Anti-inflammatory constituents from the stems and leaves of Glycosmis ovoidea Pierre.

Seven undescribed compounds, including four acridones, two coumarins, and a phenylpropanoid, together with 13 known acridone analogues were isolated from the ethanolic extract of the stems and leaves of Glycosmis ovoidea Pierre. Their structures were elucidated on the basis of comprehensive analysis of 1D and 2D NMR and HRESIMS spectroscopic data, and the absolute configurations were assigned by comparison of the experimental and calculated ECD data. Five compounds showed moderate inhibitory effects on nitric oxide production stimulated by lipopolysaccharide in BV-2 microglial cells with IC50 values in the range of 18.30-30.84 µM, and three compounds showed potent inhibition on 5-lipoxygenase (5-LOX) with IC50 values in the range of 2.08-10.26 µM. The possible binding sites of the active compounds with 5-LOX were further performed by molecular docking.

Atalantiaphyllines A-G, prenylated acridones from Atalantia monophylla DC. and their aromatase inhibition and cytotoxic activities.

Seven previously undescribed acridones, named atalantiaphyllines A-G, along with twenty-six known compounds were isolated from the dichloromethane extracts of roots and stems of Atalantia monophylla DC. Their structures were elucidated by analysis of extensive NMR and HRMS data. Aromatase inhibition, cytotoxicity against MOLT-3, HepG2, A549 and HuCCA-1 cell lines and DPPH radical scavenging activity of these compounds were evaluated. Most of the tested acridones exhibited higher potency in inhibiting aromatase than the positive control, ketoconazole, with IC50 values in the range of 0.08-2.0 µM. In the cytotoxicity assay, cycloataphylline A, N-methylbuxifoliadine E and atalantiaphylline G were selectively cytotoxic against MOLT-3 cell line with IC50 values of 8.0, 5.4 and 9.8 µM, respectively, while only atalaphyllidine exhibited highest antioxidant activity as evaluated by DPPH free radical scavenging assay with an IC50 value of 22.4 µM.

Cytotoxic activity of dimeric acridone alkaloids derived from Citrus plants towards human leukaemia HL-60 cells.

OBJECTIVES: Acridone alkaloids from Citrus and their derivatives show various kinds of biological activity. However, the anticancer activities of dimeric acridone alkaloids with unique structures and the molecular mechanism of these effects are poorly understood. METHODS: We investigated the cytotoxicity effects of dimeric acridone alkaloids isolated from Marsh grapefruit on human myeloid leukaemia HL-60 cells. KEY FINDINGS: Of the six dimeric acridone alkaloids tested, citbismine-E, the most potent, dose- and time-dependently decreased HL-60 cell viability by inducing apoptosis. The treatment of HL-60 cells with citbismine-E yielded a significant increase in levels of intracellular reactive oxygen species (ROS). Citbismine-E lowered the mitochondrial membrane potential and increased the activities of caspase-9 and -3. In addition, citbismine-E-induced apoptosis, decrease in mitochondrial membrane potential and caspase activation were significantly alleviated by pretreatment of the cells with antioxidant N-acetylcysteine (NAC). Citbismine-E induced intrinsic caspase-dependent apoptosis through ROS-mediated c-Jun N-terminal kinase activation. Citbismine-E-induced production of oxidative stress biomarkers, malondialdehyde and 8-hydroxy-2'-deoxyguanosine was also attenuated by pretreatment with NAC. CONCLUSIONS: Citbismine-E is a powerful cytotoxic agent against HL-60 cells that acts by inducing mitochondrial dysfunction-mediated apoptosis through ROS-dependent JNK activation. Citbismine-E also induced oxidative stress damage via ROS-mediated lipid peroxidation and DNA damage in HL-60 cells.

Synthesis of acridone derivatives via heterologous expression of a plant type III polyketide synthase in Escherichia coli.

