Differences in the intracellular accumulation of HIV protease inhibitors in vitro and the effect of active transport

Objectives: To investigate the intracellular accumulation of HIV protease inhibitors (PI) and to assess the effect of active transport on this accumulation. Methods: CEM cells were incubated with a PI for 18 h and the intracellular concentration determined using cell number and radioactivity. The effect of active transport was investigated using cells expressing P-glycoprotein (CEMVBL) and cells expressing multidrug resistance-associated protein 1 (MRP1; CEME1000) Incubations were also carried out at 4 degreesC and in the presence of 2-deoxyglucose plus rotenone to examine the effect of inhibiting active transport. Results: Nelfinavir (NFV) accumulated to the greatest extent (> 80-fold) followed by saquinavir (SQV; similar to 30-fold), ritonavir (RTV; 3-7-fold) and finally indinavir (IDV; extracellular equivalent to intracellular). In CEMVBL cells there was a significant reduction in the intracellular accumulation of NFV, SQV and RTV and in CEME1000 cells there was reduced accumulation of SQV and RTV Inhibition of active transport processes caused a reduction in SQV and RTV accumulation but had no effect on IDV accumulation in all cell types. NFV accumulation was increased in CEM(VBL)cells as a result of inhibition of active transport. Conclusions: Marked differences can be detected in the intracellular accumulation of HIV PI drugs in vitro. Both P-glycoprotein and MRP1 may play a role in limiting the intracellular concentration of the PI and active influx mechanisms may contribute to drug accumulation. (C) 2001 Lippincott Williams & Wilkins.