Synthesis and anti-CVB 3 evaluation of substituted 5-nitro-2-phenoxybenzonitriles

Characterization of Anti-Poliovirus Compounds Isolated from Edible Plants

Poliovirus (PV) is the causative agent of poliomyelitis and is a target of the global eradication programs of the World Health Organization (WHO). After eradication of type 2 and 3 wild-type PVs, vaccine-derived PV remains a substantial threat against the eradication as well as type 1 wild-type PV. Antivirals could serve as an effective means to suppress the outbreak; however, no anti-PV drugs have been approved at present. Here, we screened for effective anti-PV compounds in a library of edible plant extracts (a total of 6032 extracts). We found anti-PV activity in the extracts of seven different plant species. We isolated chrysophanol and vanicoside B (VCB) as the identities of the anti-PV activities of the extracts of Rheum rhaponticum and Fallopia sachalinensis, respectively. VCB targeted the host PI4KB/OSBP pathway for its anti-PV activity (EC₅₀ = 9.2 μM) with an inhibitory effect on in vitro PI4KB activity (IC₅₀ = 5.0 μM). This work offers new insights into the anti-PV activity in edible plants that may serve as potent antivirals for PV infection.

Anti-enteroviral activity of new MDL-860 analogues: Synthesis, in vitro/in vivo studies and QSAR analysis

A series of 60 nitrobenzonitrile analogues of the anti-viral agent MDL-860 were synthesized (50 of which are new) and evaluated for their activity against three types of enteroviruses (coxsackievirus B1, coxsackievirus B3 and poliovirus 1). Among them, six diaryl ethers (20e, 27e, 28e, 29e, 33e and 35e) demonstrated high in vitro activity (SI > 50) towards at least one of the tested viruses and very low cytotoxicity against human cells. Compound 27e possesses the broadest spectrum of activity towards all tested viruses in the same way as MDL-860 does. The most active derivatives (27e, 29e and 35e) against coxsackievirus B1 were tested in vivo in newborn mice experimentally infected with 20 MLD₅₀ of coxsackievirus B1. Compound 29e showed promising in vivo activity (protection index 26% and 4 days lengthening of mean survival time). QSAR analysis of the substituent effects on the in vitro cytotoxicity (CC₅₀) and anti-viral activity of the nitrobenzonitrile derivatives was carried out and adequate QSAR models for the anti-viral activity of the compounds against poliovirus 1 and coxsackievirus B1 were constructed.

Allosteric Regulation of Phosphatidylinositol 4-Kinase III Beta by an Antipicornavirus Compound MDL-860

MDL-860 is a broad-spectrum antipicornavirus compound discovered in 1982 and one of the few promising candidates effective in in vivo virus infection. Despite the effectiveness, the target and the mechanism of action of MDL-860 remain unknown. Here, we have characterized antipoliovirus activity of MDL-860 and identified host phosphatidylinositol-4 kinase III beta (PI4KB) as the target. MDL-860 treatment caused covalent modification and irreversible inactivation of PI4KB. A cysteine residue at amino acid 646 of PI4KB, which locates at the bottom of a surface pocket apart from the active site, was identified as the target site of MDL-860. This work reveals the mechanism of action of this class of PI4KB inhibitors and offers insights into novel allosteric regulation of PI4KB activity.

Anti-enteroviral triple combination of viral replication inhibitors: activity against coxsackievirus B1 neuroinfection in mice

BACKGROUND

Chemotherapy is an important tool for controlling enterovirus infections, but clinically effective anti-enterovirus drugs do not currently exist, mainly due to the development of drug resistance. We investigated the combination effects of enterovirus replication inhibitors in order to limit this process. In previous studies, we showed the efficacy of consecutive alternating administration of the triple combinations disoxaril/guanidine/oxoglaucine and pleconaril/guanidine/oxoglaucine against coxsackievirus B1 infection in newborn mice. Drug sensitivity tests of the viral brain isolates showed that these drug combinations prevented the development of drug resistance.

METHODS

In the current study, we replaced guanidine-HCl with enteroviral RNA synthesis inhibitor MDL-860 to test the effect of a new triple combination-pleconaril/MDL-860/oxoglaucine-applied via consecutive alternating administration in newborn mice infected subcutaneously with 20 MLD₅₀ of coxsackievirus B1.

