It is unclear from the table what the numbers represent. Are they % inhibition or IC50? In any case, you cannot calculate an IC50 unless you have measurements of inhibition made at several different inhibitor concentrations. The data in the table are for 4 different species, which I take to mean 4 different substances, so there is no concentration information.

A selectivity index is the ratio between the IC50 in one target or cell line and the IC50 in another. For cancer research, it is usually the ratio of the IC50 in a non-cancer cell line versus the IC50 in a cancer cell line. A higher number is better, of course, because the goal is to identify a substance that selectively kills cancer cells lines without affecting non-cancer cells.

There is no standard definition of potency of an IC50. Compounds that become drugs usually have potencies in the nanomolar range and have no effect or very little effect on non-cancer cells at any realistic concentration. Nanomolar potency is necessary because the concentration that can be safely achieved in the blood of the patient for a sufficient period of time to have an effect is typically in the single-digit micromolar or below.

Hello there.

1. No! You must have at least 4 results of viability on each speciuos to be eligible to calculate the IC50.

2.SI is defined when you test the samples on both cancer and normal cell lines. It can be measured as follows:

IC50 value of the normal cell/IC50 value of cancer cell

It can be used when the IC50 value of the normal cell is greater than cancer cells.

Hello Dalia Youssef El-Berawey

1- can i calculate the IC50 from this table (whatever cytotoxicity or viability) and does cytotoxicity =100-vaiabilty.

I agree with Adam B Shapiro with regards to the table provided. It does not provide any clear information.

To calculate IC50 value you should plot a graph of cell viability (%) on Y-axis and log concentration of the drug on the X-axis. For this purpose, you need to run a cytotoxicity assay using mammalian cancer cells with increasing concentrations of the candidate drug. From the absorbance values, calculate the cell viability (%) as follows:

Cell viability (%)= average absorbance of test / average abs of control x 100

Then plot a graph of cell viability (%) on Y-axis and log concentration of the drug on the X-axis. Calculate the IC50 value from the graph.

2- what is the meaning and indication of selectivity index (SI)

An ideal drug should kill cancer cells, but not affect the normal cells. Therefore, the selective index (SI) plays an important role. You should not only evaluate the anti-cancer activity of the herbal drug on mammalian cancer cell lines, but also evaluate its cytotoxicity on normal cells.

SI is the ratio of the toxic concentration of the candidate compound against its effective bioactive concentration.

Known as the tumor selective index,

SI= CC50 against normal cells/ IC50 against tumor cells.

where CC50 is the concentration of the candidate drug to cause death to 50% of the normal cells while IC50 is the half-maximal inhibitory concentration which is a measure of the candidate drug in inhibiting a biological function.

In an ideal situation, the IC50 value should be as low as possible while the CC50 value should be as high as possible which means that the drug is highly effective against cancer cells with minimal effect on normal cells. So, SI value gives you an idea about the selectivity of the drug. Greater SI value means your drug is more selective in killing cancer cells.

3- Does there is a standard classification of ic50

As mentioned by Adam B Shapiro there is no such thing as standard classification of IC50 value. However, in literature there has been a mention of it namely,

IC50 can be categorized as high (IC50 value below 1uM),

moderate (IC50 between 1uM and 10uM), and

low (IC50 above 10uM).

Low IC 50 value means that the drug is effective at low concentrations, and thus will show lower systemic toxicity when administered to the patient.

Best.