Furoxan derivatives demonstrated in vivo efficacy by reducing Mycobacterium tuberculosis to undetectable levels in a mouse model of infection.

OBJECTIVES: The most recent survey conducted by the World Health Organization described Tuberculosis (TB) as one of the top 10 causes of death and the leading cause of death from a single infectious agent. The increasing number of TB-resistant cases has contributed to this scenario. In light of this, new strategies to control and treat the disease are necessary. Our research group has previously described furoxan derivatives as promising scaffolds to be explored as new antitubercular drugs. RESULTS: Two of these furoxan derivatives, (14b) and (14c), demonstrated a high selectivity against Mycobacterium tuberculosis. The compounds (14b) and (14c) were also active against a latent M. tuberculosis strain, with MIC90 values of 6.67 µM and 9.84 µM, respectively; they were also active against monoresistant strains (MIC90 values ranging from 0.61 to 20.42 µM) and clinical MDR strains (MIC90 values ranging from 3.09 to 42.95 µM). Time-kill experiments with compound (14c) showed early bactericidal effects that were superior to those of the first- and second-line anti-tuberculosis drugs currently used in therapy. The safety of compounds (14b) and (14c) was demonstrated by the Ames test because these molecules were not mutagenic under the tested conditions. Finally, we confirmed the safety, and high efficacy of compounds (14b) and (14c), which reduced M. tuberculosis to undetectable levels in a mouse aerosol model of infection. CONCLUSION: Altogether, we have identified two advanced lead compounds, (14b) and (14c), as novel promising candidates for the treatment of TB infection.

In vitro and in vivo activities of the nitroimidazole TBA-354 against Mycobacterium tuberculosis.

Nitroimidazoles are a promising new class of antitubercular agents. The nitroimidazo-oxazole delamanid (OPC-67683, Deltyba) is in phase III trials for the treatment of multidrug-resistant tuberculosis, while the nitroimidazo-oxazine PA-824 is entering phase III for drug-sensitive and drug-resistant tuberculosis. TBA-354 (SN31354[(S)-2-nitro-6-((6-(4-trifluoromethoxy)phenyl)pyridine-3-yl)methoxy)-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine]) is a pyridine-containing biaryl compound with exceptional efficacy against chronic murine tuberculosis and favorable bioavailability in preliminary rodent studies. It was selected as a potential next-generation antituberculosis nitroimidazole following an extensive medicinal chemistry effort. Here, we further evaluate the pharmacokinetic properties and activity of TBA-354 against Mycobacterium tuberculosis. TBA-354 is narrow spectrum and bactericidal in vitro against replicating and nonreplicating Mycobacterium tuberculosis, with potency similar to that of delamanid and greater than that of PA-824. The addition of serum protein or albumin does not significantly alter this activity. TBA-354 maintains activity against Mycobacterium tuberculosis H37Rv isogenic monoresistant strains and clinical drug-sensitive and drug-resistant isolates. Spontaneous resistant mutants appear at a frequency of 3 × 10(-7). In vitro studies and in vivo studies in mice confirm that TBA-354 has high bioavailability and a long elimination half-life. In vitro studies suggest a low risk of drug-drug interactions. Low-dose aerosol infection models of acute and chronic murine tuberculosis reveal time- and dose-dependent in vivo bactericidal activity that is at least as potent as that of delamanid and more potent than that of PA-824. Its superior potency and pharmacokinetic profile that predicts suitability for once-daily oral dosing suggest that TBA-354 be studied further for its potential as a next-generation nitroimidazole.

An ethnobotanical survey of medicinal plants of Laos toward the discovery of bioactive compounds as potential candidates for pharmaceutical development.

