Dihydro-beta-agarofuran sesquiterpenes: a new class of reversal agents of the multidrug resistance phenotype mediated by P-glycoprotein in the protozoan parasite Leishmania.

Leishmaniasis is the most important emerging and uncontrolled infectious disease and the second cause of death among parasitic diseases, after Malaria. One of the main problems concerning the control of infectious diseases is the increased resistance to usual drugs. Overexpression of P-glycoprotein (Pgp)-like transporters represents a very efficient mechanism to reduce the intracellular accumulation of drugs in cancer cells and parasitic protozoans, thus conferring a multidrug resistance (MDR) phenotype. Pgps are active pumps belonging to the ATP-binding cassette (ABC) superfamily of proteins. The inhibition of the activity of these proteins represents an interesting way to control drug resistance both in cancer and in infectious diseases. Most conventional mammalian Pgp-MDR modulators are ineffective in the modulation of Pgp activity in the protozoan parasite Leishmania. Consequently, there is a necessity to find effective modulators of Pgp-MDR for protozoan parasites. In this review we describe a rational strategy developed to find specific Pgp-MDR modulators in Leishmania, using natural and semisynthetic dihydro-beta-agarofuran sesquiterpenes from Celastraceae plants. A series of these compounds have been tested on a MDR Leishmania tropica line overexpressing a Pgp transporter to determine their ability to revert the resistance phenotype and to modulate intracellular drug accumulation. Almost all of these natural compounds showed potent reversal activity with different degrees of selectivity and a significant low toxicity. The three-dimensional quantitative structure-activity relationship using the comparative molecular similarity indices analysis (CoMSIA), was employed to characterize the requirements of these sesquiterpenes as modulators at Pgp-like transporter in Leishmania.

A new steroidal saponin from Solanum sisymbriifolium roots.

Isonuatigenin-3-O-beta-solatriose (1) was isolated from the roots of Solanum sisymbriifolium. Its structure was determined by spectroscopic methods.

A new family of choline kinase inhibitors with antiproliferative and antitumor activity derived from natural products.

BACKGROUND: Choline kinase alpha (ChoKα) is a critical enzyme in the synthesis of phosphatidylcholine, a major structural component of eukaryotic cell membranes. ChoKα is overexpressed in a large variety of tumor cells and has been proposed as a target for personalized medicine, both in cancer therapy and rheumatoid arthritis. MATERIALS AND METHODS: Triterpene quinone methides (TPQ) bioactive compounds isolated from plants of the Celastraceae family and a set of their semisynthetic derivatives were tested against the recombinant human ChoKα. Those found active as potent enzymatic inhibitors were tested in vitro for antiproliferative activity against HT29 colorectal adenocarcinoma cells, and one of the active compounds was tested for in vivo antitumoral activity in mice xenographs of HT29 cells. RESULTS: Among 59 natural and semisynthetic TPQs tested in an ex vivo system, 14 were highly active as inhibitors of the enzyme ChoKα with IC50 <10 µM. Nine of these were potent antiproliferative agents (IC50 <10 µM) against tumor cells. At least one compound was identified as a new antitumoral drug based on its in vivo activity against xenographs of human HT-29 colon adenocarcinoma cells. CONCLUSIONS: The identification of a new family of natural and semisynthetic compounds with potent inhibitory activity against ChoKα and both in vitro antiproliferative and in vivo antitumoral activity supports further research on these inhibitors as potential anticancer agents. Their likely role as antiproliferative drugs deserves further studies in models of rheumatoid arthritis.

Multidrug resistance phenotype mediated by the P-glycoprotein-like transporter in Leishmania: a search for reversal agents.

