XTT and trypan blue..IC50..

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sophie_khiz's picture
XTT and trypan blue..IC50..

Can someone please help me.. i'm really confused now. I've got the IC50 value of my drug from XTT assay and then i treated my cancer cell line with the IC50 value and did trypan blue exclusion method.  I found that less than 10 cells were alive.  From what I understand IC50 value is the concentration of the drug/sample that could inhibit 50% cell growth but then why did the IC50 value killed almost all of the cells??
Please help me..