Synthesis of lupane-type saponins bearing mannosyl and 3,6-branched trimannosyl residues and their evaluation as anticancer agents

Fractionation, identification of chemical constituents, and biological properties of cashew (Anacardium occidentale L.) leaf extracts

The current study aimed to identify the chemical constituents and bioactivities of the crude ethanolic extract (CEE) and its fractions (ethyl acetate (EAF), hexane (HEF), and aqueous (AEF)) from leaves of cashew (Anacardium occidentale L.) grown in Vietnam. A total of 31 compounds which belong to alkanes, hydrocarbons, iodine, terpenoids, phenolics, and flavonoids were determined by a gas chromatography-mass spectrometry (GC-MS) analysis, with bis(2-ethylhexyl) phthalate being the most prevailing compound. The highest total phenolic and flavonoid contents were obtained in the EAF, followed by HEF, CEE, and AQF. All samples showed promising in vitro antibacterial activity, enzyme inhibition, and anticancer activity. Among the samples tested, the EAF exhibited the highest enzyme inhibition activity against α-amylase and α-glucosidase (IC50 values of 51.24 μg/mL and 99.29 μg/mL, respectively), cytotoxicity activity against HeLa cells (IC50 value of 79.49 μg/mL), and antibacterial activity against Bacillus subtilis and Escherichia coli with MIC values of 5 mg/mL and 2.5 mg/mL, respectively. These findings suggest that the leaves of A. occidentale cultivated in Vietnam are a promising source of bioactive components and that EAF is a promising bioactive material warranting further pharmaceutical investigation.

Progress in Antimelanoma Research of Natural Triterpenoids and Their Derivatives: Mechanisms of Action, Bioavailability Enhancement and Structure Modifications

Melanoma is one of the most dangerous forms of skin cancer, characterized by early metastasis and rapid development. In search for effective treatment options, much attention is given to triterpenoids of plant origin, which are considered promising drug candidates due to their well described anticancer properties and relatively low toxicity. This paper comprehensively summarizes the antimelanoma potential of natural triterpenoids, that are also used as scaffolds for the development of more effective derivatives. These include betulin, betulinic acid, ursolic acid, maslinic acid, oleanolic acid, celastrol and lupeol. Some lesser-known triterpenoids that deserve attention in this context are 22β-hydroxytingenone, cucurbitacins, geoditin A and ganoderic acids. Recently described mechanisms of action are presented, together with the results of preclinical in vitro and in vivo studies, as well as the use of drug delivery systems and pharmaceutical technologies to improve the bioavailability of triterpenoids. This paper also reviews the most promising structural modifications, based on structure-activity observations. In conclusion, triterpenoids of plant origin and some of their semi-synthetic derivatives exert significant cytotoxic, antiproliferative and chemopreventive effects that can be beneficial for melanoma treatment. Recent data indicate that their poor solubility in water, and thus low bioavailability, can be overcome by complexing with cyclodextrins, or the use of nanoparticles and ethosomes, thus making these compounds promising antimelanoma drug candidates for further development.

Bifunctionalized Betulinic Acid Conjugates with C-3-Monodesmoside and C-28-Triphenylphosphonium Moieties with Increased Cancer Cell Targetability

A convenient synthesis is presented for a new class of bioactive bifunctionalized conjugates of lupane-type triterpenoids with triphenylphosphonium (TPP) and glycopyranosyl targeting moieties. The main synthesis steps include glycosylation of haloalkyl esters of the triterpene acid at the C-3 position by the imidate derivatives of glycopyranose followed by the product modification at the C-28 position with triphenylphosphine. The conjugates of betulinic acid (BetA) with TPP and d-glucose, l-rhamnose, or d-mannose moieties were thus synthesized as potential next-generation BetA-derived anticancer compounds. LC-MS/MS analysis in glucose-free physiological solution indicated that the glycosides showed better accumulation in PC-3 prostate cancer cells than both BetA and TPP-BetA conjugate, while the transporting effect of monosaccharide residues increased as follows: d-mannose < l-rhamnose ≈ d-glucose. At saturated concentrations, the glycosides caused a disturbing effect on mitochondria with a more drastic drop in transmembrane potential but weaker overproduction of mitochondrial reactive oxygen species (ROS) compared to TPP-BetA conjugate. Cytotoxicity of the glycosides in culture medium was comparable with or higher than that of the nonglycosylated conjugate, depending on the cancer cell line, whereas the compounds were less active toward primary fibroblasts. Glycosylation tended to increase pro-apoptotic and decrease pro-autophagic activities of the BetA derivatives. Cytotoxicity of the synthesized glycosides was considered in comparison with the summarized data on the natural and modified BetA glycosides. The results obtained are important for the development of bifunctionalized conjugates of triterpenoids with an increased cancer cell targetability.

