Structure-activity relationship between (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BV-araU, V-araU) in inhibition of Epstein-Barr virus replication

Inhibitory effects of some derivatives of glycyrrhizic acid against Epstein-Barr virus infection: structure-activity relationships

Glycyrrhizic acid (18β-GL or GL) is a herbal drug with a broad spectrum of antiviral activities and pharmacological effects and multiple sites of action. Previously we showed that GL inhibits Epstein-Barr virus (EBV) infection in vitro by interfering with an early step of the EBV replication cycle (possibly attachment/penetration). Here we tested the effects of 15 GL derivatives against EBV infection by scoring the numbers of cell expressing viral antigens and quantifying EBV DNA copy numbers in superinfected Raji cells. The derivatives were made either by transformation of GL on carboxyl and hydroxyl groups or by conjugation of amino acid residues into the carbohydrate part. We identified seven compounds active against EBV and all showed dose-dependent inhibition as determined by both assays. Among these active compounds, the introduction of amino acid residues into the GL carbohydrate part enhanced the antiviral activity in three of the seven active compounds. However, when Glu(OH)-OMe was substituted by Glu(OMe)-OMe, its antiviral activity was completely abolished. Introduction of potassium or ammonium salt to GL reduced the antiviral activity with no significant effect on cytotoxicity. The α-isomer (18α-GL) of 18β-GL was as potent as the β-form, but its sodium salt lost antiviral activity. The metabolic product of GL, 18β-glycyrrhetinic acid (18β-GA or GA), was 7.5-fold more active against EBV than its parental compound GL but, concomitantly, exhibited increased cytotoxicity resulting in a decreased therapeutic index.

Mechanism of action of glycyrrhizic acid in inhibition of Epstein-Barr virus replication in vitro

We report here that glycyrrhizic acid (GL), a component of licorice root (Glycyrrhiza radix), is active against EBV replication in superinfected Raji cells in a dose-dependent fashion. The IC(50) values for viral inhibition and cell growth were 0.04 and 4.8mM, respectively. The selectivity index (ratio of IC(50) for cell growth to IC(50) for viral DNA synthesis) was 120. Time of addition experiments suggested that GL interferes with an early step of EBV replication cycle (possibly penetration). GL had no effect on viral adsorption, nor did it inactivate EBV particles. Thus, GL represents a new class of anti-EBV compounds with a mode of action different from that of the nucleoside analogs that inhibit viral DNA polymerase.

Inhibitory effects of novel nucleoside and nucleotide analogues on Epstein-Barr virus replication

The anti-Epstein-Barr virus (EBV) activity of different classes of compounds was assessed by means of an EBV DNA hybridization assay using a digoxigenin-labelled probe specific for the BamHI W fragment of the EBV genome, as well as by measuring viral capsid antigen (VCA) expression after a 7 day incubation period of P3HR-1 producer cells with the test substances. Acyclovir, ganciclovir, cidofovir and zidovudine were included as reference compounds. Several compounds proved to be potent and selective inhibitors of EBV DNA synthesis and VCA expression. Of the new compounds that were evaluated for their anti-EBV activity, the highest efficacy (lowest EC50) and highest selectivity index (SI) were shown by the purine nucleoside analogue 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (S2242) (EC50 0.6 ng/ml; SI 600), the acyclic nucleoside phosphonate analogues 9-(2-phosphono -methoxyethyl)-6-dimethylaminopurine (EC50 1.1 micrograms/ml; SI 91), 9-(2-phosphonomethoxyethyl)-2- amino-6-benzhydrylaminopurine (EC50 1.3 micrograms/ml; SI 29), 7-(2-phosphonomethoxyethyl)-6-dimethyl-aminopurine (EC50 0.8 microgram/ml; SI 56), 9-(R)-(2-phosphonomethoxypropyl)-6-(2-dimethylaminoethyl)-aminopur ine (EC50 0.5 microgram/ml; SI 42), the 2',3'-dideoxythymidine derivative 3'-oximino-2',3'-dideoxythymidine (EC50 1.5 micrograms/ml; SI 65), and 1-(2,3- dideoxy-3-N-hydroxyamino-beta-D-threo-pentafuranyl)pentafuranos yl)thymine (EC50 4.1 micrograms/ml; SI > 24).