Screening of large collection of compounds for anti-human parainfluenza virus type-2 activity and evaluation of hit compounds

Abstract: Human parainfluenza virus type-2 (HPIV-2) is a highly contagious respiratory pathogen that can cause severe respiratory disease known as laryngotracheobronchitis or croup-like disease in children. No specific vaccine or an antiviral drug is currently approved for treatment of HPIV-2 infections. In this project, a library of 14400 diverse compounds had been screened for anti-HPIV-2 activities in cultures of African green monkey kidney cells. All compounds that inhibited the virus induced syncytium-forming activity in these cells were considered as hit compounds. Three hit compounds showed moderate anti-HPIV-2 activity characterized by the IC50 values of 20 µM and selectivity indices of approximately 5. This suggests that the antiviral activity of these compounds was due to targeting activities of cellular rather than viral components. Another hit compound, referred to as compound 5, showed anti-HPIV-2 activity that was manifested as a reduction of area of the virus-induced plaques in cells at not cytotoxic concentrations. Interestingly, this compound did not inhibit initial infection nor the virus production in infected cells as revealed by the time-of-addition assay. Moreover, it showed no direct the virus-inactivating (virucidal activity) against HPIV-2 particles. However, relatively short pre-treatment (4 hours) of the cells with compound 5 prior to the virus infection was sufficient for its plaque size-reducing activity suggesting that anti-HPIV-2 activity of compound 5 was due to targeting activities of cellular rather than viral components. Further studies are needed to elucidate the anti-HPIV-2 mechanism of activity of hit compounds identified in the present study.