While going through many literatures I found that in SRB assay negative percent growth is evaluated and it is been mentioned as cytocidal effect of drug or any other substance. I want to know the principle of that and how it is evaluated.
Dear Naveen
It will depend on the assay being performed.
The SRB assay is a colorometric assay where the intensity of the color is directly related to the number of cells in the well of the culture plate at the end of the assay time. The more cells the more intense the color measured at the end-point.
All the assays use a range of treatment concentrations to establish a dose-survival or dose-effect curve which is adjusted for a blank and compared to a negative control (untreated) and a positive control (where a similar effect of a known compound is used to establish that the assay actually works and the limits of the sensitivity of the method). These values set the limits of the dose response curve.
If you are looking for cytotoxicity then an IC50 is determined where you compare the different treatment concentrations to an untreated set of cells, grown on the same plate. The expected growth of the treated cells will be less than for the untreated cultures and this is commonly reported as a percent survival relative to 100% (the untreated control). Some researchers report this as the percent cells that have died, often as a negative percentage.
Another way of looking at the effect on cells is to use GI50 where you are measuring the growth inhibition and this requires a standardised point to which all plates are grown (typically 24 hours) prior to any treatment with a complete plate then being assayed as representative of all the plates. The remaining plates are then treated and cultured for a further time suitable for the cell type and treatment outcome. An increase in cell number due to cell growth will give increased SRB color with the most proliferation for the untreated control (if you are expecting cytotoxicity). Anything lower than the SRB value of the untreated cells is growth inhibition but not cytocidal, while any value lower than the initial standardised point is then cytocidal as the cells have failed to increase in number and even decreased in number from the initial treatment point. These values are also reported as negative percentages.
Hope this helps.
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