Relative Mitochondrial Toxicity of Tenofovir Alafenamide (TAF) vs. Tenofovir Disoproxil Fumarate (TDF)
Condition: HIV/AIDS; Antiviral Toxicity; Antiviral Drug Adverse Reaction; Mitochondrial Alteration
MeSH terms: Acquired Immunodeficiency Syndrome; HIV Infections; Drug-Related Side Effects and Adverse Reactions
Study type: Interventional
Phase: Phase 1/Phase 2

Summary: 
      Increased comorbidities such as cardiovascular disease (CVD), are emerging problems in HIV
      infection but the mechanisms are unclear. Understanding how antiretrovirals can minimize
      morbidity in treated HIV infection is a research priority. Nucleoside/nucleotide reverse
      transcriptase inhibitors (NRTIs) are included in all HIV treatment regimens. Tenofovir (TFV)
      disoproxil fumarate (TDF) has been associated with an increased risk of nephrotoxicity and
      bone disease compared with other NRTIs. Tenofovir alafenamide (TAF) is an oral prodrug of
      TFV, but is more stable in plasma as compared with TDF and lower plasma levels of TFV are
      thought to lead to the favorable safety profile of TAF. Mitochondrial dysfunction has a key
      role in HIV pathogenesis and may be the common denominator that drives pathogenesis of
      several comorbidities. Despite the better safety profile of newer (such as TDF) compared to
      older NRTIs, there are concerns for the potential for longer term toxicity of NRTIs since the
      exact cellular effects of NRTIs remain unclear. It is unknown whether a four-fold increase in
      intracellular drug levels seen in peripheral blood mononuclear cells (PBMCs) with TAF may
      increase toxicity in mitochondria. Better understanding of these effects could provide
      insights into mechanisms of HIV pathogenesis and selection of NRTIs that improve morbidity in
      chronic HIV infection.

      Hypothesis: Despite higher intracellular levels, TAF has minimal mitochondrial toxicity
      compared to TDF in vivo. This research will explore the relative mitochondrial toxicity of
      newer NRTIs (TAF, TDF) as a possible mechanism for differential NTRI-related toxicities.
      These data will allow selection of NRTIs that may improve morbidity in chronic treated HIV
      infection. Towards this aim, the investigators will use a robust experimental approach to
      study NRTI-related mitochondrial dysfunction using novel methods, human cell lines and PBMC.
      Our specific aims are: Aim 1: To evaluate the relative in vitro effects of TAF and TDF
      compared to an older NRTI (ddC) on 5 independent measures of mitochondrial function in the
      human cell line HepG2 and PBMC. Aim 2: To explore in vivo whether there is increased
      mitochondrial dysfunction with the use of TAF vs. TDF in chronic treated HIV infection. The
      investigators anticipate that the proposed experimental approach will set the basis for
      future large scale studies to directly compare subtle potential mitochondrial toxicities of
      newer NRTIs in large HIV cohorts.
    

Detailed description: 
      Increased comorbidities such as cardiovascular disease (CVD), bone and kidney disease are
      emerging problems in HIV infection but the mechanisms are unclear. Understanding how
      antiretrovirals can minimize morbidity in treated HIV infection is a research priority.
      Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) are included in all HIV
      treatment regimens. Tenofovir (TFV) disoproxil fumarate (TDF) has been associated with an
      increased risk of nephrotoxicity and bone disease compared with other NRTIs. Tenofovir
      alafenamide (TAF) is an oral prodrug of TFV, but is much more stable in plasma as compared
      with TDF and markedly lower plasma levels of TFV are thought to lead to the favorable safety
      profile of TAF. Mitochondrial dysfunction has a key role in HIV pathogenesis and may be the
      common denominator that drives pathogenesis of several comorbidities. Despite the better
      safety profile of newer (such as TDF) compared to older NRTIs, there remain concerns for the
      potential for longer term toxicity of the current NRTIs especially since the exact cellular
      effects of NRTIs remain unclear. It is unknown whether a four-fold increase in intracellular
      drug levels seen in peripheral blood mononuclear cells (PBMCs) with TAF may increase toxicity
      in mitochondria. Better understanding of these effects could provide insights into mechanisms
      of HIV pathogenesis and selection of NRTIs that improve morbidity in chronic HIV infection.

      Hypothesis: Despite higher intracellular levels, TAF has minimal/no overall mitochondrial
      toxicity compared to TDF in vivo. The investigators anticipate that the preliminary data and
      the proposed experimental approach will set the basis for future large scale studies to
      directly compare subtle potential mitochondrial toxicities of newer NRTIs in large HIV
      cohorts.

      Primary Objective: This research application will explore the relative mitochondrial toxicity
      of newer NRTIs (TAF, TDF) as a possible mechanism for differential NTRI-related toxicities.
      These data will allow selection of NRTIs that may improve morbidity in chronic treated HIV
      infection, given the known possible role of mitochondrial dysfunction in pathogenesis of
      HIV-related comorbidities. Towards this aim, the investigators will use a robust experimental
      approach to study NRTI-related mitochondrial dysfunction using novel methods, human cell
      lines and PBMC. The specific aims of this project are: Aim 1: To evaluate the relative in
      vitro effects of TAF and TDF compared to an older NRTI (ddC) on 5 independent measures of
      mitochondrial function in the human cell line HepG2 and PBMC. Hypothesis: Despite higher
      intracellular levels, TAF has minimal/no overall mitochondrial toxicity compared to TDF in
      both the HepG2 line and PBMC. ddC will be used as a positive control for NRTI-induced
      mitochondrial dysfunction. Aim 2: To explore in vivo whether there is increased mitochondrial
      dysfunction with the use of TAF vs. TDF in chronic treated HIV infection. The overall goal of
      this proposal is to determine the in vitro and in vivo effects of TAF on mitochondria.

