Inhaled Treprostinil (Tyvaso): TETON-1/2 Results in IPF
UT's Tyvaso (inhaled treprostinil): TETON-2 FVC +95.6mL (p<0.0001), TETON-1 +130.1mL. IP/EP2/PPARγ. FDA sNDA Q3 2026, priority review.
Introduction: How a Prostacyclin Became an Antifibrotic
Inhaled Treprostinil (Tyvaso®, United Therapeutics) was originally approved for pulmonary arterial hypertension (PAH, WHO Group 1) and pulmonary hypertension associated with interstitial lung disease (PH-ILD, WHO Group 3). In 2025-2026, however, the back-to-back Phase 3 readouts of TETON-2 and TETON-1 established something unprecedented: a pulmonary vasodilator slowing FVC decline in idiopathic pulmonary fibrosis (IPF) through a mechanism entirely orthogonal to the existing antifibrotic standard of care.
Within the broader IPF treatment landscape 2026, Treprostinil now stands out as the closest-to-approval next-generation antifibrotic candidate — with FDA sNDA filing targeted for Q3 2026.
1. Development and Regulatory Snapshot
| Item | Detail |
|---|---|
| INN | Treprostinil |
| Brand | Tyvaso® (nebulized) / Tyvaso DPI® (dry-powder inhaler) |
| Sponsor | United Therapeutics Corporation |
| Modality | Chemically stable prostacyclin (PGI₂) analog |
| Route | Inhalation, four times daily. TETON-1/2 both used Tyvaso Inhalation Solution (nebulized) exclusively; Tyvaso DPI was not part of the program |
| Current indications | PAH (WHO Group 1), PH-ILD (WHO Group 3) |
| New indication under development | Idiopathic Pulmonary Fibrosis (IPF) |
| Pivotal trials | TETON-2 (NCT05255991), TETON-1 (NCT04708782) |
| Status | Both Ph3 trials met primary endpoint. FDA sNDA filing planned by end of summer 2026, Priority Review requested. |
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2. The Unmet Need: Vascular Remodeling in IPF
Since pirfenidone and nintedanib became standard of care roughly a decade ago, IPF therapy has plateaued at slowing FVC decline by ~50%. Yet many IPF patients develop pulmonary microvascular disruption and remodeling, and concomitant Group 3 pulmonary hypertension (PH-ILD) is a well-established predictor of poor prognosis.
Nintedanib's RTK inhibition suppresses angiogenesis, but the prostacyclin pathway simultaneously dilates pulmonary vessels and suppresses fibroblast proliferation / myofibroblast differentiation. This dual biology provided the pathophysiologic rationale for the TETON program — repurposing a PAH drug into an antifibrotic.
3. Mechanism: IP / EP2 / DP1 to PPARγ
Treprostinil activates multiple prostanoid and nuclear-receptor pathways:
- IP receptor (prostacyclin GPCR): Gs-coupled → cAMP ↑ → PKA activation → vasodilation. The canonical vascular axis.
- EP2 / DP1 receptors: reinforce the cAMP signal; in lung fibroblasts, downstream signaling converges on suppressed collagen synthesis and proliferation.
- PPARγ (nuclear receptor): direct agonism has been reported, leading to inhibition of TGF-β1/Smad3 signaling and rebalancing of the MMP/TIMP axis — potentially driving fibrosis resolution.
- Mitochondrial rescue: IPF fibroblasts show aberrant fusion/fission dynamics; Treprostinil normalizes these and restores cAMP-PKA-autophagy homeostasis.
Crucially, none of these targets overlap with pirfenidone's multi-target profile or nintedanib's RTK axis, providing a molecular basis for additive/synergistic combination therapy. This is reflected in the TETON-2 subgroup analyses below.
4. TETON-2 Phase 3: NEJM March 2026
Trial Design
| Item | Detail |
|---|---|
| Trial | TETON-2 (NCT05255991) |
| Design | Multicenter, randomized, double-blind, placebo-controlled |
| Population | Confirmed IPF, FVC predicted ≥45% |
| Enrollment | 593 patients in the NEJM 2026 publication (Treprostinil 298 / Placebo 295). ClinicalTrials.gov reports an Actual Enrollment of 597; the 4-patient gap reflects exclusions from the analysis population, with NEJM Nathan 2026 used as the source of record. |
| Dosing | Nebulized inhaled Treprostinil (Tyvaso Inhalation Solution), up to 12 breaths (72 µg) four times daily |
| Duration | 52 weeks |
| Primary endpoint | Absolute change in FVC from baseline to week 52 |
| Publication | Nathan SD et al., N Engl J Med 2026 (PubMed 41812190; DOI 10.1056/NEJMoa2512911) |
Key Results
- Primary endpoint (FVC at week 52): Treprostinil superior to placebo, treatment difference +95.6 mL (p<0.0001). NEJM-reported medians: Treprostinil -49.9 mL (95% CI -79.2 to -19.5) vs Placebo -136.4 mL (-172.5 to -104.0).
