Determination of P-gp and MRP1 expression and function in peripheral blood mononuclear cells in vivo

P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) mediate the efflux of many therapeutic agents and have been implicated in the treatment failure of many infectious diseases and cancers. The ability to characterise the expression and function of these transporters in vivo is important when assessing the pharmacological activity of drugs. We investigated some of the problems involved in screening the multidrug resistance status of individuals using flow cytometry. Expression of P-gp and MRP1 on the surface of lymphocytes isolated from blood samples (30 ml) was determined by indirect immunofluorescence. Functional ability was assessed by measuring the efflux of specific fluorescent dyes. Results were expressed as a mean fold increase in fluorescence from the isotype control (expression) and a change in fluorescence compared to the load (function). Using these assays, we determined the expression of P-gp to be 2.01+/-0.40, n=30 and MRP1 to be 1.46+/-0.23, n=25. Functional ability was 6.98+/-4.97, n=25 for P-gp and 1.55+/-0.25, n=25 for MRP1. The dye efflux studies were associated with a lack of specificity and a number of methodological difficulties. There was no correlation between the expression and function of P-gp (r=0.338; p=0.10) or MRP1 (r=0.283; p=0.17). Therefore, we considered determination of P-gp and MRP1 expression to be a more reproducible and accurate approach to clinical investigation into the role of multidrug resistance.