BCRP / ABCG2 is a key determinant of pharmacokinetics of substrate drugs. Several
BCRP substrates and inhibitors are of low passive permeability, and the vesicular
transport assay works well in this permeability space. Membranes were prepared from
BCRP-HEK293, MCF-7/MX, and baculovirus-infected Sf9 cells with (BCRP-Sf9-HAM), and
without (BCRP-Sf9) cholesterol loading. Km values for three substrates - estrone-3-sulfate,
sulfasalazine, topotecan - correlated well between the four expression systems. In
contrast, a 10-20-fold range in Vmax values was observed, with BCRP-HEK293 membranes
possessing the largest dynamic range. IC50 values of the different test systems were
similar to each other, with 94.4% of pairwise comparisons being within 3-fold. Substrate
dependent inhibition showed somewhat greater variation, as 81.4% of IC50 values in
the BCRP-HEK293 membranes were within 3-fold in pairwise comparisons. Overall, BCRP-HEK293
membranes demonstrated the highest activity. The IC50 values showed good concordance
but substrate dependent inhibition was observed for some drugs.
