Inhibition Assays

➦ To determine the inhibitory potential of a test item the intracellular accumulation of the labeled probe substrate is performed in the absence or presence of increasing concentrations of the test item.

Experience has shown that a two-step procedure is recommendable:

First Step

Two point Inhibition: Inhibition of transporter-mediated uptake of a probe substrate by two different concentrations of a test item.
Example: Test item identified as an inhibitor showed a significant inhibitory effect.

Two point Inhibition

Second Step

Determination of IC50 value: Concentration dependent inhibition of a probe substrate by a test item and determination of the half-maximal inhibition value (IC50).

Determination of IC50 value

Alternative Second Step

Determination of the inhibition character (Ki value): Dixon Plot analysis to determine competitive or non-competitive inhibition.