Dose response parameters
This page discusses metrics derived from curve fits, like IC50s. For details on the curve fitting process and differences between viability and DIP rate dose response curves, see curve fitting.
IC50 and inhibitory concentrations
Image: Definition of IC50 shown on a dose response curve
Half-maximal inhibitory concentration (IC50) is a measure of drug potency expressed in molar units (M).
It specifies the concentration at which the dose response curve reaches 0.5 on the y-axis (for DIP rate dose response
curves, this is 0.5 on a relative scale y-axis). The IC50 may be undefined in the event that the maximum
effect on the fitted curve does not reach 0.5 on the y-axis. On some plots in Thunor, this will show as NA.
Other inhibitory concentrations are defined analogously for any response value between 0 and 1. For DIP-based dose response curves, which can go below zero on the y-axis, IC100 denotes the concentration at which the dose response curve crosses the y-axis.
EC50, E50, and effective concentrations
Image: Definition of EC50 shown on a dose response curve
Half-maximal effective concentration (EC50) is a measure of drug potency expressed in molar units (M). It specifies the concentration at which the dose response curve reaches 50% of the maximum effect observed, based on the fitted model - i.e. the halfway point between the curves maximum and minimum y-values. The response/y-value of the curve at this point is the half-maximal effect (E50).
Relative vs absolute values
For DIP rate curve fits, EC and E values can be measured on a relative DIP rate axis, or an absolute one. Thus, metrics with "relative" in their name are measured on the relative axis. Viability is already a relative metric, so this distinction does not apply (all values correspond to viability relative to control).
Emax
Image: Definition of Emax shown on a dose response curve
The maximal effect (Emax) denotes the fitted curve's effect (i.e. the y-value) at the maximum observed concentration (the highest drug concentration for which there is data).
Emax (observed)
Image: Definition of Emax observed shown on a dose response curve
The observed maximal effect (Emax (observed)) is the maximum effect observed experimentally. Note that this is not necessarily observed at the maximum concentration.
Activity Area
Image: Definition of Activity Area shown on a dose response curve
Activity area is the area above the dose response curve, up to the no response value (1 on the y-axis), bounded by the minimum and maximum observed concentrations.
Activity area (observed)
Image: Definition of Activity Area (observed) shown on a dose response curve
Activity area (observed) is the area above the observed response values, up to the no response value (1 on the y-axis). Between doses, a straight line extrapolation is used (on a log10 dose x-axis). Response values above 1 are truncated at 1. If there are multiple response values for a particular concentration (replicates), the mean average is used.
Hill coefficient
Image: Definition of Hill coefficient shown on a dose response curve
The Hill coefficient quantifies the rate of onset of a drug's effect as drug concentration increases. It affects the steepness of the dose response curve.