A Small Sugar Molecule with Huge Potential in Targeted Cancer Therapy

The number of cancer-related diseases is still growing. Despite the availability of a large number of anticancer drugs, the ideal drug is still being sought that would be effective, selective, and overcome the effect of multidrug resistance. Therefore, researchers are still looking for ways to improve the properties of already-used chemotherapeutics. One of the possibilities is the development of targeted therapies. The use of prodrugs that release the bioactive substance only under the influence of factors characteristic of the tumor microenvironment makes it possible to deliver the drug precisely to the cancer cells. Obtaining such compounds is possible by coupling a therapeutic agent with a ligand targeting receptors, to which the attached ligand shows affinity and is overexpressed in cancer cells. Another way is to encapsulate the drug in a carrier that is stable in physiological conditions and sensitive to conditions of the tumor microenvironment. Such a carrier can be directed by attaching to it a ligand recognized by receptors typical of tumor cells. Sugars seem to be ideal ligands for obtaining prodrugs targeted at receptors overexpressed in cancer cells. They can also be ligands modifying polymers' drug carriers. Furthermore, polysaccharides can act as selective nanocarriers for numerous chemotherapeutics. The proof of this thesis is the huge number of papers devoted to their use for modification or targeted transport of anticancer compounds. In this work, selected examples of broad-defined sugars application for improving the properties of both already-used drugs and substances exhibiting anticancer activity are presented.

Fractionation and Characterization of Triterpenoids from Vaccinium vitis-idaea L. Cuticular Waxes and Their Potential as Anticancer Agents

Fruit and leaf cuticular waxes are valuable source materials for the isolation of triterpenoids that can be applied as natural antioxidants and anticancer agents. The present study aimed at the semi-preparative fractionation of triterpenoids from cuticular wax extracts of Vaccinium vitis-idaea L. (lingonberry) leaves and fruits and the evaluation of their cytotoxic potential. Qualitative and quantitative characterization of obtained extracts and triterpenoid fractions was performed using HPLC-PDA method, followed by complementary analysis by GC-MS. For each fraction, cytotoxic activities towards the human colon adenocarcinoma cell line (HT-29), malignant melanoma cell line (IGR39), clear renal carcinoma cell line (CaKi-1), and normal endothelial cells (EC) were determined using MTT assay. Furthermore, the effect of the most promising samples on cancer spheroid growth and viability was examined. This study allowed us to confirm that particular triterpenoid mixtures from lingonberry waxes may possess stronger cytotoxic activities than crude unpurified extracts. Fractions containing triterpenoid acids plus fernenol, complexes of oleanolic:ursolic acids, and erythrodiol:uvaol were found to be the most potent therapeutic candidates in the management of cancer diseases. The specificity of cuticular wax extracts of lingonberry leaves and fruits, leading to different purity and anticancer potential of obtained counterpart fractions, was also enclosed. These findings contribute to the profitable utilization of lingonberry cuticular waxes and provide considerable insights into the anticancer effects of particular triterpenoids and pharmacological interactions.

Active Compounds From Inga edulis Martius Seeds Against Multiple Myeloma

Multiple myeloma is an incurable hematological cancer with an average survival time of only 5 to 10 years due to the high rate of relapse and resistance. Although the introduction of novel classes of drugs has improved the standard of care, new strategies are urgently needed. Plants are primary sources of bioactive natural compounds for cancer treatment. This study aimed at evaluating the in vitro inhibitory activity of the Inga edulis seed extract against multiple myeloma cells, as well as the compounds isolated from this extract. The ethanolic extract of the seeds of I. edulis inhibited 85% of RPMI 8226 cell proliferation at 20 µg/mL. Then, the extract was subjected to a bioassay-guided fractionation to afford 3 saponins known as concinnoside D (1), julibroside A1 (2), and julibroside A3 (3). The isolated saponins exhibited antiproliferative activity with IC50 values in the low µM range for compounds 2 and 3. Compound 1 was considered inactive (IC50 > 20 µM). Therefore, the seeds of I. edulis could be considered as a source of active compounds against multiple myeloma.

A review on ethnobotany, phytochemistry, and pharmacology of the genus Didymocarpus wall. (Gesneriaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Medicinal plants have been extensively used to treat various illnesses since the dawn of civilization. The genus Didymorcapus Wall. comprises 100 species widely distributed in the tropical regions of Asia, with a few found scattered in Africa and Australia. Species in this genus have long been used in folk medicine to treat various illnesses, including wounds, kidney stones, inflammations, asthma, flu, eczema, dysentery, fractures, colic etc. Some species have applications as weight loss agents, laxatives, and protective medication after childbirth.

