Antihypertensive and vasorelaxing activities of synthetic xanthone derivatives

Expanding the therapeutic arsenal against cancer: a computational investigation of hybrid xanthone derivatives as selective Topoisomerase 2α ATPase inhibitors

The DNA topoisomerase II (topo II) enzyme plays an important role in the replication, recombination, and repair of DNA. Despite their widespread applications in cancer therapy, new, selective, and potent topo II inhibitors with better pharmaceutical profiles are needed to handle drug resistance and severe adverse effects. In this respect, an array of 36 new anticancer compounds was designed based on a Xanthone core tethered to multifunctional Pyridine-amines and Imidazole scaffold via alkyl chain linkers. An integrated in silico approach was used to understand the structural basis and mechanism of inhibition of the hybrid xanthone derivatives. In this study, we established an initial virtual screening workflow based on pharmacophore mapping, docking, and cancer target association to validate the target selection process. Next, a simulation-based docking was conducted along with pharmacokinetic analysis to filter out the five best compounds (7, 10, 25, 27, and 30) having binding energies within the range of -60.45 to -40.97 kcal/mol. The screened compounds were further subjected to molecular dynamics simulation for 200 ns followed by MM-GBSA and ligand properties analysis to assess the stability and binding affinity to hTOP2α. The top-ranking hits 3,7-bis(3-(2-aminopyridin-3-ylhydroxy)propoxy)-1-hydroxy-9H-xanthen-9-one (ligand 7) and 3,8-bis(3-(2-aminopyridin-3-ylhydroxy)propoxy)-1-hydroxy-9H-xanthen-9-one (ligand 25) were found to have no toxicity, optimum pharmacokinetic and, DFT properties and stable intermolecular interactions with the active site of hTopo IIα protein. In conclusion, further in vitro and in vivo experimental validation of the identified lead molecules is warranted for the discovery of new human Topoisomerase 2 alpha inhibitors.Communicated by Ramaswamy H. Sarma.

Phytochemical Composition of Lichen Parmotrema hypoleucinum (J. Steiner) Hale from Algeria

In this work, we carried out studies of the chemical composition of hexane, chloroform and ethanol extracts from two samples of the lichen Parmotrema hypoleucinum collected in Algeria. Each sample of the lichen P. hypoleucinum was collected on two different supports: Olea europaea and Quercus coccifera. Hexane extracts were prepared, in Soxhlet; each hexane extract was fractionated by its solubility in methanol; the products soluble in methanol were separated (cold): 1-Hexane, 2-Hexane; and the products insoluble in methanol (cold): 1-Cires, 2-Cires. A diazomethane esterified sample of 1-Hexane, 2-Hexane, 1-Cires and 2-Cires was analyzed by GC-MS, and the components were identified as methyl esters. In the 1-Hexane and 2-Hexane fractions, the methyl esters of the predominant fatty acids in the lichen were identified: palmitic acid, linoleic acid, oleic acid and stearic acid; a hydrocarbon was also identified: 13-methyl-17-norkaur-15-ene and several derivatives of orsellinic acid. In the 1-Cires and 2-Cires fractions, the previous fatty acids were no longer observed, and only the derivatives of orsellinic acid were found. The analysis of the 1-Hexane, 2-Hexane fractions by HPLC-MS/MS allows us to identify different chemical components, and the most characteristic products of the lichen were identified, such as Atranol, Chloroatranol, Atranorin and Chloroatranorin. In the fractions of 1-Cires and 2-Cires, the HPLC-MS/MS analysis reveals that they are very similar in their chemical components; the characteristic products of this lichen in this fraction are Atranorin and Chloroatranorin. In the extracts of chloroform, 1-Chloroform and 2-Chloroform, the analysis carried out by HPLC-MS/MS shows small differences in their chemical composition at the level of secondary products; among the products to be highlighted for this work, we have chloroatranorin, the stictic acid, norstictic acid and other derivatives. In the analysis of the most polar extracts carried out in ethanol: 1-Ethanol and 2-Ethanol, HPLC-MS/MS analysis shows very similar chemical compositions in these two extracts with small differences. In these extracts, the following acids were identified as characteristic compounds of this lichen: constictic acid, stictic acid, substictic acid and methylstictic acid. In the HPLC–MS/MS analysis of all these extracts, alectoronic acid was not found.