BACKGROUND: Acridone alkaloids are heterocyclic compounds that exhibit a broad-range of pharmaceutical and chemotherapeutic activities, including anticancer, antiviral, anti-inflammatory, antimalarial, and antimicrobial effects. Certain plant species such as Citrus microcarpa, Ruta graveolens, and Toddaliopsis bremekampii synthesize acridone alkaloids from anthranilate and malonyl-CoA. RESULTS: We synthesized two acridones in Escherichia coli. Acridone synthase (ACS) and anthraniloyl-CoA ligase genes were transformed into E. coli, and the synthesis of acridone was examined. To increase the levels of endogenous anthranilate, we tested several constructs expressing proteins involved in the shikimate pathway and selected the best construct. To boost the supply of malonyl-CoA, genes coding for acetyl-coenzyme A carboxylase (ACC) from Photorhabdus luminescens were overexpressed in E. coli. For the synthesis of 1,3-dihydroxy-10-methylacridone, we utilized an N-methyltransferase gene (NMT) to supply N-methylanthranilate and a new N-methylanthraniloyl-CoA ligase. After selecting the best combination of genes, approximately 17.3 mg/L of 1,3-dihydroxy-9(10H)-acridone (DHA) and 26.0 mg/L of 1,3-dihydroxy-10-methylacridone (NMA) were synthesized. CONCLUSIONS: Two bioactive acridone derivatives were synthesized by expressing type III plant polyketide synthases and other genes in E. coli, which increased the supplement of substrates. This study showed that is possible to synthesize diverse polyketides in E. coli using plant polyketide synthases.

Synthesis, biological evaluation and virtual screening of some acridone derivatives as potential anticancer agents.

Eleven novel acridone derivatives were synthesized and evaluated for their anticancer activity against 60 human cancer cell lines. Five compounds 8b, 8d, 8g, 8h, and 8k displayed very good in vitro antiproliferative activities well over 95% of the panels. The most active compound is 8k (5, 7-dibromo-3-phenyl-3,4-dihydroacridin-1 (2H)-one). In addition, 8k was the most sensitive agent in all 9 panels starting with prostate (0.075 µm), leukemia (0.116 µm), non-small cell lung cancer (0.164 µm), colon cancer (0.193 µm), CNS cancer (0.264 µm), melanoma (0.317 µm), renal cancer (0.403 µm), ovarian cancer (0.410 µm), and breast cancer (0.608 µm). Virtual screening studies also revealed that nine of the eleven compounds formed good binding interaction with the active site ATPase domain of human topoisomerase IIα (PDB: 1zxm). All nine derivatives exhibited binding affinities that ranged in values from -8.5 to -7.9 kcal/mol, indicating that they could be catalytic inhibitors of the nuclear enzyme, topoisomerase.

A new flavonoid from the leaves of Atalantia monophylla (L.) DC.

A new flavonoid, atalantraflavone (1) as well as eight known compounds including atalantoflavone (2), racemoflavone (3), 5,4'-dihydroxy-(3″,4″-dihydro-3″,4″-dihydroxy)-2″,2″-dimethylpyrano-(5″,6″:7,8)-flavone (4), lupalbigenin (5), anabellamide (6), citrusinine I (7), p-hydroxybenzaldehyde (8), and frideline (9), were isolated from the leaves of Atalantia monophylla (L.) DC. Focusing on Alzheimer's disease, acetylcholine esterase (AChE) inhibition and antioxidant activity were evaluated using the modified Ellman's method and the ABTS scavenging assay, respectively. It was found that isoflavonoid 5, lupalbigenin, showed 79% inhibition to AChE and was 1.4-fold stronger than the tacrine standard. In addition, acridone 7, citrusinine I, displayed 90.68% antioxidant activity.

