Outline
The invention relates to the field of assessing transport activity of OATP (Organic anion-transporting polypeptide) transport proteins. In particular, the invention relates to a real-time, add-and-read fluorescence-based method for determining whether a test compound interferes with substrate transport activity of an OATP, by using a non-fluorescent control substrate which becomes fluorescent within a cell. The method is also applicable to measure the expression of an OATP and to discriminate between a transported substrate and an inhibitor of an OATP.