Nitric-Oxide-Mediated Vasodilation of Bioactive Compounds Isolated from Hypericum revolutum in Rat Aorta

Simple Summary

Hypericum revolutum (HR) is reported to produce vasodilating activity in phenylephrine-precontracted aortae, where the chloroform fraction is the most potent. Chemical investigation of this fraction yielded two new compounds, revolutin (1) and hyperevolutin C (2), along with three known metabolites, β-sitosterol (3), euxanthone (4), and 2,3,4-tirmethoxy xanthone (5). Isolated compounds 1, 2, 3, and 5 produce vasodilation activities that are dependent on endothelial nitric oxide release.

Abstract

Vasodilators are an important class in the management of hypertension and related cardiovascular disorders. In this regard, the chloroform fraction of Hypericum revolutum (HR) has been reported to produce vasodilating activity in phenylephrine-precontracted aortae. The current work aims to identify the active metabolites in the chloroform fraction of HR and illustrate the possible mechanism of action. The vasodilation activities were investigated using the isolated artery technique. NO vascular release was assessed by utilizing the NO-sensitive fluorescent probe DAF-FM. Free radical scavenging capacity was assessed utilizing DPPH. Chemical investigation of this fraction yielded two new compounds, revolutin (1) and hyperevolutin C (2), along with three known metabolites, β-sitosterol (3), euxanthone (4), and 2,3,4-tirmethoxy xanthone (5). Compounds 1, 2, 3, and 5 showed significant vasodilation activities that were blocked by either endothelial denudation or L-NAME (nitric oxide synthase inhibitor), pointing towards a role of endothelial nitric oxide in their activities. In confirmation of this role, compounds 1–3 showed a significant release of NO from isolated vessels, as indicated by DAF-FM. On the other hand, only compound 5 showed free radical scavenging activities, as indicated by DPPH. In conclusion, isolated compounds 1, 2, 3, and 5 produce vasodilation activities that are dependent on endothelial nitric oxide release.

Antihypertensive activity, toxicity and molecular docking study of newly synthesized xanthon derivatives (xanthonoxypropanolamine)

CONTEXT

Xanthone derivatives have been reported to possess a wide range of biological properties. In effort to search new effective antihypertensive compounds, we have synthesizednovel xanthone derivatives (xanthonoxypropanolamines) and got patent for these compounds (The Patent Office, Government of India, S. No.: 011-016308, Patent No.: 250538).

OBJECTIVE

In the present work, we attempted to establish the antihypertensive activity, toxicity and molecular docking study forthese newly synthesized compounds (1a, 1b and 2).

MATERIALS AND METHOD

The preliminary antihypertensive screening was performed by administering synthesized compounds and standard drugs intraperitonially and orally into wistar rats. The change in systolic, diastolic and the mean blood pressure before and after the treatment of the drugs was measured on a Digital LE-S100 Blood Pressure Meter by Tail-cuff method non-invasively. Toxicity studies were carried out after oral administration of synthesized compounds to rats at doses of 25, 50, and 100mg/kg. The serum samples were tested for different toxicity parameters such as liver function test, kidney function test etc. The docking simulations of all the compounds were performed using Maestro, version 9.4 implemented from Schrodinger software suite.

RESULTS AND DISCUSSION

The result showed that the compound 1a, 1b and 2 have greater antihypertensive activity with almost equal or less toxicity profile in comparison to standard drug Propranolol and Atenolol. The docking score for the compound 1b was found -9.1 while for compound 1a and 2 were found -8.7 and -8.6 respectively.

CONCLUSION

These novel compounds i.e. 1a, 1b, and 2 have greater antihypertensive activity in comparison to standard drugs Propranolol and Atenolol. All these compounds do not have any toxicity.