Abstract: Protozoan parasites are responsible for important diseases that threaten the lives of nearly one-quarter of the human population world-wide. Among them, leishmaniasis has become the second cause of death, mainly due to the emergence of parasite resistance to conventional drugs. P-glycoprotein (Pgp)-like transporters overexpression is a very efficient mechanism to reduce the intracellular accumulation of many drugs in cancer cells and parasitic protozoans including Plasmodium and Leishmania, thus conferring a multidrug resistance (MDR) phenotype. Therefore, there is a great clinical interest in developing inhibitors of these transporters to overcome such a resistance. Pgps are active pumps belonging to the ATP-binding cassette (ABC) superfamily of proteins, and consist of two homologous halves, each containing a transmembrane domain (TMD) involved in drug efflux, and a cytosolic nucleotide-binding domain (NBD) responsible for ATP binding and hydrolysis. Most conventional cancer MDR modulators interact with the drug-binding sites on the TMDs of Pgps, but they are also usually transported and the required concentrations for a permanent inhibition produce subsequent side-effects that hamper their clinical use. Besides, they only poorly modulate the resistance in protozoan parasites. We review here a rational strategy developed to overcome the MDR phenotype in Leishmania, consisting in: i) the selection of an MDR Leishmania tropica line that overexpresses a Pgp-like transporter; ii) the use of their cytosolic NBDs as new pharmacological targets; iii) the search of new natural compounds that revert the MDR phenotype in Leishmania by binding to the TMDs; iv) the combination of subdoses of the above selected modulators directed to both targets in the transporter, NBDs and TMDs, to accumulate their reversal effects while diminishing their toxicity. In this way, we have reverted the MDR phenotype in Leishmania, including the resistance to the most promising new antileishmania agents, the alkyl-lysophospholipids. This approach might be extrapolated to be used in other eukaryotic cells.

New natural sesquiterpenes as modulators of daunomycin resistance in a multidrug-resistant Leishmania tropica line.

The effects produced by nine dihydro-beta-agarofuran sesquiterpenes isolated from Crossopetalum tonduzii (1-8) and Maytenus macrocarpa (9) (Celastraceae) on the reversion of the resistant phenotype on a multidrug-resistant Leishmania line and their binding to recombinant C-terminal nucleotide-binding domain of Leishmania P-glycoprotein-like transporter were studied. The structures of the new compounds (1-5) were elucidated by spectroscopic methods, including (1)H-(13)C heteronuclear correlation (HMQC), long-range correlation spectra with inversal detection (HMBC), ROESY experiments, and chemical correlations. The absolute configuration of one of them (1) was determined by CD studies. The structure-activity relationship is discussed.

Chemosensitization of a multidrug-resistant Leishmania tropica line by new sesquiterpenes from Maytenus magellanica and Maytenus chubutensis.

Parasite resistance to drugs has emerged as a major problem in current medicine, and therefore, there is great clinical interest in developing compounds that overcome these resistances. In an intensive study of South American medicinal plants, herein we report the isolation, structure elucidation, and biological activity of dihydro-beta-agarofuran sesquiterpenes from the roots of Maytenus magellanica (1-14) and M. chubutensis (14-17). This type of natural products may be considered as privileged structures. The structures of 10 new compounds, 1, 3, 6-9, and12-15, were determined by means of (1)H and (13)C NMR spectroscopic studies, including homonuclear (COSY and ROESY) and heteronuclear correlation experiments (HMQC and HMBC). The absolute configurations of eight hetero- and homochromophoric compounds, 1, 3,6-9, 12, and 13, were determined by means of CD studies. Fourteen compounds, 1-3 and 6-16, have been tested on a multidrug-resistant Leishmania tropica line overexpressing a P-glycoprotein-like transporter to determine their ability to revert the resistance phenotype and to modulate intracellular drug accumulation. From this series, 1, 2, 3, 14, and 15 showed potent activity, 1 being the most active compound. The structure-activity relationships of the different compounds are discussed.

Bioactive anthraquinone glycosides from Picramnia antidesma spp. fessonia.

A bioactivity guided fractionation, using KB cells and brine shrimp assays, of the methanolic extract from the leaves of Picramnia antidesma yielded two known anthraquinones, aloe-emodin and aloe-emodin anthrone, and three new aloe-emodin C-glycosides, named picramnioside A, picramnioside B and picramnioside C. Structures were established by spectroscopic methods (UV, IR, mass spectrometry, 1H and 13C and 2D NMR including COSY 45, HMQC, HMBC and ROESY). CD was used to establish the absolute configuration of the picramniosides.

