MTN-001: Randomized Pharmacokinetic Cross-Over Study Comparing Tenofovir Vaginal Gel and Oral Tablets in Vaginal Tissue and Other Compartments

Background: Oral and vaginal preparations of tenofovir as pre-exposure prophylaxis (PrEP) for human immunodeficiency virus (HIV) infection have demonstrated variable efficacy in men and women prompting assessment of variation in drug concentration as an explanation. Knowledge of tenofovir concentration and its active form, tenofovir diphosphate, at the putative vaginal and rectal site of action and its relationship to concentrations at multiple other anatomic locations may provide key information for both interpreting PrEP study outcomes and planning future PrEP drug development. Objective: MTN-001 was designed to directly compare oral to vaginal steady-state tenofovir pharmacokinetics in blood, vaginal tissue, and vaginal and rectal fluid in a paired cross-over design. Methods and Findings: We enrolled 144 HIV-uninfected women at 4 US and 3 African clinical research sites in an open label, 3-period crossover study of three different daily tenofovir regimens, each for 6 weeks (oral 300 mg tenofovir disoproxil fumarate, vaginal 1% tenofovir gel [40 mg], or both). Serum concentrations after vaginal dosing were 56-fold lower than after oral dosing (p<0.001). Vaginal tissue tenofovir diphosphate was quantifiable in ≥90% of women with vaginal dosing and only 19% of women with oral dosing. Vaginal tissue tenofovir diphosphate was ≥130-fold higher with vaginal compared to oral dosing (p<0.001). Rectal fluid tenofovir concentrations in vaginal dosing periods were higher than concentrations measured in the oral only dosing period (p<0.03). Conclusions: Compared to oral dosing, vaginal dosing achieved much lower serum concentrations and much higher vaginal tissue concentrations. Even allowing for 100-fold concentration differences due to poor adherence or less frequent prescribed dosing, vaginal dosing of tenofovir should provide higher active site concentrations and theoretically greater PrEP efficacy than oral dosing; randomized topical dosing PrEP trials to the contrary indicates that factors beyond tenofovir's antiviral effect substantially influence PrEP efficacy. Trial Registration: ClinicalTrials.gov NCT00592124

A mevalonate bypass system facilitates elucidation of plastid biology in malaria parasites.

Malaria parasites rely on a plastid organelle for survival during the blood stages of infection. However, the entire organelle is dispensable as long as the isoprenoid precursor, isopentenyl pyrophosphate (IPP), is supplemented in the culture medium. We engineered parasites to produce isoprenoid precursors from a mevalonate-dependent pathway, creating a parasite line that replicates normally after the loss of the apicoplast organelle. We show that carbon-labeled mevalonate is specifically incorporated into isoprenoid products, opening new avenues for researching this essential class of metabolites in malaria parasites. We also show that essential apicoplast proteins, such as the enzyme target of the drug fosmidomycin, can be deleted in this mevalonate bypass parasite line, providing a new method to determine the roles of other important apicoplast-resident proteins. Several antibacterial drugs kill malaria parasites by targeting basic processes, such as transcription, in the organelle. We used metabolomic and transcriptomic methods to characterize parasite metabolism after azithromycin treatment triggered loss of the apicoplast and found that parasite metabolism and the production of apicoplast proteins is largely unaltered. These results provide insight into the effects of apicoplast-disrupting drugs, several of which have been used to treat malaria infections in humans. Overall, the mevalonate bypass system provides a way to probe essential aspects of apicoplast biology and study the effects of drugs that target apicoplast processes

Boxplots of TFV and TFV-DP concentrations by anatomic site.

<p>Side-by-side boxplots of end-of-period visit data for all participants by anatomic site and dosing regimen are shown. Each box indicates the interquartile range with center bar as median and whiskers 1.5 times the quartile. *Lower quartile (LQ) is below the limit of quantitation (LOQ), only median and above are shown. **Median is below LOQ, so the median of values above the LOQ are shown as a single bar. X-axis key: <i>anatomic location</i>, PBMC peripheral blood mononuclear cells, CVL cervicovaginal lavage, ECC endocervical cytobrush; <i>drug moiety</i>, TFV tenofovir, TFV-DP tenofovir diphosphate; <i>sample timing</i>, C_max peak concentration following dose at clinic visit, C_pre-dose concentration prior to dose at clinic visit, C_all pools values from all participants regardless of scheduled time relative to dose.</p

Concentration ratios between dosing period by anatomic location.

<p>Pairs are included if at least one is above the limit of assay quantitation and the other is above the limit of assay detection. Other pairs are excluded. Serum and PBMC ratios are based on pooled values for data pairs from all times with research participants contributing more than one pair.</p

Ratio of unphosphorylated TFV to phosphorylated TFV-DP by anatomic sampling sites.

<p>Pairs are included if at least one value in the pair is above the limit of assay quantitation and the other is above the limit of assay detection. “N” is the number of pairs available meeting the inclusion criteria above. “Maximum N” is the number of possible pairs if all subjects at all visits provided a sample. C_max only includes US participants where multiple serum samples were available; the pair is defined by serum C_max matched with the corresponding PBMC TFV-DP concentration which is not necessarily peak TFV-DP after the same dose. Subscript “all” indicates that all PBMC-Serum pairs from each sample times are included, with participants contributing multiple pairs. All p<0.001 Wilcoxon signed rank test for TFV fmol/gm vs. TFV-DP fmol/gm. *Insufficient samples above the limit of assay quantitation and detection to estimate reliable medians given the inevaluable excluded pairs.</p

Subject Characteristics.

<p>Subject Characteristics.</p

Summary of TFV and TFV-DP concentrations at all sampled anatomic sites.

<p>Data from end-of-period visit showing median (interquartile range) by dosing regimen in common concentration units. Serum TFV C_pre-dose, PBMC TFV-DP C_pre-dose, and cervicovaginal lavage include African clinical sites; other parameters are calculable only for US clinical sites. Rectal sponges are only from one US site. For values below the LLOQ,<[median LLOQ] is shown. Cervicovaginal lavage results were corrected for estimated average 20× dilution of 0.5 mL cervicovaginal fluid in 10 mL lavage fluid <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055013#pone.0055013-Mitchell1" target="_blank">[11]</a>.</p

MTN-001 Study Schema.

<p>Formulations: Oral, 300 mg tenofovir disoproxil fumarate; Vaginal, 1% tenofovir gel.</p><p>Sampling occurs at the 3-week mid-point (blood only) and 6-week end of period visit (blood, PBMC, vaginal biopsy [intensive sites], vaginal fluid, and rectal fluid [Bronx-Lebanon site]).</p><p>Number of samples at each visit varied between intensive (US) and non-intensive (African) clinical sites.</p

Accounting of research participants from screening to data analysis.

<p>Accounting of research participants from screening to data analysis.</p

Serum TFV and TFV-DP concentration versus time.

<p>Serum TFV (panel A) and PBMC TFV-DP (panel B) concentration versus time plots are shown for the observed 8 hour interval following a dose in clinic according to dosing regimen. Median with asymmetric upper and lower quartiles is shown. Values are only for the 70 US participants where all 6 PK samples were collected.</p