Guy D. Diana

The structure of coxsackievirus B3 at 3.5 A resolution.

BACKGROUND Group B coxsackieviruses (CVBs) are etiologic agents of a number of human diseases that range in severity from asymptomatic to lethal infections. They are small, single-stranded RNA icosahedral viruses that belong to the enterovirus genus of the picornavirus family. Structural studies were initiated in light of the information available on the cellular receptors for this virus and to assist in the design of antiviral capsid-binding compounds for the CVBs. RESULTS The structure of coxsackievirus B3 (CVB3) has been solved to a resolution of 3.5 A. The beta-sandwich structure of the viral capsid proteins VP1, VP2 and VP3 is conserved between CVB3 and other picornaviruses. Structural differences between CVB3 and other enteroviruses and rhinoviruses are located primarily on the viral surface. The hydrophobic pocket of the VP1 beta-sandwich is occupied by a pocket factor, modeled as a C16 fatty acid. An additional study has shown that the pocket factor can be displaced by an antiviral compound. Myristate was observed covalently linked to the N terminus of VP4. Density consistent with the presence of ions was observed on the icosahedral threefold and fivefold axes. CONCLUSIONS The canyon and twofold depression, major surface depressions, are predicted to be the primary and secondary receptor-binding sites on CVB3, respectively. Neutralizing immunogenic sites are predicted to lie on the extreme surfaces of the capsid at sites that lack amino acid sequence conservation among the CVBs. The ions located on the icosahedral threefold and fivefold axes together with the pocket factor may contribute to the pH stability of the coxsackieviruses.

In vitro activity of WIN 51711, a new broad-spectrum antipicornavirus drug.

WIN 51711 (5-[7-[4-(4,5-dihydro-2-oxazolyl)phenoxy]heptyl]-3-methylisoxazole), a new antipicornavirus drug, is a potent inhibitor of human entero- and rhinoviruses at concentrations not inhibitory to HeLa cell growth. In plaque reduction assays, WIN 51711 reduced plaque formation by 9 enteroviruses and 33 rhinoviruses, with MICs of 0.004 to 0.17 and 0.004 to 6.2 micrograms/ml, respectively. Addition of WIN 51711 to infected cells at concentrations of 0.02 to 5.0 micrograms/ml reduced the yield of picornaviruses by 90%. Other RNA viruses (nonpicornaviruses) and DNA viruses were unaffected by the compound.

Antiviral activity of some beta-diketones. 2. Aryloxy alkyl diketones. In vitro activity against both RNA and DNA viruses.

The synthesis and in vitro antiviral evaluation of a series of substituted benzyl beta-diketones are described. The introduction of a styryl group onto the phenyl ring enhanced activity against herpesvirus type 2. The 4-methoxystyryl homologue 8 was evaluated extensively in vitro and was found to be effective against both RNA and DNA viruses. Compound 8 was evaluated in the mouse vagina against herpes simplex type 1 and produced a significant increase in survival rate as well as in survival time.

In vitro and in vivo activities of WIN 54954, a new broad-spectrum antipicornavirus drug.

WIN 54954 (5-[5-[2,6-dichloro-4-(4,5-dihydro-2-oxazolyl)phenoxy]pentyl]-3- methylisoxazole) is a new member of the class of broad-spectrum antipicornavirus compounds known to bind in a hydrophobic pocket within virion capsid protein VP1. In plaque reduction assays, WIN 54954 reduced plaque formation of 50 of 52 rhinovirus serotypes (MICs ranged from 0.007 to 2.2 micrograms/ml). A concentration of 0.28 microgram/ml was effective in inhibiting 80% of the 52 serotypes tested (EC80). WIN 54954 was also effective in inhibiting 15 commonly isolated enteroviruses, with an EC80 of 0.06 microgram/ml. Furthermore, WIN 54954 was effective in reducing the yield of two selected enteroviruses in cell culture by 90% at concentrations approximately equal to their MICs. The therapeutic efficacy of intragastrically administered WIN 54954 was assessed in suckling mice infected with coxsackievirus A-9 or echovirus type 9 (Barty) 2.5 days prior to initiation of therapy. Single daily doses of 2 and 100 mg/kg protected 50% of the mice from developing paralysis (PD50) following infection with coxsackievirus A-9 and echovirus-9, respectively. At the PD50 doses for these two viruses, levels of WIN 54954 in serum were maintained above the in vitro MICs for a significant portion of the dosing interval. The dose-dependent reduction in viral titers observed in coxsackievirus A-9-infected mice correlated well with the therapeutic dose response. The potency and spectrum of WIN 54954 make it a potentially useful compound for the treatment of human enterovirus and rhinovirus infections.