Biological activities of some Argyranthemum species.

Seven species of the genus Argyranthemum were studied for antimicrobial and cytotoxic activities. Argyranthemum adauctum, A. foeniculaceum and A. frutescens showed antimicrobial activity against Gram-positive and Gram-negative and cytotoxic activity against HeLa and Hep-2 cell lines. Two new acetylenic compounds, frutescinol isovalerate and 3'-demethyl frutescinol isovalerate, were isolated from A. frutescens and their structures elucidated by spectroscopic studies.

Antibiotic phenol nor-triterpenes from Maytenus canariensis.

The new phenols 6-oxo-tingenol, 3-O-methyl-6-oxo-tingenol and 6-oxo-iguesterol were isolated from the root bark of Maytenus canariensis. Their structures were determined by 1H and 13C NMR spectroscopic studies, including HMQC, HMBC, DEPT and ROESY and chemical transformations. The synthesis of 6-oxo-tingenol was achieved from tingenone. These compounds exhibit antibiotic activity against Gram-positive bacteria.

Xanthine oxidase inhibitory activity of some Panamanian plants from Celastraceae and Lamiaceae.

Thirty four crude extracts of Panamanian plants, from nine species of Celastraceae and Lamiaceae, were assayed for xanthine oxidase (XO) inhibitory activity. The enzymatic activity was estimated by measuring the increase in absorbance at 290 nm due to uric acid formation. Eighty five percent of the crude extracts were found to possess XO inhibitory activity at 50 micrograms/ml and all the extracts of the species from Lamiaceae were active even at 1 micrograms/ml. The ethanol extracts of Hyptis obtusiflora Presl ex Benth. (Lamiaceae) and H. lantanaefolia Poit. (Lamiaceae) exhibited the highest activity with an inhibition of approximately 40% at 1 micrograms/ml.

Inhibition of potato cyst nematode hatch by lignans fromBupleurum salicifolium (Unbelliferae).

A series of lignans fromBupleurum salicifolium Soland (Umbelliferae) were tested for nematostatic activity on the cysts and freed secondstage juveniles of the potato cyst nematodesGlobodera rostochiensis andG. pallida. None of the six lignans tested-bursehernin, matairesinol, syringaresinol, the novel product buplerol, guayarol, and a derivative, nortrachelogenin triacetate-showed nematicidal activity in an in vitro analysis with second-stage juveniles, but significant differences were noted when the lignans were assayed for nematostatic activity as cyst hatching inhibitors. Bursehernin and matairesinol showed the greatest activity, at concentrations of 50 ppm. This is the first known instance of a natural product inhibiting the hatch of the nematodeG. pallida. The HID (hatching inhibiting dose) of bursehernin was estimated, and some conclusions were drawn about the structure-activity relationships of the lignans under study.

New terpenoids from Maytenus blepharodes.

Three new terpenoids, xuxuarine Ealpha (1), a triterpene dimer based on two pristimerin units, and two sesquiterpenoids with a dihydro-beta-agarofuran skeleton (2 and 3) were isolated from Maytenus blepharodes. Their structures were elucidated on the basis of spectral analysis, including homonuclear and heteronuclear correlation NMR experiments (COSY, ROESY, HMQC, and HMBC). The absolute configurations of 1 and 2 were determined by CD studies.

Triterpene trimers from Maytenus scutioides: cycloaddition compounds?

Two novel trimers, triscutins A and B (1 and 2), based on pristimerin triterpene units, were isolated and characterized from Maytenus scutioides. Their structures were determined on the basis of spectroscopic evidence, including 1H-13C heteronuclear correlation (HMQC), long-range correlation with inverse detection (HMBC), and ROESY NMR experiments; and their absolute configurations, by means of CD studies. Compounds 1 and 2 were assayed for antimicrobial and cytotoxic activities, and their possible biosynthetic route is proposed.

New sesquiterpenes from Crossopetalum tonduzii.