- SoC-combination subgroup: Treatment benefits were observed across all subgroups including patients on background nintedanib or pirfenidone (United Therapeutics, March 2026 IR) — consistent with the orthogonal-mechanism rationale.
- Secondary endpoints (hierarchical testing): Secondary endpoints were tested in a prespecified hierarchical order to control multiplicity.
- Time to first clinical worsening event: significantly prolonged (confirmatory inference held within the hierarchy)
- Time to acute exacerbation: no substantial between-group difference observed → per the NEJM abstract, the hierarchical testing stopped at this step, and no confirmatory inference was made on subsequent secondary endpoints
- Treated as exploratory only: K-BILD (IPF-specific QoL), DLCO, 52-week overall survival — numerical trends favored Treprostinil but cannot be claimed as statistically significant from this trial due to the stopped hierarchy
- Safety: Most common AEs were cough (48.3%), headache, and throat irritation — consistent with the known inhaled prostacyclin profile. No new safety signals.
TETON-1: An Even Larger Effect
On March 30, 2026, United Therapeutics announced that TETON-1 (primarily US/Canada, n=598, NCT04708782) met its primary endpoint:
- FVC difference +130.1 mL — exceeding TETON-2's +95.6 mL
- Pooled TETON-1+2 analysis (n≈1,191): FVC difference +111.8 mL, with statistically significant effects on primary and most secondary endpoints
- United Therapeutics plans to submit an sNDA to the FDA by the end of summer 2026 and will request Priority Review.
In a cross-trial comparison, the +130 mL effect size appears comparable to or larger than nintedanib's approximately +110 mL benefit observed in the INPULSIS trials. However, TETON and INPULSIS are separate trials with different patient populations, background therapy, and historical context, and no head-to-head trial has been conducted. Absolute-value comparisons therefore cannot support a conclusion that Treprostinil "beats" nintedanib; the eventual clinical positioning will depend on combination trials and real-world use after approval.
5. Competitive Positioning
| Drug | Target | Key Data | Status |
|---|---|---|---|
| Treprostinil (inhaled) | IP/EP2/DP1/PPARγ | TETON-2 FVC +95.6 mL, TETON-1 +130.1 mL | sNDA Q3 2026 |
| Nerandomilast (Jascayd®, Boehringer Ingelheim) | Selective PDE4B | FIBRONEER-IPF FVC diff +64 mL | FDA-approved (Oct 2025 IPF, Dec 2025 PPF) [Ref 9] |
| BMS-986278 / Admilparant | LPA1 antagonist | Ph2: 62% FVC-decline reduction | Ph3 ALOFT ongoing |
| ENV-101 (Taladegib) | Hedgehog/SMO | Ph2a FVC +1.9%, TLC +200 mL | Ph2b WHISTLE-PF |
| Buloxibutid (C21) | AT2R agonist | Ph2a FVC +216 mL (36 wk) | Ph2b ASPIRE |
| Rentosertib (ISM001-055) | TNIK inhibitor | Ph2a FVC +98.4 mL (12 wk) | Ph2 |
Treprostinil's positioning: Competitors target fibroblasts, epithelium, or intracellular signaling — Treprostinil uniquely approaches fibrosis via the pulmonary vasculature. This orthogonality makes it a strong candidate for combination regimens. A Nerandomilast + Treprostinil + (future) LPA1-antagonist three-way regimen is a plausible future option under discussion, but with Treprostinil itself not yet approved for IPF, its actual clinical positioning will depend on sNDA review outcome, label, and combination-trial data.
