Histone deacetylase (HDAC) proteins are promising targets for cancer treatment, as shown by the approval of two HDAC inhibitors for the treatment of cutaneous T-cell lymphoma. HDAC1 in particular has been linked to cell growth and cell cycle regulation and is therefore an attractive target for anticancer drugs. The HDAC1 active site contains a hydrophobic 11 Å active-site channel, with a 14 Å internal cavity at the bottom of the active site. Several computational and biochemical studies have proposed an acetate-escape hypothesis where the acetate byproduct of the deacetylation reaction escapes via the 14 Å internal cavity. Selective HDAC inhibitors that bind to the 14 Å cavity have also been created. To understand the influence of amino acids lining the HDAC1 14 Å cavity in acetate escape and inhibitor binding, we used mutagenesis coupled with acetate competition assays. The results indicate that amino acids lining the 14 Å cavity are critical for catalytic activity and acetate competition, confirming the role of the cavity in acetate escape. In addition, these mutagenesis studies will aid in HDAC1-inhibitor design that exploits the 14 Å cavity.

Histone deacetylase (HDAC) proteins are promising targets for cancer treatment, with several HDAC inhibitors used clinically as anticancer drugs. Most HDAC inhibitors nonspecifically interact with all or many of the 11 HDAC isoforms. Isoform-selective HDAC inhibitors would be useful tools to dissect the individual functions of HDAC proteins in cancer formation, in addition to potentially displaying effective anticancer properties. We report here a robust HDAC activity assay for screening selective HDAC inhibitors, which is inspired by the traditional enzyme-linked immunosorbent assay (ELISA). The key feature of the ELISA-based HDAC activity assay is use of mammalian cell-derived HDAC isoforms instead of recombinant proteins. Importantly, the assay was validated with several known HDAC inhibitors. The ELISAbased HDAC activity assay will facilitate the characterization of isoform-selective HDAC inhibitors against mammalian cell-derived HDAC proteins, which will enhance HDAC-centered cancer research and provide a foundation for anticancer drug development.

Histone deacetylase (HDAC) proteins are epigenetic regulators that deacetylate protein substrates, leading to subsequent changes in cell function. HDAC proteins are implicated in cancers, and several HDAC inhibitors have been approved by the FDA as anticancer drugs, including SAHA (suberoylanilide hydroxamic acid; Vorinostat and Zolinza). Unfortunately, SAHA inhibits most HDAC isoforms, which limits its use as a pharmacological tool and may lead to side effects in the clinic. In this work SAHA analogues substituted at the C2 position were synthesized and screened for HDAC isoform selectivity and in cells. The most potent and selective compound, C2--hexyl SAHA, displayed submicromolar potency with 49- to 300-fold selectivity for HDAC6 and HDAC8 compared to HDAC1, -2, and -3. Docking studies provided a structural rationale for selectivity. Modification of the nonselective inhibitor SAHA generated HDAC6/HDAC8 dual selective inhibitors, which can be useful lead compounds toward developing pharmacological tools and more effective anticancer drugs.

A number of analogues of the marine-derived histone deacetylase inhibitor largazole incorporating major structural changes in the depsipeptide ring were synthesized. Replacing the thiazole-thiazoline fragment of largazole with a bipyridine group gave analogue 7 with potent cell growth inhibitory activity and an activity profile similar to that of largazole, suggesting that conformational change accompanying switching hybridization from sp3 to sp2at C-7 is well tolerated. Analogue 7 was more class I selective compared to largazole, with at least 464-fold selectivity for class I HDAC proteins over class II HDAC6 compared to a 22-fold selectivity observed with largazole. To our knowledge 7 represents the first example of a potent and highly cytotoxic largazole analogue not containing a thiazoline ring. The elimination of a chiral center derived from the unnatural amino acid R-α-methylcysteine makes the molecule more amenable to chemical synthesis and, coupled with its increased class I selectivity, 7 could serve as a new lead compound for developing selective largazole analogues.

In this work, design, synthesis, and screening of thiophene carboxamides 4–13 and 16–23 as dual vascular endothelial growth factor receptors (VEGFRs) and mitotic inhibitors was reported. All compounds were screened against two gastrointestinal solid cancer cells, HepG-2 and HCT-116 cell lines. The most active cytotoxic derivatives 5 and 21 displayed 2.3- and 1.7-fold higher cytotoxicity than Sorafenib against HepG-2 cells. Cell cycle and apoptosis analyses for compounds 5 and 21 showed cells accumulation in the sub-G1 phase, and cell cycle arrest at G2/M phase. The apoptotic inducing activities of compounds 5 and 21were correlated to the elevation of p53, increase in Bax/Bcl-2 ratio, and increase in caspase-3/7.Compounds 5 and 21 showed potent inhibition againstVEGFR-2 (IC50 = 0.59 and 1.29 μM) and β-tubulin polymerization (73% and 86% inhibition at their IC50 values).Molecular docking was performed with VEGFR-2 and tubulin binding sites to explain the displayed inhibitory activities.