Labdane diterpenes from Aster spathulifolius and their cytotoxic effects on human cancer cell lines

A review of natural products and small-molecule therapeutics acting on central nervous system malignancies: Approaches for drug development, targeting pathways, clinical trials, and challenges

In 2021, the World Health Organization released the fifth edition of the central nervous system (CNS) tumor classification. This classification uses histopathology and molecular pathogenesis to group tumors into more biologically and molecularly defined entities. The prognosis of brain cancer, particularly malignant tumors, has remained poor worldwide, approximately 308,102 new cases of brain and other CNS tumors were diagnosed in the year 2020, with an estimated 251,329 deaths. The cost and time-consuming nature of studies to find new anticancer agents makes it necessary to have well-designed studies. In the present study, the pathways that can be targeted for drug development are discussed in detail. Some of the important cellular origins, signaling, and pathways involved in the efficacy of bioactive molecules against CNS tumorigenesis or progression, as well as prognosis and common approaches for treatment of different types of brain tumors, are reviewed. Moreover, different study tools, including cell lines, in vitro, in vivo, and clinical trial challenges, are discussed. In addition, in this article, natural products as one of the most important sources for finding new chemotherapeutics were reviewed and over 700 reported molecules with efficacy against CNS cancer cells are gathered and classified according to their structure. Based on the clinical trials that have been registered, very few of these natural or semi-synthetic derivatives have been studied in humans. The review can help researchers understand the involved mechanisms and design new goal-oriented studies for drug development against CNS malignancies.

Aster spathulifolius Maxim. a leaf transcriptome provides an overall functional characterization, discovery of SSR marker and phylogeny analysis

Aster spathulifolius Maxim. is belongs to the Asteraceae family, which is distributed only in Korea and Japan. The species is traditionally a medicinal plant and is economically valuable in the ornamental field. On the other hand, the Aster genus, among the Asteraceae family, lacks genomic resources and its molecular functions. Therefore, in our study the high-throughput RNA-sequencing transcriptome data of A. spathulifolius were obtained to identify the molecular functions and its characterization. The de novo assembly produced 98660 uniqueness with an N50 value of 1126bp. Total unigenes were procure to analyze the functional annotation against databases like non-redundant protein, Pfam, Uniprot, KEGG and Gene ontology. The overall percentage of functional annotation to the nr database (43.71%), uniprotein database (49.97%), Pfam (39.94%), KEGG (42.3%) and to GO (30.34%) were observed. Besides, 377 unigenes were found to be involved in the terpenoids pathway and 666 unigenes were actively engaged in other secondary metabolites synthesis, given that 261 unigenes were within phenylpropanoid pathway and 81 unigenes to flavonoid pathway. A further prediction of stress resistance (9,513) unigenes and transcriptional factor (3,027) unigenes in 53 types were vastly regulated in abiotic stress respectively in salt, heat, MAPK and hormone signal transduction pathway. This study discovered 29,692 SSR markers that assist the genotyping approaches and the genetic diversity perspectives. In addition, eight Asteraceae species as in-group together with one out-group were used to construct the phylogenetic relationship by employing their plastid genome and single-copy orthologs genes. Among 50 plastid protein-coding regions, A. spathulifolius is been closely related to A. annua and by 118 single copy orthologs genes, O. taihangensis is more neighboring species to A. spathulifolius. Apart from this, A. spathulifolius and O. taihangensis, genera have recently diverged from other species. Overall, this research gains new insights into transcriptome data by revealing and exposing the secondary metabolite compounds for drug development, the stress-related genes for producing resilient crops and an ortholog gene of A. spathulifolius for the robustness of phylogeny reconstruction among Asteraceae genera.

