Aim: 

Histone deacetylase (HDAC) inhibitors are epigenetic modulator that are emerging as antineoplastic agents for the treatment of malignancies. We investigated the antiproliferative and antiinvasive mechanism of action of the retinoid 6-OH-11-hydrofenantrene (IIF), a ligand of retinoid X receptor, in combination with valproic acid (VPA), an inhibitor of HDAC activity, in the colon cancer cell line HT-29.

Methods: 

cell proliferation was evaluated by MTT and Sulphorodhamine assay; apoptosis was evaluated by Hoechst assay and by immunofluorescence of cleaved caspase 3 and 9; p53, Bcl2, Bax and HDAC-1 expression was evaluated by western blot. Metalloproteinases (MMPs) protein levels and activity were evaluated by western blot and zimography respectively.

Results: 

VPA inhibited HDAC-1 expression. IIF (10-30 microM) and VPA (1-2 mM) reduced cell proliferation in a dose and time dependent manner. The addition of VPA and IIF together enhanced the antiproliferative effect of each drug alone and increased apoptosis. In particular, Bcl2 and p53 levels decreased, while Bax and cleaved caspase 3 and caspase 9 levels increased. The same treatment also reduced MMP2 and MMP9 expression and MMP2 activity.

Conclusion: 

IIF and VPA have strong pro-apoptotic and antiinvasive effects in the colon cancer cell line HT-29 and their effects are enhanced when used together.