Antitumor activity of daphnane-type diterpene gnidimacrin isolated from Stellera chamaejasme L

LC-MS identification, isolation, and structural elucidation of anti-HIV macrocyclic daphnane orthoesters from Edgeworthia chrysantha

The occurrence of macrocyclic daphnane orthoesters (MDOs) with a 1-alkyl group originating from a C14 aliphatic chain is extremely limited in the plant kingdom and has only been isolated from Edgeworthia chrysantha. In the present study, LC-ESI-MS/MS analysis was performed on different parts of E. chrysantha, including flower buds, flowers, leaves, and stems, and resulted in the identification of seven MDOs in all the four plant parts, including two previously unreported compounds 1 and 7. Further LC-MS guided isolation was carried out to afford compounds 1 and 7, and their structures were determined by various spectroscopic analyses. These compounds were also evaluated for anti-HIV activity, thus expanding insights into the structure-activity relationships for MDOs.

Terpenoids from the Roots of Stellera chamaejasme (L.) and Their Bioactivities

An undescribed diterpene, stellerterpenoid A (1), and two undescribed sesquiterpenoids, stellerterpenoids B and C (2-3), together with six known compounds, prostratin (4) stelleraguaianone B (5), chamaejasnoid A (6), auranticanol L (7), wikstronone C (8), and oleodaphnone (9), were isolated from the roots of Stellera chamaejasme L. Their structures were elucidated by extensive spectroscopic data (1D, 2D NMR, IR, UV, and HR-ESI-MS). The absolute configuration of 1-3 was elucidated based on ECD calculation. Among them, stellerterpenoid A was a rare 13, 14-seco nortigliane diterpenoid and stellerterpenoid B was a guaiacane-type sesquiterpenoid with an unusual 1, 2-diketone moiety. The known stelleraguaianone B (5) exhibited moderate activity for suppressing NO production in lipopolysaccharide (LPS)-treated RAW 264.7 macrophages cells with an IC50 value of 24.76 ± 0.4 μM. None of the compounds showed anti-influenza virus or anti-tumor activity in vitro.

Tigliane and daphnane diterpenoids from Thymelaeaceae family: chemistry, biological activity, and potential in drug discovery

Tigliane and daphnane diterpenoids are characteristically distributed in plants of the Thymelaeaceae family as well as the Euphorbiaceae family and are structurally diverse due to the presence of polyoxygenated functionalities in the polycyclic skeleton. These diterpenoids are known as toxic components, while they have been shown to exhibit a wide variety of biological activities, such as anti-cancer, anti-HIV, and analgesic activity, and are attracting attention in the field of natural product drug discovery. This review focuses on naturally occurring tigliane and daphnane diterpenoids from plants of the Thymelaeaceae family and provides an overview of their chemical structure, distribution, isolation, structure determination, chemical synthesis, and biological activities, with a prime focus on the recent findings.

Daphnepedunins A-F, Anti-HIV Macrocyclic Daphnane Orthoester Diterpenoids from Daphne pedunculata

From the whole plant of Daphne pedunculata, 12 macrocyclic daphnane diterpenoids, including six new compounds, daphnepedunins A-F (1-4, 9, and 10), were isolated. Their structures were elucidated by physiochemical and spectroscopic data analysis, the modified Mosher's method, and X-ray crystallography. The isolated compounds were evaluated for anti-HIV activity against HIV-1 infection in MT4 cells and showed significant anti-HIV activity with IC₅₀ values of 36.3-994 nM. A consideration of the anti-HIV activity of these compounds provided further insight into the structure-activity relationships of macrocyclic daphnane diterpenoids.

Anti-HIV Macrocyclic Daphnane Orthoesters with an Unusual Macrocyclic Ring from Edgeworthia chrysantha

Edgeworthianins A-E (1-5) were isolated from Edgeworthia chrysantha as a class of macrocyclic daphnane orthoesters with an unusual macrocyclic ring formed from a C14 aliphatic chain. Their structures were elucidated by extensive physicochemical and spectroscopic analyses. Compounds 2, 4, and 5 exhibited potent anti-HIV activity against HIV-1 infection of MT4 cells with EC₅₀ values of 29.3, 8.4, and 2.9 nM, respectively. These compounds broaden the findings of the structure-activity relationship of macrocyclic daphnane orthoesters for further anti-HIV drug development.

