The FIH study was a randomized, double-blind, placebo-controlled, safety, tolerability, and pharmacokinetic (PK) adaptive design, dose-escalation study of AAB-003 in male and female subjects with mild to moderate AD (NCT01193608). Five AAB-003 dose levels were studied in escalating fashion: 0.5, 1, 2, 4 and 8 mg/kg. In each dose cohort, AAB-003 (or placebo) was administered via a 1-hour intravenous (IV) infusion once every 13 weeks for a total of three infusions (day 1, week 13 and week 26). The study was conducted in accordance with the ethical principles of the Declaration of Helsinki and was in compliance with Good Clinical Practice. A central investigational review board (IRB; Schulman Associates IRB, Cincinnati, Ohio, www.sairb.com) and individual site institutional review boards reviewed and provided approval for the protocols as well as informed consent forms. All subjects provided informed consent and consent for publication.
Subjects who successfully completed the FIH study and continued to meet study inclusion criteria were permitted to enter the 52-week OLE and receive four additional IV infusions of AAB-003 given 13 weeks apart (NCT01369225). Subjects who received active treatment in the FIH remained on the same dose in the OLE study. Subjects who received placebo during the FIH study received AAB-003 in the OLE at a dose based on their dose cohort in the FIH study.
Studies were conducted at 10 centers in the USA and 6 in Korea (see Additional file 1).
Patients between the ages of 50 and 89 years inclusive with a diagnosis of probable AD according to National Institute of Neurological and Communicative Disorders Association criteria were eligible for enrollment. Other requirements included a Mini-Mental State Exam (MMSE) score of 16 to 26 inclusive (12 or greater for OLE), Rosen Modified Hachinski Ischemic score of <4, and an MRI consistent with the diagnosis of AD. Additional study criteria can be found at www.clinicaltrials.gov. Patients with more than one microhemorrhage or lacunar infarct or evidence of a single prior infarct >1 cm3, evidence of a cerebral contusion, encephalomalacia, space occupying lesions, or brain tumors were excluded. Patients receiving approved symptomatic treatments for AD were allowed in the FIH study if on stable doses for 4 months prior to screening.
An adaptive dose finding design was employed. The initial cohort size in the FIH study was 4 to 8 subjects (3:1 active:placebo ratio) starting at a 0.5 mg/kg dose of AAB-003. Further increases were approved by an external Data Monitoring Committee (DMC) using a Bayesian escalation algorithm, after review of safety and tolerability data [15]. The algorithm used real-time emerging data on safety endpoints, ARIA-E, and dose-limiting adverse events other than ARIA-E to select the dose for the next cohort. The decision rules to escalate/de-escalate/stay were based on Bayesian posterior probabilities that the proportion of ARIA-E was ≤5 % and the proportion of dose-limiting adverse events other than ARIA-E was ≤30 %. Randomization was to continue until 80 subjects were enrolled (with ~60 allocated to active) or at least 24 subjects were allocated to active treatment at that maximum dose.
The study rules stated that if two or more cases of ARIA-E were observed within a cohort size of 4 to 8, the dose was to be de-escalated and 4 additional subjects allocated to the reduced dose. Further dose allocation was to be reassessed using the Bayesian algorithm and the additional safety experience at the reduced dose (symptomatic case counted as 2). One asymptomatic case of ARIA-E would have led to maintaining the current dose and allocating another 4 subjects to it; further dose allocation was to be reassessed based on observed safety. To generate additional FIH safety and biomarker data, 12 more subjects (10 active, 2 placebo) were enrolled at the 2 or 4 mg/kg doses once either dose was deemed safe per Bayesian escalation algorithm. Patients who completed the FIH without drug-related serious adverse events (SAE) and met inclusion criteria were permitted to enter a 52-week OLE study to provide longer term safety and tolerability data.
Safety
Safety assessments, including adverse event (AE) reports, physical and neurological examinations, suicidality assessments, 12-lead electrocardiograms (ECGs), and laboratory determinations, were performed at screening, baseline and at predetermined visits for both FIH and OLE studies. Vital signs were obtained at all visits. During and after infusion of study drug, patients were observed for 6 hours. Sitting blood pressure and pulse were measured at 15-min intervals during the infusion, for the first hour after infusion and every 30 min thereafter. Based on the bapineuzumab clinical trial experience, FIH patients were monitored for MRI brain abnormalities (ARIA-E, ARIA-H) at screening (baseline scan), 3 and 6 weeks after the first and second infusions, and 6 weeks following the third and last infusion [6, 16]. No MRI volumetric analysis was performed, nor was amyloid PET imaging performed. In the OLE study, MRIs were obtained 6 weeks after each infusion and at week 52. The study treatment duration was 39 weeks for the FIH and 52 weeks for the OLE and included a final safety follow-up visit. All subjects who received an infusion of study medication (including partial infusions) were included in the safety analysis population.
