Structural and bioactive studies of terpenes and cyclopeptides from the Genus Rubia

Diversity of cultivable endophytic fungi in two Rubia plants and their potential for production of anti-tumour Rubiaceae-type cyclopeptides

Rubia plants are one of the most important plant resources possessing significant commercial and medicinal values. Plant endophytes could benefit their host plants in different ways. Rubiaceae-type cyclopeptides (RAs), mainly isolated from Rubia plants, have attracted considerable attentions for their distinctive bicyclic structures and significant antitumor activities, but their contents in plants are low. The aim of this study is to investigate the diversity of endophytic fungi in Rubia plants and their potential for production of RAs. In this work, 143 endophytic fungi isolates were obtained from two Rubia plants. Phylogenetic analysis was performed based on the ITS rDNA sequences, and the isolates were classified into 29 genera. Among them, four endophytic fungal strains were found to produce anti-tumour RAs by LC-MS/MS analysis. This work successfully provides valuable knowledges of endophytic fungi microbiome in Rubia plants for agricultural and industrial applications, and exploits a new environmental-friendly resource of RAs.

Natural Compounds in Sex Hormone-Dependent Cancers: The Role of Triterpenes as Therapeutic Agents

Sex hormone-dependent cancers currently contribute to the high number of cancer-related deaths worldwide. The study and elucidation of the molecular mechanisms underlying the progression of these tumors was a double-edged sword, leading to the expansion and development of new treatment options, with the cost of triggering more aggressive, therapy resistant relapses. The interaction of androgen, estrogen and progesterone hormones with specific receptors (AR, ER, PR) has emerged as a key player in the development and progression of breast, ovarian, prostate and endometrium cancers. Sex hormone-dependent cancers share a common and rather unique carcinogenesis mechanism involving the active role of endogenous and exogenous sex hormones to maintain high mitotic rates and increased cell proliferation thus increasing the probability of aberrant gene occurrence and accumulation highly correlated with abnormal cell division and the occurrence of malignant phenotypes. Cancer related hormone therapy has evolved, currently being associated with the blockade of other signaling pathways often associated with carcinogenesis and tumor progression in cancers, with promising results. However, despite the established developments, there are still several shortcomings to be addressed. Triterpenes are natural occurring secondary metabolites biosynthesized by various pathways starting from squalene cyclization. Due to their versatile therapeutic potential, including the extensively researched antiproliferative effect, these compounds are most definitely a cornerstone in the research and development of new natural/semisynthetic anticancer therapies. The present work thoroughly describes the ongoing research related to the antitumor activity of triterpenes in sex hormone-dependent cancers. Also, the current review highlights both the biological activity of various triterpenoid compounds and their featured mechanisms of action correlated with important chemical structural features.

Zoopharmacology: A Way to Discover New Cancer Treatments

Zoopharmacognosy is the multidisciplinary approach of the self-medication behavior of many kinds of animals. Recent studies showed the presence of antitumoral secondary metabolites in some of the plants employed by animals and their use for the same therapeutic purposes in humans. Other related and sometimes confused term is Zootherapy, which consists on the employment of animal parts and/or their by-products such as toxins, venoms, etc., to treat different human ailments. Therefore, the aim of this work is to provide a brief insight for the use of Zoopharmacology (comprising Zoopharmacognosy and Zootherapy) as new paths to discover drugs studying animal behavior and/or using compounds derived from animals. This work is focused on the approaches related to cancer, in order to propose a new promising line of research to overcome multidrug resistance (MDR). This novel subject will encourage the use of new alternative prospective ways to find new medicines.

Rubia tinctorum root extracts: chemical profile and management of type II diabetes mellitus

The chemical and biological profiling of the root extracts of Rubia tinctorum was performed. The activities of different extracts were determined considering the antidiabetic effect against type II diabetes mellitus together with anti-obesity and hepatoprotective effects and lipid profile. The methanolic extract of Rubia tinctorum exhibited significant results in decreasing body weight, improving lipid profile, normalizing hyperglycaemia, insulin resistance, hyperinsulinemia. Additionally, it showed enhancement of liver tissue structure and function. The methanolic extract, being the most significant one, was subjected to LC-HRMS analysis to determine its chemical constituents. Finally, the chemical constituents were evaluated by molecular docking study that was carried out to identify the interaction of a panel of 45 compounds in silico and to correlate the structures to their anti-diabetic activity. Among the tested compounds, 1-hydroxy-2-hydroxymethyl anthra-quinone and naringenin-7-O-glucoside showed the most potent activity as α-amylase inhibitors.

The chemical and biological profiling of the root extracts of Rubia tinctorum was performed.

