An antiproliferative norditerpene dilactone, Nagilactone C, from Podocarpus neriifolius

A comprehensive review on the medicinal usage of Podocarpus species: Phytochemistry and pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Plants of the Podocarpus species belong to the Podocarpaceae family and are largely distributed in the southern hemisphere. Beside the commercially and ecologically valuable, plants of the Podocarpus species are also used in traditional medicines in some countries for treating asthma, fever, venereal diseases, eye diseases, etc. AIM OF THE STUDY: In recent decades, the identities and pharmacological activities of phytochemicals extracted from Podocarpus plants have been widely studied. However, there have been no comprehensive and systematic reviews. This article aims to systematically review the latest research on the putative mechanisms underlying pharmacological actions of phytochemicals from the Podocarpus species, as well as to lay a foundation for promoting the development of plant resources from this genus, further drug research, and product development.

MATERIALS AND METHODS

A comprehensive search of PubMed, Google Scholar, Web of Science, Elsevier and CNKI databases was conducted using the keywords "Podocarpus", "traditional usage", "phytochemistry", "pharmacology", "nagilactone", etc. Related papers published among July 1964 to February 2023 were collected to summarize the research progress. All plant names were determined through the "The Plant List" (http://www.theplantlist.org/).

RESULTS

To date, 262 chemical constituents have been isolated and identified from 26 Podocarpus plants; among these, norditerpene bilactone is the main pharmacologically active component. Norditerpene bilactones are reported to have anti-cancer, anti-inflammatory, antioxidant, antibacterial, anti-tyrosinase, neuroprotective, anti-plasmodial, anti-mutagenic, and anti-atherosclerotic properties as well as other pharmacological activities, which support its traditional uses.

CONCLUSION

Extensive studies on phytochemistry and pharmacology of Podocarpus species lead to discovery of a series of hopeful leading compounds with unique chemical structure, especially the nor- and bis-norditerpenoid dilactones with four isoprene units. These compounds have been proved to possess various pharmacological activities. This review will provide a reference for further research and promote the idea of combining modern research with traditional medicinal applications of Podocarpus plants.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

Involvement of a Multidrug Efflux Pump and Alterations in Cell Surface Structure in the Synergistic Antifungal Activity of Nagilactone E and Anethole against Budding Yeast Saccharomyces cerevisiae

Nagilactone E, an antifungal agent derived from the root bark of Podocarpus nagi, inhibits 1,3-β glucan synthesis; however, its inhibitory activity is weak. Anethole, the principal component of anise oil, enhances the antifungal activity of nagilactone E. We aimed to determine the combinatorial effect and underlying mechanisms of action of nagilactone E and anethole against the budding yeast Saccharomyces cerevisiae. Analyses using gene-deficient strains showed that the multidrug efflux pump PDR5 is associated with nagilactone E resistance; its transcription was gradually restricted in cells treated with the drug combination for a prolonged duration but not in nagilactone-E-treated cells. Green-fluorescent-protein-tagged Pdr5p was intensively expressed and localized on the plasma membrane of nagilactone-E-treated cells but not in drug-combination-treated cells. Quick-freeze deep-etch electron microscopy revealed the smoothening of intertwined fiber structures on the cell surface of drug-combination-treated cells and spheroplasts, indicating a decline in cell wall components and loss of cell wall strength. Anethole enhanced the antifungal activity of nagilactone E by enabling its retention within cells, thereby accelerating cell wall damage. The combination of nagilactone E and anethole can be employed in clinical settings as an antifungal, as well as a food preservative to restrict food spoilage.

Anticancer Activities and Mechanism of Action of Nagilactones, a Group of Terpenoid Lactones Isolated from Podocarpus Species

Nagilactones are tetracyclic natural products isolated from various Podocarpus species. These lactone-based compounds display a range of pharmacological effects, including antifungal, anti-atherosclerosis, anti-inflammatory and anticancer activities reviewed here. The most active derivatives, such as nagilactones C, E and F, exhibit potent anticancer activities against different cancer cell lines and tumor models. A comprehensive analysis of their mechanism of action indicates that their anticancer activity mainly derives from three complementary action: (i) a drug-induced inhibition of cell proliferation coupled with a cell cycle perturbation and induction of apoptosis, (ii) a blockade of the epithelial to mesenchymal cell transition contributing to an inhibition of cancer cell migration and invasion and (iii) a capacity to modulate the PD-L1 immune checkpoint. Different molecular effectors have been implicated in the antitumor activity, chiefly the AP-1 pathway blocked upon activation of the JNK/c-Jun axis. Nag-C is a potent inhibitor of protein synthesis binding to eukaryotic ribosomes and inhibition of different protein kinases, such as RIOK2 and JAK2, has been postulated with Nag-E. The literature survey on nagilactones highlights the therapeutic potential of these little-known terpenoids. The mechanistic analysis also provides useful information for structurally related compounds (podolactones, oidiolactones, inumakilactones) isolated from Podocarpus plants.