Design, synthesis and cardiovascular evaluation of some aminoisopropanoloxy derivatives of xanthone

A series of aminoisopropanoloxy derivatives of xanthone has been synthesized and their pharmacological properties regarding the cardiovascular system has been evaluated. Radioligand binding and functional studies in isolated organs revealed that title compounds present high affinity and antagonistic potency for α₁-(compound 2 and 8), β-(compounds 1, 3, 4, 7), α₁/β-(compounds 5 and 6) adrenoceptors. Furthermore, compound 7, the structural analogue of verapamil, possesses calcium entry blocking activity. The title compounds showed hypotensive and antiarrhythmic properties due to their adrenoceptor blocking effect. Moreover, they did not affect QRS and QT intervals, and they did not have proarrhythmic potential at tested doses. In addition they exerted anti-aggregation effect. The results of this study suggest that new compounds with multidirectional activity in cardiovascular system might be found in the group of xanthone derivatives.

Contribution of reactive oxygen species to the anticancer activity of aminoalkanol derivatives of xanthone

Reactive oxygen species (ROS) are critically involved in the action of anticancer agents. In this study, we investigated the role of ROS in the anticancer mechanism of new aminoalkanol derivatives of xanthone. Most xanthones used in the study displayed significant pro-oxidant effects similar to those of gambogic acid, one of the most active anticancer xanthones. The pro-oxidant activity of our xanthones was shown both directly (by determination of ROS induction, effects on the levels of intracellular antioxidants, and expression of antioxidant enzymes) and indirectly by demonstrating that the overexpression of manganese superoxide dismutase decreases ROS-mediated cell senescence. We also observed that mitochondrial dysfunction and cellular apoptosis enhancement correlated with xanthone-induced oxidative stress. Finally, we showed that the use of the antioxidant N-acetyl-L-cysteine partly reversed these effects of aminoalkanol xanthones. Our results demonstrated that novel aminoalkanol xanthones mediated their anticancer activity primarily through ROS elevation and enhanced oxidative stress, which led to mitochondrial cell death stimulation; this mechanism was similar to the activity of gambogic acid.

Novel xanthone-polyamine conjugates as catalytic inhibitors of human topoisomerase IIα

It has been proposed that xanthone derivatives with anticancer potential act as topoisomerase II inhibitors because they interfere with the ability of the enzyme to bind its ATP cofactor. In order to further characterize xanthone mechanism and generate compounds with potential as anticancer drugs, we synthesized a series of derivatives in which position 3 was substituted with different polyamine chains. As determined by DNA relaxation and decatenation assays, the resulting compounds are potent topoisomerase IIα inhibitors. Although xanthone derivatives inhibit topoisomerase IIα-catalyzed ATP hydrolysis, mechanistic studies indicate that they do not act at the ATPase site. Rather, they appear to function by blocking the ability of DNA to stimulate ATP hydrolysis. On the basis of activity, competition, and modeling studies, we propose that xanthones interact with the DNA cleavage/ligation active site of topoisomerase IIα and inhibit the catalytic activity of the enzyme by interfering with the DNA strand passage step.

Synthesis and biological evaluation of C1-O-substituted-3-(3-butylamino-2-hydroxy-propoxy)-xanthen-9-one as topoisomerase IIα catalytic inhibitors

Topoisomerase II poison blocks the transitorily generated DNA double-strand breaks (DSBs) from religation, thereby causes severe DNA damage and gene toxicity. While topoisomerase II catalytic inhibitor does not form cleavable DNA-enzyme complex because its function attributes to inhibition of the catalytic steps of the enzyme such as before generating DNA DSBs or in the last step of the catalytic cycle after religation. It has been reported that the stabilizing effect of etoposide on transient cleavable DNA-topoisomerase IIβ complex attributes to its secondary malignancy. Therefore, topoisomerase IIα has been considered as more attractive target than topoisomerase IIβ for the development of chemotherapeutic agents. In the previous work, we reported compounds I and II as novel topoisomerase IIα catalytic inhibitors targeting for ATP binding site of human topoisomerase IIα ATP-binding domain. As a continuous work, we have designed and synthesized 43 compounds of C1-O-alkyl and arylalkyl substitiuted compounds with or without methoxy group on ring A. In the topoisomerase IIα inhibitory test, among the tested C1-O-4-chlorophenethyl substituted compounds 37 and 47 were more active than others, and compound 37 showed strongest topoisomerase IIα inhibitory activity with 94.4% and 23.0% inhibition, respectively, at 100 and 20 μM. Compounds 37 and 47 have also showed much enhanced cytotoxic activity against T47D cells; IC50 (μM): 0.63 ± 0.01 and 0.19 ± 0.02, respectively, which are stronger than reference drugs. Band depletion assay and cleavage complex assay results showed compounds 37 and 47 were potential topoisomerase IIα catalytic inhibitor with low DNA damage.

