Hi everyone,I have to calculate the GI50 (inhibition of growth by 50%) of some cell lines that are super resitant to the drug I am testing, and I can only reach 40% of death in my strongest dose. Because the cells don´t even reach 50% of death, the graphpad can not calculate the GI50. We can not test higher concentrations of drug because we don´t have enought drug. However, I know what is the absorbance given when the cells don´t proliferate (i.e. 100% of growth inhibition) I just can´t associate this absorbance with a dose point. it would be posible to put this absorbance as a baseline to the calculations?
I would like to know how can I configurate my analysis to find the GI50 of these cell lines giving the program the absorbance of the cells when there is 100% of growth inhibition.
I hope someone could help me =)
Priscila
te escribo en espanyol porque veo que estas en la Universidad en la que yo me doctore, si necesitas que lo haga en ingles no hay problema. Yo creo que en lugar de calcular el GI50 deberias calcular el GI75 ya que es el valor que si puede conseguir con tu droga. Si no, desde mi punto de vista, la unica solucion es aumentar la concentracion de la droga para conseguir el 50 % de muerte celular.
Saludos y disfruta la Autonoma.
if there is a linear effect of dose on GI up to 40%, construct a regression line of dose on GI and back extrapolate from estimated 50%GI to dose GI50.
Hola Joan,
¡Sin problema en preguntar en español y gracias contestarme! Calcular el IC75 (¿no sería IC25?) me parece una buena idea, al menos voy a concluir el ensayo con un número para estas líneas resistentes. Y es lo que quiero porque tengo que comparar la resistencia a la droga entre muchas líneas celulares, si calculo el IC75 para todas puedo compararlas y llegar a la misma conclusión.
Saludos!
Dear James,
Thank you for your answer! The normalized data seems to behave as a linear system but when I transform to Log scale it doesn´t show linear values…the value of last dose point becomes higher than the previous two dose points. Not sure how I could construct a regression line with this data...I am gonna try...
Hi Priscila,
You can fit a curve to your data and then, you may extrapolate to approximate GI50. In order to estimate the GI50 with this method, you have to be sure of the behaviour of your data to use the most appropriate fitting function. If you are not sure, you will have to do more experiments to generate new points.
Good luck!
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