Modulation of the intracellular accumulation of saquinavir in peripheral blood mononuclear cells by inhibitors of MRP1, MRP2, P-gp and BCRP

Background: The efflux transporters P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRP) and breast cancer resistance protein (BCRP) limit the accumulation of antiretrovirals in cell lines but it is more important to know whether the expression of these transporters in peripheral blood mononuclear cells (PBMC) impacts cellular drug concentrations.

Objectives: To study the transport and accumulation of saquinavir (SQV) in PBMC and the effects of specific inhibitors of MRP1, MRP2, P-gp and BCRP.

Methods: Transport and accumulation of [H-3]-SQV was measured in PBMC in the absence or presence of specific and non-specific inhibitors of MRP1, MRP2, P-gp and BCRP. Flow cytometric, western blot and real-time PCR assays were used to examine the relative expression of the drug efflux transporters in the same batches of PBMC.

Results: MRP2 is present in PBMC. The expression of P-gp, MRP1, MRP2 (mRNA) and BCRP all displayed batch-to-batch variability. Specific and non-specific inhibitors of MRP1, P-gp and MRP2 significantly increased the baseline accumulation of SQV. Accumulation of SQV was not correlated with the expression of any single transporter.

Conclusions: Multiple drug efflux transporters are important in the intracellular accumulation of SQV in PBMC. If drug efflux contributes towards virological failure, then all contributing transporters will need to be inhibited.