Baicalein, 7,8-Dihydroxyflavone and Myricetin as Potent Inhibitors of Human Ornithine Decarboxylase

Background: Human ornithine decarboxylase (ODC) is a well-known oncogene, and the discovery of ODC enzyme inhibitors is a beneficial strategy for cancer therapy and prevention. Methods: We examined the inhibitory effects of a variety of flavone and flavonol derivatives on ODC enzymatic activity, and performed in silico molecular docking of baicalein, 7,8-dihydroxyflavone and myricetin to the whole dimer of human ODC to investigate the possible binding site of these compounds on ODC. We also examined the cytotoxic effects of these compounds with cell-based studies. Results: Baicalein, 7,8-dihydroxyflavone and myricetin exhibited significant ODC suppression activity with IC₅₀ values of 0.88 µM, 2.54 µM, and 7.3 µM, respectively, which were much lower than that of the active-site irreversible inhibitor α-DL-difluoromethylornithine (IC₅₀, the half maximal inhibitory concentration, of approximately 100 µM). Kinetic studies and molecular docking simulations suggested that baicalein, and 7,8-dihydroxyflavone act as noncompetitive inhibitors that are hydrogen-bonded to the region near the active site pocket in the dimer interface of the enzyme. Baicalein and myricetin suppress cell growth and induce cellular apoptosis, and both of these compounds suppress the ODC-evoked anti-apoptosis of cells. Conclusions: Therefore, we suggest that the flavone or flavonol derivatives baicalein, 7,8-dihydroxyflavone, and myricetin are potent chemopreventive and chemotherapeutic agents that target ODC.     

Synthesis and antiproliferative evaluation of 23-hydroxybetulinic acid derivatives

Based on structural modifications of the natural 23-hydroxybetulinic acid, a series of novel its derivatives had been synthesized. The new compounds were screened for in vitro antiproliferative activity against cancer cell lines HeLa, MCF-7, HepG2, B16 and A375 using doxorubicin as a reference. The vast majority of derivatives had exhibited potent tumor growth inhibitory activity than original compound. The derivatives 4, 5, 7, 20, 23, 26, 43 and 44 with IC50 values lower than 10 μM on all tested cell lines were regarded as the most promising compounds. The structure-activity relationships of 23-hydroxybetulinic acid derivatives were also discussed in the present investigations.     

Synthesis and biological activity of novel inhibitors of topoisomerase I: 2-aryl-substituted 2-bis-1H-benzimidazoles

Inhibitors of topoisomerase I constitute a novel family of antitumor agents. The class of benzimidazole derivatives contains compounds possessing affinity to DNA. For example, fluorescent stains Hoechst 33342 and Hoechst 33258 interact with DNA as ligand and produce nonspecific inhibition of the catalytic activity of many enzymes involved in DNA synthesis, including DNA topoisomerase and DNA helicase. Several 2-aryl-5-substituted-2,5-bisbenzimidazole derivatives were synthesized and ability of these derivatives to induce DNA cleavage in the presence of topoisomerase I was evaluated in vitro. These analogs were also assayed for their cytotoxicity against U87, MCF7 and HeLa human tumor cells. All the four compounds showed a potent growth inhibitory effect on all the cell lines, with IC₅₀ in the μM range.     

Synthesis of N-aryl-5-amino-4-cyanopyrazole derivatives as potent xanthine oxidase inhibitors

Some pyrazolo[3,4-d]pyrimidines, structurally related with allopurinol, a well known xanthine oxidase inhibitor, clinically used in the therapy of gout, have also been reported as potent inhibitors of xanthine oxidase and the growth of several human tumour cell lines. Considering the potential interest of this family of compounds, the aim of the present study was to synthesise and provide a full chemical characterization of new N-aryl-5-amino-4-cyanopyrazole derivatives and their corresponding pyrazolo[3,4-d]pyrimidines. Their biological activity pertaining to the xanthine oxidase inhibition and effect on the growth of three tumour cell lines (MCF-7, NCI-H460, and SF-268) are also provided. With only one exception, the synthesised compounds showed no effect on the growth of the three tumour cell lines. However, a strong xanthine oxidase inhibitory activity was observed for almost all pyrazolo[3,4-d]pyrimidines tested, revealing some of them IC(50) values below 1 microM. The results of the molecular docking studies of these compounds, against xanthine oxidoreductase are also described, providing an atomistic explanation of the differences in the inhibitory efficiency. MEP calculations were used to explain different inhibitory efficiency of similar inhibitors.     