Isolation, Characterization and Antiproliferative Activity of New Metabolites from the South African Endemic Red Algal Species Laurencia alfredensis

The marine red algae of the genus Laurencia have been widely studied for their structurally diverse and biologically active secondary metabolites. We report here the natural product investigation of the organic extract of a newly identified South African endemic species, Laurencia alfredensis. A sequence of column chromatography, preparative TLC and normal phase HPLC resulted in the isolation of eleven compounds comprising three labdane-type diterpenes (1–3), four polyether triterpenes (4–7), three cholestane-type ecdysteroids (8–10) and a glycolipid (11). Compounds 1–3, 5–8 and 10 have not previously been reported, while compound 9 is reported here for the first time from a natural source and the known compound 11 isolated for the first time from the genus Laurencia. The structural elucidation and the relative configuration assignments of the compounds were accomplished by extensive use of 1D- and 2D-NMR, HR-ESI-MS, UV and IR spectroscopic techniques, while the absolute configuration of compound 1 was determined by single-crystal X-ray diffraction analysis. All compounds were evaluated against the MDA-MB-231 breast and HeLa cervical cancer cell lines. Compound 2 exhibited low micromolar antiproliferative activity (IC₅₀ = 9.3 µM) against the triple negative breast carcinoma and compound 7 was similarly active (IC₅₀ = 8.8 µM) against the cervical cancer cell line.

Aster spathulifolius Maxim extract reduces body weight and fat mass in obese humans

Aster spathulifolius Maxim (AS), a perennial herb of the genus Aster within the family Asteraceae, induced weight loss in a rat model of diet-induced obesity. We hypothesized that AS could also reduce body weight in obese humans. Therefore, we performed a randomized, double-blind, placebo-controlled clinical trial in Korea to evaluate the effect of AS extract (ASE) on body weight and fat mass and its safety in obese humans. Forty-four obese participants (body mass index [BMI], 25-30 kg/m(2)) aged ≥20 years were randomly assigned to the placebo or ASE group (700 mg/d of ASE) and were instructed to take a once-daily pill for 12 weeks. Weight, BMI, waist circumference, fat mass (measured using bioimpedance, dual-energy X-ray absorptiometry, and computed tomography), and laboratory tests were assessed at baseline and at 12 weeks. Body weight significantly decreased after 12 weeks of treatment in the ASE group (placebo vs ASE: -0.08 ± 2.11 kg vs -3.30 ± 3.15 kg, P < .05), and so did body fat mass (placebo vs ASE; bioimpedance method: -0.51 ± 1.89 kg vs -2.38 ± 2.30 kg, P < .05; dual-energy X-ray absorptiometry: 0.38 ± 1.59 kg vs -2.26 ± 2.37 kg, P < .05). Changes in lipid profiles, fasting plasma glucose, and hemoglobin A1c did not differ between the 2 groups. No drug-related adverse events were observed during the study. In conclusion, ASE significantly decreases body weight and fat mass in obese humans, suggesting that ASE may be a potential therapeutic candidate for reducing obesity.

Anti-Diabetic Effect of Aster sphathulifolius in C57BL/KsJ-db/db Mice

In this study, we investigated the anti-diabetic effect of Aster sphathulifolius (AS) extract in C57BL/KsJ-db/db mice. The db/db mice were orally administered with AS 50% ethanol extract at concentrations of 50, 100, and 200 mg/kg/day (db/db-AS50, db/db-AS100, and db/db-AS200, respectively) for 10 weeks. Food and water intake, fasting blood glucose concentrations, blood glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the db/db-AS200 group than in the vehicle-treated db/db group; whereas glucose tolerance was significantly improved in the db/db-AS200 group. Moreover, AS dose dependently increased both insulin receptor substrate 1 and glucose transporter type 4 expression in skeletal muscle, significantly increased glucokinase expression, and decreased glucose 6-phosphatase and phosphoenolpyruvate carboxykinase expressions in the liver. The expressions of transcription factors, such as sterol-regulatory element-binding protein, peroxisome proliferator-activated receptor γ, and adipocyte protein 2, were upregulated in adipose tissue. Furthermore, immunohistochemical analysis showed that AS upregulated insulin production by increasing pancreatic β-cell mass. In summary, AS extract normalized hyperglycemia by multiple mechanisms: inhibition of glyconeogenesis, acceleration of glucose metabolism and lipid metabolism, and increase of glucose uptake. Using in vivo assays, this study has shown the potential of AS as a medicinal food and suggests the efficacy of AS for the use of prevention of diabetes.

A new cembrane glycoside in Asterothamnus centrali-asiaticus from Gobi Desert

A new cembrane glycoside, nephthenol 15-O-β-d-quinovoside, was isolated from the aerial parts of Asterothamnus centrali-asiaticus. Its structure was elucidated by 1D and 2D NMR spectroscopic analysis, as well as by mass spectrometry. This is the first report of the occurrence of a cembrane glycoside in vascular plants.

