Synthesis and induction of apoptosis signaling pathway of ent-kaurane derivatives

Anticancer diterpenes of African natural products: Mechanistic pathways and preclinical developments

BACKGROUND

The African continent is home to five biodiversity hotspots, boasting an immense wealth of medicinal flora, fungi and marine life. Diterpenes extracted from such natural products have compelling cytotoxic activities that warrant further exploration for the drug market, particularly in cancer therapy, where mortality rates remain elevated worldwide.

PURPOSE

To demonstrate the potential of African natural products on the global stage for cancer therapy development and provide an in-depth analysis of the current literature on the activity of cancer cytotoxic diterpenes from African natural sources (to our knowledge, the first of its kind); not only to reveal the most promising candidates for clinical development, but to demonstrate the importance of preserving the threatened ecosystems of Africa.

METHODS

A comprehensive search by means of the PRISMA strategy was conducted using electronic databases, namely Web of Science, PubMed, Google Scholar and ScienceDirect. The search terms employed were 'diterpene & mechanism & cancer' and 'diterpene & clinical & cancer'. The selection process involved assessing titles in English, Portuguese and Spanish, adhering to predefined eligibility criteria. The timeframe for inclusion spanned from 2010 to 2023, resulting in 218 relevant papers. Chemical structures were visualized using ChemDraw 21.0, PubChem was utilized to search for CID numbers.

RESULTS

Despite being one of the richest biodiverse zones in the world, African natural products are proportionally underreported compared to Asian countries or otherwise. The diterpenes andrographolide (Andrographis paniculata), forskolin (Coleus forskohlii), ent-kauranes from Isodon spp., euphosorophane A (Euphorbia sororia), cafestol & kahweol (Coffea spp.), macrocylic jolkinol D derivatives (Euphorbia piscatoria) and cyathane erinacine A (Hericium erinaceus) illustrated the most encouraging data for further cancer therapy exploration and development.

CONCLUSIONS

Diterpenes from African natural products have the potential to be economically significant active pharmaceutical and medicinal ingredients, specifically focussed on anticancer therapeutics.

Synthesis and Antibacterial Activity of Polyalthic Acid Analogs

Polyalthic acid (PA) is a diterpene found in copaiba oil. As a continuation of our work with PA, we synthesized PA analogs and investigated their antibacterial effects on preformed biofilms of Staphylococcus epidermidis and determined the minimal inhibitory concentration (MIC) of the best analogs against planktonic bacterial cells. There was no difference in activity between the amides 2a and 2b and their corresponding amines 3a and 3b regarding their ability to eradicate biofilm. PA analogs 2a and 3a were able to significantly eradicate the preformed biofilm of S. epidermidis and were active against all the Gram-positive bacteria tested (Enterococcus faecalis, Enterococcus faecium, S. epidermidis, Staphylococcus aureus), with different MIC depending on the microorganism. Therefore, PA analogs 2a and 3a are of interest for further in vitro and in vivo testing to develop formulations for antibiotic drugs against Gram-positive bacteria.

Grandiflorenic acid from Wedelia trilobata plant induces apoptosis and autophagy cell death in breast adenocarcinoma (MCF7), lung carcinoma (A549), and hepatocellular carcinoma (HuH7.5) cells lines

INTRODUCTION

Wedelia trilobata (Sphagneticola trilobata) is a plant used in this popular medicine for treating infectious, sores and swellings in some rural communities, and their extract has antioxidant, anti-inflammatory, antitumor and hepatoprotective effect. Cancer is a molecularly heterogeneous disease caused by environmental and, genetic factors, among others. Since the complexity of the disease leads to low response rates to the different treatments used, it is necessary to find alternative drugs aimed at its control. The objective of our study was to assess whether grandiflorenic acid (GFA) has antitumor activity on breast (MCF7), liver (HuH7.5), and lung (A549) tumor cell lines.

METHODS

We used cell integrity assessment methods to assess whether (GFA) would be cytotoxic for tumor cell lines at doses ranging from and the pattern of death involved in this effect.

