Drug Sensitivity Score (DSS) Analysis

To quantitatively profile the drug sensitivity with a more robust parameter than the IC₅₀ or EC₅₀ values, the drug sensitivity score (DSS) analysis was employed. DSS values are essentially normalized area under the curve (AUC) measures of dose-response inhibition data (Yadav et al., 2014). Drug response data files (in Excel) ready for online analysis were prepared according to the example file obtained from the DSS pipeline website, called Breeze¹ (Potdar et al., 2020). Either raw fluorescence intensity measurements or normalized % inhibition data (for BRET assay analysis) were uploaded.

The output file provides several drug sensitivity measures including EC₅₀ and AUC. We plotted the DSS₃ value (Yadav et al., 2014), which was calculated as

where DSS₂ is given by the equation DSS2=DSS1log⁡a

and DSS₁ is given by the equation DSS1=AUC-t(x2-x1)(100-t)(Cmax-Cmin)

DSS₃ was employed to emphasize drugs that obtain their response area over a relatively wide dose window, as compared to drugs that show increased response only at the higher end of the concentration range. After logistic fitting of the dose-response inhibition data, the area under the curve (AUC) was determined as the exact solution. A 10% minimal activity threshold (t) was set. The maximum (C_max) and minimum (C_min) concentrations were used for screening of the inhibitors, with C_max = x₂ and x₁ concentration with minimal activity t. The parameter a is the value of the top asymptote, which can be different from 100% inhibition as obtained from 100 μM benzethonium chloride treatment.