Antitumor agents 220. Antitumor-promoting effects of cimigenol and related compounds on Epstein-Barr virus activation and two-stage mouse skin carcinogenesis

Hydroxy(phenyl)pyruvic acid reductase in Actaea racemosa L.: a putative enzyme in cimicifugic and fukinolic acid biosynthesis

MAIN CONCLUSION

Hydroxy(phenyl)pyruvic acid reductase from Actaea racemosa catalyzes dual reactions in reducing 4-hydroxyphenylpyruvic acid as well as β-hydroxypyruvic acid. It thus qualifies to be part of fukinolic and cimicifugic acid biosynthesis and also photorespiration. The accumulation of fukinolic acid and cimicifugic acids is mainly restricted to Actaea racemosa (Ranunculaceae) and other species of the genus Actaea/Cimicifuga. Cimicifugic and fukinolic acids are composed of a hydroxycinnamic acid part esterified with a benzyltartaric acid moiety. The biosynthesis of the latter is unclear. We isolated cDNA encoding a hydroxy(phenyl)pyruvic acid reductase (GenBank OR393286) from suspension-cultured material of A. racemosa (ArH(P)PR) and expressed it in E. coli for protein production. The heterologously synthesized enzyme had a mass of 36.51 kDa and catalyzed the NAD(P)H-dependent reduction of 4-hydroxyphenylpyruvic acid to 4-hydroxyphenyllactic acid or β-hydroxypyruvic acid to glyceric acid, respectively. The optimal temperature was at 38 °C and the pH optimum at pH 7.5. NADPH is the preferred cosubstrate (Km 23 ± 4 µM). Several substrates are accepted by ArH(P)PR with β-hydroxypyruvic acid (Km 0.26 ± 0.12 mM) followed by 4-hydroxyphenylpyruvic acid (Km 1.13 ± 0.12 mM) as the best ones. Thus, ArH(P)PR has properties of β-hydroxypyruvic acid reductase (involved in photorespiration) as well as hydroxyphenylpyruvic acid reductase (possibly involved in benzyltartaric acid formation).

Structure-activity relationship of Triterpenes and derived Glycosides against cancer cells and mechanism of apoptosis induction

Triterpenoids possess a wide range of biological effects. Here, the cytotoxic activities of 55 triterpenes and derived glycosides against BEL-7404 and SGC-7901 cells were assessed, and structure-activity relationships were analysed accordingly. Nine of them effectively inhibited the two cell lines. In particular, compounds 49 and 52 inhibited BEL-7404 cells as efficiently as 5'-fluorouracil (IC₅₀ values 0.46 and 1.48, respectively). Moreover, we found that compounds 49 and 52 induced apoptosis in BEL-7404 cells. Indeed, DNA fragmentation assay showed a time-dependent degradation of DNA after treatment of cells with compounds 49 and 52. In addition, Bax gene expression levels were increased after treatment with these compounds, in a concentration-dependent manner. Taken together, our findings suggested that compounds 49 and 52 induce apoptosis in BEL-7404 cells by upregulating the Bax gene without affecting Bcl-2 gene expression.

Bioactive activities of natural products against herpesvirus infection

More than 90% of adults have been infected with at least one human herpesvirus, which establish long-term latent infection for the life of the host. While anti-viral drugs exist that limit herpesvirus replication, many of these are ineffective against latent infection. Moreover, drug-resistant strains of herpesvirus emerge following chemotherapeutic treatment. For example, resistance to acyclovir and related nucleoside analogues can occur when mutations arise in either HSV thymidine kinase or DNA polymerases. Thus, there exists an unmet medical need to develop new anti-herpesvirus agents with different mechanisms of action. In this Review, we discuss the promise of anti-herpetic substances derived from natural products including extracts and pure compounds from potential herbal medicines. One example is Glycyrrhizic acid isolated from licorice that shows promising antiviral activity towards human gammaherpesviruses. Secondly, we discuss anti-herpetic mechanisms utilized by several natural products in molecular level. While nucleoside analogues inhibit replicating herpesviruses in lytic replication, some natural products can disrupt the herpesvirus latent infection in the host cell. In addition, natural products can stimulate immune responses against herpesviral infection. These findings suggest that natural products could be one of the best choices for development of new treatments for latent herpesvirus infection, and may provide synergistic anti-viral activity when supplemented with nucleoside analogues. Therefore, it is important to identify which natural products are more efficacious anti-herpetic agents, and to understand the molecular mechanism in detail for further advance in the anti-viral therapies.