      Treatment regimen: Healthy HIV-uninfected > 18 years old with no known comorbidities
      including metabolic disease will be recruited for PBMC isolation for the in vitro studies
      described in Aim 1 (n=30). For Aim 1, cells will be exposed to 10 μM (and other dose that
      will be determined after discussions with Gilead) NRTIs (TDF, TAF, ddC) for up to 14 days of
      treatment. To evaluate the relative mitochondrial toxicity of TDF vs. TAF in vivo (Aim 2), an
      open-label switch study will be conducted in virologically-suppressed, HIV-1 positive
      participants. The switch regimen will be Stribild® (elvitegravir 150 mg/cobicistat 150
      mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg; E/C/F/TDF) to Genvoya®
      (elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/tenofovir alafenamide 10 mg;
      E/C/F/TAF). For inclusion and exclusion criteria see respective sections.

      Primary Endpoint: Overall, the above in vitro and in vivo measurements of mitochondrial
      function before and after TAF and TDF will test the hypotheses that newer NRTIs have minimal
      overall mitochondrial toxicity in humans. From all the measures of mitochondrial function,
      cellular oxygen consumption (COC; as determined by Seahorse technology) will be considered
      the "gold standard" given it is a measure of the most important mitochondrial function
      (oxidative phosphorylation) that relates to clinical outcome. Given the uncertainty of what
      measure of mitochondrial function can best predict NRTI-induced mitochondrial toxicity,
      comparison of relative fold induction of mitochondrial dysfunction in PBMC vs. HepG2 cells in
      response to a specific concentration of a known NRTI inducer of mitochondrial dysfunction
      (ddC) will be used to guide analysis. The baseline measurement will be used to control for
      confounders of NRTI-related mitochondrial dysfunction (each person will serve as his/her own
      control) and results will be expressed as relative-fold change compared to baseline. In
      addition, using similar approach, Aim 2 will explore whether switch from TDF to a TAF-based
      regimen will induce any changes in measures of mitochondrial function. This approach ensures
      that any changes in the mitochondrial function at 6 and/or 12 months will be secondary only
      to the NRTI switch.

      Secondary Endpoints: It is accepted that two independent measures of mitochondrial function
      can more reliably predict mitochondrial dysfunction compared to each one of the measures
      separately. The investigators will define NRTI-induced mitochondrial toxicity as significant
      change in any of other major measures of mitochondrial toxicity [reduction in membrane
      potential (Δψm), increase in mitochondrial reactive oxygen species (mito-ROS), decrease in
      the amount of mitochondrial DNA (mtDNA), abnormal mitochondrial dynamics (increase
      fragmentation of mitochondria)). Finally, other exploratory secondary endpoints (based on
      available left-over resources) will be measurement of intracellular levels of TAF
      metabolites. Flow cytometry and live cell imaging will be determined as needed.

      The investigators will define NRTI-induced mitochondrial toxicity as significant change in
      any of the measures of mitochondrial toxicity (COC, Δψm, mito-ROS, mtDNA, mitochondrial
      dynamics). The baseline measurement will be used to control for confounders of NRTI-related
      mitochondrial dysfunction (each person will serve as his/her own control) and results will be
      expressed as relative-fold change compared to baseline. In addition, using similar approach,
      Aim 2 will explore whether switch from TDF to a TAF-based regimen will induce any changes in
      measures of mitochondrial function. This approach ensures that any changes in the
      mitochondrial function at 6 and/or 12 months will be secondary only to the NRTI switch.

      Since each donor will contribute samples to all experimental groups (baseline, follow up
      measurement), paired t-test, linear mixed effects model and nonparametric test (as needed)
      will be used to compare expression measures between groups adjusting for donor effects (age,
      sex, race.

      The results from this research will yield useful information on NRTI-related overall
      mitochondrial dysfunction that can further be validated in large studies with data on
      clinical outcomes.
    

Intervention name(s): Switch to E/C/FTC/TAF daily
Intervention type(s): Drug
Intervention description(s): If the participant is on an antiretroviral regimen other than Elvitegravir (ELV)/cobicistat CO)/emtricitabine (FTC)/tenofovir (TDF)] (E/C/FTC/TDF) then the participant will be asked to switch to E/C/FTC/TDF for up to 6 months. This will allow for future switch (after these 6 months) from E/C/FTC/TDF 1 tablet once daily to elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide (E/C/FTC/TAF) 1 tablet once daily for a period of 12 months.
b) If the participant is on E/C/FTC/TDF 1 tablet once daily then the participant will be asked to switch from /C/FTC/TDF 1 tablet once daily to /C/FTC/TAF 1 tablet once daily for a period of 12 months.
Other intervention name(s): E/C/FTC/TDF 1 tablet once daily
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: HIV/AIDS; Tenofovir disoproxil fumarate (TDF); Tenofovir alafenamide (TAF); mitochondria; toxicity