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 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.     

Quinazoline‐Based Hydroxamic Acids: Design,Synthesis, and Evaluation of Histone Deacetylase Inhibitory Effects and Cytotoxicity

In our search for novel histone deacetylases inhibitors, we have designed and synthesized a series of novel hydroxamic acids and N‐hydroxybenzamides incorporating quinazoline heterocycles ( 4a  –  4i , 6a  –  6i ). Bioevaluation showed that these quinazoline‐based hydroxamic acids and N‐hydroxybenzamides were potently cytotoxic against three human cancer cell lines (SW620, colon; PC‐3, prostate; NCI‐H23, lung). In term of cytotoxicity, several compounds, e.g., 4g , 4c , 4g  –  4i , 6c , and 6h , displayed from 5‐ up to 10‐fold higher potency than SAHA (suberoylanilidehydroxamic acid, vorinostat). The compounds were also generally comparable to SAHA in inhibiting HDACs with IC₅₀ values in sub‐micromolar range. Some compounds, e.g., 4g , 6c , 6e , and 6h , were even more potent HDAC inhibitors compared to SAHA in HeLa extract assay. Docking studies demonstrated that the compounds tightly bound to HDAC2 at the active binding site with binding affinities higher than that of SAHA. Detailed investigation on the estimation of absorption, distribution, metabolism, excretion, and toxicity (ADMET) suggested that compounds 4g , 6c , and 6g , while showing potent HDAC2 inhibitory activity and cytotoxicity, also potentially displayed ADMET characteristics desirable to be expected as promising anticancer drug candidates.     

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.     

Utilization of tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidinone as a cap moiety in design of novel histone deacetylase inhibitors

A series of novel 5,6,7,8-Tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one derivatives bearing a hydroxamic acid, 2-aminoanilide and hydrazide moieties as zinc-binding group (ZBG) were designed, synthesized and evaluated for the HDAC inhibition activity and antiproliferative activity. 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 IVa, IVb, IXa and IXb exhibited significant anti-proliferative activity against the three cell lines tested compared to SAHA as a reference. Compound IVb is equipotent inhibitor for HDAC1 and HDAC2 as SAHA. It is evident that the presence of free hydroxamic acid group is essential for Zn binding affinity with maximal activity with a linker of aliphatic 6 carbons. Docking study results revealed that compound IVb could occupy the HDAC2 binding site and had the potential to exhibit antitumor activity through HDAC inhibition, which merits further investigation.     

Design,synthesis and biological evaluation of novel hydroxamic acids bearing artemisinin skeleton

A series of novel hydroxamic acids bearing artemisinin skeleton was designed and synthesized. Some compounds in this series exhibited moderate inhibition against the whole cell HDAC enzymes. Especially, compound 6g displayed potent cytotoxicity against three human cancer cell lines, including HepG2 (liver cancer), MCF-7 (breast cancer) and HL-60 (leukemia cancer), with IC₅₀ values of 2.50, 2.62 and 1.28 μg/mL, respectively. Docking studies performed with two potent compounds 6a and 6g using Autodock Vina showed that both compounds bound to HDAC2 with relatively high binding affinities from −7.1 to 7.0 kcal/mol compared to SAHA (−7.4 kcal/mol). It was found in this research that most of the target compounds seemed to be more cytotoxic toward blood cancer cells (HL-60) than liver (HepG2), and breast (MCF-7) cancer cells.     

Design,synthesis and activity evaluation of indole-based double – Branched HDAC1 inhibitors

Histone deacetylases inhibitors (HDACIs) represents effective treatments for cancer. In continuing our efforts to develop novel and potent HDACIs, a series of N-hydroxycinnamamide-based HDACIs with aromatic ring and various aliphatic linker have been successfully designed and synthesized. Biological evaluations established that compounds 4h, 4i, 4j, 4l, 4r showed superior inhibition on histone deacetylase and antiproliferative activity in some solid tumor cell lines [HeLa, SK-N-BE(2), PC-3] compared to the known inhibitor SAHA. Among these analogs, 4l exhibited selectivity to HDAC1.     

New aryldithiolethione derivatives as potent histone deacetylase inhibitors

A series of dithiolethione derivatives was synthesized and the in vitro HDAC inhibitory activity was tested. The most active compounds, 1 and 2, exhibited an IC₅₀ in nM range with a strong hyperacetylation of histone H4 in A549 cells. The HDAC inhibitory activity comparable to that of SAHA and the inhibition of A549 cell proliferation suggest that these compounds are worthy of further studies as potential anticancer agents.     

