The activity of pleconaril in cell culture against prototypic enterovirus strains and 215 clinical isolates of the most commonly isolated enterovirus serotypes was examined. The latter viruses were isolated by the Centers for Disease Control and Prevention during the 1970s and 1980s from clinically ill subjects. Pleconaril at a concentration of ≤0.03 μM inhibited the replication of 50% of all clinical isolates tested. Ninety percent of the isolates were inhibited at a drug concentration of ≤0.18 μM. The most sensitive serotype, echovirus serotype 11, was also the most prevalent enterovirus in the United States from 1970 to 1983. Pleconaril was further tested for oral activity in three animal models of lethal enterovirus infection: coxsackievirus serotype A9 infection in suckling mice, coxsackievirus serotype A21 strain Kenny infection in weanling mice, and coxsackievirus serotype B3 strain M infection in adult mice. Treatment with pleconaril increased the survival rate in all three models for both prophylactic and therapeutic dosing regimens. Moreover, pleconaril dramatically reduced virus levels in target tissues of coxsackievirus serotype B3 strain M-infected animals. Pleconaril represents a promising new drug candidate for potential use in the treatment of human enteroviral infections.

https://aac.asm.org/content/aac/43/9/2109.full.pdf

Activity of Pleconaril against Enteroviruses

The structure of coxsackievirus B3 at 3.5 å resolution

Coxsackievirus infections have previously been shown to cause acute or chronic myocarditis in humans, and several mouse models have been established to study the pathology of this disease. Myocardial injury may result from direct viral effects and/or may be immune mediated. To determine the relative roles of these processes in pathogenesis, we have compared coxsackievirus B3 (CVB3) infections of normal and immuno-compromised transgenic knockout (ko) mice. CVB3 was able to infect all strains used (C57BL/6, CD4ko, and beta-microglobulin ko [beta 2Mko]), and following intraperitoneal injection, two disease processes could be distinguished. First, the virus caused early (3 to 7 days postinfection) death in a viral dose-dependent manner. Immunocompetent C57BL/6 mice were highly susceptible (50% lethal dose = 70 PFU), while immunodeficient transgenic ko mice were less susceptible, showing 10- and 180-fold increases in the 50% lethal dose (for CD4ko and beta 2Mko mice, respectively). Second, a histologic examination of surviving CD4ko mice at 7 days postinfection revealed severe myocarditis; the inflammatory infiltrate comprised 40 to 50% macrophages, 30 to 40% NK cells, and 10 to 20% CD8+ T lymphocytes. The infiltration resolved over the following 2 to 3 weeks, with resultant myocardial fibrosis. In vivo depletion of CD8+ T lymphocytes from these CD4ko mice led to a marked reduction in myocarditis and an increase in myocardial virus titers. beta 2Mko mice, which lack antiviral CD8+ T cells, are much less susceptible to early death and to the development of myocarditis. We conclude that our data support a strong immunopathologic component in CVB3-induced disease and implicate both CD4+ and CD8+ T cells. Compared with immunocompetent animals, (i) mice lacking CD4+ T cells (CD4ko) were more resistant to virus challenge, and (ii) mice lacking CD8+ T cells (beta 2Mko and in vivo-depleted CD4ko) showed enhanced survival and a reduced incidence of the later myocarditis. Nevertheless, the picture is complex, since (iii) removal of the CD4+ component, while protecting against early death, greatly magnified the severity of myocarditis, and (iv) removal of the CD8+ cells from CD4ko mice, although protecting against early death and later myocarditis, led to markedly increased virus titers in the heart. These data underscore the complex balance between the costs and benefits of effective antiviral immune responses.

The role of CD8+ T lymphocytes in coxsackievirus B3-induced myocarditis.

An Antiviral Mechanism of Nitric Oxide: Inhibition of a Viral Protease

Group B coxsackieviruses (CVB) utilize the coxsackievirus-adenovirus receptor (CAR) to recognize host cells. CAR is a membrane protein with two Ig-like extracellular domains (D1 and D2), a transmembrane domain and a cytoplasmic domain. The three-dimensional structure of coxsackievirus B3 (CVB3) in complex with full length human CAR and also with the D1D2 fragment of CAR were determined to ∼22 A resolution using cryo-electron microscopy (cryo-EM). Pairs of transmembrane domains of CAR associate with each other in a detergent cloud that mimics a cellular plasma membrane. This is the first view of a virus–receptor interaction at this resolution that includes the transmembrane and cytoplasmic portion of the receptor. CAR binds with the distal end of domain D1 in the canyon of CVB3, similar to how other receptor molecules bind to entero- and rhinoviruses. The previously described interface of CAR with the adenovirus knob protein utilizes a side surface of D1.

/pdf/interaction-of-coxsackievirus-b3-with-the-full-length-3jvgu3cmz3.pdf

Interaction of coxsackievirus B3 with the full length coxsackievirus-adenovirus receptor.

Inoculation of adolescent CD-1 mice with one variant of coxsackievirus B3 (CVB3m) results in induction of readily observable myocardial lesions, whereas inoculation of siblings with a second variant (CVB3o) results in little or no myocarditis. These variants could not be distinquished from each other on the basis of replication properties in HeLa cells or cardiac tissues in vivo, sensitivity to human interferon in HeLa cells, induction of interferon in the mouse, generation of detectable levels of defective-interfering particles in HeLa cells or in cardiac tissue in vivo, stimulation of serum-neutralizing antibody titers, nor in their rate of clearance by the spleen. Infectivity of CVB3o was slightly more heat labile at 34 degrees C than CVB3m. Little if any replication of either CVB3o or CVB3m occurred in either adherent or nonadherent populations of normal murine lymphoid cells. Cardiac tissues from mice inoculated with CVB3m but not CVBo contain new antigens that can inhibit migration of sensitized lymphocytes from CVB3m-immunized mice in an in vitro cell-migration-inhibition assay. However, the CVB3o variant was shown to have the genetic capability of inducing myocarditis if the mice were treated with cyclophosphamide prior to virus inoculation. These results suggest, in agreement with our previously published work, that induction of myocarditis by CVB3 requires destruction of myocytes by virus and subsequent stimulation of cell-mediated responses to new antigens produced in the myocardium during virus replication.

D. R. L. Labadie

Papers

Properties of coxsackievirus B3 variants which are amyocarditic or myocarditic for mice.