2.7. Cytotoxicity assay

Cell viability was determined by CCK8 kit following the manufacturer's instructions. First, exponentially growing ACE2^h cells were collected and seeded into 96‐well plates at a density of 5 × 10³ cells/well, and then the cells were treated with different concentrations of drugs (0, 0.1, 1, 10, 50, 100, 200, 300 and 400 μM) for 24 h, then CCK8 solution were added to each well and incubated at 37°C for 2 h. the absorbance at 450 nm was measured with a microplate reader (Bio‐Rad, Carlsbad, California) to evaluate the relative cell viability. The formula for calculating the survival rate of ACE2^h cells is as follows: