VeroE6 (ATCC CRL-1586) and Caco-2 (ATCC HTB-37) cells
Virus strain
SARS-CoV-2 strain BavPat1 was obtained from Pr Drosten through EVA GLOBAL (https://www.european-virus-archive.com/). To prepare the virus working stock, a 25 cm2
Antiviral screen
One day prior to infection for the antiviral screening 5 × 104 VeroE6 cells were seeded in 100 µL assay medium (containing 2.5% FCS) in 96 well plates. The next day, a single dilution of each compound of the PCL at 10 µM final concentration was added to the cells (25 µL/well, in 2.5% FCS-containing medium). Six virus control wells were supplemented with 25 µL medium (positive controls hereafter named vc) and eight cell control wells were supplemented with 50 µL of medium (negative controls, hereafter named nc). Two internal well controls of viral inhibition were added, corresponding to the addition of 10 µM arbidol (SIGMA, St Louis, USA) in the infected cell culture (arbidol controls, hereafter named arb). After 15 min, 25 µL of a virus mix diluted in 2.5% FCS-containing medium was added to the wells at MOI 0.002.
Three days after infection, cell supernatant media were discarded and CellTiter-Blue reagent (PROMEGA, Fitchburg, USA) was added following the manufacturer’s instructions. Plates were incubated for 2 h prior recording fluorescence (560/590 nm) with a Tecan Infinite 200Pro machine (TECAN, Zurich, Switzerland). From the measured OD590nm, the Inhibition Index was calculated as follows: first, cell viability for compounds, vc and arb were calculated: (OD590nm value/mean OD590nm of nc) × 100. For vc and arb, mean cell viability were calculated. Then all cell viabilities were normalized by subtracting mean vc. cell viability of the 96 well plates. Finally, Inhibition index was calculated as follows: Inh. Index = normalized cell viability of the compound/normalized cell viability of arb in the same 96 well plate.