Repurposing a Combination Antiretroviral Drug Therapy to Target Retrotransposons and Treat Early Alzheimer's Disease

Objectives:

To conduct a phase 1b trial to determine the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of multiple ascending doses of emtricitabine (FTC) and tenofovir disoproxil fumarate (TDF) combination administered daily for 4 weeks in older adults with early Alzheimer's disease (AD).

Primary:

1. To evaluate safety and tolerability, we will conduct structured monitoring of adverse events (AEs) and serious AEs (SAEs). Additionally, we will perform safety laboratory tests including blood counts and chemistries, coagulation profile, physical exams, vital signs, and electrocardiogram (ECG).

Secondary:

1. To study the PK of two ascending dose regimens of FTC-TDF combination, we will measure the circulating levels of these drugs pre-dose and at 0.5, 1, 2, 4, 8, and 24 hours on Days 0 and 28. Additional single nadir blood samples will be obtained on days 3, 7, and 14 approximately 24 hours following the previous dose. Single and multiple dose PK parameters will be calculated using nonparametric methods on days 0 and 28: Caverage 0-24h, Cmax, Tmax, lambda z, AUClast, AUC24hr, and T1/2.
2. The trial's primary PD endpoint reflecting target engagement will be the steady-state serum concentration of the active metabolites, tenofovir biphosphate (TBP) and emtricitabine triphosphate (ETP), in peripheral blood mononuclear cells (PBMCs) measured pre-dose and at 4 and 8 hours after administration of study drug on days 0 and 28.
3. We will measure the activity of reverse transcriptase for the human active Long Interspersed Nuclear Elements (LINE-1) in PBMCs using reverse transcription coupled with polymerase chain reaction (PCR) for human LINE-1 transposon sequences on days 0 and 28.
4. We will measure hsCRP, IL-6, and TNF alpha as markers of systemic inflammation on days 0, 14, and 28.

Study Design/ Methodology:

This is a phase 1b, single-center, placebo-controlled, multiple ascending dose study of 20 participants with early AD.

The intervention duration is 28 days. Please see the Schedule of Events table.

There will be a single performance site for the clinical trial at the Center for Alzheimer Research and Treatment (CART) at Brigham and Women's Hospital (BWH).

Starting on day 0, the study participants will be randomized to either placebo or active drug (two dose strengths). The participants will take the study drug orally once daily for 28 days.

Questionnaires will be administered at screening (Clinical Dementia Rating [CDR], Mini-Mental State Exam [MMSE], Logical Memory, 15-item Geriatric Depression Scale [GDS], and Columbia-Suicide Severity Rating Scale [C-SSRS]), which will last up to 45 days.

Number of Participants:

A total of 20 participants will be enrolled in this trial. Participants discontinued from study for any reason or lost-to-follow up before completing the study will be replaced.

Investigational Product, Dosage and Mode of Administration:

Product: FTC and TDF combination tablets at two dose strengths that are in clinical use: 133 mg FTC plus 200 mg TDF, and 200 mg FTC plus 300 mg TDF.

Dosing Cohort: Two dosing cohorts of 10 participants each will be studied successively in ascending order. The first cohort of 10 participants will receive either one tablet of FTC (133 mg) and TDF (200 mg) combination once daily (n=7), or one placebo tablet daily (n=3) for 28 consecutive days. The second cohort of 10 participants will receive either one tablet of FTC (200 mg) and TDF (300 mg) combination once daily (n=7) or one placebo tablet once daily (n=3) for 28 consecutive days.

Duration of Treatment:

Participants will take FTC and TDF combination or placebo tablets once daily for 28 days.

Reference Therapy, Dosage and Mode of Administration:

Placebo tablets once daily for 28 days.

