Inhibitory effects on Epstein-Barr virus activation of anthraquinones: correlation with redox potentials

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.

Correlation between cytotoxic activities and reduction potentials of heterocyclic quinones

To search for possible anti-tumor agents or anti-tumor promoters among natural or synthetic products, we used cyclic voltammetry to determine the reduction-oxidation potentials of heterocyclic quinones in phosphate buffer at pH 7.2. We determined the growth inhibitory- and cytotoxic activities of 12 heterocyclic quinone anti-tumor agent candidates against a panel of 39 human cancer cell lines (JFCR39). The average concentrations of the heterocyclic quinones required for 50% growth inhibition (GI₅₀) against JFCR39 ranged from 0.045 to 13.2 μM, and the 50% lethal concentration (LC₅₀) against JFCR39 ranged from 0.398 to 77.7 μM. The average values of GI₅₀ or LC₅₀ of the heterocyclic quinones correlated significantly with their reduction potentials. These results suggested that reduction-oxidation potentials could be a useful method for the discovery of novel antitumor agents.

Correlation between reduction potentials and inhibitions of Epstein-Barr virus activation by anthraquinone derivatives

As a continuation of studies using natural and synthetic products as cancer chemopreventive agents, we used cyclic voltammetry to examine the reduction-oxidation potentials of methylated emodin derivatives prepared from emodin in phosphate buffer at pH 7.2. A good correlation was found between the inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation and the reduction potential of methylated emodin derivatives. Furthermore, there was significant correlation between EBV-EA activation and the reduction potential of 35 anthraquinone derivatives including methylated emodin derivatives. It was further shown that the correlation could be enhanced by including LUMO energy and the number of hydroxy groups as additional parameters.

Anti-cancer properties of anthraquinones from rhubarb

Rhubarb has been used as a traditional Chinese medicine since ancient times and today it is still present in various herbal preparations. In this review the toxicological and anti-neoplastic potentials of the main anthraquinones from Rhubarb, Rheum palmatum, will be highlighted. It is interesting to note that although the chemical structures of various anthraquinones in this plant are similar, their bioactivities are rather different. The most abundant anthraquinone of rhubarb, emodin, was capable of inhibiting cellular proliferation, induction of apoptosis, and prevention of metastasis. These capabilities are reported to act through tyrosine kinases, phosphoinositol 3-kinase (PI3K), protein kinase C (PKC), NF-kappa B (NF-kappaB), and mitogen-activated protein kinase (MAPK) signaling cascades. Aloe-emodin is another major component in rhubarb found to have anti-tumor properties. Its anti-proliferative property has been demonstrated to be through the p53 and its downstream p21 pathway. Our recent proteomic study also suggests that the molecular targets of these two anthraquinones are different. However, both components were found to be able to potentiate the anti-proliferation of various chemotherapeutic agents. Rhein is the other major rhubarb anthraquinone, although less well studied. This compound could effectively inhibit the uptake of glucose in tumor cells, caused changes in membrane-associated functions and led to cell death. Interestingly, all three major rhubarb anthraquinones were reported to have in vitro phototoxic. This re-evaluation of an old remedy suggests that several bioactive anthraquinones of rhubarb possess promising anti-cancer properties and could have a broad therapeutic potential.

Correlation between reduction potentials and inhibitory effects on Epstein–Barr virus activation by emodin derivatives

As a continuation of studies using natural and synthetic products as cancer chemopreventive agents, we examined the reduction-oxidation potentials of hydroxylated emodin derivatives prepared from emodin in phosphate buffer at pH 7.2 using cyclic voltammetry. A significant correlation was found between the reduction potentials and number of the hydroxyl groups and the inhibitory effects of the hydroxylated emodin derivatives on Epstein-Barr virus early antigen activation. The electronic properties, i.e. LUMO energy and atomic charges of carbon at the 9-position (C(9)) and oxygen at the 11-position (O(11)), may also be useful for estimating the inhibitory effect on EBV-EA activation.

Structure-activity relations of azafluorenone and azaanthraquinone as antimicrobial compounds

Antimicrobial activities of two azafluorenones, four 1-azaanthraquinones, five 2-azaanthraquinones, and one 2-azaquinone were tested. Several azaanthraquinones possessed broad, potent activity, while the azafluorenones demonstrated weak activity. The following structure-activity relationship was postulated: (1) activity decreased in the order 2-azaanthraquinones>1-azaanthraquinones>azafluorenones; and (2) a hydroxyl group at the peri-carbonyl group enhanced activity. In addition, correlations among reduction potential, hydrophobic parameter, and antimicrobial activity were discussed.

Correlation between reduction potentials and inhibitory effects on Epstein-Barr virus activation of poly-substituted anthraquinones

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the reduction potentials of some poly-substituted anthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the reduction potentials and the inhibitory effects of the poly-substituted anthraquinones on Epstein-Barr virus early antigen activation. It has been further shown that the correlation can be enhanced by introducing log P as an additional parameter.

Correlation of redox potentials and inhibitory effects on Epstein-Barr virus activation of 2-azaanthraquinones

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the standard redox potentials of some 2-azaanthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the 2-azaanthraquinones on Epstein-Barr virus early antigen (EBV-EA) activation. It has been further shown that the correlation can be enhanced by introducing an electronic properties, i.e. the atomic charges at the C5 and O12 atoms in the quinone skeleton ring and the HOMO energy as additional parameters.

Correlation of redox potentials and inhibitory effects on Epstein–Barr virus activation of naphthoquinones

As a continuation of our studies using natural and synthetic products as cancer chemopreventive agents, we examined the standard redox potentials of some naphthoquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the naphthoquinones on Epstein-Barr virus early antigen activation. It has been further shown that the correlation can be enhanced by introducing an electronic property, i.e. the atomic charges at the C(4) and O(10) atoms in the quinone skeleton ring as additional parameters.

Chemopreventive effects of emodin and cassiamin B in mouse skin carcinogenesis

In continuation of our works of natural and synthetic products as cancer chemopreventive agents, we have examined emodin and cassiamin B, which were isolated from Cassia siamea. These compounds exhibited the remarkable anti-tumor promoting effect on two-stage carcinogenesis test of mouse skin tumors induced by 7,12-dimethylbenz[a]anthracene as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter by both topical application. Furthermore, emodin exhibited potent inhibitory activity on two-stage carcinogenesis test of mouse skin tumors induced by nitric oxide donor, (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamide as an initiator and TPA as a promoter.

Inhibitory effects of anthraquinones and bianthraquinones on Epstein-Barr virus activation

Short-term in vitro assays for anti-tumor promoters were carried out for several anthraquinones and bianthraquinones, which were isolated from Cassia siamea and derived from cascaroside A. Anthraquinone monomers showed higher anti-tumor promoting activity than that of bianthraquinones.

Correlation with redox potentials and inhibitory effects on Epstein-Barr virus activation of azaanthraquinones

The redox potentials have been determined for nine azaanthraquinones in phosphate buffer at pH 7.2 by means of cyclic voltammetry. A definite correlation has been found between the redox potentials and the inhibitory effects of the azaanthraquinones on Epstein-Barr virus early antigen (EBV-EA) activation. It has further been shown that the correlation can be made better by introducing an electronic property, i.e., the atomic charge at O11 as an additional parameter.