RESULTS

The pleconaril/MDL-860/oxoglaucine combination via consecutive alternating administration showed high activity at the 75 mg/kg MDL-860 dose: a protective effect of 50% and a pronounced suppression of brain virus titers. Moreover, along with prevention of drug resistance, a phenomenon of increased drug sensitivity was established. MDL-860 sensitivity in pleconaril/MDL-860/oxoglaucine increased 8.2 times vs. placebo (29 times vs. monotherapy) on day 7 and oxoglaucine sensitivity-4.9 times vs. placebo (by 6.8 times vs. monotherapy) on day 13. As concerns pleconaril, a demonstrable prevention of drug resistance was registered without increase of drug sensitivity. Daily, simultaneous administration of pleconaril/MDL-860/oxoglaucine showed no protective effects and led to a rapid development of drug resistance.

CONCLUSIONS

These results add new support for using consecutive alternating administration treatment courses to achieve clinically effective chemotherapy of enterovirus infections.

The RNA template channel of the RNA-dependent RNA polymerase as a target for development of antiviral therapy of multiple genera within a virus family

The genus Enterovirus of the family Picornaviridae contains many important human pathogens (e.g., poliovirus, coxsackievirus, rhinovirus, and enterovirus 71) for which no antiviral drugs are available. The viral RNA-dependent RNA polymerase is an attractive target for antiviral therapy. Nucleoside-based inhibitors have broad-spectrum activity but often exhibit off-target effects. Most non-nucleoside inhibitors (NNIs) target surface cavities, which are structurally more flexible than the nucleotide-binding pocket, and hence have a more narrow spectrum of activity and are more prone to resistance development. Here, we report a novel NNI, GPC-N114 (2,2'-[(4-chloro-1,2-phenylene)bis(oxy)]bis(5-nitro-benzonitrile)) with broad-spectrum activity against enteroviruses and cardioviruses (another genus in the picornavirus family). Surprisingly, coxsackievirus B3 (CVB3) and poliovirus displayed a high genetic barrier to resistance against GPC-N114. By contrast, EMCV, a cardiovirus, rapidly acquired resistance due to mutations in 3Dpol. In vitro polymerase activity assays showed that GPC-N114 i) inhibited the elongation activity of recombinant CVB3 and EMCV 3Dpol, (ii) had reduced activity against EMCV 3Dpol with the resistance mutations, and (iii) was most efficient in inhibiting 3Dpol when added before the RNA template-primer duplex. Elucidation of a crystal structure of the inhibitor bound to CVB3 3Dpol confirmed the RNA-binding channel as the target for GPC-N114. Docking studies of the compound into the crystal structures of the compound-resistant EMCV 3Dpol mutants suggested that the resistant phenotype is due to subtle changes that interfere with the binding of GPC-N114 but not of the RNA template-primer. In conclusion, this study presents the first NNI that targets the RNA template channel of the picornavirus polymerase and identifies a new pocket that can be used for the design of broad-spectrum inhibitors. Moreover, this study provides important new insight into the plasticity of picornavirus polymerases at the template binding site.

Efficient discovery of potent anti-HIV agents targeting the Tyr181Cys variant of HIV reverse transcriptase

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) that interfere with the replication of human immunodeficiency virus (HIV) are being pursued with guidance from molecular modeling including free-energy perturbation (FEP) calculations for protein-inhibitor binding affinities. The previously reported pyrimidinylphenylamine 1 and its chloro analogue 2 are potent anti-HIV agents; they inhibit replication of wild-type HIV-1 in infected human T-cells with EC(50) values of 2 and 10 nM, respectively. However, they show no activity against viral strains containing the Tyr181Cys (Y181C) mutation in HIV-RT. Modeling indicates that the problem is likely associated with extensive interaction between the dimethylallyloxy substituent and Tyr181. As an alternative, a phenoxy group is computed to be oriented in a manner diminishing the contact with Tyr181. However, this replacement leads to a roughly 1000-fold loss of activity for 3 (2.5 μM). The present report details the efficient, computationally driven evolution of 3 to novel NNRTIs with sub-10 nM potency toward both wild-type HIV-1 and Y181C-containing variants. The critical contributors were FEP substituent scans for the phenoxy and pyrimidine rings and recognition of potential benefits of addition of a cyanovinyl group to the phenoxy ring.

Design, synthesis, and biological evaluation of novel coxsackievirus B3 inhibitors

The synthesis and SAR study of a novel class of coxsackievirus B3 (CVB3) inhibitors are reported. These compounds could be considered as the 6-chloropurines substituted at position 9 with variously substituted bicyclic scaffolds (bicyclo[2.2.1]heptane/ene-norbornane or norbornene). The synthesis and biological evaluation of 31 target compounds are described. Several of the analogues inhibited CVB3 in the low micromolar range (0.66-2muM). Minimal or no cytotoxicity was observed.