Oridonin, a Promising ent-Kaurane Diterpenoid Lead Compound

Therapeutic Potential of Oridonin and Its Analogs: From Anticancer and Antiinflammation to Neuroprotection

Oridonin, a diterpenoid natural product commonly used in East Asian herbal medicine, is garnering increased attention in the biomedical community due to its extensive biological activities that include antitumor, anti-inflammatory, antimicrobial, hepatic fibrosis prevention, and neurological effects. Over the past decade, significant progress has been made in structure activity relationship and mechanism of action studies of oridonin for the treatment of cancer and other diseases. This review provides a brief summary on oridonin and its analogs in cancer drug discovery and antiinflammation and highlights its emerging therapeutic potential in neuroprotection applications.

Effect of Oridonin on Cytochrome P450 Expression and Activities in HepaRG Cell

Oridonin, the major terpene found in Rabdosia rubescens, is widely used as a dietary supplement or therapeutic drug. However, the effects of oridonin on major CYP450s are still unclear. As oridonin can enhance the effect of other clinical drugs, in this study, we investigated the influence of oridonin on CYP450s mRNA expression and its impact on activities in human HepaRG cell to evaluate the safety by studying its potential drug interaction. HepaRG cells were cultured with series concentrations of oridonin (1, 5, 10, and 20 μmol/L), and the major CYP450s mRNA and protein expression, as well as enzyme activities were analyzed by real-time polymerase chain reaction, Western blot analysis and UPLC-MS/MS-based metabolite assay. In general, ordonin has induced effects on the major member of CYP450s mRNA and protein expression, as well as on the enzyme activity in human HepaRG cells, especially on CYP3A4 and CYP2C9. To our knowledge, this is the first systematic research about the inductive effects of oridonin on the major member of CYP450s in human cell line. These results may provide at least partly of the basis for potential drug-drug interactions and oridonin should be used with caution to avoid potential risk.

Oridonin inhibits migration, invasion, adhesion and TGF-β1-induced epithelial-mesenchymal transition of melanoma cells by inhibiting the activity of PI3K/Akt/GSK-3β signaling pathway

Epithelial-mesenchymal transition (EMT) has been reported to play pivotal roles in tumor invasion and metastasis. Inhibition of EMT may exert beneficial effects in regulating metastasis. Oridonin (ORI), an active diterpenoid compound isolated from Rabdosia rubescens, was found to be a potent anti-metastatic agent. However, the possible involvement of ORI in the EMT in malignant melanoma is unclear. The present study found that ORI inhibited cell migration, invasion, and adhesion in A375 and B16-F10 melanoma cells. The transforming growth factor-β1 (TGF-β1)-induced EMT was also inhibited in ORI-treated cells, as reflected in the upregulation of E-cadherin, and downregulation of vimentin and Snail. Similar results were observed in A375 and B16-F10 melanoma cells treated with ORI. Furthermore, pre-treatment with ORI blocked the TGF-β1-induced phosphoinositide 3-kinase (PI3K)/AKT serine/threonine kinase (Akt)/glycogen synthase kinase (GSK)-3β signaling pathway activation. These effects mimicked PI3 kinase inhibitor LY294002 treatment. ORI interfered with the PI3K/Akt/GSK-3β pathway, and reversed TGF-β1-induced EMT, which suppressed the invasion and metastasis of melanoma cells. Taken together, the present study demonstrated that ORI inhibits melanoma cells migration, invasion, and adhesion and TGF-β1-induced EMT through the PI3K/Akt/GSK-3β signaling pathway. These findings suggest that ORI is a promising anti-metastasis agent for melanoma.