Phytochemistry and Pharmacological Activities of the Diterpenoids from the Genus Daphne

There are abundant natural diterpenoids in the plants of the genus Daphne from the Thymelaeaceae family, featuring a 5/7/6-tricyclic ring system and usually with an orthoester group. So far, a total of 135 diterpenoids has been isolated from the species of the genus Daphne, which could be further classified into three main types according to the substitution pattern of ring A and oxygen-containing functions at ring B. A variety of studies have demonstrated that these compounds exert a wide range of bioactivities both in vitro and in vivo including anticancer, anti-inflammatory, anti-HIV, antifertility, neurotrophic, and cholesterol-lowering effects, which is reviewed herein. Meanwhile, the fascinating structure-activity relationship is also concluded in this review in the hope of providing an easy access to available information for the synthesis and optimization of efficient drugs.

Chamaejasmin B Decreases Malignant Characteristics of Mouse Melanoma B16F0 and B16F10 Cells

Chamaejasmin B (CHB), a natural biflavone isolated from Stellera chamaejasme L., has been reported to exhibit anti-cancer properties; however, its effect in melanoma cells is not clear. Here, we aimed to investigate the anticancer effect of CHB in mouse melanoma B16F0 and B16F10 cells. We found that CHB significantly suppressed cell proliferation and promoted cell cycle arrest at G0/G1 phase in B16F0 cells; it also induced cell differentiation and increased melanin content by increasing tyrosinase (TYR) activity and mRNA levels of melanogenesis-related genes in B16F0 cells. Meanwhile, wound closure, invasion, and migration of B16F0 and B16F10 cells were dramatically inhibited. Moreover, CHB significantly increased ROS levels and decreased ΔΨm, resulting in B16F0 and B16F10 cell apoptosis. Finally, in vivo studies showed that CHB inhibited tumor growth and induced tumor apoptosis in a mouse xenograft model of murine melanoma B16F0 and B16F10 cells. Overall, CHB decreases malignant characteristics and may be a promising therapeutic agent for malignant melanoma cells via multiple signaling pathways.

Rapid Recognition and Targeted Isolation of Anti-HIV Daphnane Diterpenes from Daphne genkwa Guided by UPLC-MSn

Daphnane diterpenes with a 5/7/6-tricyclic ring system exhibit potent anti-HIV activity but are found in low abundance as plant natural products. In this study, an effective approach based on mass spectrometric fragmentation pathways was conducted to specifically recognize and isolate anti-HIV compounds of this type from Daphne genkwa. Briefly, the fragmentation pathways of reference analogues were elucidated based on characteristic ion fragments of m/z 323 → 295 → 267 or m/z 253 → 238 → 197 by ultra-high-performance liquid chromatography-ion trap tandem mass spectrometry (UPLC-IT-MSⁿ) and then applied to the differentiations of substances with or without an oxygenated group at C-12. Twenty-seven daphnane diterpenes were successfully recognized from a petroleum ether extract of D. genkwa, including some potential new compounds and isomers that could not be identified accurately only from the ion fragments. Further separation of these target compounds using high-speed countercurrent chromatography (HSCCC) and preparative HPLC led to the isolation of three new (11, 25, and 27) and 14 known compounds, whose structures were identified and confirmed based on MS, NMR, and electronic circular dichroism (ECD) spectroscopy. The isolates exhibited anti-HIV activities at nanomolar concentrations. The results demonstrated that this strategy is feasible and reliable to rapidly recognize and isolate daphnane diterpenes from D. genkwa.

Daphneodorins A-C, Anti-HIV Gnidimacrin Related Macrocyclic Daphnane Orthoesters from Daphne odora

Three novel gnidimacrin related macrocyclic daphnanes (GMDs), daphneodorins A-C (2-4), were isolated from Daphne odora Thunb., together with gnidimacrin (1). Their structures were established by extensive physicochemical and spectroscopic analyses. Compounds 2 and 3 potently inhibited HIV-1 replication at subnanomolar concentrations (EC50 0.16 and 0.25 nM, respectively). Compounds 2-4 represent a novel type of GMDs that are highly oxygenated on the macrocyclic ring, suggesting good potential for anti-HIV drug development by further chemical modification.

Phytochemicals in Anticancer Drug Development

BACKGROUND

In spite of major technological advances in conventional therapies, cancer continues to remain the leading cause of mortality worldwide. Phytochemicals are gradually emerging as a rich source of effective but safer agents against many life-threatening diseases.

