Anticancer effects of the HDAC inhibitor, 3β,6β‑dihydroxyurs‑12‑en‑27‑oic acid, in MCF‑7 breast cancer cells via the inhibition of Akt/mTOR pathways

Astilbe chinensis (A. chinensis) is a perennial herb that is used to treat chronic bronchitis and pain. The anticancer activity of 3β,6β-dihydroxyurs-12-en-27-oic acid (ACT-3), a major component isolated from A. chinensis, has not yet been investigated in detail. The purpose of the present study was to investigate the histone deacetylase (HDAC) inhibitory and anticancer activities of ACT-3 compared with suberoylanilide hydroxamic acid (SAHA) in MCF-7 human breast cancer cells. The purity of ACT-3 was determined using high-performance liquid chromatography. In the present study, the effects of ACT-3 on anticancer effects of MCF-7 cells were determined by measuring the level of apoptotic cell death and cell cycle regulator using flow cytometry analysis and western blot analysis, respectively. The effects of ACT-3 on HDAC enzyme activity were measured using assay kits. ACT-3 and SAHA increased the levels of acetylated histone H3 and reduced the levels of HDAC1 and HDAC3 in MCF-7 cells. ACT-3 significantly decreased the cell viability in a concentration-dependent manner and induced different morphological changes at high concentrations. ACT-3 and SAHA significantly inhibited the colony formation in MCF-7 cells. ACT-3 inhibited total HDAC activity in a dose-dependent manner. ACT-3 significantly reduced the expression levels of cyclin D1 and cyclin-dependent kinase 4, and upregulated the expression levels of p21(WAF1) and p53. A significant increase in the G(1) phase cell population was observed in MCF-7 cells and ACT-3 induced apoptosis by reducing the ratio of B-cell lymphoma-2 (Bcl-2)/Bcl-2-associated X (Bax) and releasing cleaved caspase 9. Additionally, ACT-3 significantly increased autophagic cell death by inhibiting the serine-threonine kinase/mammalian target of the rapamycin pathway. Autophagy induction was confirmed via acridine orange staining. ACT-3 significantly increased the pERK1/2 and p21 in MCF-7 cells. Thus, the activated ERK pathway played an important role in cell cycle arrest and apoptosis via ERK-dependent induction of p21 in MCF-7 cells. These data indicated that ACT-3 can be used as a promising anticancer agent to overcome the limitations and reduce the side effects of conventional anticancer drugs.