CONTEXT: An ethnobotany-based approach in the selection of raw plant materials to study was implemented. OBJECTIVE: To acquire raw plant materials using ethnobotanical field interviews as starting point to discover new bioactive compounds from medicinal plants of the Lao People's Democratic Republic. METHODS: Using semi-structured field interviews with healers in the Lao PDR, plant samples were collected, extracted, and bio-assayed to detect bioactivity against cancer, HIV/AIDS, TB, malaria. Plant species demonstrating activity were recollected and the extracts subjected to a bioassay-guided isolation protocol to isolate and identify the active compounds. RESULTS: Field interviews with 118 healers in 15 of 17 provinces of Lao PDR yielded 753 collections (573 species) with 955 plant samples. Of these 955, 50 extracts demonstrated activity in the anticancer, 10 in the anti-HIV, 30 in the anti-TB, and 52 in the antimalarial assay. Recollection of actives followed by bioassay-guided isolation processes yielded a series of new and known in vitro-active anticancer and antimalarial compounds from 5 species. DISCUSSION: Laos has a rich biodiversity, harboring an estimated 8000-11,000 species of plants. In a country highly dependent on traditional medicine for its primary health care, this rich plant diversity serves as a major source of their medication. CONCLUSIONS: Ethnobotanical survey has demonstrated the richness of plant-based traditional medicine of Lao PDR, taxonomically and therapeutically. Biological assays of extracts of half of the 955 samples followed by in-depth studies of a number of actives have yielded a series of new bioactive compounds against the diseases of cancer and malaria.

Ethnobotanical approach versus random approach in the search for new bioactive compounds: support of a hypothesis.

CONTEXT: Whether natural product drug discovery programs should rely on wild plants collected "randomly" from the natural environment, or whether they should also include plants collected on the basis of use in traditional medicine remains an open question. OBJECTIVE: This study analyzes whether plants with ethnomedical uses from Vietnam and Laos have a higher hit rate in bioassay testing than plants collected from a national park in Vietnam with the goal of maximizing taxonomic diversity ("random" collection). MATERIALS AND METHODS: All plants were extracted and subjected to bioassay in the same laboratories. Results of assays of plant collections and plant parts (samples) were scored as active or inactive based on whether any extracts had a positive result in a bioassay. Contingency tables were analyzed using χ(2) statistics. RESULTS: Random collections had a higher hit rate than ethnomedical collections, but for samples, ethnomedical plants were more likely to be active. Ethnomedical collections and samples had higher hit rates for tuberculosis, while samples, but not collections, had a higher hit rate for malaria. Little evidence was found to support an advantage for ethnomedical plants in HIV, chemoprevention and cancer bioassays. Plants whose ethnomedical uses directly correlated to a bioassay did not have a significantly higher hit rate than random plants. DISCUSSION: Plants with ethnomedical uses generally had a higher rate of activity in some drug discovery bioassays, but the assays did not directly confirm specific uses. CONCLUSIONS: Ethnomedical uses may contribute to a higher rate of activity in drug discovery screening.

Byrsonima fagifolia Niedenzu Apolar Compounds with Antitubercular Activity.

Bioassay-guided fractionation of the chloroform extract of Byrsonima fagifolia leaves led to the isolation of active antitubercular compounds alkane dotriacontane (Minimal Inhibitory Concentration-MIC, 62.5 µg mL(-1)), triterpenoids as bassic acid (MIC = 2.5 µg mL(-1)), α-amyrin acetate (MIC = 62.5 µg mL(-1)), a mixture of lupeol, α- and ß-amyrin (MIC = 31.5 µg mL(-1)) and a mixture of lupeol, and acetates of α- and ß-amyrin (MIC = 31.5 µg mL(-1)). The antimycobacterial activity was determined by the Microplate Alamar Blue Assay (MABA) and the structures of promising compounds were determined by spectroscopic analysis. This investigation constitutes the first report of a chemical and antitubercular study of apolar compounds from B. fagifolia Niedenzu (IK).

Activity of 7-methyljuglone in combination with antituberculous drugs against Mycobacterium tuberculosis.

The recent increase in the incidence of tuberculosis with the emergence of multidrug-resistant (MDR) cases has lead to the search for new drugs that are effective against MDR strains of Mycobacterium tuberculosis and can augment the potential of existing drugs against tuberculosis. In the present study, we investigated the activities of a naphthoquinone, 7-methyljuglone, isolated from the roots of Euclea natalensis alone and in combination with other antituberculous drugs against extracellular and intracellular M. tuberculosis. Combinations of 7-methyljuglone with isoniazid or rifampicin resulted in a four to six-fold reduction in the minimum inhibitory concentration of each compound. Fractional inhibitory concentration (FIC) indexes obtained were 0.2 and 0.5, respectively, for rifampicin and isoniazid, suggesting a synergistic interaction between 7-methyljuglone and these anti-TB drugs. The ability of 7-methyljuglone to enhance the activity of isoniazid and rifampicin against both extracellular and intracellular organisms suggests that 7-methyljuglone may serve as a promising compound for development as an anti-tuberculous agent.

