I use a drug for my cancer cell line, but I cannot a convenient concentration for my experiments. After reading some papers, I used 7 concentrations; 10, 25, 50, 100, 125, 150 and 200 uM. Interestingly, I cannot take a decrease of cell proliferation towards to high concentrations, when I look into 200 uM, it is similar to control, but in others there is a little decreasing about 20%.
I used WST-1 for 3 hours and values reached to above 3. I made this experiment for 3 days and results are same for 3 days.
What can I do to find the convenient drug concentration range and then IC50 value?