Cytotoxic clerodane diterpenoids from Casearia obliqua

Fragmentation study of clerodane diterpenes from Casearia species by tandem mass spectrometry (quadrupole time-of-flight and ion trap)

RATIONALE

Clerodane-type diterpenes from Casearia species show important pharmacological activites such as antitumor, antimicrobial and anti-inflamatory. There are several mass spectrometry (MS)-based methods for identification of diterpenes; however, there is still a lack of MS procedures capable of providing characteristic fragmentation pathways for a rapid and unambiguous elucidation of casearin-like compounds.

METHODS

Casearin-like compounds were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The fragmentation studies were carried out by tandem mass spectrometry in space (quadrupole time-of-flight (QTOF)) using different collision energies and also by tandem mass spectrometry in time (QIT) by selective isolation of product ions.

RESULTS

Casearin-like compounds presented a predominance of sodium- and potassium-cationized precursor ions. Both QIT and QTOF techniques provided sequential neutral losses of esters related to the R₁ to R₅ substituents linked to the nucleus of the clerodane diterpenes. The fragmentation pathway is initiated with a cleavage of the ester moieties R₂ followed by the elimination of the ester groups R₃ , both losing neutral carboxylic acids. Using QIT, it was also possible to observe the cleavage of the ester groups R₁ or R₅ by MS⁴ experiments.

CONCLUSIONS

Through a rational analysis of the fragmentation mechanisms of Casearia diterpenes it was possible to suggest an annotation strategy based on the sequential cleavages of the ester groups related to the R₂ , R₃ and R₅ substituents. These results will assist studies of the dereplication and metabolomics involving casearin-like compounds present in complex extracts of Casearia species.

Diterpenoids from the leaves of Casearia kurzii showing cytotoxic activities

A phytochemical investigation to obtain bioactive substances as lead compounds or agents for cancer led to the obtainment of six new and two known clerodane diterpenoids from the leaves of Casearia kurzii. Their structures were elucidated using NMR techniques and electronic circular dichroism (ECD) calculations. The subsequent biological cytotoxicity evaluation of these isolates toward human lung cancer A549, human cervical cancer HeLa, human chronic myeloid leukemia K562, and human hepatocellular carcinoma HepG2 was carried out. The most active compound 4 with an IC₅₀ value of 9.7 μM against HepG2 cells was selected to examine the cytotoxic mechanism, which induced the apoptosis and arrested the HepG2 cell cycle at S stage. The in vivo zebrafish experiments revealed that compound 4 had the property of inhibiting tumor proliferation and migration.

Clerodane Diterpenoids Isolated from the Leaves of Casearia graveolens

A phytochemical survey aiming to acquire pharmacologically active substances has resulted in the isolation of nine new clerodane diterpenoids, named graveospenes A-I (1-9), from the leaves of Casearia graveolens. Spectroscopic methods were employed to establish the structures with their absolute configurations being confirmed by ECD data analysis. A biological evaluation was performed, and compound 1 was found to be cytotoxic to both human lung cancer cells (A549) and human hepatocellular carcinoma cells (HepG2). A mechanism-of-action study on 1 revealed this compound to induce apoptosis of A549 cells and impede them at the G₀/G₁ stage.

Clerodane diterpenoids from Casearia kurzii and their cytotoxic activities

A search for bioactive natural products as anticancer lead compounds resulted in the isolation of one previously undescribed and three known clerodane diterpenoids (1-4) from Casearia kurzii. The structures of these compounds were established by analysis of their NMR, MS, and electronic circular dichroism data. The cytotoxic activities of four compounds against three human cancer cell lines were evaluated. Compound 2 was found to be the most active with an IC₅₀ value of 4.1 μM against HeLa cells, and was selected to investigate the possible cytotoxic mechanism.