Acridone alkaloids from the stem bark of Citrus aurantium display selective cytotoxicity against breast, liver, lung and prostate human carcinoma cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Citrus aurantium L. (Rutaceae) is used, either singly or as a part of a polyherbal preparation, in Nigerian traditional medicine for the management of cancer and inflammatory diseases. Currently, there is a dearth of knowledge demonstrating its anticancer potential. AIM OF THE STUDY: This study was carried out to determine the in vitro cytotoxicity of the crude extract of the stem bark of C. aurantium, identify and isolate the bioactive constituents and to establish the cytotoxicity of such constituents. MATERIALS AND METHODS: The powdered bark of C. aurantium was extracted by MeOH at room temperature (25-34 °C) and the crude extract was partitioned successively, with n-hexane, dichloromethane and methanol. Amongst the fractions, the DCM fraction was the most active and compounds were isolated from this fraction using a combination of chromatographic techniques. The structures of the isolated compounds were elucidated by spectroscopic means (MS, 1D and 2D NMR). The cytotoxicity of the extract, and the isolated compounds were evaluated by the MTT assay against four human cancer cell lines: A549 (lung), HepG2 (liver), MCF7 (breast) and PC3 (prostate). The selectivity of the isolated compounds was assessed using the normal human prostate epithelium cells (PNT2). RESULTS AND DISCUSSION: Of the three plant fractions, the DCM fraction showed significant cytotoxicity, with its highest activity against A549 cells (IC50 = 3.88 µg/mL) and the least activity on HepG2 cells (IC50 = 5.73 µg/mL). Six acridone alkaloids, citrusinine-I (1), citracridone-I (2), 5-hydroxynoracronycine (3), natsucitrine-I (4), glycofolinine (5) and citracridone-III (6), were isolated from the DCM fraction of C. aurantium. The isolated compounds demonstrated potent to moderate cytotoxicity (IC50 = 12.65-50.74 µM) against the cancer cells under investigation. It is noteworthy that the compounds exerted cytotoxicity at least four times more selective towards the carcinoma cells than the PNT2 cells. CONCLUSION: The results obtained from this study have provided some evidence for the ethnomedicinal use of C. aurantium against cancer and the acridone alkaloids present in its stem bark, have appeared to be responsible for the anticancer effects.

Synthesis and insecticidal activity of acridone derivatives to Aedes aegypti and Culex quinquefasciatus larvae and non-target aquatic species.

A serious Mosquito borne yellow fever is one of the grave diseases which affect the major population. Since there is no specific treatment for yellow fever, there is a necessity to develop an effective agent. The series of acridinone analogues 3 to 5 were synthesized with help of non-conventional microwave heating and confirmed by respective spectral characterization. 5c and 3b showed highest activity to kill 90% of larvae against A. aegypti and C. quinquefasciatus, respectively. Also the active products were treated to check the mortality of non-target aquatic species. Through the reports of the larvicidal bioassay, compounds 3b against C. quinquefasciatus whereas 5c against A. aegypti were found to be more active. By keeping this as a platform, further extension of the work can be done to find out a valuable drug for controlling disease vectors.

Antiproliferative Effects of Various Furanoacridones Isolated from Ruta graveolens on Human Breast Cancer Cell Lines.

BACKGROUND/AIM: Thanks to its biologically active constituents, Ruta graveolens L. (Rutaceae) is a widely used medicinal plant. In our study, six furanoacridone alkaloids isolated from Ruta graveolens were investigated for their antiproliferative and pro-apoptotic effects on human breast cancer cell lines (MCF-7, MDA-MB-361, MDA-MB-231 and T47D). MATERIALS AND METHODS: The cell lines were pretreated with alkaloid components (rutacridone, isogravacridone chlorine (IGC), gravacridonediol monomethyl ether, gravacridonediol, gravacridonetriol, a 1:1 mixture of gravacridonetriol and - diol monoglucosides) and their antiproliferative effects were determined by the MTT assay. RESULTS: IGC had the most marked effect on cell proliferation of MDA-MB-231 (half maximal inhibitory concentration (IC50)=2.27 µM). Cell-cycle analysis was applied to quantify the effect of IGC on subpopulations of MDA-MB-231 and MCF-7 cells. It caused a cell-cycle disturbance by decreasing the G2/M and G0/G1 and increasing the S phase and the appearance of the subdiploid (sub-G1) population. Hoechst 33258-propidium iodide staining was used to evaluate the morphological changes in IGC-pretreated MDA-MB-231 and MCF-7 cells, revealing the appearance of apoptotic features. IGC was found to cause a modest activation of caspase-3 and -9, but not caspase-8, indicating the activation of an intrinsic apoptotic pathway in MDA-MB-231 cells. CONCLUSIONS: These in vitro findings indicate that furanoacridones are suitable candidates for anticancer drug development.

