Valproic acid is a selective antiproliferative agent in estrogen-sensitive breast cancer cells.

Treatment efficacy of breast cancer can be impaired by cell resistance. The aim of the study was to investigate the anti-tumour effects of valproic acid (VPA), the only clinically available histone deacetylase inhibitor, on both estrogen-sensitive and -insensitive breast cancer cells. VPA, at a concentration lacking severe adverse effects in human, reduces cell viability in estrogen-sensitive cell lines, inducing p21 expression and impairing cell cycle. In ZR-75-1, cell cycle is selectively arrested in G1, whereas MCF-7 cells massively accumulated in sub-G1. Actually, in MCF-7 cells, VPA induces apoptosis, down-regulates Bcl-2 and up-regulates Bak expression. In conclusion, VPA is a powerful antiproliferative agent in estrogen-sensitive breast cancer cells, making this drug of clinical interest as a new approach to treat breast cancer.