AIM

To provide comprehensive information on the current knowledge of the ethnobotanical uses, phytochemical compounds, pharmacological applications, and toxicology of genus Didymocarpus to reveal its therapeutic potential, offering insights into future research opportunities.

MATERIALS AND METHODS

Data were systematically obtained from books and online databases such as PubMed, Web of Science, Scopus, Sci Finder, Google Scholar, Science direct, ACS Publications, Elsevier, Wiley Online Library.

RESULTS

Seventeen Didymocarpus species have applications in traditional medicine in different Asian countries. A total of 166 compounds have been isolated from the genus Didymocarpus including terpenoids, flavonoids, phenolic compounds, fatty acids, chalcones, steroids, and others. Among these constituents, terpenoids, flavonoids, chalcones, and phenolics are the significant contributors to pharmacological activities of the genus Didymocarpus, possessing wide-reaching biological activities both in vivo and in vitro. The crude extracts and isolated phytochemical compounds from this genus have been shown to exhibit various pharmacological activities, including antiurolithiatic, nephro-protective, antimicrobial, anticancer, antidiabetic, cytotoxic, wound healing, and antioxidant activities.

CONCLUSIONS

Traditional uses and scientific evaluation of Didymocarpus indicate that Didymocarpus pedicellata is one of the most widely used species in some parts of the world. Although substantial progress on the chemical and pharmacological properties of Didymocarpus species has been made, further studies on the pharmacology and toxicology of these species are needed to ensure safety, efficacy, and quality. Also, further research on the structure-activity relationship of some of the isolated phytocompounds may improve their biological potency and scientific exploitation of traditional uses of the Didymocarpus taxa.

Synthesis, In Vitro and In Silico Analysis of New Oleanolic Acid and Lupeol Derivatives against Leukemia Cell Lines: Involvement of the NF-κB Pathway

Oleanolic acid (OA) and Lupeol (LU) belong to the class of natural triterpenes and are endowed with a wide range of biological activities, including cytotoxicity toward several cancer cell lines. In this context, we investigated a set of compounds obtained from the two natural precursors for the cytotoxicity against leukemia HL60 cells and the multidrug-resistant (MDR) variant HL60R. Six new semi-synthetic triterpenes have been synthetized, fully characterized, and were investigated together with other triterpenes compounds for their pharmacological mechanism of action. The interaction of the more cytotoxic compounds with the nuclear factor kappa B (NF-κB) pathway has been also evaluated with the aid of docking. The lupane-like compounds were more active than the precursor, while the oleane-like compounds showed more complex behavior. Both OA and LU derivatives possess a similar interaction pattern with the p65 subunit of NF-κB, justifying the similar trend in their ability to inhibit the binding of p65 to DNA. Further, some of the derivatives tested were able to increase IκB-α levels preventing the translocation of NF-κB to the nucleus. In conclusion, this study offers a deeper insight on the pharmacological action of triterpenes toward leukemia cells, and it improves the background useful for the development of new anti-cancer drugs.

Chemical Synthesis of Saponins

Saponins are a large family of amphiphilic glycosides of steroids and triterpenes found in plants and some marine organisms. By expressing a large diversity of structures on both sugar chains and aglycones, saponins exhibit a wide range of biological and pharmacological properties and serve as major active principles in folk medicines, especially in traditional Chinese medicines. Isolation of saponins from natural sources is usually a formidable task due to the microheterogeneity of saponins in Nature. Chemical synthesis can provide access to large amounts of natural saponins as well as congeners for understanding their structure-activity relationships and mechanisms of action. This article presents a comprehensive account on chemical synthesis of saponins. First highlighted are general considerations on saponin synthesis, including preparation of aglycones and carbohydrate building blocks, assembly strategies, and protecting-group strategies. Next described is the state of the art in the synthesis of each type of saponins, with an emphasis on those representative saponins having sophisticated structures and potent biological activities.

