Design, synthesis and docking studies on benzamide derivatives as histone deacetylase inhibitors

A series of benzamide derivatives including two scaffolds were designed and synthesized as potential histone deacetylase inhibitors. Most of synthesized compounds showed moderate enzymatic potency at the same order of magnitude, and compound 12b possessed better potency to the positive control (3.8 μM vs 13.0 μM). It also showed a 50-fold increase in vitro anticancer activity against DU-145 cell-lines. Molecular docking studies were carried out and used to explain the structure-activity relationships observed in vitro. Then we found that the cavity surrounded by ASP104, HIS33, PRO34 and PHE155 may be crucial for the inhibitors’ activity. The docking results provide some useful information for future design of more potent inhibitors.     

Development of novel ferulic acid derivatives as potent histone deacetylase inhibitors

Histone deacetylase inhibitors (HDACIs) offer a promising strategy for cancer therapy. The discovery of potent ferulic acid-based HDACIs with hydroxamic acid or 2-aminobenzamide group as zinc binding group was reported. The halogeno-acetanilide was introduced as novel surface recognition moiety (SRM). The majority of title compounds displayed potent HDAC inhibitory activity. In particular, FA6 and FA16 exhibited significant enzymatic inhibitory activities, with IC₅₀ values of 3.94 and 2.82 μM, respectively. Furthermore, these compounds showed moderate antiproliferative activity against a panel of human cancer cells. FA17 displayed promising profile as an antitumor candidate. The results indicated that these ferulic acid derivatives could serve as promising lead compounds for further optimization.     

Search for novel histone deacetylase inhibitors. Part II: Design and synthesis of novel isoferulic acid derivatives

Previously, we described the discovery of potent ferulic acid-based histone deacetylase inhibitors (HDACIs) with halogeno-acetanilide as novel surface recognition moiety (SRM). In order to improve the affinity and activity of these HDACIs, twenty seven isoferulic acid derivatives were described herein. The majority of title compounds displayed potent HDAC inhibitory activity. In particular, IF5 and IF6 exhibited significant enzymatic inhibitory activities, with IC₅₀ values of 0.73 ± 0.08 and 0.57 ± 0.16 μM, respectively. Furthermore, these compounds showed moderate antiproliferative activity against human cancer cells. Especially, IF6 displayed promising profile as an antitumor candidate with IC₅₀ value of 3.91 ± 0.97 μM against HeLa cells. The results indicated that these isoferulic acid derivatives could serve as promising lead compounds for further optimization.     

An efficient synthesis of SK-658 and its analogs as potent histone deacetylase inhibitors

SK-658 is a potent histone deacetylase (HDAC) inhibitor that showed higher activity than SAHA due to the presence of extended hydrophobic group. We designed and synthesized thioester and SS-hybrid bearing SK-658 analogs as HDAC inhibitors. All the compounds were active in nano molar range and showed higher inhibitory activity than SAHA and SK-658. Among these, disulfide compounds showed the highest activity.     

Design and synthesis of aryl ether and sulfone hydroxamic acids as potent histone deacetylase (HDAC) inhibitors

A series of novel hydroxamic acid based histone deacetylases (HDAC) inhibitors with aryl ether and aryl sulfone residues at the terminus of a substituted, unsaturated 5-carbon spacer moiety have been synthesized for the first time and evaluated. Compounds with meta- and para-substitution on the aryl ring of ether hydroxamic acids 19c, 20c, 19e, 19f and 19g are potent HDAC inhibitors with activities at low nanomolar levels.     

Molecular design of histone deacetylase inhibitors by aromatic ring shifting in chlamydocin framework

Chlamydocin, a cyclic tetrapeptide containing aminoisobutyric acid (Aib), l-phenylalanine (l-Phe), d-proline (d-Pro), and a unique amino acid l-2-amino-8-oxo-9,10-epoxydecanoic acid, inhibits the histone deacetylases (HDACs), a class of enzymes, which play important roles in regulation of gene expression. Sulfur containing amino acids can also inhibit potently, so zinc ligand, such as sulfhydryl group connected with a linker to the so-called capping group, corresponding to cyclic tetrapeptide framework in case of chlamydocin is supposed to interact with the surface of HDAC molecule. Various changes in amino acid residues in chlamydocin may afford specific inhibitors toward HDAC paralogs. To find out specific inhibitors, we focused on benzene ring of l-Phe in chlamydocin framework to shift to various parts of cyclic tetrapeptide. We prepared and introduced several aromatic amino acids into the cyclic tetrapeptides. By evaluating inhibitory activity of these macrocyclic peptides against HDACs, we could find potent inhibitors by shifting the aromatic ring to the Aib site.     

