Tenofovir (TFV) undergoes renal elimination by a combination of glomerular filtration and active tubular secretion. While transporter-mediated uptake of TFV from the blood into proximal-tubule cells has been well characterized, comparatively little is known about the efflux system responsible for transporting TFV into the lumen during active tubular secretion. Therefore, members of the ATP-binding cassette family of efflux pumps expressed at the apical side of proximal-tubule cells were studied for the ability to transport TFV. Studies in multiple independent in vitro systems show TFV not to be a substrate for P glycoprotein (Pgp) or multidrug resistance protein type 2 (MRP2). In contrast to Pgp and MRP2, TFV was observed to be a substrate for MRP4. TFV accumulated to fivefold lower levels in MRP4-overexpressing cells, and its accumulation could be increased by an MRP inhibitor. Furthermore, MRP4-overexpressing cells were found to be 2.0-to 2.5-fold less susceptible to cytotoxicity caused by TFV. ATP-dependent uptake of TFV was observed in membrane vesicles containing MRP4 but not in vesicles lacking the transporter. On the basis of these and previous results, the molecular transport pathway for the active tubular secretion of TFV through renal proximal-tubule cells involves uptake from the blood mediated by human organic anion transporters 1 and 3 and efflux into urine by MRP4. A detailed understanding of the molecular mechanism of TFV active tubular secretion will facilitate the assessment of potential renal drug-drug interactions with coadministered agents.
Human immunodeficiency virus protease inhibitors (PIs) modestly affect the plasma pharmacokinetics of tenofovir (TFV; ؊15% to ؉37% change in exposure) following coadministration with the oral prodrug TFV disoproxil fumarate (TDF) by a previously undefined mechanism. TDF permeation was found to be reduced by the combined action of ester cleavage and efflux transport in vitro. Saturable TDF efflux observed in Caco-2 cells suggests that at pharmacologically relevant intestinal concentrations, transport has only a limited effect on TDF absorption, thus minimizing the magnitude of potential intestinal drug interactions. Most tested PIs increased apical-to-basolateral TDF permeation and decreased secretory transport in MDCKII cells overexpressing P-glycoprotein (Pgp; MDCKII-MDR1 cells) and Caco-2 cells. PIs were found to cause a multifactorial effect on the barriers to TDF absorption. All PIs showed similar levels of inhibition of esterase-dependent degradation of TDF in an intestinal subcellular fraction, except for amprenavir, which was found to be a weaker inhibitor. All PIs caused a dose-dependent increase in the accumulation of a model Pgp substrate in MDCKII-MDR1 cells. Pgp inhibition constants ranged from 10.3 M (lopinavir) to >100 M (amprenavir, indinavir, and darunavir). Analogous to hepatic cytochrome P450-mediated drug interactions, we propose that the relative differences in perturbations in TFV plasma levels when TDF is coadministered with PIs are based in part on the net effect of inhibition and induction of intestinal Pgp by PIs. Combined with prior studies, these findings indicate that intestinal absorption is the mechanism for changes in TFV plasma levels when TDF is coadministered with PIs.Tenofovir disoproxil fumarate (TDF; Viread, Gilead Sciences, Inc.), a prodrug of the nucleotide reverse transcriptase inhibitor tenofovir (TFV), is used to effectively deliver TFV across the gut wall. Following absorption, TDF rapidly degrades to TFV and TDF is not observed in the systemic circulation. When administered by itself, TFV has poor oral bioavailability (7). TDF is a common once-a-day backbone for use with human immunodeficiency virus (HIV) protease inhibitors (PIs). Clinical trials have shown TDF with emtricitabine in combination with either lopinavir (LPV) or atazanavir (ATV), each boosted with ritonavir (RTV, or "r" when referred to as a boosting agent), to be efficacious and well tolerated (22,30).Polypharmacy in HIV patients creates the potential for drug interactions (8,35). No interaction between PIs and TDF would be anticipated due to the lack of cytochrome P450 involvement in the elimination pathway of TDF or TFV (25). However, modest changes in TFV plasma pharmacokinetic parameters have been reported for TDF coadministered with PIs. As summarized in Table 1, PIs can be categorized into three different groups based on their effects on TFV plasma pharmacokinetics. The first group encompasses PIs that cause modest increases in TFV plasma exposure (area under the concentration-time curve from 0 h t...