Potential targeting of Hep3B liver cancer cells by lupeol isolated from Avicennia marina

Medicinal plants are valuable sources of different active constituents that are known to have important pharmacological activities including anticancer effects. Lupeol, a pentacyclic triterpenoid, present in many medicinal plants, has a wide range of biological activities. Although the anticancer activity of lupeol was reported, the published data are inconsistent and the clear mechanism of action has never been assigned. The current study aims at investigating the anticancer specificity and mechanism of lupeol isolated from Avicennia marina, which grows in the desert of the United Arab Emirates. The compound was purified by chromatography and identified by spectroscopy. Compared with a negative control, lupeol caused significant (p < .001) growth inhibitory activity on MCF-7 and Hep3B parental and resistant cells by 45%, 46%, 72%, and 35%, respectively. The mechanism of action of lupeol was further explored by measuring its effect on key players in cancer development and progression, BCL-2 anti-apoptotic and BAX pro-apoptotic proteins. Lupeol significantly (p < .01) downregulated BCL-2 gene expression in parental and resistant Hep3B cells by 33 and 3.5 times, respectively, contributing to the induction of apoptosis in Hep3B cells, whereas it caused no effect on BAX. Furthermore, the immunoblotting analysis revealed that lupeol cleaved the executioner caspase-3 into its active form. Interestingly, lupeol showed no significant effect on the proliferation of monocytes, whereas it caused an increase in the sub-G1 population and a reduction in the apoptosis rates of monocytes at 48 and 72 h, indicative of no immuno-inflammatory responses. Collectively, lupeol can be considered as promising effective and safe anticancer agent, particularly against Hep3B cancer cells.

Avicennia marina a natural reservoir of phytopharmaceuticals: Curative power and platform of medicines

ETHNOPHARMACOLOGICAL RELEVANCE

Avicennia marina (Forssk.) Vierh. is a historic plant, well-known for many centuries in traditional and folk use medicine. A. marina is an evergreen tree belongs to Acanthaceae family. The plant is the most widespread mangrove in the tropical and subtropical regions of Indo-West-Pacific area. Current scientific data confirmed the medicinal values of A. marina. The pharmacological activity of the plant is attributed to the presence of several phytochemical classes.

AIM OF THE STUDY

To evaluate the link between the traditional use of the plant and the scientific data accumulated over time including both the phytochemical analysis and therapeutic activities. Additionally, to evaluate the usage of obtained data for further development of the plant and its products in the pharmaceutical market.

MATERIALS AND METHODS

The data related to traditional medicine, therapeutic uses, phytochemical analysis and market availability of A. marina and its products from different geographical regions were collected. The collected data was compared and the research gaps were identified in order to highlight areas that can be employed to improve plant-based research and development.

RESULTS

Although the wide geographical distribution of the plant, its historic traditional use, richness of phytochemicals and diverse pharmacological activities, the utilization of these data has never been exploited for human health and several gaps were identified. These gaps include the lack of phyto-geographical comparison of the plant, the lack of proper mapping of traditional use to the scientific data and inadequate exploration of plant phytochemicals by researchers.

CONCLUSIONS

A. marina is an old tree that has evolved over centuries and adapted diverse climates. It contains a pool of potential phytochemicals that can be employed for the discovery of drugs after careful studies. Scientists are required to invest money and time to explore these renewable and natural sources of drugs and design drug formulations to overcome current difficult to treat health issues and fight against the era of drug resistant.

Hegazy ME, Naqishbandi AM, Efferth T. Induction of Apoptosis, Autophagy and Ferroptosis by Thymus vulgaris and Arctium lappa Extract in Leukemia and Multiple Myeloma Cell Lines

Thymus vulgaris and Arctium lappa have been used as a folk remedy in the Iraqi Kurdistan region to deal with different health problems. The aim of the current study is to investigate the cytotoxicity of T. vulgaris and A. lappa in leukemia and multiple myeloma (MM) cell lines and determine the mode of cell death triggered by the most potent cytotoxic fractions of both plants in MM. Resazurin assay was used to evaluate cytotoxic and ferroptosis activity, apoptosis, and modulation in the cell cycle phase were investigated via Annexin V-FITC/PI dual stain and cell-cycle arrest assays. Furthermore, we used western blotting assay for the determination of autophagy cell death. n-Hexane, chloroform, ethyl acetate, and butanol fractions of T. vulgaris and A. lappa exhibited cytotoxicity in CCRF-CEM and CEM/ADR 5000 cell lines at concentration range 0.001–100 μg/mL with potential activity revealed by chloroform and ethyl acetate fractions. NCI-H929 displayed pronounced sensitivity towards T. vulgaris (TCF) and A. lappa (ACF) chloroform fractions with IC₅₀ values of 6.49 ± 1.48 and 21.9 ± 0.69 μg/mL, respectively. TCF induced apoptosis in NCI-H929 cells with a higher ratio (71%), compared to ACF (50%) at 4 × IC₅₀. ACF demonstrated more potent autophagy activity than TCF. TCF and ACF induced cell cycle arrest and ferroptosis. Apigenin and nobiletin were identified in TCF, while nobiletin, ursolic acid, and lupeol were the main compounds identified in ACF. T. vulgaris and A. lappa could be considered as potential herbal drug candidates, which arrest cancer cell proliferation by induction of apoptosis, autophagic, and ferroptosis.