METHODS

Various phytochemicals with reported anticancer activity have been simply categorized into major phytoconstituents- alkaloids, polyphenols, saponins, tannins and terpenoids.

RESULTS

The adverse effects associated with currently available anticancer medications may be overcome by using plant-derived compounds either alone or in combination. Exploration of plant kingdom may provide new leads for the accelerated development of new anticancer agents.

CONCLUSION

Although numerous potent synthetic drugs have been introduced for cancer chemotherapy, yet their serious toxicity concerns to normal cells apart from drug resistance have emerged as the major obstacles for their clinical utility over a prolonged duration of time. Current status and potential of phytochemicals and their derivatives in cancer therapy have been briefly reviewed in the present manuscript.

Protein kinase C as a target for new anti-cancer agents

Cancer joins the category of diseases involving abnormalities in the rate of proliferation of cells and is associated with uncontrolled cell division, where cells either generate their own growth-promoting stimuli or neighboring cells or do not respond to growth inhibitory signals. Protein kinase C (PKC) is one of the key elements in the tumor growth signal transduction pathways and is found to be overexpressed in several malignant cell types. A way to control cell proliferation and cell differentiation is by influencing signal transduction pathways by modulation of PKC. PKC encloses 12 different isoenzymes, and each isoenzyme is found to have a different functional property. Because specific PKC isoenzyme types are present in different (malignant) cell species, they may be an attractive target in the development of anti-cancer agents. Classification and identification of the available PKC isoenzymes in different tumor cells could be useful in targeting specific tumors. PKC also tends to be overexpressed in association with the multidrug resistance pheno-type. This concise review deals with the role of PKC isoenzymes in (tumor) cell biology and evaluates the antineoplastic agents interacting on PKC isoenzymes.

Altered profile of gut microbiota after subchronic exposure to neochamaejasmin A in rats

Neochamaejasmin A, isolated from Stellera chamaejasme L., has been widely used in China. Gut microbiota represent the first barrier against xenobiotics. This study aimed to evaluate the effects of subchronic exposure to neochamaejasmin A on the composition of gut microbiota. We found that neochamaejasmin A altered 21 OTUs in female rats and 46 OTUs in male rats. Among these OTUs, OTU86, OTU338 and OTU482 were shared in neochamaejasmin A-fed groups in both genders, implying that neochamaejasmin A might promote the growth of these three genera. In contrast, little or no effect on 226 OTUs was observed at all doses in both genders, suggesting their resistance to neochamaejasmin A. These findings could help improve our understanding of the health effects of neochamaejasmin A and provide an example of the risk assessment of pharmaceuticals or food contaminants on the gut microbiota composition.

In vitro inhibitory and pro-apoptotic effect of Stellera chamaejasme L extract on human lung cancer cell line NCI-H157

OBJECTIVE

To investigate the inhibitory and pro-apoptotic effect of Stellera Chamaejasme L extract (ESC) in vitro.

METHODS

ESC was first extracted with ethanol, and then washed using a polyamide column with 60% ethanol. ESC was then decompressively recycled and vacuum dried at room temperature to obtain active fractions. Subsequently, the cytotoxic and apoptotic effects of ESC on NCI-H157 human lung cancer cells were determined.

RESULTS

The results showed that ESC was rich in isomers of Chamaejasminor, neochamaejasmine and Sikokianin. ESC had significant cytotoxicity against NCI-H157 cells, with an IC50 of approximately 18.50 microg x mL(-). ESC caused significant increase in total apoptotic rate, the activity of caspase 3 and 8,

CONCLUSION

The inhibitory effect of ESC on NCI-H157 tumor cells might partly be attributed to its apoptotic induction through activation of the Fas death receptor pathway.

Anticancer drugs from traditional toxic Chinese medicines

Many anticancer drugs are obtained from natural sources. Nature produces a variety of toxic compounds, which are often used as anticancer drugs. Up to now, there are at least 120 species of poisonous botanicals, animals and minerals, of which more than half have been found to possess significant anticancer properties. In spite of their clinical toxicity, they exhibit pharmacological effects and have been used as important traditional Chinese medicines for the different stages of cancer. The article reviews many structures such as alkaloids of Camptotheca acuminata, Catharanthus roseus and Cephalotaxus fortunei, lignans of Dysosma versipellis and Podophyllum emodi, ketones of Garcinia hanburyi, terpenoids of Mylabris and Ginkgo biloba, diterpenoids of Tripterygium wilfordii, Euphorbia fischeriana, Euphorbia lathyris, Euphorbia kansui, Daphne genkwa, Pseudolarix kaempferi and Brucea javanica, triterpenoids of Melia toosendan, steroids of Periploca sepium, Paris polyphylla and Venenum Bufonis, and arsenic compounds including Arsenicum and Realgar. By comparing their related phytochemistry, toxic effects and the recent advances in understanding the mechanisms of action, this review puts forward some ideals and examples about how to increase antitumour activity and/or reduce the side effects experienced with Chinese medicine.

