An isopropylalaninyl monoamidate phenyl monoester prodrug of tenofovir (GS 7340) was prepared, and its in vitro antiviral activity, metabolism, and pharmacokinetics in dogs were determined. The 50% effective concentration (EC 50 ) of GS 7340 against human immunodeficiency virus type 1 in MT-2 cells was 0.005 M compared to an EC 50 of 5 M for the parent drug, tenofovir. The (L)-alaninyl analog (GS 7340) was >1,000-fold more active than the (D)-alaninyl analog. GS 7340 has a half-life of 90 min in human plasma at 37°C and a half-life of 28.3 min in an MT-2 cell extract at 37°C. The antiviral activity (>10؋ the EC 50 ) and the metabolic stability in MT-2 cell extracts (>35؋) and plasma (>2.5؋) were also sensitive to the stereochemistry at the phosphorus. After a single oral dose of GS 7340 (10 mg-eq/kg tenofovir) to male beagle dogs, the plasma bioavailability of tenofovir compared to an intravenous dose of tenofovir was 17%. The total intracellular concentration of all tenofovir species in isolated peripheral blood mononuclear cells at 24 h was 63 g-eq/ml compared to 0.2 g-eq/ml in plasma. A radiolabeled distribution study with dogs resulted in an increased distribution of tenofovir to tissues of lymphatic origin compared to the commercially available prodrug tenofovir DF (Viread).Highly active antiretroviral therapy (HAART) for the treatment of human immunodeficiency virus is effective in reducing plasma viral loads below current assay detection limits and is responsible for significant reductions in AIDS-related mortality in the United States (13). Combinations of protease and reverse transcriptase inhibitors are extremely potent at blocking de novo infection; however, they have no effect on latently infected cells. The half-lives of these latent cellular reservoirs were originally estimated to be Ͼ3 years, leading to the conclusion that it may not be possible to eradicate human immunodeficiency virus (HIV) from an infected individual by using current HAART (2). It has subsequently been shown that even in patients who have undetectable plasma viremia (Ͻ50 copies/ ml), low-level replication is ongoing (11,15,36), resulting in repopulation of latent reservoirs and thus accounting for the long apparent half-lives observed (12,22,23,35). The failure of HAART to completely shut down virus replication in vivo is a function of both the intrinsic potency of the drug regimen and its distribution to the cellular sites of virus replication. The lymphatic tissues and the peripheral blood mononuclear cells (PBMCs) are the primary sites of virus replication and potential virus latency (9,19). A drug targeting strategy that selectively enhances active drug concentrations in these tissues without excessive systemic exposure is conceptually attractive and would potentially lead to a more effective HAART with fewer potential side effects.Tenofovir, {9-[(R)-2(phosphonomethoxy)propyl]adenine} (PMPA) (Fig.

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Bictegravir (BIC; GS-9883), a novel, potent, once-daily, unboosted inhibitor of HIV-1 integrase (IN), specifically targets IN strand transfer activity (50% inhibitory concentration [IC50] of 7.5 ± 0.3 nM) and HIV-1 integration in cells. BIC exhibits potent and selective in vitro antiretroviral activity in both T-cell lines and primary human T lymphocytes, with 50% effective concentrations ranging from 1.5 to 2.4 nM and selectivity indices up to 8,700 relative to cytotoxicity. BIC exhibits synergistic in vitro antiviral effects in pairwise combinations with tenofovir alafenamide, emtricitabine, or darunavir and maintains potent antiviral activity against HIV-1 variants resistant to other classes of antiretrovirals. BIC displayed an in vitro resistance profile that was markedly improved compared to the integrase strand transfer inhibitors (INSTIs) raltegravir (RAL) and elvitegravir (EVG), and comparable to that of dolutegravir (DTG), against nine INSTI-resistant site-directed HIV-1 mutants. BIC displayed statistically improved antiviral activity relative to EVG, RAL, and DTG against a panel of 47 patient-derived HIV-1 isolates with high-level INSTI resistance; 13 of 47 tested isolates exhibited >2-fold lower resistance to BIC than DTG. In dose-escalation experiments conducted in vitro, BIC and DTG exhibited higher barriers to resistance than EVG, selecting for HIV-1 variants with reduced phenotypic susceptibility at days 71, 87, and 20, respectively. A recombinant virus with the BIC-selected M50I/R263K dual mutations in IN exhibited only 2.8-fold reduced susceptibility to BIC compared to wild-type virus. All BIC-selected variants exhibited low to intermediate levels of cross-resistance to RAL, DTG, and EVG (<8-fold) but remained susceptible to other classes of antiretrovirals. A high barrier to in vitro resistance emergence for both BIC and DTG was also observed in viral breakthrough studies in the presence of constant clinically relevant drug concentrations. The overall virologic profile of BIC supports its ongoing clinical investigation in combination with other antiretroviral agents for both treatment-naive and -experienced HIV-infected patients.

hOAT1 is a renal membrane protein able to efficiently transport acyclic nucleoside phosphonates (ANPs). When expressed in CHO cells, hOAT1 mediates the uptake and cytotoxicity of ANPs suggesting that it plays an active role in the nephrotoxicity associated with cidofovir CMV therapy and high-dose adefovir HIV therapy. Although efficiently transported by hOAT1, tenofovir did not show any significant cytotoxicity in isolated human proximal tubular cells, which correlates with the lack of nephrotoxicity observed in HIV-infected patients on prolonged tenofovir therapy.

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