Synthesis of novel substituted 1,3-diaryl propenone derivatives and their antimalarial activity in vitro

The synthesis of novel 1,3-diaryl propenone derivatives and their antimalarial activity in vitro against asexual blood stages of human malaria parasite, Plasmodium falciparum, are described. Chalcone derivatives were prepared via Claisen-Schmidt condensation of substituted aldehydes with substituted methyl ketones. Antiplasmodial IC(50) (half maximal inhibitory concentration) activity of these compounds ranged between 1.5 and 12.3 microg/ml. The chloro-series, 1,2,4-triazole substituted chalcone was found to be the most effective in inhibiting the growth of P. falciparum in vitro while pyrrole and benzotriazole substituted chalcones showed relatively less inhibitory activity. This is the first report on antiplasmodial activity of chalcones with azoles on acetophenone ring.     

Synthesis, structure and anticancer activity of novel alkenyl-1,3,5-triazine derivatives

A series of novel 4-(E)-ethenyl-6-alkylamino-1,3,5-triazin-2-ylamine derivatives 9-17 have been synthesized by a Wittig reaction of corresponding alkyltriphenylphosphonium bromides 5-8 with (hetero)aromatic aldehydes. The E configuration of these alkenes was confirmed by 1H NMR spectroscopic data. All the compounds prepared were screened at the National Cancer Institute (NCI) for their activity against a panel of 56 tumor cell lines and relationship between structure and in vitro antitumor activity is discussed. The most active compounds 14 and 17 showed 50% growth inhibitory activity in low micromolar concentrations against renal cancer A498 cell line and colon cancer cell line COLO 205, respectively.     

Efficient synthesis of 6-(hetero)arylthieno[3,2-b]pyridines by Suzuki-Miyaura coupling. Evaluation of growth inhibition on human tumor cell lines, SARs and effects on the cell cycle

A wide variety of new bi(hetero)aryl derivatives of the thieno[3,2-b]pyridine skeleton was obtained in high to excellent yields (65-91%) by Suzuki-Miyaura cross-coupling of the methyl 3-amino-6-bromothieno[3,2-b]pyridine-2-carboxylate, recently reported by us, with aryl or heteroaryl pinacolboranes or potassium trifluoroborates. The coupling products obtained were evaluated for their growth inhibitory effect on three human tumor cell lines, representing different tumor models, MCF-7 (breast adenocarcinoma), A375-C5 (melanoma) and NCI-H460 (non-small cell lung cancer). Some of the compounds showed an interesting activity against the tested cell lines, with GI50 values in the μM range, and it was possible to establish some structure-activity relationships (SARs). Several compounds presented GI50 values below 15 μM, particularly a bithiophene and an o-aniline thienopyridine derivative. The first presented selectivity for MCF-7 and NCI-H460 cell lines, with very low GI50 values (0.7-1.0 μM), while the latter was active against the three cell lines tested in this study, also presenting very low GI50 values (2.5-4.2 μM). The effect of these two compounds on cell cycle progression was analyzed in the NCI-H460 cell line. Results showed that both compounds interfered with the normal cell cycle distribution.     

Design, synthesis and structure-activity relationships of antiproliferative 1,3-disubstituted urea derivatives

Twenty-four new 1,3-disubstituted urea derivatives were synthesized and reported for the first time. The antiproliferative activities of these compounds were evaluated against a panel of one human liver cell line (L02) and two human tumor cell lines (KB and K562) by applying the MTT colorimetric assay. The series of 1,3-disubstituted urea derivatives show good antiproliferative activity against human cancer cell lines (KB and K562) and no antiproliferative activity against liver cell line (L02). The potent in vitro antiproliferative activity of these derivatives and their selectivity for L02 are quite important points for an anticancer drug candidate with fewer side effects. Structure-activity relationships were also discussed based on the obtained experimental data. The hydroxyl groups on the phenyl ring reduced the antiproliferative activities of 1,3-disubstituted urea derivatives. The OH groups could be responsible for a reduction in the permeability of the cell membrane. Generally, an aromatic ring on N-3 seems to be in favor of enhancing the inhibitory activity, compounds introduced a nitro group substituent at C-3 position on the aromatic ring approved to generally decrease activity.     

