BackgroundDuring COVID19 pandemic, a small molecule antiviral agent PAXLOVIDTM was authorised for emergency use. The main antiviral component is nirmatrelvir, a coronavirus MPRO inhibitor, but it was combined with ritonavir to achieve persistent cell exposure. Respiratory virus usually infects through the nose and intranasal treatment is an attractive option for prophylactic treatment but challenging. Therefore, alternate strategies to deliver and retain nirmatrelvir within a treated cell is of great importance.AimThe aim of this project is to investigate antiviral effects of nirmatrelvir in a novel nanoemulsion formulation on coronavirus infected human primary nasal epithelium.MethodSeasonal coronavirus (HCOV-229E) was inoculated to the apical surface of air liquid interface (ALI) cultured human primary nasal epithelium. Viral load in apical wash was determined by a 50% tissue culture infectious dose (TCID50) assay and RT-PCR. Cell integrity, a marker of cell damage by virus infection, was measured as a transmembrane electrical resistance (TEER). 50 µL of nirmatrelvir (0.1 µM) prepared in water or as a nanoemulsion was applied to apical surface of ALI nasal epithelium for 10 min, and virus inoculum (0.2 MOI) was then applied to apical surface on top of the treatment for 1 hr. Apical surface wash with media was collected after treatment, then 1, 2 and 3 days post virus inoculation.ResultsHCoV viral load was maximal at Day 1 post inoculation. Analysis of the area under the curve (AUC) of viral load for 3 days post inoculation revealed that nirmatrelvir in water, nanoemulsion alone, and nirmatrelvir in nanoemulsion showed 69.5%, 89.8% and 100% inhibition of viral load vs. control, respectively. RT-PCR AUC was also inhibited by 13.5%, 52.2% and 100%, respectively, suggesting nirmatrelvir and nanoemulsion component showed synergistic effects. The nirmatrelvir in nanoemulsion also protected from virus induced reduction of TEER. The nirmatrelvir in nanoemulsion was well tolerated and not cytotoxic.ConclusionNovel nanoemulsion formulation of nirmatrelvir was found to show better antiviral effects against COV infection in human primary nasal epithelium.Please refer to page A291 for declarations of interest related to this abstract.