Ethnobotany/ethnopharmacology and mass bioprospecting: issues on intellectual property and benefit-sharing.

Ethnobotany/ethnopharmacology has contributed to the discovery of many important plant-derived drugs. Field explorations to seek and document indigenous/traditional medical knowledge (IMK/TMK), and/or the biodiversity with which the IMK/TMK is attached, and its conversion into a commercialized product is known as bioprospecting or biodiversity prospecting. When performed in a large-scale operation, the effort is referred to as mass bioprospecting. Experiences from the mass bioprospecting efforts undertaken by the United States National Cancer Institute, the National Cooperative Drug Discovery Groups (NCDDG) and the International Cooperative Biodiversity Groups (ICBG) programs demonstrate that mass bioprospecting is a complex process, involving expertise from diverse areas of human endeavors, but central to it is the Memorandum of Agreement (MOA) that recognizes issues on genetic access, prior informed consent, intellectual property and the sharing of benefits that may arise as a result of the effort. Future mass bioprospecting endeavors must take heed of the lessons learned from past and present experiences in the planning for a successful mass bioprospecting venture.

Antimycobacterial flavones from Haplopappus sonorensis.

Crude extracts of Haplopappus sonorensis (A. Gray) S.F. Blake (Asteraceae), showed activity against Mycobacterium tuberculosis H(37)Rv. By assay-guided fractionation, 5-hydroxy-3,7,4'-trimethoxyflavone (1). 5,7-dihydroxy-3,4'-dimethoxyflavone (2). and 5,4'-dihydroxy-3,7-dimethoxyflavone (3). were identified as the antimycobacterial principles. Compound 2 was the most active compound.

Antimycobacterial plant terpenoids.

Abstract. Tuberculosis (TB), mainly caused by Mycobacterium tuberculosis, is the leading killer among all infectious diseases worldwide and is responsible for more than two million deaths annually. For over thirty years no antitubercular agents with new mechanisms of action have been developed. The recent increase in the number of multi-drug resistant clinical isolates of M. tuberculosis has created an urgent need for the discovery and development of new antituberculosis leads. This review covers recent reports on plant-derived terpenoids that have demonstrated moderate to high activity in in vitro bioassays against M. tuberculosis. In this review, mono-, sesqui-, di- and triterpenes, and sterols, their structural analogs and semisynthetic derivatives will be discussed, with particular emphasis on the structural features essential for antimycobacterial activity.

Evaluation of the flora of Puerto Rico for in vitro antiplasmodial and antimycobacterial activities.

The emergence of resistant strains of Plasmodium falciparum and Mycobacterium tuberculosis underscores the need for novel drugs that are effective against these microorganisms. As part of our screening programme of the flora of Puerto Rico, we tested a number of ethanol extracts of higher plants for antiplasmodial and antimycobacterial activities. A total of 40 extracts belonging to 23 plant families and 37 species were tested for antiplasmodial activity. Five extracts demonstrated activity against Plasmodium falciparum in vitro (50%-100% parasite suppression at 5 microg/mL). Another 63 extracts belonging to 30 plant families and 50 species were tested in vitro against Mycobacterium tuberculosis. Two extracts were found to be active, Ficus citrifolia and Pisonia borinquena (85% or more inhibition of microbial growth at 100 microg/mL of extract).

(+)-Totarol from Chamaecyparis nootkatensis and activity against Mycobacterium tuberculosis.

The isolation of (+)-totarol as active compound against Mycobacterium tuberculosis is reported from Chamaecyparis nootkatensis outerbark.

Drug targeting Mycobacterium tuberculosis cell wall synthesis: genetics of dTDP-rhamnose synthetic enzymes and development of a microtiter plate-based screen for inhibitors of conversion of dTDP-glucose to dTDP-rhamnose.