Accelerated degradation of cFLIPL and sensitization of the TRAIL DISC-mediated apoptotic cascade by pinoresinol, a lignan isolated from Rubia philippinensis

Plant-derived lignans have numerous biological effects including anti-tumor and anti-inflammatory activities. Screening of purified constituents of Rubia philippinensis from human glioblastoma cells resistant to TNF-related apoptosis-inducing ligand (TRAIL) has suggested that the lignan pinoresinol was a highly active TRAIL sensitizer. Here we show that treatment with nontoxic doses of pinoresinol in combination with TRAIL induced rapid apoptosis and caspase activation in many types of glioblastoma cells, but not in normal astrocytes. Analyses of apoptotic signaling events revealed that pinoresinol enhanced the formation of TRAIL-mediated death-inducing signaling complex (DISC) and complete processing of procaspase-8 within the DISC in glioblastoma cells, in which caspase-8 was inactivated. Mechanistically, pinoresinol downregulated the expression of cellular FLICE-inhibitory protein (cFLIP_L) and survivin through proteasome-mediated degradation, without affecting death receptors or downstream intracellular apoptosis-related proteins. Furthermore, the sensitization of TRAIL-mediated apoptosis by pinoresinol strictly depended on the expression level of cFLIP_L, which was regulated through de novo protein synthesis, rather than by NF-κB or p53 signaling. Taken together, our results indicate that pinoresinol facilitates DISC-mediated caspase-8 activation by targeting cFLIP_L in an early event in apoptotic signaling, which provides a potential therapeutic module for TRAIL-based chemotherapy.

Antithrombotic and Antiplatelet Activities of New Isohopane Triterpene From the Roots of Rubia akane

A new isohopane triterpenoid (1) and two known triterpenoids (2-3) were isolated from the roots of Rubia akane (Rubiaceae). The molecular formula C30H46O4 of 1 was determined by HRESIMS. Detailed NMR spectroscopic data analysis suggested that compound 1 is a new isohopane triterpenoid with a ketone moiety at C-16. Based on the key NOE correlations of H-3/H-5 and H-21/H3-28, compound 1 was determined as 3β-hydroxy-16-oxo-21β-isohop-22(29)-en-24-oic acid. The anticoagulant activities of new isohopane 1 were evaluated by monitoring activated partial thromboplastin time (aPTT), prothrombin time (PT), and the activities of thrombin (Factor IIa, FIIa) and activated factor X (FXa). The effects of 1 on expression of plasminogen activator inhibitor type 1 (PAI-1) and tissue-type plasminogen activator (t-PA) were evaluated in tumor necrosis factor-α activated human umbilical vein endothelial cells. Treatment with 1 (200 μM) resulted in the prolongation of aPTT and PT and the inhibition of relative thrombin (28%) and FXa (29%) activities. In addition, 1 inhibited thrombin-catalyzed fibrin polymerization (18% inhibition at 100 μM) and platelet aggregation (21.8% inhibition at 100 μM). Compound 1 also elicited anticoagulant effects in mice in a dose-dependent manner ranging from 18.8 to 94.0 μg/mouse. In addition, treatment with 1 resulted in significant reduction of the PAI-1 to t-PA ratio (25% decreased). Collectively, the new isohopane triterpenoid 1 possesses antithrombotic activities and offers a basis for the development of a new anticoagulant agent.

Colletopeptides A-D, Anti-inflammatory Cyclic Tridepsipeptides from the Plant Endophytic Fungus Colletotrichum sp. S8

Four new hybrid peptide-polyketide cyclic tridepsipeptides, colletopeptides A-D (1-4), were isolated and characterized from the endophytic fungus Colletotrichum sp. S8 derived from the stems of Rubia podantha with the guidance of LC-UV-MS detection. Their structures were elucidated by extensive spectroscopic analysis and X-ray crystallography. Compounds 1-4 are rare natural 12-membered cyclic tridepsipeptides containing a 3,5,11-trihydroxy-2-methyl dodecanoic acid unit in their structures. 1-4 inhibited lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages with the IC₅₀ values of 8.3, 38.7, 13.5, and 22.2 μM, respectively. 1 also inhibited the production of inflammatory factors IL-6 and TNF-α, and decreased the phosphorylation of NF-κB-associated proteins IκBα and p65.