RESULTS

Treatment using GFA significantly inhibited cell proliferation in the three studied cells, followed by a decrease in cell size. The assessment of the death mechanisms showed the treatments increased the production of reactive oxygen species, caused exposure of phosphatidylserine, depolarization of the mitochondrial membrane, and, decrease plasma membrane integrity, indicating mechanisms related to apoptosis. Besides, we found the formation of autophagy vacuoles in our tests.

CONCLUSION

Finally, our study found the effect of GFA on breast (MCF7), lung (A549), and liver (HuH7.5) tumor cell lines induce cytotoxicity and patterns of death associated with apoptosis and autophagy, and oxidative stress generation plays a role in these two pathways of cell death. Thus, this study revealed GFA exhibits anti-cancer activity in vitro and could help future studies to improve strategies for cancer treatment with involving natural compounds.

Selective cytotoxicity of ent-kaurene diterpenoids isolated from Baccharis lateralis and Baccharis retusa (Asteraceae)

This study presents the cytotoxic activity evaluation of the natural diterpenes ent-kaurenoic acid (1) and its 15β-hydroxy (2), 15β-senecioyloxy (3), and 15β-tiglinoyloxy (4) derivatives, isolated from Brazilian native plants, Baccharis retusa and B. lateralis (Asteraceae). Using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay, it was observed that compound 1 displayed in vitro activity towards the aggressive MDA-MB-231 adenocarcinoma cell line and reduced toxicity against MCF-10A nontumorigenic epithelial cells, indicating expressive selectivity. On the contrary, compounds 2-4 exhibited reduced toxicity and selectivity in both tested cell lines. Based on the chemical structures of compounds 1-4, it is suggested that the presence of additional functional groups at the C-15 position-a hydroxyl group in compound 2 and isomeric isoprene units in compounds 3 and 4-might be responsible for the reduction in the potential/selectivity. In silico studies show, for compounds 1-4, good predictions regarding bioavailability and ADME (absorption, distribution, metabolism, and excretion) properties as well as no alerts for PAINS (pan-assay structures interference). In conclusion, ent-kaurenoic acid (1), a common diterpenoid isolated in high amounts from different plants belonging to the Baccharis genus, has been shown to be a promising cytotoxic agent against an aggressive adenocarcinoma cell line (MDA-MB-23) and, if well exploited, could be used as a scaffold in the development of molecular prototypes for the treatment of breast cancer.

Anticancer Activity of Continentalic Acid in B-Cell Lymphoma

Aralia continentalis has been used in Korea as a folk remedy for arthralgia, rheumatism, and inflammation. However, its anti-lymphoma effect remains uncharacterized. Here, we demonstrate that A. continentalis extract and its three diterpenes efficiently kill B-lymphoma cells. Our in vitro and in vivo results suggest that the cytotoxic activities of continentalic acid, a major diterpene from A. continentalis extract, are specific towards cancer cells while leaving normal murine cells and tissues unharmed. Mechanistically, continentalic acid represses the expression of pro-survival Bcl-2 family members, such as Mcl-1 and Bcl-xL. It dissociates the mitochondrial membrane potential, leading to the stimulation of effector caspase 3/7 activities and, ultimately, cell death. Intriguingly, this agent therapeutically synergizes with roflumilast, a pan-PDE4 inhibitor that has been successfully repurposed for the treatment of aggressive B-cell malignancies in recent clinical tests. Our findings unveiled that A. continentalis extract and three of the plant’s diterpenes exhibit anti-cancer activities. We also demonstrate the synergistic inhibitory effect of continentalic acid on the survival of B-lymphoma cells when combined with roflumilast. Taken in conjunction, continentalic acid may hold significant potential for the treatment of B-cell lymphoma.

Grandiflorenic acid isolated from Sphagneticola trilobata against Trypanosoma cruzi: Toxicity, mechanisms of action and immunomodulation