Picomolar dichotomous activity of gnidimacrin against HIV-1

Highly active antiretroviral therapy (HAART) has offered a promising approach for controlling HIV-1 replication in infected individuals. However, with HARRT, HIV-1 is suppressed rather than eradicated due to persistence of HIV-1 in latent viral reservoirs. Thus, purging the virus from latent reservoirs is an important strategy toward eradicating HIV-1 infection. In this study, we discovered that the daphnane diterpene gnidimacrin, which was previously reported to have potent anti-cancer cell activity, activated HIV-1 replication and killed persistently-infected cells at picomolar concentrations. In addition to its potential to purge HIV-1 from latently infected cells, gnidimacrin potently inhibited a panel of HIV-1 R5 virus infection of peripheral blood mononuclear cells (PBMCs) at an average concentration lower than 10 pM. In contrast, gnidimacrin only partially inhibited HIV-1 ×4 virus infection of PBMCs. The strong anti-HIV-1 R5 virus activity of gnidimacrin was correlated with its effect on down-regulation of the HIV-1 coreceptor CCR5. The anti-R5 virus activity of gnidimacrin was completely abrogated by a selective protein kinase C beta inhibitor enzastaurin, which suggests that protein kinase C beta plays a key role in the potent anti-HIV-1 activity of gnidimacrin in PBMCs. In summary, these results suggest that gnidimacrin could activate latent HIV-1, specifically kill HIV-1 persistently infected cells, and inhibit R5 viruses at picomolar concentrations.

Function-oriented synthesis: studies aimed at the synthesis and mode of action of 1alpha-alkyldaphnane analogues

[reaction: see text] An efficient synthetic route to the ABC tricyclic core of 1alpha-alkyldaphnanes has been developed. The conformational bias imparted by the C6-C9 oxo-bridge of BC-ring system 12 was used to elaborate the ABC-ring system precursor including the introduction of the beta-C5 hydroxyl group. A completely diastereoselective palladium-catalyzed enyne cyclization was then employed to establish the A-ring with a C1 appendage.

Orthogonal test design for optimization of supercritical fluid extraction of daphnoretin, 7-methoxy-daphnoretin and 1,5-diphenyl-1-pentanone from Stellera chamaejasme L. and subsequent isolation by high-speed counter-current chromatography

Supercritical fluid extraction (SFE) of daphnoretin, 7-methoxy-daphnoretin and 1,5-diphenyl-1- pentanone from Stellera chamaejasme L. was performed. An orthogonal L9 (3)4 test design was applied to select the optimum extraction parameters including pressure, temperature, modifier and sample particle size on yield using an analytical-scale SFE system. The process was then scaled up by 100 times using a preparative SFE system under the optimized conditions of 25 MPa of pressure, 45 degrees C of temperature, 40-60 mesh of sample particle size and modified CO2 with 20% methanol. The yield of the crude extract from preparative SFE was 2.65%, which contained daphnoretin 25.2%, 7-methoxy-daphnoretin 22.8% and 1,5-diphenyl-1-pentanone 21.1%, respectively. Then the crude extract was successfully isolated and separated by preparative high-speed counter-current chromatography (HSCCC) with a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (10:13:13:10, v/v) by increasing the flow-rate of the mobile phase stepwise from 1.0 to 2.0 ml/min after 90 min. The target compounds isolated and purified by HSCCC were analyzed by high-performance liquid chromatography (HPLC). The separation produced total of 69.2mg of daphnoretin at 99.2% purity, 63.4 mg of 7-methoxy-daphnoretin at 98.7% purity and 58.3 mg of 1,5-diphenyl-1-pentanone at 98.1% purity from 300 mg of the crude extract in one-step separation. The recoveries of daphnoretin, 7-methoxy-daphnoretin and 1,5-diphenyl-1-pentanone were 90.8, 91.5 and 90.4%, respectively, in HSCCC isolation step and the chemical structure identification was carried out by MS, 1H NMR and 13C NMR.

