Caiguo Huang

Sulfur-Containing Cytotoxic Curvularin Macrolides from Penicillium sumatrense MA-92, a Fungus Obtained from the Rhizosphere of the Mangrove Lumnitzera racemosa

Sumalarins A-C (1-3), the new and rare examples of sulfur-containing curvularin derivatives, along with three known analogues (4-6), were isolated and identified from the cytotoxic extract of Penicillium sumatrense MA-92, a fungus obtained from the rhizosphere of the mangrove Lumnitzera racemosa . Their structures were established by detailed interpretation of NMR and MS data, and compound 1 was confirmed by X-ray crystallographic analysis. Compounds 1-3 and 5 showed potent cytotoxicity against some of the tested tumor cell lines. Sulfur substitution at C-11 or a double bond at C-10 significantly increased the cytotoxic activities of the curvularin analogues.

Brocazines A-F, Cytotoxic Bisthiodiketopiperazine Derivatives from Penicillium brocae MA-231, an Endophytic Fungus Derived from the Marine Mangrove Plant Avicennia marina

Six new disulfide-bridged diketopiperazine derivatives, brocazines A-F (1-6), along with one known analogue (7), were isolated and identified from the cytotoxic extract of Penicillium brocae MA-231, a fungus obtained from the fresh tissue of the marine mangrove plant Avicennia marina. The structures of these compounds were established on the basis of detailed interpretation of NMR and mass spectroscopic data. X-ray crystallographic analysis confirmed the structure of 1 and established the structure and absolute configuration of 5, while the absolute configurations for compounds 1, 4, and 6 were deduced by comparison of the CD data with those of 5. Compounds 1, 2, 5, and 6 showed cytotoxic activities against several tumor cell lines.

The novel agent ophiobolin O induces apoptosis and cell cycle arrest of MCF-7 cells through activation of MAPK signaling pathways.

Ophiobolin O is a natural compound that has been isolated from Aspergillus ustus 094102. This is the first study to demonstrate the anti-proliferative effect of ophiobolin O in human breast cancer MCF-7 cells. The results of present study show that ophiobolin O induced cycle G(0)/G(1) phase arrest in MCF-7 cells using a cell cycle analysis. In addition, we demonstrated that ophiobolin O reduced the viability of human breast cancer MCF-7 cells in a time- and dose-dependent manner and efficiently induced apoptosis in MCF-7 cells using the Annexin V/PI binding assay. Ophiobolin O also caused the activation of JNK (c-Jun NH(2)-terminal kinase), p38 MAPK (mitogen activated protein kinase) and ERK (extracellular signal-regulated kinase) as well as the degradation of Bcl-2 phosphorylation (Ser70). Bax protein expression was not changed in ophiobolin O-treated cells. Taken together, ophiobolin O may be considered as a novel therapeutic agent in breast cancer.

Synthesis and antitumor evaluation of methyl spongoate analogs

A series of novel methyl spongoate (1) analogs has been synthesized and evaluated for their in vitro cytotoxic properties. It was found that the nature of the C-20 side chain had significant effects on their bioactivities and some analogs showed higher cytotoxicity than 1 against A549, HCT-116, HepG2, SW-1990, MCF-7 and NCI-H460 tumor cell lines. The pharmacological results confirmed that the α,β-unsaturated carbonyl moiety, a Michael acceptor in ring A, plays a pivotal role in the cytotoxic effect of these derivatives. The compiled pharmacological data may be useful for the design of novel analogous anticancer drugs.

Asperolide A, a Marine-Derived Tetranorditerpenoid, Induces G2/M Arrest in Human NCI-H460 Lung Carcinoma Cells, Is Mediated by p53-p21 Stabilization and Modulated by Ras/Raf/MEK/ERK Signaling Pathway

Here we first demonstrate that asperolide A, a very recently reported marine-derived tetranorditerpenoid, leads to the inhibition of NCI-H460 lung carcinoma cell proliferation by G2/M arrest with the activation of the Ras/Raf/MEK/ERK signaling and p53-dependent p21 pathway. Treatment with 35 μM asperolide A (2 × IC50) resulted in a significant increase in the proportion of G2/M phase cells, about a 2.9-fold increase during 48 h. Immunoblot assays demonstrated time-dependent inhibition of G2/M regulatory proteins. Moreover, asperolide A significantly activated MAP kinases (ERK1/2, JNK and p38 MAP kinase) by phosphorylation, and only the inhibition of ERK activation by PD98059 reversed downregulation of G2/M regulatory proteins CDC2, and suppressed upregulation of p21 and p-p53 levels. Transfection of cells with dominant-negative Ras (RasN17) mutant genes up-regulated asperolide A-induced the decrease of cyclin B1 and CDC2, suppressed Raf, ERK activity and p53-p21 expression, and at last, abolished G2/M arrest. This study indicates that asperolide A-induced G2/M arrest in human NCI-H460 lung carcinoma cells relys on the participation of the Ras/Raf/MEK/ERK signaling pathway in p53-p21 stabilization. An in vivo study with asperolide A illustrated a marked inhibition of tumor growth, and little toxcity compared to Cisplatin therapy. Overall, these findings provide potential effectiveness and a theoretical basis for the therapeutic use of asperolide A in the treatment of malignancies.