Grandiflorenic acid (GFA) is one of the main kaurane diterpenes found in different parts of Sphagneticola trilobata. It has several biological activities, especially antiprotozoal action. In turn, Chagas disease is a complex systemic disease caused by the protozoan Trypanosoma cruzi, and the drugs available to treat it involve significant side effects and impose an urgent need to search for therapeutic alternatives. In this context, our goal was to determine the effect of GFA on trypomastigote and intracellular amastigote forms. Our results showed that GFA treatment led to significantly less viability of trypomastigote forms, with morphological and ultrastructural changes in the parasites treated with IC₅₀ of GFA (24.60 nM), and larger levels of reactive oxygen species (ROS), mitochondrial depolarization, lipid droplets accumulation, presence of autophagic vacuoles, phosphatidylserine exposure, and plasma membrane damage. In addition, the GFA treatment was able to reduce the percentage of infected cells and the number of amastigotes per macrophage (J774A.1) without showing cytotoxicity in mammalian cell lines (J774A.1, LLCMK₂, THP-1, AMJ2-C11), in addition to increasing TNF-α and reducing IL-6 levels in infected macrophages. In conclusion, the GFA treatment exerted influence on trypomastigote forms through an apoptosis-like mechanism and by eliminating intracellular parasites via TNF-α/ROS pathway, without generating cellular cytotoxicity.

Stingless Bee Propolis: New Insights for Anticancer Drugs

Natural products are important sources of biomolecules possessing antitumor activity and can be used as anticancer drug prototypes. The rich biodiversity of tropical and subtropical regions of the world provides considerable bioprospecting potential, including the potential of propolis produced by stingless bee species. Investigations of the potential of these products are extremely important, not only for providing a scientific basis for their use as adjuvants for existing drug therapies but also as a source of new and potent anticancer drugs. In this context, this article organizes the main studies describing the anticancer potential of propolis from different species of stingless bees with an emphasis on the chemical compounds, mechanisms of action, and cell death profiles. These mechanisms include apoptotic events; modulation of BAX, BAD, BCL2-L1 (BCL-2 like 1), and BCL-2; depolarization of the mitochondrial membrane; increased caspase-3 activity; poly (ADP-ribose) polymerase (PARP) cleavage; and cell death induction by necroptosis via receptor interacting protein kinase 1 (RIPK1) activation. Additionally, the correlation between compounds with antioxidant and anti-inflammatory potential is demonstrated that help in the prevention of cancer development. In summary, we highlight the important antitumor potential of propolis from stingless bees, but further preclinical and clinical trials are needed to explore the selectivity, efficacy, and safety of propolis.

Patterns of Cell Death Induced by Thiohydantoins in Human MCF-7 Breast Cancer Cells

BACKGROUND

Conventional therapies for breast cancer is still a challenge due to use of cytotoxic drugs not highly effective with major adverse effects. Thiohydantoins, are biologically active heterocyclic compounds reported by several biological activities, including anticarcinogenic properties, i.e., this work aimed to assess the use of thiohydantoin as a potential antitumor agent against MCF-7 breast cancer cells.

METHODS

MTT and neutral red assays were used to assess the possible cytotoxic activity of compounds against MCF-7 cells. Cell volume measurement and analysis were performed by flow cytometry, fluorescence analysis was carried out to determine patterns of cell death induced by thiohydantoins.

RESULTS

The treatment with micromolar doses of thiohydantoins promoted a decrease in the viability of MCF-7 breast tumor cells. Also were observed the increase in ROS and NO production, reduction in cell volume, loss of membrane integrity, mitochondrial depolarization, and increased fluorescence for annexin V and caspase-3. These findings indicate cell death by apoptosis and increased formation of autophagic vacuoles and stopping the cell cycle in the G1/ G0 phase.

CONCLUSIONS

Our results indicate that thiohydantoins are cytotoxic to breast tumor cells, and this effect is linked to the increase in ROS production. This phenomenon changes tumorigenic pathways, that lead to a halt of the cell cycle in G1/G0, an important checkpoint for DNA errors, which may have altered the process by which cells produce energy, causing a decrease in mitochondrial viability and thus leading to the apoptotic process. Furthermore, the results indicate increased autophagy, a vital process linked to a decrease in lysosomal viability and considered as a cell death and tumor suppression mechanism.

