Noélia Duarte

Antitumor activity of terpenoids against classical and atypical multidrug resistant cancer cells.

Nineteen terpenoids, including macrocyclic diterpenes, diterpenic lactones and other polycyclic diterpenes, steroids and a triterpene isolated from the methanolic extracts of Euphorbia species, were evaluated for their potential antineoplastic activity in various human cancer cell lines that were derived from three tumor entities: gastric (EPG85-257), pancreatic (EPP85-181) and colon (HT-29) carcinomas. Furthermore, different multidrug-resistant variants of these cancer cell lines with over-expression of MDR1/P-gp or no MDR1/P-gp expression were also investigated. In parental drug-sensitive cell lines, the tested compounds showed a moderate/weak antiproliferative effect or were inactive. Most of them were found more effective in drug-resistant cells than in the parental, drug-sensitive ones, and some of them showed high antineoplastic efficacy in classical or atypical drug-resistant cells. The most active compounds were the lathyrane diterpenes latilagascenes C and D, and the diterpenic lactones 3beta-acetoxy-helioscopinolide B and helioscopinolide E which exhibited high antineoplastic activities against the drug-resistant subline EPG85-257RDB derived from gastric carcinoma. In addition, the macrocyclic lathyrane diterpene jolkinol B was found to be highly effective in the multidrug-resistant variant HT-29RNOV.

Antileishmanial activity of piceatannol isolated from Euphorbia lagascae seeds

In the search for biologically active compounds from Euphorbia lagascae Spreng, an herbaceous plant native to southeast of Iberic Peninsula, a stilbene, two coumarins and two 12‐deoxyphorbol diterpene esters were isolated by chromatographic methods, from the methanol extracts of its defatted seeds. The structures of these compounds were elucidated by a combination of physical and spectral data (IR, MS and high‐resolution 1H‐NMR and 13C‐NMR spectroscopy utilizing COSY, HMBC, HMQC and NOESY experiments). The stilbene, piceatannol, was screened for its antileishmanial activity against promastigotes as an extracellular form of Leishmania donovani, Leishmania infantum and Leishmania major, and amastigotes of Leishmania donovani as an intracellular form. Pentostan® (sodium stibogluconate), the first line clinical drug, was used as a standard reference. Piceatannol was moderately active against the extracellular forms of the three tested Leishmania species, and more active than the reference compound against the intracellular form of Leishmania donovani. Copyright

Multidrug Resistance Reversal and Apoptosis Induction in Human Colon Cancer Cells by Some Flavonoids Present in Citrus Plants

Multidrug resistance (MDR) of cancer cells constitutes one of the main reasons for chemotherapy failure. The search for nontoxic modulators that reduce MDR is a task of great importance. An ability to enhance apoptosis of resistant cells would also be beneficial. In the present study, the MDR reversal and apoptosis-inducing potency of three flavonoids produced by Citrus plants, namely, naringenin (1a), aromadendrin (2), and tangeretin (3), and the methylated naringenin derivatives (1b, 1c), have been studied in sensitive (LoVo) and multidrug-resistant (LoVo/Dx) human colon adenocarcinoma cells. Cytotoxicity of methoxylated flavonoids was higher as compared to hydroxylated analogues. Only 3 turned out to inhibit P-glycoprotein, as demonstrated by a rhodamine 123 accumulation assay. It also increased doxorubicin accumulation in LoVo/Dx cells and enabled doxorubicin to enter cellular nuclei. In addition, 3 was found to be an effective MDR modulator in resistant cells by sensitizing them to doxorubicin. Tangeretin-induced caspase-3 activation and elevated surface phosphatidylserine exposure demonstrated its apoptosis-inducing activity in LoVo/Dx cells, while the other flavonoids evaluated were not active. Additionally, 3 was more toxic to resistant rather than to sensitive cancer cells. Its apoptosis-inducing activity was also higher in LoVo/Dx than in LoVo cells. It was concluded that the activity of 3 against multidrug-resistant cancer cells may be enhanced by its apoptosis-inducing activity.

Zanthoxylum capense constituents with antimycobacterial activity against Mycobacterium tuberculosis in vitro and ex vivo within human macrophages.