Anthraquinone-type inhibitor of α-glucosidase enhances glucose uptake by activating an insulin-like signaling pathway in C2C12 myotubes

This study assesses the ability of anthraquinone derivative, 2-methyl-1,3,6-trihydroxy-9,10-anthraquinone (MTAQ) to decrease postprandial hyperglycemia or enhance glucose uptake and to elucidate the underlying molecular mechanism. We investigated α-glucosidase inhibition, glucose uptake, and translocation of glucose transporter 4 (GLUT4) in C2C12 myotubes. The data indicate that MTAQ strongly inhibited α-glucosidase activity in a concentration-dependent manner, with an IC₅₀ value of 6.49 ± 1.31 μM, and functioned as a reversible competitive inhibitor, with a dissociation constant of 41.88 μM. Moreover, MTAQ significantly augmented basal and insulin-stimulated glucose uptake as well as translocation of GLUT4 to the plasma membrane. It also stimulated the phosphorylation of insulin receptor β isoform, insulin receptor substrate-1,3-phosphoinositide-dependent protein kinase 1, and protein kinase B (AKT). A pretreatment with an AKT inhibitor, LY294002, attenuated the ability of MTAQ to activate an insulin-like signaling pathway and to enhance basal and insulin-stimulated glucose uptake and stimulate GLUT4 translocation to the plasma membrane. These findings reveal the fact that MTAQ may have potential for the development of new antidiabetic drugs to manage blood glucose levels.

Network pharmacology-based research on the active component and mechanism of the antihepatoma effect of Rubia cordifolia L

Rubia cordifolia L. is widely used in Asia and its antihepatoma effect has been proved by in vitro and in vivo experiments. However, there are few studies on its specific mechanism. In the present study, the network pharmacology method was used to construct the component/target/pathway molecular regulatory network for the antihepatoma effect of Rubia cordifolia L. to explore the effective components of Rubia cordifolia L. and its potential mechanism. The chemical components of Rubia cordifolia L. were identified through literature and databases, and the components were evaluated and screened by drug likeness and pharmacokinetic characteristics (ADMET). The targets of active components were predicted according to the reverse pharmacophore matching model. The hepatic carcinoma-related genes were found in databases, and antihepatoma-related gene targets were selected through comparison. The functions of target genes and related pathways were analyzed and screened using the Database for Annotation, Visualization and Integrated Discovery, and the component/target/pathways network of antihepatoma effect of Rubia cordifolia L. was constructed using Cytoscape software. Finally, 16 active compounds were screened from Rubia cordifolia L., and 39 gene targets, including AKT1, mitogen-activated protein kinase 1, and epidermal growth factor receptor, were involved. Rubia cordifolia L. also affected the hepatitis B, phosphoinositide-3-kinase-protein kinase B, and mitogen-activated protein kinase signaling pathways. Many direct-acting tumor-related signaling pathways and indirect-acting hepatitis pathways inhibit the generation of liver cancer. The present study provided a scientific basis for further elucidating the mechanism of Rubia cordifolia L. against liver cancer.

Natural cyclopeptide RA-V inhibits the NF-κB signaling pathway by targeting TAK1

Rubiaceae-type cyclopeptides (RAs) are a type of plant cyclopeptides from the Rubia that have garnered significant attention owing to their unique bicyclic structures and amazing antitumour activities. Our recent work has shown that RAs suppress inflammation and angiogenesis and induce apoptosis. However, the underlying mechanism and targets remained unknown. Nuclear factor κB (NF-κB) signaling pathway plays a critical role in these biological processes, prompting us to investigate whether and how RAs affect this pathway. By screening compound libraries using NF-κB-dependent luciferase reporter, we observed that RA-V is the best NF-κB inhibitor. Further experiments demonstrated that RA-V interrupted the TAK1-TAB2 interaction and targeted TAK1 in this pathway. Moreover, RA-V prevented endotoxin shock and inhibited NF-κB activation and tumor growth in vivo. These findings clarify the mechanism of RA-V on NF-κB pathway and might account for the majority of known bioactivities of RA-V, which will help RA-V develop as new antiinflammatory and antitumour therapies.

In vitro investigation of cytotoxic and antioxidative activities of Ardisia crispa against breast cancer cell lines, MCF-7 and MDA-MB-231

Background

Ardisia crispa Thunb. D.C is used mostly in some parts of the Asian region by traditional practitioners to treat certain diseases associated with oxidative stress and inflammation including cancer and rheumatism. In Malaysia, it is popularly known as ‘Mata Ayam’ and local traditional practitioners believed that the root of the plant is therapeutically beneficial.

Methods

The cytotoxic effect of hydromethanolic extract of A. crispa and its solvents partitions (ethyl acetate and aqueous extracts) against breast cancer cells were evaluated by using MTT assay. The cells were treated with concentration of extracts ranging from 15.63 μg/mL- 1000 μg/mL for 72 h. The quantification of phenolic and flavonoid contents of the extracts were carried out to determine the relationship between of phytochemical compounds responsible for cytotoxic and antioxidative activities. The antioxidant capacity was measured by DPPH and ABTS free radical scavenging assay and expressed as milligram (mg) Trolox equivalent antioxidant capacity per 1 g (g) of tested extract.