Induction of apoptosis in K562 cells by jolkinolide B

Jolkinolide B, a bioactive diterpene isolated from the roots of Euphorbia fischeriana Steud, has various biological and pharmacological properties. In this study, the cytotoxicity of highly purified jolkinolide B was tested in human chronic myeloid leukemia (K562) and 2 other cell lines (human esophageal carcinoma Eca-109 and human hepatoma HepG2). The results indicate a significant decrease in the proliferation of all the 3 cell lines when treated with jolkinolide B for 24 h; the IC50 value of cytotoxicity was 12.1 μg/mL (for K562 cells), >50.0 μg/mL (for HepG2 cells), and 23.7 μg/mL (for Eca-109 cells). Further study of K562 cells involving fluorescence and transmission electron microscopy revealed characteristic apoptotic features, such as cell shrinkage, membrane blebbing, loss of microvilli, and nuclear condensation. Agarose electrophoresis of genomic DNA showed a typical fragmentation pattern for apoptotic cells. A kinetic cell-cycle analysis demonstrated that the cell cycle was arrested in the G1 phase. All these results suggest that the anti-proliferation effect of jolkinolide B on K562 cells is achieved by arresting the cell cycle in the G1 phase and subsequently inducing apoptosis.

Induction of differentiation and apoptosis in three human leukemia cell lines by a new compound from Dendrostellera lessertii

It has previously been shown that Dendrostellera lessertii (Thymelaeaceae) has strong anticancer activity. In this study, the antileukemic activity of another new compound from the same plant extract is reported. Promyelocytic (NB4 and HL-60) and erythroleukemia (K562) cells were cultured in the presence of various concentrations of the new compound (0.5-3.0 mug/ml) for 3 d. The cell numbers were then determined by trypan blue exclusion test. The new compound inhibited growth and proliferation of NB4, HL-60 and K562 with IC50 values of 1.5, 2.0 and 2.5 mg/ml, respectively. We also found that the new compound inhibited cell proliferation in a dose- and time-dependent manner. At low concentrations and after 48 h of treatment, approximately 50%-70% of NB4 and HL-60 cells were differentiated to monocyte/macrophage lineage and approximately 30%-40% of the treated K562 cells were differentiated in the megakaryocytic lineage, as evidenced by morphological changes and nitro blue tetrazolium reduction assays. Results of Hoechst 33258 staining also indicated that the new compound induced NB4 and HL-60 cell apoptosis at their respective IC50 values after 72 h of treatment. Based on the present data, the new compound seems a good candidate for further evaluation as an effective chemotherapeutic agent acting through induction of differentiation and apoptosis.

Isolation and structure elucidation of a new potent anti-neoplastic diterpene from Dendrostellera lessertii

Two diterpene esters were isolated from Dendrostellera lessertii. These compounds were identified as compound I (12-O-benzoyl-3,5-hydroxy-6,7-epoxy-resiniferonol-9,13,14-orthobenzoate) and compound 11 (12-O-benzoyl-5-hydroxy-6,7-epoxy-resiniferonol-9,13,14-orthodecanoate). Cytotoxicity evaluation of these two compounds, using seven different cancerous cell lines, indicated that compound I with IC50 of 5-25 nmol, is 2.5 times more active than compound II. Using flow cytometry technique, it was found that treatment of the most responsive cells (K562) with compound I inhibited the progression of cells through G1 phase by almost 20% compared to the untreated cells.