Synthesis and in vitro antiproliferative activity of novel 1-benzhydrylpiperazine derivatives against human cancer cell lines

In order to explore the antiproliferative effect associated with the piperazine framework, several 1-benzhydrylpiperazine derivatives 8(a-d), 9(a-d) and 10(a-h) were synthesized. Variation in the functional group at N-terminal of the piperazine led to three sets of compounds, bearing the sulfonyl, amide and thiourea, respectively. Their chemical structures were confirmed by (1)H NMR, LCMS, IR and elemental analysis. The antiproliferative effect of the compounds were evaluated in vitro using the MTT colorimetric method against one normal cell line (NF-103 skin fibroblast cells) and four human cancer cell lines (MCF-7 breast carcinoma cell line, HepG-2 hepatocellular carcinoma cell line, HeLa cervix carcinoma cell line and HT-29 colon carcinoma cell line) for the time period of 24 h. Among the series, four compounds exhibited interesting growth inhibitory effects against all four cell lines.     

Synthesis and antiproliferative activity of aryl- and heteroaryl-hydrazones derived from xanthone carbaldehydes

In order to explore the antiproliferative effect associated with the xanthone framework, several arylhydrazonomethyl derivatives were synthesized from various isomeric 1,3-dihydroxyxanthone carbaldehydes. Variation in the position of the aldehydic function led to three sets of compounds, bearing the hydrazonomethyl chain at positions 5, 6 or 7 on the xanthone nucleus, respectively. The antiproliferative effect of the compounds was evaluated in vitro using the MTT colorimetric method against two human cancer cell lines (MCF-7, breast adenocarcinoma, and KB 3.1, squamous cell oral carcinoma) for two time periods (24 h and 72 h). Among the series, four compounds exhibited interesting growth inhibitory effects against both the cell lines, with IC(50) values in the micromolar concentration range. When compared with doxorubicin, the xanthone derivatives showed moderate cytotoxic effects. Surprisingly, unlike doxorubicin, these compounds displayed no significant time-dependent change in the concentration causing 50% inhibitory effect in proliferation. This unusual cytotoxicity profile led to the hypothesis that these molecules could be endowed with a mechanism of action distinct to that of doxorubicin.     

Synthesis, brain antihypoxic activity and cell neuroprotection of 1-substituted-3,7-dimethylxanthines

Five newly synthesised original compounds were investigated for acute toxicity, influence on hexobarbital sleeping time, effect on the locomotor activity, and brain antihypoxic activity. Two of the compounds were tested in a model of glutamate induced neurotoxicity in the brain cell culture using a cell viability test. Our studies indicate that compounds 2a-c and 4 prolonged the survival time of mice in the model of anoxic hypoxia. Only compound 3 expressed antihypoxic activity in the model of circulatory hypoxia, evaluated with a statistical significant increase of the survival time. Compound 4 (1-[3-(2,3-dihydro-3-oxobenzisosulfonazol2-yl)-propyl]-3,7-dimethylxanthine) in concentration range 0.3-3 microM statistically significantly antagonised the glutamate induced neurotoxicity. Compound 4 is important for further investigations on in vivo models of brain dementia.     

Synthesis and in vitro evaluation of 1,8-diazaanthraquinones bearing 3-dialkylaminomethyl or 3-(N-alkyl- or N-aryl)carbamoyloxymethyl substituent

A series of 1,8-diazaanthraquinone derivatives carrying a 3-dialkylaminomethyl or a 3-(N-alkyl or aryl)carbamoyloxymethyl substituent was synthesised and their in vitro cytotoxic activities were evaluated against eight human cancer cell lines (HOP62, SK-OV-3, HCT-15, SF295, MCF7, SNU-354, KB-3-1 and KB-V-1). A number of compounds including 8c, 8d and 11c showed cytotoxic activity comparable to that of doxorubicin against all human cancer cell lines tested. The compounds 8c and 8d were 2-100 times more potent than doxorubicin against HCT-15, MCF7 and SNU-354 cancer cell lines. Furthermore, these compounds retained considerable cytotoxic activity against the doxorubicin-resistant cell line KB-V-1, implying their therapeutic potential to treat doxorubicin-resistant tumours. These compounds inhibited topoisomerase II-mediated DNA relaxation in vitro, suggesting that this inhibitory effect be attributable to their cytotoxicity.     

