Practical application of the ΔΔlog(max/EC50) scale to quantify selectivity
| Procedure | Rationale |
|---|---|
| 1) Fits dose-response data to function to yield max (maximal response) and EC50 | Furnishes individual values for log(max/EC50), a single index of agonism |
| 2) Choose a reference agonist for comparison of all test agonists; use the same reference agonist for all systems (receptors, pathways, cell types) | Ratios to the index for the reference agonist cancels differences in receptor density, cell sensitivity, assay sensitivity, etc. |
| 3) Calculate Δlog(max/EC50) values for each test agonist (Δlog(max/EC50) = log(max/EC50)ref - log(max/EC50)test) | Scales agonist activity of the test agonist to that of the reference agonist within a given system (receptor type, signaling pathway, cell type, etc.) |
| 4) Calculate ΔΔlog(max/EC50) values across the two systems being compared (different receptors, signaling pathways, cell types, protein sequence, etc.) (ΔΔlog(max/EC50) = Δlog(max/EC50)ref – Δlog(max/EC50)test) | With the individual differences in sensitivity between the two systems cancelled, ΔΔlog(max/EC50) values provide a system-independent measure of the relative agonism of each test agonist in both systems |