Inhibition of STAT3 signaling contributes to the anti-melanoma effects of chrysoeriol

Melanoma is an aggressive malignancy with a high mortality rate. Signal transducer and activator of transcription 3 (STAT3), an oncoprotein, is considered as an effective target for treating melanoma. Chrysoeriol is a flavonoid compound, and possesses anti-tumor activity in lung cancer, breast cancer and multiple myeloma; while whether it has anti-melanoma effects is still not known. Chrysoeriol has been shown to restrain STAT3 signaling in an inflammation mouse model.In this study, the anti-melanoma effects of chrysoeriol and the involvement of STAT3 signaling in these effects were investigated.CCK8 assays, 5-ethynyl-2'-deoxyuridine (EdU) staining, Annexin V-FITC/PI staining, Western blot analyses of cleaved caspase-9 and wound healing assays were used to study the anti-melanoma effects of chrysoeriol in cell models. A B16F10 melanoma bearing mouse model was used to evaluate the in vivo anti-melanoma effects of chrysoeriol. Indicators of cell proliferation, cell apoptosis and angiogeneis in melanoma tissues were detected by immunohistochemistry (IHC) staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Immune cells in melanoma tissues were analyzed by flow cytometry. STAT3-overactivated cell models were used to investigate the involvement of STAT3 signaling in the anti-melanoma effects of chrysoeriol. Molecular dynamics (MD) simulations and surface plasmon resonance (SPR) assays were conducted to determine whether chrysoeriol binds to Src, an upstream kinase of STAT3.The results of cell experiments showed that chrysoeriol dose-dependently inhibited viability, proliferation and migration of, and induced apoptosis in, A375 and B16F10 melanoma cells. Chrysoeriol inhibited the phosphorylation of STAT3, and downregulated the expression of STAT3-target genes involved in melanoma growth and metastasis. Mouse studies showed that chrysoeriol restrained melanoma growth and tumor-related angiogenesis, and altered compositions of immune cells in melanoma microenvironment. Chrysoeriol also inhibited STAT3 signaling in B16F10 allografts. Chrysoeriol's viability-inhibiting effects were attenuated by over-activating STAT3 in A375 cells. Furthermore, chrysoeriol bound to the protein kinase domain of Src, and suppressed Src phosphorylation in melanoma cells and tissues.This study, for the first time, demonstrates that chrysoeriol has anti-melanoma effects, and these effects are partially due to inhibiting STAT3 signaling. Our findings indicate that chrysoeriol has the potential to be developed into an anti-melanoma agent.