A new DNA-intercalative cytotoxic allylic xanthone from Swertia corymbosa

Phytochemical investigation of the CHCl3 fraction of Swertia corymbosa resulted in the isolation of a new 3-allyl-2,8-dihydroxy-1,6-dimethoxy-9H-xanthen-9-one (1), along with four known xanthones, gentiacaulein (3), norswertianin (4), 1,3,6,8-tetrahydroxyxanthone (5), and 1,3-dihydroxyxanthone (6). Structure of compound 1 was elucidated with the aid of IR, UV, NMR, and MS data, and chemical transformation via new allyloxy xanthone derivative (2). Compounds 1-6 exhibited various levels of antioxidant and anti-α-glucosidase activities. Absorption and fluorescence spectroscopic studies on 1-6 indicated that these compounds could interact with calf thymus DNA (CT-DNA) through intercalation and with bovine serum albumin (BSA) in a static quenching process. Compound 1 was found to be significantly cytotoxic against human cancer cell lines HeLa, HCT116, and AGS, and weakly active against normal NIH 3T3 cell line.

Synthesis and spectroscopic properties of β-triazoloporphyrin-xanthone dyads

A novel series of β-triazoloporphyrin-xanthone conjugates and xanthone-bridged β-triazoloporphyrin dyads has been synthesized in moderate to good yields through Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of copper(II) 2-azido-5,10,15,20-tetraphenylporphyrin or zinc(II) 2-azidomethyl-5,10,15,20-tetraphenylporphyrin with various alkyne derivatives of xanthones in DMF containing CuSO4 and ascorbic acid at 80 °C. Furthermore, these metalloporphyrins underwent demetalation under acidic conditions to afford the corresponding free-base porphyrins in good to excellent yields. After successful spectroscopic characterization, these porphyrins have been evaluated for their photophysical properties. The preliminary results revealed a bathochromic shift in the UV-vis and fluorescence spectra of these porphyrin-xanthone dyads.

Biofunctional studies of new 2-methoxyphenylpiperazine xanthone derivatives with α₁-adrenolytic properties

BACKGROUND

The aim of this study was to assess the selectivity of the studied xanthone derivatives for α1-adrenoceptor subtypes (α1A, α1B, α1D, α1L) in functional experiments in order to verify if they possess any selectivity for a distinct subtype of α1-adrenoceptor. Moreover, several pharmacological tests were carried out to assess whether they reveal other than α1-adrenoceptor blocking properties such as: antagonistic for 5-HT2 receptors, vasorelaxant or spasmolytic.

METHODS

The influence on α1A-adrenoceptors was examined in biofunctional studies employing isolated rat vas deferens, on α1B-adrenoceptors in guinea-pig spleen, on α1D-adrenoceptors in rat aorta, and on α1L-adrenoceptors in rabbit spleen. Affinity for 5-HT2 receptors was measured in radioligand binding assay, whereas antagonistic potency for 5-HT2 receptors was studied on isolated rat aorta. Vasorelaxant effect of tested compounds was assessed in functional study employing rat aorta, whereas direct spasmolytic activity was investigated using the isolated rabbit small intestine.

RESULTS

The present study provides evidences that the tested 2-methoxyphenylpiperazine xanthone derivatives are non-selective α1-adrenoceptor blockers. However, at higher concentrations the direct spasmolytic effect could enhance their hypotensive activity. The obtained results indicate that the studied xanthones possessed weak calcium entry blocking activity, as well as antagonistic properties for 5-HT2A receptors.

CONCLUSIONS

The results of the present study support the idea that the hypotensive activity of the studied compounds is related to their α1-adrenolytic properties.

