Antiproliferative activity of various flavonoids and related compounds: additive effect of interferon-α2b

Structural (at 100 K) and DFT studies of 2'-nitro-flavone

The geometry of the title mol-ecule [systematic name: 2-(2-nitro-phen-yl)-4H-chromen-4-one], C15H9NO4, is determined by two dihedral angles formed by the mean plane of phenyl ring with the mean planes of chromone moiety and nitro group, being 50.73 (5) and 30.89 (7)°, respectively. The crystal packing is determined by π-π inter-actions and C-H⋯O contacts. The results of DFT calculations at the B3LYP/6-31G* level of theory provided an explanation of the unusually large dihedral angle between the chromone moiety and the phenyl group. The electrostatic potential map on the mol-ecular surface was calculated in order to determine the potential binding sites to receptors.

An In Silico Approach for Assessment of the Membrane Transporter Activities of Phenols: A Case Study Based on Computational Models of Transport Activity for the Transporter Bilitranslocase

Phenols are the most abundant naturally accessible antioxidants present in a human normal diet. Since numerous beneficial applications of phenols as preventive agents in various diseases were revealed, the evaluation of phenols bioavailability is of high interest of researchers, consumers and drug manufacturers. The hydrophilic nature of phenols makes a cell membrane penetration difficult, which imply an alternative way of uptake via membrane transporters. However, the structural and functional data of membrane transporters are limited, thus the in silico modelling is really challenging and urgent tool in elucidation of transporter ligands. Focus of this research was a particular transporter bilitranslocase (BTL). BTL has a broad tissue expression (vascular endothelium, absorptive and excretory epithelia) and can transport wide variety of poly-aromatic compounds. With available BTL data (pKi [mmol/L] for 120 organic compounds) a robust and reliable QSAR models for BTL transport activity were developed and extrapolated on 300 phenolic compounds. For all compounds the transporter profiles were assessed and results show that dietary phenols and some drug candidates are likely to interact with BTL. Moreover, synopsis of predictions from BTL models and hits/predictions of 20 transporters from Metrabase and Chembench platforms were revealed. With such joint transporter analyses a new insights for elucidation of BTL functional role were acquired. Regarding limitation of models for virtual profiling of transporter interactions the computational approach reported in this study could be applied for further development of reliable in silico models for any transporter, if in vitro experimental data are available.

Dietary apigenin potentiates the inhibitory effect of interferon-α on cancer cell viability through inhibition of 26S proteasome-mediated interferon receptor degradation

Background

Type I interferons (IFN-α/β) have broad and potent immunoregulatory and antiproliferative activities. However, it is still known whether the dietary flavonoids exhibit their antiviral and anticancer properties by modulating the function of type I IFNs.

Objective

This study aimed at determining the role of apigenin, a dietary plant flavonoid abundant in common fruits and vegetables, on the type I IFN-mediated inhibition of cancer cell viability.

Design

Inhibitory effect of apigenin on human 26S proteasome, a known negative regulator of type I IFN signaling, was evaluated in vitro. Molecular docking was conducted to know the interaction between apigenin and subunits of 26S proteasome. Effects of apigenin on JAK/STAT pathway, 26S proteasome-mediated interferon receptor stability, and cancer cells viability were also investigated.

Results

Apigenin was identified to be a potent inhibitor of human 26S proteasome in a cell-based assay. Apigenin inhibited the chymotrypsin-like, caspase-like, and trypsin-like activities of the human 26S proteasome and increased the ubiquitination of endogenous proteins in cells. Results from computational modeling of the potential interactions of apigenin with the chymotrypsin site (β5 subunit), caspase site (β1 subunit), and trypsin site (β2 subunit) of the proteasome were consistent with the observed proteasome inhibitory activity. Apigenin enhanced the phosphorylation of signal transducer and activator of transcription proteins (STAT1 and STAT2) and promoted the endogenous IFN-α-regulated gene expression. Apigenin inhibited the IFN-α-stimulated ubiquitination and degradation of type I interferon receptor 1 (IFNAR1). Apigenin also sensitized the inhibitory effect of IFN-α on viability of cervical carcinoma HeLa cells.