An L-rhamnosyl residue plays an essential structural role in the cell wall of Mycobacterium tuberculosis. Therefore, the four enzymes (RmlA to RmlD) that form dTDP-rhamnose from dTTP and glucose-1-phosphate are important targets for the development of new tuberculosis therapeutics. M. tuberculosis genes encoding RmlA, RmlC, and RmlD have been identified and expressed in Escherichia coli. It is shown here that genes for only one isotype each of RmlA to RmlD are present in the M. tuberculosis genome. The gene for RmlB is Rv3464. Rv3264c was shown to encode ManB, not a second isotype of RmlA. Using recombinant RmlB, -C, and -D enzymes, a microtiter plate assay was developed to screen for inhibitors of the formation of dTDP-rhamnose. The three enzymes were incubated with dTDP-glucose and NADPH to form dTDP-rhamnose and NADP(+) with a concomitant decrease in optical density at 340 nm (OD(340)). Inhibitor candidates were monitored for their ability to lower the rate of OD(340) change. To test the robustness and practicality of the assay, a chemical library of 8,000 compounds was screened. Eleven inhibitors active at 10 microM were identified; four of these showed activities against whole M. tuberculosis cells, with MICs from 128 to 16 microg/ml. A rhodanine structural motif was present in three of the enzyme inhibitors, and two of these showed activity against whole M. tuberculosis cells. The enzyme assay was used to screen 60 Peruvian plant extracts known to inhibit the growth of M. tuberculosis in culture; two extracts were active inhibitors in the enzyme assay at concentrations of less than 2 microg/ml.

Antitubercular activity of triterpenoids from Lippia turbinata.

Assay-guided fractionation of the antitubercular MeOH-CH(2)Cl(2) extract obtained from Lippia turbinata led to the isolation of four novel triterpenoids-3beta,25-epoxy-3alpha,21alpha-dihydroxy-22beta-(3-methylbut-2-en-1-oyloxy)olean-12-ene-28-oic acid (1); 3beta,25-epoxy-3alpha,21alpha-dihydroxy-22beta-angeloyloxyolean-12-ene-28-oic acid (2); 3beta,25-epoxy-3alpha,21alpha-dihydroxy-22beta-tigloyloxyolean-12-ene-28-oic acid (3); and 3beta,25-epoxy-3alpha-hydroxy-22beta-(2-methylbutan-1-oyloxy)olean-12-ene-28-oic acid (4)-together with the known triterpenoids lantanilic acid (5), camaric acid (6), lantanolic acid (7), and rehmannic acid (8). The MIC values of 1-8 for growth inhibition of Mycobacterium tuberculosis were determined in the radiorespirometric BACTEC system.

Assessment of antimycobacterial activity of a series of mainly marine derived natural products.

A series of mainly marine derived natural products were tested for their activities against Mycobacterium tuberculosis and M. avium. Of the thirty-nine compounds tested fifteen demonstrated minimum inhibition concentrations (MICs) of 32 micrograms/ml or less, and eleven had MICs of 16 micrograms/ml or less. The most active compound found in this study was the sponge derived metabolite axisonitrile-3 (MIC 2 micrograms/ml).

Agelasine F from a Philippine Agelas sp. sponge exhibits in vitro antituberculosis activity.

Marine sponge samples were collected in Baler, Aurora, Philippines, and extracts were tested for in vitro antituberculosis activity. An orange Agelas sp. sponge yielded the known compound, agelasine F, which inhibited some drug resistant strains of Mycobacterium tuberculosis in vitro at concentrations as low as 3.13 micrograms/ml. Activity against M. tuberculosis residing within macrophages required concentrations of 13-22 micrograms/ml which was below the IC50 for Vero cells (34 micrograms/ml).

New phenylethanoids from Buddleja cordata subsp. cordata.

Bioassay-guided fractionation of a crude extract of the stem bark of Buddleja cordata subsp. cordata with significant antimycobacterial activity led to the isolation of a mixture composed by ten new long-chain esters of 2[4'-hydroxyphenyl]-ethanol (1-10), along with the lichen metabolites methyl beta-orcinolcarboxylate (11) and beta-orcinolcarboxylate (12). Extensive HPLC allowed the separation of the major components of the mixture, which were characterized by spectral means as 2[4'-hydroxyphenyl]-ethyl stearate (3), 2[4'-hydroxyphenyl]-ethyl behenate (6), and 2[4'-hydroxyphenyl]-ethyl lignocerate (8). The minor esters were identified as 2[4'-hydroxyphenyl]-ethyl palmitate (1), 2[4'-hydroxyphenyl]-ethyl heptadecanoate (2), 2[4'-hydroxyphenyl]-ethyl nonadecanoate (4), 2[4'-hydroxyphenyl]-ethyl arachidate (5), 2[4'-hydroxyphenyl]-ethyl tricosanoate (7), 2[4'-hydroxyphenyl]-ethyl pentacosanoate (9), and 2[4'-hydroxyphenyl]-ethyl hexacosanoate (10) by GC-MS analysis of the methyl esters derivatives of the fatty acids obtained by alkaline hydrolysis of the mixture. Compound 8 exhibited moderate antibacterial activity against Mycobacterium tuberculosis (MIC = 64 micrograms/ml).

