Emtricitabine/tenofovir in the treatment of HIV infection: current PK/PD evaluation

Antivirals for prevention of hepatitis B virus mother-to-child transmission in human immunodeficiency virus positive pregnant women co-infected with hepatitis B virus

BACKGROUND

Hepatitis B virus (HBV)-human Immunodeficiency virus (HIV) co-infection promotes an aggressive disease course of HBV infection. In the only available non-Cochrane systematic review on antiviral therapy during pregnancy for prevention of mother-to-child transmission of HBV, none of the women studied had HBV-HIV co-infection but were either HBV- or HIV-seropositive. Treatment of HBV alone may develop HIV-strains that are resistant to non-nucleoside reverse transcriptase inhibitors. Accordingly, co-treatment of the HIV infection is recommended.

OBJECTIVES

To evaluate the benefits and harms of tenofovir-based antiviral combination regimens versus placebo, tenofovir alone, or non-tenofovir-based antiviral regimen either alone or in combination with HBV for the prevention of mother-to-child transmission of HBV in HIV-positive pregnant women co-infected with HBV.

SEARCH METHODS

We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, Cochrane Central Register of Controlled Trials, MEDLINE Ovid, Embase Ovid, LILACS (Bireme), Science Citation Index Expanded (Web of Science), and Conference Proceedings Citation Index-Science (Web of Science) on 30 January 2023. We manually searched the reference lists of included trials, searched on-line trial registries, and contacted experts in the field and pharmaceutical companies for any further potential trials.

SELECTION CRITERIA

We aimed to include randomised clinical trials comparing tenofovir-based antiviral combination regimens (anti-HIV regimen with lopinavir-ritonavir therapy, or any other antiviral therapy, and two drugs with activity against HBV, specifically, tenofovir alafenamide (TAF) or tenofovir disoproxil fumarate (TDF), plus lamivudine or emtricitabine) with placebo alone, or tenofovir alone, or non-tenofovir-based antiviral regimen (zidovudine, lamivudine, telbivudine, emtricitabine, entecavir, lopinavir-ritonavir, or any other antiviral therapy) either alone or in combination with at least two other antivirals.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Primary outcomes included all-cause infant mortality, proportion of infants with serious adverse events, proportion of infants with HBV mother-to-child transmission, all-cause maternal mortality, and proportion of mothers with serious adverse events. Secondary outcomes included proportion of infants with adverse events not considered serious, proportion of mothers with detectable HBV DNA (deoxyribonucleic acid) (before delivery), maternal hepatitis B e antigen (HBeAg) to HBe-antibody seroconversion (before delivery) and maternal adverse events not considered serious. We used RevMan Web to carry out analyses and presented results, where feasible, using a random-effects model and risk ratios (RR) with 95% confidence intervals (CIs). We performed sensitivity analysis. We assessed risk of bias using predefined domains, assessed the certainty of the evidence using GRADE, controlled risk of random errors with Trial Sequential Analysis, and presented outcome results in a summary of findings table.

MAIN RESULTS

Five completed trials were included, of which four trials contributed data to one or more of the outcomes. They included a total of 533 participants randomised to tenofovir-based antiviral combination regimens (196 participants) versus control (337 participants). The control groups received non-tenofovir-based antiviral regimens either as zidovudine alone (three trials) or as a combination of zidovudine, lamivudine and lopinavir-ritonavir (five trials). None of the trials used placebo or tenofovir alone. All trials were at unclear risk of bias. Four trials used intention-to-treat analyses. In the remaining trial, two participants in the intervention group and two in the control group were lost to follow-up. However, the outcomes of these four participants were not described. Tenofovir-based antiviral combination regimen versus control We are very uncertain about the effect of a tenofovir-based antiviral combination regimen versus control on all-cause infant mortality (RR 2.24, 95% CI 0.72 to 6.96; participants = 132; trials = 1; very low-certainty evidence); proportion of infants with serious adverse events (RR 1.76, 95% CI 1.27 to 2.43; participants = 132; trials = 1; very low-certainty evidence), and proportion of mothers with serious adverse events (RR 0.90, 95% CI 0.62 to 1.32; participants = 262; trials = 2; very low-certainty evidence). No trial reported data on the proportion of infants with HBV mother-to-child transmission and all-cause maternal mortality. We are also very uncertain about the effect of tenofovir-based antiviral combination regimens versus control on the proportion of infants with adverse events not considered serious (RR 0.94, 95% CI 0.06 to 13.68; participants = 31; trials = 1; very low-certainty evidence), and proportion of mothers with detectable HBV DNA (before delivery) (RR 0.66, 95% CI 0.42 to 1.02; participants = 169; trials = 2; very low-certainty evidence). No trial reported data on maternal hepatitis B e antigen (HBeAg) to HBe-antibody seroconversion (before delivery) and maternal adverse events not considered serious. All trials received support from industry.