Preparation of Antiproliferative Terpene-Alkaloid Hybrids by Free Radical-Mediated Modification of ent-Kauranic Derivatives

A convenient strategy for molecular editing of available ent-kauranic natural scaffolds has been developed based on radical mediated C-C bond formation. Iodine atom transfer radical addition (ATRA) followed by rapid ionic elimination and radical azidoalkylation were investigated. Both reactions involve radical addition to the exo-methylenic double bond of the parent substrate. Easy transformations of the obtained adducts lead to extended diterpenes of broad structural diversity and artificial diterpene-alkaloid hybrids possessing lactam and pyrrolidine pharmacophores. The cytotoxicity of selected diterpenic derivatives was examined by in vitro testing on several tumor cell lines. The terpene-alkaloid hybrids containing N-heterocycles with unprecedented spiro-junction have shown relevant cytotoxicity and promising selectivity indexes. These results represent a solid basis for following research on the synthesis of such derivatives based on available natural product templates.

4t-CHQ a Spiro-Quinazolinone Benzenesulfonamide Derivative Induces G0/G1 Cell Cycle arrest and Triggers Apoptosis Through Down-Regulation of Survivin and Bcl2 in the Leukemia Stem-Like KG1-a Cells

OBJECTIVE

Many experiments have revealed the anti-tumor activity of spiro-quinazolinone derivatives on different cell types. Exposing KG1-a cells to N-(4- tert- butyl- 4'- oxo- 1'H- spiro [cyclohexane- 1, 2'- quinazoline]- 3'(4'H)- yl)- 4- methyl benzenesulfonamide (4t-CHQ), as an active sub-component of spiroquinazolinone benzenesulfonamides, the experiment investigated the possible mechanisms that manifest the role of 4t-CHQ in leukemic KG1-a progenitor cells. Mechanistically, the inhibitory effects of 4t-CHQ on KG1-a cells emerge from its modulating function on the expression of Bax/Bcl2 and survinin proteins.

METHODS

Cell viability was assessed using MTT assay. The IC₅₀ value of cells was calculated to be 131.3μM, after 72h-incubation with 4t-CHQ, ranging from 10 to 150μM. Apoptotic changes were studied using Acridine Orange/Ethidium Bromide (AO/EB) staining. DNA fragmentation was analyzed by agarose gel electrophoresis method. To evaluate the percentage of apoptotic cells and cell growth dynamic apoptotic features, we performed Annexin V/PI double staining assay and cell cycle analysis by flow cytometry.

RESULTS

According to the results, apoptosis induction was initiated by 4t-CHQ in the KG1-a cells (at IC₅₀ value). Cell dynamic analysis revealed that the cell cycle at the G1 phase was arrested after treatment with 4t- CHQ. Western blotting analysis showed enhancement in the expression ratio of Bax/Bcl-2, while the expression of survinin protein decreased in a time-dependent manner in the KG1-a cells. According to the docking simulation data, the effectiveness of 4t-CHQ on KG1-a cells commenced by its reactions with the functional domain of BH3 and Bcl2 and BIR domains of survivin protein.

CONCLUSION

These results demonstrate a remarkable role of 4t- CHQ in arresting leukemia KG1-a stem cells both by induction of apoptosis as well as by down-regulating survivin and Bcl2 proteins.

An ent-Kaurane Diterpenoid Isolated from Rabdosia excisa Suppresses Bcr-Abl Protein Expression in Vitro and in Vivo and Induces Apoptosis of CML Cells

Chronic myelogenous leukemia (CML) is a disease of the blood stem cells that features the oncoprotein Bcr-Abl. Tyrosine kinase inhibitors (TKIs) are used to treat CML patients, but these have limited efficacy due to the emergence of resistance via genetic mutation. Kamebakaurin is an ent-kaurane diterpenoid that has been isolated from Rabdosia excisa (Maxim.) H.Hara. Herein, we investigate the potential of kamebakaurin as a chemotherapy reagent for the treatment of CML. We conducted in vitro and in vivo biological experiments and found that kamebakaurin potently inhibits cell proliferation, mainly by enhancing cell apoptosis and down-regulating Bcr-Abl protein levels. In addition, kamebakaurin was found to inhibit tumor growth and has no side effects on five internal organs for in vivo experiment. These results suggest that kamebakaurin is a potential anticancer agent and is a key compound for further investigations.

Non-volatile natural products in plant glandular trichomes: chemistry, biological activities and biosynthesis

The investigation methods, chemistry, bioactivities, and biosynthesis of non-volatile natural products involving 489 compounds in plant glandular trichomes are reviewed.

