Determination of the class and isoform selectivity of small-molecule histone deacetylase inhibitors
Résumé
The human histone deacetylase (HDAC) family, a well-validated anti-cancer target, plays a key role in the control of gene expression through regulation of transcription. While HDACs can be subdivided into three main classes, the class I, class II and class III HDACs (Sirtuins), it is presently unclear whether inhibiting multiple HDACs using pan HDAC inhibitors, or targeting specific isoforms that show aberrant levels in tumors, will prove more effective as an anti-cancer strategy in the clinic. To address the above issues, we have tested a number of clinically relevant HDAC inhibitors (HDACi) against a panel of recombinant human HDAC (rhHDAC) isoforms. Eight rhHDACs were expressed using a baculoviral system, and a Fluor de Lys TM} (FDL) HDAC assay was optimized for each purified isoform. The potency and selectivity of ten HDAC inhibitors on class I isoforms (rhHDAC1, 2, 3 and 8) and class II HDAC isoforms (rhHDAC 4, 6, 7 and 9) was determined. MS-275 was HDAC1 selective, MGCD0103 was HDAC1 and HDAC2 selective, apicidin was HDAC2 and HDAC3 selective and valproic acid was an HDAC class I specific inhibitor. The hydroxamic acid-derived compounds (TSA, NVP-LAQ824, panobinostat, ITF2357, vorinostat and belinostat) were potent pan HDAC inhibitors. The growth inhibitory effect of the HDACi on HeLa cells showed that both pan HDAC and class I specific inhibitors inhibited cell growth. The data also showed that both pan HDAC and class I specific inhibitor treatment resulted in increased acetylation of histones, but only the pan HDAC inhibitors resulted in increased tubulin acetylation, which is in agreement with their activity on the HDAC6 isoform.
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