Results

The hydromethanolic and ethyl acetate extracts showed moderate cytotoxic effect against MCF-7 with IC₅₀ values of 57.35 ± 19.33 μg/mL, and 54.98 ± 14.10 μg/mL, respectively but aqueous extract was inactive against MCF-7. For MDA-MB-231, hydromethanolic, ethyl acetate and aqueous extracts exhibited weak cytotoxic effects against MDA-MB-231 with IC₅₀ values more than 100 μg/mL. The plant revealed high total phenolic content, total flavonoid and antioxidant capacity.

Conclusion

The response of different type of breast cancer cell lines towards A. crispa extract and its partitions varied. Accordingly, hydromethanolic and ethyl acetate extracts appear to be more cytotoxic to oestrogen receptor (ER) positive breast cancer than oestrogen receptor (ER) negative breast cancer. However, aqueous extract appears to have poor activity to both types of breast cancer. Besides that, hydromethanolic and ethyl acetate extracts exhibit higher TPC, TFC and antioxidant capacity compared to aqueous extract. Synergistic effect of anticancer and antioxidant bioactives compounds of A. crispa plausibly contributed to the cytotoxic effects of the extract.

Rubipodanones A-D, naphthohydroquinone dimers from the roots and rhizomes of Rubia podantha

Four previously undescribed naphthohydroquinone dimers named rubipodanones A-D, together with 19 known quinones containing three known napthohydroquinone dimers named rubioncolin C, methyl 5-hydroxy-dinaphtho[1,2-2',3']furan-7,12-dione-6-carboxylate and rubialatin B, were isolated from the roots and rhizomes of Rubia podantha. Their structures and absolute configurations were determined mainly by NMR, X-ray diffraction, and computational methods. Rubipodanones C and D, the glycosides of rubipodanone A and a pair of C-3 epimer, are the first identified dimeric napthohydroquinone glycosides from the Rubia plants. All naphthohydroquinone dimers were evaluated for their cytotoxicities against ten tumor cell lines and effects on the tumor-associated NF-κB signaling pathway, and rubioncolin C showed the best cytotoxicity with IC₅₀ value of 1.53 μM and NF-κB inhibitory activity with IC₅₀ value of 2.97 μM. These results also demonstrated that the key roles of C-3 configuration and sugar group for biological activities of rubipodanone C.

Arborinane Triterpenoids from Rubia philippinensis Inhibit Proliferation and Migration of Vascular Smooth Muscle Cells Induced by the Platelet-Derived Growth Factor

The abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are associated with cardiovascular diseases and related complications. Such deleterious proliferation and migration events are triggered by cytokines and growth factors, and among them, platelet-derived growth factor (PDGF) is recognized as the most potent inducer. Despite the genus Rubia being researched to identify valuable commercial and medicinal virtues, Rubia philippinensis has rarely been investigated. Nine arborinane-type triterpenoids (1-9) were identified from this underutilized plant species. In particular, 4 was identified as the first arborinane derivative carrying a ketocarbonyl motif at C-19. The presence of the cyclopentanone moiety and the associated configurational assignment were determined by utilizing NOE and coupling constant analysis. These compounds were assessed for their inhibitory potential on PDGF-induced proliferation and the migration of VSMCs. Treatment with 5 μM compound 5 (62.6 ± 10.7%) and compound 9 (41.1 ± 4.7%) impeded PDGF-stimulated proliferation without exerting cytotoxicity. Compound 7 exhibited antimigration activity in a dose-dependent manner (38.5 ± 3.0% at 10 μM, 57.6 ± 3.2% at 30 μM). These results suggest that the arborinane-type triterpenoids may be a pertinent starting point for the development of cardiovascular drugs capable of preventing the intimal accumulation of VSMCs.

Rubiaceae-Type Cyclopeptides from Galianthe thalictroides

Two Rubiaceae-type cyclopeptides, 6-O-methylbouvardin (1) and the new cyclopeptide 5β-hydroxy-RA-III (2), were isolated from the roots of Galianthe thalictroides. Employing the sulforhodamine B assay, compounds 1 and 2 were tested in vitro against three cancer cell lines--786-0 (kidney carcinoma), PC-3 (prostate carcinoma), and HT-29 (colon carcinoma)--and showed GI50 values ranging from 0.06 to 1.80 μg mL(-1). This is the first report on the isolation of Rubiaceae-type cyclopeptides from a genus other than Rubia or Bouvardia.