STAT3-mediated apoptotic-enhancing function of sclareol against breast cancer cells and cell sensitization to cyclophosphamide

Sclareol is an organic compound with potential anti-tumor effects against various cancer types. However, its precise molecular mechanism in suppression of tumor growth has not been fully elucidated. In the present study the anti-proliferative and apoptosis-inducing effects of sclareol with cyclophosphamide was investigated in breast cancer cells and the involvement of JAK/STAT pathway was evaluated. For this purpose, MCF-7 breast cancer cells were cultured and treated with various concentrations of sclareol to determine its IC50. Cell viability was measured by MTT assay and apoptosis was assessed by fluocytometric analysis of annexin V binding. Gene and protein expression were examined by real-time PCR and Western blotting, respectively. The activity of caspase enzymes was also measured. The results showed that sclareol significantly reduced cell viability and triggered cell death and its coadministration with cyclophosphamide enhanced its anti-cancer properties. Additionally, sclareol up-regulated the expression of p53 and BAX while reduced the expression of Bcl-2. Caspases 8 and 9 were also activated by sclareol, an effect that was augmented by cyclophosphamide. Docking studies indicated an interaction between sclareol and STAT3 which was proved by attenuation of STAT3 phosphorylation after treatment of cells with sclareol. Sclareol was also capable of suppressing the function of IL-6 in modulating the expression of apoptosis-associated genes. Altogether these data suggest the potential of sclareol as an anti-cancer agent and demonstrate that combination of sclareol with cyclophosphamide might serve as an effective chemotherapeutic approach resulting in improvements in the treatment of breast cancer.