Synthesis and aldose reductase inhibitory activity of a new series of 5-[[2-(ω-carboxyalkoxy)aryl]methylene]-4-oxo-2-thioxothiazolidine derivatives

Anew series of 5-[[2-(ω-carboxyalkoxy)aryl]methylene]-4-oxo-2-thioxothiazolidine derivatives was synthesized and evaluated for their potency as aldose reductase inhibitors (ARIs). Their activities were examined in terms of their inhibitory effect on rat lens aldose reductase in vitro and in terms of the preventive effect on sorbitol accumulation in the sciatic nerve of streptozotocin (STZ)-induced diabetic rats in vivo. Of these compounds, some of the naphthylmethylene thiazolidine derivatives were comparable to Zenarestat in the inhibitory potency in vitro and in vivo. In particular, compound 30 was 1.5 times more potent than Zenarestat in the in vivo activity, and had an adequate potency for clinical development.     

Design, synthesis and discovery of 5-hydroxyaurone derivatives as growth inhibitors against HUVEC and some cancer cell lines

A series of 4'-substituted 5-hydroxyaurone derivatives were synthesized and their inhibitory activities against the proliferation of endothelial cells and two cancer cell lines were studied. Some of these compounds functioned as potent inhibitors against the proliferation of endothelial cells and cancer cells but possessed much weaker cytotoxic activities against non-cancer cell line of CCC-HPF-1. It was demonstrated that two most active compounds 16 and 27 effectively inhibited in vitro endothelial cell motility and tube formation, which are basic properties of endothelial cells for angiogenesis. Moreover, 16 and 27 also showed significant activities against in vitro cancer cell invasion, indicating that they have potential to inhibit cancer metastasis. These composite results suggest that 4'-substituted 5-hydroxyaurone is indeed a candidate structural scaffold for anticancer agent targeting activated endothelial cells and fast-proliferating cancer cells.     

Synthesis and in vitro antitumor activity of new quinoxaline derivatives

A series of novel 5,7-diamino-3-phenyl-2-benzylamino, 2-phenoxy, and 2-thiophenyl substituted quinoxalines has been designed, synthesized and evaluated for their in vitro antitumor activity towards cell lines of nine different types of human cancers. Some of these compounds exhibited inhibitory effects on the growth of a wide range of cancer cell lines generally at 10(-6) M, in some cases at 10(-7) M and 10(-8) M concentrations. Within this series the benzylamino quinoxaline derivatives 1b-7b were the most active, whereas compound 2c showed the highest MG_MD value (-5.66).     

Aryl-substituted methyleneaminoxymethyl (MAOM) analogues of diarylcyclopentenyl cyclooxygenase-2 inhibitors: effects of some structural modifications on their biological properties

The (E)-[2-(4-aminosulfonylphenyl)-1-cyclopentenyl-1-methyliden]-(arylmethyloxy)amines (6a,b), which are the sulfonamidic analogues of the previously described methylsulfonyl derivatives 5a,b, and their corresponding sulfides (7a,b) and sulfoxides (8a,b) were synthesised in order to obtain information about the role played by these different sulphur-containing groups in the cyclooxygenase-2 inhibitory activity of this class of compounds. In addition, other chemical manipulations concerning the oxime-ether substituent of this type of derivatives were affected by preparing compounds 9a,b, which present a methyl group on the oximic carbon of the oxime-ether chain of 5a,b, and compounds 10 and 11, in which the atomic sequence (C=NOCH(2)) of the MAOMM of 8b and 5b, respectively, is inverted. Compounds 6-11 were tested in vitro for their inhibitory activity towards COX-1 and COX-2 by measuring prostaglandin E2 (PGE2) production in U937 cell lines and activated J774.2 macrophages, respectively. Some of the new compounds showed an appreciable in vitro COX-2 inhibitory activity, with IC(50) values in the microM (7a,b, 8a and 9b) or sub-microM (8b) range. This last compound was also assayed in vivo for its antiinflammatory activity by means of the carrageenan-induced paw edema test in rats. No inhibitory effects were detected up to dose of 30 mg kg(-1) orally administered.     