Antimalarial and vasorelaxant constituents of the leaves ofAllanblackia monticola(Guttiferae)

Phytochemical investigation of the leaves of Allanblackia monticola led to the isolation and characterisation of five prenylated xanthones [1,6-dihydroxy-3,7-dimethoxy-2-(3-methylbut-2-enyl)xanthone 1, alpha-mangostin 2, tovophyllin A 3, allanxanthone C 4 and 1,7-dihydroxy-3-methoxy-2-(3-methylbut-2-enyl)xanthone 5], two biflavonoid derivatives (amentoflavone 6 and podocarpusflavone A 7) and one pentacyclic triterpene (friedelan-3-one 8). The structures of these compounds were established on the basis of homo- and hetero-nuclear, one- and two-dimensional, nuclear magnetic resonance. Compounds 2-8 and a crude methanolic extract of A. monticola leaves were each tested for antimalarial activity in vitro, using the chloroquine-sensitive F32 and chloroquine-resistant FcM29 strains of Plasmodium falciparum; the median inhibitory concentrations (IC(50)) recorded varied from 0.7 to 83.5 mug/ml. The cytotoxicities of the compounds and crude extract, against cultures of human melanoma cells (A375), were then investigated, and cytotoxicity/antimalarial IC(50) ratios of 0.6-16.75 were recorded. In tests involving aortic rings from guinea pigs, a crude extract of the leaves of A. monticola was found to induce concentration-dependent vasorelaxation, causing up to 82% and 42% inhibition of noradrenaline- and KCl-induced contractions, respectively. The corresponding values for compounds 2 and 6 when tested against noradrenaline-induced contractions were approximately 18% and 35%, respectively.

Synthesis and preliminary evaluation of pharmacological properties of some piperazine derivatives of xanthone

A series of 9 piperazine derivatives of xanthone were synthesized and evaluated for cardiovascular activity. The following pharmacological experiments were conducted: the binding affinity for adrenoceptors, the influence on the normal electrocardiogram, the effect on the arterial blood pressure and prophylactic antiarrhythmic activity in adrenaline induced model of arrhythmia (rats, iv). Three compounds revealed nanomolar affinity for α(1)-adrenoceptor which was correlated with the strongest cardiovascular (antiarrhythmic and hypotensive) activity in animals' models. The most promising compound was 4-(3-(4-(2-methoxyphenyl)piperazine-1-yl)propoxy)-9H-xanthen-9-one hydrochloride (12) which revealed antiarrhythmic activity with ED(50) value of 0.69 mg/kg in adrenaline induced arrhythmia (rats, iv). Other synthesized xanthone derivatives, that is, (R,S)-4-(2-hydroxy-3-(4-(2-methoxyphenyl)piperazine-1-yl)propoxy)-9H-xanthen-9-one hydrochloride (10) and (R,S)-4-(2-acetoxy-3-(4-(2-methoxyphenyl)piperazine-1-yl)propoxy)-9H-xanthen-9-one hydrochloride (11) also acted as potential antiarrhythmics in adrenaline induced model of arrhythmia in rats after intravenous injection (ED(50) = 0.88 mg/kg and 0.89 mg/kg, respectively). These values were lower than values obtained for reference drugs such as propranolol and urapidil, but not carvedilol. Results were quite promising and suggested that in the group of xanthone derivatives new potential antiarrhythmics and hypotensives might be found.

Synthesis of new chiral xanthone derivatives acting as nerve conduction blockers in the rat sciatic nerve