Clerodane diterpenes: sources, structures, and biological activities

Covering: 1990 to 2015The clerodane diterpenoids are a widespread class of secondary metabolites and have been found in several hundreds of plant species from various families and in organisms from other taxonomic groups. These substances have attracted interest in recent years due to their notable biological activities, particularly insect antifeedant properties. In addition, the major active clerodanes of Salvia divinorum can be used as novel opioid receptor probes, allowing greater insight into opioid receptor-mediated phenomena, as well as opening additional areas for chemical investigation. This article provides extensive coverage of naturally occurring clerodane diterpenes discovered from 1990 until 2015, and follows up on the 1992 review by Merritt and Ley in this same journal. The distribution, chemotaxonomic significance, chemical structures, and biological activities of clerodane diterpenes are summarized. In the cases where sufficient information is available, structure activity relationship (SAR) correlations and mode of action of active clerodanes have been presented.

Discovery of a Novel Diterpene in Brown Propolis from the State of Parana, Brazil

Propolis is a resinous substance collected by honeybees from certain plant sources. The components of propolis depend on the vegetation of the area in which apiculture is practiced. In Brazil, there are several types of propolis including ‘green,’ ‘red’ and ‘brown'. Brazilian brown propolis from the state of Parana characteristically includes diterpenes, and we discovered a novel clerodane diterpene, rel-(5 S,6 S,8 R,9 R,10 S,18 R,19 S)-18,19-epoxy-2-oxocleroda-3,12( E),14-triene-6,18,19-triol 18,19-diacetate 6-benzoate (3) and five known diterpenes (1, 2, 4, 5 and 6). The chemical structure of the novel diterpene 3 was determined using 1D- and 2D-NMR spectroscopic analyses. Furthermore, the activities of the isolated diterpenes on growth inhibition of several human cancer cell lines (LNCaP, MCF-7, DLD-1 and A549) were evaluated in vitro; diterpene 3 exhibited a potent inhibition of cell growth, and its activity was approximately 15 times higher than that of the other diterpenes.

Di- and Triterpenoids from the Leaves of Casearia balansae and Neurite Outgrowth Promoting Effects of PC12 Cells

A bioassay-guided phytochemical investigation of the leaves of Casearia balansae led to the isolation of six new cucurbitane-type triterpenoid derivatives (balanterpenes A-F, 1-6) and four new clerdoane-type diterpenoids (balanterpenes G-J, 7-10). The structures of 1-10 were established on the basis of extensive analysis of NMR spectroscopic data, X-ray crystallography, and experimental and calculated electronic circular dichroism spectra. Compound 1 features a ring-expanded triterpenoid skeleton with the C-19 methyl involved in the ring formation, compound 6 possesses a rare hexanortriterpenoid scaffold, and compounds 7-10 may be four new diterpenoid artifacts presumably formed during the extraction and purification processes. Compounds 3 and 7-10 showed promoting effects on neurite outgrowth of PC12 cells with EC50 values in the range 2.9-10.0 μM.

A New Cytotoxic Clerodane Diterpene from Casearia Graveolens Twigs

The first phytochemical investigation of Casearia graveolens twigs led to the isolation and identification of a new clerodane diterpene, caseariagraveolin (1), together with six known compounds (2–7). Their structures were elucidated by intensive analysis of their spectroscopic data. Compound 1 showed strong cytotoxicity against oral cavity and breast cancer cell lines with IC50 values of 2.48 and 6.63 μM, respectively.

Cytotoxic Clerodane Diterpenoids from the Leaves of Casearia grewiifolia

Two new clerodane diterpenoids (1 and 2) and the known compound caseanigrescen D (3) were isolated from the leaves of Casearia grewiifolia by bioassay-guided fractionation. Their structures were determined by analyses of MS and 2D NMR data. The absolute configurations of 1 and 3 were established by analysis of X-ray diffraction data. Compounds 1-3 were evaluated for their cytotoxicity against four cancer cell lines, KB (mouth epidermal carcinoma cells), HepG-2 (human liver hepatocellular carcinoma cells), LU-1 (human lung adenocarcinoma cells), and MCF-7 (human breast cancer cells). Caseagrewifolin B (2) had inhibitory activity against KB and HepG-2 cell lines with IC50 values of 6.2 to 7.0 μM, respectively. When tested against the normal cells (NIH/3T3), caseagrewifolin B (2) exhibited a significant selective inhibition against cancer cells in comparison with the normal cells. Caseanigrescen D (3) was cytotoxic against four cancer cell lines; however it had no selective inhibition compared with normal cells.

