Inhibitor dose-response curve analysis and effect-measure calculations

Raw absorbance values were adjusted to a reference blank value (average of positive-control wells containing a drug combination of flavopiridol, staurosporine and velcade), normalized to untreated control wells, and bounded at 0 and 100 to produce cell viability percentages. Normalized viability percentages¹⁶ at each dose of single agent or combination 7-point dilution series were analyzed for all patient samples that passed a quality control inspection (based on plate- and profile-specific expectations of drug-induced cell inhibition). A two-parameter probit regression curve was fit to each 7-point log₁₀-transformed dose-response profile using maximum likelihood estimation for the intercept and slope. This parametric model was chosen over a polynomial because the probit’s monotonic shape reflects a dose-response curve typically seen in samples incubated with cytotoxic or inhibitory agents¹⁷. From the fitted probit curve for each sample-drug pairing, the half maximum inhibitory concentration (IC₅₀) was defined as the lowest concentration to achieve 50% predicted viability and the area under the curve (AUC) was computed by integration of the curve height across the tested dose range. If the predicted cell viability (i.e., probit curve height) was ≤ 50% at the lowest tested dose or > 50% across the entire dose range, the IC₅₀ was designated as the lowest dose or highest dose, respectively. For sensitivity profiles with 100% normalized viability at all 7 dose points, the IC₅₀ and AUC were designated as the highest tested dose and the maximum possible AUC, respectively. For sensitivity profiles with 0% viability at all 7 dose points, the IC₅₀ and AUC were designated as the lowest tested dose and a value (0.01) just below the minimum probit-derived AUC, respectively.