molecular biology - What is the IC50 exactly?

I am reading the paper "Activity of the bcr-abl kinase inhibitor PD180970" but I don't understand how IC50 works on table 1. Can you tell with simple words and give me an easy example?

Answer

The IC₅₀ is the concentration of an inhibitor at which you observe the half maximal inhibition. See the figure from the Wikipedia:

The IC₅₀ can be seen as a way to measure the effectiveness of an inhibitor on a biological function as an enzyme. In the case of PD180970 you have an inhibitor which inhibits the p210 Bcr-Abl tyrosine kinase. The IC₅₀ is the concentration at which 50% of the kinase is inhibited.

In table 1 different mutations of the tyrosine kinase are tested against the inhibitor to see, if the mutations have an influence on the IC₅₀. This is important as PD180970 is considered as an anti-cancer drug and possible mutations would make it less effective here.