Ophiobolin-O Reverses Adriamycin Resistance via Cell Cycle Arrest and Apoptosis Sensitization in Adriamycin-Resistant Human Breast Carcinoma (MCF-7/ADR) Cells

Multidrug-resistance is a major obstacle facing cancer chemotherapy. This paper demonstrates that novel compound Ophiobolin-O reverses MCF-7/ADR resistance to adriamycin (ADM). The IC50 of ADM treated MCF-7 cells was 2.02 ± 0.05 µM and 74.00 ± 0.18 µM treated MCF-7/ADR cells, about 37-fold, compared to the former. However, 0.1 µM Ophiobolin-O (less than 20% inhibition concentration) combined with ADM caused the decreased IC50 of ADM to 6.67 ± 0.98 µM, indicating it reversed ADM resistance of MCF-7/ADR cells (11-fold). Furthermore, Ophiobolin-O increased ADM-induced mitochondrial pathway apoptosis and G2/M phase arrest, which is partly due to the elevation level of ROS in MCF-7/ADR cells. As we described in this paper, the reversal effect of Ophiobolin-O may be due to the reduction of resistance-related protein P-Glycoprotein (P-gp, also known as MDR1) through inhibiting the activity of the multidrug resistance 1 (MDR1) gene promoter, which makes MCF-7/ADR cells more sensitive to ADM treatment. Assays in nude mice also showed that the combination of ADM and Ophiobolin-O significantly improved the effect of ADM.

Ophiobolin O Isolated from Aspergillus ustus Induces G1 Arrest of MCF-7 Cells through Interaction with AKT/GSK3β/Cyclin D1 Signaling

Ophiobolin O is a member of ophiobolin family, which has been proved to be a potent anti-tumor drug candidate for human breast cancer. However, the anti-tumor effect and the mechanism of ophiobolin O remain unclear. In this study, we further verified ophiobolin O-induced G1 phase arrest in human breast cancer MCF-7 cells, and found that ophiobolin O reduced the phosphorylation level of AKT and GSK3β, and induced down-regulation of cyclin D1. The inverse docking (INVDOCK) analysis indicated that ophiobolin O could bind to GSK3β, and GSK3β knockdown abolished cyclin D1 degradation and G1 phase arrest. Pre-treatment with phosphatase inhibitor sodium or thovanadate halted dephosphorylation of AKT and GSK3β, and blocked ophiobolin O-induced G1 phase arrest. These data suggest that ophiobolin O may induce G1 arrest in MCF-7 cells through interaction with AKT/GSK3β/cyclin D1 signaling. In vivo, ophiobolin O suppressed tumor growth and showed little toxicity in mouse xenograft models. Overall, these findings provide theoretical basis for the therapeutic use of ophiobolin O.

Tanghinigenin from seeds of Cerbera manghas L. induces apoptosis in human promyelocytic leukemia HL-60 cells

Tanghinigenin, a cardiac glycoside, is isolated from the seeds of Cerbera manghas L. In this study, we demonstrated that tanghinigenin reduced the viability of human promyelocytic leukemia HL-60 cells in a time- and dose-dependent manner, and efficiently induced apoptosis in HL-60 cells as evidenced by the Annexin V/PI binding assay, DNA fragmentation and AO/EB staining studies. In addition, stimulation of HL-60 cells with tanghinigenin induced a series of intracellular events including the activation of caspase-3, -8, and -9, as well as up-regulation of Fas and FasL protein level. Taken together, caspase activation and Fas/FasL interaction was found to be involved in tanghinigenin-induced HL-60 cell apoptosis.

Neriifolin from seeds of Cerbera manghas L. induces cell cycle arrest and apoptosis in human hepatocellular carcinoma HepG2 cells.

The effects of neriifolin, a cardiac glycoside from Cerbera manghas L. on various end-points of oncologic relevance (cell growth, cell cycle regulation, and apoptosis in HepG2 cells) were investigated. Neriifolin reduced viability of HepG2 cells, induced S and G2/M phase arrests of the cell cycle, and stimulated apoptosis of HepG2 cells. Stimulation of HepG2 cells with neriifolin induced activation of caspase-3, -8, and -9, and up-regulated expression of Fas and FasL proteins. Based on these results, neriifolin could be considered a candidate for the treatment of hepatocellular carcinoma.

2′-Epi-2′-O-acetylthevetin B induces apoptosis partly via Ca2+-mediated mitochondrial pathway in human hepatocellular carcinoma HepG2 cells

2′‐Epi‐2′‐O‐acetylthevetin B (GHSC‐74), a cardiac glycoside, can be isolated from the seeds of Cerbera manghas L. We demonstrated that GHSC‐74 reduced the viability of HepG2 cells in a time‐ and dose‐dependent manner, and efficiently induced apoptosis without significantly decreasing the viability of Chang human liver cells and Swiss albino 3T3 fibroblasts, as indicated by annexin‐V/PI binding assay and Hoechst 33342 staining. In addition, stimulation of HepG2 cells with GHSC‐74 induced a series of intracellular events: (1) loss of mitochondrial membrane potential; (2) sustained elevation of cytosolic [Ca2+]; and (3) downregulation of Bcl‐2. BAPTA‐AM, a cytosolic Ca2+ chelator, partly suppressed cell death and prevented mitochondrial membrane potential from losing in GHSC‐74‐treated HepG2 cells. In contrast, EGTA, an extracellular Ca2+ chelator, exhibited a weaker effect as compared to that of BAPTA‐AM. Taken together, the Ca2+‐mediated mitochondrial pathway was found to be involved in GHSC‐74‐induced HepG2 cell apoptosis.