Five new sesquiterpenes (1-5) with a dihydro-beta-agarofuran skeleton were isolated from Crossopetalum tonduzii. Their structures were elucidated by means of 1H and 13C NMR spectroscopic studies, including homonuclear and heteronuclear correlation experiments (COSY, ROESY, HMQC, and HMBC). The absolute configurations of 1 and 2 were determined by CD studies and chemical correlation. Compounds 1-3 were assayed against Spodoptera littoralis in an election test and showed low insect-antifeedant activity.

A new bioactive norquinone-methide triterpene from Maytenus scutioides.

By antimicrobial and cytotoxic-guided fractionation, a bioactive norquinone-methide triterpene, 15 alpha-hydroxypristimerin, was isolated from a South American medicinal plant, Maytenus scutioides. Its structure was determined on the basis of spectroscopic evidence. Successful chemical transformation of pristimerin to netzahualcoyene indicates that the 15-hydroxy compounds seems to be a possible percursor of 14(15)-ene-quinone-methide-triterpenoids in the biogenetic pathway.

New phenolic and quinone-methide triterpenes from Maytenus amazonica.

The new nortriterpene methylene quinones amazoquinone (1) and (7S, 8S)-7-hydroxy-7,8-dihydro-tingenone (2), and the new norphenolic triterpenes 7,8-dihydro-6-oxo-tingenol (3), 23-nor-6-oxo-tingenol (4), and 23-oxo-iso-tingenone (5) were isolated from Maytenus amazonica. Their structures were elucidated by spectroscopic methods. Compounds 1, 2, 3, and 5 showed low antitumor activity against four cancer cell lines.

Friedelane triterpenoids from Maytenus macrocarpa.

A set of friedelane triterpenoids has been isolated from the stem bark exudates of Maytenus macrocarpa. It includes a new friedelan triterpene (1), together with the known compounds friedelin, 3-oxo-29-hydroxyfriedelane, 3-oxofriedelan-25-al, and canophyllol. The structures of these compounds were elucidated by spectroscopic and chemical evidence. Complete 1H and 13C assignments were achieved by 2D NMR spectroscopy. The new compound showed weak activity against aldose reductase. It did not display antitumor activity against P-388 lymphoid neoplasm, A-549 human lung carcinoma, HT-29 human colon carcinoma, or MEL-28 human melanoma cell lines.

Mode of action of netzahualcoyone.

The activity of netzahualcoyone on Bacillus subtilis and Escherichia coli was studied. The product inhibited the respiration of intact cells of B. subtilis but had no effect on the respiration of E. coli. However, when preparations of sonically disrupted cells were examined, inhibitory activity on both bacteria was observed.

Acetylenic acids from the aerial parts of Nanodea muscosa.

The aerial parts of Nanodea muscosa, collected in Chile, yielded two new acetylenic acids. Their structures were elucidated by spectroscopic analyses, including 2D NMR techniques, as (13E)-octadec-13-en-11-ynoic acid (1) and (2E)-octadec-2-en-4-ynedioic acid (2). Compound 2 constitutes the first example of a conjugated ene-yne fatty diacid isolated from a natural source. Compounds 1 and 2 did not exhibit toxicity toward a panel of DNA damage checkpoint defective yeast mutants or show affinity for the 5-HT(1A), 5-HT(2A), D(2), and H(1) receptors.

Antibiotic activity and absolute configuation of 8S-heptadeca-2(Z),9(Z)-diene-4,6-diyne-1,8-diol from Bupleurum salicifolium.

A polyacetylene has been isolated from Bupleurum salicifolium. Its structure and absolute configuration were determined to be 8S-heptadeca-2(Z),9(Z)-diene-4,6-diyne-1,8-diol [1] by means of 1H- and 13C-nmr spectroscopic studies, including 1H-13C heteronuclear correlation (HMQC) and long-range correlation spectra with inverse detection (HMBC). Its absolute configuration was determined by application of the Horeau method. This compound exhibited significant antibiotic activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis. Also isolated during this investigation were the known compounds; betulin, herniarin, 6,7,8-trimethoxycoumarin, p-hydroxyphenethyl alcohol, pluviatolide, guamaroline, bursehernin, guayadequiol, kaerophyllin, and matairesinol dimethyl ether.