In vitro cytotoxicity and structure-activity relationship approaches of ent-kaurenoic acid derivatives against human breast carcinoma cell line

In this study, ent-kaurenoic acid derivatives were obtained by microbial transformation methodologies and tested against breast cancer cell lines (MCF-7). A multivariate quantitative-structure activity relationship (QSAR) analysis was performed taking into account both microbial transformation derivatives and other analogues previously reported in literature to give some insight into the main features behind the cytotoxic activity displayed by kaurane-type diterpenes against MCF-7 cells. The partial least square regression (PLS) method was employed in the training set and the best PLS model was built with a factor describing 69.92% of variance and three descriptors (logP, ε_HOMO and ε_HOMO-1) selected by the Ordered Predictors Selection (OPS) algorithm. The QSAR model provided reasonable regression (Q² = 0.64, R² = 0.72, SEC = 0.29 and SEV = 0.33). The model was validated by leave-N-out cross-validation, y-randomization and external validation (R²_pred = 0.89 and SEP = 0.27). The selected descriptors indicated that the activity was mainly related to electronic parameters (HOMO and HOMO-1 molecular orbital energies), as well as to logP. These findings suggest that higher activity values are directly related with both higher logP and frontier orbital energy values. The positive relationship between these orbitals and the activity suggests that the ent-kaurenoic acid analogues interaction with the target involves charge displacement, which is entirely consistent with the literature. Based on these findings, three compounds were proposed and one of them was synthesized and tested. The experimental result confirmed the activity predicted by the model.

Ent-kaurane diterpenoids from the cherries of Coffea arabica

Four new rearranged ent-kaurane diterpenoids named as caffruenol A (1), caffruenol B (2), caffruolide A (3), caffruolide B (4), along with eleven known analogues (5-15) were isolated from the cherries of Coffea arabica. The structures of new compounds were elucidated by extensive spectroscopic analysis and X-ray crystallography. Coffruenols A and B (1 and 2) possessed an ent-4(18)-kaurene framework and might play an important role on the biosynthesis of the rearranged diterpenes that occurred in C. arabica. Moreover, inhibitory effects of compounds 1-4 on nitric oxide (NO) production in lipopolysaccharide-activited RAW 264.7 macrophages were evaluated.

Grandiflorenic acid promotes death of promastigotes via apoptosis-like mechanism and affects amastigotes by increasing total iron bound capacity

BACKGROUND

American tegumentary leishmaniasis (ATL) is a zoonotic disease caused by protozoa of the genus Leishmania. The high toxicity, high costs and resistance of some strains to current drugs has prompted the search for therapeutic alternatives for the management of this disease. Sphagneticola trilobata is a plant that has diterpenes as main constituents, including grandiflorenic acid (GFA) that has antiinflammatory, antiprotozoal, antibacterial and antinociceptive activity.

PURPOSE

The aim of our study was to determine the effect of GFA on both the promastigotes and the amastigotes of Leishmania amazonensis.

METHODS

Isolation by chromatographic methods and chemical identification of GFA, then evaluation of the in vitro leishmanicidal activity of this compound against Leishmania amazonensis promastigotes and L. amazonensis infected peritoneal Balb/c macrophages, as well its action and microbicide mechanisms.

RESULTS

GFA treatment significantly inhibited the proliferation of promastigotes. This antiproliferative effect was accompanied by morphological changes in the parasite with 25 nM GFA. Afterwards, we investigated the mechanisms involved in the death of the protozoan; there was an increase in the production of reactive oxygen species (ROS), phosphatidylserine exposure, permeabilization of the plasma membrane and decreased mitochondrial depolarization. In addition, we observed that the treatment caused a reduction in the percentage of infected cells and the number of amastigotes per macrophage, without showing cytotoxicity in low doses to peritoneal macrophages and sheep erythrocytes. GFA increased IL-10 and total iron bound to transferrin in infected macrophages. Our results showed that GFA treatment acts on promastigote forms through an apoptosis-like mechanism and on intracellular amastigote forms, dependent of regulatory cytokine IL-10 modulation with increase in total iron bound to transferrin.

