Liposomal Fisetin Suppresses Inflammatory SASP Without Killing Senescent Cells

Cellular senescence is a double-edged biological process: while it prevents damaged cells from proliferating, persistent senescent cells secrete pro-inflammatory and pro-tumorigenic factors collectively called the SASP. This secretory profile can accelerate cancer progression, promote metastasis, and complicate recovery after chemotherapy. Senotherapy — targeting senescent cells pharmacologically — is therefore a compelling strategy in oncology and longevity medicine. Fisetin, a polyphenol flavonoid, is widely cited as a senolytic candidate, but its cell-type specificity and poor bioavailability have raised questions about its real-world utility.

This study systematically evaluated fisetin delivered via liposomes against two DOX-induced senescent lung cell models: WI-38 normal fibroblasts and A549 adenocarcinoma cells. Senescence was rigorously confirmed using SA-β-galactosidase staining, EdU proliferation assays, confocal morphology analysis (including SAHF in WI-38 nuclei), flow cytometry for cell size, and ELISA measurement of IL-6 and IL-8. Liposomes were formulated from DOPC, DSPE, and cholesterol via thin-layer hydration, yielding particles of approximately 95–116 nm with a polydispersity index below 0.2 and acceptable zeta potential stability over 30 days. Encapsulation efficiency for fisetin was 13.68%, and Nile red-labeled liposomes confirmed cellular internalization in both cell types, with senescent WI-38 cells showing higher uptake than A549 cells at 4 hours.

The key finding is that fisetin-loaded liposomes did not reduce senescent cell viability or restore proliferation — ruling out senolytic activity in these models — but did produce a significant and dose-relevant reduction in IL-6 and IL-8 secretion. This senomorphic effect was more pronounced with the liposomal formulation than with free fisetin, with the encapsulated version achieving comparable cytokine suppression even at the lowest concentration tested. This suggests that encapsulation overcomes fisetin's hydrophobicity limitations and improves intracellular bioavailability.

The dual-cell-line design is particularly informative: senescence induction required markedly different DOX concentrations (1 μM for WI-38; 0.2 μM for A549), and the senescence phenotypes differed morphologically — A549 cells enlarged substantially while WI-38 cells formed SAHF. Despite these differences, both cell types responded to the senomorphic action of liposomal fisetin, suggesting a degree of generalizability across lung cell contexts.

Importantly, these results challenge the prevailing classification of fisetin as primarily senolytic and highlight the value of context-specific testing. The senomorphic mechanism — likely through NF-κB and mTOR pathway modulation — may be sufficient to reduce the tumor-promoting microenvironment created by SASP without requiring cell elimination. Liposomal delivery represents a practical route to enhance fisetin's therapeutic window, though encapsulation efficiency (13.68%) warrants optimization before clinical translation.