cells behaving differently - (Apr/14/2015 )

Hi eveyone,

I am in such a dilemma. I did a dose-response curve for some inhibitors in some cell lines and generated IC50s of the inhibitors. 

I calculated the IC25 from the IC50 in other to combine with the IC50 of another inhibitor previously generated. The IC25s seem to inhibit about 50% of the cells now and the IC50 inhibits about 60-70%, Is there an explanations for this. Has anyone come across such a thing.... It is driving me nuts as I don't know how to explain the results.

Thanks for your help.

Are the cells used from the same source, stock, and passage #?

Assuming that you performed the experiments in exactly the same way, this could indeed be a batch difference.

Sometimes when you use cells with different passage numbers, from different sources, different stocks and everything else that is variable between two cell batches, it causes differences in the results you obtain. In this case, as your IC25 causes more than 25% inhibition, it seems your cells are less 'potent' or capable (so to speak) to handle the inhibitory substance.

Thanks SusieQ and yl2j. The cells are from the same source and batch but of course different passage numbers the experiments were carried out few months apart. Like you said the cells might've undergone phenotypic changes. Is this a big issue or does it occur very often? 

I'll give you the most used answer in science; it depends, in this case on the cell line you're using. Some cell lines are extremely sensitive to external influences and it can take a lot of training and 'fingerspitzegefühl' to culture the cells without altering them dramatically, usually these are primary cell lines that have not been immortalized. In contrast, other cell lines can survive earthquakes, so to speak. It's just the differences that exist between the large array of cell types that can be cultured.

Overall, I would advise you to first try and reproduce the first results you want to combine your second results to. If you're trying to combine or compare something that was generated several months ago with something you only just did, it's best to first try and see if you can obtain similar results to what you previously saw, and only then perform your next experiment with which you want to compare the data. Whether or not that's practical depends on the experiment itself, of course.