Disruption of Biofilm Formation and Quorum Sensing in Pathogenic Bacteria by Compounds from Zanthoxylum Gilletti (De Wild) P.G. Waterman

Microbial resistance is facilitated by biofilm formation and quorum-sensing mediated processes. In this work, the stem bark (ZM) and fruit extracts (ZMFT) of Zanthoxylum gilletii were subjected to column chromatography and afforded lupeol (1), 2,3-epoxy-6,7-methylenedioxyconiferyl alcohol (3), nitidine chloride (4), nitidine (7), sucrose (6) and sitosterol-β-D-glucopyranoside (2). The compounds were characterized using MS and NMR spectral data. The samples were evaluated for antimicrobial, antibiofilm and anti-quorum sensing activities. Highest antimicrobial activity was exhibited by compounds 3, 4 and 7 against Staphylococcus aureus (MIC 200 µg/mL), compounds 3 and 4 against Escherichia coli (MIC = 100 µg/mL) and compounds 4 and 7 against Candida albicans (MIC = 50 µg/mL). At MIC and sub-MIC concentrations, all samples inhibited biofilm formation by pathogens and violacein production in C. violaceum CV12472 except compound 6. Good disruption of QS-sensing in C. violaceum revealed by inhibition zone diameters were exhibited by compounds 3 (11.5 ± 0.5 mm), 4 (12.5 ± 1.5 mm), 5 (15.0 ± 0.8 mm), 7 (12.0 ± 1.5 mm) as well as the crude extracts from stem barks (16.5 ± 1.2 mm) and seeds (13.0 ± 1.4 mm). The profound inhibition of quorum sensing mediated processes in test pathogens by compounds 3, 4, 5 and 7 suggests the methylenedioxy- group that these compounds possess as the possible pharmacophore.

Two new secondary metabolites with antibacterial activities from Conyza aegyptiaca (Asteraceae)

The bio guided fractionation of the dichloromethane/methanol (1:1) crude extract of the air-dried whole plant of C. aegyptiaca led to the isolation of one new flavone derivative designated conyflavone (1) and one new clerodane diterpene type designated conyclerodane (2) along with five known compounds including two flavonoids Gardenin C (3), chrysosplenetin (4) and two steroids glucoside of β-sitosterol (5), the mixture of stigmasterol (6) and β-sitosterol (6') and ent-2b,18,19trihydroxycleroda-3,13-dien-16,15-olide (7). The structures were established by spectroscopic methods including IR, 1D and 2D NMR in conjunction with mass spectroscopy and by comparison to data of related compounds described in literature. The stereocentres in compound 2 were determined by SC-XRD analysis. Crude extract as well as fractions and pure compounds were evaluated in vitro for their antibacterial activities against four pathogenic and two clinical isolate strains using microdilution methods. Extracts and compounds displayed a moderate antibacterial activity with MIC values ranging from 125 to 500 µg/mL.

Pyrrovobasine, hybrid alkylated pyrraline monoterpene indole alkaloid pseudodimer discovered using a combination of mass spectral and NMR-based machine learning annotations

A new vobasine-tryptamine-based monoterpene indole alkaloid pseudodimer was isolated from the stem bark of Voacanga africana. As a minor constituent occurring in a thoroughly investigated plant, this molecule was targeted based on a molecular networking strategy and a rational MS²-guided phytochemical investigation led to its isolation. Its structure was formally established based on HRMS, 1D/2D NMR data, and the application of the tool Small Molecule Accurate Recognition Technology (SMART 2.0). Its absolute configuration was assigned by the exciton chirality method and TD-DFT ECD calculations. Besides featuring an unprecedented intermonomeric linkage in the small group of vobasine/tryptamine hybrids, pyrrovobasine also represents the first pyrraline-containing representative in the whole monoterpene indole alkaloids group. Biosynthetic hypotheses possibly underpinning these structural oddities are proposed here.

Voatriafricanines A and B, Trimeric Vobasine-Aspidosperma-Aspidosperma Alkaloids from Voacanga africana

Voatriafricanines A and B (1 and 2), the first examples of vobasine-aspidosperma-aspidosperma monoterpene trisindole alkaloids, were isolated from the stem barks of Voacanga africana, guided by a molecular networking strategy. Their structures, including absolute configurations, were elucidated by spectroscopic methods and ECD calculations. Compounds 1 and 2 possess intramolecular hydrogen bonding, sufficiently robust to transfer homonuclear and heteronuclear magnetizations. Compound 1 exhibited potent antimycobacterial activity with no discernible cytotoxic activity.