Stereospecific Induction of Nuclear Factor-κB Activation by Isochamaejasmin

The root of Stellera chamaejasme L. is a traditional Chinese herb termed Rui Xiang Lang Du and has been used to treat solid tumors, tuberculosis and psoriasis. Exactly how S. chamaejasme L. regulates cellular responses remains unclear. We examined four biflavonoids isolated from S. chamaejasme L., including isochamaejasmin, two of its stereo-isomers and a methyl derivative, in functional assays originally designed to screen ligands for the G protein-coupled formyl peptide receptor-like 1 (FPRL1). Isochamaejasmin was found to induce the expression of a nuclear factor (NF)-kappaB-directed reporter gene in transfected HeLa cells with an EC50 of 3.23 microM, independently of FPRL1. The isochamaejasmin-stimulated NF-kappaB reporter activity was accompanied by nuclear translocation of NF-kappaB proteins and was blocked by a dominant-negative construct of IkappaBalpha. Isochamaejasmin also induced time-dependent phosphorylation of the mitogen-activated protein kinases extracellular signal-regulated kinase 1/2 and p38, and a novel protein kinase C (PKCdelta). Likewise, inhibition of these kinases with the respective pharmacological inhibitors significantly reduced the isochamaejasmin-stimulated NF-kappaB activation. It is noteworthy that the two stereoisomers and the methyl derivative did not induce detectable activation of NF-kappaB and were more cytotoxic than isochamaejasmin, which could partially rescue cycloheximide-induced apoptosis. Inhibition of NF-kappaB activation reversed the anti-apoptotic effect of isochamaejasmin. These results provide the first evidence for a potential mechanism of action by S. chamaejasme L., and indicate that structurally similar compounds derived from S. chamaejasme L. may have different pharmacological properties.

The Cytotoxic and Anti-proliferative Effects of 3-Hydrogenkwadaphnin in K562 and Jurkat Cells Is Reduced by Guanosine

3-hydrogenwadaphnin (3-HK) is a new daphnane-type diterpene ester isolated from Dendrostellera lessertii with strong anti-tumoral activity in animal models and in cultures. Here, prolonged effects of this new agent on proliferation and viability of several different cancerous cell lines were evaluated. Using [(3)H]thymidine incorporation, it was found that the drug inhibited cell proliferation and induced G1/S cell cycle arrest in leukemic cells 24 h after a single dose treatment. The cell viability of Jurkat cells was also decreased by almost 10 %, 31 % and 40 % after a single dose treatment (7.5 nM) at 24, 48 and 72 h, respectively. The drug-treated cells were stained with acridine orange/ ethidium bromide to document the chromatin condensation and DNA fragmentation. These observations were further confirmed by detection of DNA laddering pattern in the agarose gel electrophoresis of the extracted DNA from the treated cells. Treatment of K562 cells with the drug at 7.5, 15 and 30 nM caused apoptosis in 25 %, 45 % and 65 % of the cells, respectively. Exogenous addition of 25-50 microM guanosine and/or deoxyguanosine to the cell culture of the drug-treated cells restored DNA synthesis, released cell arrest at G1/S checkpoint and decreased the apoptotic cell death caused by the drug. These observations were not made using adenosine. However, the drug effects on K562 cells were potentiated by hypoxanthine. Based on these observations, perturbation of GTP metabolism is considered as one of the main reasons for apoptotic cell death by 3-HK.

Nucleic acid synthesis in cancerous cells under the effect of gnidilatimonoein from Daphne mucronata

Cytotoxicity evaluation of gnidilatimonoein, the most active isolated diterpene ester from Daphne mucronata [Sadeghi H, Mianabadi M, Yazdanparast R, (2002) Journal of Tropical. Medicinal Plant1 3: 169-173], revealed the strong antiproliferative activity among several different human cancer cell lines (K562, CCRF-CEM, HL-60 and MOLT-4 leukemia cell lines, LNCaP-FGC-10 a prostate cancer cell line) and a mouse BALB/C fibrosarcoma cell line (WEHI-164). Using flow cytometry technique, it was found that treatment of the most responsive cells (K562) with gnidilatimonoein inhibited the progression of cells through G1 phase by almost 15% compared to the untreated cells. The population of the treated cells in the S and G2 phases also reduced by 8.3% and 5.4%, respectively. Based on the extent of [3H]-thymidine and [3H]-uridine incorporation into DNA and RNA, respectively, the major metabolic effects of gnidilatimonoein were found to be mainly on DNA and to a less extent on RNA synthesis. Additionally, the activity of inosine-5'-monophosphate dehydrogenase (IMPDH), under the effects of genidilatimonoein, was reduced in the treated cells by 44%. These data strongly suggest that the purine biosynthetic pathway is significantly affected by gnidilatimonoein.