ETHNOPHARMACOLOGICAL RELEVANCE Zanthoxylum capense Thunb. (Rutaceae) is a medicinal plant traditionally used in Mozambique to treat tuberculosis. AIMS OF THE STUDY The main aim of the study was to find antimycobacterial lead compounds from Zanthoxylum capense. Another goal was to provide scientific validation for the use of this plant in traditional medicine. METHODS AND MATERIALS By bioassay-guided fractionation, 16 compounds were isolated and screened for their in vitro antimycobacterial activity against two different strains of Mycobacterium tuberculosis. Their in vitro cytotoxicity to human THP-1 macrophages was also assessed. The compounds with favourable selectivity index values (SI>10) were further investigated for their ability to inhibit the growth of Mycobacterium tuberculosis H37Rv in an intracellular macrophage model of infection. RESULTS The best results were obtained for a benzophenanthridine alkaloid, decarine (1), and an N-isobutylamide, N-isobutyl-(2E,4E)-2,4-tetradecadienamide (15), which showed high activity against Mycobacterium tuberculosis H37Rv (MIC of 1.6 μg/ml), and a low macrophage cytotoxicity (IC50>60 μg/ml), indicating considerable selective activity. The benzophenanthridine alkaloid 6-acetonyldihydronitidine (6) revealed cytotoxicity (IC50 1.7 μg/ml), despite the determined MIC of 6.2-12.5 μg/ml. In infected macrophages, decarine (1) was able to reduce bacterial survival by almost two log units at a concentration of 6.2 μg/ml 5 days post-drug exposure. Compound 15 exhibited an intermediate activity at drug concentrations ranging from 6.2 to 25 μg/ml. CONCLUSIONS The high antimycobacterial activity of decarine found, both in vitro and ex vivo against mycobacteria, and the low cytotoxicity towards human macrophages indicate that it may be valuable as a lead scaffold for the development of anti-TB drugs.

Synergistic interaction between p-glycoprotein modulators and epirubicine on resistant cancer cells.

The macrocyclic lathyrane diterpene latilagascene B, previously isolated from Euphorbia lagascae, was acylated to afford three new diterpene esters, latilagascenes G (1), H (2), and I (3), whose structures were assigned by spectroscopic methods. These acyl derivatives, and the macrocyclic diterpenes of the jatrophane-type, tuckeyanols A (4) and B (5), and euphotuckeyanol (6), isolated from Euphorbia tuckeyana, were tested for P-gp modulating properties on human MDR1 gene-transfected and parental L5178 mouse lymphoma cell lines. All the compounds displayed very strong activity. The molecular orbital energies (HOMO and LUMO) of diterpenes 1-6 and 7-13, previously isolated, have also been calculated in order to estimate their probable charge transfer interactions with P-gp. Structure-activity relationships (SAR) are discussed. Furthermore, compounds (1-6) were assayed, in vitro, for their antiproliferative effects in combination with epirubicine and all of them synergistically enhance the effect of the antitumor drug.

Jatrophane Diterpenes from Euphorbia mellifera and Their Activity as P-Glycoprotein Modulators on Multidrug-Resistant Mouse Lymphoma and Human Colon Adenocarcinoma Cells

Three new macrocyclic jatrophane diterpenes, named euphomelliferine (1) and euphomelliferenes A (2) and B (3), and one new tetracyclic triterpene, 19(10→9)-abeo-8α,9β,10α-tirucalla-5,25-diene-3β,24-diol (6, C-24 epimers), were isolated from the methanolic extract of Euphorbia mellifera. A known ingenane (7) and two jatrophane diterpenes (4 and 5) were also isolated. Their structures were elucidated by extensive spectroscopic methods, including 1D and 2D homo- and heteronuclear NMR experiments. Jatrophane diterpenes 1-3 and 5 were evaluated for their effects on the reversion of multidrug resistance (MDR) mediated by P-glycoprotein, by using the rhodamine-123 exclusion test, on human MDR1 gene-transfected mouse lymphoma cells (L5178Y MDR) and on human colon adenocarcinoma cells (COLO 320). The apoptosis-inducing activity of these compounds was also tested on COLO 320 cells, using the annexin-V/propidium iodide assay. Diterpenes 1 and 2 displayed significant MDR reversing activity, in a dose-dependent manner, on both cancer cell models. The tested compounds did not induce apoptosis in the COLO 320 cells.

Three New Jatrophane Polyesters and Antiproliferative Constituents from Euphorbia tuckeyana

Three new jatrophane diterpene polyesters named tuckeyanols A and B and euphotuckeyanol, as well as ten known compounds, helioscopinolides A, B, D and E, naringenin, aromadendrin, coniferaldehyde, 4,20-dideoxy-5-hydroxyphorbol 12,13-diisobutyrate, 4,20-dideoxy-5-hydroxyphorbol 12-benzoate-13-isobutyrate and dehydrodiconiferyl diacetate, were isolated from the methanolic extract of Euphorbia tuckeyana. Their structures were elucidated by physical and spectroscopic methods including 1 D and 2 D homo- and heteronuclear NMR techniques (COSY, HMQC, HMBC and NOESY), and HR-mass spectrometry. Four of the isolated compounds were investigated for their antiproliferative activity in three human gastrointestinal cancer cell lines: gastric (EPG85-257), pancreatic (EPP85-181) and colon (HT-29) carcinomas. Three of them have showed to be moderate inhibitors of the growth of gastric and pancreatic tumor cell lines.

