Rationale: The role of the innate immune system in idiopathic pulmonary fibrosis (IPF) remains poorly understood. However, a functional myeloid compartment is required to remove dying cells and cellular debris, as well as to mediate innate immune responses against pathogens. Aberrant macrophage activity has been described in patients with post-acute sequelae of COVID fibrosis (PASC-F), and caveolin scaffolding domain (CSD) peptides have been found to attenuate inflammation and fibrosis in mouse lung injury models. Therefore, we examined, for the first time, the effects of CSD peptide LTI-2355 on the functional and synthetic properties of human myeloid cells isolated from lung explant tissue of donor lungs as well as IPF and PASC-F lung explant tissue. Methods and Results: CD45⁺ myeloid cells isolated from lung explant tissue from IPF and PASC-F patients exhibited an impaired capacity to clear autologous dead cells and cellular debris. The uptake of pathogen-coated bioparticles was impaired in myeloid cells from both fibrotic patient groups independent of the type of pathogen, highlighting an intrinsic functional cell impairment. LTI-2355 improved the phagocytic activity of both IPF and PASC-F myeloid cells, and this improvement was paired with decreased proinflammatory and pro-fibrotic synthetic activity. LTI-2355 was also shown to primarily target CD206-expressing IPF and PASC-F myeloid cells. Conclusions: Primary myeloid cells from IPF and PASC-F patients exhibit dysfunctional phagocytic and synthetic properties that are modulated by LTI-2355. LTI-2355 treatment of IPF myeloid cells resulted in significantly reduced sCD163, IFN-α2, IFN-γ, IL-2, IL-10, IL-12p40, and MMP-1 in the cell supernatant. This study highlights an additional mechanism of action of the CSD peptide in the treatment of IPF and progressive fibrotic lung disease.

Idiopathic pulmonary fibrosis (IPF) features excessive extracellular matrix deposition driven by activated fibroblasts and dysregulated signaling pathways. To assess the anti-fibrotic effects of LTI-03, a caveolin-1 scaffolding domain peptide, ex vivo precision-cut lung slices (PCLS) from patients with IPF were evaluated using bulk RNA sequencing, Ingenuity Pathway Analysis, and immunofluorescence. LTI-03 dose-dependently reduced collagen protein levels, suppressed pro-fibrotic cytokines, inhibited pro-fibrotic pathways, and activated protective mechanisms such as PTEN and PPAR signaling. Modulation was comparable to nintedanib but without the induction of apoptosis or necrosis pathways. These results demonstrate LTI-03’s potential therapeutic efficacy in a highly relevant translational disease model and support LTI-03 as a promising next-generation therapeutic to halt IPF progression and improve patient outcomes.

Rationale LTI-03 is a novel inhaled therapeutic in development for idiopathic pulmonary fibrosis (IPF). LTI-03 has been shown to promote alveolar epithelial cell survival and reduce profibrotic protein expression in experimental models of lung disease. Objectives To evaluate the safety and pharmacokinetics (PK) of LTI-03 and effects on disease biomarkers in patients with IPF. Methods This Phase 1b, randomized, controlled, dose-escalation study randomized 24 participants, 3:1 into 2 sequential dose cohorts, to receive inhaled LTI-03 (5 or 10 mg/day) or placebo for 14 days. The primary endpoint was the incidence of treatment-related adverse events (TEAEs). Exploratory analyses included PK and change from baseline in fibrosis-related and epithelial integrity-related biomarkers in plasma, peripheral blood mononuclear cells (PBMCs), and deep bronchial brushings (DBB). Measurements and Main Results Inhaled LTI-03 was well-tolerated, with no treatment-related AEs leading to treatment discontinuation. All TEAEs were mild or moderate in severity. Cough was the most common TEAE and the only treatment-related TEAE experienced by more than 1 participant. There was no evidence of airway obstruction by symptoms or spirometry. LTI-03 did not induce inflammation (phosphorylated AKT) in PBMCs. In DBB samples, LTI-03 significantly reduced the expression of interleukin-11, chemokine ligand 7, thymic stromal lymphopoietin, and galectin 7; dose-related reductions were also observed for collagen type 1 alpha chain 1 and plasma surfactant protein D. Conclusions Inhaled LTI-03 exhibited a favorable safety and tolerability profile over 14 days. Exploratory biomarker analyses suggest a positive effect on epithelial homeostasis and corresponding antifibrotic effects. Scientific Knowledge on the Subject Current standard of care therapies for IPF do not halt or reverse disease progression, and systemic side effects commonly result in discontinued use. LTI-03 is a caveolin scaffolding domain (CSD) peptide formulated as an excipient-free dry powder for the treatment of IPF. It has demonstrated anti-fibrotic and epithelial protective effects in animal models of fibrosis and in IPF precision cut lung slices via putative replenishment of endogenous Cav-1 signaling, which is lost in fibrotic diseases. What This Study Adds to the Field The results of this study support the conclusion that LTI-03 was well tolerated in patients with IPF at doses of 5 and 10 mg/day. Exploratory biomarker analyses from deep bronchial brushings suggested that positive pharmacodynamic effects were achieved on target cell types. Taken together, these results support the initiation of a Phase 2 efficacy study in patients with IPF. Data sharing statement Rein Therapeutics, Inc. (“Rein”) understands and acknowledges the need to share clinical study data with the research community in an open and transparent manner and has provided de-identified patient data in the manuscript. Rein will not consider further requests pertaining to clinical data outside of what has been accepted and published by the journal. Any queries regarding clinical study data must be submitted in writing to https://info{at}reintx.com. A data supplement for this article is available via the Supplements tab at the top of the online article.