6. Preclinical Evidence and Recommended Models
Treprostinil's antifibrotic activity has been consistently demonstrated in bleomycin-induced lung fibrosis models.
| Model | Key Finding | Reference |
|---|---|---|
| Bleomycin-induced mouse lung fibrosis (orotracheal) | Attenuation of lung injury, vascular remodeling, and fibrosis; reduced collagen deposition and Ashcroft score | Nikitopoulou I et al., Pulm Circ 2019 (PMID 31819797) |
| Bleomycin-induced rat lung fibrosis (inhaled INS1009, therapeutic dosing) | Dose-dependent reduction in lung hydroxyproline by 44-88% at 10-100 µg/kg | Corboz MR et al., Pulm Pharmacol Ther 2018 (PMID 29408757) |
Recommended Preclinical Workflow
As outlined in our bleomycin pulmonary fibrosis model pitfalls guide, dosing timing (prophylactic vs therapeutic) and endpoint selection critically shape data interpretation. A distinguishing feature of Treprostinil is that efficacy holds under therapeutic dosing (post-Day 7) — a key contrast with failed candidates like pamrevlumab.
Recommended endpoints:
- Fibrosis: lung hydroxyproline, Sirius Red quantification, Ashcroft score
- Vascular: RV/LV+S ratio, small pulmonary artery wall thickness (α-SMA staining)
- Functional: compliance, ex vivo contraction in precision-cut lung slices
- Molecular: 6-keto-PGF1α (prostacyclin metabolite), TGF-β1, PAI-1, collagen I/III
7. Key Forward-Looking Questions
- FDA sNDA review (Q3 2026 - H1 2027): If Priority Review is granted, IPF labeling could come in H1 2027, making Treprostinil the second novel-mechanism IPF drug (after Nerandomilast) and meaningfully expanding therapeutic options after a decade of SoC stagnation (pending regulatory outcome).
- Differentiation in PH-ILD patients: The dual vasculature/fibroblast effect may shine most in IPF patients with concomitant Group 3 pulmonary hypertension — detailed subgroup reporting is eagerly awaited.
- Triple combination therapy (as a possibility): Nerandomilast + Treprostinil + SoC (pirfenidone or nintedanib) is being discussed as a future paradigm, but Treprostinil is not yet IPF-approved and no prospective trials support this triplet today. Non-overlapping molecular targets motivate combination research, but the actual clinical positioning will depend on post-approval combination trials and safety data.
- Competition from Deupirfenidone (LYT-100): As the deuterated pirfenidone improves GI tolerability post-2027, Treprostinil's inhaled delivery will need to justify the device burden.
- Biomarker stratification: If plasma 6-keto-PGF1α or vascular markers (e.g., FGF-23) can predict responders, the precision-medicine use case expands substantially.
References
- Nathan SD, Smith P, Deng C, et al. Inhaled Treprostinil for Idiopathic Pulmonary Fibrosis. N Engl J Med. 2026. PMID: 41812190. DOI: 10.1056/NEJMoa2512911
- United Therapeutics. Announces Full Results of TETON-2 Phase 3 Clinical Trial Published in NEJM. Press release, March 11, 2026.
- United Therapeutics. TETON-1 Pivotal Study of Tyvaso Meets Primary Endpoint for IPF, Exceeding TETON-2 Treatment Effect. Press release, March 30, 2026.
- Nikitopoulou I, Manitsopoulos N, Kotanidou A, et al. Orotracheal treprostinil administration attenuates bleomycin-induced lung injury, vascular remodeling, and fibrosis in mice. Pulm Circ. 2019;9(4). PMID: 31819797
- Corboz MR, Zhang J, LaSala D, et al. Therapeutic administration of inhaled INS1009, a treprostinil prodrug formulation, inhibits bleomycin-induced pulmonary fibrosis in rats. Pulm Pharmacol Ther. 2018;49:95-103. PMID: 29408757
- TETON-2 ClinicalTrials.gov: NCT05255991
- TETON-1 ClinicalTrials.gov: NCT04708782
- Nathan SD. The Antifibrotic Effects of Inhaled Treprostinil: An Emerging Option for ILD. Adv Ther. 2022;39(9):3881-3895.
- Boehringer Ingelheim. Jascayd® (nerandomilast). FDA-approved for idiopathic pulmonary fibrosis (October 2025) and progressive pulmonary fibrosis (December 2025). Phosphodiesterase-4 (PDE4) inhibitor, oral administration. Orphan Drug Designation (IPF) and Breakthrough Therapy Designation (PPF) granted.
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- Lung Fibrosis Model Selection Guide 2026 — bleomycin, silica, aging model comparison
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