Bioactivity-Guided Isolation of Totarane-Derived Diterpenes from Podocarpus neriifolius and Structure Revision of 3-Deoxy-2α-hydroxynagilactone E

Bioactivity-guided phytochemical investigation of Podocarpus neriifolius D. Don. (Podocarpaceae) has led to the isolation of one new (2) and three known (1, 3, and 4) B-type podolactones, along with three totarane-type diterpenes (5-7). Their structures were determined by interpretation of High Resolution ElectroSpray Ionization Mass Spectrometry (HRESIMS) and 1D and 2D NMR data, and comparison with the values reported in the literature. The structure of compound 1, previously identified as 3-deoxy-2α-hydroxynagilactone E (8), was revised as its 2β-epimer, which has been reported recently as a new compound. All of the isolates were evaluated for their antiproliferative activity against a panel of four human cancer cell lines, namely, ovarian (OVCAR3), breast (MDA-MB-231), colon (HT-29), and melanoma (MDA-MB-435), and compounds 1 and 3 were found to be cytotoxic with IC50 values in the low micromolar range for most of the cell lines used. The major compound, inumakilactone A (3), was further tested in vivo using the HT-29, MDA-MB-435, and OVCAR3 cells in a murine hollow fiber model, for the first time.

Effect of nagilactone E on cell morphology and glucan biosynthesis in budding yeast Saccharomyces cerevisiae

Nagilactones are norditerpene dilactones isolated from the root bark of Podocarpus nagi. Although nagilactone E has been reported to show antifungal activities, its activity is weaker than that of antifungals on the market. Nagilactone E enhances the antifungal activity of phenylpropanoids such as anethole and isosafrole against nonpathogenic Saccharomyces cerevisiae and pathogenic Candida albicans. However, the detailed mechanisms underlying the antifungal activity of nagilactone E itself have not yet been elucidated. Therefore, we investigated the antifungal mechanisms of nagilactone E using S. cerevisiae. Although nagilactone E induced lethality in vegetatively growing cells, it did not affect cell viability in non-growing cells. Nagilactone E-induced morphological changes in the cells, such as inhomogeneous thickness of the glucan layer and leakage of cytoplasm. Furthermore, a dose-dependent decrease in the amount of newly synthesized (1, 3)-β-glucan was detected in the membrane fractions of the yeast incubated with nagilactone E. These results suggest that nagilactone E exhibits an antifungal activity against S. cerevisiae by depending on cell wall fragility via the inhibition of (1, 3)-β-glucan biosynthesis. Additionally, we confirmed nagilactone E-induced morphological changes of a human pathogenic fungus Aspergillus fumigatus. Therefore, nagilactone E is a potential antifungal drug candidate with fewer adverse effects.

Downregulation of Cyclin B1 mediates nagilactone E-induced G2 phase cell cycle arrest in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) is one of the most common forms and leading causes of cancer-related mortality worldwide, and discovery of new effective drugs still remains imperative to improve the survival rate. Nagilactone E (NLE) is a natural product isolated from Podocarpus nagi seeds, which has been used as raw materials for edible oil and industrial oil extraction. This study aimed to investigate the anticancer potential of NLE against NSCLC A549 and NCI-H1975 cells. MTT assay revealed that NLE inhibited the proliferation of A549 and NCI-H1975 cells with IC₅₀s of 5.18 ± 0.49 and 3.57 ± 0.29 μM, respectively. NLE treatment inhibited clone formation in both cancer cell lines. Cell cycle analysis indicated that NLE treatment effectively induced G2 phase cell cycle arrest in A549 and NCI-H1975 cells. NLE downregulated the phosphorylation of cdc2 (Tyr15) and cdc25C (Ser216) as well as the expression level of the protein kinase Wee1 in concentration- and time-dependent manners. In addition, NLE treatment decreased the protein level of Cyclin B1 as well as its nuclear localization, which might decrease the activity of the Cyclin B1/cdc2 complex and induce G2 phase arrest. Long-term NLE treatment also induced caspase-dependent cell apoptosis, as evidenced by increase in Annexin V positive cells and the cleavage of PARP. To sum, NLE inhibited proliferation, induced G2 phase arrest, and triggered caspase-dependent apoptosis in NSCLC cells, suggesting it to be a potential leading compound for cancer treatment.

