Differential Effect of HIV-1 Protease Inhibitors on P-Glycoprotein Function in Multidrug-Resistant Variants of the Human CD4+ T Lymphoblastoid CEM Cell Line

Background: P-glycoprotein causing multidrug resistance (MDR) and limiting the efficacy of antineoplastic drugs and protease inhibitors (PIs) is expressed in human CD4+ T lymphocytes, one of the main targets of HIV, in a range of pharmacological barriers and at varying degrees in non-Hodgkin’s lymphoma and Kaposi’s sarcoma. Methods: The differential effect of PIs on P-glycoprotein function was studied by measuring drug efflux inhibition, MDR-reversing ability and MAb UIC2 epitope modulation in MDR variants of the human T lymphoblastoid CEM cell line. Results: The treatment of MDR cells with PIs induces different UIC2 epitope modulations indicating a differential recognition and binding of these antiviral drugs by MDR1 P-glycoprotein. In fact, ritonavir, saquinavir and indinavir act differently to the P-glycoprotein blocker in CEM-VBL10 cells. The MDR level of these cells was markedly affected by ritonavir and saquinavir in the order, while the PI indinavir does not seem to compete with the P-glycoprotein drug transport function. In CEM-VBL100 cells, expressing a very high number of P-glycoprotein molecules, only ritonavir acts as an efficient drug efflux inhibitor and MDR-reversing agent. Conclusion: TheHIV-1 PIs ritonavir and saquinavir even at different levels act as genuine P-glycoprotein substrates by inhibiting dye substrate efflux, modulating UIC2 epitope and reversing drug resistance. Conversely, at least in the in vitrosystem used in the present study, the PI indinavir does not significantly alter P-glycoprotein drug transport activities and function.