Conclusion

These results suggest that apigenin potentiates the inhibitory effect of IFN-α on cancer cell viability by activating JAK/STAT signaling pathway through inhibition of 26S proteasome-mediated IFNAR1 degradation. This may provide a novel mechanism for increasing the efficacy of IFN-α/β.

Activities of wogonin analogs and other flavones against Flavobacterium columnare

In our on-going pursuit to discover natural products and natural product-based compounds to control the bacterial species Flavobacterium columnare, which causes columnaris disease in channel catfish (Ictalurus punctatus), we synthesized flavone and chalcone analogs, and evaluated these compounds, along with flavonoids from natural sources, for their antibacterial activities against two isolates of F. columnare (ALM-00-173 and BioMed) using a rapid bioassay. The flavonoids chrysin (1a), 5,7-dihydroxy-4'-methoxyflavone (11), isorhamnetin (26), luteolin (27), and biochanin A (29), and chalcone derivative 8b showed strong antibacterial activities against F. columnare ALM-00-173 based on minimum inhibition concentration (MIC) results. Flavonoids 1a, 8, 11, 13 (5,4'-dihydroxy-7-methoxyflavone), 26, and 29 exhibited strong antibacterial activities against F. columnare BioMed based upon MIC results. The 24-h 50% inhibition concentration (IC50 ) results revealed that 27 and 29 were the most active compounds against F. columnare ALM-00-173 (IC50 of 7.5 and 8.5 mg/l, resp.), while 26 and 29 were the most toxic compound against F. columnare BioMed (IC50 of 9.2 and 3.5 mg/l, resp.). These IC50 results were lower than those obtained for wogonin against F. columnare ALM-00-173 and F. columnare BioMed (28.4 and 5.4 mg/l, resp.). However, based on MIC results, none of the compounds evaluated in this study were as active as wogonin (MIC 0.3 mg/l for each F. columnare isolate). Further modification of the wogonin structure to enhance antibacterial is of interest.

A novel caffeic acid-1-piperonylpiperazine hybridization compound HBU-47 inhibits LPS-mediated inflammation in RAW264.7 macrophage cells

In the present study, we synthesized a new hybrid compound by coupling caffeic acid and 1-piperonylpiperazine. The synthetic compound, acetyl-caffeic acid-1-piperonylpiperazine (HBU-47), showed potent anti-inflammatory effects inhibiting lipopolysaccharide (LPS)-induced production of nitric oxide (NO) in RAW264.7 macrophage cells. HBU-47 inhibited LPS-caused induction of inducible NO synthase (iNOS), cyclooxygenase-2, interleukin-6 and interleukin-1β in RAW264.7 cells in time- and dose-dependent manner. Compared to HBU-47, neither caffeic acid nor 1-piperonylpiperazine displayed significant inhibition of LPS responses. HBU-47 did not affect LPS-caused activation of mitogen-activated kinases (MAPKs) or IκB-α degradation. Instead, LPS-mediated NF-κB activation and DNA bindings of p65, p50 and c-Rel to the NF-κB binding site of iNOS promoter were inhibited by HBU-47. Overall, our data suggest that the novel caffeic acid hybrid compound downregulates inflammatory responses through inhibition of NF-κB and NF-κB-dependent gene expressions, thus, further suggesting its efficacy as a promising therapeutic agent.

Luteolin sensitizes the antiproliferative effect of interferon α/β by activation of Janus kinase/signal transducer and activator of transcription pathway signaling through protein kinase A-mediated inhibition of protein tyrosine phosphatase SHP-2 in cancer cells