6,7-Seco-ent-Kauranoids Derived from Oridonin as Potential Anticancer Agents

Structurally unique 6,7-seco-ent-kaurenes, which are widely distributed in the genus Isodon, have attracted considerable attention because of their antitumor activities. Previously, a convenient conversion of commercially available oridonin (1) to 6,7-seco-ent-kaurenes was developed. Herein, several novel spiro-lactone-type ent-kaurene derivatives bearing various substituents at the C-1 and C-14 positions were further designed and synthesized from the natural product oridonin. Moreover, a number of seven-membered C-ring-expanded 6,7-seco-ent-kaurenes were also identified for the first time. It was observed that most of the spiro-lactone-type ent-kaurenes tested markedly inhibited the proliferation of cancer cells, with an IC₅₀ value as low as 0.55 μM. An investigation on its mechanism of action showed that the representative compound 7b affected the cell cycle and induced apoptosis at a low micromolar level in MCF-7 human breast cancer cells. Furthermore, compound 7b inhibited liver tumor growth in an in vivo mouse model and exhibited no observable toxic effects. Collectively, the results warrant further preclinical investigations of these spiro-lactone-type ent-kaurenes as potential novel anticancer agents.

Biosynthesis of the oxygenated diterpene nezukol in the medicinal plant Isodon rubescens is catalyzed by a pair of diterpene synthases

Plants produce an immense diversity of natural products (i.e. secondary or specialized metabolites) that offer a rich source of known and potentially new pharmaceuticals and other desirable bioproducts. The Traditional Chinese Medicinal plant Isodon rubescens (Lamiaceae) contains an array of bioactive labdane-related diterpenoid natural products. Of these, the ent-kauranoid oridonin is the most prominent specialized metabolite that has been extensively studied for its potent antimicrobial and anticancer efficacy. Mining of a previously established transcriptome of I. rubescens leaf tissue identified seven diterpene synthase (diTPSs) candidates. Here we report the functional characterization of four I. rubescens diTPSs. IrTPS5 and IrTPS3 were identified as an ent-copalyl diphosphate (CPP) synthase and a (+)-CPP synthase, respectively. Distinct transcript abundance of IrTPS5 and the predicted ent-CPP synthase IrTPS1 suggested a role of IrTPS5 in specialized ent-kaurene metabolism possibly en route to oridonin. Nicotiana benthamiana co-expression assays demonstrated that IrTPS4 functions sequentially with IrTPS3 to form miltiradiene. In addition, IrTPS2 converted the IrTPS3 product (+)-CPP into the hydroxylated tricyclic diterpene nezukol not previously identified in I. rubescens. Metabolite profiling verified the presence of nezukol in I. rubescens leaf tissue. The proposed IrTPS2-catalyzed reaction mechanism proceeds via the common ionization of the diphosphate group of (+)-CPP, followed by formation of an intermediary pimar-15-en-8-yl+ carbocation and neutralization of the carbocation by water capture at C-8 to yield nezukol, as confirmed by nuclear magnetic resonance (NMR) analysis. Oxygenation activity is rare for the family of class I diTPSs and offers new catalysts for developing metabolic engineering platforms to produce a broader spectrum of bioactive diterpenoid natural products.

Oridonin Induces Apoptosis in Human Nasopharyngeal Carcinoma Cells Involving ROS Generation

Oridonin, an ent-kaurene diterpenoid isolated from the traditional Chinese herb Rabdosia rubescens, has been reported to be a potent cytotoxic agent against a wide array of cancer cells. However, its effect on human nasopharyngeal carcinoma (NPC) cells has not been well investigated. The present study aimed to explore the anti-tumour effect of oridonin in NPC cells and its underlying mechanisms. Cell viability was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay and colony formation assay. Apoptosis, mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and expression of apoptosis-related proteins were analysed by flow cytometry with propidium iodide staining, JC-1 staining, DCFH-DA staining, and Western blot analysis, respectively. The results showed that oridonin concentration-dependently inhibited the cell viability, decreased the colony formation, and enhanced the apoptotic rate in NPC cells. Further, oridonin-induced apoptosis was mediated by the mitochondrial pathway in NPC cells, which was confirmed by the loss of MMP, downregulation of anti-apoptotic Bcl-2 family protein Mcl-1 and Bcl-2, upregulation of pro-apoptotic Bcl-2 family member Bax, and activation of caspase-3 and PARP. Notably, the augmented ROS generation played an essential role in oridonin-induced apoptosis in NPC cells, as the apoptosis-inducing effect was attenuated by ROS scavenger N-acetyl-L-cysteine. These results indicate that oridonin triggers apoptosis through the ROSmediated mitochondrial pathway in NPC cells. This study supports oridonin to be an interesting candidate drug for the treatment of human NPC.