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.