Proteasome inhibitors from Neoboutonia melleri

Thirty new cycloartane derivatives (1-3, 5-12, 14-32) have been isolated from the leaves of Neoboutonia melleri. Their novelty stems from the loss of one of the C-4 methyl groups (1-3, 5-12, 14-25, and 32) and from the presence of an "extra" carbon atom in the side chain (1-3, 5-12, 14-20, 26-29, and 30-32). Furthermore, compound 32 possesses a rare triterpene skeleton with the cyclopropane ring fused onto C-1 and C-10, instead of C-9 and C-10. The structures were determined by spectrometric means, chemical correlations, and X-ray crystallography of derivative 1c. The substitution pattern in ring A, with a cyclopropyl ring conjugated with an α,β-unsaturated carbonyl moiety, confers to the molecule a particular reactivity, giving rise to a formal inversion of the stereochemistry of the cyclopropane ring under UV irradiation. These compounds showed an interesting level of activity on the proteasome pathway, thus motivating their evaluation as possible anticancer agents. The large number of isolated compounds permitted a structure-activity relationship analysis, which showed that the presence of the two enone functions was a requirement for the activity.

Cancer preventive agents 11. Novel analogs of dimethyl dicarboxylate biphenyl as potent cancer chemopreventive agents(†)

CONTEXT

Dimethyl dicarboxylate biphenyl (DDB) is a clinically used hepatoprotectant and has also been found to have chemopreventive activity.

MATERIALS AND METHODS

Sixteen novel analogs (5-20) were designed, synthesized, and evaluated for their cancer preventive activity. The 2,2'-bismethyl ester (5-18) and ether (19, 20) DDB analogs were synthesized by insertion of various linear alkyl, short fatty acid, polar, and aromatic groups. All synthesized analogs were evaluated in an in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced Epstein Barr virus early antigen (EBA-EA) activation assay. Three of the most potent compounds were also tested for inhibitory effects on skin tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter.

RESULTS

Compound 19 with bisprenyl ethers had the most significant cancer preventive activity (100% inhibition of activation at 1 × 10(3) mol ratio/TPA, 78.4%, 49.7%, and 10.9% inhibition at 5 × 10(2), 1 × 10(2), 1 × 10 mol ratio/TPA, respectively) in vitro. Compound 19 also exhibited a remarkable inhibitory effect on skin tumor promotion in the in vivo two-stage mouse-skin carcinogenesis test.

DISCUSSION AND CONCLUSIONS

Thus, DDB analog 19 could be a valuable candidate as a cancer preventive agent or as a lead for the development of new antitumor promoter drugs.

Cancer preventive agents 10. Prenylated dehydrozingerone analogs as potent chemopreventive agents

Dehydrozingerone analogs and related compounds were screened as potential antitumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced Epstein-Barr virus early antigen activation assay. Among the 40 synthesized compounds, the prenylated analogs 16 and 34-36 showed the most significant and promising activity (100% inhibition of activation at 1 x 10(3) mol ratio/TPA, and 82-80%, 37-35%, and 13-11% inhibition at 5 x 10(2), 1 x 10(2), and 1 x 10 mol ratio/TPA, respectively) in this screening. Their activity profiles were comparable to those of the reference standard curcumin. While a prenyl moiety conferred potent chemopreventive activity, an extended prenyl unit such as a farnesyl moiety did not improve activity. Because in vitro inhibitory effects in this assay generally correlate well with in vivo inhibitory effects on tumor promotion, our results strongly suggested that prenylated 16 and 34-36 are likely to be promising antitumor promoters.

Cimicifoetisides A and B, two cytotoxic cycloartane triterpenoid glycosides from the rhizomes of Cimicifuga foetida, inhibit proliferation of cancer cells

Two new cycloartane-type triterpene glycosides, namely cimicifoetisides A (1) and B (2), along with seven known compounds cimigenol, 25-O-acetylcimigenol, cimigenol 3-O-beta-D-xylopyranoside, 12beta-hydroxycimigenol 3-O-beta-D-xylopyranoside, cimigenol 3-O-alpha-L-arabinopyranoside, 25-deoxyshengmanol 3-O-beta-D-xylopyranoside and cimilactone A, were isolated from the rhizomes of Cimicifuga foetida. Their structures were elucidated as cimigenol 3-O-(2'-O-acetyl)-alpha-L-arabinopyranoside (1) and 25-O-acetylcimigenol 3-O-(2'-O-acetyl)-alpha-L-arabinopyranoside (2). Both compounds 1 and 2 exhibited potent cytotoxicity against rat EAC (Ehrlich ascites carcinoma) and MDA-MB-A231 (human breast cancer) cells with IC50 values of 0.52 and 6.74 microM for 1, and 0.19 and 10.21 microM for 2, suggesting their potential for further investigation as anti-cancer agents.