AUTHORS' CONCLUSIONS

We do not know what the effects of tenofovir-based antiviral combination regimens are on all-cause infant mortality, proportion of infants with serious adverse events and proportion of mothers with serious adverse events, proportion of infants with adverse events not considered serious, and proportion of mothers with detectable HBV DNA before delivery because the certainty of evidence was very low. Only one or two trials, with insufficient power, contributed data for analyses. We lack randomised clinical trials at low risk of systematic and random errors, and fully reporting all-cause infant mortality, serious adverse events and reporting on clinical and laboratory outcomes, such as infants with HBV mother-to-child transmission, all-cause maternal mortality, maternal hepatitis B e antigen (HBeAg) to HBe-antibody seroconversion before delivery and maternal adverse events not considered serious.

Mathematical Modelling of the Molecular Mechanisms of Interaction of Tenofovir with Emtricitabine against HIV

The combination of the two nucleoside reverse transcriptase inhibitors (NRTI) tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) is used in most highly active antiretroviral therapies for treatment of HIV-1 infection, as well as in pre-exposure prophylaxis against HIV acquisition. Administered as prodrugs, these drugs are taken up by HIV-infected target cells, undergo intracellular phosphorylation and compete with natural deoxynucleoside triphosphates (dNTP) for incorporation into nascent viral DNA during reverse transcription. Once incorporated, they halt reverse transcription. In vitro studies have proposed that TDF and FTC act synergistically within an HIV-infected cell. However, it is unclear whether, and which, direct drug–drug interactions mediate the apparent synergy. The goal of this work was to refine a mechanistic model for the molecular mechanism of action (MMOA) of nucleoside analogues in order to analyse whether putative direct interactions may account for the in vitro observed synergistic effects. Our analysis suggests that depletion of dNTP pools can explain apparent synergy between TDF and FTC in HIV-infected cells at clinically relevant concentrations. Dead-end complex (DEC) formation does not seem to significantly contribute to the synergistic effect. However, in the presence of non-nucleoside reverse transcriptase inhibitors (NNRTIs), its role might be more relevant, as previously reported in experimental in vitro studies.

Immucillins in Infectious Diseases

The Immucillins are chemically stable analogues that mimic the ribocation and leaving-group features of N-ribosyltransferase transition states. Infectious disease agents often rely on ribosyltransferase chemistry in pathways involving precursor synthesis for nucleic acids, salvage of nucleic acid precursors, or synthetic pathways with nucleoside intermediates. Here, we review three infectious agents and the use of the Immucillins to taget enzymes essential to the parasites. First, DADMe-Immucillin-G is a purine nucleoside phosphorylase (PNP) inhibitor that blocks purine salvage and shows clinical potential for treatment for the malaria parasite Plasmodium falciparum, a purine auxotroph requiring hypoxanthine for purine nucleotide synthesis. Inhibition of the PNPs in the host and in parasite cells leads to apurinic starvation and death. Second, Helicobacter pylori, a causative agent of human ulcers, synthesizes menaquinone, an essential electron transfer agent, in a pathway requiring aminofutalosine nucleoside hydrolysis. Inhibitors of the H. pylori methylthioadenosine nucleosidase (MTAN) are powerful antibiotics for this organism. Synthesis of menaquinone by the aminofutalosine pathway does not occur in most bacteria populating the human gut microbiome. Thus, MTAN inhibitors provide high-specificity antibiotics for H. pylori and are not expected to disrupt the normal gut bacterial flora. Third, Immucillin-A was designed as a transition state analogue of the atypical PNP from Trichomonas vaginalis. In antiviral screens, Immucillin-A was shown to act as a prodrug. It is active against filoviruses and flaviviruses. In virus-infected cells, Immucillin-A is converted to the triphosphate, is incorporated into the viral transcript, and functions as an atypical chain-terminator for RNA-dependent RNA polymerases. Immucillin-A has entered clinical trials for use as an antiviral. We also summarize other Immucillins that have been characterized in successful clinical trials for T-cell lymphoma and gout. The human trials support the potential development of the Immucillins in infectious diseases.