Characterization and Biological Evaluation of Diterpenoids from Casearia graveolens

Biologically active substances that promote the neurite outgrowth of nerve cells against neuron degeneration may be useful for the treatment of Alzheimer's disease. In a continuing search for bioactive compounds from plants, an ethyl acetate-soluble extract of the twigs of Casearia graveolens showed moderate stimulatory activity of neurite outgrowth from PC12 cells. Further investigation to obtain bioactive compounds led to the isolation of 10 new clerodane diterpenoids, graveopenes A-J (1-10). Their structures including absolute configurations were elucidated based on analysis of their NMR spectroscopic data and experimental and calculated ECD spectra. Compounds 3-6 and 8 were shown to stimulate NGF-mediated neurite outgrowth from PC12 cells.

Studies toward the Development of Antiproliferative Neoclerodanes from Salvinorin A

The success rate for central nervous system (CNS) drug candidates in the clinic is relatively low compared to the industry average across other therapeutic areas. Penetration through the blood-brain barrier (BBB) to reach the therapeutic target is a major obstacle in development. The rapid CNS penetration of salvinorin A has suggested that the neoclerodane nucleus offers an excellent scaffold for developing antiproliferative compounds that enter the CNS. The Liebeskind-Srogl reaction was used as the main carbon-carbon bond-forming step toward the synthesis of quinone-containing salvinorin A analogues. Quinone-containing salvinorin A analogues were shown to have antiproliferative activity against the MCF7 breast cancer cell line, but show no significant activity at the κ-opioid receptors. In an in vitro model of BBB penetration, quinone-containing salvinorin A analogues were shown to passively diffuse across the cell monolayer. The analogues, however, are substrates of P-glycoprotein, and thus further modification of the molecules is needed to reduce the affinity for the efflux transporter.

Antiparasitic activity and effect of casearins isolated from Casearia sylvestris on Leishmania and Trypanosoma cruzi plasma membrane

Leishmaniasis and Chagas disease are infectious diseases caused by parasite Leishmania sp. and Trypanosoma cruzi, respectively, and are included among the most neglected diseases in several underdeveloped and developing countries, with an urgent demand for new drugs. Considering the antiparasitic potential of MeOH extract from leaves of Casearia sylvestris Sw. (Salicaceae), a bioguided fractionation was conducted and afforded four active clerodane diterpenes (casearins A, B, G, and J). The obtained results indicated a superior efficacy of tested casearins against trypomastigotes of T. cruzi, with IC50 values ranging from 0.53 to 2.77 μg/ml. Leishmania infantum promastigotes were also susceptible to casearins, with IC50 values in a range between 4.45 and 9.48 μg/ml. These substances were also evaluated for mammalian cytotoxicity against NCTC cells resulting in 50% cytotoxic concentrations (CC50) ranging from 1.46 to 13.76 μg/ml. Additionally, the action of casearins on parasite membranes was investigated using the fluorescent probe SYTOX Green. The obtained results demonstrated a strong interaction of casearins A and B to the plasma membrane of T. cruzi parasites, corroborating their higher efficacy against these parasites. In contrast, the tested casearins induced no alteration in the permeability of plasma membrane of Leishmania parasites, suggesting that biochemical differences between Leishmania and T. cruzi plasma membrane might have contributed to the target effect of casearins on trypomastigotes. Thus, considering the importance of studying novel and selective drug candidates against protozoans, casearins A, B, G, and J could be used as tools to future drug design studies.