Novel pyrazole integrated 1,3,4-oxadiazoles: Synthesis,characterization and antimicrobial evaluation

A novel series of 2-(5-methyl-1,3-diphenyl-1H-pyrazol-4-yl)-5-phenyl-1,3,4-oxadiazoles 7(a–m) were synthesized either by cyclization of N′-benzoyl-5-methyl-1,3-diphenyl-1H-pyrazole-4-carbohydrazide 4a using POCl₃ at 120 °C or by oxidative cyclization of hydrazones derived from various arylaldehyde and (E)-N′-benzylidene-5-methyl-1,3-diphenyl-1H-pyrazole-4-carbohydrazide 5(a–d) using chloramine-T as oxidant. Newly synthesized compounds were characterized by analytical and spectral (IR, ¹H NMR, ¹³C NMR and LC–MS) methods. The synthesized compounds were evaluated for their antimicrobial activity and were compared with standard drugs. The compounds demonstrated potent to weak antimicrobial activity. Among the synthesized compounds, compound 7m emerged as an effective antimicrobial agent, while compounds 7d, 7f, 7i and 7l showed good to moderate activity. The minimum inhibitory concentration of the compounds was in the range of 20–50 μg mL⁻¹ against bacteria and 25–55 μg mL⁻¹ against fungi. The title compounds represent a novel class of potent antimicrobial agents.     

Novel benzothiazine-piperazine derivatives by peptide-coupling as potential anti-proliferative agents

In an attempt to develop potential and selective anti-proliferative agents, a series of novel benzothiazine-piperazine derivatives 8a–i and 10a–g were synthesized by coupling of 2H-1,4-benzothiazin-3(4H)-one with various amines 7a–i and 9a–g in excellent yields and evaluated for their in vitro anti-proliferative activity against four cancer cell lines, HeLa (cervical), MIAPACA (pancreatic), MDA-MB-231 (breast) and IMR32 (neuroblastoma). In vitro inhibitory activity indicated that compounds 8a, 8d, 8g, 10a, 10b, 10e, 10f were found to be good anti-proliferative agents. Among them the derivatives 8g, 10e and 10f were found to be the most active members exhibiting remarkable growth inhibitory activity. Molecular docking was undertaken to investigate the probable binding mode and key active site interactions in HDAC8 and EHMT2 proteins. The docking results are complementary to the experimental results.     

Quinazolin‐4(3H)‐one‐Based Hydroxamic Acids: Design,Synthesis and Evaluation of Histone Deacetylase Inhibitory Effects and Cytotoxicity

The present article describes the synthesis and biological activity of various series of novel hydroxamic acids incorporating quinazolin‐4(3H)‐ones as novel small molecules targeting histone deacetylases. Biological evaluation showed that these hydroxamic acids were potently cytotoxic against three human cancer cell lines (SW620, colon; PC‐3, prostate; NCI?H23, lung). Most compounds displayed superior cytotoxicity than SAHA (suberoylanilide hydroxamic acid, Vorinostat) in term of cytotoxicity. Especially, N‐hydroxy‐7‐(7‐methyl‐4‐oxoquinazolin‐3(4H)‐yl)heptanamide ( 5b ) and N‐hydroxy‐7‐(6‐methyl‐4‐oxoquinazolin‐3(4H)‐yl)heptanamide ( 5c ) (IC₅₀ values, 0.10–0.16 μm ) were found to be approximately 30‐fold more cytotoxic than SAHA (IC₅₀ values of 3.29–3.67 μm ). N‐Hydroxy‐7‐(4‐oxoquinazolin‐3(4H)‐yl)heptanamide ( 5a ; IC₅₀ values of 0.21–0.38 μm ) was approximately 10‐ to 15‐fold more potent than SAHA in cytotoxicity assay. These compounds also showed comparable HDAC inhibition potency with IC₅₀ values in sub‐micromolar ranges. Molecular docking experiments indicated that most compounds, as represented by 5b and 5c , strictly bound to HDAC2 at the active binding site with binding affinities much higher than that of SAHA.     