In vitro evaluation of immunobiological activity of simple mannolipids

Immunomodulation, cytotoxicity and anti-cancer activity of selected amphiphilic non-ionic (thio)alkyl α-D-mannosides (with aglycone of C6-C12) were investigated in vitro in human cervix epitheloid carcinoma cell line HeLa, murine melanoma cancer cells B16, murine lymphocytic leukemia cell line L1210, murine fibroblast cell line NIH 3 T3 and murine macrophage cell line RAW 264.7. Toxicological studies revealed structure-dependent immunobiological effectivity based on a tight interaction with relevant cells. The results demonstrated diverse immunomodulation of macrophage cell-line RAW264.7 proliferation and production of Th1 and Th2 cytokines, and induction of pro-inflammatory interleukins IL-1α, TNFα, IL-6, IL-12 and IL-17 and anti-inflammatory IL-10 following (thio)alkyl α-D-mannosides 24 and 48 h exposure. Direct application of alkyl mannosides MOC10 and MOC12 and their thio analogues MSC10 and MSC12 in reconstructed human EpiDerm™ and MOC12 and MSC12 in EpiOcular™ model assays for dermal and ocular irritation together with quantification of human proinflammatory cytokines IL-1α, TNFα, IL-6 and IL-8 culture media release was used to ascertain toxicological safety.

Design, synthesis and biological evaluation of betulin-3-yl 2-amino-2-deoxy-β-d-glycopyranosides

Betulin is a natural pentacyclic triterpenoid, possessing a lupane-structure, with a wide range of pharmacological activities. Its weak hydrosolubility hinders the biological activity of the compound and its derivatives. To circumvent this problem, we synthesized and tested in vitro three d-glycosaminosides of betulin. The structure of betulin was modified by incorporation of 2-amino-2-deoxy-d-gluco- and -d-galactopyranosyl moieties to its C-3 position. So far betulinyl glycosides containing these amino-sugars have not been reported in the literature. The structure of the studied derivatives was confirmed by ¹H and ¹³C NMR spectroscopy as well as mass spectrometry. The 28-O-acetylbetulin-3-yl 2-amino-2-deoxy-β-d-glucopyranoside and betulin-3-yl 2-amino-2-deoxy-β-d-gluco- and β-d-galactopyranoside were tested against the human pathogenic fungi and Gram-positive and Gram-negative bacteria. Moreover, the MTT assay of their cytotoxicity was performed on the MCF-7 breast cancer cell line and on the HDFa, human dermal fibroblasts. The Ames test on mutagenic properties completed our biological assays.

Synthesis and anti-cancer activities of glycosides and glycoconjugates of diterpenoid isosteviol

A series of glycosides and glycoconjugates of diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) with various monosaccharide residues were synthesized and their cytotoxicity against some human cancer and normal cell lines was assayed. Most of the synthesized compounds demonstrated moderate to significant cytotoxicity against human cancer cell lines M-HeLa and MCF-7. Three lead compounds exhibited selective cytotoxic activities against M-HeLa (IC50 = 10.0-15.1 μM) that were three times better than the cytotoxicity of the anti-cancer drug Tamoxifen (IC50 = 28.0 μM). Moreover, the lead compounds were not cytotoxic with respect to the normal human cell line Chang liver (IC50 > 100 μM), whereas Tamoxifen inhibited the viability of normal human Chang liver cells with an IC50 value of 46.0 μM. It was determined that the cytotoxicity of the lead compounds was due to induction of apoptosis proceeding along the mitochondrial pathway. The cytotoxic activity of the synthesized compounds substantially depended on the nature of the monosaccharide residue and its position, that is, whether the monosaccharide residue was attached directly to the isosteviol skeleton or was moved away from it by means of a polymethylene linker.

Synthesis, cytotoxicity and anti-inflammatory activity of rhamnose-containing ursolic and betulinic acid saponins

Betulinic acid and ursolic acid are ubiquitous, naturally-occurring triterpenoids exhibiting various pharmacological activities including cytotoxic and anti-inflammatory activities. However, these triterpenoids display unfavorable pharmacokinetic properties as well as low aqueous solubility. It has been shown that the presence of α-l-rhamnose moieties positively modulates the anticancer activity of secondary metabolites. Herein we report the synthesis and in vitro evaluation of cytotoxic and anti-inflammatory activities of a series of rhamnose-containing ursolic and betulinic acid saponins. Relying on Schmidt's normal and inverse procedures, monorhamnosides, (1→4)-linked dirhamnosides as well as branched trirhamnosides and tetrarhamnosides were synthesized in high yields with full control of stereoselectivity. A betulinic acid saponin bearing a 3-O-α-l-rhamnopyranosyl-(1→4)-α-l-rhamnopyranosyl residue was found to be a potent cytotoxic agent against human colorectal adenocarcinoma cells without damaging the healthy cells (selectivity ratio > 20) whereas rhamnose-containing ursolic acid saponins potently inhibited NO overproduction induced by LPS-stimulated macrophages. Our results reveal that rhamnose-containing ursolic and betulinic acid saponins represent promising therapeutic agents.