Bioassay-guided isolation and identification of cytotoxic compounds from Gymnosperma glutinosum leaves

Bioassay-guided fractionation of hexane extracts of Gymnosperma glutinosum (Asteraceae) leaves, collected in North Mexico, afforded the known compounds hentriacontane (1) and (+)-13S,14R,15-trihydroxy-ent-labd-7-ene (2), as well as the new ent-labdane diterpene (−)-13S,14R,15-trihydroxy-7-oxo-ent-labd-8(9)-ene (3). In addition, D-glycero-D-galactoheptitol (4) was isolated from the methanolic extract of this plant. Their structures were established on the basis of high-field 1D- and 2D NMR methods supported by HR-MS data. The cytotoxic activity was determined by using the in vitro L5178Y-R lymphoma murine model. Hentriacontane (1) and the new ent-labdane 3 showed weak cytotoxicity, whereas the ent-labdane 2 showed significant (p < 0.05) and concentration dependent cytotoxicity (up to 78%) against L5178Y-R cells at concentrations ranging from 7.8 to 250 µg/mL.

The labdane diterpene sclareol (labd-14-ene-8, 13-diol) induces apoptosis in human tumor cell lines and suppression of tumor growth in vivo via a p53-independent mechanism of action

The labdane diterpene sclareol has demonstrated significant cytotoxicity against human tumor cell lines and human colon cancer xenografts. Therefore, there is need to elucidate the mode of action of this compound as very little information is known for the anticancer activity of sclareol and other labdane diterpenes, in general. COMPARE analysis of GI(50) values for a number of human cancer cell lines was initially implicated in an effort to assign a putative mechanism of action to the compound. Sclareol-induced cell cycle arrest and apoptosis were assessed by flow cytometry and Western blot analyses. Finally, the anticancer ability of sclareol in vivo was assessed by using human colon cancer xenograft/mouse models. Sclareol arrested in vitro the growth of p53-deficient (HCT116(p53-/-)) human colon cancer cells and subsequently induced apoptosis by activating both caspases-8 and -9. Intraperitoneal administration of liposome-encapsulated sclareol at the maximum tolerated dose induced a marked growth suppression of HCT116(p53-/-) tumors established as xenografts in immunodeficient NOD/SCID mice. In conclusion, we demonstrate herein that sclareol kills human tumor cells by inducing arrest at the G(1)-phase of the cell cycle followed by apoptosis that involves activation of caspases-8, -9 and -3 via a p53-independent mechanism. These findings suggest that liposome-encapsulated sclareol possesses chemotherapeutic potential for the treatment of colorectal and other types of human cancer regardless of the p53-status.

Diterpenoids from Pinus massoniana resin and their cytotoxicity against A431 and A549 cells

Five diterpenoids and 14 known diterpenoids were isolated from the petroleum ether extract of Pinus massoniana resin. Their structures were elucidated by spectroscopic data interpretation. The cytotoxic activities of these compounds were evaluated using the MTT method. The results showed that three of the less polar diterpenoids had strong cytotoxicity against A431 and A549 cancer cells, whereas those of high polarity had none.

Guaiane sesquiterpene lactones and amino acid-sesquiterpene lactone conjugates from the aerial parts of Saussurea pulchella

Two new guaiane sesquiterpene lactones ( 1 and 2) and seven new amino acid-sesquiterpene lactone conjugates ( 3- 9), together with six known sesquiterpene lactones ( 10- 15), were isolated from the methanol extract of the aerial parts of Saussurea pulchella. Their structures were determined on the basis of spectroscopic and chemical methods to be 8alpha- O-(3'-hydroxy-3'-methylbutyryl)desacylcynaropicrin ( 1), 8alpha- O-(2', 3'-dihydroxyisobutyryl)11beta,13-dihydrodesacylcynaropicrin ( 2), and pulchellamines A, B, C, D, E, F, and G ( 3- 9). The structures of the new amino acid-sesquiterpene lactone conjugates, pulchellamines A, B, C, D, E, F, and G ( 3- 9), were confirmed by synthesis. The isolated compounds were evaluated for cytotoxic activity against four human tumor cell lines. Compounds 11 and 12 exhibited cytotoxicity against skin melanoma (SK-MEL-2) and ovary malignant ascites (SK-OV-3) human tumor cell lines with ED 50 values of 1.53 and 4.07 microM, and 2.49 and 7.42 microM, respectively.

