Suberoylanilide hydroxamic acid (SAHA) crosses the blood-brain barrier and inhibits growth of human multiforme glioblastomas in the brains of immunodeficient mice

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Histone acetylation and DNA methylation are two of the main mechanisms involved in the regulation of gene expression. During carcinogenesis, tumor suppressor genes can be silenced by aberrant DNA methylation and histone deacetylation. These epigenetic modifications have become important targets for tumor therapy. Both the histone acetylation inhibitor, suberoylanilide hydroxamic acid (SAHA), and the methylation inhibitor 5’-aza-2’-deoxycytidine (DAC), can induce growth arrest in transformed cells. In this study, we initially examined the effects of DAC (10⁻⁶ M, 4 days) and SAHA (2.5 x 10⁻⁶ M, last 24 hours of culture) on gene expression in U87 glioma cells by microarray, and found that many pro-apoptotic, anti-proliferation genes increased in their expression (e.g. Trail, TNFα, TNFRα, Bak, Bid, p21, p27), and many anti-apoptotic, pro-growth gene decreased in their levels (e.g. E2F1, Cdk2, Cdc25A, cyclin E2, CDK4, Cdk1, Cdc25c, Cdk6, Cdc20, cylin A2, Bcl-xl, Bcl-2). Chromosome immunoprescription (ChIP) assay found that deacetylation of p21 promoter was markedly increased by SAHA. Proliferation of glioblastoma multiforme (GBM) cell lines and explants were inhibited in vitro by either SAHA (ED₅₀ 2x10⁻⁶-2x10⁻⁵ M, 5 days) or DAC (ED₅₀ 10⁻⁵-10⁻³ M, 5 days), and the two agents together had enhanced antiproliferation activity. These cells developed a G2/M cell cycle arrest associated with an increased protein expression of p21^WAF1, p27^KIP1 and a decreased levels of cyclin D2, CDK2, CDK4 and E2F1. Murine experiments demonstrated that low dose SAHA (10 mg/kg, i.v. injection) crossed the blood-brain barrier as shown by a prominent increased levels of acetyl-H3, -H4, and p21^WAF1 in the brain cells; furthermore, the drug significantly (p<0.05) inhibited the growth of GL26 human GBM cells growing in the nude mice. In summary, these remarkable results shows that SAHA can inhibit the growth of human glioma cells in the brain, and may provide the foundation for a novel treatment for this devastating disease.