Modulation of P-glycoprotein function in human lymphocytes and Caco-2 cell monolayers by HIV-1 protease inhibitors

AIDS. 1999 Sep 10;13(13):1623-7. doi: 10.1097/00002030-199909100-00004.


Objectives: To determine the effect of the protease inhibitors ritonavir, nelfinavir and indinavir on the P-glycoprotein (P-gp)-mediated transport of saquinavir in Caco-2 cell monolayers. To study the modulation of P-gp function in human lymphocytes by saquinavir, ritonavir, nelfinavir and indinavir.

Methods: We examined the effect of the protease inhibitors on P-gp function in human lymphocytes by using Rhodamine 123 (Rh 123; a fluorescent substrate of P-gp) by flow cytometry. Efflux of Rh 123 correlates with P-gp function and inhibition of P-gp results in dye retention. Verapamil, a P-gp modulator and inhibitor of active transport at 4 degrees C was used as a positive control. The transport of [14C]saquinavir (1 microM) across Caco-2 cell monolayers was investigated, alone and in the presence of verapamil and ketoconazole (500 microM) and the protease inhibitors at 100 microM. Caco-2 cells are an in vitro model of the intestinal epithelium that is widely used for the study of P-gp function. The transport of saquinavir was determined in both the apical to basolateral (AP-BL) and basolateral to apical (BL-AP) directions.

Results: Saquinavir and ritonavir (10 microM) markedly inhibited Rh 123 efflux with an increase in fluorescence intensity similar to that obtained with verapamil. A small but statistically significant increase in fluorescence intensity was observed with nelfinavir; however indinavir did not modulate Rh 123 efflux. In Caco-2 cells the apparent permeability coefficient for BL-AP efflux of saquinavir exceeded that for AP-BL efflux by a factor of 26: this is indicative of an active efflux pump. Known P-gp modulators caused a decrease in BL-AP efflux and an increase in AP-BL transport. The protease inhibitors displayed some P-gp modulation with ritonavir having the most potent effect.

Conclusions: We have demonstrated that saquinavir is a substrate for P-gp and that ritonavir, nelfinavir and indinavir modulate P-gp function in both human lymphocytes and Caco-2 cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / antagonists & inhibitors
  • ATP Binding Cassette Transporter, Subfamily B, Member 1 / physiology*
  • Biological Transport / drug effects
  • Caco-2 Cells
  • Flow Cytometry
  • Fluorescent Dyes
  • HIV Protease Inhibitors / pharmacology*
  • Humans
  • Indinavir / pharmacology
  • Lymphocytes / metabolism*
  • Nelfinavir / pharmacology
  • Rhodamine 123
  • Ritonavir / pharmacology
  • Saquinavir / pharmacokinetics*
  • Temperature
  • Verapamil / pharmacology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Fluorescent Dyes
  • HIV Protease Inhibitors
  • Rhodamine 123
  • Indinavir
  • Verapamil
  • Nelfinavir
  • Saquinavir
  • Ritonavir