Two New Anti-Proliferative C18 -Norditerpenes from the Roots of Podocarpus macrophyllus

Activity-guided fractionation strategy was used to investigate chemical constituents from the roots of Podocarpus macrophyllus. Successfully, two new norditerpenes, 2β-hydroxymakilactone A (1) and 3β-hydroxymakilactone A (2), along with ten known analogues (3 - 12) were isolated. The structures of 1 and 2 were elucidated by spectroscopic analysis including 1D-, 2D-NMR, and HR-ESI-MS data. The previously reported structure of 2,3-dihydro-2α-hydroxypodolide was revised as 2,3-dihydro-2β-hydroxypodolide (3) by spectroscopic analysis, and was further confirmed by X-ray crystallographic analysis. Cytotoxic activities of all isolated compounds against five human solid tumour cell lines (AGS, HeLa, MDA-MB-231, HepG-2, and PANC-1) were evaluated. All of them exhibited anti-proliferative activities (IC₅₀  = 0.3 - 27 μm), except for 10. Compounds 1, 4, 5, 6, and 8 exhibited potent inhibitory activities with IC₅₀  < 1 μm against HeLa and AGS cells.

7α,8α-Epoxynagilactones and their glucosides from the twigs of Podocarpus nagi: Isolation, structures, and cytotoxic activities

A phytochemical investigation of twigs of Podocarpus nagi resulted in the identification of eight new type B nagilactones (1-8), all bearing a 7α,8α-epoxy-9(11)-enolide substructure, along with two known analogs (9-10). Their structures were determined on the basis of spectroscopic analysis, including HRESIMS, IR and NMR experiments, and X-ray crystallographic analysis. In vitro cytotoxic assay exhibited that compounds 1, 2, 9 and 10 could induce antiproliferation against three different types of human cancer cells while compounds 3 and 5 were inactive. Notably, the IC₅₀ value of compound 1 is 0.208μM for A431 human epidermoid carcinoma cells, reaching the same level as the positive control combretastatin A-4 (0.104μM). Furthermore, compound 1 performed a strong inhibition of cancer cells by triggering apoptosis and arresting the cell cycle at G₁ phase. These results unfold potential anticancer therapeutic applications of type B nagilactones.

Norditerpenoids and Dinorditerpenoids from the Seeds of Podocarpus nagi as Cytotoxic Agents and Autophagy Inducers

Nine new norditerpenoids and dinorditerpenoids, 2-oxonagilactone A (1), 7β-hydroxynagilactone D (2), nagilactones K and L (3 and 4), 3β-hydroxynagilactone L (5), 2β-hydroxynagilactone L (6), 3-epi-15-hydroxynagilactone D (7), 1α-chloro-2β,3β,15-trihydroxynagilactone L (8), and 15-hydroxynagilactone L (9), were isolated from the seeds of Podocarpus nagi, along with eight known analogues. The structures of the new compounds were established based on detailed NMR and HRESIMS analysis, as well as from their ECD spectra. The absolute configuration of the known compound 1-deoxy-2α-hydroxynagilactone A (16) was confirmed by single-crystal X-ray diffraction. All of the isolates were tested for their cytotoxic activities against cancer cells. The results indicated that compounds 4 and 6, as well as several known compounds, displayed cytotoxicity against A2780 and HEY cancer cells. Among the new compounds, 2β-hydroxynagilactone L (6) showed IC₅₀ values of less than 2.5 μM against the two cell lines used. Furthermore, compound 6 induced autophagic flux in A2780 cells, as evidenced by an enhanced expression level of the autophagy marker phosphatidylethanolamine-modified microtubule-associated protein light-chain 3 (LC3-II) and increased mRFP-GFP-LC3 puncta. Also, compound 6 activated the c-Jun N-terminal kinase (JNK) pathway, while pretreatment with the JNK inhibitor SP600125 decreased compound 6-induced autophagy.

Terpenoids and More Polar Compounds from the Male Cones of Wollemia nobilis

The analysis of metabolites contained in the male cones of Wollemia nobilis was investigated for the first time in this study. Several diterpenoids of chemosystematic relevance were recognized for the first time from the genus and/or from the Araucariaceae family, namely isocupressic acid (1), acetyl-isocupressic acid (2), methyl (E)-communate (3) and sandaracopimaric acid (4). All these terpenoids are also endowed with interesting biological activities and may play a primary role in the self defence toward herbivores. The presence of a new norlabdane (norlabda-8(16)-12-dien-14,17-diol) trivially named as wollemol (5) was also recognized. Norditerpenes are scarcely distributed in Plant Kingdom and in particular in Gymnosperms and this aspect was discussed. The structure of 5 was determined by extensive NMR analysis employing mono- and bidimensional experiments. The 7-4‴-dimethoxyagathisflavone (6), a biflavonoid already recognized in Araucariaceae and W. nobilis, was also isolated from male cones together with shikimic acid (7), a biogenetic precursor of polyphenolic compounds, besides carbohydrates such as glucose (8) and saccharose (9), and arginine (10) a quite common amino acid.

