Przewaquinone A, as a natural STAT3 inhibitor, suppresses the growth of melanoma cells and induces autophagy

Background Melanoma is a deadly malignant skin cancer with common risk factors including prolonged ultraviolet exposure. Understanding the mechanisms of signal transducer and activator of transcription (STAT3) signaling and discovering inhibitors of STAT3 signaling are considered promising melanoma treatments for melanoma. Przewaquinone A (PrA), a lipophilic diterpene quinone isolated from Salvia przewalskii Maxim. var. mandarinorum (Diels) Stib, has been shown to have neuro-protective properties. Nevertheless, it remains unclear how PrA functions in the anti-melanoma process. Purpose Herein, the aim was to investigate the suppressive action of PrA on melanoma growth and metastasis as well as the underlying mechanisms. Methods The in vitro proliferation ratio, cell migration, cell invasion, cell cycle and cell apoptosis were determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 5-ethynyl-2′-deoxyuridine (EdU) staining, wound-healing, transwell assays, flow cytometry and western blotting, respectively. The amount of STAT3 signaling-related proteins was determined using western blotting and immunofluorescence. The interaction between PrA and STAT3 was assessed using conducted by molecular docking, molecular dynamics (MD), surface plasmon resonance imaging (SPRi) and cellular thermal shift assay (CETSA). Autophagic fluxautophagic flux in melanoma cells was determined using the RFP-GFP-LC3 double-staining method. The STAT3C plasmid was used to overexpress STAT3 and investigate its role in the anti-melanoma action of PrA . The action of PrA on melanoma growth was validated in vivo. Results PrA reduced cell proliferation, caused cell cycle arrest, and increased cell apoptosis, and inhibited cell migration and invasion. Additionally, PrA inhibited Src/STAT3 signaling and decreased the amount of STAT3 in the nucleus. We further confirmed that STAT3 was a direct target of PrA using molecular docking, MD, SPRi assay and CETSA. Additionally, STAT3 overexpression partially blocked the anti-melanoma effects of PrA. PrA induced autophagy in melanoma cells via STAT3 signaling. Moreover, combination with the autophagy inhibitors CQ (chloroquine) or 3MA (3-methyladenine) enhanced its anti-melanoma effects. PrA inhibited tumor growth and suppressed STAT3 signaling in vivo. Conclusion These findings collectively demonstrated that PrA inhibits the growth and metastasis of melanoma cells and induces protective autophagy of melanoma cells by inhibiting STAT3 signaling. Therefore, PrA may be a viable candidate for the treatment of melanoma and the results of this study may help to guide the development of new therapeutic approaches for patients with melanoma.