Antiproliferative activity of a new xanthone derivative from leaves of Garcinia nobilis Engl

A new xanthone, mboudiexanthone (1), together with five known compounds, euxanthone (2), isogarcinol (3), garcinol (4), betulinic acid (5) and zeorin (6) were isolated from the leaves of Garcinia nobilis Engl. The structures were determined by 1D and 2D NMR techniques and X-ray diffraction for 6. The in vitro antiproliferative properties of isolated compounds were evaluated against the human breast cancer cell line MCF-7. All compounds showed an antiproliferative activity with an IC₅₀ value down to ∼11 µM for isogarcinol.

Cytotoxicity of a naturally occurring furoquinoline alkaloid and four acridone alkaloids towards multi-factorial drug-resistant cancer cells

INTRODUCTION

Chemotherapy is one of the preferred mode of treatment of malignancies, but is complicated by the expression of diverse resistance mechanisms of cancer cells.

METHODS

In the present study, we investigated the cytotoxicity of five alkaloids including a furoquinoline montrofoline (1) and four acridones namely 1-hydroxy-4-methoxy-10-methylacridone (2), norevoxanthine (3), evoxanthine (4), 1,3-dimethoxy-10-methylacridone (5) against 9 drug-sensitive and multidrug-resistant (MDR) cancer cell lines. The resazurin reduction assay was used to evaluate the cytotoxicity of these compounds, whilst caspase-Glo assay was used to detect caspase activation. Cell cycle, mitochondrial membrane potential (MMP) and levels of reactive oxygen species (ROS) were all analyzed via flow cytometry.

RESULTS

Furoquinoline 1 as well as the acridone alkaloids 2-5 displayed cytotoxic effects with IC50 values below 138 µM on all the 9 tested cancer cell lines. The IC50 values ranged from 41.56 µM (towards hepatocarinoma HepG2 cells) to 90.66 µM [towards colon carcinoma HCT116 (p53(-/-)) cells] for 1, from 6.78 µM [towards HCT116 (p53(-/-)) cells) to 106.47 µM [towards breast adenocarcinoma MDA-MB-231-pcDNA cells] for 2, from 5.72 µM (towards gliobastoma U87MG.ΔEGFR cells) to 137.62 µM (towards leukemia CCRF-CEM cells] for 3, from 6.11 µM [towards HCT116 (p53(+/+)) cells] to 80.99 µM (towards HepG2 cells] for 4, from 3.38 µM (towards MDA-MB-231-BCRP cells) to 58.10 µM (towards leukemia CEM/ADR5000 cells] for 5 and from 0.20 µM (against CCRF-CEM cells) to 195.12 µM (against CEM/ADR5000 cells) for doxorubicin. Acridone alkaloid 5 induced apoptosis in CCRF-CEM leukemia cells, mediated by increased ROS production.

CONCLUSIONS

The five tested alkaloids and mostly acridone 5 are potential cytotoxic natural products that deserve more investigations to develop novel cytotoxic compounds against multifactorial drug-resistant cancers.

Antibacterial and antioxidant xanthones and benzophenone from garcinia smeathmannii

A new prenylated xanthone, 1,3,5,8-tetrahydroxy-2-(3-methybut-2-enyl)-4-(3,7-dimethylocta-2,6-dienyl) xanthone (1), and a new benzophenone (2), together with four known xanthone derivatives, cheffouxanthone (3), smeathxanthone A (4), smeathxanthone B (5), ananixanthone (6), and two pentacyclic triterpenes, epi-friedelinol (7) and friedelin (8), were isolated from the stem bark of Garcinia smeathmannii. The structures of the compounds were elucidated on the basis of 1D and 2D NMR experiments, and compound 2 was further characterized and confirmed by single X-ray analysis. Compounds 1, 2, and 3 exhibited the most prominent antibacterial activity against gram-positive Enterococcus faecalis with minimal inhibitory concentration values of 8, 8, and 2 µg/mL, respectively, while compounds 1, 3, 4, and 6 showed the capacity to scavenge free radicals.

