This is not as easy at it seems. Often molecules' IC50s are defined by direct screen of a molecule against its molecular target, however when you move to a cell it is much different. When will you measure IC50? After 1 day? 2 days? 6 days? Time is a major factor, and you can see potency of a molecule shift significantly based on duration of exposure. Additionally, another variable that must be accounted for is cell density. You can absolutely alter how potent your molecules appear to be based simply on how many cells you use. i mean it makes sense right--you'll simply have more or less molecules of inhibtor per cell depending on the number of cells you use. Ideally to perform the most through science you'd have a plate, or even multiple plates setup to see how dose, time, and cell densit affect your molecule's potency.