Direct Evidence that Saquinavir Is Transported by Multidrug Resistance-Associated Protein (MRP1) and Canalicular Multispecific Organic Anion Transporter (MRP2)

Abstract

The oral bioavailabilities of the human immunodeficiency virus (HIV) protease inhibitors (saquinavir, ritonavir, indinavir, nelfinavir, and amprenavir) are low and/or variable, with limited penetration into the central nervous system (CNS) (18). Saquinavir mesylate was the first drug approved in this class. The two marketed saquinavir capsule formulations have mean oral bioavailabilities that range from 4 to 16% and are highly variable, as indicated by area under the concentrationtime curve (AUC) coefficients of variation that are Ն30% (11). Saquinavir's low and variable bioavailability is primarily attributed to metabolism by cytochrome P-450 3A4 (27). However, there is increasing understanding that membrane transporters contribute significantly to the biopharmaceutic characteristics of saquinavir and this entire class of drugs.To relate bioavailability to molecular transport characteristics, we, like many others, speculated that an efflux (countertransport) mechanism might contribute to the low and variable bioavailability of saquinavir and other HIV protease inhibitors. Saquinavir efflux (basolateral to apical [BL3AP] permeability Ͼ AP3BL permeability) and the inhibition of saquinavir efflux with verapamil hydrochloride, a substrate for multiple transporters and a nonspecific efflux inhibitor, were demonstrated with a Caco-2 cell model (3). In preliminary work, we demonstrated that saquinavir efflux from rat intestinal tissue is an active process (27). However, these studies did not specifically identify the transporter or transporters involved within these complex tissues. Since Caco-2 cells and rat intestinal tissue are known to express multiple transporters, the observed saquinavir transport behavior may be related to multiple transporters with multiple affinities.Recent studies have shown that the HIV protease inhibitors are substrates for the P glycoprotein (Pgp [ABCB1]) efflux pump and have demonstrated reduced saquinavir cytotoxicity due to saquinavir transport by Pgp (17). Saquinavir transport by Pgp has also been correlated with reduced bioavailability and CNS penetration (18). However, saquinavir transport by Pgp does not rule out saquinavir being a substrate for other putative membrane transporters. To this end, other investigators have demonstrated that saquinavir inhibits multidrug resistance-associated protein (MRP) family (MRP1 and MRP2)-mediated transport (15,20,24) and that a fluorescent saquinavir derivative is transported by MRP2 (14). Additionally, intracellular saquinavir concentrations were shown to be reduced in MRP1-expressing human lymphocytes relative to those in control cells (15,16).To determine if unmodified saquinavir is a substrate of human MRP1 (hMRP1 [ABCC1]) or the human canalicular multispecific organic anion transporter hMRP2 (cMOAT, or

Intestinal absorption of novel-dipeptide prodrugs of saquinavir in rats

“…Thus peptide prodrug derivatization of SQV is a viable strategy to bypass P-gp mediated efflux and to completely shut down repeated exposure to intestinal CYP3A mediated metabolism. Saquinavir is also known to be a substrate for several MRP's which also play an important role in intestinal permeability and metabolism of SQV (Williams et al, 2002). The role of MRP mediated efflux in the disposition of SQV is under investigation in our laboratory.…”

“…Several reports speculate that low and variable oral bioavailability of SQV and other protease inhibitors is primarily caused by membrane bound efflux proteins like Pglycoprotein and multi drug resistance proteins (MRPs) and partly due to CYP3A4 mediated metabolism (Dupre et al, 1995;Fitzsimmons and Collins, 1997;Kim et al, 1998;Polli et al, 1999;Williams et al, 2002). Presence of P-gp on blood brain barrier further limits the entry of these drugs into the brain making it a sanctuary site for viral replication (Bachmeier et al, 2005).…”

Intestinal transporters for endogenic and pharmaceutical organic anions: the challenges of deriving in-vitro kinetic parameters for the prediction of clinically relevant drug–drug interactions

“…p-Aminohippuric acid [92] 372 Bilirubin biglucuronide [93] 0.8 a Daunorubicin [94,95] 1.4 Atazanavir [59] Bilirubin bisglucuronide [93] Bilirubin monoglucuronide [93] 0.4 a Grepafloxacin [96] Benzbromarone [97,98] Bilirubin monoglucuronide [93] E217bG [99] 22 Irinotecan [100] Benzylpenicillin [98] DHEAS [101] 5 Estradiol sulfate [102] 0.4 Methotrexate [98,103,104] 930/2150 Daunorubicin [99]~8a DNP-GS [105] 3.6 E23SO417bG [99] 1.7 Doxorubicin [99]~5 0 a E217bG [99,[105][106][107] 1.5-4.8 E316bG [99] 45 Mitoxantrone [108] Flurbiprofen [109] Estrone-3-sulfate [102] 0.7/4.2 E317bG [99] 1.4 Saquinavir [110] Furosemide [98] Folic acid [103] Estrone-3-sulfate [102] 0.5 Vinblastine [111] Glibenclamide [77] Glutathione [97,112] Glycholate [99] Vincristine [95,113] Indinavir [114] Leucovorin [103] Glycolithocholate-3-sulfate [99] 1.4 Indometacin …”

Both P-gp and MRP2 mediate transport of Lopinavir, a protease inhibitor

“…Functionally it is similar to P-gp mediated elimination of toxic compounds in gut and placenta (Kruh and Belinsky, 2003). It has been fairly established that MRP2 effluxes PIs (Huisman et al, 2002;Williams et al, 2002).…”