New negative regulators of interferon (IFN) signaling, preferably with tissue specificity, are needed to develop therapeutic means to enhance the efficacy of type I IFNs (IFN-α/β) and reduce their side effects. We conducted cell-based screening for IFN signaling enhancer and discovered that luteolin, a natural flavonoid, sensitized the antiproliferative effect of IFN-α in hepatoma HepG2 cells and cervical carcinoma HeLa cells. Luteolin promoted IFN-β-induced Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway activation by enhancing the phosphorylation of Jak1, Tyk2, and STAT1/2, thereby promoting STAT1 accumulation in the nucleus and endogenous IFN-α-regulated gene expression. Of interest, inhibition of phosphodiesterase (PDE) abolished the effect of IFN-β and luteolin on STAT1 phosphorylation. Luteolin also increased the cAMP-degrading activity of PDE bound with type I interferon receptor 2 (IFNAR2) and decreased the intracellular cAMP level, indicating that luteolin may act on the JAK/STAT pathway via PDE. Protein kinase A (PKA) was found to negatively regulate IFN-β-induced JAK/STAT signaling, and its inhibitory effect was counteracted by luteolin. Pull-down and immunoprecipitation assays revealed that type II PKA interacted with IFNAR2 via the receptor for activated C-kinase 1 (RACK-1), and such interaction was inhibited by luteolin. Src homology domain 2 containing tyrosine phosphatase-2 (SHP-2) was further found to mediate the inhibitory effect of PKA on the JAK/STAT pathway. These data suggest that PKA/PDE-mediated cAMP signaling, integrated by RACK-1 to IFNAR2, may negatively regulate IFN signaling through SHP-2. Inhibition of this signaling may provide a new way to sensitize the efficacy of IFN-α/β.

Development of a new class of aromatase inhibitors: design, synthesis and inhibitory activity of 3-phenylchroman-4-one (isoflavanone) derivatives

Aromatase (CYP19) catalyzes the aromatization reaction of androgen substrates to estrogens, the last and rate-limiting step in estrogen biosynthesis. Inhibition of aromatase is a new and promising approach to treat hormone-dependent breast cancer. We present here the design and development of isoflavanone derivatives as potential aromatase inhibitors. Structural modifications were performed on the A and B rings of isoflavanones via microwave-assisted, gold-catalyzed annulation reactions of hydroxyaldehydes and alkynes. The in vitro aromatase inhibition of these compounds was determined by fluorescence-based assays utilizing recombinant human aromatase (baculovirus/insect cell-expressed). The compounds 3-(4-phenoxyphenyl)chroman-4-one (1h), 6-methoxy-3-phenylchroman-4-one (2a) and 3-(pyridin-3-yl)chroman-4-one (3b) exhibited potent inhibitory effects against aromatase with IC(50) values of 2.4 μM, 0.26 μM and 5.8 μM, respectively. Docking simulations were employed to investigate crucial enzyme/inhibitor interactions such as hydrophobic interactions, hydrogen bonding and heme iron coordination. This report provides useful information on aromatase inhibition and serves as a starting point for the development of new flavonoid aromatase inhibitors.

7-Hydroxy-benzopyran-4-one derivatives: a novel pharmacophore of peroxisome proliferator-activated receptor alpha and -gamma (PPARalpha and gamma) dual agonists

Design, synthesis, and in vitro bioevaluation of a new class of potential dual PPARalpha and gamma agonists discovered through a structure-driven design paradigm are described. The 7-hydroxy-benzopyran-4-one moiety (includes flavones, flavanones, and isoflavones) is the key pharmacophore of these novel molecules, exhibiting similarity to the core structure of both fibrates and thiazolidinediones. New lead PPAR ligands were identified from "natraceuticals" and synthetic analogues. In total, 77 molecules, including chalcones, flavones, flavanones, isoflavones, and pyrazole derivatives, were screened and structure-activity relationship studies of the dual agonists undertaken. Compounds 68, 70, 72, and 76 were identified as novel and potent dual PPARalpha and gamma agonists. These novel molecules may have the potential to be the future leads in PPAR-related disorders, including type II diabetes mellitus and metabolic syndrome.

