Inhibitors of histone deacetylases are promising compounds for the treatment of cancer but have not been systematically explored in malignant brain tumors. Here, we characterize the benzamide MS-275, a class I histone deacetylase inhibitor, as potent drug for experimental therapy of glioblastomas. Treatment of four glioma cell lines (U87MG, C6, F98, and SMA-560) with MS-275 significantly reduced cell growth in a concentration-dependent manner (IC(90), 3.75 micromol/L). Its antiproliferative effect was corroborated using a bromodeoxyuridine proliferation assay and was mediated by G(0)-G(1) cell cycle arrest (i.e., up-regulation of p21/WAF) and apoptotic cell death. Implantation of enhanced green fluorescent protein-transfected F98 glioma cells into slice cultures of rat brain confirmed the cytostatic effect of MS-275 without neurotoxic damage to the organotypic neuronal environment in a dose escalation up to 20 micromol/L. A single intratumoral injection of MS-275 7 days after orthotopic implantation of glioma cells in syngeneic rats confirmed the chemotherapeutic efficacy of MS-275 in vivo. Furthermore, its propensity to pass the blood-brain barrier and to increase the protein level of acetylated histone H3 in brain tissue identifies MS-275 as a promising candidate drug in the treatment of malignant gliomas.