Molecular determinants of cancer cell sensitivity and resistance towards the sesquiterpene farnesol.

Farnesol is a non-cyclic sesquiterpene (isoprenoid) found in the essential oils of many plants. In cancer biology, farnesylation of mutated Ras oncoproteins allows the proteins to dock to the membrane and be functionalized. Therefore, farnesyltransferase is a target for drug development to inhibit Ras. Farnesol exhibits cytotoxic activity against tumor cells in vitro and in vivo, implying that novel treatment strategies may be devised independent of Ras farnesylation. Tumors frequently develop resistance towards standard chemotherapies, and thus novel agents are urgently required that bypass the cross-resistance evoked by established anticancer drugs. We investigated whether classical mechanisms of drug resistance such as ATP-binding cassette transporters (P-glycoprotein/MDR1, MRP1, BCRP), the tumor suppressor gene TP53, and the oncogene EGFR play a role in the response of tumor cells to farnesol. Remarkably, none of these genes conferred resistance to farnesol, indicating that this compound may be useful for the treatment of otherwise drug-resistant and refractory tumors expressing these mechanisms of resistance. Furthermore, we applied a pharmacogenomic approach to explore molecular determinants of sensitivity and resistance to farnesol. Among the candidates were genes involved in apoptosis (STAB2, NUMBL), regulation of transcription (CDYL, FOXA2) and diverse other functional groups (INE1, CTRL, MRS2, NEB, LMO7, C9orf3, EHBP1). The fact that these genes are not associated with resistance to traditional anticancer drugs suggests farnesol may possess a novel mechanism of action, and consequently might bypass drug resistance to established chemotherapeutics.

Phytotoxic, antifungal activities and acute toxicity studies of the crude extract and compounds from Diospyros canaliculata.

In vitro biological activities including phytotoxic, antifungal activities as well as acute toxicity of the methanol extract, fractions and/or isolated compounds from the stem bark of Diospyros canaliculata were investigated. Well agar diffusion and macrodilution assays were used for investigating the antifungal activity. A phytotoxicity assay was performed against Lemna minor while an acute toxicity assay was performed in mice via oral administration. As a result, plumbagin (5-hydroxy-2-methyl-1,4-naphtoquinone) and two known pentacyclic triterpenes (lupeol and lupenone) were isolated from the extract. With regards the antifungal activities, the inhibition zones varied from 16.51 to 24.86 mm and from 20.50 to 25.10 mm for the extract and plumbagin, respectively. The minimum inhibitory concentrations of the extract and plumbagin ranged between 12.5-25 and 0.78-1.56 µg mL(-1), respectively. At 50 µg mL(-1), the hexane fraction showed phytotoxic activities similar to paraquat, the standard phytotoxic inhibitor. The extract was found to be non-toxic to mice after administration per os. Based on the current findings, we can conclude that this extract is non toxic, with significant phytotoxic and antifungal properties due to the presence of plumbagin.

Antibacterial activity of some natural products against bacteria expressing a multidrug-resistant phenotype.

The present study assessed the antimicrobial activities of various natural products belonging to the terpenoids, alkaloids and phenolics against a collection of Gram-negative multidrug-resistant (MDR) bacteria. The results demonstrated that most of the compounds were extruded by bacterial efflux pumps. In the presence of the efflux pump inhibitor phenylalanine arginine ß-naphthylamide (PAßN), the activities of laurentixanthone B (xanthone), plumbagin (naphthoquinone), 4-hydroxylonchocarpin (flavonoid) and MAB3 (coumarin) increased significantly against all studied MDR bacteria. Laurentixanthone B, 4-hydroxylonchocarpin and MAB3 contained the same pharmacophoric moiety as plumbagin. This study indicates that the AcrAB-TolC (Enterobacteriaceae) and MexAB-OprM (Pseudomonas aeruginosa) efflux pumps are involved in resistance of Gram-negative bacteria to most of the natural products.

Evaluation of flavonoids from Dorstenia barteri for their antimycobacterial, antigonorrheal and anti-reverse transcriptase activities.