The experimental pharmacoenhancer cobicistat (COBI), a potent mechanism-based inhibitor of cytochrome P450 3A enzymes, was found to inhibit the intestinal efflux transporters P-glycoprotein and breast cancer resistance protein. Consistent with its transporter inhibition, COBI significantly increased the absorptive flux of potential candidates for clinical coadministration, including the HIV protease inhibitors atazanavir and darunavir and the lymphoid cell-and tissue-targeted prodrug of the nucleotide analog tenofovir, GS-7340, through monolayers of Caco-2 cells in vitro.C obicistat (COBI) is being developed as a pharamacoenhancer (booster) for coformulation with drugs that are metabolized by cytochrome P450 3A (CYP3A) enzymes. Similar to ritonavir (RTV; currently used as a pharmacoenhancer of protease inhibitors [PIs] used to treat human immunodeficiency virus [HIV]), COBI is a potent mechanism-based CYP3A inhibitor, and its coadministration with CYP3A substrates can lead to desired boosting effects and unintended drug-drug interactions. COBI has been found to have a number of potentially differentiating attributes relative to RTV: (i) it has more selective CYP3A inhibition over other CYP enzymes, (ii) it has improved solubility and coformulatability, (iii) it has a reduced induction potential mediated by the pregnane X receptor (PXR; also known as the nuclear receptor subfamily 1, group 1, member 2 [NR1I2]), and (iv) it has decreased effects on adipocytes in vitro (21). COBI's lack of anti-HIV activity also eliminates the potential for selection of PI resistance mutations when boosting non-HIV PI drugs (21). Clinically, COBI increases systemic levels of the CYP3A substrates midazolam and elvitegravir (EVG) to a similar extent as RTV (7, 13), and coadministration with COBI allows EVG to be administered once daily (16). A fixed-dose, once-daily, single-tablet regimen that includes EVG/COBI and the nucleos(t)ide reverse transcriptase inhibitors tenofovir disoproxil fumarate and emtricitabine, colloquially known as "QUAD," has completed registrational trials, including meeting its primary endpoints in phase 3 studies (2,3,19,20).Inhibition of efflux transporters expressed in the intestine can serve as a secondary mechanism for a pharmacoenhancer to increase systemic exposure to coadministered drugs by increasing their absorption. P-glycoprotein (Pgp; also known as multidrug resistance protein 1 [MDR1] or ATP-binding cassette subfamily B member 1 [ABCB1]) and the breast cancer resistance protein (BCRP; also known as ATP-binding cassette subfamily G member 2 [ABCG2]), both expressed at the apical side of the small intestine, have been highlighted by regulatory agencies and in the literature as key transporters affecting xenobiotic pharmacokinetics (5, 6). In addition to the role of CYP3A enzymes in RTV boosting, HIV PIs are known to be substrates for transporters, including Pgp (11). Determination of the relative roles of transport and CYP3A inhibition in limiting HIV PI exposure is difficult due to their being sub...
Matrix metalloproteinase (MMP)-9 is a zinc-dependent protease associated with early immune responses to Mycobacterium tuberculosis infection, macrophage recruitment and granuloma formation. We evaluated whether adjunctive inhibition of MMP-9 could improve the response to standard TB treatment in a mouse model that develops necrotic lesions. Six weeks after an aerosol infection with M. tuberculosis, C3HeB/FeJ mice received standard TB treatment (12 weeks) comprising rifampin, isoniazid and pyrazinamide alone or in combination with either anti-MMP-9 antibody, etanercept (positive control) or isotype antibody (negative control) for 6 weeks. Anti-MMP-9 and the isotype control had comparable high serum exposures and expected terminal half-life. The relapse rate in mice receiving standard TB treatment was 46.6%. Compared to the standard TB treatment, relapse rates in animals that received adjunctive treatments with anti-MMP-9 antibody or etanercept were significantly decreased to 25.9% (P = 0.006) and 29.8% (P = 0.019) respectively, but were not different from the arm that received the isotype control antibody (25.9%). Immunostaining demonstrated localization of MMP-9 primarily in macrophages in both murine and human lung tissues infected with M. tuberculosis, suggesting the importance of MMP-9 in TB pathogenesis. These data suggest that the relapse rates in M. tuberculosis-infected mice may be non-specifically improved by administration of antibodies in conjunction with standard TB treatments. Future studies are needed to evaluate the mechanism(s) leading to improved outcomes with adjunctive antibody treatments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.