Inhaled Treprostinil Slows Lung Function Decline, Reduces Clinical Worsening in IPF

Navigating Progressive Lung Fibrosis: The Search for Enhanced Therapies

Idiopathic pulmonary fibrosis (IPF) remains a progressive and fatal interstitial lung disease, primarily affecting older adults and leading to substantial morbidity [1, 2]. Current standard-of-care antifibrotic therapies, nintedanib and pirfenidone, can slow the rate of lung function decline but do not halt or reverse the disease process, highlighting a persistent unmet need for more effective interventions [3, 1]. The unpredictable trajectory of IPF and its severe impact on patient function and quality of life drive the continued search for new therapeutic strategies [4]. While many past trials have struggled to demonstrate a favorable balance of efficacy and tolerability, research into compounds with antifibrotic mechanisms continues, with a recent study offering new data on inhaled treprostinil.

Investigating Treprostinil's Role in IPF Management

The investigation of inhaled treprostinil for idiopathic pulmonary fibrosis was founded on two phase 3, randomized trials, TETON-1 and TETON-2. This research was prompted by preclinical and clinical evidence suggesting that treprostinil, a stable prostacyclin analogue, possesses an antifibrotic mechanism relevant to the progressive lung scarring in IPF. Following the prior publication of the TETON-2 results, a new report now details the findings from the TETON-1 trial and includes a combined analysis of both studies. TETON-1 was a double-blind trial in which patients with IPF were randomly assigned to receive either inhaled treprostinil or a placebo, administered as 12 breaths four times daily over the 52-week study period.

Defining Key Clinical Outcomes

The TETON-1 trial's primary endpoint was the change in forced vital capacity (FVC) from baseline to week 52. FVC is a standard spirometric measure of the total volume of air exhaled after a maximal inhalation, and its decline is a core indicator of disease progression in idiopathic pulmonary fibrosis (IPF). In addition to this primary measure, the trial evaluated several secondary endpoints, which were analyzed in a prespecified hierarchical order. This statistical approach, designed to control for multiplicity, helps prevent the inflation of false-positive findings when multiple outcomes are tested. The first secondary endpoint was clinical worsening, a composite measure defined as the first occurrence of death from any cause, hospitalization for a respiratory cause, or a relative FVC decline of 10% or more. This was followed by the time to an acute exacerbation of IPF. Other secondary endpoints included survival, quality of life, and change in the diffusion capacity of the lungs for carbon monoxide at week 52.

Trial Demographics and Patient Disposition

The TETON-1 trial enrolled a cohort representative of a typical clinical population with idiopathic pulmonary fibrosis. A total of 598 patients were randomized and received at least one dose, with 299 patients in the inhaled treprostinil group and 299 in the placebo group. Of these, 434 patients (218 in the treprostinil group and 216 in the placebo group) completed the full 52-week assessment period. The mean age of participants was 73.0 years, and the cohort was predominantly male (77.3%). Crucially for clinical context, a majority of patients (77.6%) were already receiving background antifibrotic therapy with nintedanib or pirfenidone. This indicates the study was largely evaluating treprostinil as an add-on therapy. At baseline, the mean percentage of predicted FVC was 74.6%, signifying a population with moderate lung function impairment at enrollment.

Impact on Lung Function and Clinical Progression

Treatment with inhaled treprostinil significantly attenuated the decline in lung function over 52 weeks. The median change in forced vital capacity (FVC) was -43.3 ml (95% confidence interval [CI], -92.1 to -9.1) in the treprostinil group, compared with a much larger decline of -196.2 ml (95% CI, -227.1 to -155.6) in the placebo group. The resulting difference of 130.1 ml (95% CI, 82.2 to 178.1; P<0.001) in favor of treprostinil was statistically significant. Furthermore, treprostinil was associated with a lower risk of clinically significant deterioration. Clinical worsening events occurred in 95 patients (31.8%) receiving treprostinil versus 133 patients (44.5%) receiving placebo, corresponding to a hazard ratio of 0.67 (95% CI, 0.52 to 0.88; P = 0.003). However, the study found no significant difference between groups in the time to an acute idiopathic pulmonary fibrosis exacerbation. Because of the prespecified hierarchical testing sequence, this non-significant finding meant that formal statistical testing for all subsequent secondary endpoints, including survival and quality of life, was not performed.

Safety Profile and Discontinuation Rates

The safety analysis of inhaled treprostinil highlighted a notable difference in local airway effects. The most frequent adverse event was cough, which was reported in 54.8% of patients in the treprostinil group compared to 33.1% in the placebo group. This side effect likely contributed to the higher rate of treatment discontinuation observed in the active treatment arm. Overall, 40.5% of patients receiving treprostinil discontinued the trial intervention, compared to 32.8% of patients on placebo. Adverse events were the primary reason for discontinuation for 20.7% of patients in the treprostinil group and 14.7% in the placebo group. The authors note that a combined analysis incorporating data from both the TETON-1 and TETON-2 trials yielded similar efficacy and safety outcomes, reinforcing the consistency of these findings.

Clinical Implications for IPF Management

The findings from the TETON-1 trial suggest that inhaled treprostinil can meaningfully slow disease progression in patients with idiopathic pulmonary fibrosis (IPF), including those already on standard antifibrotic therapy. Over 52 weeks, treatment resulted in a significantly smaller decline in forced vital capacity (FVC) and a 33% lower risk of clinical worsening events (hazard ratio, 0.67) compared to placebo. The observed 130.1 ml difference in FVC decline is a clinically relevant magnitude in this disease. For the practicing clinician, these results position inhaled treprostinil as a potential add-on therapy that can further preserve lung function and reduce major adverse clinical events. However, this benefit must be weighed against the treatment's tolerability profile. The high incidence of cough (54.8%) and the increased rate of discontinuation due to adverse events (20.7%) are practical considerations for patient selection and counseling. The study was funded by United Therapeutics; TETON-1 ClinicalTrials.gov number, NCT04708782.

References

1. Cottin V, Valenzuela C. Evidence from recent clinical trials in fibrotic interstitial lung diseases.. Current opinion in pulmonary medicine. 2024. doi:10.1097/MCP.0000000000001089

2. Thong L, McElduff EJ, Henry MT. Trials and Treatments: An Update on Pharmacotherapy for Idiopathic Pulmonary Fibrosis. Life. 2023. doi:10.3390/life13020486

3. Wu X, Li W, Luo Z, Chen Y. A comprehensive comparison of the safety and efficacy of drugs in the treatment of idiopathic pulmonary fibrosis: a network meta-analysis based on randomized controlled trials. BMC Pulmonary Medicine. 2024. doi:10.1186/s12890-024-02861-w

4. Raghu G, Ghazipura M, Fleming TR, et al. Meaningful Endpoints for Idiopathic Pulmonary Fibrosis (IPF) Clinical Trials: Emphasis on ‘Feels, Functions, Survives’. Report of a Collaborative Discussion in a Symposium with Direct Engagement from Representatives of Patients, Investigators, the National Institutes of Health, a Patient Advocacy Organization, and a Regulatory Agency. American Journal of Respiratory and Critical Care Medicine. 2024. doi:10.1164/rccm.202312-2213so