In the vesicular transport assay so-called “inside-out” membrane vesicles containing ABC transporters are applied. Incubating substrates of the respective efflux transporter in the presence of the inverted membrane vesicles and ATP will allow measuring accumulation of the substrates into the vesicles. In many cases radiolabeled reporter substrates are used but SOLVO developed the PREDIVEZTM Vesicular Transport Reagent Kits that use fluorescent reporter substrates.
The standard vesicular transport assay is an inhibitory assay performed with cold test articles. This assay provides information on any interaction between the ABC transporter and the test article. The transport of the reporter substrate is measured in the presence of the test article (typically in 7 concentrations) and IC50 is defined as the concentration inhibiting the transport of the reporter substrate by 50%.
Should radiolabeled form of the investigated compound or adequate analytical methods (LC/MS, HPLC) be available, the vesicular transport assay may be performed in a direct format without the reporter substrate and may identify substrate nature of the test article. The vesicular transport substrate assay is a low throughput assay. It is suitable for low permeability test compounds as high permeability compounds may escape from the vesicles through the lipid bilayer.
Figure 1. Working principle of the vesicular transport assay
Figure 2. Vesicular transport of 3H-taurocholate into SB-BSEP-Sf9-VT membranes
in the presence of different concentrations of the test drugs