New Synthetic Flavonol Clears Senescent Cells and Reverses Lung Fibrosis in Mice

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal lung disease strongly linked to aging. Current FDA-approved drugs (nintedanib, pirfenidone) slow decline but do not meaningfully improve survival. Emerging evidence implicates accumulation of senescent cells—cells that have permanently exited the cell cycle and secrete inflammatory mediators—as key drivers of fibrotic disease. Clearing senescent cells pharmacologically (senolytics) has therefore emerged as a compelling therapeutic strategy.

The Mayo Clinic team began by confirming that natural flavonols quercetin and fisetin, while senolytic, require concentrations above 30 μM to induce apoptosis in senescent lung fibroblasts—a level associated with poor pharmacokinetics in vivo. To improve on this, they constructed a custom structural diversity library of natural, metabolite, and synthetic flavonols and screened them using a high-content immunocytochemistry platform measuring cleaved caspase-3 (a hallmark of apoptosis) in senescent versus proliferating human lung fibroblasts. The key structural finding was that a para-ethoxy substitution on the B-ring of the flavonol scaffold dramatically enhanced both potency and selectivity. The best commercially available analog, F-19, showed an EC50 of ~2.4 μM in senescent cells versus ~25 μM in proliferating cells—a roughly 10-fold improvement over natural flavonols.

Building on F-19 as a hit, the team performed medicinal chemistry optimization through iterative analog synthesis, ultimately generating F-4N. This lead compound demonstrated approximately 50-fold greater senolytic potency in vitro compared to quercetin or fisetin, with strong selectivity for senescent over healthy proliferating cells. F-4N also showed favorable pharmacokinetic properties that supported in vivo dosing.

In bleomycin-injured mouse models of lung fibrosis, daily oral or systemic administration of F-4N (10–30 mg/kg) produced multiple beneficial outcomes: reduced lung senescence burden (measured by markers including p16/CDKN2A, p21/CDKN1A, and SA-β-galactosidase), resolution of established fibrotic remodeling (reduced collagen deposition), and upregulation of mature alveolar epithelial markers (Sftpc, Hopx), suggesting facilitation of alveolar regeneration. These effects were also validated ex vivo using precision-cut lung slices from aged, bleomycin-injured mice, where F-4N outperformed nintedanib in reducing senescence-associated gene expression.

These results collectively suggest that medicinal chemistry optimization of the flavonol scaffold can yield potent, selective senolytics with genuine therapeutic potential in IPF. F-4N represents a significant step forward from earlier natural product senolytics toward a clinically translatable drug candidate, though further safety, toxicology, and human studies are required.