The aim of this study was to evaluate the antimycobacterial, antigonorrheal and reverse transcriptase activities of five flavonoids: isobachalcone (IBC); kanzanol C (KAN); 4-hydroxylonchocarpin (4-LCP); stipulin (SPL) and amentoflavone (AMF) from Dortenia barteri, together with the crude extract from this plant. The Agar disc diffusion, broth microdilution, microplate alamar blue assay (MABA), radiometric respiratory technique using BACTEC 460 system and the reverse transcriptase (RT) assay were used for the investigations. The results of the antimycobacterial assay showed that the crude extract and compounds were able to prevent the growth of Mycobacteria with MIC<10 microg/ml being recorded with IBC on M. tuberculosis. Results of the killing rate experiment revealed that total inhibition effect on M. tuberculosis H37Rv strain was noted with IBC and SPL at day 9 when tested at 4x MIC. The results of the antigonorrheal assay indicated that MIC values below 10 microg/ml were also recorded with IBC on all the tested N. gonorrhoeae strains, meanwhile good activities (MIC<10 microg/ml) were also noted with the extract, KAN, 4-LCP and SPL on some of these strains. The anti-reverse transcriptase activities of extract and compounds also demonstrated that all samples were able to inhibit at various extents the reverse transcriptase activity, with IBC and 4-LCP showing the best effects. The overall results of this work provided evidence that the crude extract as well as some flavonoids from D. barteri could be potential sources of new antimicrobial drug against tuberculosis (TB), gonorrhea and probably the acquired immunodeficiency syndrome.

Antimicrobial activity of the methanolic extract and compounds from Morus mesozygia stem bark.

AIM OF THE STUDY: This study was aimed at investigating the antimicrobial activity of the methanolic extract (MMB) and compounds isolated from the stem bark of Morus mesozygia, namely 3beta-acetoxyurs-12-en-11-one (1), moracin Q (2), moracin T (3), artocarpesin (4), cycloartocarpesin (5), moracin R (6), moracin U (8), moracin C (9), and moracin M (10). MATERIALS AND METHODS: The liquid microdilution assay was used in the determination of the minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC), against nine bacterial and two fungal species. RESULTS: The results of the MIC determination showed that the compounds 3, 4, 8 and 9 were able to prevent the growth of all tested microbial species. All other samples showed selective activities. Their inhibitory effects were noted on 90.9% studied organisms for the crude extract, 81.8% for compound 6, 72.7% for compound 10, 63.6% for compound 1, 54.5% for compound 5, and 45.5% for compound 2. The lowest MIC value of 39 microg/ml was obtained with the crude extract against Escherichia coli. The corresponding value for compounds (5 microg/ml) was registered with compound 9 on Shigella dysenteriae and compound 3 on E. coli, S. dysenteriae, Pseudomonas aeruginosa, Salmonella typhi and Bacillus cereus. The lowest MIC value (39 microg/ml) observed with the crude extract (on E. coli) was only eightfold greater than that of gentamycin used as reference antibiotic (RA) while the corresponding value (5 microg/ml) recorded with compounds 3 and 9 was equal to that of RA on the corresponding microorganisms. CONCLUSIONS: The obtained results highlighted the interesting antimicrobial potency of M. mesozygia as well as that of the studied compounds, and provided scientific basis for the traditional use of this species.

Antimicrobial activity of the crude extracts and compounds from Ficus chlamydocarpa and Ficus cordata (Moraceae).

The aim of this study was to evaluate the antimicrobial activity of the methanol extracts from Ficus chlamydocarpa (FCR), Ficus cordata (FCB), mixture of the two plants (FCM), as well as that of the isolated flavonoids Alpinumisoflavone (2), Genistein (3), Laburnetin (4), Luteolin (5) (isolated from FCR), Catechin (7) and Epiafzelechin (8) (isolated from FCB). Mycobacteria, fungi, Gram-positive and Gram-negative bacterial species were tested for their susceptibility to the above samples. The microplate dilution and radiometric respiratory methods were used to determine the susceptibility testing of the samples against Mycobacterium smegmatis and Mycobacterium tuberculosis, respectively. The disc diffusion assay was used to determine the sensitivity of the samples, whilst the micro-dilution method was used for the determination of the minimal inhibition concentration (MIC) and the minimal microbicidal concentration (MMC) against fungi, Gram-positive and Gram-negative bacterial species. All the samples except compound 7 were found to be active to Mycobacterium smegmatis and the MIC ranged from 0.61 to 312.50microg/ml. Compound 4 showed the best activity against Mycobacterium tuberculosis exhibiting an MIC of 4.88microg/ml. The results of the diffusion test indicated that the crude extract from FCB, FCM as well as compounds 5 and 8 were able to prevent the growth of all tested (fungi, Gram-positive and Gram-negative bacteria) organisms. The inhibition effect of the crude extract from Ficus chlamydocarpa was observed on 10 (62.5%) of the 16 tested microorganisms (excluding mycobacteria) whereas that of compounds 4, 2 and 3 was respectively noted on 14 (87.5%), 8 (50.0%) and 7 (39.9%) of the tested microbial species. FCB was found to be more active than FCR on most of the tested organisms. The results provided evidence that the studied plants extract, as well as some of the isolated compounds might be potential sources of new antimicrobial drug.

