Aberrant histone post-translational modifications including acetylation are common in human cancers and result in dysregulation of gene expression. Histone acetylation is regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) and HDAC inhibitors (HDACi) are promising anticancer therapeutics. Our laboratory has focused on studying the effects of hydroxamic acid based HDACis including TSA, SAHA and CG-1521. We have previously shown that CG-1521 induces cell cycle arrest and apoptosis in various cell lines of breast and prostate cancer.

The purpose of this study is to gain insight into the mechanism of the HDAC inhibitor CG-1521 and identify potential combinatorial drug targets. We have employed a whole genome yeast deletion library screen to determine which gene deletions confer sensitivity and resistance to CG-1521. 407 sensitive and 80 resistant strains were identified. We used gene ontology enrichment analysis to determine which pathways are modulated by CG-1521. Sensitive strains are highly enriched in processes regulating chromatin remodeling and transcription. The list of resistant strains contains many genes involved in the regulation of transcription and tRNA modification. Deletions of components of the SAGA HAT complex are highly overrepresented in the sensitive strains, including the catalytic subunit Gcn5. It appears that the SAGA complex is required to reduce the effect of CG-1521 on cell growth. Cell cycle analysis shows that CG-1521 treatment in Saccharomyces cerevisiae results in G1 arrest in both the wild type and the gcn5Δ strain. The gcn5Δ strain displays increased sensitivity to CG-1521 induced cell death compared to the wild type strain. In contrast to the highly sensitive gcn5 deletion strain, a yeast strain expressing a catalytically inactive variant of the Gcn5 protein is less sensitive to CG-1521. This indicates that functions other than the acetyltransferase activity are partially sufficient to attenuate the effects of CG-1521.

We have identified that disruption of the SAGA HAT complex can sensitize cells to CG-1521 and are validating whether loss of the human Gcn5 homologs, Gcn5 and PCAF, also confers sensitivity to CG-1521 in breast cancer cell lines. Taken together, our work suggests that the combination of selective HAT and HDAC inhibitors might be effective for the treatment of cancer.

Citation Format: Ann-Christin Gaupel, Thomas J. Begley, Martin P. Tenniswood. Deletion of GCN5 confers sensitivity to the histone deacetylase inhibitor CG-1521. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1002. doi:10.1158/1538-7445.AM2013-1002