using IC50 to determine dosing of inhibitor in cell culture - (Jul/17/2015 )

Hi,

I'm working in a lab for the first time and need to determine multiple concentrations of an enzyme inhibitor to use on cells in vitro.  If I know the IC50 of the inhibitor, how do I determine what range of concentrations of the inhibitor I can use if I am looking for dose-dependence of downstream effects caused be inhibiting the enzyme.

the ic50 is the half maximal inhibitor concentration. you want to set up a dose response curve. i recommend that you start by selecting concentrations which span from one log lower to one log higher and go from there (you may end up going lower, not likely to have to go higher)

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.