Low dosed interferon alpha augments the anti-tumor potential of histone deacetylase inhibition on prostate cancer cell growth and invasion.

We evaluated whether low-dosed interferon alpha (IFNa) may augment the anti-tumor potential of the histone deacetylase (HDAC)-inhibitor valproic acid (VPA) on prostate cancer cells in vitro and in vivo. PC-3, DU-145, or LNCaP prostate cancer cells were treated with VPA (1 mM), IFNa (200 U/ml), or with the VPA-IFNa combination. Tumor cell growth, cell cycle progression, and cell cycle regulating proteins were then investigated by the MTT assay, flow cytometry, and western blotting. Tumor cell adhesion to endothelium or to immobilized extracellular matrix proteins, as well as migratory properties of the cells, were evaluated. Integrin α and ß adhesion molecules and alterations of cell signaling pathways were analyzed. Finally, effects of the drug treatment on prostate cancer growth in vivo were determined in the NOD/SCID mouse model. VPA reduced tumor cell adhesion, migration, and growth in vitro. A much stronger anti-cancer potential was evoked by the VPA-IFNa combination, although IFNa in itself did not block growth or adhesion. The same effect was seen when tumor growth was evaluated in vivo. Molecular analysis revealed distinct elevation of histone H3 acetylation caused by VPA which was further up-regulated by VPA-IFNa, whereas IFNa alone did not alter H3 acetylation. The combinatorial benefit became obvious in Akt phosphorylation, p21 and p27 and integrin α1, α3, and ß1 expression. Application of low-dosed IFNa to a VPA based regimen profoundly boosts the anti-tumor properties of VPA. The combined use of VPA and low-dosed IFNa may therefore be an innovative option in treating advanced prostate cancer.