Improving the MDR reversal activity of 6,17-epoxylathyrane diterpenes

Aiming to optimize macrocyclic lathyrane-type diterpenes as effective Pgp modulators, the phytochemical study of the methanolic extract of Euphorbia boetica aerial parts was carried out. Two new macrocyclic 6,17-epoxylathyrane-type diterpenes, named epoxyboetiranes A (1) and B (2), along with three known analogues (3-5) were isolated. Epoxyboetirane A (1), a triacetate isolated in large amounts, was hydrolyzed to give epoxylathyrol (6). In order to study the effect of the substitution pattern of the macrocyclic scaffold on MDR reversal, 6 was acylated with aroyl, phenylacetyl, cinnamoyl and alkanoyl chlorides/anhydrides, yielding eight new esters, epoxyboetiranes C-J (7-14). The ability of compounds 1-14 as P-glycoprotein (Pgp, ABCB1) modulators was evaluated through combination of transport and chemosensitivity assays, using L5178Y mouse T lymphoma cell line transfected with the human MDR1 gene. In the transport assay, excepting 1, 3 and 6, the compounds, at non-cytotoxic concentrations, displayed strong MDR reversing activity in a dose-dependent mode, exhibiting all the new acyl derivatives (7-14) a many fold increase in the activity when compared with 1. Apart from 11 and 12, all compounds exhibited remarkable synergistic effects in combination with doxorubicin. An ATPase assay, using membrane vesicles from mammalian cells overexpressing Pgp, was also performed with two representatives of the modulators (4 and 5). The results suggest that both compounds compete with substrates for the Pgp drug-binding sites.

Euphorbia and Momordica metabolites for overcoming multidrug resistance

Multidrug resistance (MDR) is the major obstacle for cancer chemotherapy. MDR is a multifactorial phenomenon that can result from several mechanisms, including an increased drug efflux, due to overexpression of P-glycoprotein (P-gp) that transports anticancer drugs out of the cells. Thus, the role of this transporter has made it a therapeutic target and the development of P-gp modulators considered among the most realistic approaches for overcoming P-gp-mediated MDR. Many other strategies have been proposed. One of them is the identification of compounds that selectively kill multidrug resistant cells. In our search for MDR modulators from plants, the P-gp inhibition ability of a large number of compounds on resistant cancer cells was evaluated. These compounds, presented in this review, comprise mainly diterpenes, triterpenes and phenolic derivatives. The most relevant results were obtained from two sets of compounds: macrocyclic diterpenes with the jatrophane and lathyrane scaffold, and triterpenes of the cucurbitane-type isolated from Euphorbia species and Momordica balsamina L., respectively. Additionally, some of those macrocyclic diterpenes, and ent-abietane diterpenic lactones, also isolated from Euphorbia species, were found to be selectively toxic to drug-resistant phenotypes.

Colon Adenocarcinoma Multidrug Resistance Reverted by Euphorbia Diterpenes: Structure-Activity Relationships and Pharmacophore Modeling

Multidrug resistance (MDR) is a limiting step on the success of cancer chemotherapy. The drug efflux mediated by P-gp (Pglycoprotein) is one of the best studied mechanisms of MDR. This paper focuses on the inhibitory P-gp efflux activity, pharmacophore modeling and structure-activity relationships studies of sixteen macrocyclic diterpenes and polycyclic derivatives obtained from Euphorbia species. The MDR human colon adenocarcinoma cells (COLO 320 MDR) overexpressing P-gp were used as the biological model to screen for P-gp dependent efflux inhibitors. Most of the compounds showed potential as MDR reversal agents. Combined analysis of two different statistic algorithms, K-means clustering and Principal Component Analysis discriminated two clusters and showed a strong correlation between log P and MDR reversal activity for compounds 1-5. The most effective compounds (1-4 and 11-12) were tested in combination with doxorubicin and all potentiated its activity lowering the ID50. Pharmacophore modeling allowed the definition of an aromatic moiety as an additional feature to a previous published P-gp pharmacophore, creating a new five-point pharmacophore with enhanced selectivity for the most active compounds of the present study. Docking results also show the importance of an aromatic moiety, positively identifying the most relevant residues that can be linked to an inhibitory activity increase.