Cytotoxicity and modes of action of three naturally occurring xanthones (8-hydroxycudraxanthone G, morusignin I and cudraxanthone I) against sensitive and multidrug-resistant cancer cell lines

BACKGROUND

Resistance of cancer to chemotherapy remains a challenging issue for scientists as well as physicians. Naturally occurring xanthones possess a variety of biological activities such as anti-inflammatory, anti-bacterial, and anti-cancer effects. The present study was aimed at investigating the cytotoxicity and the modes of action of three naturally occurring xanthones namely, morusignin I (1), 8-hydroxycudraxanthone G (2) and cudraxanthone I (3) against a panel of nine cancer cell lines, including various sensitive and drug-resistant phenotypes.

METHODS

The cytotoxicity of the compounds was determined using a resazurin reduction assay, whereas the caspase-Glo assay was used to detect the activation of caspases 3/7, caspase 8 and caspase 9 in cells treated with compounds 3. Flow cytometry was used for cell cycle analysis and detection of apoptotic cells, analysis of mitochondrial membrane potential (MMP) as well as measurement of reactive oxygen species (ROS).

RESULTS

Compounds 1 and 3 inhibited the proliferation of all tested cancer cell lines including sensitive and drug-resistant phenotypes. Compound 2 was active on 8/9 cell lines with the IC50 values ranging from 16.65 μM (against leukemia CCRF-CEM cells) to 70.38 μM (against hepatocarcinoma HepG2 cells). The IC50 value ranged from 7.15 μM (against CCRF-CEM cells) to 53.85 μM [against human glioblastoma U87MG.ΔEGFR cells] for compound 1, and from 2.78 μM (against breast cancer MDA-MB231 BCRP cells) to 22.49 μM (against U87MG cells) for compound 3. P-glycoprotein expressing CEM/ADR5000 cells were cross-resistant to compounds 1 and 2 (4.21- to 610-fold) while no cross-resistance or even collateral cross-sensitivity were observed in other drug-resistant cell lines to the three compounds. Normal AML12 liver cells were more resistant to the three compounds than HepG2 liver cancer cells. Compounds 3 arrested the cell cycle between G0/G1 and S phases, strongly induced apoptosis via caspases 3/7, caspase 8, caspase 9 activation and disrupted the MMP in CCRF-CEM cells.

CONCLUSIONS

The cytotoxicity of the studied xanthones and especially compound 3 deserve more detailed exploration in the future to develop novel anticancer drugs against sensitive and otherwise drug-resistant phenotypes.

Antibacterial constituents of three Cameroonian medicinal plants: Garcinia nobilis, Oricia suaveolens and Balsamocitrus camerunensis

BACKGROUND

Multidrug resistance is a worrying cause of treatment failure in bacterial infections. The search of bioactive constituents from medicinal plants against multidrug resistant (MDR) bacteria has significantly evolved in the two last decades. In the present study, twenty-two compounds (three terpenoids, eleven phenolics and eight alkaloids) isolated from three Cameroonian medicinal plants, namely Garcinia nobilis, Oricia suaveolens and Balsamocitrus camerunensis, as well as the crude extracts were tested for their antibacterial activities against Mycobacterium tuberculosis and Gram-negative bacteria amongst which were MDR active efflux pumps expressing phenotypes.

METHODS

The microplate alamar blue assay (MABA) and the broth microdilution methods were used to determine the minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) of the studied samples.

RESULTS

The results of the MIC determinations indicate that, the best crude extract was that from G. nobilis (GNB), its inhibitory effects being noted against 12 of the 14 tested bacteria. The extract of GNB also exhibited better anti-tuberculosis (MIC of 128 μg/ml M. tuberculosis against ATCC 27294 strain) and antibacterial (MIC of 64 μg/ml against Escherichia coli ATCC10536) activities compared to the extracts of O. suaveolens and B. camerunensis. Interestingly, 4-prenyl-2-(3,7-dimethyl-2,6-octadienyl)-1,3,5,8-tetrahydroxyxanthone (2), isolated from the most active extract GNB, also showed the best activity amongst compounds, inhibiting the growth of all the fourteen tested microorganisms. The lowest MIC value obtained with compound 2 was 8 μg/ml against M. tuberculosis ATCC 27294 and M. tuberculosis clinical MTCS2 strains. Other compounds showed selective activities with 11 of the 14 tested bacteria being sensitive to the xanthone, morusignin I (5) and the alkaloid, kokusaginine (13).

CONCLUSIONS

The results of the present investigation provide evidence that the crude extract from G. nobilis, O. suaveolens and B. camerunensis as well as some of their compounds, and mostly compound 2 (isolated from G. nobilis,) could be considered as interesting natural antibacterial products.