NMR and molecular mechanics study of pyrethrins I and II.

Bioassay-directed fractionation of the organic extract of the Kenyan pyrethrum flowers (Chrysanthemum cinerariaefolium Vissiani) resulted in the isolation of two natural pyrethrin esters, pyrethrin I (PI) and pyrethrin II (PII) as the major constituents. These esters elicited inhibition of the multiple drug resistant (MDR) Mycobacterium tuberculosis. The high-field (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of PI and PII were unequivocally assigned using modern two-dimensional (2D) proton-detected heteronuclear multiple-quantum coherence (HMQC) and heteronuclear multiple-bond correlation (HMBC) experiments. The conformations of both esters were deduced from (1)H-(1)H vicinal coupling constants and confirmed by 2D nuclear Overhauser effect spectroscopy (NOESY). Computer molecular modeling (MM) studies revealed that PI and PII molecules adopt a "love-seat" conformation in chloroform (CDCl(3)) solution.

Phytochemical, morphological, and biological investigations of propolis from Central Chile.

Propolis from central Chile was investigated for its plant origin by microscopical analysis of pollen grains and leaf fragments found in the sample. The pollen grains that appear with significant higher frequency in the sample corresponded to four native and two introduced species, whereas leaf fragments corresponded to four native species. Seventeen phenolic compounds that belong to the phenylpropane, benzaldehyde, dihydrobenzofuran, or benzopyran classes, were isolated from an organic extract that was found to have a moderate growth inhibitory activity against Mycobacterium avium, M. tuberculosis, and two strains of Staphylococcus aureus. The components responsible for activity were determined.

Antimycobacterial eudesmanolides from Inula helenium and Rudbeckia subtomentosa.

In a bioassay guided search for antimycobacterial compounds from higher plants, the root extracts of Elecampane (Inula helenium L.; Asteraceae) and Sweet Coneflower (Rudbeckia subtomentosa Pursh.; Asteraceae) were chemically investigated for their active constituents. Chromatographic fractions of root extracts of l. helenium, which exhibited significant activity against Mycobacterium tuberculosis, provided the known eudesmanolides alantolactone, isoalantolactone, and 11 alpha H, 13-dihydroisoalantolactone. Peracid epoxidation of alantolactone and isoalantolactone provided 5 alpha-epoxyalantolactone and 4(15) alpha-epoxyisoalantolactone, respectively and oxidation of alantolactone with OsO4 gave 11,13-dihydroxyalantolactone. Active fractions from R subtomentosa contained the known alloalantolactone and 3-oxoalloalantolactone. The structures of the above compounds were established by spectroscopic methods including 1D and 2D NMR techniques as well as spectral comparison with previously reported data. The molecular structure of 5 alpha-epoxyalantolactone was determined by single crystal X-ray diffraction. Eleven natural and semisynthetic eudesmanolides were tested in a radiorespirometric bioassay for activity against M. tuberculosis. 5 alpha-Epoxyalantolactone and encelin from Montanoa speciosa showed minimum inhibitory concentrations (MICs) of 8 and 16 micrograms ml-1, respectively. Alantolactone, isoalantolactone and its 4 alpha, 15-epoxide, 1,2-dehydro-3-epi-isotelekin and alloalantolactone gave MICs of 32 micrograms ml-1. All other compounds showed MIC values of 128 micrograms ml-1 or higher.

Antimycobacterial triterpenes from Melia volkensii.

In a bioassay-guided search for antimycobacterial compounds from higher plants, we have chemically investigated methanolic extracts of seeds of Melia volkensii. Chromatographic fractions provided two new euphane (20R)-type triterpenoids. The structures of the new compounds, 12beta-hydroxykulactone (1) and 6beta-hydroxykulactone (2), were elucidated by 1D and 2D NMR (13C, 1H, 1H-1H COSY, HMQC, HMBC, and NOESY spectra) and FABMS studies and shown to be hydroxyl derivatives of kulactone (3). Also isolated was the known kulonate (4). In a radiorespirometric bioassay against Mycobacterium tuberculosis, compounds 1, 2, and 4 exhibited minimum inhibitory concentrations of 16, 4, and 16 microg/mL, respectively.