QSAR, action mechanism and molecular design of flavone and isoflavone derivatives with cytotoxicity against HeLa

The quantitative structure-activity relationship (QSAR) of 32 flavone and isoflavone derivatives with cytotoxicity expressed as pGC50, which is defined as the negative value of the logarithm of necessary molar concentration of this series of compounds to cause 50% growth inhibition against the human cervical epithelioid carcinoma cell line (HeLa), has been studied by using the density functional theory (DFT), molecular mechanics (MM2) and statistical methods. In order to obtain QSAR model with high predictive ability, the original dataset was randomly divided into a training set comprising 26 compounds and a test set comprising the rest 6 compounds. An optimal model for the training set with significant statistical quality (RA2=0.852) and predictive ability (q2=0.818) was established. The same model was further applied to predict pGC50 values of the 6 compounds in the test set, and the resulting predictive correlation coefficient Rpred2 reaches 0.738, further showing that this QSAR model has high predictive ability. It is very interesting to find that the cytotoxicities of these compounds against HeLa appear to be mainly governed by two quantum-chemical factors, i.e., the energy (ELUMO) of the lowest unoccupied molecular orbital (LUMO) and the net charges of C atom at site 6 on aromatic rings (QC6). Here the possible action mechanism of these compounds was analyzed and discussed in detail, in particular, the fact why the flavone derivatives have considerably higher cytotoxicity than isoflavone derivatives was reasonably explained. Based on this QSAR equation, 5 new compounds with higher cytotoxicity have been theoretically designed. Such results can offer useful theoretical references for experimental works.

Antitumor activity of some natural flavonoids and synthetic derivatives on various human and murine cancer cell lines

The effect of various natural flavonoids, cinnamic acid derivatives, and a series of synthetic flavones on cell proliferation was evaluated in vitro in a panel of established human and murine tumor cell lines. The most potent antiproliferative agents were caffeic acid n-butyl ester (12) > 2'-nitroflavone (26) > caffeic acid ethyl ester (11) approximately = 2',6-dinitroflavone (27) > apigenin (3) > 3'-bromoflavone (20) approximately = 2'-fluoro-6-bromoflavone (31). Some compounds showed a moderate effect, the order of cytotoxic activities being chrysin (2) > 2'-fluoro-6-chloroflavone (30) approximately = 2'-chlorochrysin (32) > alpha-naphthoflavone (7) > beta-naphthoflavone (8) approximately = 6-chloroflavone (14) approximately = 6-bromoflavone (15) approximately = 4'-nitroflavone (23). A structure-activity relationship analysis of each group of compounds was performed. None of the natural or synthetic compounds tested affected the proliferation of epithelial cells derived from normal mammary gland of mice or fibroblastic cells from mouse embryo, suggesting a selective action against tumor cells.

Synthesis, antiproliferative, and antiplatelet activities of oxime- and methyloxime-containing flavone and isoflavone derivatives

Certain oxime- and methyloxime-containing flavone and isoflavone derivatives were synthesized and evaluated for their antiproliferative activity against three solid cancer cells, human cervical epithelioid carcinoma (HeLa), hepatocellular carcinoma (SKHep1), and oral squamous cell carcinoma (SAS), which are commonly seen in Asian countries, including Taiwan. Selective compounds were also evaluated in the full panel of 60 human tumor cell lines and their mean GI50 values were obtained. The preliminary assays indicated flavone-6-yl derivatives are the most cytotoxic while isoflavone-7-yl derivatives are the best antiplatelet agents. Among them, (E)-6-(2-methoxyiminopropoxy)-2-phenyl-4H-1-benzopyran-4-one (14), (Z)-6-(2-hydroxyimino-2-phenylethoxy)-2-phenyl-4H-1-benzopyran-4-one (18a), and (Z)-6-[2-hydroxyimino-2-(4-methoxyphenyl)ethoxy]-2-phenyl-4H-1-benzopyran-4-one (18c) are three of the best antiproliferative agents with GI50 values of 0.8, 0.7, and 0.8 microM, respectively, against the growth of SKHep1; 0.9, 0.8, and 1.0 microM, respectively, against the growth of HeLa cells. Compound 18c is not only the most cytotoxic with a mean GI50 value of 0.08 microM against the full panel of 60 human tumor cell lines but also the only flavone derivative that exhibited a GI50 value of less than 1 microM against the growth of SAS. Flow cytometric analyses revealed that growth inhibition by 18c was due to accumulation in G2/M phase arrest and followed by apoptosis.