Secondary metabolites from the aerial parts of Salvia palaestina Bentham

Three sesterterpenes (1-3), one triterpene (4) and five diterpenes (5-9) were isolated from the aerial parts of Salvia palaestina Bentham (Lamiaceae), together with two sesquiterpenes, 10 known diterpenes, three triterpenes, and rosmarinic acid. Their structural elucidation was accomplished by extensive spectroscopic methods including 1D ((1)H, (13)C, (13)C DEPT, TOCSY, NOESY) and 2D NMR experiments (DQF-COSY, HSQC, HMBC, ROESY) as well as ESIMS analysis and chemical analysis.

Sclareol induces apoptosis in human HCT116 colon cancer cells in vitro and suppression of HCT116 tumor growth in immunodeficient mice

Labd-14-ene-8, 13-diol (sclareol) is a labdane-type diterpene, which has demonstrated significant cytotoxic activity against human leukemic cell lines, but its effect on solid tumor-derived cells is uknown. Here, we demonstrate that addition of sclareol to cultures of human colon cancer HCT116 cells results in inhibition of DNA synthesis, arrest of cells at the G(1) phase of the cell cycle, activation of caspases-8, -9, PARP degradation, and DNA fragmentation, events characteristic of induction of apoptosis. Intraperitoneal (ip) administration of sclareol alone, at the maximum tolerated dose, was unable to induce suppression of growth of HCT116 tumors established as xenografts in immunodeficient SCID mice. In contrast, ip administration of liposome-encapsulated sclareol, following a specific schedule, induced suppression of tumor growth by arresting tumor cell proliferation as assessed by detecting the presence of the cell proliferation-associated nuclear protein, Ki67, in thin tumor sections. These findings suggest that sclareol incorporated into liposomes may possess chemotherapeutic potential for the treatment of colorectal and other types of human cancer.

A new sesquiterpene glycoside from the aerial parts of Saussurea triangulata

Column chromatographic separation of a MeOH extract of the aerial parts of Saussurea triangulata led to the isolation of a new sesquiterpene glycoside 6, together with three quinic acid derivatives, two phenolics, two sesquiterpene glycosides and two flavonoids. The new compound 6 was identified as amarantholidol A glycoside by spectroscopic and chemical methods.

Labdane Diterpenoid Glycosides fromAster veitchianus

Four new labdane-type rhamnopyranosides derived from 13-epimanool, compounds 1-4, with differently acetylated sugar moieties, were isolated from A. veitchianus. Their structures and absolute configurations were elucidated by chemical transformation, spectroscopic and mass-spectrometric analyses (IR, 1D- and 2D-NMR, HR-ESI-MS), as well as by single-crystal X-ray diffraction (compound 1). The isolates 2-4 were investigated for their cytotoxic properties against cultured human hepatoma (SMMC-7721), ovarian neoplasm (HO-8910), and leukemia (HL-60) cells, and for their antibacterial activities against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus.

Cytotoxic terpene hydroperoxides from the aerial parts ofAster spathulifolius

Three new sesquiterpene hydroperoxides, 1-[3-(2-hydroperoxy-3-methylbut-3-en)-4-hydroxyphenyl]ethanone (2), 7beta-hydroperoxy-eudesma-11-en-4-ol (3), and 7alpha-hydroperoxymanool (4), together with three known compounds, germacrone (1), ent-germacra-4(15),5,10(14)-trien-1alpha-ol (5) and teucdiol A (6) were isolated from the aerial parts of Aster spathulifolius (Compositae). Their structures were characterized using chemical and spectroscopic methods. The isolated compounds were tested for their cytotoxicity against five human tumor cell lines in vitro using a SRB method. The two new compounds, 3 and 4, showed moderate cytotoxicity against human cancer cells with ED50 values ranging from 0.24 to 13.27 microg/mL.

Diterpenoids

This review covers the isolation and structures of diterpenoids, including labdanes, clerodanes,pimaranes, abietanes, kauranes, cembranolides, taxanes and marine diterpenoids. The literature from January to December 2005 is reviewed, and 195 references are cited.