ABSTRACT
Cellular drug response (concentration required for obtaining 50% of a maximum cellular effect, EC50) can be predicted by the intracellular bioavailability (F ic) and biochemical activity (half-maximal inhibitory concentration, IC50) of drugs. In an ideal model, the cellular negative log of EC50 (pEC50) equals the sum of log F ic and the negative log of IC50 (pIC50). Here, we measured F ic's of remdesivir, favipiravir, and hydroxychloroquine in various cells and calculated their anti-SARS-CoV-2 EC50's. The predicted EC50's are close to the observed EC50's in vitro. When the lung concentrations of antiviral drugs are higher than the predicted EC50's in alveolar type 2 cells, the antiviral drugs inhibit virus replication in vivo, and vice versa. Overall, our results indicate that both in vitro and in vivo antiviral activities of drugs can be predicted by their intracellular bioavailability and biochemical activity without using virus. This virus-free strategy can help medicinal chemists and pharmacologists to screen antivirals during early drug discovery, especially for researchers who are not able to work in the high-level biosafety lab.