FDA grants Fast Track Designation to Rein's LTI-03 for idiopathic pulmonary fibrosis
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Rein Therapeutics has received FDA Fast Track Designation for LTI-03, a novel inhaled synthetic peptide targeting idiopathic pulmonary fibrosis (IPF).
Austin, Texas-based Rein Therapeutics announced that the US FDA has granted Fast Track Designation to LTI-03, a first-in-class inhaled synthetic peptide derived from Caveolin-1 biology, for the treatment of idiopathic pulmonary fibrosis (IPF). The designation follows publication of Phase Ib data for LTI-03 in Nature Communications.
LTI-03 targets Caveolin-1 signaling, a pathway involved in regulating fibrotic activity in the lung. The drug is designed to simultaneously suppress profibrotic signaling and preserve alveolar progenitor cells involved in tissue repair — a dual mechanism that differentiates it from approved antifibrotics pirfenidone and nintedanib, which slow lung-function decline but do not reverse established fibrosis.
The Nature Communications publication reported results from a randomized, placebo-controlled Phase Ib dose-escalation study (NCT05954988) in 24 antifibrotic-naïve adults with newly diagnosed IPF. At the higher dose of 10 mg/day over 14 days, LTI-03 produced statistically significant reductions in multiple profibrotic biomarkers measured in deep bronchial brushing samples. All treatment-emergent adverse events were mild or moderate, with no discontinuations due to treatment-related adverse events. The findings were consistent with Phase Ib Cohort 2 topline data reported in November 2024, when four of eight biomarkers reached statistical significance in the combined Cohort 1 and Cohort 2 dataset.
LTI-03 previously received FDA and European orphan drug designations for IPF. The Fast Track decision also follows an earlier regulatory setback: FDA placed the US program on clinical hold in June 2025 following a nonclinical toxicology finding before clearing development to resume in October.
Rein is now enrolling approximately 120 patients in the randomized, placebo-controlled RENEW Phase II trial, which is evaluating LTI-03 over 24 weeks, including its effect on forced vital capacity. Interim data remain expected in H2 2026. The study represents the first substantive test of whether the biomarker changes observed during the short Phase Ib study translate into preservation of lung function.