Flavonoids induce apoptosis in human leukemia U937 cells through caspase- and caspase-calpain-dependent pathways

Flavonoids are polyphenolic phytochemicals that are ubiquitous in plants and present in the common human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. In this study we tested the apoptotic activity of 22 flavonoids and related compounds in leukemic U937 cells. Several flavones but none of the isoflavones or flavanones tested induced apoptotic cell death under these conditions, as determined by reduction in cell viability, flow cytometry, and oligonucleosomal DNA fragmentation. Structure-activity relationship showed that at least two hydroxylations in positions 3, 5, and 7 of the A ring were needed to induce apoptosis, whereas hydroxylation in 3' and/or 4' of the B ring enhanced proapoptotic activity. At lower concentrations, these compounds were also able to sensitize these cells to apoptosis induced by tumor necrosis factor-alpha. Regarding the mechanisms, galangin, luteolin, chrysin, and quercetin induced apoptosis in a way that required the activation of caspases 3 and 8, but not caspase 9. In contrast, an active role of calpains in addition to caspases was demonstrated in apoptosis induced by fisetin, apigenin, and 3,7-dihydroxyflavone. Our data show evidence of the proapoptotic properties of some flavonoids that could support their rational use as chemopreventive and therapeutic agents against carcinogenic disease.     

Adamantane derivatives of thiazolyl-N-substituted amide, as possible non-steroidal anti-inflammatory agents

A series of adamantane derivatives of thiazolyl-N-substituted amides were synthesized in a three-step reaction and tested for anti-inflammatory activity as well as lipoxygenase and cycloxygenase inhibitory actions. Theoretical calculation of their lipophilicity, as ClogP was performed. The effect of the synthesized compounds on inflammation, using the carrageenin-induced mouse paw oedema model was studied and compared to indomethacin. In general, the studied compounds were found to be potent anti-inflammatory agents (29.6-81.5%). Anti-inflammatory activity was influenced by some structural characteristics of the synthesized compounds. The lipoxygenase inhibitory activity was tested by the conversion of sodium linoleate to 13-hydroperoxylinoleic acid. Low inhibitory activity was observed. Evaluation of COX-1 and COX-2 inhibitory activities of the compounds revealed a COX-1 inhibitory potential, comparable to that of naproxen for some of the compounds and a low to moderate COX-2 inhibitory potential. Comparison of the in vivo and in vitro results leads to the conclusion that most compounds of this series may be involved in other mechanisms of inflammation, too.     

Synthesis and biological evaluation of some thiazolylpyrazole derivatives as dual anti-inflammatory antimicrobial agents

The synthesis of a novel series of 4-thiazolylpyrazolyl derivatives is described in the present report. All the newly synthesized compounds were examined for their anti-inflammatory activity using cotton pellet-induced granuloma and carrageenan-induced rat paw edema bioassays. Their inhibitory activities of cyclooxygenase-1 and cyclooxygenase-2 (COX-1 and COX-2), ulcerogenic effect and acute toxicity were also determined. Furthermore, all compounds were evaluated for their in vitro antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans. A docking pose for compounds 8b, 10a and 10b separately in the active site of the human COX-2 enzyme and DNA-gyrase B was also obtained. The results revealed that compounds 8b, 10a and 10b exhibited good anti-inflammatory activity with no or minimal ulcerogenic effect and good safety margin. Compounds 10a and 10b were found to be the most potent anti-inflammatory agents in the present study. Meanwhile, 10a and 10b displayed higher selective inhibitory activity towards COX-2 compared to indomethacin. Moreover, compounds 10a and 10b exhibited promising antibacterial against both E. coli and S. aureus. Docking studies for 8b, 10a and 10b with COX-2 (PDB ID: 1CX2) and DNA-gyrase B (PDB ID: 1EI1) showed good binding profile.     

Synthesis and biological evaluation of novel 7-acyl homocamptothecins as Topoisomerase I inhibitors

A series of novel 7-acyl derivatives of homocamptothecin (hCPT) were designed and synthesized with the purpose to improve antitumor activity of hCPT, via Minisci free-radical reaction from 10-methoxyhomocamptothecin. All the compounds were evaluated for in vitro cytotoxicity against three cancer cell lines (A549, MDA-MB-435 and HCT116). For MDA-MB-435 cell line, compounds, 6a, 6b, 6k and all of 7-alkylcabonyl homocamptothecin derivatives showed higher in vitro inhibitory activities than topotecan (TPT). Furthermore, compounds 6d, 6e, and 6k showed highly potent inhibitory activities with the IC50 values from less than 1 nM to 2.2 nM. In Topoisomerase I (Topo I)-induced DNA cleavage assay, compounds 6a, 6d, and 6k, as compared to CPT, revealed higher Topo I inhibitory activity.