Pre-treatment with a novel synthetic TLR4 agonist prior to challenge with mouse-adapted H1N1 and H2N3 influenza strains reduced morbidity and mortality in BALB/c mice

Abstract

Abstract According to the World Health Organization, influenza causes 3–5 million cases of severe illness and 250,000 – 500,000 deaths annually despite the availability of a seasonal vaccine. As an alternative therapy for use in high-risk groups and environments, we evaluated the efficacy of prophylactic treatment with a novel synthetic TLR4 agonist in BALB/c mice. Animals were anesthetized and treated with a TLR4 agonist intranasally (IN) 0 to 28 days prior to a lethal challenge with either H1N1 or H3N2 mouse-adapted human influenza. Animals were monitored daily for weight loss, decreased body temperature, body score, and mortality. Initial dose-response experiments demonstrated that mice treated with 50 μg or 10 μg of our novel TLR4 agonist in an aqueous formulation were similarly protected from H3N2 influenza challenge with respect to weight loss and survival. However, initial weight loss data demonstrated that 50 μg was not as well tolerated as 10 μg. The 10 μg dose was therefore selected as the lead dose in subsequent experiments. In a series of formulation comparison experiments, the lead formulation resulted in marked improvement in both percent weight loss and survival compared to initial TLR4 agonist formulations. Animals treated with all formulations of our novel synthetic TLR4 agonist 0, 7, or 14 days prior to infection resulted in 80–90% survival. The lead formulation also resulted 80–90% survival when given prophylactically 21 or 28 days prior to infection compared to 0–20% survival in untreated mice. Overall, our results show that pre-treatment with our novel synthetic TLR4 agonist prior to exposure to mouse-adapted H1N1 and H2N3 influenza strains reduced morbidity and mortality in infected mice for up to 28 days after treatment. This work was supported by NIH grant 5R44AI136081-03