Involvement of PKC betaII in anti-proliferating action of a new antitumor compound gnidimacrin

Daphnane-type diterpene gnidimacrin (NSC 252940) shows significant antitumor activity against murine tumors and human tumor cell lines. This compound binds to and directly activates protein kinase C (PKC), arresting the cell cycle at the G(1) phase through inhibition of cdk2 activity in human K562 leukemia cells. In our study, we examined whether cellular PKC is involved in the antiproliferating effect of gnidimacrin. In a 24-hr exposure of K562 cells to high concentrations of bryostatin 1 (0.11-3.3 microM), both expression of PKC alpha and PKC betaII was downregulated, and thereafter these cells became resistant to gnidimacrin in response to the degree of PKC downregulation. In addition, PKC alpha and PKC betaII genes were transfected to gnidimacrin-resistant human hepatoma HLE cells that demonstrated positive expression of PKC alpha and negative expression of PKC betaII. PKC betaII gene-transfected cells became sensitive to gnidimacrin in relation to the degree of PKC betaII expression. The most sensitive clone to show 0.001 microg/mL (1.2 nM) as IC(50) in a continuous 4-day exposure was obtained. While PKC alpha gene-transfected cells exhibited an increase in PKC alpha expression and became sensitive to gnidimacrin, sensitivity was one-hundredth of that in PKC betaIotaIota gene-transfected cells. These results suggest that PKC, in particular PKC betaIotaIota, is necessary in the antitumor effect of gnidimacrin.

Effect of Dendrostellera lessertii on the intracellular alkaline phosphatase activity of four human cancer cell lines

The cytotoxicity of an alcoholic extract of Dendrostellera lessertii (Thymelaeaceae) and one of its purified components was evaluated using four different human cancer cell lines. The IC(50) of the crude extract was found to be 28, 33, 31 and 30 microl for K562, CCRF-CEM, HL-60 and LNCaP-FGC-10 cells, respectively. Each microliter of the crude extract corresponds to 0.02 mg of the plant powder material. Similarly the IC(50) of the purified component was 5 x 10(-9), 20 x 10(-9), 8 x 10(-9) and 8 x 10(-9)M for K562, CCRF-CEM, HL-60 and LNCaP-FGC-10 cells, respectively. In addition, besides significant reduction in cell proliferation rates, the crude extract, at a dose of 18 microl/ml and the purified component at a dose of 3.5 x 10(-9)M, were capable of enhancing the intracellular protein content of each of the cell lines by almost 160% while the intracellular alkaline phosphatase activity was increased up to 450%.

Antitumor action of the PKC activator gnidimacrin through cdk2 inhibition

Daphnane-type diterpene gnidimacrin (NSC252940), isolated from a Chinese plant, exhibited antitumor activity against murine leukemias and solid tumors. At concentrations of 10(-9) to 10(-10) M, this agent strongly inhibited the growth of human tumor cell lines. In sensitive human leukemia K562 cells, gnidimacrin is a PKC activator that arrests the cell cycle in the G(1) phase by inhibiting cdk2 activity. A 4 hr exposure of K562 cells to gnidimacrin induced the CDK inhibitor p21(WAF1/Cip1), but this effect was transient and did not correlate temporally with the onset of G(1) arrest. Expression of cdc25A, a phosphatase that activates cdk2, was reduced during 24-hr exposure to gnidimacrin. Moreover, the suppression corresponded in a concentration- and time-dependent manner to both the inhibition of cdk2 activity and the mobility shift observed when cdk2 was electrophoresed on SDS-PAGE, indicating that the phosphorylation state of cdk2 must change. Cyclin E, the other regulator of cdk2 activity, was not influenced by gnidimacrin. These results suggest that gnidimacrin exerts antitumor activity through suppression of cdc25A and inhibition of cdk2 activity.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Inter- and intramolecular reductive coupling reactions: an approach to the phorbol skeleton

[reaction: see text] An expeditious convergent route to the ABC-tricyclic core of the phorbol esters is described. The chemistry capitalizes upon both inter- and intramolecular reductive coupling processes promoted electrochemically and via the use of samarium diiodide.

