HIV-1 Protease Inhibitors Are Substrates for the<i>MDR</i>1 Multidrug Transporter

TLDR

The FDA‑approved HIV‑1 protease inhibitors ritonavir, saquinavir, and indinavir effectively inhibit viral replication, but their long‑term efficacy remains uncertain. The study aimed to determine whether these drugs are recognized by the MDR1 multidrug transporter (P‑glycoprotein), which could reduce their intracellular accumulation and thus in vivo efficacy. In vitro and cell‑based assays showed that the inhibitors stimulate P‑glycoprotein ATPase activity, compete with IAAP labeling, inhibit transport of known P‑glycoprotein substrates (though less potently than verapamil or cyclosporin A), and reduce HIV‑1 replication in MDR1‑expressing cells, with the antiviral effect restored by MDR1 inhibitors, confirming that these protease inhibitors are substrates of the transporter and that MDR1 expression may limit their efficacy and alter their pharmacokinetics.

Abstract

The FDA approved HIV-1 protease inhibitors, ritonavir, saquinavir, and indinavir, are very effective in inhibiting HIV-1 replication, but their long-term efficacy is unknown. Since in vivo efficacy depends on access of these drugs to intracellular sites where HIV-1 replicates, we determined whether these protease inhibitors are recognized by the MDR1 multidrug transporter (P-glycoprotein, or P-gp), thereby reducing their intracellular accumulation. In vitro studies in isolated membrane preparations from insect cells infected with MDR1-expressing recombinant baculovirus showed that these inhibitors significantly stimulated P-gp-specific ATPase activity and that this stimulation was inhibited by SDZ PSC 833, a potent inhibitor of P-gp. Furthermore, photoaffinity labeling of P-gp with the substrate analogue [125I]iodoarylazidoprazosin (IAAP) was inhibited by all three inhibitors. Cell-based approaches to evaluate the ability of these protease inhibitors to compete for transport of known P-gp substrates showed that all three HIV-1 protease inhibitors were capable of inhibiting the transport of some of the known P-gp substrates but their effects were generally weaker than other documented P-gp modulators such as verapamil or cyclosporin A. Inhibition of HIV-1 replication by all three protease inhibitors was reduced but could be restored by MDR1 inhibitors in cells expressing MDR1. These results indicate that the HIV-1 protease inhibitors are substrates of the human multidrug transporter, suggesting that cells in patients that express the MDR1 transporter will be relatively resistant to the anti-viral effects of the HIV-1 protease inhibitors, and that absorption, excretion, and distribution of these inhibitors in the body may be affected by the multidrug transporter.