Polyphenolic constituents of Actaea racemosa

A new lignan, actaealactone (1), and a new phenylpropanoid ester derivative, cimicifugic acid G (2), together with 15 known polyphenols, protocatechuic acid, protocatechualdehyde, p-coumaric acid, caffeic acid, methyl caffeate, ferulic acid, ferulate-1-methyl ester, isoferulic acid, 1-isoferuloyl-beta-d-glucopyranoside, fukinolic acid, and cimicifugic acids A, B, and D-F, were isolated from an extract of the rhizomes and roots of black cohosh (Actaea racemosa). The structures of the new compounds were determined on the basis of NMR spectroscopic analysis. Compounds 1 and 2 displayed antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free-radical assay with IC(50) values of 26 and 37 microM, respectively. Other antioxidants identified from A. racemosa include cimicifugic acid A (3), cimicifugic acid B (4), and fukinolic acid (5). Compounds 1 and 2 also exhibited a small stimulating effect on the growth of MCF-7 breast cancer cell proliferation 1.24-fold (14 microM) and 1.14-fold (10 microM), respectively, compared to untreated cells.

Evaluation of cell death caused by triterpene glycosides and phenolic substances from Cimicifuga racemosa extract in human MCF-7 breast cancer cells

We previously reported that the antiproliferative effect of an isopropanolic-aqueous extract of black cohosh (iCR) on MCF-7 estrogen-responsive breast cancer cell line was due to the induction of apoptosis. Here we address the question to what extent apoptosis induction can be ascribed to one of the two major fractions of iCR, the triterpene glycosides (TTG) or the cinnamic acid esters (CAE). Furthermore, as black cohosh is routinely administered orally, we studied whether its pharmacological effects would withstand simulated liver metabolism. The antiproliferative activity of TTG and CAE as well as of rat liver microsomal S9 fraction-pretreated iCR on MCF-7 cells were investigated by WST-1 assay. The features of cell death induced were tested for apoptosis by flow cytometry (light scatter characteristics, Annexin V binding). Irrespective of S9-pretreatment, 72 h iCR treatment induced a dose-dependent down regulation of cell proliferation with the same IC50 of 55.3 microg/ml dry residue which corresponds to 19.3 microg/ml TTG and 2.7 microg/ml CAE. The degree of apoptotic MCF-7 cells was also comparable. Both, isolated TTG and CAE fractions inhibited cell growth, the IC50 being 59.3 microg/ml and 26.1 microg/ml, respectively. Interestingly, whereas IC50 and apoptosis induction correspond well for the whole extract, TTG and CAE fractions induced apoptosis at concentrations (25 and 5 microg/ml) well below those required for significant growth inhibition. Observation of this study firstly showed that the cell death induced by iCR withstood a metabolic activation system. In addition, TTG and CAE compounds significantly contributed to its apoptotic effect, CAE being the more potent inhibitor of proliferation and apoptosis inducer.

Cancer preventive agents. Part 1: Chemopreventive potential of cimigenol, cimigenol-3,15-dione, and related compounds

In continuation of our previous report, cimigenol (1) and 15 related compounds were screened as potential antitumor promoters by using the in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)--induced Epstein-Barr virus early antigen (EBV-EA) activation assay. Cimigenol-3,15-dione (2) displayed the greatest potency (100% inhibition at 1000 mol ratio/TPA) and consequently was further examined for antitumor-promoting activity in a two-stage carcinogenesis assay of mouse skin tumors (DMBA/TPA). In this assay, compound 2 showed significant activity, reducing the number of papillomas per mouse to 48% of the control group at 20 weeks. In addition, compounds 1 and 2 were examined for antitumor-initiating activity in a two-stage carcinogenesis assay of mouse skin tumors induced by peroxynitrite as an initiator and TPA as a promoter. Results showed that these two triterpenoids were almost equipotent with epigallocatechin gallate (EGCG) and slightly more potent than tocinol (group V), the positive controls. Thus, compounds 1 and 2 exhibited not only strong antitumor-promoting activity but also significant antitumor-initiating effect on mouse skin. These data suggest that both compounds might be valuable chemopreventors.

Cytotoxicity of three cycloartane triterpenoids from Cimicifuga dahurica

We first investigated the cytotoxicity of three cycloartane triterpenoids isolated from the aerial part of C. dahurica. Their cytotoxic activity was investigated on several cancer cell lines including solid tumor (HepG2), blood tumor (HL-60), drug resistant tumor (R-HepG2) and primary cultured normal mouse and rat hepatocytes in order to find efficient anti-tumor agents against both parental and drug-resistant tumor with reduced toxicity. Evident cytotoxicity of these compounds on all tested neoplastic cell lines revealed that they are efficient on both drug-resistant tumor and parental tumor. Furthermore, they all showed relatively selective cytotoxicity on cancerous cells based on the higher IC(50) values of them on normal cells than that on tumor cells. Morphological observation and cell cycle analysis were employed to elucidate the cytotoxicity of the tested compounds. They brought out similar apoptotic morphological changes and G(2)/M cell cycle arrest in HepG2, R-HepG2 and HL-60 cells. Moreover, they suppressed the expression of cdc2 and COX-2 protein. These results imply that the three compounds possess potential anti-tumor activities and they exert their cytotoxicity via apoptosis and G(2)/M arrest. In addition, inhibition of cdc2 protein expression correlates with mechanism of G(2)/M arrest.