In vitro identification of decreased function genetic variants of ABCB1.

The efflux transporter ABCB1 (P-glycoprotein, P-gp) has an important role in drug disposition, and thus, genetic variants that lead to decreased transport function might increase drug exposure. Complete loss of function of ABCB1 is rare but a few nonfunctional variants have been found. We studied the transport activity of the common S893A/T (c.2677T>G/A) variants and a set of 14 other naturally occurring non-synonymous single nucleotide variants to find new decreased function variants. The reference ABCB1 (c.1236T, c.2677T, c.3435T haplotype) and variants (N21D, H61Y, Y116C, N183S, I261V, L305P, R580P, C717Y, S795C, I836V, Y853N, S893A, S893T, V907F, Y928S, and A980P) were expressed in Sf9 cells. These cells were then used to prepare membrane vesicles, which were used to study N-methyl-quinidine (NMQ) and aliskiren transport. Aliskiren kinetics were characterised, as it has not previously been used in vesicle transport assays. Compared to the reference, C717Y caused a complete loss of NMQ and aliskiren transport, and L305P and V907F decreased transport to <25 % of the reference. In addition, R580P and A980P decreased the transport of both substrates to ≤50 %, while S795C affected only NMQ transport. Based on our results, carriers of the C717Y, L305P, or V907F variants may experience altered distribution and exposure of ABCB1 substrate drugs.