Austin, Texas-based Rein Therapeutics (Nasdaq: RNTX) 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.