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.

A novel acridone akaloid from Atalantia buxifolia.

Study of the chemical constituents of ethanol extract from the aerial parts of Atalantia buxifolia led to the identification of a new acridone alkaloid named as buxifoliadine (1), along with known compounds citrusinine--I (2), N-methylatalaphylline (3), Severinolid (4) and cycloseverinolide (5). Structural elucidation of compound 1 was carried out by a combination of mass spectrometry and (1)H and (13)C NMR spectroscopy analyses.

Two new acridone alkaloids from the branch of Atalantia buxifolia and their biological activity.

Two new acridone alkaloids, 3-methoxy-1,4,5-trihydroxy-10-methylacridone (1) and 2,3-dimethoxy-1,4,5-trihydroxy-10-methylacridone (2), were isolated from the ethanol extract of the branch of Atalantia buxifolia. Their structures were elucidated by spectroscopic methods including 1D and 2D NMR. Compounds 1 and 2 exhibited significant antibacterial activity against Staphylococcus aureus and weak inhibitory effect on acetylcholinesterase.

New acridone from the wood of Citrus reticulata Blanco.

A new acridone, named citruscridone (1) together with five known compounds were isolated from the wood of Citrus reticulata Blanco. Their structures were established based on spectroscopic evidence. The antibacterial and antifungal activities of the wood extracts and pure compounds were evaluated.

A template model for studying anticancer drug efflux transporter inhibitors in vitro.

Efflux transporters play an important role in drug absorption and also in multidrug resistance. ABCG2 (BCRP) is an efflux transporter conferring cross-resistance to mitoxantrone (Mit), irinotecan (CPT11), and its active metabolite SN38. MBLI87, a new ABCG2 inhibitor has proven its efficacy against ABCG2-mediated efflux in vitro and in vivo. This work aimed at modeling and quantifying the cellular interaction between MBLI87 and different substrates using a mechanistic template model. An in vitro competition experiment study was carried out with HEK293 cells overexpressing ABCG2 exposed to fixed concentrations of substrates (Mit, CPT11, SN38) and to MBLI87 at several concentration levels. A nonlinear mixed-effects transport inhibition model was developed to fit intracellular drug concentrations. In this model, drugs cross the cell membrane through passive diffusion, active drug efflux is ABCG2 mediated, interaction between substrates and inhibitor occurs within the transporter. The interaction was found to be noncompetitive. The MBLI87 Ki was estimated to 141 nm for Mit, 289 nm for CPT11, and 1160 nm for SN38. The ratio of intrinsic transport clearance divided by diffusion clearance was estimated to 2.5 for Mit, 1.01 for CPT11, and 5.4 for SN38. The maximal increase in the intracellular substrate concentration that is possible to achieve by inhibition of the transporter was estimated to 1.5 for Mit, 0.1 for CPT11, and 4.4 for SN38. This mechanistic template model describes both drug accumulation and cellular transport, and the mixed-effects approach allows an estimation of intra- and interassay variability. This model is of great interest to study cytotoxic cellular pharmacokinetics.

Copper-catalyzed intramolecular direct amination of sp2 C-H bonds for the synthesis of N-aryl acridones.

A copper-catalyzed approach for the synthesis of N-aryl acridones via sp(2) C-H bond amination using air as oxidant under neutral conditions is disclosed. This reaction not only provides a complementary method for synthesizing medicinally important acridones, but also offers a new strategy for sp(2) C-H bond amination.

Mechanism-based CYP2D6 inactivation by acridone alkaloids of Indonesian medicinal plant Lunasia amara.

