Pulmonology · Medical Literature
Inhaled LTI-03 for idiopathic pulmonary fibrosis: a randomized dose escalation study.
Abstract
Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease with limited treatment options. LTI-03 promotes alveolar epithelial cell survival and reduces profibrotic protein expression in experimental models of IPF. In this Phase 1b, randomized, double-blind, placebo-controlled dose-escalation study, 24 participants with IPF were randomized 3:1 to inhaled LTI-03 5 mg/day (N = 9), LTI-03 10 mg/day (N = 9) or placebo (N = 6) for 14 days and included in all analyses (ClinicalTrials.gov: NCT05954988). The primary endpoint was the incidence of treatment-emergent adverse events (TEAEs). Exploratory analyses included pharmacokinetics and disease-related biomarkers. LTI-03 was well-tolerated, with no treatment-related discontinuations, no severe TEAEs, and no evidence of airway obstruction by spirometry and associated symptoms. In deep bronchial brushings, both LTI-03 doses significantly reduced interleukin-11 (p = 0.0406 at 5 mg/day; p = 0.044 at 10 mg/day) and thymic stromal lymphopoietin (p = 0.0256 at 5 mg/day; p = 0.0128 at 10 mg/day) versus placebo. The 10 mg/day dose suppressed collagen type 1 alpha chain 1 (p = 0.0248), CXC chemokine ligand 7 (p = 0.0248) and galectin-7 (p = 0.0332). Other measured biomarkers were not significantly changed. The favorable safety profile and reductions in disease-related biomarkers support further evaluation of inhaled LTI-03 for IPF. This study was fully funded by Rein Therapeutics, Inc.
Clinical relevance
IPF is a progressive, fatal interstitial lung disease with a median survival of 3–5 years and only two FDA-approved therapies (nintedanib and pirfenidone) that slow but do not halt progression, underscoring a critical unmet need for novel disease-modifying agents. LTI-03 represents a first-in-class inhaled approach targeting alveolar epithelial cell survival and profibrotic signaling, offering a lung-directed delivery strategy that may minimize systemic toxicity. This Phase 1b signal-finding trial provides the first human safety and biomarker data for LTI-03, making it immediately relevant to pulmonologists managing IPF patients with intolerance to or inadequate response to existing antifibrotic therapy.
Key findings
1. SAFETY — PRIMARY ENDPOINT: LTI-03 was well-tolerated across both dose levels (5 mg/day and 10 mg/day) over 14 days in 24 IPF participants (3:1 randomization active:placebo); no treatment-related discontinuations, no severe TEAEs, and no spirometric evidence of airway obstruction were observed. 2. IL-11 REDUCTION: Both doses significantly reduced interleukin-11 (a key profibrotic cytokine) in deep bronchial brushings versus placebo (p = 0.0406 at 5 mg/day; p = 0.044 at 10 mg/day). 3. TSLP REDUCTION: Thymic stromal lymphopoietin (TSLP), an epithelial-derived profibrotic alarmin, was significantly suppressed at both doses versus placebo (p = 0.0256 at 5 mg/day; p = 0.0128 at 10 mg/day), with a dose-response trend. 4. DOSE-DEPENDENT FIBROTIC MATRIX SUPPRESSION: The 10 mg/day dose selectively suppressed collagen type 1 alpha chain 1 (COL1A1; p = 0.0248) and CXC chemokine ligand 7 (CXCL7; p = 0.0248), both implicated in fibroblast activation and extracellular matrix remodeling. 5. GALECTIN-7 REDUCTION: The 10 mg/day dose significantly reduced galectin-7 (p = 0.0332), a lectin associated with epithelial apoptosis and fibrotic tissue remodeling, versus placebo. 6. STUDY LIMITATIONS: This was a small (N = 24), short-duration (14-day) Phase 1b dose-escalation trial with an exploratory biomarker design; no clinically meaningful efficacy endpoints (e.g., FVC decline, 6MWT, HRCT fibrosis score) were powered or reported, and no confidence intervals or effect sizes for biomarker changes were provided in the abstract.
Practice implications
At this stage, LTI-03 should not alter standard-of-care antifibrotic prescribing (nintedanib or pirfenidone), but the favorable safety profile and absence of airway obstruction support enrollment of IPF patients — including those on background antifibrotic therapy — into upcoming Phase 2 trials, particularly patients with progressive disease or antifibrotic intolerance who lack alternative options. The dose-dependent biomarker suppression pattern (with 10 mg/day demonstrating a broader profibrotic signal reduction including COL1A1, CXCL7, and galectin-7) suggests the 10 mg/day dose should be prioritized for Phase 2 efficacy evaluation, with deep bronchial brushing biomarkers (IL-11, TSLP, COL1A1) considered as pharmacodynamic endpoints. Clinicians should note the industry funding source (Rein Therapeutics, Inc.) and the exploratory, hypothesis-generating nature of the biomarker data when interpreting results, pending larger randomized trials with functional and radiographic endpoints.