CONCLUSION

GFA showed in vitro antileishmanial activity on L. amazonensis promastigotes forms and on L. amazonensis-infected macrophages.

ent-Kaurene Glycosides from Ageratina cylindrica

The aqueous extract of the leaves of Ageratina cylindrica afforded six new ent-kaurenoic acid glycosides together with the known diterpenoid paniculoside V, the flavonoid astragalin, chlorogenic acid, and L-chiro-inositol. The structures were elucidated mainly by NMR and MS methods, and the absolute configuration was established by vibrational circular dichroism spectroscopy. The new compounds showed moderate antiprotozoal activity against Entamoeba histolytica and Giardia lamblia trophozoites.

Synthesis and biological evaluation of polyalthic acid derivatives for the treatment of neglected diseases

Polyalthic acid is a naturally occurring diterpene found in copaiba oil, one of the most popular natural medicines in the Amazon. Based on the reported antileishmanial activity of copaiba oil, a series of amides and diols derivatives of polyalthic acid were synthesized and tested against Leishmania donovani and Trypanosoma brucei. Polyalthic acid was active in both assays with IC50 ranging from 3.87 to 8.68 μg/mL. The compound with best antileishmanial activity was 2 h (IC50=3.84 μg/mL) and compound 2c showed the best antitrypanosomal activity with an IC50 of 2.54 μg/mL.

New Non-Toxic Semi-Synthetic Derivatives from Natural Diterpenes Displaying Anti-Tuberculosis Activity

We report herein the synthesis of six diterpene derivatives, three of which are new, generated through known organic chemistry reactions that allowed structural modification of the existing natural products kaurenoic acid (1) and copalic acid (2). The new compounds were fully characterized using high resolution mass spectrometry, infrared spectroscopy, ¹H- and ¹³C-NMR experiments. We also report the evaluation of the anti-tuberculosis potential for all compounds, which showed some promising results for Micobacterium tuberculosis inhibition. Moreover, the toxicity for each of the most active compounds was also assessed.

Theoretical Research into Anticancer Activity of Diterpenes Isolated from the Paraiban Flora

Many studies of the scientific literature discuss the anticancer activity of diterpenes inhibiting the Akt/IKK/NF-κB pro-survival signaling cascade, mainly by the activation of serine/threonine phosphatase PP2A. The aim of this work was to evaluate and compare the anticancer potential of three atisane, three kaurane and three trachylobane diterpenes extracted from the roots of Xylopia langsdorffiana. Thus, we investigated the reactivity (H-LGAP parameter), HOMO atmosphere favorable to neutralize the radical reactivity, and the docking of compounds with PP2A. With all approaches, this theoretical study showed that atisane diterpenes have favorable characteristics for antitumor activity, like electron donating ability and greater hydrophilic interactions with the enzyme, by inhibition of Akt/IKK/NF-κB, and activation of PP2A.

Specific 12α-hydroxylation of grandiflorenic acid by permeabilised fungus Fusarium graminearum

Biotransformation of grandiflorenic acid by permeabilised fungus Fusarium graminearum to yield its hydroxylation derivative, 12α-hydroxygrandiflorenic acid, was studied. The biotransformed product was isolated by column chromatography and its structure was determined by mass spectrum and nuclear magnetic resonance analysis. Grandiflorenic acid was efficiently metabolised by the fungus. After 72 h, the substrate was almost completely converted into the product.

meta-Chloroperbenzoic acid (mCPBA): a versatile reagent in organic synthesis

This review aims to collect and discuss the synthetic applications of meta-chloroperbenzoic acid (mCPBA) over the past few decades.

Synthesis, cytotoxicity and antiplasmodial activity of novel ent-kaurane derivatives

This paper reports on the syntheses and spectrometric characterisation of eleven novel ent-kaurane diterpenoids, including a complete set of (1)H, (13)C NMR and crystallographic data for two novel ent-kaurane diepoxides. Moreover, the antineoplastic cytotoxicity for kaurenoic acid and the majority of ent-kaurane derivatives were assessed in vitro against a panel of fourteen cancer cell lines, of which allylic alcohols were shown to be the most active compounds. The good in vitro antimalarial activity and the higher selectivity index values observed for some ent-kaurane epoxides against the chloroquine-resistant W2 clone of Plasmodium falciparum indicate that this class of natural products may provide new hits for the development of antimalarial drugs.