Lamivudine Therapy Exacerbates Bilirubinemia in Patients Underlying Severely Advanced Hepatitis

Lamivudine belongs to the set of antiviral agents effective against hepatitis B virus infection. Given case reports on liver injuries after certain antiviral agent treatments, this study examined the effects of lamivudine on alanine aminotransferase (ALT) and total bilirubin (TB) using a medical system database. A total of 1,321 patients taking lamivudine alone or with others were evaluated using laboratory hits in an electronic medical system at Seoul National University Hospital from 2005 through 2011. The patients were grouped according to prior ALT results: G#1, ALT < 40 IU/L; G#2, 40 IU/L ≤ ALT < 120 IU/L; G#3, 120 IU/L ≤ ALT < 240 IU/L; and G#4, ALT ≥ 240 IU/L. In G#1 and G#2 patients, lamivudine or adefovir treatment decreased ALT and TB compared to prior values. In G#3 and G#4 patients with three times the upper limit of normal (ULN) ≤ ALT < 15 times the ULN, both ALT and TB were decreased after treatment with lamivudine alone, or adefovir following lamivudine therapy, indicating that lamivudine therapy ameliorated liver functions. However, in G#4 patients who experienced severely advanced hepatitis (ALT ≥ 15 times the ULN, or ≥ 600 IU/L), lamivudine augmented TBmax (6.3→13.3 mg/dL) despite a slight improvement in ALT (839→783 IU/L), indicative of exacerbation of bilirubinemia. Patients who used adefovir after lamivudine also showed a high incidence of hyperbilirubinemia when they experienced severely advanced hepatitis. Treatment with adefovir alone did not show the effect. In conclusion, lamivudine may increase the risk of hyperbilirubinemia in patients with severely advanced hepatitis, implying that caution should be exercised when using lamivudine therapy in certain patient populations.

Model Linking Plasma and Intracellular Tenofovir/Emtricitabine with Deoxynucleoside Triphosphates

The coformulation of the nucleos(t)ide analogs (NA) tenofovir (TFV) disoproxil fumarate (TDF) and emtricitabine (FTC) is approved for HIV-infection treatment and prevention. Plasma TFV and FTC undergo complicated hybrid processes to form, accumulate, and retain as their active intracellular anabolites: TFV-diphosphate (TFV-DP) and FTC-triphosphate (FTC-TP). Such complexities manifest in nonlinear intracellular pharmacokinetics (PK). In target cells, TFV-DP/FTC-TP compete with endogenous deoxynucleoside triphosphates (dNTP) at the active site of HIV reverse transcriptase, underscoring the importance of analog:dNTP ratios for antiviral efficacy. However, NA such as TFV and FTC have the potential to disturb the dNTP pool, which could augment or reduce their efficacies. We conducted a pharmacokinetics-pharmacodynamics (PKPD) study among forty subjects receiving daily TDF/FTC (300 mg/200 mg) from the first-dose to pharmacological intracellular steady-state (30 days). TFV/FTC in plasma, TFV-DP/FTC-TP and dNTPs in peripheral blood mononuclear cells (PBMC) were quantified using validated LC/MS/MS methodologies. Concentration-time data were analyzed using nonlinear mixed effects modeling (NONMEM). Formations and the accumulation of intracellular TFV-DP/FTC-TP was driven by plasma TFV/FTC, which was described by a hybrid of first-order formation and saturation. An indirect response link model described the interplay between TFV-DP/FTC-TP and the dNTP pool change. The EC₅₀ (interindividual variability, (%CV)) of TFV-DP and FTC-TP on the inhibition of deoxyadenosine triphosphate (dATP) and deoxycytidine triphosphate (dCTP) production were 1020 fmol/10⁶ cells (130%) and 44.4 pmol/10⁶ cells (82.5%), resulting in (90% prediction interval) 11% (0.45%, 53%) and 14% (2.6%, 35%) reductions. Model simulations of analog:dNTP molar ratios using IPERGAY dosing suggested that FTC significantly contributes to the protective effect of preexposure prophylaxis (PrEP). Simulation-based intracellular operational multiple dosing half-lives of TFV-DP and FTC-TP were 6.7 days and 33 hours. This model described the formation of intracellular TFV-DP/FTC-TP and the interaction with dNTPs, and can be used to simulate analog:dNTP time course for various dosing strategies.

Preclinical assessments of vaginal microbicide candidate safety and efficacy

Sexually transmitted infections like HIV, HPV, and HSV-2, as well as unplanned pregnancy, take a huge toll on women worldwide. Woman-initiated multipurpose prevention technologies that contain antiviral/antibacterial drugs (microbicides) and a contraceptive to simultaneously target sexually transmitted infections and unplanned pregnancy are being developed to reduce these burdens. This review will consider products that are applied topically to the vagina. Rectally administered topical microbicides in development for receptive anal intercourse are outside the scope of this review. Microbicide and microbicide/contraceptive candidates must be rigorously evaluated in preclinical models of safety and efficacy to ensure that only candidates with favorable risk benefit ratios are advanced into human clinical trials. This review describes the comprehensive set of in vitro, ex vivo, and in vivo models used to evaluate the preclinical safety and antiviral efficacy of microbicide and microbicide/contraceptive candidates.