Coumarin-suberoylanilide hydroxamic acid as a fluorescent probe for determining binding affinities and off-rates of histone deacetylase inhibitors

Histone deacetylases (HDACs) are intimately involved in epigenetic regulation and, thus, are one of the key therapeutic targets for cancer, and two HDAC inhibitors, namely suberoylanilide hydroxamic acid (SAHA) and romidepsin, have been recently approved for cancer treatment. Because the screening and detailed characterization of HDAC inhibitors has been time-consuming, we synthesized coumarin-SAHA (c-SAHA) as a fluorescent probe for determining the binding affinities (K_d) and the dissociation off-rates (k_off) of the enzyme–inhibitor complexes. The determination of the above parameters relies on the changes in the fluorescence emission intensity (λ_ex = 325 nm, λ_em = 400 nm) of c-SAHA due to its competitive binding against other HDAC inhibitors, and such determination neither requires employment of polarization accessories nor is dependent on the fluorescence energy transfer from the enzyme’s tryptophan residues to the probe. Our highly sensitive and robust analytical protocol presented here is applicable to most of the HDAC isozymes, and it can be easily adopted in a high-throughput mode for screening the HDAC inhibitors as well as for quantitatively determining their K_d and k_off values.     

2,5-Disubstituted-1,3,4-oxadiazoles/thiadiazole as surface recognition moiety: design and synthesis of novel hydroxamic acid based histone deacetylase inhibitors

The enzymatic inhibition of histone deacetylase activity has come out as a novel and effectual means for the treatment of cancer. Two novel series of 2-[5-(4-substitutedphenyl)-[1,3,4]-oxadiazol/thiadiazol-2-ylamino]-pyrimidine-5-carboxylic acid (tetrahydro-pyran-2-yloxy)-amides were designed and synthesized as novel hydroxamic acid based histone deacetylase inhibitors. The antiproliferative activities of the compounds were investigated in vitro using histone deacetylase inhibitory assay and MTT assay. The synthesized compounds were also tested for antitumor activity against Ehrlich ascites carcinoma cells in Swiss albino mice. The efforts were also made to establish structure-activity relationships among synthesized compounds. The results of the present studying indicates 2,5-disubstituted 1,3,4-oxadiazole/thiadiazole as promising surface recognition moiety for development of newer hydroxamic acid based histone deacetylase inhibitor.     

Design,synthesis, docking studies and biological evaluation of novel chalcone derivatives as potential histone deacetylase inhibitors

A group of novel chalcone derivatives comprising hydroxamic acid or 2-aminobenzamide group as zinc binding groups (ZBG) were synthesized. The structure of the prepared compounds was fully characterized by IR, NMR and elemental microanalyses. Most of the tested compounds displayed strong to moderate HDAC inhibitory activity. Some of these compounds showed potent anti-proliferative activity against human HepG2, MCF-7 and HCT-116 cell lines. In particular, compounds 4a and 4b exhibited significant anti-proliferative activity against the three cell lines compared to SAHA as reference drug and displayed promising profile as anti-tumor candidates. The results indicated that these chalcone derivatives could serve as a promising lead compounds for further optimization as antitumor agents.     

Design and synthesis of novel and highly-active pan-histone deacetylase (pan-HDAC) inhibitors

Histone deacetylase (HDAC) inhibitions are known to elicit anticancer effects. We designed and synthesized several HDAC inhibitors. Among these compounds, compound 40 exhibited a more than 10-fold stronger inhibitory activity compared with that of suberoylanilide hydroxamic acid (SAHA) against each human HDAC isozyme in vitro (IC₅₀ values of 40: HDAC1, 0.0038 μM; HDAC2, 0.0082 μM; HDAC3, 0.015 μM; HDAC8, 0.0060 μM; HDAC4, 0.058 μM; HDAC9, 0.0052 μM; HDAC6, 0.058 μM). The dose of the administered HDAC inhibitors that contain hydroxamic acid as the zinc-binding group may be reduced by 40. Because the carbostyril subunit is a time-tested structural component of drugs and biologically active compounds, 40 most likely exhibits good absorption, distribution, metabolism, excretion, and toxicity (ADMET). Thus, compound 40 is expected to be a promising therapeutic agent or chemical tool for the investigation of life process.     

