IC50 is lower than 0

Some of the IC50 value in drug sensitivity databases is lower than 0. I am confused that how should we explain this data. For instance, IC50 of vinblastine (GDSC2:1004) on CCK81 is -5.550494585nM. (in Drug sensitivity IC50 (Sanger GDSC2))

Does it mean that this compound would enhance the cell proliferation instead of suppress the cell viability?

I would appreciate it if someone could give any reply. Thanks in advance :slight_smile:

Hi Yuwei,

My bet is you are looking at ln(IC50). It’s always good practice to plot histograms of your values, this quickly explains such confusions.