a Phase 3 decision [3].

Our model estimates a 3% chance this drug is eventually approved. It starts from the historical base rate for Phase 2 drugs in this area (about 24%), then adjusts using ten facts about the trial and sponsor. What moves the number most: it is held back by heavier-than-usual blinding, the sponsor's thin or weak approval record, weak or limited earlier-phase results, and a randomized design. The other facts land near average for this stage, so they leave the estimate roughly where the base rate put it.

Efficacy risk is anchored on the RISE-IIP precedent: same enzyme family (though a different subclass), same disease space, terminated for harm [2]. Mosliciguat's program is a rebet that both route of administration and activator mechanism flip the risk-benefit. If inhaled dosing still produces meaningful systemic absorption, the V/Q mismatch problem could resurface as PVR-lowering that comes with oxygen desaturation. The Phase 1 lung deposition and PK data support pulmonary exposure with modest systemic levels [5], but healthy volunteers are not ILD patients whose distorted alveolar architecture changes deposition patterns. The Phase 1b ATMOS single-dose PVR data in PAH and CTEPH patients is a meaningful positive prior, but those patients do not have the parenchymal disease that drives V/Q concerns in PH-ILD [10]. Safety risk also includes syncope and hypotension, which are class effects of sGC modulators; the sole prior sGC activator (cinaciguat) was abandoned in acute heart failure for hypotension when given intravenously, so systemic exposure matters. Pharmacodynamic interaction with PDE5 inhibitors is contraindicated for riociguat [8], and while the labeling risk for an inhaled activator is unclear, patients on background sildenafil or tadalafil (common in PH management) may need washout, complicating enrollment and real-world uptake. Execution risk: PHocus is fully enrolled, so recruitment risk is behind them, though enrollment landed at ~120 vs. the 135 target. The open question is whether a ~120-patient Phase 2 with a hemodynamic endpoint gives a clean enough signal to trigger Roivant to fund a Phase 3. Commercial risk: inhaled treprostinil (Tyvaso, United Therapeutics) is the incumbent, added to the PH-ILD label after INCREASE in 2021 [4]. A new entrant either needs to beat inhaled treprostinil head-to-head (unlikely in a first key) or show clean add-on benefit. Pulmovant is hedging with PHactor, testing the combination directly [3]. Payers will not embrace a second inhaled PH therapy without clear differentiation on oxygenation, exercise capacity, or mortality. Mosliciguat's once-daily single-puff DPI regimen versus Tyvaso's multiple-puffs-QID nebulized regimen is a real patient-burden differentiator that could support uptake even at parity efficacy [9].

Worth watching, and the mechanistic story is stronger than a base-rate reading suggests once the stimulator/activator distinction and the Phase 1b ATMOS data are folded in. The RISE-IIP shadow still sits over the program, but it is a less direct read-across than it first appears. The specific data point that separates signal from noise is the pairing of PVR change and arterial oxygen saturation (SpO2, measured by pulse oximetry) in the PHocus Phase 2 readout, along with the ILD subtype breakdown of the enrolled cohort. A statistically significant PVR drop with stable or improved SpO2 would be a genuine advance for PH-ILD and would justify Phase 3 investment. A PVR drop with oxygen desaturation replays the riociguat story and likely ends the program. A flat readout on both is a soft failure that Roivant could spin, but investors should not. Market context: United Therapeutics' Tyvaso generated approximately $800M in annualized PH-ILD revenue following the INCREASE label expansion in 2021, establishing a commercially validated market ceiling. A new entrant capturing even 20-30% of that opportunity, whether on a differentiated once-daily monotherapy label or as add-on to Tyvaso, represents a material asset. Pulmovant is a Roivant subsidiary, so the value of a positive readout flows through Roivant public equity (ROIV) [7]. Roivant has a pattern of building single-asset vants and monetizing through partnership, subsidiary IPO, or reverse merger. Check back H2 2026 for the PHocus topline per Pulmovant's guidance [9]. In parallel, watch the inhaled treprostinil combination data from PHactor (NCT07333183), which reports safety and tolerability on a much smaller sample and will land earlier [3]. If the combination is well-tolerated, Roivant has an easier commercial story regardless of whether mosliciguat wins on monotherapy: add-on to the standard of care rather than displacement of it. This is not investment advice.