Benzothiazole-containing hydroxamic acids as histone deacetylase inhibitors and antitumor agents

Data from clinical studies indicate that inhibitors of Class I and Class II histone deacetylase (HDAC) enzymes show great promise for the treatment of cancer. Zolinza (SAHA, Zolinza) was recently approved by the FDA for the treatment of the cutaneous manifestations of cutaneous T-cell lymphoma. As a part of our ongoing effort to identify novel small molecules to target these important enzymes, we have prepared two series of benzothiazole-containing analogues of SAHA. It was found that several compounds with 6C-bridge linking benzothiazole moiety and hydroxamic functional groups showed good inhibition against HDAC3 and 4 at as low as 1 μg/ml and exhibited potent cytotoxicity against five cancer cell lines with average IC₅₀ values of as low as 0.81 μg/ml, almost equipotent to SAHA.     

Design,synthesis and preliminary bioactivity studies of 1,2-dihydrobenzo[d]isothiazol-3-one-1,1-dioxide hydroxamic acid derivatives as novel histone deacetylase inhibitors

Histone deacetylase (HDAC) is a clinically validated target for antitumor therapy. In order to increase HDAC inhibition and efficiency, we developed a novel series of saccharin hydroxamic acids as potent HDAC inhibitors. Among them, compounds 11e, 11m, 11p exhibited similar or better HDACs inhibitory activity compared with the approved drug SAHA. Further biological evaluation indicated that compound 11m had potent antiproliferative activities against MDA-MB-231 and PC-3.     

Aurones as histone deacetylase inhibitors: Identification of key features

In this study, a total of 22 flavonoids were tested for their HDAC inhibitory activity using fluorimetric and BRET-based assays. Four aurones were found to be active in both assays and showed IC₅₀ values below 20 μM in the enzymatic assay. Molecular modelling revealed that the presence of hydroxyl groups was responsible for good compound orientation within the isoenzyme catalytic site and zinc chelation.     

Discovery of indole-3-butyric acid derivatives as potent histone deacetylase inhibitors

In discovery of HDAC inhibitors (HDACIs) with improved anticancer potency, structural modification was performed on the previous derived indole-3-butyric acid derivative. Among all the synthesised compounds, molecule I13 exhibited high HDAC inhibitory and antiproliferative potencies in the in vitro investigations. The IC₅₀ values of I13 against HDAC1, HDAC3, and HDAC6 were 13.9, 12.1, and 7.71 nM, respectively. In the cancer cell based screening, molecule I13 showed increased antiproliferative activities in the inhibition of U937, U266, HepG2, A2780, and PNAC-1 cells compared with SAHA. In the HepG2 xenograft model, 50 mg/kg/d of I13 could inhibit tumour growth in athymic mice compared with 100 mg/kg/d of SAHA. Induction of apoptosis was revealed to play an important role in the anticancer potency of molecule I13. Collectively, a HDACI (I13) with high anticancer activity was discovered which can be utilised as a lead compound for further HDACI design.     

Design,synthesis and evaluation of novel indirubin-based N-hydroxybenzamides,N-hydroxypropenamides and N-hydroxyheptanamides as histone deacetylase inhibitors and antitumor agents

