Design and Synthesis of Novel Pirfenidone Analogues for Targeting Fibroblast Differentiation via Transforming Growth Factor-β/Smad Pathway Using In Vitro and In Vivo Models

Pulmonary fibrosis is a progressive interstitial lung disease characterized by excessive extracellular matrix (ECM) deposition, resulting in impaired respiratory function. Due to the limited efficacy of current antifibrotic therapies, there is an urgent need to develop novel agents or optimize existing drugs. In this study, a series of pirfenidone (PFD) derivatives were rationally designed and synthesized with targeted modifications at the third position of the core scaffold to enhance antifibrotic efficacy. A total of 30 derivatives (100 μM) were screened using a TGF-β-induced differentiation model, leading to the identification of hit compounds with superior activity compared to PFD (500 μM). Selected candidates were further validated both in vitro (LL29 and DHLF cells) and in the bleomycin (BLMN)-induced pulmonary fibrosis mouse model. In vitro, compounds 6a and 10b (50 and 100 μM) demonstrated robust suppression of fibrotic markers, as confirmed by RT-qPCR and immunofluorescence, indicating a dose-dependent antifibrotic effect. In vivo, BLMN administration significantly increased the lung index and fibrotic marker expression. In contrast, compounds 6a and 10b significantly downregulated the expression of fibrotic markers (including FN1, α-SMA, and collagen1α1). Histopathological analysis revealed that compound 10b effectively mitigated BLMN-induced alveolar wall thickening and collagen deposition, and significantly restored lung function in a dose-dependent manner, outperforming the PFD group. Mechanistic studies further indicated that 10b exerts its effects through modulation of the SMAD3/SMAD7 signaling pathway. Additionally, compound 10b exhibited a pharmacokinetic profile comparable to PFD. Collectively, these findings support compound 10b as a promising antifibrotic candidate with strong potential for clinical translation.