Rhamnose-containing saponins featuring betulinic and ursolic acid as aglycones were synthesized using both Schmidt's normal and inverse procedures. Some of these synthetic saponins exhibited selective cytotoxic and/or anti-inflammatory activities.

Cytotoxic activity of the bioactive principles from Ficus burtt-davyi

Ficus burtt-davyi (Moraceae) is a medicinal plant species indigenous to Southern Africa. In this study, a phytochemical and cytotoxic investigation on F. burtt-davyi was conducted to evaluate its ethno-medicinal use. The phytochemical study of the fruits yielded triterpenoids (lupeol and α-amyrin). The cytotoxic evaluation was done on the methanolic extracts and selected compounds, lupeol, α-amyrin, lupeol acetate and (+)-catechin isolated from F. burtt-davyi stem bark and fruits. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay was carried out against two human cancer cell lines, breast adenocarcinoma (MCF-7) and colorectal adenocarcinoma (Caco-2), and normal human embryonic kidney cells (HEK293). The methanol extract from the stem bark was significantly cytotoxic to MCF-7 and Caco-2 cell lines (p < 0.05) in a concentration-dependent manner with IC₅₀ values of 6.6 and 8.1 µg mL^-1, respectively relative to the control. Lupeol and (+)-catechin showed cytotoxic activity against MCF-7 cell lines with IC₅₀ values of 22.6 and 29.8 µg mL^-1, respectively and greater cytotoxic activity against Caco-2 cell lines with IC₅₀ values of 10.7 and 9.0 µg mL^-1, respectively. Data from this study suggests that F. burtt-davyi exhibits cytotoxicity with no significant inhibitory effects against HEK293. The results also indicate that (+)-catechin and lupeol, the most abundant bioactive principles in the stem bark, are responsible for the synergistic cytotoxic effects against tested human cancer cell lines. This study provides evidence on the pharmaceutical potential of the medicinal plant, F. burtt-davyi, as a chemotherapeutic agent against cancer.

Picolyl amides of betulinic acid as antitumor agents causing tumor cell apoptosis

A series of picolyl amides of betulinic acid (3a-3c and 6a-6c) was prepared and subjected to the cytotoxicity screening tests. Structure-activity relationships studies resulted in finding differences in biological activity in dependence on o-, m- and p-substitution of the pyridine ring in the target amides, when cytotoxicity data of 3a-3c and 6a-6c were obtained and compared. The amides 3b and 3a displayed cytotoxicity (given in the IC₅₀ values) in G-361 (0.5 ± 0.1 μM and 2.4 ± 0.0 μM, respectively), MCF7 (1.4 ± 0.1 μM and 2.2 ± 0.2 μM, respectively), HeLa (2.4 ± 0.4 μM and 2.3 ± 0.5 μM, respectively) and CEM (6.5 ± 1.5 μM and 6.9 ± 0.4 μM, respectively) tumor cell lines, and showed weak effect in the normal human fibroblasts (BJ). Selectivity against all tested cancer cells was determined and compared to normal cells with therapeutic index (TI) between 7 and 100 for compounds 3a and 3b. The therapeutic index (TI = 100) was calculated for human malignant melanoma cell line (G-361) versus normal human fibroblasts (BJ). The cytotoxicity of other target amides (3c and 6a-6c) revealed lower effects than 3a and 3b in the tested cancer cell lines.

