Abstract C186: In vitro profiling and compare analysis of the novel HDAC6-selective inhibitor ST80 in 42 human tumor cell lines.

Abstract

Abstract Inhibitors of histone deacetylases (HDAC) have been shown to be potent anti-proliferative agents mediated in part by induction of histone acetylation, resulting in growth arrest, cell differentiation and apoptosis. ST80, a novel HDAC inhibitor of the hydroxamate class was investigated for anti-tumor activity towards a panel of human tumor cell lines. At Oncotest a cellular profiling screen was developed in which new compounds are being tested in a standard cell line panel consisting of 42 cell lines from all major solid tumor types. The read-out of the assay is propidium iodide-based fluorescence, which is a measure of viable cell number. For the purpose of mechanism of action (MOA) analysis, the IC50 pattern of the new compounds is compared with the corresponding patterns of 118 agents with a known MOA. Additionally, Compare Analysis can indicate off-target effects of compounds for which targets have previously only been confirmed biochemically. Simultaneously, particularly sensitive and resistant cell lines are identified, helpful for the selection of cell lines and tumor xenografts for follow-up studies like the ex vivo tumor colony assay or in vivo studies using human tumor xenografts growing in nude mice. Concentration-dependent antitumor activity was detected for ST80 towards all cell lines tested with a mean IC50 value of 26.8 μM. Compare Analysis revealed the highest correlations towards HDAC inhibitors M344 (spearman's rho=0.84) and SBHA (rho=0.80) of the hydroxamate class, followed by apicidin (cyclic peptide, rho=0.60) and SAHA (hdroxamate, rho=0.57). Only the 5th ranked compound in Compare Analysis (daunorubicin, rho=0.53) was not an HDAC inhibitor, underscoring ST80's highly specific activity towards HDAC. The relative HDAC inhibiting potential was compared against immunoprecipitated FLAG-tagged HDAC1 and 6. ST80 demonstrated a 31-fold higher catalytic inhibition of purified HDAC6 activity (IC50= 0.9 μM) relative to HDAC1 activity (IC50= 29 μM). HDAC6 selectivity of ST80 was confirmed by acetylation of alpha-tubulin, an HDAC6 specific substrate, relative to acetylation of lysine 12 on histone H4 by immunoblotting whole cell lysate from SKBR3 cells treated for 24 h with 50 μM of ST80. In conclusion, by using Oncotest's Compare Analysis inhibition of HDAC by ST80 was clearly confirmed. Selective catalytic activity towards HDAC6 was demonstrated biochemically. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C186.