Abstract 2620: Identification of cell context specific and pleiotropic effects of the histone deacetylase inhibitors romidepsin (depsipeptide) and vorinostat (SAHA) (2011)

Abstract Histone deacetylase inhibitors (HDIs) constitute a promising new class of anticancer agents that can induce growth arrest and apoptosis in malignant cells through histone decompaction and other, yet unknown mechanisms. Although HDIs are effective in T-cell lymphomas, only occasional responses have been reported for solid tumors. To better understand these disparate effects, we have performed a systematic survey of 19 different cell lines representing various solid tumors with different molecular phenotypes. The cell lines were derived from breast (MCF-7, MCF-10A, SK-Br-3, MDA-MB-231), lung (A549, H460, EKVX, H146, H526), colon (HCT-116, HCT-116 p21-/-, S1, SW620), melanoma (MDA-MB-435, LOX IMVI, UACC-62), CNS (SF295), prostate (PC-3), and lymphoma (HUT-78), and their response to HDIs was studied at both the molecular and cellular level. The effect of two different HDIs, romidepsin (depsipeptide) and vorinostat (SAHA), at several concentrations (3-fold serial dilutions of 0.1 – 30 nM depsipeptide, 0.1 – 30 uM vorinostat) and at different time points (8 – 24 – 48 – 72 – 96 h) were analyzed. The response parameters included cytotoxicity (MTT assay), flow cytometric analysis of cell cycle (propidium iodide), apoptosis (short exposure Annexin V), and mitotic arrest (TG3 staining). In addition, to enable high throughput screening of protein expression and modification (including histone acetylation, methylation, and phosphorylation), we took advantage of a newly developed, custom designed, reverse phase dot blot microarray containing 4992 spots per slide. Multivariate analysis, including multiple regression and unsupervised hierarchical clustering of the data organized in heat-maps, revealed that the effects of HDIs are complex involving multiple proteins and pathways, and depend on the cellular context. In particular, cell cycle analysis revealed major differences in response to HDIs between cell lines, ranging from only minor changes in G1/S/G2/M distribution to profound G2 arrest (HCT-116 p21-/-) even at the lowest concentration (0.1 nM) of HDI. Such a nuanced picture was not observed with the standard MTT cytotoxicity assay, underscoring the value of cell cycle analysis in future drug-response studies. With a few notable exceptions, we observed good agreement between the Annexin V assay and the Sub-G0 population, both measures of apoptosis. In conclusion, the two HDIs, romidepsin and vorinostat, have pleiotropic effects that are not confined to histone modification. The heterogeneous responses that we observe across different cell lines reflect the clinical situation with very variable outcome of HDI treatment. We believe that the mechanistic insights obtained in the current study will aid in the design of new and improved HDI treatment regimens, including combination therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2620. doi:10.1158/1538-7445.AM2011-2620