Assessment of active transport of HIV protease inhibitors in various cell lines and the in vitro blood-brain barrier

Objective: To investigate the involvement of P-glycoprotein (Pgp) and the m ultidrug resistance-associated protein (MRP) on the active transport of the HIV protease inhibitors amprenavir, ritonavir and indinavir. Methods: The transport behaviour of ritonavir, indinavir and amprenavir in the presence and absence of Pgp modulators and probenecid was investigated in an in vitro blood-brain barrier (BBB) co-culture model and in monolayers of LLC-PK1, LLC-PK1:MDR1, LLC-PK1:MRP1 and Caco-2 cells. Results: All three HIV protease inhibitors showed polarized transport in th e BBB model, LLC-PK1:MDR1 and Caco-2 cell line. The Pgp modulators SDZ-PSC 833, verapamil and LY 335979 inhibited polarized transport, although their potency was dependent on both the cell model and the HIV protease inhibitor used. Ritonavir and indinavir also showed polarized transport in the LLC-P K1 and LLC-PK1:MRP1 cell line, which could be inhibited by probenecid. HIV protease inhibitors were not able to inhibit competitively polarized transp ort of other HIV protease inhibitors in the LLC-PK1:MDR1 cell line. Conclusions: Amprenavir, ritonavir and indinavir are mainly actively transp orted by Pgp, while MRP also plays a role in the transport of ritonavir and indinavir. This indicates that inhibition of Pgp could be useful therapeut ically to increase HIV protease inhibitor concentrations in the brain and i n other tissues and cells expressing Pgp. The HIV protease inhibitors were not able to inhibit Pgp-mediated efflux when given simultaneously, suggesti ng that simultaneous administration of these drugs will not increase the co ncentration of antiretroviral drugs in the brain. (C) 2001 Lippincott Willi ams & Wilkins.