Antimicrobial and antileishmanial xanthones from the stem bark of Allanblackia gabonensis (Guttiferae).

The phytochemical study of stem bark of Allanblackia gabonensis has resulted in the isolation and characterisation of one new xanthone derivative, named allanxanthone D, together with 10 known compounds, including 6 xanthones derivatives, allanxanthone A, 1,5-dihydroxyxanthone, 1,7-dihydroxyxanthone and 1,3,6,7-tetrahydroxy-2-(3-methylbut-2-enyl)xanthone, forbexanthone, 6-deoxyisojacareubin, one polyisoprenylated benzophenone, guttiferone F, one flavanol, epicathechin, two phytosterols, beta-sitosterol and campesterol. The structures of these compounds were established on the basis of one- and two-dimensional NMR homo- and hetero-nuclear evidence. These compounds were evaluated for their activity against Leishmania amazonensis in vitro and antimicrobial activities against a range of Gram negative and Gram positive bacteria.

Antimicrobial activity of the methanolic extract and of the chemical constituents isolated from Newbouldia laevis.

The methanolic extract (NLB) and ten compounds isolated from the root bark of Newbouldia laevis Seem, namely chrysoeriol (1), newbouldiaquinone (2), 2-acetylfuro-1,4-naphthoquinone (3), 2-hydroxy-3-methoxy-9,10-dioxo-9,10-dihydroanthracene-1-carbaldehyde (4), lapachol (5), beta-sitosterol-3-O-beta-D-glucopyranoside (6), oleanolic acid (7), canthic acid (8) newbouldiamide (9) and 2-(4-hydroxyphenyl)-ethyltrioctanoate (10), were tested for in vitro antimicrobial activity. Twenty one microorganisms belonging to six Gram-positive and twelve Gram-negative bacterial species as well as three yeasts from Candida species were tested for their susceptibility to NLB and the pure isolated compounds based on the Agar Hole Diffusion test and the Liquid Dilution method. The Hole Diffusion assay indicated that NLB and compound 7 were active against all tested pathogens while other compounds showed selective activity with the antimicrobial spectra varying from 76% (compound 10) to 95 % (compound 6). Minimal inhibitory concentrations (MIC) also illustrated the important antimicrobial activity of NLB and of the isolated compounds. MIC values obtained varied from 9.76 to 312.50 microg/ml for NLB, and 0.038 to 9.76 microg/ml for pure compounds against most of the tested microorganisms. The antimicrobial activities of compounds 2, 4 and 9 are described here extensively for the first time. The results indicate a promising basis for the use of Newbouldia laevis and some of its active principles in the treatment of infectious diseases.

Antimicrobial activity of the methanolic extract from the stem bark of Tridesmostemon omphalocarpoides (Sapotaceae).

The methanolic extract and fractions from the stem bark of Tridesmostemon omphalocarpoides were investigated for their in vitro antimicrobial properties as well as their phytochemical constituents. The stem bark was collected from Yaoundé, in the Centre Province of Cameroon. The antimicrobial activity of the extract and fractions against two Candida species and seven aerobic bacteria was evaluated on the basis of the inhibition zones (IZ) using agar hole diffusion method, the minimal inhibition concentration (MIC) and the minimal microbicidal concentration (MMC) by the macrodilution method. The results indicated significant anticandidal and antibacterial effect of the methanolic extract and fractions against all the nine microorganisms tested. Preliminary phytochemical analysis of methanolic extract showed the presence of biologically active components namely alkaloids, steroids, tannins, saponins, phenols, polyphenols and flavonoids. The acute toxicity of the methanolic extract was also studied. This was found to be non-toxic to the inbred Wistar rats treated per os. The results of this study suggested that the stem bark of this plant could be safely used in the treatment of some infectious diseases.

Xanthones from Garcinia smeathmannii (Oliver) and their antimicrobial activity.

Two new xanthones, smeathxanthone A (1) (2-(3,7-dimethyl-2,6-octadienyl)-1,3,5,8-tetrahydroxyxanthone) and smeathxanthone B (2) (5,7,10-trihydroxy-2-methyl-2-(4-methylpent-3-enyl)[2H, 6H]pyrano[3,2-b]xanthen-6-one), have been isolated from the stem bark of Garcinia smeathmannii, and their structures elucidated on the basis of 1D and 2D NMR experiments. 1,3,5-Trihydroxyxanthone and 1,5-dihydroxyxanthone were also obtained. The compounds showed only modest activity against a range of bacteria and yeasts.