PK and PD in the FIH Study
Serum AAB-003, Plasma Aβx-40 and anti-AAB-003 antibodies
Standard, model-independent, noncompartmental PK methods were used to characterize the serum concentration–time profiles of AAB-003 and plasma Aβx-40. Standard PK parameters were derived from the concentration–time data following AAB-003 administration: peak concentration (Cmax), time to Cmax (Tmax), total area under the concentration–time curve to 13 weeks (AUC0-13weeks) and infinity (AUCinf), apparent terminal phase elimination half-life (t1/2), systemic clearance (CL) and steady-state volume of distribution (Vss). Blood samples for serum AAB-003 PK evaluations in the FIH study were collected on day 1 (predose, 1 hour (end of infusion), 1.5, 2, 4 and 6 hours postinfusion start), day 2 (24 hours postinfusion start), weeks 1, 3, 6, 10, 13 (predose, 1 hour (end of infusion)), week 19, week 26 (predose, 1 hour (end of infusion), 1.5, 2, 4, 6, and 24 hours postinfusion start), and weeks 32 and 39.
Blood samples for exploratory analysis of plasma Aβx-40 were collected from all patients on day 1 (predose, 1 hour (end of infusion) and 2 hours postinfusion start), day 2, weeks 1, 6, and 13 (predose, 1 hour (end of infusion) and 2 hours postinfusion start), week 19, week 26 (predose, 1 hour (end of infusion) and 2 hours postinfusion start), week 32 and week 39. Intensive blood sampling was implemented after the first and third doses in the FIH study to evaluate AAB-003 PK and plasma Aβx-40 after a single dose and at steady state. In the OLE study, PK and pharmacodynamics (PD) samples were collected less frequently. Therefore, PK and PD data presentation and discussion is limited to the FIH study. Serum samples for anti-AAB-003 antibodies were collected prior to dosing in the FIH study at weeks 13, 26 and 39.
The PK/PD analysis population included all randomized subjects who received at least one infusion of study medication and had at least one postdose PK/PD assessment.
Cerebrospinal Fluid Biomarkers in the FIH study
Cerebrospinal fluid (CSF) samples were collected at baseline and at approximately week 32 (or early withdrawal) from a subset of subjects who provided consent from the 2 mg/kg, 4 mg/kg and 8 mg/kg cohorts in the FIH. CSF samples were analyzed for Aβx-40, Aβx-42, t-tau, p-tau and AAB-003 concentrations. CSF sample collection was only made mandatory in the FIH after reaching the highest dose of 8 mg/kg. No more than 5 patients provided consent for CSF collection at week 45 of the OLE. Due to this small number of CSF samples, CSF exposure and biomarker data are limited to the FIH.
The CSF analysis population consisted of subjects in the 8 mg/kg AAB-003 cohort who provided sufficient CSF samples at baseline and 32 weeks to allow for the assaying of both samples, and who had no ARIA-E occurrence. There were insufficient numbers of subjects on AAB-003 in the 2 mg/kg and 4 mg/kg cohorts for group analysis. Placebo data from the 2 mg/kg and 4 mg/kg cohorts were included in the analysis. The change from baseline for each of the CSF biomarkers in the 8 mg/kg AAB-003 cohort was analyzed using one-sample paired t-test. To compare AAB-003 and placebo-treated subjects, an exploratory analysis using a mixed model with fixed effects for treatment, center, age, baseline MMSE category, baseline biomarker value and random subject effect was also performed.
Assay Methods
All assays were conducted using validated methodologies developed in compliance with Janssen AI Bioanalytical Development operating procedures and documented in method validation reports. Enzyme-linked immunosorbent assay methodologies were used to measure AAB-003 and anti-AAB-003 antibody concentrations in serum and t-tau and p-tau concentrations in CSF (Innotest, Fujirebio). CSF AAB-003 concentrations were determined using an electrochemiluminescence methodology. Plasma Aβx-40 samples, CSF Aβx-40 and Aβx-42 concentrations were determined by Meso Scale Discovery technology and plate reader.
Efficacy Endpoints in the FIH and OLE studies
Exploratory efficacy of AAB-003 was evaluated using the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog), Disability Assessment for Dementia (DAD), Neuropsychiatric Inventory (NPI), Clinical Dementia Rating (CDR) and MMSE. These endpoints were summarized by treatment group based on a full analysis population set consisting of all randomized patients who received at least one infusion of study medication.