Design,synthesis and antitumor activity of novel pyrazolo[3,4-d]pyrimidine derivatives as EGFR-TK inhibitors

A novel series of 2-(3,6-dimethyl-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4-yloxy)-N-(4-substitutedbenzylidene)acetohydrazide (12a–g) was prepared and their structures were confirmed by spectral and elemental analyses. The cytotoxic activity of the newly synthesized compounds was evaluated against breast carcinoma (MCF-7), non-small cell lung cancer (A549) and human colorectal adenocarcinoma (HT-29) cell lines using MTT and colony formation assays. The tested compounds showed a marked anticancer activity against all the tested cell lines, especially compound 12g, which was the most potent anticancer agent with half maximal inhibitory concentrations (IC₅₀) between 5.36 and 9.09 μM. Docking studies into ATP binding site of EGFR protein tyrosine kinase were performed to predict their scores and mode of binding to amino acids, In addition, the inhibitory activity of the target compounds against epidermal growth factor receptor tyrosine kinase (EGFR-TK) was evaluated. Results indicated the ability of the target compounds to inhibit EGFR-TK with half maximal inhibitory concentrations (IC₅₀) in the range of 4.18–35.88 μM. Furthermore, The most active compounds 12g, 12c and 12d were assayed against Fibroblast Growth Factor Receptor (FGFR), Insulin Receptor (IR) and Vascular Endothelial Growth Factor Receptor (VEGFR). The activity of the reported compounds warrants further optimization as novel members in cancer treatment protocols.     

Synthesis and biological evaluation of N-alkyl-N-(4-methoxyphenyl)pyridin-2-amines as a new class of tubulin polymerization inhibitors

Based on our prior antitumor hits, 32 novel N-alkyl-N-substituted phenylpyridin-2-amine derivatives were designed, synthesized and evaluated for cytotoxic activity against A549, KB, KB_VIN, and DU145 human tumor cell lines (HTCL). Subsequently, three new leads (6a, 7g, and 8c) with submicromolar GI₅₀ values of 0.19–0.41 μM in the cellular assays were discovered, and these compounds also significantly inhibited tubulin assembly (IC₅₀ 1.4–1.7 μM) and competitively inhibited colchicine binding to tubulin with effects similar to those of the clinical candidate CA-4 in the same assays. These promising results indicate that these tertiary diarylamine derivatives represent a novel class of tubulin polymerization inhibitors targeting the colchicine binding site and showing significant anti-proliferative activity.     

Novel N-hydroxyfurylacrylamide-based histone deacetylase (HDAC) inhibitors with branched CAP group (Part 2)

Histone deacetylases (HDACs) are significant enzymes involved in tumor genesis and development. Herein, we report a series of novel N-hydroxyfurylacryl-amide-based HDAC inhibitors, which are marked by introducing branched hydrophobic groups as the capping group. The inhibitory activity of the synthesized compounds against HDACs and several tumor cell lines are firstly determined. Fifteen compounds with promising activities are selected for further evaluation of target selectivity profile against recombinant human HDAC1, HDAC4 and HDAC6. Compounds 10a, 10b, 10d and 16a exhibit outstanding selectivity against HDAC6. Analysis of HDAC4 X-ray structure and HDAC1, HDAC6 homology model indicates that these enzyme differ significantly in the rim near the surface of the active site. Although TSA has been known as a pan-HDAC inhibitor, it exhibits outstanding selectivity for HDAC6 over HDAC4. For further physicochemical properties study, six compounds are chosen for determination of their physicochemical properties including log D_7.4 and aqueous solubility. The results suggest that compounds with a smaller framework and with hydrophilicgroups are likely to have better aqueous solubility.     

N-Hydroxy-1,2-disubstituted-1H-benzimidazol-5-yl acrylamides as novel histone deacetylase inhibitors: Design,synthesis, SAR studies,and in vivo antitumor activity

A series of N-hydroxy-1,2-disubstituted-1H-benzimidazol-5-yl acrylamides were designed and synthesized as novel HDAC inhibitors. General SAR has been established for the substituents at positions 1 and 2, as well as the importance of the ethylene group and its attachment to position 5. Optimized compounds are much more potent than SAHA in both enzymatic and cellular assays. A representative compound, 23 (SB639), has demonstrated antitumor activity in a colon cancer xenograft model.     

Synthesis,pharmacological screening and in silico studies of new class of Diclofenac analogues as a promising anti-inflammatory agents