Statistical Methods:

Statistical Power and Sample Size Estimation:

By convention, the sample size of 10 participants per dose group (7 active, 3 placebo) is considered sufficient for evaluation of safety, tolerability, PK, and PD. In previous PK studies of FTC and TDF in adults without HIV infection, the changes from baseline in the plasma concentrations of these drugs were large (>2 standard deviation [SD]); the proposed sample size will provide >80% power to detect changes of similar magnitude in this phase 1b trial. All P values will be considered nominal.

Statistical Analyses:

Safety Analysis: Safety assessments will be based on AE reports and the results of vital signs, ECGs, physical examinations, and laboratory tests, with particular attention to gastrointestinal symptoms, transaminases, creatinine and eGFR, glycosuria, hypophosphatemia, amylase, and lipase. All AEs will be coded and summarized by system organ class (SOC), and preferred term using Medical Dictionary for Regulatory Activities (MedDRA), and Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

Changes in laboratory measures from baseline to final visit will be compared across groups using mixed-model repeated measures regression (MMRM) with treatment, visit, treatment-by-visit interaction and baseline value adjusted for sex. Shift tables will be generated for the ECG changes from baseline to the post dose by dose groups. Relationship between dose level (linear and discrete) and safety data (change from baseline) will be explored by mixed-effects regression model. Estimates and 95% confidence intervals (CIs) extracted from this model will also be provided. Type 1 error will be set at 0.05, no adjustment will be made for multiplicity, and results will be reported as relative risks and corresponding 95% CIs. In addition to the frequency of AEs, the seriousness and nature of AEs will be considered.

PK Analysis: The PK parameters will be calculated from TDF and FTC plasma concentrations and will include maximum and minimum concentration (Cmax, Cmin), time of the maximum concentration (tmax), area under the concentration curve (AUC) over 24 hours (AUC0-24h), average steady-state concentration (Cssave), AUC from the time of dosing to the last measurable concentration (AUC0-tlast), AUC extrapolated to infinity (AUC0-∞) (where estimable), and terminal phase half-life (t1/2). PK modeling will utilize the Phoenix WinNonlin for non-compartmental analysis, widely considered the industry standard and accepted by the FDA. The following conventions will be utilized: 1) for initial time points, concentrations below the lowest limit of quantification (LLOQ) will be treated as "zero", embedded and/or termination concentrations below the LLOQ are not expected in our assay, but, if observed, will be treated as missing.

Standard single and multiple dose PK parameters will be summarized by dose group using descriptive statistics. Geometric means and coefficients of variation will be presented for Cmax, AUC0-24h, AUClast, and AUCinf. Median and ranges will be presented for Tmax. Means and standard deviations will be provided for the other PK parameters. Dose proportionality will be analyzed using linear regression adjusting for baseline values. Cssave will be compared with historical values from healthy control participants receiving the standard FTC-TDF dose where the same assay and procedures were used.

PD Analysis: Only participants with available baseline values and at least one post-dose value for PD parameters will be included in the change from baseline analyses. The changes from baseline over the 28-day treatment period in the PBMC TDF-DP and FTC-TP concentrations, normalized by DNA content, by dose group will be compared using MMRM with treatment, visit, treatment-by-visit interaction adjusted for baseline. An unstructured covariance matrix will be used to account for intra-individual serial correlation of measures. If unstructured covariance structure matrix results in a lack of convergence, a compound symmetry covariance structure will be employed. The same MMRM approach will be used for the analyses of the change in reverse transcriptase activity in the PBMCs.

PD assessments will be summarized using descriptive statistics for each dose and time point. PD effects will be evaluated in relation to the TDF-DP and FTC-TP exposure (Cssave) by participant and/or by group according to dose level. Time course of PD effects will be plotted.

PK/PD Analysis: Relation between dose level and PK parameters will be analyzed using linear regression models. Estimates and 95% CIs extracted from this model will be employed to assess magnitude of the association. In addition to the PD analysis above, a population PK-PD model will be developed to describe the time course and relation of plasma and TDF-DP and FTC-TP concentrations and PD markers.