Acetyl-lupeolic acid inhibits Akt signaling and induces apoptosis in chemoresistant prostate cancer cells in vitro and in vivo

The triterpenoid acetyl-lupeolic acid (ac-LA) isolated from the oleogum resin of Boswellia carterii reduced the viability of a panel of cancer cell lines more efficiently than lupeol. There was no detectable intracellular conversion of ac-LA to lupeol and vice versa. In contrast to docetaxel, ac-LA did not induce selection of treatment-resistant cancer cells. By various parameters including DNA fragmentation, ac-LA was shown to induce apoptosis in androgen-independent PC-3 cells, whereas in MDA-MB-231 breast cancer cells, ac-LA led to cell accumulation in the G₂/M phase of the cell cycle, but not to apoptosis. In silico docking combined with in vitro kinase assays implied that ac LA potently inhibits Akt mainly by direct binding to the pleckstrin homology domain. Consistently, an Akt1 mutant deficient of the PH domain afforded partial resistance to ac-LA and complete resistance to lupeol and the Akt inhibitor III. Ac-LA inhibited phosphorylation of downstream targets of the Akt signaling pathway, which was followed by inhibition of the mTOR target p70 ribosomal six protein kinase and the nuclear accumulation of p65/NF-κB, β-catenin, and c-myc, as well as loss of the mitochondrial membrane potential. Ac-LA exhibited antiproliferative, proapoptotic, and antitumorigenic effects on PC-3-tumors xenografted either on chick chorioallantoic membranes or in nude mice. Ac-LA exhibited a clearly better safety profile than docetaxel or lupeol during chronic administration in vivo. In contrast to lupeol, ac-LA also inhibited release of vascular endothelial growth factor in vitro and accordingly angiogenesis in vivo. Thus, ac-LA deserves further exploration as a potential new antitumor compound.

Influence of intramolecular hydrogen bonds on regioselectivity of glycosylation. Synthesis of lupane-type saponins bearing the OSW-1 saponin disaccharide unit and its isomers

A series of lupane-type saponins bearing OSW-1 disaccharide unit as well as its regio- and stereoisomers were prepared and used for the structure-activity relationships (SAR) study. Unexpected preference for 1→4-linked regioisomers and an unusual inversion of the conformation of the sugar rings were noted. Cytotoxic activity of new lupane compounds was evaluated in vitro and revealed that some saponins exhibited an interesting bioactivity profile against human cancer cell lines. Influence of the protecting groups on the cytotoxicity was investigated. These results open the way to the synthesis of various lupane-type triterpene and saponin derivatives as potential anticancer compounds.

Synthesis, Formulation, and Adjuvanticity of Monodesmosidic Saponins with Olenanolic Acid, Hederagenin and Gypsogenin Aglycones, and some C-28 Ester Derivatives

In an attempt to discover a new synthetic vaccine adjuvant, the glycosylation of hederagenin, gypsogenin, and oleanolic acid acceptors with di- and trisaccharide donors to generate a range of mimics of natural product QS-21 was carried out. The saponins were formulated with phosphatidylcholine and cholesterol, and the structures analyzed by transmission electron microscopy. 3-O-(Manp(1→3)Glcp)hederagenin was found to produce numerous ring-like micelles when formulated, while C-28 choline ester derivatives preferred self-assembly and did not interact with the liposomes. When alone and in the presence of cholesterol and phospholipid, the choline ester derivatives produced nanocrystalline rods or helical micelles. The effects of modifying sugar stereochemistry and the aglycone on the immunostimulatory effects of the saponins was then evaluated using the activation markers MHC class II and CD86 in murine bone marrow dendritic cells. The most active saponin, 3-O-(Manp(1→3)Glcp)hederagenin, was stimulatory at high concentrations in cell culture, but this did not translate to strong responses in vivo.

Chemical synthesis of saponins

Saponins are a large family of amphiphilic glycosides of steroids and triterpenes found in plants and some marine organisms. By expressing a large diversity of structures on both sugar chains and aglycones, saponins exhibit a wide range of biological and pharmacological properties and serve as major active principles in folk medicines, especially in traditional Chinese medicines. Isolation of saponins from natural sources is usually a formidable task due to the microheterogeneity of saponins in Nature. Chemical synthesis can provide access to large amounts of natural saponins as well as congeners for understanding their structure-activity relationships and mechanisms of action. This article presents a comprehensive account on chemical synthesis of saponins. First highlighted are general considerations on saponin synthesis, including preparation of aglycones and carbohydrate building blocks, assembly strategies, and protecting-group strategies. Next described is the state of the art in the synthesis of each type of saponins, with an emphasis on those representative saponins having sophisticated structures and potent biological activities.

Betulinic Acid and its Derivatives as Potential Antitumor Agents

Betulinic acid (BA) is a lupane-type pentacyclic triterpene, distributed ubiquitously throughout the plant kingdom. BA and its derivatives demonstrate multiple bioactivities, particularly an antitumor effect. This review critically describes the recent research on isolation, synthesis, and derivatization of BA and its natural analogs betulin and 23-hydroxybetulinic acid. The subsequent part of the review focuses on the current knowledge of antitumor properties, combination treatments, and pharmacological mechanisms of these compounds. A 3D-QSAR analysis of 62 BA derivatives against human ovarian cancer A2780 is also included to provide information concerning the structure-cytotoxicity relationships of these compounds.

