Intracellular Metabolism and In Vitro Activity of Tenofovir against Hepatitis B Virus

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Antimicrobial Agents and Chemotherapy (Impact Factor: 4.48). 08/2006; 50(7):2471-7. DOI: 10.1128/AAC.00138-06
Source: PubMed


Tenofovir is an acyclic nucleotide analog with activity against human immunodeficiency virus (HIV) and hepatitis B virus (HBV). Tenofovir disoproxil fumarate (tenofovir DF), a bis-alkoxyester prodrug of tenofovir, is approved for the treatment of HIV and is currently being developed to treat chronic hepatitis B. In this report, we further characterize the in vitro activity of tenofovir against HBV as well as its metabolism in hepatic cells. We show that tenofovir is efficiently phosphorylated to tenofovir diphosphate (TFV-DP) in both HepG2 cells and primary human hepatocytes. TFV-DP has a long intracellular half-life (95 h) and is a potent and competitive inhibitor of HBV polymerase (Ki = 0.18 microM). Tenofovir has a 50% effective concentration of 1.1 microM against HBV in cell-based assays, and potency is improved > 50-fold by the addition of bis-isoproxil progroups. Tenofovir has previously demonstrated full activity against lamivudine-resistant HBV in vitro and clinically. Here we show that the major adefovir resistance mutation, rtN236T, confers three- to fourfold-reduced susceptibility to tenofovir in cell culture; the clinical significance of this susceptibility shift has not yet been determined. The rtA194T HBV polymerase mutation recently identified in tenofovir DF-treated HIV/HBV-coinfected patients did not confer in vitro resistance to tenofovir as a single mutation or in a lamivudine-resistant viral background. Overall, the antiviral and metabolic profile of tenofovir supports its development for the treatment of chronic hepatitis B.

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    • "Genotypic resistance to TDF has been detected in several patients with HIV-HBV coinfection. The substitution rtA194T (plus rtL180M + rtM204V) has been associated with TDF resistance,15 albeit that a second report failed to confirm this.16 It has been shown that rtA181V + rtN236T double mutants are resistant to TDF in vitro, but clinical data suggest that patients with rtA181 or rtN236T remain susceptible to TDF.17 "
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    ABSTRACT: Tenofovir disoproxil fumarate (TDF) is widely used to treat hepatitis B virus (HBV) patients in the USA and Europe. No confirmed report of resistance selection during treatment with TDF in treatment-naïve and nucleoside/nucleotide analog-treated chronic hepatitis B patients has yet been reported. Here, we report for the first time a patient with chronic hepatitis B and cirrhosis who emerged with virologic breakthrough during combination therapy with TDF and entecavir (ETV), against ETV-resistant virus. A 51-year-old Japanese woman with hepatitis B e-antigen (HBeAg), whose genotype was C, received ETV monotherapy continuously followed by TDF and ETV combination therapy, because her HBV DNA levels had been >3.5 log copies/mL. At the start of combination therapy, amino acid substitutions of the reverse transcriptase (rt) gene, rtL180M, rtT184I/M, and rtM204V, were detected. After this, serum HBV DNA decreased to less than 2.1 log copies/mL and remained at this level until 31 months of combination therapy, when it again began to increase. Amino acid substitutions of rtL180M, rtS202G, and rtM204V emerged and were associated with an increase in serum HBV DNA at virologic breakthrough. Long-term therapy with TDF against the ETV-resistant virus has the potential to induce virologic breakthrough and resistance, and careful follow-up should be carried out.
    Full-text · Article · Jun 2014 · Drug Design, Development and Therapy
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    • "The rtA194T polymerase mutation is associated with partial TDF drug resistance. But Delaney et al.,25 rtA194T did not cause a significant change in TDF susceptibility either alone or when expressed in combinated with LAM resistance mutations (1.5- to 2.5-fold). Whether the rtA194T mutation truly confers resistance against TDF has remained controversial. "
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    ABSTRACT: We investigated the efficacy and safety of tenofovir disoproxil fumarate (TDF)-based treatment in chronic hepatitis B (CHB) patients who failed previous antiviral therapies. Seventeen patients who failed to achieve virological responses during sequential antiviral treatments were included. The patients were treated with TDF monotherapy (four patients) or a combination of TDF and lamivudine (13 patients) for a median of 42 months. Hepatitis B virus (HBV) DNA and hepatitis B e antigen (HBeAg) were measured, and renal function was also monitored. Prior to TDF therapy, 180 M, 204 I/V/S, 181 T/V, 236 T, and 184 L mutations were detected. After TDF therapy, the median HBV DNA level decreased from 4.6 log10 IU/mL to 2.0 log10 IU/mL and to 1.6 log10 IU/mL at 12 and 24 months, respectively. HBV DNA became undetectable (≤20 IU/mL) in 14.3%, 41.7%, and 100% of patients after 12, 24, and 48 months of treatment, respectively. HBeAg loss was observed in two patients. Viral breakthrough occurred in five patients who had skipped their medication. No significant changes in renal function were observed. TDF-based rescue treatment is effective in reducing HBV DNA levels and is safe for patients with CHB who failed prior antiviral treatments. Patients' adherence to medication is related to viral rebound.
    Full-text · Article · Jan 2014 · Gut and Liver
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    • "Few data on virological resistance to TDF exist, but decreased susceptibility (twofold to threefold) to TDF was found in cell cultures in the presence of rtA181T/ V change, especially if associated with rtN236T [Villet et al., 2008]. In patients co-infected with HBV and HIV, A194T mutation was associated with TDF resistance both in vitro and in vivo [Sheldon et al., 2005; Shaw et al., 2006; Amini-Bavil-Olyaee et al., 2009], although others studies did not confirm this finding [Delaney et al., 2006; Audsley et al., 2009]. However, in a three-dimensional model of the HBV reverse transcriptase, introduction of the threonine substitution at position 194 created a side branch, possibly changing the deoxyribonucleotide triphosphate-binding pocket of the beta-sheet and suggesting sterical alterations as the basis for tenofovir resistance, thus the association between A194T exchange and TDF resistance seems possible [Sheldon et al., 2005]. "
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    ABSTRACT: Nucleos(t)ide analogs such as tenofovir, lamivudine, or emtricitabine are active against both HBV and HIV. Tenofovir confers potent and durable HBV-DNA suppression but the best strategy in case of resistance of HBV to tenofovir remains unknown. A case of a 22-year-old patient with co-infection with HBV and HIV transmitted perinatally is reported. After prolonged and intermittent treatment of HIV with lamivudine and tenofovir, HBV became resistant to lamivudine. Subsequently, clinical resistance to tenofovir occurred, manifesting as HBV-DNA breakthrough. The non-compliance was reasonable excluded and HIV-RNA remained constantly suppressed. Entecavir (1 mg daily) was added and the combination therapy resulted in a rapid and continuous suppression of HBV-DNA for over 12 months. The treatment was well-tolerated and safe. No known mutations, such as rtA181T/V associated with rtN236T or A194T that are associated with reduced susceptibility or resistance to tenofovir were detected. However, a unique and complex HBV substitution pattern was found: with a development of rtR192PR mutation at the time of virological failure. Adding entecavir to failing therapy with tenofovir and emtricitabine was feasible, well-tolerated and resulted in virological success. The rtR192PR, which is located in the B domain near the rtA194T, occurring in a context of a very complex substitutions patterns, might be associated with resistance to tenofovir.
    Full-text · Article · Sep 2012 · Journal of Medical Virology
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