Sulforaphane induces autophagy by inhibition of HDAC6-mediated PTEN activation in triple negative breast cancer cells

Aims: To study the underlying mechanisms of sulforaphane, a natural histone deacetylase (HDAC) inhibitor, in inhibiting triple negative breast cancer cells growth and the therapeutic effects of combination of sulforaphane and doxorubicin in TNBC treatment. Materials and methods: The antineoplastic activity of sulforaphane was evaluated in MDA-MB-231, BT549 and MDA-MB-468 cells with MTT assay. Cell apoptosis was detected with Annexin V/PI double staining by Flow cytometry. Cell autophagy was detected with fluorescence microscope. The effects of Sulforaphane and Doxorubicin combination treatments on cells growth were determined with Chou-Talalay median effect/combination index (CI) model. mRNA and protein expression of genes were assayed respectively with real-time PCR and Western bloting. Protein-protein interaction was detected with co-immunoprecipation. Gene knock-down was performed with small interfere RNA. In vivo assay of combinational treatment with sulforaphane and doxorubicin was investigated in athymic nude mice bearing MDA-MB-231 xenografts. Key findings: Results showed that sulforaphane inhibited cell growth and induced autophagy in MDA-MB-231, BT549 and MDA-MB-468 cells. Further study demonstrated that sulforaphane induced autophagy by down-regulating expression of HDAC6, which resulted in increased membrane translocation and acetylation modification of phosphatase and tensin homolog (PTEN). Sulforaphane and doxorubicin combination exhibited a synergistic inhibition on TNBC cells growth. In nude mice, the combination of sulforaphane and doxorubicin displayed a greater inhibitory effect on MDA-MB-231 xenografts growth as compared to either treatment alone. Significance: Our study suggested that induction of autophagy by targeting HDAC6 in combination with chemotherapeutic reagent may provide a novel strategy for TNBC therapy.