Synthesis, anti-tumor activity, and mechanistic study of triphenylphosphonium (TPP) conjugates of diosgenin

Diosgenin (DSG), a naturally occurring steroidal sapogenin, has attracted considerable attention because of its broad spectrum of pharmacological activities, including anti-cancer effects. However, its further development as an anti-tumor agent has been hindered by its limited potency. In this study, thirteen triphenylphosphonium (TPP)-conjugated DSG derivatives were designed and synthesized to enhance mitochondrial targeting and improve anti-tumor activity. The in vitro anti-proliferative activities of these compounds were evaluated against five cancer cell lines (PC-3, A549, MCF-7, HeLa, and HCT116) and one normal human liver cell line (L02) using the CCK-8 assay. Notably, compound 11f exhibited an IC₅₀ value of 0.1 μM in HeLa cells, representing up to a 226-fold increase in cytotoxicity compared to DSG (IC₅₀ = 22.6 μM). Additionally, compound 11f showed relatively low toxicity toward L02 cells (IC₅₀ = 39.0 μM), indicating good selectivity. Further biological studies demonstrated that compound 11f depolarizes the mitochondrial membrane potential (Δψm), reduces ATP production, and results in an abnormal increase in intracellular reactive oxygen species (ROS). In addition, compound 11f promoted apoptosis, as evidenced by Annexin V/PI staining and modulation of apoptosis-related proteins, including upregulation of Bax, cytochrome c, cleaved caspase 9, cleaved caspase 3, and cleaved PARP-1, together with downregulation of Bcl-2. Moreover, in vivo experiments showed that compound 11f inhibited the proliferation of HeLa cells in a zebrafish xenograft model. These findings suggest that TPP conjugation is an effective strategy for enhancing the anti-tumor activity of DSG and that compound 11f deserves further investigation as a lead compound for cervical cancer therapy.