A new cyclopeptide and a new lignan from Podocarpus neriifolius

A new cyclopeptide, neriitide A (1) and a new lignan, neriilignan (2), along with six known compounds including two diterpenoids, three sesquiterpenoids and one sterol were isolated from the leaves of Podocarpus neriifolius. Their structures were elucidated by means of extensive spectroscopic analysis including HREIMS, 1D and 2D NMR techniques. This is the first report of cyclopeptide and lignan separated from this plant.

Mutagenicity, antimutagenicity and cytotoxicity evaluation of South African Podocarpus species

ETHNOPHARMACOLOGICAL RELEVANCE

Four species of Podocarpus are used in traditional medicine both in human and animal healthcare in South Africa. In vitro pharmacological screening of leaf and stem extracts of these species exhibited potent antimicrobial, anti-inflammatory, anti-tyrosinase, anthelmintic, acetylcholinesterase inhibitory and antioxidant activities.

AIM OF THE STUDY

To investigate the mutagenicity, antimutagenicity and cytotoxicity effects of leaf and stem extract of South African Podocarpus species.

MATERIAL AND METHODS

The mutagenicity and cytotoxic effects of extracts from four species of Podocarpus were tested using the Salmonella/microsome assay with and without metabolic activation, based on the plate-incorporation method and neutral red uptake (NRU) assay respectively. Five Salmonella typhimurium tester strains; TA98, TA100, TA102, TA1535 and TA1537 were used for mutagenicity testing. The relative cytotoxicity of the extracts was assessed by determining their NI(50) values (50% inhibition of NRU).

RESULTS

The extracts did not show any mutagenic effects against all the tester strains with or without metabolic activation. All extracts demonstrated a strong antimutagenic effect on the mutations induced by 4NQO, decreasing its mutagenic effect in a dose-dependent manner. Strong cytotoxic effects were exhibited by petroleum ether extracts as compared to 80% ethanol extracts. When HepG2 cells were in contact with plant extracts in an increasing concentration, slopes of NRU decreased (highest-lowest %) following a concentration-dependent pattern. For 80% ethanol extracts, the most toxic extract in terms of percentage viability was leaves of Podocarpus falcatus whereby at 0.2 mg/ml, the viability of the cells was 38.9%. Stem extract of Podocarpus latifolius was the most toxic among PE extracts, giving a percentage viability of 46.4 at 0.1 mg/ml.

CONCLUSION

Absence of mutagenicity does not indicate lack of toxicity, as was observed from these extracts. These findings will help in assessing the safety measures to be considered in the use of these species and also the need to determine the cytotoxic potential of these species against various forms of human cancer cells.

New constituent from Podocarpus macrophyllus var. macrophyllus shows anti-tyrosinase effect and regulates tyrosinase-related proteins and mRNA in human epidermal melanocytes

A new biflavonoid, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5), and five known compounds, (-)-catechin (1), quercetin (2), 2,3-dihydrosciadopitysin (3), sciadopitysin (4), and isoginkgetin (6), were isolated from Podocarpus macrophyllus var. macrophyllus (Podocarpaceae). These compounds were evaluated their ability to inhibit cellular tyrosinase activity and for their melanin inhibitory activity in human epidermal melanocytes (HEMn). In the melanin synthesis assay, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5) showed a potent anti-tyrosinase effect with IC(50)=0.098 mM in HEMn. It also significantly decreased both protein and mRNA levels of the tyrosinase-related protein-2 (TRP-2) by Western blot and quantitative real-time PCR (qRT-PCR) analysis. These findings suggest that the new compound, 2,3-dihydro-4',4'''-di-O-methylamentoflavone (5), is the most active component of P. macrophyllus var. macrophyllus in inhibiting pigmentation and that this inhibition is exerted through inhibition of transcription of the genes encoding TRP2.

Eukaryotic protein synthesis inhibitors identified by comparison of cytotoxicity profiles

The National Cancer Institute (NCI) Human Tumor Cell Line Anti-Cancer Drug Screen has evaluated the cytotoxicity profiles of a large number of synthetic compounds, natural products, and plant extracts on 60 different cell lines. The data for each compound/extract can be assessed for similarity of cytotoxicity pattern, relative to a given test compound, using an algorithm called COMPARE. In applying a chemical biology approach to better understand the mechanism of eukaryotic protein synthesis, we used these resources to search for novel inhibitors of translation. The cytotoxicity profiles of 31 known protein synthesis inhibitors were used to identify compounds from the NCI database with similar activity profiles. Using this approach, two natural products, phyllanthoside and nagilactone C, were identified and characterized as novel protein synthesis inhibitors. Both compounds are specific for the eukaryotic translation apparatus, function in vivo and in vitro, and interfere with translation elongation. Our results demonstrate the feasibility of utilizing cytotoxicity profiles to identify new inhibitors of translation.