Cytotoxic clerodane diterpenes from Zuelania guidonia

The leaves of Zuelania guidonia yielded eight new clerodane diterpenes, namely, zuelaguidins A-H (1-8), and the known clerodane diterpene esculentin A (9). Some of these structures contained a 3,6-dihydro-1,2-dioxin moiety. The new compounds were isolated and identified using 1D- and 2D-NMR experiments. All compounds were evaluated for cytotoxicity against the CCRF-CEM (human acute lymphocytic leukemia), CEM-ADR5000 (human acute lymphocytic leukemia resistant to doxorubicin), and MIA-PaCa-2 (human pancreatic carcinoma) cell lines as well as for their selectivity against peripheral blood mononuclear cells from healthy human subjects. Zuelaguidins B, C, and E were the most potent compounds against the CCRF-CEM cell line, with IC50 values ranging from 1.6 to 2.5 μM.

Cytotoxic clerodane diterpenoids from the leaves and twigs of Casearia balansae

Ten new clerodane diterpenoids (1-10), caseabalansins A-G, 18-epicaseabalansin A, 2-epicaseabalansin B, and 2-epicaseabalansin C, one new triterpenoid, balansinone (11), and seven known diterpenoids (12-18) were obtained from the leaves and twigs of Casearia balansae. Compounds 1 and 2 are the first examples of clerodane diterpenoids with an oxygen bridge between C-2 and C-19, and compounds 5-7 are three new diterpenoid artifacts presumably formed during the extraction process. The structures of the new compounds were established on the basis of extensive spectroscopic data, and that of 11 was verified by single-crystal X-ray crystallographic analysis. Compound 15 showed cytotoxic activity against the tumor cell lines PC3, DU145, SKOV3, and A549 with IC₅₀ values of 4.5, 4.3, 5.1, and 5.7 μM, respectively. Compounds 1a, 2a, and 4 showed selective activity against PC3 tumor cells.

Natural products from Brazilian biodiversity as a source of new models for medicinal chemistry

Natural products are the inspiration for many valuable therapeutic agents and attest to biodiversity being a rich source of new molecular structures. Their value as templates for medicinal chemistry remains undisputed, even after the growth of the combinatorial chemistry era. Tropical environments, such as Brazilian biomes, offer a particularly rich potential for biologically active compounds with unique structures and continue to contribute toward modern drug discovery. Our bioprospecting of plant species of the Cerrado and Atlantic Forest biomes has yielded promising bioactive secondary metabolites, and we describe some of these molecules and semisynthetic derivatives as potential acetylcholinesterase (AChE) inhibitors.

Folk uses and pharmacological properties of Casearia sylvestris: a medicinal review

Folk uses and scientific investigations have highlighted the importance of Casearia sylvestris extracts and their relevant bioactive potential. The aim of this work was to review the pharmacological properties of C. sylvestris, emphasizing its anti-ulcer, anti-inflammatory, anti-ophidian and antitumor potentialities. Ethanolic extracts and essential oil of their leaves have antiulcerogenic activity and reduce gastric volume without altering the stomach pH, which corroborates their consumption on gastrointestinal disorders. Leaf water extracts show phospholipase A2 inhibitory activity that prevents damage effects on the muscular tissue after toxin inoculation. This antiphospholipasic action is probably related to the use as an anti-inflammatory, proposing a pharmacological blockage similar to that obtained with non-steroidal anti-inflammatory drugs on arachidonic acid and cyclooxygenase pathways. Bioguided-assay fractionations lead to the identification of secondary metabolites, especially the clerodane diterpenes casearins (A-X) and casearvestrins (A-C), compounds with a remarkable cytotoxic and antitumor action. Therefore, the C. sylvestris shrub holds a known worldwide pharmacological arsenal by its extensive folk utilization, exciting searches for new molecules and a better comprehension about biological properties.

Screening of plants used in Mayan traditional medicine to treat cancer-like symptoms

AIM OF THE STUDY

To investigate the potential of plants used in Mayan traditional medicine to treat cancer-like symptoms using the Mayan ethnobotany literature, and evaluate their organic extracts for in vitro cytotoxic activity on cancer cell lines.

