Molecular mechanisms of underlying synergistic effect of combinations of histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) with docetaxel and trastuzumab against human breast cancer cells

560 Background: Suberoylanilide hydroxamic acid (SAHA) is a histone deacetylase (HDAC) inhibitor (HDI), which inhibits class I and II HDACs, induces hyperacetylation of the core nucleosomal histones, increases p21WAF1, and induces growth arrest and apoptosis of human breast cancer cells. In the present studies, we determined the effects of SAHA on Her-2, AKT and c-Raf (all hsp90 client proteins) levels, as well as on the cytotoxic effects of docetaxel and trastuzumab on human breast cancer BT-474 and SKBR-3 cells containing Her-2 amplification. Methods: The cells were treated with SAHA (1.0 to 5.0 μM) and/or trastuzumab (10 to 20 μg/ml) or docetaxel (5 to 20 nM) for 24 to 48 hours. Following this, % of apoptotic cells was determined or Western blot analyses of p21, p27, acetylated histones H3 and H4, AKT, c-Raf, and Her-2, as well as of Bcl-2, Bcl-xL, Bak, Bax, Bim, XIAP and survivin were performed. Attenuation of HDAC6 levels was achieved by siRNA to HDAC6 and estimated by immunoblot analysis. Synergisti...