The synthesis and structure elucidation of three new chiral xanthone (9H-xanthon-9-one) derivatives (2-4) are fully reported. The coupling reactions of the synthesized building block 6-methoxy-9-oxo-9H-xanthene-2-carboxylic acid (1) with two enantiomerically pure amino alcohols ((S)-(+)-valinol and (S)-(+)-leucinol) and one amine ((S)-(-)-α-4-dimethylbenzylamine), were carried out using the coupling reagent O-(benzotriazol-1-yl-)-N,N,N',N'-tetramethylluronium tetrafluoroborate (TBTU). The coupling reactions were performed with yields higher than 97% and enantiomeric excess higher than 99%. The structures of the compounds were established by IR, MS, and NMR ((1)H, (13)C, HSQC, and HMBC) techniques. Taking into account that these new chiral xanthone derivatives have molecular moieties structurally very similar to local anaesthetics, the ability to block compound action potentials (CAP) at the isolated rat sciatic nerve was also investigated. Nerve conduction blockade might result from a selective interference with Na(+) ionic currents or from a non-selective modification of membrane stabilizing properties. Thus, the mechanism, by which the three chiral xanthone derivatives cause conduction blockade in the rat sciatic nerve and their ability to prevent hypotonic haemolysis, given that erythrocytes are non-excitable cells devoid of voltage-gated Na(+) channels, are also described. Data suggest that nerve conduction blockade caused by newly-synthesized xanthone derivatives might result predominantly from an action on Na(+) ionic currents. This effect can be dissociated from their ability to stabilize cell membranes, which became apparent only upon increasing the concentration of compounds 2-4 to the higher micromolar range.

Antioxidant xanthone derivatives induce cell cycle arrest and apoptosis and enhance cell death induced by cisplatin in NTUB1 cells associated with ROS

In an effort to develop novel antioxidant as anticancer agents, a series of xanthones were prepared. In vitro screening, the synthetic xanthones revealed significant inhibitory effects on xanthine oxidase and ABTS radical-cation scavenging activity. The selective compounds 2 and 8 induced an accumulation of NTUB1 cells in the G(1) phase arrest and cellular apoptosis by the increase of ROS level. The combination of cisplatin and 2 significantly enhanced the cell death in NTUB1 cells. Compounds 2 and 8 did not show cytotoxic activity in selected concentrations against SV-HUC1 cells. The present results suggested that antioxidants 2 and 8 may be used as anticancer agent for enhancing the therapeutic efficacy of anticancer agents and to reduce their side effect.

Synthesis, biological evaluation, and molecular docking study of 3-(3'-heteroatom substituted-2'-hydroxy-1'-propyloxy) xanthone analogues as novel topoisomerase IIα catalytic inhibitor

Epoxide ring-opened xanthone derivatives were synthesized and tested for their topoisomerase inhibitory activity and cytotoxicity. Most of the compounds showed topo IIα specific inhibitory activity. To clarify the mechanism of action of these compounds, the most potent compound (compound 14) of the synthesized analogues was further studied by testing its ATPase inhibitory activity and through molecular docking experiments. The results showed that the topo IIα inhibitory activity of compound 14 was inversely proportional to ATP concentration. In the ATPase inhibitory test, ATP hydrolysis was reduced less efficiently by compound 14 (28.5±4.6%) than novobiocin (60.4±8.1%). Molecular docking study revealed compound 14 to have a stable binding pattern to the ATP-binding domain of human topo II.

Cytotoxic activity and DNA-binding properties of xanthone derivatives

In this study, the interactions of different groups substituted xanthone derivatives with calf thymus DNA (ct DNA) have been investigated by spectrophotometric methods and viscosity measurements. Results indicate that xanthone derivatives can intercalate into the DNA base pairs by the plane of xanthone ring and the various substituents may influence the binding affinity with DNA according to the calculated quenching constant values and the melting temperature of DNA. Furthermore, three tumor cell lines including esophagus squamous cancer cell line (ECA109), stomach cancer cell line (SGC7901) and lung cancer cell line (GLC-82) have been used to evaluate the cytotoxic activities of xanthone derivatives by MTT (microculture tetrazolium) method. Analysis show that the oxiranylmethoxy or piperidinylethoxy substituted xanthones exhibit more effective cytotoxic activity against three cancer cells than the other substituted xanthones. The effects on the inhibition of tumor cells in vitro agree with the studies of DNA-binding.