Mechanism of antitumor action of PKC activator, gnidimacrin

Daphnane-type diterpene gnidimacrin isolated from the Chinese plant Stellera chamaejasme L. is an antitumor agent that activates protein kinase C (PKC). The mechanism of antitumor action of gnidimacrin and the possible involvement of PKC were examined using sensitive K562 and refractory HLE cells. Gnidimacrin did bind to K562 cells 3 times more than to HLE cells. Immunoblot analyses revealed pronounced PKC betaII expression in gnidimacrin sensitive cell lines including K562 cells, while refractory HLE cells strongly expressed PKC alpha, but not PKC betaII. In a 24-hr exposure of K562 cells to gnidimacrin, G1 phase arrest and inhibition of cdk2 kinase activity was found at growth-inhibitory concentration (0.0005 microg/ml). Complete inhibition of cdk2 activity and maximum G1 phase arrest were observed at 0.005 microg/ml, however, these biological effects were reduced at 0.05 microg/ml (260 times the 50% inhibitory concentration). Cellular PKC after a 24-hr exposure was examined by immunoblot analysis and specific binding of [3H]phorbol-12,13-dibutyrate as a ligand of PKC. Expression and the amount of functional PKC of K562 cells were not changed at 0.002 microg/ml, but down-regulated to less than 1/10th of the control at 0.05 microg/ml. The reduction of biological effects at 0.05 microg/ml is most likely due to PKC down-regulation. Our results suggest that PKC (particularly betaII) is one of the major determinants of the ability of cells to respond to gnidimacrin and that the antitumor action might be associated with cell-cycle regulation through suppression of cdk2 activity.

Anti-tumour activities of a new benzo[c]phenanthridine agent, 2,3-(methylenedioxy)-5-methyl-7-hydroxy-8-methoxybenzo[c]phena nthridini um hydrogensulphate dihydrate (NK109), against several drug-resistant human tumour cell lines

Drug resistance is one of the problems severely limiting chemotherapy in cancer patients. Thus, it is very important to develop new drugs that are effective against drug-resistant tumour cells. The novel anti-tumour agent NK109 has been developed from benzo[c]phenanthridine derivatives by Nippon Kayaku (Tokyo, Japan). We have confirmed that NK109 shows anti-tumour effects against a number of human tumour cell lines by inhibiting DNA topoisomerase II activity through the stabilization of the cleavable complex. Further, its efficacy against several drug-resistant tumour cell lines was also shown. NK109 showed potent anti-tumour activity against doxorubicin-resistant human tumour cell lines that have a typical multidrug resistance phenotype caused by P-glycoprotein. NK109 was not pumped extracellularly by P-glycoprotein and, consequently, NK109 accumulated in resistant cells. Cisplatin-resistant human tumour cell lines, which demonstrated decreased cisplatin accumulation, were sensitive to NK109. NK109 non-cross-resistance was confirmed using xenografts of tumour cells that were resistant to cisplatin in SCID mice. Furthermore, etoposide-resistant cells, with decreased topoisomerase II activity, were markedly sensitive to NK109 when compared with their parent cells, suggesting the possibility that the cytotoxic mechanism of NK109 differs from that of etoposide. In conclusion, NK109 is a very promising new anti-tumour drug for clinical use, because the efficacy of NK109 is not susceptible to several known molecular alterations that are associated with drug resistance. A clinical study of this compound is now in progress in Japan.

Phorbol ester augments butyrate-induced apoptosis of colon cancer cells

Butyrate is a potentially selective therapeutic agent for many adenocarcinomas. Butyrate causes reversible growth arrest as well as some death of VACO 5 colon cancer cells. Combined treatment with butyrate and the phorbol ester TPA leads instead only to cell death, while TPA causes little death on its own. Cells dying during treatment with TPA and butyrate, as well as those dying in the presence of butyrate alone, exhibit features typical of apoptosis, including detachment, shrinkage and internucleosomal DNA cleavage. Pre-treating VACO 5 cell cultures with TPA for as little as 6 hr prior to butyrate addition led to a markedly diminished enhancement of butyrate-induced apoptosis. Treatment with a distinct PKC activator, bryostatin 1, was ineffective in enhancing butyrate-induced death and, furthermore, counteracted the death-enhancing actions of TPA. Such antagonism was apparent when bryostatin was added after 12 hr of TPA/butyrate treatment but was much less effective thereafter. The duration of TPA/butyrate treatment required for depressing cell survival by >95% was thereby estimated to be 24 hr. Other colon cancer cell lines were examined for the extent of cell death following treatment with TPA/butyrate. In each of these lines, butyrate inhibited cell replication in a reversible manner, similar to that seen in VACO 5. However, the combination of butyrate and TPA led to high levels of cell death in only a subset of these lines. TPA/butyrate-treated cultures of COLO 201 exhibited extensive apoptosis, similar in timing and magnitude to the response by VACO 5, whereas HCT 116 was reversibly growth-arrested. Our findings indicate that the PKC system plays a critical role in maintaining cell survival during butyrate-induced growth arrest.