A novel series of 5-[2-(2,6-dichlorophenylamino)benzyl]-3-(substituted)-1,3,4-oxadiazol-2(3H)-thione (4a–k) derivatives have been synthesized by the Mannich reaction of 5-[2-(2,6-dichlorophenylamino)benzyl]-1,3,4-oxadiazol-2(3H)-thione (3) with an appropriately substituted primary/secondary amines, in the presence of formaldehyde and absolute ethanol. Structures of these novel compounds were characterized on the basis of physicochemical, spectral and elemental analysis. The title compounds (4a–k) were screened for in vivo acute anti-inflammatory and analgesic activities at a dose of 10 mg/kg b.w. Compound 4k exhibited the most promising and significant anti-inflammatory profile while compounds 4a, 4d, 4e, 4i, and 4j showed moderate to good inhibitory activity at 2nd and 4th h, respectively. These compounds were also found to have considerable analgesic activity (acetic acid induced writhing model) and antipyretic activity (yeast induced pyrexia model). In addition, the tested compounds were also found to possess less degree of ulcerogenic potential as compared to the standard NSAIDs. Compounds that displayed promising anti-inflammatory profile were further evaluated for their inhibitory activity against cyclooxygenase enzyme (COX-1/COX-2), by colorimetric COX (ovine) inhibitor screening assay method. The results revealed that the compounds 4a, 4e, 4g and 4k exhibited effective inhibition against COX-2. In an attempt to understand the ligand–protein interactions in terms of the binding affinity, docking studies were performed using Molegro Virtual Docker (MVD-2013, 6.0) for those compounds, which showed good anti-inflammatory activity. It was observed that the binding affinities calculated were in agreement with the IC₅₀ values.     

Design and synthesis of novel HDAC8 inhibitory 2,5-disubstituted-1,3,4-oxadiazoles containing glycine and alanine hybrids with anti cancer activity

Oxadiazole is a heterocyclic compound containing an oxygen atom and two nitrogen atoms in a five-membered ring. Of the four oxadiazoles known, 1,3,4-oxadiazole has become an important structural motif for the development of new drugs and the compounds containing 1,3,4-oxadiazole cores have a broad spectrum of biological activity. Herein, we describe the design, synthesis and biological evaluation of a series of novel 2,5-disubstituted 1,3,4-oxadiazoles (10a–10j) as class I histone deacetylase (HDAC) inhibitors. The compounds were designed and evaluated for HDAC8 selectivity using in silico docking software (Glide) and the top 10 compounds with high dock score and obeying Lipinski’s rule were synthesized organically. Further the biological HDAC inhibitory and selectivity assays and anti-proliferative assays were carried out. In in silico and in vitro studies, all compounds (10a–10j) showed significant HDAC inhibition and exhibited HDAC8 selectivity. Among all tested compounds, 10b showed substantial HDAC8 inhibitory activity and better anticancer activity which is comparable to the positive control, a FDA approved drug, vorinostat (SAHA). Structural activity relation is discussed with various substitutions in the benzene ring connected on 1,3,4-oxadizole and glycine/alanine. The study warranted further investigations to develop HDAC8-selective inhibitory molecule as a drug for neoplastic diseases. Novel 1,3,4-oxadizole substituted with glycine/alanine showed HDAC8 inhibition.     

Synthesis and biological evaluation of 2-quinolineacrylamides

A series of C6-substituted N-hydroxy-2-quinolineacrylamides (3–15), with four types of bridging groups have been synthesized. Most of these compounds exhibit antiproliferative activity against A549 and HCT116 cells and Western blot analysis revealed that they are able to inhibit HDAC. Measurement of the HDAC isoform activity of ether-containing compounds showed that compound 9 has distinct HDAC6 selectivity, more than 300-fold over other isoforms. This paper describes the development of 6-aryloxy-N-hydroxy-2-quinolineacrylamides as potential HDAC6 inhibitors.     

Synthesis,analgesic and anti-inflammatory activities of some novel pyrazolines derivatives

In search for a new analgesic and anti-inflammatory agent with improved potency, we designed and synthesized a series of 3,2-(4,5-dihydro-5-(4-morphilinophenyl)-1H-pyarazol-3-yl)phenols 6(a–g) and its N-phenylpyrazol-1-carbothioamide 7(a–g) by Claisan–Schmidt condensation followed by the reaction of hydrazine hydrate. All the synthesized compounds were assayed for their in vivo analgesic and anti-inflammatory activities. All the compounds synthesized showed the potential to demonstrate analgesic and anti-inflammatory activity, of particular interest compounds 6a, 6b, 6g, 7a, 7d and 7g were found comparable to Diclofenac.     

Green synthesis,inhibition studies of yeast α-glucosidase and molecular docking of pyrazolylpyridazine amines

An efficient and environmentally benign simple fusion reaction of 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (1a) or 3-chloro-6-(3,5-dimethyl-4-nitro-1H-pyrazol-1-yl)pyridazine (2a) with different aliphatic/aromatic amines have produced a series of novel pyrazolylpyridazine amines (4a–4c & 5a–5m). All compounds exhibited moderate in vitro yeast α-glucosidase inhibition except m-chloro derivative 5g, which was found potent inhibitor of this enzyme with IC₅₀ value of 19.27 ± 0.005 µM. The molecular docking further helped in understanding the structure activity relationship of these compounds including 5g.