P-glycoprotein expression affects the intracellular concentration and antiviral activity of the protease inhibitor saquinavir in a T cell line

A number of ATP-binding cassette proteins, which function as cellular efflux pumps, are known to be expressed on the membranes of human cells, including CD4-positive lymphocytes. It has also been shown recently that most anti-HIV protease inhibitors (PIs) are first-rate substrates of one of these membrane transporters, P-glycoprotein (Pgp). These findings raise the question of whether Pgp expression could influence HIV replication and/or affect the action of PIs. To gain new insight into this, initially unexpected, phenomenon, a study was undertaken with the aims of investigating whether treatment with saquinavir (SQV) induces Pgp expression in primary or transformed human T cell lines and, primarily, establishing whether Pgp expression could modify both the uptake of SQV and its antiviral action. Pgp expression, mainly measured by reverse transcription-PCR, was found to be variably detectable in healthy individuals, and short or prolonged SQV treatment was unable to induce or increase the expression of Pgp in a lymphoblastoid cell line or in primary lymphocytes derived from these individuals. However, further experiments, performed in a cell line with high Pgp expression (CEM V B L 1 0 0 cells) and its parental cell line (CEM cells), demonstrated that over-expression of Pgp reduces the uptake of SQV. This result is consistent with the finding that CEM V B L 1 0 0 cells are less sensitive to the antiviral activity of SQV, the ID 5 0 value (100 μM) being significantly higher than the corresponding value in parental CEM cells (4 μM).