Recent Advances in Transition Metal-Catalyzed Glycosylation

Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of α- and β-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation.

Saponins as cytotoxic agents: a review

Saponins are natural glycosides which possess a wide range of pharmacological properties including cytotoxic activity. In this review, the recent studies (2005-2009) concerning the cytotoxic activity of saponins have been summarized. The correlations between the structure and the cytotoxicity of both steroid and triterpenoid saponins have been described as well as the most common mechanisms of action.

Specific targeting of Wnt/β-catenin signaling in human melanoma cells by a dietary triterpene lupeol

Wingless (Wnt) signaling pathway regulates a variety of cellular processes including proliferation, differentiation, survival, apoptosis and cell motility. Aberrant activation of Wnt/β-catenin pathway has been observed in approximately one-third of melanomas and this subset has very poor prognosis suggesting that targeting Wnt signaling could be a promising strategy against this subtype. Mel 928 and Mel 1241 melanoma cells representative of cells with constitutive activation of Wnt/β-catenin signaling pathway and Mel 1011 representative of cells that lack this pathway were treated with a dietary triterpene lupeol and its effects on growth, proliferation, β-catenin transcriptional activity and Wnt target genes were determined both in vitro and in vivo. Lupeol treatment to Mel 928 and Mel 1241 but not Mel 1011 cells resulted in a dose-dependent (i) decrease in cell viability, (ii) induction of apoptosis, (iii) decrease in colonogenic potential, (iv) decrease in β-catenin transcriptional activity and (v) decrease in the expression of Wnt target genes. Most importantly, lupeol restricted the translocation of β-catenin from the cytoplasm to the nucleus. Lupeol also decreased the growth of Mel 928 but not Mel 1011-derived tumors implanted in the athymic nude mice. The decrease in Mel 928-derived tumor growth was associated with a decrease in the expression of Wnt target genes c-myc, cyclin D1, proliferation markers proliferating cell nuclear antigen and Ki-67 and invasion marker osteopontin. We suggest that lupeol alone or as an adjuvant to current therapies could be developed as an agent for the management of human melanomas harboring constitutive Wnt/β-catenin signaling.

Triterpenoids as new promising anticancer drugs

Triterpenoids are structurally diverse organic compounds, characterized by a basic backbone modified in multiple ways, allowing the formation of more than 20 000 naturally occurring triterpenoid varieties. Several triterpenoids, including ursolic and oleanolic acid, betulinic acid, celastrol, pristimerin, lupeol, and avicins possess antitumor and anti-inflammatory properties. To improve antitumor activity, some synthetic triterpenoid derivatives have been synthesized, including cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic (CDDO), its methyl ester (CDDO-Me), and imidazolide (CDDO-Im) derivatives. Of these, CDDO, CDDO-Me, and betulinic acid have shown promising antitumor activities and are presently under evaluation in phase I studies. Triterpenoids are highly multifunctional and the antitumor activity of these compounds is measured by their ability to block nuclear factor-kappaB activation, induce apoptosis, inhibit signal transducer, and activate transcription and angiogenesis.

Lupeol, a novel anti-inflammatory and anti-cancer dietary triterpene

In the Western world, an average of 250 mg per day of triterpenes (member of phytosterol family), largely derived from vegetable oils, cereals, fruits and vegetables is consumed by humans. During the last decade, there has been an unprecedented escalation of interest in triterpenes due to their cholesterol-lowering properties and evidence of this phenomenon include at least 25 clinical studies, 20 patents and at least 10 major commercially triterpene-based products currently being sold all around the world. Lupeol a triterpene (also known as Fagarsterol) found in white cabbage, green pepper, strawberry, olive, mangoes and grapes was reported to possess beneficial effects as a therapeutic and preventive agent for a range of disorders. Last 15 years have seen tremendous efforts by researchers worldwide to develop this wonderful molecule for its clinical use for the treatment of variety of disorders. These studies also provide insight into the mechanism of action of Lupeol and suggest that it is a multi-target agent with immense anti-inflammatory potential targeting key molecular pathways which involve nuclear factor kappa B (NFkappaB), cFLIP, Fas, Kras, phosphatidylinositol-3-kinase (PI3K)/Akt and Wnt/beta-catenin in a variety of cells. It is noteworthy that Lupeol at its effective therapeutic doses exhibit no toxicity to normal cells and tissues. This mini review provides detailed account of preclinical studies conducted to determine the utility of Lupeol as a therapeutic and chemopreventive agent for the treatment of inflammation and cancer.