Cytotoxicity, apoptosis-inducing effects and structure-activity relationships of four natural xanthones from Gentianopsis paludosa Ma in HepG2 and HL-60 cells

Four xanthones were isolated from Gentianopsis paludosa Ma and were identified by modern spectroscopic methods. Cytotoxicity of the four xanthones was tested on HepG2 cells and HL-60 cells by sulphorhodamine B (SRB) assay. Clonogenic survival assay, trypan blue exclusion method, AO/EB staining and DNA fragmentation assay were conducted to investigate the effect on growth inhibition and apoptosis in the two cell lines in vitro. At the same time, structure-activity relationships (SARs) of the xanthones were investigated. The results showed that the xanthones had significant cytotoxicity and inhibition of proliferation in both HepG2 cells and HL-60 cells, and could induce apoptosis in these two cell lines. SARs indicated that the methoxy group had more cytotoxic contribution than the hydroxyl group at site C-8 in the structural scaffold of xanthone. The glycosidea at site C-1 may aggravate the stereospecific blockade of compound 4 and reduced its cytotoxic activity.

Vasodilatory actions of xanthones isolated from a Tibetan herb, Halenia elliptica

In this study, six major xanthones, isolated and identified from Halenia elliptica were investigated for their vasodilatory actions in isolated rat coronary artery. The xanthones, including 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1), 1-hydroxy-2,3,4,7-tetramethoxy-xanthone (HM-2), 1-hydroxy-2,3,4,5-tetramethoxy-xanthone (HM-3), 1,7-dihydroxy-2,3,4,5-tetramethoxy-xanthone (HM-4), 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5) and 1,7-dihydroxy-2,3-dimethoxy-xanthone (HM-7) caused vasodilation in the coronary artery pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with EC(50) values ranging from 1.4+/-0.1 microM (HM-1) to 6.6+/-1.4 microM (HM-2). The EC(50) values of the other xanthones were between those of HM-1 and HM-2. Removal of endothelium of the coronary artery led to decreases in the vasorelaxant effects of HM-1, HM-7 but not HM-2, HM-3, HM-4 and HM-5. Our results showed that xanthones isolated from Halenia elliptica are vasoactive substances which exhibit either endothelium-dependent or endothelium-independent mechanisms in rat coronary artery. The potency and mechanism(s) of the vasorelaxant effects of these xanthones may be relevant to the structure-activity differences in the level and the position of the substituent groups with the primary xanthone structure.

Anti-proliferation, cell cycle arrest and apoptosis induced by a natural xanthone from Gentianopsis paludosa Ma, in human promyelocytic leukemia cell line HL-60 cells

1-hydroxy-3,7,8-trimethoxyxanthone (xanthone 1) was isolated from Gentianopsis paludosa Ma and identified by MS and NMR in our laboratory. In this study, the results showed that xanthone 1 is a potent inducer of anti-proliferation and apoptosis in HL-60 cells. When the cells treated with lower concentrations of xanthone 1 (12.4-74.4microM), significant proliferation inhibition was detected by cell viability assay and morphological analyses, and conspicuous G1 and G2/M cell cycle arrest were observed by flow cytometric (FCM) analysis. However, when the cells treated with higher doses of xanthone 1 (82.7-330.8microM), significant apoptosis was observed by double sequential AO/EB staining, DNA fragmentation assay and FCM analysis. In addition, conspicuous DNA damage was detected by comet assay. In short, all the results showed that xanthone 1 had a significant cytotoxic effect and could induce proliferation inhibition and apoptosis in HL-60 cells in a time- and dose-dependent manner. It was possible that xanthone 1 could induce DNA damage in HL-60 cells, which resulted in G1 phase arrest at the lower concentrations and G2/M phase arrest at the higher concentrations, thus inhibiting the cell proliferation, and irreparable DNA damage at the higher concentrations might be responsible for the occurrence of apoptosis.

Mechanisms of the vasorelaxant effect of 1-hydroxy-2, 3, 5-trimethoxy-xanthone, isolated from a Tibetan herb, Halenia elliptica, on rat coronary artery