STABILIZATION OF HUMAN RHINOVIRUS SEROTYPE 2 AGAINST PH-INDUCED CONFORMATIONAL CHANGE BY ANTIVIRAL COMPOUNDS

Four WIN compounds with anti-picornavirus activities were tested for their ability to stabilize human rhinovirus serotype 2 (HRV-2) against low pH-induced conformational changes in vitro, as determined by specific immunoprecipitation. These results were compared to the minimal inhibitory concentration (MIC) as measured in a plaque reduction assay. A direct relationship was observed between the concentration of the compound that prevented the low pH-induced conformational changes and the MIC, indicating that stabilization is an important element in the mode of action of these drugs against HRV-2.

Antipicornavirus drugs: current status

Considerable efforts have been made over the past several years to discover a broad-spectrum antipicornavirus agent. The X-ray crystal structure of several rhinovirus serotypes, as well as a coxsackievirus, has provided valuable information with respect to the virus structure as well as the location of the binding site of several capsid-binding compounds. This has aided in the design of broad-spectrum compounds. Several potential drug candidates have reached clinical status and some progress has been made in achieving efficacy. However, none of these compounds has as yet become a marketable drug. This review summarizes the current status of efforts in this area.

Binding affinities of structurally related human rhinovirus capsid-binding compounds are related to their activities against human rhinovirus type 14.

The binding affinities (Kds) and the rates of association and dissociation of members of a chemical class of antiviral compounds at their active sites in human rhinovirus type 14 (HRV-14) were determined. On the basis of analysis by LIGAND, a nonlinear curve-fitting program, of saturation binding experiments with HRV-14, the Kds for Win 52084, Win 56590, disoxaril (Win 51711), and Win 54954 were found to be 0.02, 0.02, 0.08, and 0.22 microM, respectively. The independently determined kinetic rates of association and dissociation resulted in calculated Kd values which were in agreement with the Kd values determined in saturation binding experiments. Scatchard plots of each of four compounds for the binding data indicated that approximately 40 to 60 molecules were bound per HRV-14 virion. Hill plots showed no evidence of cooperativity in binding. Furthermore, the antiviral activities (MICs in plaque reduction assays with HRV-14) for this limited series of compounds (n = 4) correlated well (r = 0.997) with the observed Kds. Likewise, the absence of detectable binding of Win 54954 to the drug-resistant mutant HRV-14 (Leu-1188) corresponded to a lack of antiviral activity. The positive relationship between the antiviral activities and the Kds that were determined may have implications for the molecular design of capsid-binding antirhinovirus drugs.

Inhibitors of picornavirus uncoating as antiviral agents

The discovery of the antiviral drugs known today can be attributed primarily to the tenacity of researchers and the serendipity of circumstances. Their development, however, has been carefully orchestrated by intense study of the mode of action of these compounds and increased understanding of molecular events involved in virus replication. We are presently entering a new era of development in antiviral chemotherapy characterized by the synthesis of chemicals designed to inhibit specific viral targets. One target of chemical interference is the process of viral uncoating, an essential step in viral replication which results in the release of the viral genome into either the cytoplasm (RNA viruses) or nucleus (DNA viruses) of the cell. Our goal has been to synthesize and develop compounds which inhibit the uncoating process of picornaviruses. If successful, this could result in the identification of compounds effective in the treatment of diseases caused by the enteroand rhinovirus members of the picornavirus family, including the causative agents of aseptic meningitis, poliomyelitis and the common cold.

Common cold viruses

Abstract The structure of a human common cold (rhinovirus) serotype, human rhinovirus 14 (HRV14) is providing extensive information on viral assembly, stability, neutralization by antibodies and antiviral agents as well as the site of receptor attachment.

Antipicornavirus Compounds: Use of Rational Drug Design and Molecular Modelling

The discovery of antipicornavirus activity associated with disoxaril 1 and related compounds, and the elucidation of the 3-dimensional structure of human rhinovirus-14 and −1A has lead to the use of rational drug design in the search for more potent and broad spectrum agents. The use of volume maps based on the X-ray conformation of these compounds in human rhinovirus-14 has revealed space filling requirements for activity for this serotype which has been confirmed by the use of the programme CoMFA. The principle interactions of the compounds within the binding site appear hydrophobic in nature. These studies have shown that maximum occupancy of the binding site is associated with good antiviral activity.