Several novel indirubin-based N-hydroxybenzamides, N-hydropropenamides and N-hydroxyheptanamides (4a-h, 7a-h, 10a-h) were designed using a fragment-based approach with structural features extracted from several previously reported HDAC inhibitors, such as SAHA (vorinostat), MGCD0103 (mocetinostat), nexturastat A and PXD-101 (belinostat). The biological results reveal that our compounds showed excellent cytotoxicity toward three common human cancer cell lines (SW620, PC-3 and NCI-H23) with IC₅₀ values ranging from 0.09 to 0.007 µM. The cytotoxicity of the compounds was equipotent or even up to 10-times more potent than adriamycin and up to 205-times more potent than SAHA. Among the series of N-hydroxypropenamides, compounds 10a-d were the most potent HDAC inhibitors as well as cytotoxicity toward the cell lines tested. In addition, the strong inhibitory activites toward HDAC of our compounds were observed with IC₅₀ values of below-micromolar range. Especially, compound 4a inhibited HDAC6 with an IC₅₀ value of 29-fold lower than that against HDAC2 isoform. Representative compounds 4a and 7a were found to significantly arrest SW620 cells at G0/G1 phase. Compounds 7a and 10a were found to strongly induce apoptosis in SW620 cells. Docking studies revealed some important features affecting the selectivity against HDAC6 isoform. The results clearly demonstrate the potential of the indirubin-hydroxamic acid hybrids and these compounds should be very promising for further development.     

Design,synthesis and biological evaluation of di-substituted cinnamic hydroxamic acids bearing urea/thiourea unit as potent histone deacetylase inhibitors

A novel class of di-substituted cinnamic hydroxamic acid derivatives containing urea or thiourea unit was designed, synthesized and evaluated as HDAC inhibitors. All tested compounds demonstrated significant HDAC inhibitory activities and anti-proliferative effects against diverse human tumor cell lines. Among them, 7l exhibited most potent pan-HDAC inhibitory activity, with an IC₅₀ value of 130 nM. It also showed strong cellular inhibition against diverse cell lines including HCT-116, MCF-7, MDB-MB-435 and NCI-460, with GI₅₀ values of 0.35, 0.22, 0.51 and 0.48 μM, respectively.     

Design, synthesis and preliminary biological evaluation of new hydroxamate histone deacetylase inhibitors as potential antileukemic agents

This study concerns the synthesis of new histone deacetylase inhibitors (HDACi) characterized by a 1,4-benzodiazepine ring used as the cap, joined through an amide function or a triple bond as connection units, to a linear alkyl chain bearing the hydroxamate function as Zn2+-chelating group. Biological tests performed in human acute promyelocytic leukemia NB4 cells showed that new hybrids can induce histone H3/H4 acetylation, growth arrest, and also apoptosis. Notably, chiral compounds exhibit stereoselective activity.     

The design, synthesis and structure-activity relationships of novel isoindoline-based histone deacetylase inhibitors

The design, synthesis and biological evaluation of a novel series of isoindoline-based hydroxamates is described. Several analogs were shown to inhibit HDAC1 with IC₅₀ values in the low nanomolar range and inhibit cellular proliferation of HCT116 human colon cancer cells in the sub-micromolar range. The cellular potency of compound 17e was found to have greater in vitro anti-proliferative activity than several compounds in late stage clinical trials for the treatment of cancer. The in vitro safety profiles of selected compounds were assessed and shown to be suitable for further lead optimization.     

Design,synthesis and evaluation of novel N-hydroxybenzamides/N-hydroxypropenamides incorporating quinazolin-4(3H)-ones as histone deacetylase inhibitors and antitumor agents

In our search for novel small molecules targeting histone deacetylases, we have designed and synthesized several series of novel N-hydroxybenzamides/N-hydroxypropenamides incorporating quinazolin-4(3H)-ones (4a-h, 8a-d, 10a-d). Biological evaluation showed that these hydroxamic acids were generally cytotoxic against three human cancer cell lines (SW620, colon; PC-3, prostate; NCI-H23, lung cancer). It was found that the N-hydroxypropenamides (10a-d) were the most potent, both in term of HDAC inhibition and cytotoxicity. Several compounds, e.g. 4e, 8b-c, and 10a-c, displayed up to 4-fold more potent than SAHA (suberoylanilide hydroxamic acid, vorinostat) in term of cytotoxicity. These compounds also comparably inhibited HDACs with IC₅₀ values in sub-micromolar range. Docking experiments on HDAC2 isozyme revealed some important features contributing to the inhibitory activity of synthesized compounds, especially for propenamide analogues. Importantly, the free binding energy computed was found to have high quantitative correlation (R² ∼ 95%) with experimental results.