MATERIALS AND METHODS

The selection of the plants studied in this investigation was based on the Mayan ethnobotanical information provided by different literature sources. Extracts were obtained by maceration with methanol for 72 h of each plant part used and evaporated in vacuo to give the corresponding dried extract. Each methanol extract was tested for its cytotoxicity using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay performed in 96-well tissue plates on seven cancer cell lines, lung carcinoma (A549), cervix adenocarcinoma (HeLa), laryngeal carcinoma (Hep-2), nasopharynx carcinoma (KB), breast adenocarcinoma (MCF-7), prostate adenocarcinoma (PC-3), and cervix squamous carcinoma cells (SiHa), as well as normal human embryonic kidney cell line (HEK-293). Cell proliferation/viability was spectrophotometrically assessed at 540 nm after addition of MTT.

RESULTS

51 plants were found in the literature to be used for the treatment of symptoms suggestive of cancer, 21 were chosen to evaluate the cytotoxic activity. Aeschynomene fascicularis root bark extract showed a pronounced cytotoxic activity on Hela and KB cell lines and Bonellia macrocarpa stem and root bark extracts showed similar prominent activities on KB cells.

CONCLUSION

21 plants were selected according to their use in the treatment of cancer-like symptoms recorded in the ethnobotanical literature. Plant extracts prepared from Aeschynomene fascicularis root bark and Bonellia macrocarpa stem and root bark have been selected for extensive studies leading to the isolation of the active constituents.

Cytotoxic clerodane diterpenes from Casearia rupestris

Four new clerodane diterpenes, casearupestrins A-D (1-4), were isolated from the leaves of Casearia rupestris. Compounds 1 and 4 were acetylated to yield 2,7-di-O-acetylcasearupestrin A (5) and 2,6-di-O-acetylcasearupestrin D (6). All compounds were evaluated for cytotoxicity against a small panel of human cancer cell lines. Casearupestrin A (1) exhibited the most potent activity against MDA/MB-435 (human melanoma) and SF-295 (human glioblastoma) cells, superior to that of the standard drug doxorubicin.

Clerodane diterpenes from Casearia arguta that act as synergistic TRAIL sensitizers

Casearia arguta was investigated as part of the ongoing search for synergistic TRAIL (tumor necrosis factor-α-related apoptosis-inducing ligand) sensitizers. As a result of this study, argutins A-H, eight new highly oxygenated clerodane diterpenes, were isolated from the plant Casearia arguta collected in Guatemala. The modified Mosher ester method was utilized to establish the absolute configuration of argutins A and F. Each of the argutins showed varying levels of synergy with TRAIL. Argutin B showed the highest TRAIL sensitization; the synergistic effect of argutin B and TRAIL together was 3-fold greater than argutin B alone.

Casearin X exhibits cytotoxic effects in leukemia cells triggered by apoptosis

Clerodane diterpenes have demonstrated cytotoxic, antiplasmodial and anti-ulcer properties. In the present work, we determined the cytotoxic effect of casearin L (Cas L), O (Cas O) and X (Cas X) and (-)-hardwickiic acid isolated from Casearia sylvestris leaves, and investigated the underlying mechanisms involved in in vitro cell death induced by Cas X in HL-60 leukemia cells (0.7, 1.5 and 3.0μM). Cytotoxicity tests demonstrated that Cas X was the most active compound studied, showing greater cytotoxic effects against CEM and HL-60 lines (IC(50) of 0.4μM) and human peripheral blood mononuclear cells (PBMC, IC(50) of 1.2μM). After 24h exposure, Cas X caused a decrease in 5-bromo-20-deoxyuridine (BrdU) incorporation (36.6 and 24.5% labeling at 0.7 and 1.5μM, respectively), reduction in viability, and increase in apoptotic and necrotic leukemia cells in a dose-dependent manner evidenced by the trypan blue and AO/EB (acridine orange/ethidium bromide) assays. Moreover, Cas X-treated cells exhibited nuclear fragmentation and cytoplasmic vacuolization depending on the concentration tested. These characteristics of apoptosis or secondary necrosis were confirmed by flow cytometry which revealed DNA fragmentation, phosphatidylserine externalization, activation of the effector caspases 3/7 and mitochondrial depolarization. We then found evidence that Cas X causes cell death via apoptotic pathways, corroborating the potential of casearins as compounds with promising antitumor-related properties.