The novel parainfluenza virus hemagglutinin-neuraminidase inhibitor BCX 2798 prevents lethal synergism between a paramyxovirus and Streptococcus pneumoniae

Abstract

An association exists between respiratory viruses and bacterial infections. Prevention or treatment of the preceding viral infection is a logical goal for reducing this important cause of morbidity and mortality. The ability of the novel, selective parainfluenza virus hemagglutinin-neuraminidase inhibitor BCX 2798 to prevent the synergism between a paramyxovirus and Streptococcus pneumoniae was examined in this study. A model of secondary bacterial pneumonia after infection with a recombinant Sendai virus whose hemagglutinin-neuraminidase gene was replaced with that of human parainfluenza virus type 1 [rSV(hHN)] was established in mice. Challenge of mice with a sublethal dose of S. pneumoniae 7 days after a sublethal infection with rSV(hHN) (synergistic group) caused 100% mortality. Bacterial infection preceding viral infection had no effect on survival. The mean bacterial titers in the synergistic group were significantly higher than in mice infected with bacteria only. The virus titers were similar in mice infected with rSV(hHN) alone and in dually infected mice. Intranasal administration of BCX 2798 at 10 mg/kg per day to the synergistic group of mice starting 4 h before virus infection protected 80% of animals from death. This effect was accompanied by a significant reduction in lung viral and bacterial titers. Treatment of mice 24 h after the rSV(hHN) infection showed no protection against synergistic lethality. Together, our results indicate that parainfluenza viruses can prime for secondary bacterial infections. Prophylaxis of parainfluenza virus infections with antivirals might be an effective strategy for prevention of secondary bacterial complications in humans.

FIG. 1.

Chemical structure of BCX 2798 and its parent compound. (A) Neu5Ac2en (2-deoxy-2,3-dehydro-N-acetylneuraminic acid); (B) BCX2798 (4-azido-5-isobutyrylamino-2,3-didehydro-2,3,4,5-tetradeoxy-d-glycero-d-galacto-2-nonulopyranosic acid).

FIG. 2.

Effect of different doses of rSV(hHN) on weight loss (A) and survival (B) of mice in a secondary pneumonia model. Mice (n = 10 per group) were infected with a sublethal dose of 10^3.5, 10^4.5, or 10^5.5 TCID₅₀ per mouse of rSV(hHN) and then challenged 7 days later with a sublethal dose of 25 CFU of S. pneumoniae per mouse. Mice in a control virus group were challenged with PBS instead of bacteria and had 100% of survival (data not shown). Weight loss and survival of mice were monitored through 21 days after the bacterial challenge. Mean values for weight loss are plotted with error bars indicating the standard deviation. An asterisk indicates a significant difference in weight change or survival compared to the control groups infected with virus or bacteria alone (P < 0.05).

FIG. 3.

Effect of BCX 2798 on weight loss (A) and survival (B) of mice in a secondary bacterial pneumonia model after rSV(hHN) infection. Mice (n = 10 per group) were infected with a sublethal dose of 10^5.5 TCID₅₀ of rSV(hHN) per mouse and then challenged 7 days later with a sublethal dose of 25 CFU of S. pneumoniae per mouse. Mice in the control groups were infected either with virus or with bacteria alone. Treatment at 10 mg/kg per day with BCX 2798 or PBS as a placebo was started 4 h before viral infection. Weight loss and survival of mice were monitored through 21 days after the bacterial challenge. Mean values for weight loss are plotted with error bars indicating the standard deviation. An asterisk indicates a significant difference in weight change or survival for the drug-treated group compared to the synergism group receiving placebo (P < 0.05).

FIG. 4.

Lung viral (A) and bacterial (B) titers in a secondary pneumonia model following rSV(hHN) infection. Mice (n = 4 per group) were infected with a sublethal dose of 10^5.5 TCID₅₀ of rSV(hHN) per mouse and then challenged 7 days later with a sublethal dose of 25 CFU of S. pneumoniae per mouse. Mice in the control group were infected either with virus or bacteria alone. Treatment at 10 mg/kg per day with BCX 2798 or PBS was started 4 h before the viral infection in the treatment and placebo groups. Lungs were collected 4, 48, and 96 h after challenge with S. pneumoniae. Each point represents the results from a single mouse. A single asterisk indicates a significant difference in titers at that time point compared to the control group infected with a single agent (P < 0.05), and two asterisks indicate a significant difference in titers at that time point compared to the placebo group of mice. ND, not determined because of death of mice.

FIG. 5.

Histopathologic changes in the lungs of mice infected in a secondary bacterial pneumonia model. Mice received PBS only (A); S. pneumoniae D39 at 25 CFU per mouse 7 days after PBS mock infection (B); rSV(hHN) at 10^5.5 TCID₅₀ per mouse, followed 7 days later by PBS mock infection (C); rSV(hHN), followed 7 days later by pneumococci with placebo treatment (D); or rSV(hHN), followed 7 days later by pneumococci with BCX 2978 treatment (E). High-power magnification (×40) views of representative lung sections obtained 3 days after secondary challenge and stained with hematoxylin and eosin are pictured. The arrow in panel D highlights an area of extensive necrosis that is not present in the lungs of mice represented by panel E.