Fourteen acridone alkaloids isolated from Lunasia amara Blanco were tested for their mechanism-based inhibition on human liver microsomal dextromethorphan O-demethylation activity, a prototype marker for cytochrome P450 2D6 (CYP2D6). Among the 14 compounds, 5-hydroxygraveroline (1), 8-methoxyifflaiamine (2), lunamarine (3), and lunine (12) increased their inhibitory activity with increasing preincubation time. Then, we further examined the possibility of mechanism-based inhibition on 5-hydroxygraveroline (1) and lunamarine (3), which showed the potent inhibition. Further investigations on 1 and 3 showed that the characteristic time- and concentration-dependent inhibition, which required a catalytic step with NADPH, was not protected by nucleophiles, and was decreased by the presence of a competitive inhibitor. Thus, 1 and 3 were concluded as mechanism-based inactivators of CYP2D6.

Acridanone alkaloid in Baliospermum montanum--evaluation of its effect against anaphylaxis.

Baliospermum montanum leaves yielded 3-hydroxy-2,4-dimethoxy-10-methyl-9-acridanone (1), an alkaloid from the CHCl3 fraction. Spectroscopic analysis was performed to assign the structure of the new compound (1) and its absolute configuration. The compound was evaluated for its effect in anaphylaxis by estimation of the release of histamine in systemic anaphylaxis model. The acridanone alkaloid significantly inhibited the degranulation of mast cells up to 65.22 % and 75.12 % at a dose of 50 and 75 mg/kg, respectively.

Two new acridone alkaloids from Glycosmis macrantha.

Extraction and chromatographic separation of the extracts of dried stem barks of Glycosmis macrantha lead to isolation of two new acridone alkaloids, macranthanine and 7-hydroxynoracronycine, and a known acridone, atalaphyllidine. The structures of these alkaloids were determined by detailed spectral analysis and also by comparison with reported data.

Anti-leishmanial activity of plant-derived acridones, flavaglines, and sulfur-containing amides.

Visceral and cutaneous leishmaniases are an important public health problem in endemic geographic regions in 88 countries worldwide, with around 12 million infected people. Treatment options are limited due to toxicity and teratogenicity of the available drugs, response problems in HIV/Leishmania co-infections, and upcoming resistances. In this study, we investigated the anti-leishmanial activity of 13 plant-derived compounds in vitro aiming to find new drug candidates. Toxicity of the compounds was evaluated in human primary hepatocytes, and hemolytic activity was examined in freshly isolated erythrocytes. Two acridones, 5-hydroxynoracronycine and yukocitrine, two flavaglines, aglafoline and rocaglamide, and the sulfur-containing amide methyldambullin showed promising anti-leishmanial activities with 50% effective concentrations (EC50s) of 34.84, 29.76, 7.45, 16.45, and 6.29 µM, respectively. Hepatotoxic activities of 5-hydroxynoracronycine, yukocitrine, and methyldambullin were significantly lower compared to miltefosine and lower or equal compared to artesunate, whereas the ones of rocaglamide and aglafoline were slightly higher compared to miltefosine and significantly higher compared to artesunate. None of the compounds showed hemolytic activity.

O-prenylated acridone alkaloids from the stems of Balsamocitrus paniculata (Rutaceae).

Two new O-prenylated acridone alkaloids, balsacridone A (1) and B (2), together with eighteen known compounds were isolated from the methanol extract from the stems of Balsamocitrus paniculata, a Cameroonian medicinal plant. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral (EI and ESI) data, and chemical reactions. N-methyl-6-methoxybenzoxazolinone (16) was isolated for the first time from a natural source while compounds 13, 14, and 15 for the first time from this genus. Pure compounds were tested for their activity against bacteria, fungi, and plant pathogen oomycetes, using the paper disk agar diffusion assay. The agar diffusion test delivered low to missing antimicrobial activities, corresponding to MICs > 1 mg/mL. However, compounds 1-15 exhibited a strong suppressive effect on phagocytosis response upon activation with serum opsonized zymosan in the range of IC50 = 0.5-7.2 µM, and the acridone alkaloids (1-5), N-trans-p-coumaroyltyramine (13), and N-trans-pcoumaroyloctopamine (14) displayed weak cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3, with IC50 values ranging from 69.8 to 99.0 µM.