P-glycoprotein expression in HTLV-III cells after treatment with HIV-1 protease inhibitors

Abstract

Introduction: P-glycoprotein (P-gp), a membrane protein that pumps drugs out of cells, affects the availability and effectiveness of drugs and their extrusion from cells. HIV-1 protease inhibitors (PIs), part of the antiretroviral treatment known as highly active antiretroviral treatment, are substrates and possibly inhibitors of the P-gp pump. Their interaction may represent a potential effect on treatment efficiency. Our objective is to evaluate how the P-gp/PI interaction limits drug effectiveness.

Methods: HTLV IIIcc cell cultures were exposed to ritonavir and saquinavir for 24 hours. Supernatant solution was recovered for viral load assessment. Cells were labeled with monoclonal antibody against P-gp and analyzed by flow cytometery.

Results: Upregulation in P-gp expression from 1% to 7% was observed when cells were exposed to PIs, compared with cells not exposed to PIs (P = .05). Ritonavir 10 microg/mL caused a similar P-gp increment as did 20 microg/ mL saquinavir. To evaluate P-gp functionality, cells were exposed to rhodamine-123, a fluorescent dye that is also a P-gp substrate. Its accumulation was measured by flow cytometry. Slightly more rhodamine was observed in cells treated with higher PI concentration (P = .05). Higher viral load was obtained in suspension of cells with upregulated P-gp. Statistically significant decreased viral load was obtained in supernatants of cells expressing less P-gp (P < .04). Ritonavir 20 microg/mL caused the most marked reduction in viral load.

Conclusions: Our results suggest that the use of PIs upregulates the expression of P-glycoprotein on HTLV IIIcc cells, showing slightly inhibited functionality for those treated with higher concentrations. The rapid extrusion of the drug by P-gp seems to limit its action. Decreased viral load in suspensions with ritonavir 20 microg/mL may represent the inactivation of the transport pump, allowing the drug to work more efficiently.