Antiviral Compound Evaluation: Selectivity Index

The 50% effective concentrations (EC50), defined as a compound’s concentration inhibiting viral replication by 50%, was determined using a four- or three-parameter logistic regression (AAT Bioquest IC50 Calculator) to fit the dose–response curves. The cytotoxic concentration 50 (CC50), defined as a compound’s concentration reducing cell viability by 50%, was determined for each compound and cell type by the same method (AAT Bioquest IC50 Calculator). When our measurements did not reach 50% toxicity or 50% inhibition by studied concentrations, we used the estimated EC50 or CC50 value for further calculation of Selectivity Index (indicated as > 200 in Tables 2, 3). The Selectivity Index (SI) was calculated as previously reported^{21 (link)} by dividing the CC50 by the EC50 of every compound for each virus tested. A low SI (< 1) indicates a poor candidate for further development in therapeutical antiviral strategies. A high selectivity index (SI > 1) reflects an important range of concentrations that show an effective antiviral effect with low toxicity.