1-Hydroxy-2, 3, 5-trimethoxyxanthone (HM-1) is a xanthone isolated from Halenia elliptica, a Tibetan medicinal herb. HM-1 (0.33-42.1 microM) produced a concentration-dependent relaxation in rat coronary artery rings pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with an EC(50) of 1.67+/-0.27 microM. Removal of the endothelium significantly affected the vasodilator potency of HM-1, resulting in 46% decrease in E(max) value. The endothelium-dependent effects of HM-1 was confirmed when its vasorelaxant effect was inhibited after addition of nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (100 microM) or the soluble guanylate cyclase inhibitor 1H-[1, 2, 4] oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ, 10 microM). Atropine (100 nM), flurbiprofen (10 microM), propranolol (100 microM), pyrilamine (10 microM), cimetidine (10 microM) and SQ22536 (100 microM) had no effect on the vasorelaxant activity of HM-1 indicated the non-involvement of other receptor/enzyme systems. In endothelium-denuded coronary artery rings, the vasorelaxant effect of HM-1 was unaffected by potassium channel blockers such as tetraethylammonium (10 mM), iberiotoxin (100 nM), barium chloride (100 microM) and 4-aminopyridine (1 mM). The involvement of Ca(2+) channel in 5-HT-primed artery ring preparations incubated with Ca(2+)-free buffer was confirmed when HM-1 (9.93 microM) partially abolished the CaCl(2)-induced vasoconstriction (87% inhibition in intact-endothelium artery rings; 50% inhibition in endothelium-denuded rings). In the KCl-primed preparations incubated with Ca(2+)-free buffer, HM-1 (9.93 microM) produced a 27.3% inhibition in endothelium-denuded rings. HM-1 (3.31-33.1 microM) had minimal relaxant effects (14.4%-20.3%) on the contractile response generated by 10 microM phorbol 12,13-diacetate (PDA) in Ca(2+)-free solutions, suggesting minimal effects on intracellular Ca(2+) mechanisms. These findings suggest the vasodilator action of HM-1 involved both an endothelium-dependent mechanism involving NO and an endothelium-independent mechanism by inhibiting Ca(2+) influx through L-type voltage-operated Ca(2+) channels; a minor contribution to the effects of HM-1 may be related to inhibition of the protein kinase C-mediated release of intracellular Ca(2+) stores.

Leishmanicidal and cholinesterase inhibiting activities of phenolic compounds from Allanblackia monticola and Symphonia globulifera

In a preliminary antiprotozoal screening of several Clusiaceae species, the methanolic extracts of Allanblackia monticola and Symphonia globulifera showed high in vitro leishmanicidal activity. Further bioguided phytochemical investigation led to the isolation of four benzophenones: guttiferone A (1), garcinol (2), cambogin (3) and guttiferone F (4), along with three xanthones: allanxanthone A (5), xanthone V1 (6) and globulixanthone C (7) as active constituents. Compounds 1 and 6 were isolated from S. globulifera leaves, while compounds 2-5 were obtained from A. monticola fruits. Guttiferone A (1) and F (4) showed particulary strong leishmanicidal activity in vitro, with IC50 values (0.2 microM and 0.16 microM, respectively) comparable to that of the reference compound, miltefosine (0.46 microM). Although the leishmanicidal activity is promising, the cytotoxicity profile of these compounds prevent at this state further in vivo biological evaluation. In addition, all the isolated compounds were tested in vitro for their anticholinesterase properties. The four benzophenones showed potent anticholinesterase properties towards acetylcholinesterase (AChE) and butylcholinesterase (AChE). For AChE, the IC50 value (0.66 microM) of garcinol (2) was almost equal to that of the reference compound galanthamine (0.50 microM). Furthermore, guttiferone A (1) and guttiferone F (4) (IC50 = 2.77 and 3.50 microM, respectively) were more active than galanthamine (IC50 = 8.5) against BChE.

Synthesis of new xanthone analogues and their biological activity test--cytotoxicity, topoisomerase II inhibition, and DNA cross-linking study

In this report, we prepared some 3-(2',3'-epoxypropoxy)xanthones and their epoxide ring opened halohydrin analogues, and evaluated their cytotoxicity and topoisomerase II inhibition activity using doxorubicin and etoposide as references, respectively. Another xanthone compound 9, 1,3-di(2',3'-epoxypropoxy)xanthone, was also synthesized and its DNA cross-linking property including other two biological activities investigated. The biological test results showed compound 9 possessed excellent cytotoxic and topoisomerase II inhibitory activity than other compounds tested. It also exhibited significant DNA cross-linking activities.