How to calculate GI50 - (Nov/15/2009 )

Hi,

I've found that NCI commonly uses GI50 to calculate the anticancer potential of new drugs. Since now, I've calculated the IC50 of a drug after a 3 days exposure of cancer cell lines to the compound at different concentration, simply calculating : "number of cells in treated well/number of cells in control well" . It is obvious that in cancer cell lines that have a faster growth you will find lower IC50, so it would be better to have another parameter, possibly less influenced by this. Does GI50 answer to these questions? How to calculate ?

Thanks

Your extrapolation is wrong... the IC50 will only be lower in faster growing cells if the drug has a greater affect on the cells than it did for the slower growing cells. Otherwise the cells will grow at the same rate relative to the control, not relative to another cell line.